Ncma Tek Manual Parts 1-5
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NCMA TEK National Concrete Masonry Association an information series from the national authority on concrete masonry technology
ASTM SPECIFICATIONS FOR CONCRETE MASONRY UNITS Keywords: absorption, ASTM specifications, calcium silicate brick, compressive strength, concrete brick, dimensions, face shell and web thickness, gross area, net area, specifications, testing, water absorption
TEK 1-1E Codes & Specs (2007)
2003 and 2006 editions of the International Building Code (IBC) (refs. 1, 2), as well as the most current ASTM edition. Code officials will commonly accept more current editions of ASTM standards than that referenced in the code, as they represent more state-of-the-art requirements for a specific material or system.
INTRODUCTION The most widely-used standards for specifying concrete masonry units in the United States are published by ASTM International. These ASTM standards contain minimum requirements that assure properties necessary for quality performance. These requirements include items such as conformance to specified component materials, compressive strength, permissible variations in dimensions, and finish and appearance criteria. Currently, seven ASTM standards apply to units intended primarily for construction of concrete masonry walls, beams, columns or specialty applications (see Table 1). The letter and first number of an ASTM designation is the fixed designation for that standard. For example, ASTM C 55 is the fixed designation for concrete building brick. The number immediately following indicates the year of last revision (i.e., ASTM C 55-06 is the version of C 55 published in 2006). ASTM standards are required to be updated or reapproved at least every five years. If the standard is reapproved, the reapproval date is placed in parentheses after the last revision date. Because significant changes can be introduced into subsequent editions, the edition referenced by the building code or by a project specification can be an important consideration when determining specific requirements. Also note that it may take several years between publication of a new ASTM standard and its subsequent reference by a building code. For this reason, Table 1 includes the editions referenced in the
LOADBEARING CONCRETE MASONRY UNITS— ASTM C 90 As the most widely-referenced of the ASTM standards for concrete masonry units, ASTM C 90 is under continuous review and revision. The bulk of these revisions are essentially editorial, although two recent major changes are discussed here. In 2006, the minimum face shell thickness requirements were modified for units 10-in. (254-mm) and wider. Prior to ASTM C 90-06 (ref. 2), two minimum face shell thicknesses for these units were listed: • a standard thickness, 13/8 in. for 10-in. units, 11/2 in. for 12-in. and greater (35 mm for 254-mm units and 38 mm for 305-mm and greater), and • a reduced thickness that can be used when the allowable loads in empirical design are correspondingly reduced. Similarly, in the engineered design methods (allowable stress design and strength design), capacity is automatically reduced as the section properties are reduced. With the introduction of ASTM C 90-06, the two sets of face shell thicknesses were replaced with one minimum thickness requirement (see Table 2). In 2000, a prior change was made to ASTM C 90, removing the Type I (moisture-controlled) and Type II (non moisturecontrolled) unit designations which is reflected in the ASTM C 90 editions adopted by the 2003 and 2006 editions of the
Table 1—ASTM Specifications for Concrete Masonry Units ASTM Edition referenced in Type of unit: Designation: the 2003 IBC: the 2006 IBC: Most current edition: Concrete Building Brick C 55 C 55-01a C 55-03 C 55-06 Calcium Silicate Brick C 73 C 73-99a C 73-99a C 73-05 Loadbearing Concrete Masonry Units C 90 C 90-01a C 90-03 C 90-06b Nonloadbearing Concrete Masonry Units C 129 C 129-99aA C 129-01A C 129-06 B Catch Basin and Manhole Units C 139 N/A N/AB C 139-05 Prefaced Concrete Units C 744 C 744-99 C 744-99 C 744-05 Concrete Facing Brick C 1634 N/AB N/AB C 1634-06 A Although not directly referenced in the IBC, C 129 is referenced in Specification for Masonry Structures (refs. 17, 18) B This standard is not referenced in the IBC. 1 TEK 1-1E © 2007 National Concrete Masonry Association (replaces TEK 1-1D)
IBC. The designations were withdrawn because they were difficult to effectively use and enforce, and because of newly developed concrete masonry crack control provisions. The new crack control guidelines are based on anticipated total volume changes, rather than on the specified moisture contents that formed the basis for Type I requirements. Because the Type designations no longer influenced recommended control joint spacing or other crack control strategies, Type designations were removed. Control joint criteria can be found in References 5 and 6. Physical Requirements Physical requirements prescribed by ASTM C 90 include dimensional tolerances, minimum face shell and web thicknesses for hollow units, minimum strength and maximum absorption requirements, and maximum linear shrinkage. Overall unit dimensions (width, height and length) can vary by no more than ± 1/8 in. (3.2 mm) from the standard specified dimension. Exceptions are faces of split-face units and faces of slump units which are intended to provide a random surface texture. In these cases, consult local suppliers to determine achievable tolerances. Molded features such as ribs, scores, hex-shapes and patterns must be within ± 1/16 in. (1.6 mm) of the specified standard dimension and within ± 1/16 in. (1.6 mm) of the specified placement on the mold. For dry-stack masonry units, the physical tolerances are typically limited to ± 1/16 in. (1.6 mm), which precludes the need for mortaring, grinding of face shell surfaces or shimming to even out courses during construction (ref. 7). Minimum face shell and web thicknesses are those deemed necessary to obtain satisfactory structural and nonstructural performance. Note that although there are some unique face shell thickness requirements for split-faced units (see Table 2 Table 2—ASTM C 90 Minimum Thickness of Face Shells and Webs for Hollow Units (ref. 3) Web thickness Nominal Face shell Equivalent width thicknessB, C, web thickness, of units, minimum, WebsB, C, D in./linear ftE in. (mm) in. (mm) in. (mm) (mm/linear m) 3 3 3 (76.2) & 4 (102) /4 (19) /4 (19) 15/8 (136) 6 (152) 1 (25)D 1 (25) 21/4 (188) 1 D 8 (203) 1 /4 (32) 1 (25) 21/4 (188) 1 1 10 (254) and greater 1 /4 (32) 1 /8 (29) 21/2 (209) A Average of measurements on a minimum of 3 units when measured as described in Test Methods C 140. B When this standard is used for units having split surfaces, a maximum of 10% of the split surface is permitted to have thickness less than those shown, but not less than 3/4 in. (19.1 mm). When the units are to be solid grouted, the 10% limit does not apply and Footnote C establishes a thickness requirement for the entire face shell. C When the units are to be solid grouted, minimum face shell and web thickness shall be not less than 5/8 in. (16 mm). D The minimum web thickness for units with webs closer than 1 in. (25.4 mm) apart shall be 3/4 in. (19.1 mm). E Equivalent web thickness does not apply to the portion of the unit to be filled with grout. The length of that portion shall be deducted from the overall length of the unit for the calculation of the equivalent web thickness.
footnote B), ground-face units (i.e., those ground after manufacture) must meet the face shell thickness requirements contained in the body of Table 2. In addition to minimum permissible web thicknesses for individual webs, the specification also requires a minimum total thickness of webs per foot of block length. When evaluating this equivalent web thickness, the portion of a unit to be filled with grout is exempted from the minimum requirement. This provision avoids excluding units intentionally manufactured with reduced webs, including bond beam units and open-end block, where grout fulfills the structural role of the web. For a unit to be considered a solid unit, the net cross-sectional area in every plane parallel to the bearing surface must be at least 75% of the gross cross-sectional area measured in the same plane. Minimum face shell and web thicknesses are not prescribed for solid units. The net area used to determine compressive strength is the “average” net area of the block, calculated from the unit net volume based on water displacement tests described in ASTM C 140 (ref. 8). For cored units having straight-tapered face shells and webs, average net area approximately equals the net cross-sectional area at the block mid-height. Gross and net areas of a concrete masonry unit are shown in Figure 1. Net area compressive strength is used for engineered masonry design, taking into account the mortar bedded and grouted areas. Compressive strength based on gross area is still used for masonry designed by the empirical provisions of IBC Section 2109. Maximum permissible water absorption is shown in Table 3. Absorption is a measure of the total water required to fill all voids within the net volume of concrete. It is determined from the weight-per-unit-volume difference between saturated and oven-dry concrete masonry units. Because absorption measures the water required to fill voids, aggregates with relatively large pores, such as some lightweight aggregate, would have a greater absorption than dense, nonporous aggregates, given the same compaction. As a result, lightweight units are permitted higher absorption values than medium or normal weight units. Because concrete masonry units tend to contract as they dry, ASTM C 90 limits their potential drying shrinkage to 0.065%, measured using ASTM C 426, Standard Test Method for Linear Drying Shrinkage of Concrete Masonry Units (ref. 9) 9). Finish and Appearance Finish and appearance provisions prohibit defects that would impair the strength or permanence of the construction,
Gross area* (shaded) = width (actual) x length (actual)
Net area* (shaded) = net volume (actual) height (actual) = (% solid) x (gross area) * For design calculations, a masonry element's section properties are based upon minimum specified dimensions instead of actual dimensions.
Figure 1—Gross and Net Areas
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but permit minor cracks incidental to usual manufacturing methods. For units to be used in exposed walls, the presence of objectionable imperfections is based on viewing the unit face or faces from a distance of at least 20 ft (6.1 m) under diffused lighting. Five percent of a shipment may contain chips not larger than 1 in. (25.4 mm) in any dimension, or cracks not wider than 0.02 in. (0.5 mm) and not longer than 25% of the nominal unit height. Similarly, the specification requires that color and texture be specified by the purchaser. An approved sample of at least four units, representing the range of color and texture permitted, is used to determine conformance. CONCRETE BUILDING BRICK—ASTM C 55 ASTM C 55-03 (ref. 10) included two grades of concrete brick: Grade N for veneer and facing applications and Grade S for general use. In 2006, however, the grades were removed from C 55 and requirements for concrete brick used in veneer and facing applications were moved into a new standard: C 1634 (see below). ASTM C 55-06 (ref. 11) now applies to concrete building brick only, defined as concrete masonry units with: a maximum width of 4 in. (102 mm); a weight that will typically permit it to be lifted and placed using one hand; and an intended use in nonfacing, utilitarian applications. Requirements for C 55-06 building brick include: • 2,500 psi (17.2 MPa) minimum compressive strength (average of three units), • 0.065% maximum linear drying shrinkage, • 75% minimum percent solid, and • maximum average absorption requirements of 13 pcf for normal weight brick, 15 pcf for medium weight brick and 18 pcf for lightweight brick (208, 240 and 288 kg/m3). The finish and appearance section of C 55-06 only addresses defects which might affect placement or permanence of the resulting construction. CONCRETE FACING BRICK—ASTM C 1634 The introduction of this new standard in 2006 reflects the rise in popularity of concrete brick used in architectural facing applications. A facing brick (C 1634) is distinguished
from a building brick (C 55) primarily by its intended use. ASTM C 1634 (ref. 12) defines a concrete facing brick as a concrete masonry unit with: a maximum width of 4 in. (102 mm); a weight that will typically permit it to be lifted and placed using one hand; and an intended application where one or more faces of the unit will be exposed. Compression and absorption requirements are listed in Table 4. Linear drying shrinkage, dimensional tolerances and finish and appearance requirements are similar to those in C 90, with the exception that chip size is limited to + 1/2 in. (13 mm). The minimum permissible distance between any core holes in the brick and the edge of the brick is 3/4 in. (19 mm), as it is in C 55. Both C 1634 and C 55 refer to C 140 for compression testing, which requires compression test specimens to have a height that is 60% + 10% of its least lateral dimension, to minimize the potential impact of specimen aspect ratio on tested compressive strengths. NONLOADBEARING CONCRETE MASONRY UNITS—ASTM C 129 ASTM C 129 (ref. 13) covers hollow and solid nonloadbearing units, intended for use in nonloadbearing partitions. These units are not suitable for exterior walls subjected to freezing cycles unless effectively protected from the weather. ASTM C 129 requires that these units be clearly marked to preclude their use as loadbearing units. Minimum net area compressive strength requirements are 500 psi (3.45 MPa) for an individual unit and 600 psi (4.14 MPa) average for three units. CALCIUM SILICATE FACE BRICK—ASTM C 73 ASTM C 73 (ref. 14) covers brick made from sand and lime. Two grades are included: • Grade SW—Brick intended for use where exposed to temperatures below freezing in the presence of moisture. Minimum compressive strength requirements are 4,500 psi (31 MPa) for an individual unit and 5,500 psi (37.9 MPa) for an average of three units, based on average gross area. The maximum water absorption is 15 lb/ft3 (240 kg/m3). • Grade MW—Brick intended for exposure to temperatures
Table 3—Strength and Absorption Requirements for Concrete Masonry Units, ASTM C 90 (ref. 3)A Oven-dry density Maximum water Minimum net area Weight of concrete, lb/ft3 (kg/m3) absorption, lb/ft3 (kg/m3) compressive strength, psi (MPa) classification Average of 3 units Average of 3 units Individual units Average of 3 units Individual units Lightweight Less than 105 (1,680) 18 (288) 20 (320) 1,900 (13.1) 1,700 (11.7) Medium weight 105 to less than 125 (1,680 - 2,000) 15 (240) 17 (272) 1,900 (13.1) 1,700 (11.7) Normal weight 125 (2,000) or more 13 (208) 15 (240) 1,900 (13.1) 1,700 (11.7) A
Note that ASTM C 90-01a does not include requirements for maximum water absorption of individual units. Otherwise, the requirements are identical between C 90-03 and C 90-06b. Table 4—Strength and Absorption Requirements for Concrete Facing Brick, ASTM C 1634 (ref. 12)
Oven-dry density of concrete, Density lb/ft³ (kg/m³) classification Average of 3 units Lightweight less than 105 (1,680) Medium weight 105 (1,680) to less than 125 (2,000) Normal weight 125 (2,000) or more
Minimum net area compressive strength, psi (MPa) Average of Individual 3 units units 3,500 (24.1) 3,000 (20.7) 3,500 (24.1) 3,000 (20.7) 3,500 (24.1) 3,000 (20.7)
Maximum water absorption, lb/ft³ (kg/m³) Average of Individual 3 units units 15 (240) 17 (272) 13 (208) 15 (240) 10 (160) 12 (192)
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below freezing, but unlikely to be saturated with water. Minimum compressive strength requirements are 3,000 psi (20.7 MPa) for an individual unit and 3,500 psi (24.1 MPa) for an average of three units, based on average gross area. The maximum water absorption is 18 lb/ft3 (288 kg/m3). PREFACED CONCRETE AND CALCIUM SILICATE MASONRY UNITS—ASTM C 744 ASTM C 744 (ref. 15) for prefaced units establishes requirements for the facing materials applied to masonry unit surfaces. For the concrete masonry units onto which the surface is molded, C 744 requires compliance with the requirements contained in ASTM C 55, C 90 or C 129, as appropriate. Facing requirements in C 744 include: resistance to crazing,
surface burning characteristics, adhesion, color permanence, chemical resistance, cleansability, abrasion, and dimensional tolerances. CONCRETE MASONRY UNITS FOR CATCH BASINS AND MANHOLES—ASTM C 139 ASTM C 139 (ref. 16) covers solid precast segmental concrete masonry units intended for use in catch basins and manholes. Units are required to be at least 5 in. (127 mm) thick, with a minimum gross area compressive strength of 2,500 psi (17 MPa) (average of 3 units) or 2,000 psi (13 MPa) for an individual unit, and a maximum water absorption of 10 pcf (16 kg/m³) (average of 3 units). The overall unit dimensions must be within ± 3% of the specified dimensions.
REFERENCES 1. International Building Code 2003. International Code Council, 2003. 2. International Building Code 2006. International Code Council, 2006. 3. Standard Specification for Loadbearing Concrete Masonry Units Units,, ASTM C 90-06b. ASTM International, 2006. 4.. Standard Specification for Loadbearing Concrete Masonry Units Units,, ASTM C 90-03. ASTM International, 2003. 5. Control Joints for Concrete Masonry Walls Walls—Empirical Empirical Method Method,, TEK 10-2B. National Concrete Masonry Association, 2005. 6. Control Joints for Concrete Masonry Walls Walls—Alternative Alternative Engineered Method. TEK 10-3. National Concrete Masonry Association, 2003. 7. Design and Construction of Dry-Stack Masonry Walls Walls,, TEK 14-22. National Concrete Masonry Association, 2003. 8. Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units Units,, ASTM C 140-03. ASTM International, 2003. 9. Standard Test Method for Linear Drying Shrinkage of Concrete Masonry Units Units,, ASTM C 426-06. ASTM International, 2006. 10. Standard Specification for Concrete Brick Brick,, ASTM C 55-03. ASTM International, 2003. 11. Standard Specification for Concrete Building Brick Brick,, ASTM C 55-06. ASTM International, 2006. 12. Standard Specification for Concrete Facing Brick Brick,, ASTM C 1634-06. ASTM International, 2006. 13. Standard Specification for Nonloadbearing Concrete Masonry Units Units,, ASTM C 129-06. ASTM International, 2006. 14. Standard Specification for Calcium Silicate Brick (Sand-Lime Brick) Brick),, ASTM C 73-99a. ASTM International, 1999. 15. Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units Units,, ASTM C 744-99. ASTM International, 1999. 16. Standard Specification for Concrete Masonry Units for Construction of Catch Basins and Manholes Manholes,, ASTM C 139-05. ASTM International, 2005. 17. Specification for Masonry Structures Structures,, ACI 530.1-02/ASCE 6-02/TMS 602-02. Reported by the Masonry Standards Joint Committee, 2002. 18. Specification for Masonry Structures Structures,, ACI 530.1-05/ASCE 6-05/TMS 602-05. Reported by the Masonry Standards Joint Committee, 2005.
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NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication. NATIONAL CONCRETE MASONRY ASSOCIATION 13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org
To order a complete TEK Manual or TEK Index, contact NCMA Publications (703) 713-19004
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SPECIFICATION FOR MASONRY STRUCTURES
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concrete
masonry
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TEK 1-2C
Codes & Specs (2010)
INTRODUCTION Specification for Masonry Structures (MSJC Specification) (ref. 1) is a national consensus standard intended to be incorporated by reference into the contract documents of masonry construction projects. Compliance with this Specification is mandatory for structures designed in accordance with Building Code Requirements for Masonry Structures (MSJC Code) (ref. 2). The masonry design and construction provisions in Chapter 21 of the International Building Code (IBC) (ref. 3) are based primarily on the MSJC Code and Specification. When adopting the MSJC Code and Specification, the IBC typically amends or modifies some provisions. Because significant changes can be introduced into subsequent editions of both the MSJC and the IBC, the edition referenced by the local building code can be an important consideration when determining the specific requirements to be met. Note that building officials will often accept design and construction standards which are more current than those referenced in the applicable code, as they represent more state-of-the art requirements for the specific material or system. This TEK provides a broad overview of the MSJC Specification's content, references other NCMA TEK which describe the various provisions in greater detail, outlines updates incorporated into the 2008 edition of the MSJC Specification, and notes differences between the 2008 MSJC Specification and the 2009 IBC. THE MSJC SPECIFICATION The MSJC Specification covers material requirements, storage and handling of materials, construction, and clean-
Related TEK: 1-3C NCMA TEK 1-2C
ing, as well as provisions for quality assurance, testing and inspection. Construction includes requirements for masonry placement, bonding and anchorage, and the placement of grout, reinforcement and prestressing tendons. The document is formatted to allow the designer to modify those provisions which include a choice of alternatives. Thus, the MSJC Specification may be tailored to meet the specific needs of a project. Modifications are considered to be a supplemental specification to the MSJC Specification. The advantages of a standard specification include consistency, coordination and understanding among all parties involved. A Commentary, which accompanies the MSJC Specification, explains the mandatory requirements and further clarifies the Specification's intent. The document is written in the three-part section format of the Construction Specifications Institute. Each of the three parts (General, Products and Execution) is described in the following sections. In addition to these three parts, checklists are included at the end of the MSJC Specification to help the designer prepare the contract documents. The checklists identify the decisions that must be made when preparing any supplemental specifications. They are not a mandatory part of the Specification. Several articles of the MSJC Specification are prefaced with the phrase "when required..." These articles do not become a part of the contract documents unless action is taken by the designer to include a requirement in the supplemental specifications. Other articles are prefaced with the phrase "unless otherwise required..." These articles are a part of the contract documents unless the designer takes
Keywords: building codes, construction, quality assurance, specifications
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specific action to modify the article in the supplemental specifications. PART 1—GENERAL Part 1 of the MSJC Specification covers: • definitions, • referenced standards, • system description, which includes: 1. compressive strength requirements, 2. compressive strength determination (choice of two methods). See TEK 18-1A, Compressive Strength Evaluation of Concrete Masonry (ref. 4), for more detailed information. 3. adhered veneer requirements (choice of two methods to determine adhesion), • submittals, which includes a minimum list of required submittals. If the designer wishes to specify a higher level of quality assurance, additional submittals may be required. • quality assurance, which includes quality control measures as well as testing and inspection. The services and duties of the testing agency, inspection agency and contractor are included here (see TEK 18-3B, Concrete Masonry Inspection (ref. 5), for more detailed information), • delivery, storage and handling requirements, and • cold weather and hot weather construction requirements (see TEK 3-1C, All-Weather Concrete Masonry Construction (ref. 6)). Updates to 2008 MSJC Specification From the 2005 edition of the MSJC Specification to the 2008 edition, Tables 3, 4 and 5 which define Level A Quality Assurance, Level B Quality Assurance and Level C Quality Assurance, respectively, were revised. Columns were added to the tables to define the frequency of inspection for the various items. New inspection tasks in the tables are: • verification of the grade, type and size of anchor bolts prior to grouting for Levels B and C quality assurance, and • verification of the grade and size of prestressing tendons and anchorages for Level B quality assurance. Part 1 also includes new provisions addressing the addition of self-consolidating grout to the MSJC specification. See TEK 9-2B, Self-Consolidating Grout for Concrete Masonry (ref. 7) for further information. The 2008 Specification includes minor modifications to the provisions for verifying compliance with the specified compressive strength of masonry, f'm, using the unit strength method. In prior editions of the MSJC Specification, the unit strength table for concrete masonry implied
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that the minimum compressive strength of units could be less than the 1,900 psi (13.1 MPa) required by ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units (ref 8). To avoid potential confusion, Table 2 was revised to reflect a minimum unit compressive strength of 1,900 psi (13.1 MPa). IBC Inspection Requirements The International Building Code inspection requirements are almost identical to the MSJC requirements but are organized a little differently. MSJC Level A requirements correspond to the basic inspection requirements performed by the building official as required in Section 110.3 of the IBC. The special inspection requirements of IBC for masonry are found in Section 1704.5 of that code. MSJC Level B corresponds to IBC Level 1 and MSJC Level C corresponds to IBC Level 2. IBC Section 2105 addresses quality assurance of masonry. These provisions are essentially the same as those in the MSJC Specification, with the exception that the IBC addresses testing prisms from constructed masonry. Such prisms are addressed only to a minor extent within the MSJC Specification, via one of the referenced standards, ASTM C1314-07, Standard Test Method for Compressive Strength of Masonry Prisms (ref.9). PART 2—PRODUCTS Part 2 of the MSJC Specification covers: • required material properties for masonry units, mortar, grout, reinforcement, prestressing tendons, metal accessories and other accessories such as movement joint materials. These material properties are primarily references to applicable ASTM standards. See TEKs 1-1E, ASTM Specifications for Concrete Masonry Units (ref. 10), and 12-4D, Steel Reinforcement for Concrete Masonry (ref. 11), for further information. • mortar and grout mixing requirements, found within Article 2.1 A via ASTM C270, Standard Specification for Mortar for Unit Masonry (ref. 12), and also within Article 2.6A (see TEK 3-8A, Concrete Masonry Construction (ref. 13), for more detailed information), and • reinforcement fabrication requirements. Updates to 2008 MSJC Specification The Part 2 provisions were not greatly modified between the 2005 and 2008 editions of the MSJC Specification. The reinforcement used for stirrups and lateral ties that are terminated with a standard hook is now limited to a maximum reinforcing bar size of No. 5 (M# 16), because of the difficulty of bending, placing and developing larger diameter bars in typical masonry construction.
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As in Part 1, Part 2 also includes new provisions addressing the addition of self-consolidating grout to the MSJC Specification. See TEK 9-2B, Self-Consolidating Grout for Concrete Masonry (ref. 7) for further information. IBC Masonry Material Requirements IBC Section 2103 addresses masonry construction materials, and the requirements are essentially the same as in the corresponding MSJC Specification. The IBC does include a provision for surface bonding mortar however, which is not addressed in the MSJC Specification. PART 3—EXECUTION Part 3, Execution, covers: • inspection prior to the start of masonry construction, • preparation of reinforcement and masonry prior to grouting (see TEK 3-2A, Grouting Concrete Masonry Walls (ref. 14)), • masonry erection, including site tolerances (see TEK 3-8A, Concrete Masonry Construction (ref. 13)), • bracing, which simply requires bracing to be designed and installed to assure stability (see TEK 3-4B, Bracing Masonry Walls During Construction (ref. 15) for detailed guidance), • placement of reinforcement, ties and anchors (see TEK 12-1A, Anchors and Ties for Masonry (ref. 16)), • grout placement (see TEK 3-2A, Grouting Concrete Masonry Walls (ref. 14)), • procedures for prestressing tendon installation and stressing (see TEK 3-14, Post-Tensioned Concrete Masonry Wall Construction (ref. 17)), • field quality control requirements, and • cleaning (see TEK 8-4A, Cleaning Concrete Masonry (ref. 18)).
To help ensure structural continuity between subsequent grout pours, Article 3.5F now requires a 11/2-in. (38mm) grout key (i.e., terminating the grout at least 11/2-in. (38-mm) below a mortar joint) when the previous grout lift has set before the next lift is poured. Grout keys may not be formed within masonry bond beams or lintels. IBC Construction Requirements IBC Section 2104 addresses masonry construction procedures, which essentially references the MSJC Specification without modification. In the 2006 IBC, many of the provisions of the 2005 MSJC requirements were reiterated in the IBC. In the 2009 IBC however, most of the text of these requirements was removed from the IBC and a simple reference was made to the 2008 MSJC. FINISH AND APPEARANCE The MSJC Specification addresses structural requirements only and not finish or appearance, though several Articles, such as 1.6 D Sample Panels and 3.3 F Site Tolerances certainly may affect such. Additionally, several MSJC reference standards, such as ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units, specifically address this topic. Further guidance may be found by including reference to state standards such as Arizona Masonry Guild Standard 107, Levels of Quality (ref. 19), as well as to NCMA TEK 1-1E ASTM Specifications for Concrete Masonry Units and TEK 8-4A Cleaning Concrete Masonry.
Updates to 2008 MSJC Specification In addition to changes addressing self-consolidating grout, several changes have been incorporated into the Part 3 provisions, dealing with foundation dowels and with grouting procedures. MSJC Specification Article 3.4 B.8(d) is a new provision, allowing foundation dowels that interfere with masonry unit webs to be bent up to 1 in. (25 mm) horizontally for each 6 in. (152 mm) of vertical height. This provision is similar to that used in reinforced concrete construction. Article 3.5A of the MSJC Specification requires that grout be placed within 11/2 hours from the introduction of water into the mix. The 2008 edition exempts transitmixed grout from this requirement, as long as the grout meets the specified slump.
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REFERENCES 1. Specification for Masonry Structures, TMS 602/ACI 530.1/ASCE 6. Reported by the Masonry Standards Joint Committee, 2005 and 2008. 2. Building Code Requirements for Masonry Structures. TMS 402/ACI 530/ASCE 5. Reported by the Masonry Standards Joint Committee, 2005 and 2008. 3. International Building Code. International Code Council, 2006 and 2009. 4. Compressive Strength Evaluation of Concrete Masonry, TEK 18-1A. National Concrete Masonry Association, 2004. 5. Concrete Masonry Inspection, TEK 18-3B. National Concrete Masonry Association, 2006. 6. All-Weather Concrete Masonry Construction, TEK 3-1C. National Concrete Masonry Association, 2002. 7. Self-Consolidating Grout for Concrete Masonry, TEK 9-2B. National Concrete Masonry Association, 2007. 8. Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-09. ASTM International, 2009. 9. Standard Test Method for Compressive Strength of Masonry Prisms, ASTM C1314-07. ASTM International, 2007. 10. ASTM Specifications for Concrete Masonry Units, TEK 1-1E. National Concrete Masonry Association, 2007. 11. Steel Reinforcement for Concrete Masonry, 12-4D. National Concrete Masonry Association, 2007. 12. Standard Specification for Mortar for Unit Masonry, ASTM C270-07a. ASTM International, 2007. 13. Concrete Masonry Construction, TEK 3-8A. National Concrete Masonry Association, 2001. 14. Grouting Concrete Masonry Walls, TEK 3-2A. National Concrete Masonry Association, 2005. 15. Bracing Masonry Walls During Construction, TEK 3-4B. National Concrete Masonry Association, 2005. 16. Anchors and Ties for Masonry, TEK 12-1A. National Concrete Masonry Association, 2001. 17. Post-Tensioned Concrete Masonry Wall Construction, TEK 3-14. National Concrete Masonry Association, 2002. 18. Cleaning Concrete Masonry, TEK 8-4A. National Concrete Masonry Association, 2005. 19. Levels of Quality, Standard AMG 107-98. Arizona Masonry Guild, 1998.
NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication. NATIONAL CONCRETE MASONRY ASSOCIATION
13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org To order a complete TEK Manual or TEK Index, contact NCMA Publications (703) 713-1900
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NCMA TEK 1-2C
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NCMA TEK National Concrete Masonry Association an information series from the national authority on concrete masonry technology
BUILDING CODE REQUIREMENTS FOR CONCRETE MASONRY
TEK 1-3C Codes & Specs (2007)
Keywords: building codes, construction, masonry design, quality assurance, specifications
INTRODUCTION
2003 INTERNATIONAL BUILDING CODE
The majority of jurisdictions in the United States adopt a national model code, most commonly the International Building Code (IBC) (refs. 1, 2), as the basis of their building code. The intent of the IBC is to reference and coordinate other standardized documents, rather than to develop design and construction provisions from scratch. With this in mind, the IBC masonry design and construction provisions are based primarily on Building Code Requirements for Masonry Structures (MSJC code) (refs. 3, 4) and Specification for Masonry Structures (MSJC specification) (refs. 5, 6). The code adoption process is shown schematically in Figure 1. In adopting the MSJC code and specification, the IBC typically amends or modifies some provisions. Similarly, depending on state laws, modifications can be made to the IBC at the state or local level to better suit local building practices or design traditions. However, most state codes require that any modifications to the IBC be more stringent than the corresponding requirement in the IBC. Because significant changes can be introduced into subsequent editions of both the MSJC and IBC, the edition referenced by the local building code can be an important consideration when determining the specific requirements to be met. Note that code officials will often accept more current design and construction standards than those referenced in the code, as they represent more state-of-the-art requirements for a specific material or system. To help determine which code provisions apply and highlight changes of note, this TEK outlines the major modifications to the MSJC code and specification made in the 2003 and 2006 IBC, as well as the principal changes made between the 2002 and 2005 editions of the MSJC code and specification. Note that the scope of the MSJC code and specification covers structural design and construction. Hence, requirements for items such as fire resistance, sound insulation and energy efficiency are not addressed in the MSJC documents.
The 2003 International Building Code (ref. 1) adopts by reference the 2002 editions of the MSJC code and MSJC specification (refs. 3, 5). The MSJC code covers the design of concrete masonry, clay masonry, glass unit masonry, stone masonry, as well as masonry veneer. The MSJC code requires compliance with the MSJC specification, which governs masonry construction requirements and quality assurance provisions (see also TEK 1-2B, ref. 7).
N a t i o n a l p r o c e s s
Consensus process
MSJC Code and Specification adoption with modifications and additions International Building Code adoption, possibly with modifications
State/ local process
State or Local Building Code
Figure 1—Masonry Structural Code Development Process 9
TEK 1-3C © 2007 National Concrete Masonry Association (replaces TEK 1-3B)
The 2002 MSJC Code and Specification Compared to earlier editions of the MSJC code and specification, updates included in the 2002 edition are summarized below. Masonry Design Changes to masonry design provisions included: • for the design of masonry structures, the 2002 MSJC code included new strength design provisions (see TEK 14-4A, ref. 8), offering a design method in addition to allowable stress design and empirical design, • revised seismic design requirements, including prescriptive shear wall reinforcement (see TEK 14-18A, ref. 9) and transition from Seismic Performance Categories to Seismic Design Categories (SDCs) (see TEK 14-18A, ref. 9), • for allowable stress design, revised allowable flexural tension values for unreinforced grouted masonry elements when subjected to flexural tension perpendicular to the bed joints, • new prohibition on the use of wall ties with drips (bends intended to inhibit moisture migration from one masonry wythe to the other), • for empirical design, revised wind speed threshold from a design wind pressure of 25 psf (1,197 MPa) to a wind speed of 110 mph (145 km/h) three-second gust, • for empirical design, revised shear wall spacing requirements (see TEK 14-8A, ref. 10), and • revisions to the types of masonry veneer permitted to be supported by wood construction (see TEK 3-6B, ref. 11). Construction and Quality Assurance Specification revisions included: • new corrosion protection requirements for joint reinforcement, anchors and ties depending on their intended use or exposure conditions (see TEK 12-4D, ref. 12), • new prestressed masonry quality assurance provisions for Level 2 (moderate) and Level 3 (rigorous) programs (see TEK 18-3B, ref. 13), • the addition of grout demonstration panels as a means of meeting grout pour requirements (see TEK 3-2A, ref. 14), • revised cold weather construction requirements, including new protection procedures for grouted masonry (see TEK 3-1C, ref. 15), • new veneer anchor placement requirements (see TEK 3-6B, ref. 11), and • updating of ASTM C 270 (ref. 16) mortar specification tables to include mortar cement. Differences Between the 2003 IBC and the 2002 MSJC The 2002 editions of the MSJC code and specification are included in their entirety (by reference) in the 2003 IBC. The IBC modifies several areas of the MSJC code and specification applicable to concrete masonry. The most significant of these are summarized below. In addition, quality assurance provisions are close, but not identical between the IBC and MSJC.
Seismic Design Requirements • The IBC bases loads on ASCE 7-02 (ref. 17), rather than the 1998 edition (ref. 18) referenced by the MSJC, • the IBC includes prescriptive seismic requirements for posttensioned masonry shear walls, which are not included in the MSJC, and • the IBC has some more stringent seismic requirements than the MSJC, applicable to SDCs B, C, D, E and F. Allowable Stress Design For masonry designed using allowable stress design procedures, the IBC: • modifies load combinations to be based on IBC section 1605, rather than those in MSJC code section 2.1.2.1, • modifies minimum inspections required during construction, • includes separate design requirements for columns used only to support light-frame roofs of carports, porches, sheds or similar structures with a maximum area of 450 ft2 (41.8 m2) and assigned to Seismic Design category A, B or C, • modifies the minimum required lap splice length for reinforcing bars (Note that development length and corresponding lap splice length requirements have changed frequently in recent years. NCMA recommends using the lap splice requirements published in the 2006 IBC. See TEK 12-4D (ref. 12) for more detailed information.), • sets a maximum reinforcing bar size based on the size of the cell or collar joint where the reinforcement is placed (see ref. 12), and • sets a limit on the amount of reinforcement permitted in the in-plane direction for special reinforced masonry shear walls. Strength Design For masonry designed using strength design procedures, the IBC: • sets a maximum width for the equivalent stress block of six times the nominal thickness of the masonry wall or spacing between reinforcement (whichever is less), or six times the thickness of the flange for in-plane bending of flange walls, • modifies welded and mechanical splice requirements (see ref. 12), and • adds maximum reinforcement percentage for special posttensioned masonry shear walls. Empirical Design The IBC includes empirical design procedures within the body of the code and references the MSJC code as an alternate means of compliance. However, the IBC and MSJC empirical requirements are essentially the same, except that the IBC also includes: • an exception allowing shear walls of one-story buildings to be a minimum of 6 in. (152 mm) thick, rather than 8 in. (203 mm), • provisions for empirically-designed surface-bonded masonry walls, and 10
• additional parapet wall requirements, covering flashing and copings. 2006 INTERNATIONAL BUILDING CODE The 2006 International Building Code (ref. 2) adopts by reference the 2005 editions of the MSJC code and MSJC specification (refs. 4, 6). The first section below highlights the major changes between the 2002 and 2005 MSJC code and specification. The following section summarizes important changes between the 2005 MSJC and the 2006 IBC. The 2005 MSJC Code and Specification Compared to the 2002 edition of the MSJC code and specification, the 2005 edition includes the following changes and additions. Allowable Stress Design For masonry designed using allowable stress design procedures: • the use of the one-third increase in allowable stresses has been tied to specific load combinations, • the minimum required lap splice and development lengths for reinforcing bars are the same for allowable stress design and strength design (Note that development length and corresponding lap splice length requirements have changed frequently in recent years. NCMA recommends using the lap splice requirements published in the 2006 IBC. See TEK 12-4D (ref. 12) for more detailed information.), and • in-plane allowable flexural tension has been changed from zero to be the same value as for out-of-plane flexural tension. Strength Design For masonry designed using strength design procedures: • the 2005 MSJC code includes explicit bearing strength provisions, • the modulus of rupture for in-plane bending is now the same as that for out-of-plane bending, • the maximum reinforcement limits have been modified, based on less restrictive assumptions that are related directly to the expected seismic ductility demand, • new provisions for noncontact splices have been added, • the minimum required lap splice and development lengths for reinforcing bars are the same for allowable stress design and strength design (Note that development length and corresponding lap splice length requirements have changed frequently in recent years. NCMA recommends using the lap splice requirements published in the 2006 IBC. See TEK 12-4D (ref. 12) for more detailed information.), and • provisions for computing effective compression width have been added, using the same requirements historically employed for allowable stress design.
Other Revisions The post-tensioned masonry design provisions have been updated. The most significant change is that design is now based on strength design with serviceability checks, rather than on allowable stress design with strength checks, making the design procedures easier to use for those accustomed to strength design of prestressed concrete. For grouted masonry, the maximum grout lift height has been increased from 5 ft to 12 ft-8 in (1.5 to 3.9 m) under controlled conditions, such as a consistent grout slump between 10 and 11 in. (254 and 279 mm), the absence of reinforced bond beams between the top and bottom of the grout pour, and a minimum masonry curing time of 4 hours prior to grouting. See TEK 3-2A (ref. 14) for further information. Empirical design includes several revisions to the limitations that define where empirical design can be used. In the 2002 MSJC documents, the three levels of quality assurance were designated Levels 1, 2 and 3, which were replaced by Levels A, B and C, respectively in the 2005 edition. This change in nomenclature is wholly editorial and does not affect the requirements specified for each level. For masonry veneers, prescriptive seismic requirements have been modified (several requirements that previously applied in SDC D and higher now apply in SDC E and higher), and new prescriptive requirements have been introduced for areas with high winds (wind speeds between 110 and 130 mph (177 and 209 km/hr)). Prescriptive requirements for corbelled masonry have been moved from the empirical design chapter to Chapter 1, making the corbel requirements independent of the design procedure used. In addition, design and construction provisions for autoclaved aerated concrete (AAC) appear in the MSJC for the first time. Differences Between the 2006 IBC and the 2005 MSJC The 2005 editions of the MSJC code and specification are included in their entirety (by reference) in the 2006 IBC. In addition to the modifications listed under the 2003 IBC (which are also included in the 2006 IBC unless noted below), the 2006 IBC modifies several areas of the MSJC code and specification applicable to concrete masonry. The most significant of these are summarized below. • Development length and minimum lap splice length for reinforcing bars has been updated to 48 bar diameters for Grade 60 steel, with some exceptions. See TEK 12-4D (ref. 12) for more detailed information. • Design loads and load combinations are based on ASCE 7-05 (ref. 19), rather than ASCE 7-02. • For grouted masonry, the IBC requires a "grout key" between grout pours, i.e. a horizontal construction joint formed by stopping the grout pour 11/2 in. (38 mm) below a mortar joint. • For certain special reinforced masonry shear walls, the IBC prescribes a maximum reinforcement percentage, applicable in the in-plane direction.
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REFERENCES 1. International Building Code 2003. International Code Council, 2003. 2. International Building Code 2006. International Code Council, 2006. 3. Building Code Requirements for Masonry Structures, ACI 530-02/ASCE 5-02/TMS 402-02. Reported by the Masonry Standards Joint Committee, 2002. 4. Building Code Requirements for Masonry Structures, ACI 530-05/ASCE 5-05/TMS 402-05. Reported by the Masonry Standards Joint Committee, 2005. 5. Specification for Masonry Structures, ACI 530.1-02/ASCE 6-02/TMS 602-02. Reported by the Masonry Standards Joint Committee, 2002. 6. Specification for Masonry Structures, ACI 530.1-05/ASCE 6-05/TMS 602-05. Reported by the Masonry Standards Joint Committee, 2005. 7. Specification for Masonry Structures, TEK 1-2B. National Concrete Masonry Association, 2004. 8. Strength Design of Concrete Masonry, TEK 14-4A. National Concrete Masonry Association, 2002. 9. Prescriptive Seismic Reinforcement Requirements for Masonry Structures, TEK 14-18A. National Concrete Masonry Association, 2003. 10. Empirical Design of Concrete Masonry Walls, TEK 14-8A. National Concrete Masonry Association, 2001. 11. Concrete Masonry Veneers, TEK 3-6B. National Concrete Masonry Association, 2005. 12. Steel Reinforcement for Concrete Masonry, TEK 12-4D. National Concrete Masonry Association, 2006. 13. Concrete Masonry Inspection, TEK 18-3B. National Concrete Masonry Association, 2006. 14. Grouting Concrete Masonry Walls, TEK 3-2A. National Concrete Masonry Association, 2005. 15. All-Weather Concrete Masonry Construction, TEK 3-1C. National Concrete Masonry Association, 2002. 16. Standard Specification for Mortar for Unit Masonry, ASTM C 270-99b. ASTM International, Inc., 1999. 17. Minimum Design Loads for Buildings and Other Structures, ASCE 7-02. American Society of Civil Engineers, 2002. 18. Minimum Design Loads for Buildings and Other Structures, ASCE 7-98. American Society of Civil Engineers, 1998. 19. Minimum Design Loads for Buildings and Other Structures, ASCE 7-05. American Society of Civil Engineers, 2005.
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GLOSSARY OF CONCRETE MASONRY TERMS Keywords: definitions, glossary, terminology “A” block: Hollow masonry unit with one end closed by a cross web and the opposite end open or lacking an end cross web. (See “Open end block.”) Absorption: The difference in the amount of water contained within a concrete masonry unit between saturated and ovendry conditions, expressed as weight of water per cubic foot of concrete. [4] Accelerator: A liquid or powder admixture added to a cementitious paste to speed hydration and promote early strength development. An example of an accelerator material is calcium nitrite. Adhesive anchor : An anchoring device that is placed in a predrilled hole and secured using a chemical compound. Admixture: Substance other than prescribed materials of water, aggregate and cementitious materials added to concrete, mortar or grout to improve one or more chemical or physical properties. [3] Aggregate: An inert granular or powdered material such as natural sand, manufactured sand, gravel, crushed stone, slag, fines and lightweight aggregate, which, when bound together by a cementitious matrix forms concrete, grout or mortar. [3] Air entraining: The capability of a material or process to develop a system of uniformly distributed microscopic air bubbles in a cementitious paste to increase the workability or durability of the resulting product. Some admixtures act as air entraining agents. Anchor: Metal rod, tie, bolt or strap used to secure masonry to other elements. May be cast, adhered, expanded or fastened into masonry. [1] Angle: A structural steel section that has two legs joined at 90 degrees to one another. Used as a lintel to support masonry over openings such as doors or windows in lieu of a masonry arch or reinforced masonry lintel. Also used as a shelf to vertically support masonry veneer. Sometimes referred to as a relieving angle. Arch: A vertically curved compressive structural member spanning openings or recesses. May also be built flat by using special masonry shapes or specially placed units. Area, gross cross-sectional: The area delineated by the out-toout dimensions of masonry in the plane under consideration. This includes the total area of a section perpendicular to the
TEK 1-4 Codes & Specs (2004)
direction of the load, including areas within cells and voids. [1] Area, net cross-sectional: The area of masonry units, grout and mortar crossed by the plane under consideration, based on out-to-out dimensions and neglecting the area of all voids such as ungrouted cores, open spaces, or any other area devoid of masonry. [1] Axial load: The load exerted on a wall or other structural element and acting parallel to the element’s axis. Axial loads typically act in a vertical direction, but may be otherwise depending on the type and orientation of the element. Backing: The wall or surface to which veneer is secured. The backing material may be concrete, masonry, steel framing or wood framing. [1] Beam: A structural member, typically horizontal, designed to primarily resist flexure. Burnished block: (See “Ground face block.”) Bedded area: The surface area of a masonry unit that is in contact with mortar in the plane of the mortar joint. Blast furnace slag cement: A blended cement which incorporates blast furnace slag. Blended cement: Portland cement or air-entrained portland cement combined through blending with such materials as blast furnace slag or pozzolan, which is usually fly ash. May be used as an alternative to portland cement in mortar. Block: A solid or hollow unit larger than brick-sized units. (See also “Concrete block, concrete masonry unit, masonry unit”) Block machine: Equipment used to mold, consolidate and compact shapes when manufacturing concrete masonry units. Bond: (1) The arrangement of units to provide strength, stability or a unique visual effect created by laying units in a prescribed pattern. See reference 6 for illustrations and descriptions of common masonry bond patterns. (2) The physical adhesive or mechanical binding between masonry units, mortar, grout and reinforcement. (3) To connect wythes or masonry units. Bond beam: (1) The grouted course or courses of masonry units reinforced with longitudinal bars and designed to take the longitudinal flexural and tensile forces that may be induced in a masonry wall. (2) A horizontal grouted element within masonry in which reinforcement is embedded. Bond beam block: A hollow unit with depressed webs or with "knock-out" webs (which are removed prior to placement) to accommodate horizontal reinforcement and grout. Bond breaker: A material used to prevent adhesion between two surfaces. 13
TEK 1-4 © 2004 National Concrete Masonry Association
Bond, running: The placement of masonry units such that head joints in successive courses are horizontally offset at least onequarter the unit length. [1] Centering head joints over the unit below, called center or half bond, is the most common form of running bond. A horizontal offset between head joints in successive courses of one-third and one-quarter the unit length is called third bond and quarter bond, respectively. Bond, stack: For structural design purposes, Building Code Requirements for Masonry Structures considers all masonry not laid in running bond as stack bond. [1] In common use, stack bond typically refers to masonry laid so head joints in successive courses are vertically aligned. Also called plumb joint bond, straight stack, jack bond, jack-on-jack and checkerboard bond. Bond strength: The resistance to separation of mortar from masonry units and of mortar and grout from reinforcing steel and other materials with which it is in contact. Brick: A solid or hollow manufactured masonry unit of either concrete, clay or stone. Cantilever: A member structurally supported at only one end through a fixed connection. The opposite end has no structural support. Cap block: A solid slab used as a coping unit. May contain ridges, bevels or slopes to facilitate drainage. (See also “Coping block.”) Cavity: A continuous air space between wythes of masonry or between masonry and its backup system. Typically greater than 2 in. (51 mm) in thickness. (See “Collar joint.”) Cell: The hollow space within a concrete masonry unit formed by the face shells and webs. Also called core. Cementitious material: A generic term for any inorganic material including cement, pozzolanic or other finely divided mineral admixtures or other reactive admixtures, or a mixture of such materials that sets and develops strength by chemical reaction with water. In general, the following are considered cementitious materials: portland cement, hydraulic cements, lime putty, hydrated lime, pozzolans and ground granulated blast furnace slag. [3] Cleanout/cleanout hole: An opening of sufficient size and spacing so as to allow removal of debris from the bottom of the grout space. Typically located in the first course of masonry. [2] Cold weather construction: Procedures used to construct masonry when ambient air temperature or masonry unit temperature is below 40°F (4.4°C). Collar joint: A vertical longitudinal space between wythes of masonry or between masonry wythe and backup construction, sometimes filled with mortar or grout. Typically less than 2 in. (51 mm) in thickness. [1] (See also “Cavity.”) Color (pigment): A compatible, color fast, chemically stable admixture that gives a cementitious matrix its coloring. Column: (1) In structures, a relatively long, slender structural compression member such as a post, pillar, or strut. Usually vertical, a column supports loads that act primarily in the direction of its longitudinal axis. (2) For the purposes of design, an isolated vertical member whose horizontal dimension measured at right angles to the thickness does not exceed 3 times its thickness and whose height is greater than 4 times it thickness. [1] Composite action: Transfer of stress between components of a member designed so that in resisting loads, the combined components act together as a single member. [1] Compressive strength: The maximum compressive load that a specimen will support divided by the net cross-sectional area of the specimen.
Compressive strength of masonry: Maximum compressive force resisted per unit of net cross-sectional area of masonry, determined by testing masonry prisms or as a function of individual masonry units, mortar and grout in accordance with ref. 2. [2] (See also “Specified compressive strength of masonry.”) Concrete: A composite material that consists of a water reactive binding medium, water and aggregate (usually a combination of fine aggregate and coarse aggregate) with or without admixtures. In portland cement concrete, the binder is a mixture of portland cement, water and may contain admixtures. Concrete block: A hollow or solid concrete masonry unit. Larger in size than a concrete brick. Concrete brick: A concrete hollow or solid unit smaller in size than a concrete block. Concrete masonry unit: Hollow or solid masonry unit, manufactured using low frequency, high amplitude vibration to consolidate concrete of stiff or extremely dry consistency. Connector: A mechanical device for securing two or more pieces, parts or members together; includes anchors, wall ties and fasteners. May be either structural or nonstructural. [1] Connector, tie: A metal device used to join wythes of masonry in a multiwythe wall or to attach a masonry veneer to its backing. [1] (See also “Anchor.”) Control joint: A continuous unbonded masonry joint that is formed, sawed or tooled in a masonry structure to regulate the location and amount of cracking and separation resulting from dimensional changes of different parts of the structure, thereby avoiding the development of high stresses. Coping: The materials or masonry units used to form the finished top of a wall, pier, chimney or pilaster to protect the masonry below from water penetration. Coping block: A solid concrete masonry unit intended for use as the top finished course in wall construction. Corbel: A projection of successive courses from the face of masonry. [1] Core: (See “Cell.”) Corrosion resistant: A material that is treated or coated to retard corrosive action. An example is steel that is galvanized after fabrication. Course: A horizontal layer of masonry units in a wall or, much less commonly, curved over an arch. Crack control: Methods used to control the extent, size and location of cracking in masonry including reinforcing steel, control joints and dimensional stability of masonry materials. Cull: A masonry unit that does not meet the standards or specifications and therefore has been rejected. Curing: (1) The maintenance of proper conditions of moisture and temperature during initial set to develop a required strength and reduce shrinkage in products containing portland cement. (2) The initial time period during which cementitious materials gain strength. Damp-proofing: The treatment of masonry to retard the passage or absorption of water or water vapor, either by application of a suitable coating or membrane to exposed surfaces or by use of a suitable admixture or treated cement. Damp check: An impervious horizontal layer to prevent vertical penetration of water in a wall or other masonry element. A damp check consists of either a course of solid masonry, metal or a thin layer of asphaltic or bituminous material. It is generally placed near grade to prevent upward 14 migration of moisture by capillary action.
Diaphragm: A roof or floor system designed to transmit lateral forces to shear walls or other lateral load resisting elements. [1] Dimension, actual: The measured size of a concrete masonry unit or assemblage. Dimension, nominal: The specified dimension plus an allowance for mortar joints, typically 3/8 in. (9.5 mm). Nominal dimensions are usually stated in whole numbers. Width (thickness) is given first, followed by height and then length. [1] Dimension, specified: The dimensions specified for the manufacture or construction of a unit, joint or element. Unless otherwise stated, all calculations are based on specified dimensions. Actual dimensions may vary from specified dimensions by permissible variations. [1] Dowel: A metal reinforcing bar used to connect masonry to masonry or to concrete. Drip: A groove or slot cut beneath and slightly behind the forward edge of a projecting unit or element, such as a sill, lintel or coping, to cause rainwater to drip off and prevent it from penetrating the wall. Drying shrinkage: The change in linear dimension of a concrete masonry wall or unit due to drying. Dry stack: Masonry work laid without mortar. Eccentricity: The distance between the resultant of an applied load and the centroidal axis of the masonry element under load. Effective height: Clear height of a braced member between lateral supports and used for calculating the slenderness ratio of the member. [1] Effective thickness: The assumed thickness of a member used to calculate the slenderness ratio. Efflorescence: A deposit or encrustation of soluble salts (generally white), that may form on the surface of stone, brick, concrete or mortar when moisture moves through the masonry materials and evaporates on the surface. In new construction, sometimes referred to as new building bloom. Once the structure dries, the bloom normally disappears or is removed with water. Equivalent thickness: The solid thickness to which a hollow unit would be reduced if the material in the unit were recast into a unit with the same face dimensions (height and length) but without voids. The equivalent thickness of a 100% solid unit is equal to the actual thickness. Used primarily to determine masonry fire resistance ratings. Expansion anchor: An anchoring device (based on a friction grip) in which an expandable socket expands, causing a wedge action, as a bolt is tightened into it. Face: (1) The surface of a wall or masonry unit. (2) The surface of a unit designed to be exposed in the finished masonry. Face shell: The outer wall of a hollow concrete masonry unit. [5] Face shell mortar bedding: Hollow masonry unit construction where mortar is applied only to the horizontal surface of the unit face shells and the head joints to a depth equal to the thickness of the face shell. No mortar is applied to the unit cross webs. (See also “Full mortar bedding.”) Facing: Any material forming a part of a wall and used as a finished surface. Fastener: A device used to attach components to masonry, typically nonstructural in nature. Fire resistance: A rating assigned to walls indicating the length of time a wall performs as a barrier to the passage of
flame, hot gases and heat when subjected to a standardized fire and hose stream test. For masonry, fire resistance is most often determined based on the masonry’s equivalent thickness and aggregate type. Flashing: A thin impervious material placed in mortar joints and through air spaces in masonry to prevent water penetration and to facilitate water drainage. Fly ash: The finely divided residue resulting from the combustion of ground or powdered coal. Footing: A structural element that transmits loads directly to the soil. Freeze-thaw durability: The ability to resist damage from the cyclic freezing and thawing of moisture in materials and the resultant expansion and contraction. Full mortar bedding: Masonry construction where mortar is applied to the entire horizontal surface of the masonry unit and the head joints to a depth equal to the thickness of the face shell. (See also “Face shell mortar bedding.”) Glass unit masonry: Masonry composed of glass units bonded by mortar. [1] Glazed block: A concrete masonry unit with a permanent smooth resinous tile facing applied during manufacture. Also called prefaced block. Ground face block: A concrete masonry unit in which the surface is ground to a smooth finish exposing the internal matrix and aggregate of the unit. Also called burnished or honed block. Grout: (1) A plastic mixture of cementitious materials, aggregates, water, with or without admixtures initially produced to pouring consistency without segregation of the constituents during placement. [3] (2) The hardened equivalent of such mixtures. Grout, prestressing: A cementitious mixture used to encapsulate bonded prestressing tendons. [2] Grout, self-consolidating: Highly fluid and stable grout used in high lift and low lift grouting that does not require consolidation or reconsolidation. Grout lift: An increment of grout height within a total grout pour. A grout pour consists of one or more grout lifts. [2] Grout pour: The total height of masonry to be grouted prior to erection of additional masonry. A grout pour consists of one or more grout lifts. [2] Grouted masonry: (1) Masonry construction of hollow units where hollow cells are filled with grout, or multiwythe construction in which the space between wythes is solidly filled with grout. (2) Masonry construction using solid masonry units where the interior joints and voids are filled with grout. Grouting, high lift: The technique of grouting masonry in lifts for the full height of the wall. Grouting, low lift: The technique of grouting as the wall is constructed, usually to scaffold or bond beam height, but not greater than 4 to 6 ft (1,219 to 1,829 mm), depending on code limitations. “H” block: Hollow masonry unit lacking cross webs at both ends forming an “H” in cross section. Used with reinforced masonry construction. (See also “Open end block.”) Header: A masonry unit that connects two or more adjacent wythes of masonry. Also called a bonder. [1] Height of wall: (1) The vertical distance from the foundation wall or other similar intermediate support to the top of the 15 wall. (2) The vertical distance between intermediate supports.
Height-to-thickness ratio: The height of a masonry wall divided by its nominal thickness. The thickness of cavity walls is taken as the overall thickness minus the width of the cavity. High lift grouting: (See “Grouting, high lift.”) Hollow masonry unit: A unit whose net cross-sectional area in any plane parallel to the bearing surface is less than 75 % of its gross cross-sectional area measured in the same plane. [4] Honed block: (See “Ground face block.”) Hot weather construction: Procedures used to construct masonry when ambient air temperature exceeds 100°F (37.8°C) or temperature exceeds 90°F (32.2°C) with a wind speed greater than 8 mph (13 km/h). Inspection: The observations to verify that the masonry construction meets the requirements of the applicable design standards and contract documents. Jamb block: A block specially formed for the jamb of windows or doors, generally with a vertical slot to receive window frames, etc. Also called sash block. Joint: The surface at which two members join or abut. If they are held together by mortar, the mortar-filled volume is the joint. Joint reinforcement: Steel wires placed in mortar bed joints (over the face shells in hollow masonry). Multi-wire joint reinforcement assemblies have cross wires welded between the longitudinal wires at regular intervals. Lap: (1) The distance two bars overlap when forming a splice. (2) The distance one masonry unit extends over another. Lap splice: The connection between reinforcing steel generated by overlapping the ends of the reinforcement. Lateral support: The means of bracing structural members in the horizontal span by columns, buttresses, pilasters or cross walls, or in the vertical span by beams, floors, foundations, or roofs. Lightweight aggregate: Natural or manufactured aggregate of low density, such as expanded or sintered clay, shale, slate, diatomaceous shale, perlite, vermiculite, slag, natural pumice, volcanic cinders, diatomite, sintered fly ash or industrial cinders. Lightweight concrete masonry unit: A unit whose oven-dry density is less than 105 lb/ft3 (1,680 kg/m3). [4] Lime: Calcium oxide (CaO), a general term for the various chemical and physical forms of quicklime, hydrated lime and hydraulic hydrated lime. Lintel: A beam placed or constructed over a wall opening to carry the superimposed load. Lintel block: A U-shaped masonry unit, placed with the open side up to accommodate horizontal reinforcement and grout to form a continuous beam. Also called channel block. Loadbearing: (See “Wall, loadbearing.”) Low lift grouting: (See “Grouting, low lift.”) Manufactured masonry unit: A man-made noncombustible building product intended to be laid by hand and joined by mortar, grout or other methods. [5] Masonry: An assemblage of masonry units, joined with mortar, grout or other accepted methods. [5] Masonry cement: (1) A mill-mixed cementitious material to which sand and water is added to make mortar. (2) Hydraulic cement produced for use in mortars for masonry construction. Medium weight concrete masonry unit: A unit whose ovendry density is at least 105 lb/ft3 (1,680 kg/m3) but less than
125 lb/ft3 (2,000 kg/m3). [4] Metric: The Systeme Internationale (SI), the standard international system of measurement. Hard metric refers to products or materials manufactured to metric specified dimensions. Soft metric refers to products or materials manufactured to English specified dimensions, then converted into metric dimensions. Mix design: The proportions of materials used to produce mortar, grout or concrete. Modular coordination: The designation of masonry units, door and window frames, and other construction components that fit together during construction without customization. Modular design: Construction with standardized units or dimensions for flexibility and variety in use. Moisture content: The amount of water contained within a unit at the time of sampling expressed as a percentage of the total amount of water in the unit when saturated. [4] Mortar: (1) A mixture of cementitious materials, fine aggregate water, with or without admixtures, used to construct unit masonry assemblages. [3] (2) The hardened equivalent of such mixtures. Mortar bed: A horizontal layer of mortar used to seat a masonry unit. Mortar bond: (See “Bond.”) Mortar joint, bed: The horizontal layer of mortar between masonry units. [1] Mortar joint, head: The vertical mortar joint placed between masonry units within the wythe. [1] Mortar joint profile: The finished shape of the exposed portion of the mortar joint. Common profiles include: Concave: Produced with a rounded jointer, this is the standard mortar joint unless otherwise specified. Recommended for exterior walls because it easily sheds water. Raked: A joint where 1/4 to 1/2 in. (6.4 to 13 mm) is removed from the outside of the joint. Struck: An approximately flush joint. See also “Strike.” Net section: The minimum cross section of the member under consideration. Nonloadbearing: (See “Wall, nonloadbearing.”) Normal weight concrete masonry unit: A unit whose ovendry density is 125 lb/ft3 (2000 kg/m3) or greater. [4] Open end block: A hollow unit, with one or both ends open. Used primarily with reinforced masonry construction. (See “A” block and “H” block.) Parging: (1) A coating of mortar, which may contain dampproofing ingredients, over a surface. (2) The process of applying such a coating. Pier: An isolated column of masonry or a bearing wall not bonded at the sides to associated masonry. For design, a vertical member whose horizontal dimension measured at right angles to its thickness is not less than three times its thickness nor greater than six times its thickness and whose height is less than five times its length. [1] Pigment: (See “Color.”) Pilaster: A bonded or keyed column of masonry built as part of a wall. It may be flush or project from either or both wall surfaces. It has a uniform cross section throughout its height and serves as a vertical beam, a column or both. Pilaster block: Concrete masonry units designed for use in the construction of plain or reinforced concrete masonry pilasters and columns. 16 Plain masonry: (See “Unreinforced masonry.”)
Plaster: (See "Stucco.") Plasticizer: An ingredient such as an admixture incorporated into a cementitious material to increase its workability, flexibility or extensibility. Post-tensioning: A method of prestressing in which prestressing tendons are tensioned after the masonry has been placed. [1] See also “Wall, prestressed.” Prestressing tendon: Steel element such as wire, bar or strand, used to impart prestress to masonry. [1] Prism: A small assemblage made with masonry units and mortar and sometimes grout. Primarily used for quality control purposes to assess the strength of full-scale masonry members. Prism strength: Maximum compressive force resisted per unit of net cross-sectional area of masonry, determined by testing masonry prisms. Project specifications: The written documents that specify project requirements in accordance with the service parameters and other specific criteria established by the owner or owner’s agent. Quality assurance: The administrative and procedural requirements established by the contract documents and by code to assure that constructed masonry is in compliance with the contract documents. [1] Quality control: The planned system of activities used to provide a level of quality that meets the needs of the users and the use of such a system. The objective of quality control is to provide a system that is safe, adequate, dependable and economic. The overall program involves integrating factors including: the proper specification; production to meet the full intent of the specification; inspection to determine whether the resulting material, product and service is in accordance with the specifications; and review of usage to determine any necessary revisions to the specifications. Reinforced masonry: (1) Masonry containing reinforcement in the mortar joints or grouted cores used to resist stresses. (2) Unit masonry in which reinforcement is embedded in such a manner that the component materials act together to resist applied forces. Reinforcing steel: Steel embedded in masonry in such a manner that the two materials act together to resist forces. Retarding agent: An ingredient or admixture in mortar that slows setting or hardening, most commonly in the form of finely ground gypsum. Ribbed block: A block with projecting ribs (with either a rectangular or circular profile) on the face for aesthetic purposes. Also called fluted. Sash block: (See “Jamb block.”) Scored block: A block with grooves on the face for aesthetic purposes. For example, the grooves may simulate raked joints. Screen block: An open-faced masonry unit used for decorative purposes or to partially screen areas from the sun or from view. Shell: (See “Face shell.”) Shoring and bracing: The props or posts used to temporarily support members during construction. Shrinkage: The decrease in volume due to moisture loss, decrease in temperature or carbonation of a cementitious material. Sill: A flat or slightly beveled unit set horizontally at the base of an opening in a wall. Simply supported: A member structurally supported at top and bottom or both sides through a pin-type connection, which assumes no moment transfer. Slenderness ratio: (1) The ratio of a member’s effective
height to radius of gyration. (2) The ratio of a member's height to thickness. Slump: (1) The drop in the height of a cementitious material from its original shape when in a plastic state. (2) A standardized measurement of a plastic cementitious material to determine its flow and workability. Slump block: A concrete masonry unit produced so that it slumps or sags in irregular fashion before it hardens. Slushed joint: A mortar joint filled after units are laid by “throwing” mortar in with the edge of a trowel. Solid masonry unit: A unit whose net cross-sectional area in every plane parallel to the bearing surface is 75 percent or more of its gross cross-sectional area measured in the same plane. [4] Note that Canadian standards define a solid unit as 100% solid. Spall: To flake or split away due to internal or external forces such as frost action, pressure, dimensional changes after installation, vibration, impact, or some combination. Specified dimensions: (See “Dimension, specified.”) Specified compressive strength of masonry, f'm: Minimum masonry compressive strength required by contract documents, upon which the project design is based (expressed in terms of force per unit of net cross-sectional area). [1] Split block: A concrete masonry unit with one or more faces purposely fractured to produce a rough texture for aesthetic purposes. Also called a split-faced or rock-faced block. Stirrup: Shear reinforcement in a flexural member. [1] Strike: To finish a mortar joint with a stroke of the trowel or special tool, simultaneously removing extruded mortar and smoothing the surface of the mortar remaining in the joint. Stucco: A combination of cement and aggregate mixed with a suitable amount of water to form a plastic mixture that will adhere to a surface and preserve the texture imposed on it. Temper: To moisten and mix mortar to a proper consistency. Thermal movement: Dimension change due to temperature change. Tie: (See “Connector, tie.”) Tolerance: The specified allowance in variation from a specified size, location, or placement. Tooling: Compressing and shaping the face of a mortar joint with a tool other than a trowel. See "Mortar joint profile" for definitions of common joints. Unreinforced masonry: Masonry in which the tensile resistance of the masonry is taken into consideration and the resistance of reinforcement, if present, is neglected. Also called plain masonry. [1] Veneer, adhered: Masonry veneer secured to and supported by the backing through adhesion. [2] Veneer, anchored: Masonry veneer secured to and supported laterally by the backing through anchors and supported vertically by the foundation or other structural elements. Veneer, masonry: A masonry wythe that provides the finish of a wall system and transfers out-of-plane loads directly to a backing, but is not considered to add load resisting capacity to the wall system. [1] Wall, bonded: A masonry wall in which two or more wythes are bonded to act as a composite structural unit. Wall, cavity: A multiwythe noncomposite masonry wall with a continuous air space within the wall (with or without insulation), which is tied together with metal ties. [1] Wall, composite: A multiwythe wall where the individual masonry wythes act together to resist applied loads. (See 17 also “Composite action.”)
Wall, curtain: (1) A nonloadbearing wall between columns or piers. (2) A nonloadbearing exterior wall vertically supported only at its base, or having bearing support at prescribed vertical intervals. (3) An exterior nonloadbearing wall in skeleton frame construction. Such walls may be anchored to columns, spandrel beams or floors, but not Wall, foundation: A wall below the floor nearest grade serving as a support for a wall, pier, column or other structural part of a building and in turn supported by a footing. Wall, loadbearing: Wall that supports vertical load in addition to its own weight. By code, a wall carrying vertical loads greater than 200 lb/ft (2.9 kN/m) in addition to its own weight. [1] Wall, multiwythe: Wall composed of 2 or more masonry wythes. Wall, nonloadbearing: A wall that supports no vertical load other than its own weight. By code, a wall carrying vertical loads less than 200 lb/ft (2.9 kN/m) in addition to its own weight. [1] Wall, panel: (1) An exterior nonloadbearing wall in skeleton frame construction, wholly supported at each story. (2) A nonloadbearing exterior masonry wall having bearing support at each story. Wall, partition: An interior wall without structural function. [2] Wall, prestressed: A masonry wall in which internal compressive stresses have been introduced to counteract stresses resulting from applied loads. [1] Wall, reinforced: (1) A masonry wall reinforced with steel embedded so that the two materials act together in resisting forces. (2) A wall containing reinforcement used to resist shear and tensile stresses. Wall, retaining: A wall designed to prevent the movement of soils and structures placed behind the wall. Wall, screen: A masonry wall constructed with more than 25% open area intended for decorative purposes, typically to partially screen an area from the sun or from view. Wall, shear: A wall, bearing or nonbearing, designed to resist lateral forces acting in the plane of the wall. [1] Wall, single wythe: A wall of one masonry unit thickness.
Wall, solid masonry: A wall either built of solid masonry units or built of hollow units and grouted solid. Wall tie: A metal connector that connects wythes of masonry. Wall tie, veneer: A wall tie used to connect a facing veneer to the backing. Water permeance: The ability of water to penetrate through a substance such as mortar or brick. Waterproofing: (1) The methods used to prevent moisture flow through masonry. (2) The materials used to prevent moisture flow through masonry. Water repellency: The reduction of absorption. Water repellent: Material added to the masonry to increase resistance to water penetration. Can be a surface treatment or integral water repellent admixture. Web: The portion of a hollow concrete masonry unit connecting the face shells. Weep hole: An opening left (or cut) in mortar joints or masonry face shells to allow moisture to exit the wall. Usually located immediately above flashing. Workability: The ability of mortar or grout to be easily placed and spread. Wythe: Each continuous vertical section of a wall, one masonry unit in thickness. [1] REFERENCES 1. Building Code Requirements for Masonry Structures, ACI 53002/ASCE 5-02/TMS 402-02. Reported by the Masonry Standards Joint Committee, 2002. 2. Specification for Masonry Structures, ACI 530.1-02/ASCE 6-02/ TMS 602-02. Reported by the Masonry Standards Joint Committee, 2002. 3. Standard Terminology of Mortar and Grout for Unit Masonry, ASTM C 1180-03. ASTM International, 2003. 4. Standard Terminology of Concrete Masonry Units and Related Units, ASTM C 1209-01a. ASTM International, 2001. 5. Standard Terminology of Masonry, ASTM C 1232-02. ASTM International, 2002. 6. Concrete Masonry Bond Patterns, TEK 14-6. National Concrete Masonry Association, 1999.
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Disclaimer: Although care has been taken to ensure the enclosed information is as accurate and complete as possible, NCMA does not assume responsibility for errors or omissions resulting from the use of this TEK. NATIONAL CONCRETE MASONRY ASSOCIATION 13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org
To order a complete TEK Manual or TEK Index, 18 contact NCMA Publications (703) 713-1900
NCMA TEK National Concrete Masonry Association an information series from the national authority on concrete masonry technology
TYPICAL SIZES AND SHAPES OF CONCRETE MASONRY UNITS Keywords: architectural units, bond beams, concrete brick, dimensions, equivalent thickness, lintels, screen block, sizes and shapes INTRODUCTION Concrete masonry is one of the most versatile building products available because of the wide variety of appearances that can be achieved using concrete masonry units. Concrete masonry units are manufactured in different sizes, shapes, colors, and textures to achieve a number of finishes and functions. In addition, because of its modular nature, different concrete masonry units can be combined within the same wall to achieve variations in texture, pattern, and color. Certain concrete masonry sizes and shapes are considered standard, while others are popular only in certain regions. Local manufacturers can provide detailed information on specific products, or the feasibility of producing custom units. A more complete guide to concrete masonry units is the Shapes and Sizes Directory (ref. 2).
TEK 2-1A Unit Properties
UNIT SIZES Typically, concrete masonry units have nominal face dimensions of 8 in. (203 mm) by 16 in. (406 mm), available in nominal thicknesses of 4 , 6, 8, 10, and 12 in. (102, 152, 203, 254, and 305 mm). Nominal dimensions refer to the module size for planning bond patterns and modular layout with respect to door and window openings. Actual dimensions of concrete masonry units are typically 3/ 8 in. (9.5 mm) less than nominal dimensions, so that the 4 or 8 in. (102 or 203 mm) module is maintained with 3/ 8 in. (9.5 mm) mortar joints. Figure 1 illustrates nominal and actual dimensions for a nominal 8 x 8 x 16 in. (203 x 203 x 406 mm) concrete masonry unit. In addition to these standard sizes, other unit heights, lengths, and thicknesses may be available from local concrete masonry producers. Standard Specification for Load-Bearing Concrete Masonry Units, ASTM C 90 (ref. 5) is the most frequently referenced standard for concrete masonry units. ASTM C 90 includes minimum face shell and web thicknesses for
8" (203 mm)
8" (2 03 m m)
) mm 6 0 4 ( 16" Nominal Unit Dimensions
Stretcher unit
Single corner unit Concrete brick
75/8" (194 mm)
7 5/8"
(194 mm)
m) 97 m 3 ( " 55 /8
1 Actual Unit Dimensions
Figure 1—Nominal and Actual Unit Dimensions TEK 2-1A © 2002 National Concrete Masonry Association
Corner return unit
Double corner or plain end unit
Figure 2—Typical Concrete Masonry Units
19
(2002)
the different sizes of concrete masonry units as listed in Table 1. Overall unit dimensions (height, width, or length) are permitted to vary by ±1/8 in. (3.2 mm) from the dimensions specified by the manufacturer. Where required, units may be manufactured to closer tolerances than those permitted in ASTM C 90. ASTM C 90 also defines the difference between hollow and solid concrete masonry units. The net cross-sectional area of a solid unit is at least 75% of the gross cross-sectional area. In addition to the “standard” sizes listed above, concrete brick is available in typical lengths of 8 and 16 in. (203 and 406 mm), nominal 4 in. (102 mm) width, and a wide range of heights. They may be 100% solid, or may have two or three cores. Like ASTM C 90, Standard Specification for Concrete Building Brick, ASTM C 55 (ref. 4), permits overall unit dimensions to vary ±1/8 in. (3.2 mm) from the dimensions specified by the manufacturer. Nominal dimensions of modular concrete brick equal the actual dimensions plus 3/8 in. (9.5 mm), the thickness of one standard mortar joint. However, nominal dimensions of nonmodular sized concrete brick usually exceed the standard dimensions by 1/8 to 1/4 in. (3.2 to 6.4 mm).
UNIT SHAPES Concrete masonry unit shapes have been developed for a wide variety of applications. The most common shapes are shown in Figure 2. Typically, the face shells and webs are tapered on concrete masonry units. Depending on the core molds used in the manufacture of the units, face shells and webs may be tapered with a flare at one end, or may have a straight taper from top to bottom. The taper provides a wider surface for mortar and easier handling for the mason. The shapes illustrated in Figure 3 have been developed specifically to accommodate reinforcement. Open-ended units allow the units to be threaded around reinforcing bars. This eliminates the need to lift units over the top of the reinforcing bar, or to thread the reinforcement through the masonry cores
Table 1—Minimum Thickness of Face Shells and Webs (ref. 5) Web thickness Equivalent Face shell web thickness, Nominal width thicknessa, Websa, in./linear footb,c of unit, in. (mm) in. (mm) in. (mm) (mm/m) 3/4 (19) 3 (76) and 4 (102) 3/4 (19) 15/8 (136) d 6 (152) 1 (25) 1 (25) 21/4 (188) d 1 8 (203) 1 /4 (32) 1 (25) 21/4 (188) d 10 (254) 13/8 (35) 11/8 (29) 21/2 (209) 11/4 (32)d,e 12 (305) 11/2 (38) 11/8 (29) 21/2 (209) d,e 11/4 (32)
Open end, or "A" shaped unit
Double open end unit
Lintel unit
a
Average of measurements on 3 units taken at the thinnest point when measured as described in ASTM C 140 (ref. 3). When this standard is used for split face units, a maximum of 10% of a split face shell area is permitted to have thicknesses less than those shown, but not less than ¾ in. (19.1 mm). When the units are solid grouted, the 10% limit does not apply. b Average of measurements on 3 units taken at the thinnest point when measured as described in ASTM C 140. The minimum web thickness for units with webs closer than 1 in. (25.4 mm) apart shall be ¾ in. (19.1 mm). c Sum of the measured thickness of all webs in the unit, multiplied by 12 and divided by the length of the unit. Equivalent web thickness does not apply to the portion of the unit to be filled with grout. The length of that portion shall be deducted from the overall length of the unit for the calculation. d For solid grouted masonry construction, minimum face shell thickness not less than 5/8 in. (16 mm). e This face shell thickness is applicable where allowable design load is reduced in proportion to the reduction in thickness from basic face shell thicknesses shown, except that allowable design loads on solid grouted units shall not be reduced.
Bond beam units
Pilaster units
Figure 3—Shapes to Accommodate Reinforcement after the wall is constructed. Bond beams in concrete masonry walls can be accommodated either by saw-cutting out of a standard unit, or by using bond beam units. Bond beam units are either manufactured with reduced webs or with “knock-out” webs, which are removed prior to placement in the wall. Horizontal bond beam reinforcement is easily accommodated in these units. Lintel units are similar to the U shaped bond beam units. Lintel units are available in various depths to carry appropriate lintel loads over door and window openings. The solid bottom confines grout to the lintel. Pilaster and column units are used to easily accommodate a wall-column or wallpilaster interface, allowing space for vertical reinforcement in 20
Sash unit
All purpose or kerf unit
Control joint unit
Bevelled unit
Bull-nosed unit
Screen units
Figure 4—Special Shapes
Figure 5—Examples of Concrete Masonry Units Designed For Energy Efficiency
Figure 6—Examples of Acoustical Concrete Masonry Units
the hollow center. Figure 4 shows units developed for specific wall applications. Sash block have a vertical groove molded into one end to accommodate a window sash. Sash block can be laid with the grooves adjacent to one another to accommodate a preformed control joint gasket. Control joint units are manufactured with one male and one female end to provide lateral load transfer across control joints. An all-purpose or kerf unit contains two closely spaced webs in the center, rather than the typical single web. This allows the unit to be easily split on the jobsite, producing two 8 in. (203 mm) long units, which are typically used adjacent to openings or at the ends or corner of a wall. Bullnosed units are available with either a single or double bull nose, to soften corners. Screen units are available in many sizes and patterns. Typical applications include exterior fences, interior partitions, and openings within interior concrete masonry walls. Bevelled-end units, forming a 45o angle with the face of the unit, are used to form walls intersecting at 135o angles. Units in adjacent courses overlap to form a running bond pattern at the corner. A variety of concrete masonry units are designed to increase energy efficiency. These units, examples of which are shown in Figure 5, may have reduced web areas to reduce heat loss through the webs. Web areas can be reduced by reducing the web height or thickness, reducing the number of webs, or both. In addition, the interior face shell of the unit can be made thicker than a typical face shell for increased thermal storage, and hence further increase energy efficiency. Insulating inserts can also be incorporated into standard concrete masonry units to increase energy efficiency. Acoustical units (Figure 6) dampen sound, thus improving the noise reduction attributes of an interior space. Acoustical units are often used in schools, industrial plants, and churches, and to improve internal acoustics. SURFACE FINISHES The finished appearance of a concrete masonry wall can be varied with the size of units, shape of units, color of units and mortar, bond pattern, and surface finish of the units. The various shapes and sizes of concrete masonry units described above are often available in a choice of surface finishes. Some of the surfaces are molded into the units during the manufacturing process, while others are applied separately. Figure 7 shows some of the more common surface textures available. Ribs, flutes, striations, offsets, and scores are accomplished by using a unit mold with the desired characteristics. Split-faced units are molded with two units face-to-face and then the units are mechanically split apart. Glazed units are manufactured by bonding a permanent colored facing to a concrete masonry unit, providing a smooth impervious surface. Glazed units are often used for brightlycolored accent bands, and in gymnasiums, rest rooms, and indoor swimming pools where the stain and moisture resistant finish reduces maintenance. Glazed units comply to Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units, ASTM C 744 (ref. 6). Ground-face units are ground to achieve a smooth finish which reveals the natural colors of the aggregates. Often, specific aggregates will be used to enhance the appearance. For more information on surface finishes, see TEK 2-3A 21 Architectural Concrete Masonry Units (ref. 1).
Figure 7—Examples of Surface Finishes Available For Concrete Masonry Units (clockwise from bottom left: split face with three scores; single score ground face; glazed corner unit; ground face; ground face; single score glazed ; split face; ground face; split face; center: eight-ribbed split face)
REFERENCES 1. Architectural Concrete Masonry Units, TEK 2-3A, National Concrete Masonry Association, 2001. 2. Shapes and Sizes Directory, National Concrete Masonry Association, 1995. 3. Standard Methods of Sampling and Testing Concrete Masonry Units and Related Units, ASTM C 140-01ae1. American Society for Testing and Materials, 2001. 4. Standard Specification for Concrete Building Brick, ASTM C 55-01a. American Society for Testing and Materials, 2001. 5. Standard Specification for LoadBearing Concrete Masonry Units, ASTM C 90-01a. American Society for Testing and Materials, 2001. 6. Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units, ASTM C 744-99. American Society for Testing and Materials, 1999.
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Disclaimer: Although care has been taken to ensure the enclosed information is as accurate and complete as possible, NCMA does not assume responsibility for errors or omissions resulting from the use of this TEK.
NATIONAL CONCRETE MASONRY ASSOCIATION 13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org
To order a complete TEK Manual or TEK Index, contact NCMA Publications (703) 713-1900 22
An
information
series
from
the
national
authority
on
CONSIDERATIONS FOR USING SPECIALTY CONCRETE MASONRY UNITS INTRODUCTION Concrete masonry is an extremely versatile building product in part because of the wide variety of aesthetic effects that can be achieved using concrete masonry units. Concrete masonry units are manufactured in different sizes, shapes, colors, and textures to achieve a number of finishes and functions. In addition, because of its modular nature, different concrete masonry units can be combined within the same wall to produce variations in texture, pattern, and color. For the purposes of this TEK, “standard” concrete masonry units are considered to be two-core units (i.e., those with three cross webs), 8 in. (203 mm) high, 16 in. (406 mm) long and 4, 6, 8, 10 or 12 in. (102, 154, 203, 254 or 305 mm) wide. In addition, concrete brick is available in typical lengths of 8, 9, 12 and 16 in. (203, 229, 305 and 406 mm), nominal 4 in. (102 mm) width, and a wide range of heights. In addition to these "standard" units, many additional units have been developed for a variety of specific purposes, such as aesthetics, ease of construction and improved thermal or acoustic performance. For the purposes of this TEK, units other than those described above as standard will be referred to as specialty units. Specialty units can include units of different sizes or different unit configurations. Units of specialty configuration which are used at discreet wall locations rather than to construct an entire wall, such as sash units, pilaster units, etc. are not discussed here, nor are proprietary units discussed in detail. See TEK 2-1A, Concrete Masonry Unit Shapes and Sizes (ref. 1), for information on these units. By definition, specialty units are not available from all concrete masonry manufacturers. In some cases, such as the A- and H-shaped units used for reinforced construction,
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1-1E, 2-1A, 5-12, 5-15, 14-1B, 14-13B NCMA TEK 2-2B
concrete
masonry
technology
TEK 2-2B
Unit Properties (2010)
the “specialty” is commonly available in certain geographic areas. In California, for example, A- and H-shaped units are considered to be standard units. Other unit configurations discussed below may be available across the country, but from a relatively small number of producers. For this reason, it is imperative that the designer communicate with local concrete masonry manufacturers to establish the availability of the units discussed in this TEK, as well as other specialty units that may be available. Local manufacturers can provide detailed information on specific products, or the feasibility of producing custom units. Regardless of unit size or configuration, concrete masonry units are required to comply with Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90 (ref. 2). See TEK 1-1E, ASTM Specifications for Concrete Masonry Units (ref. 3), for more detailed information. This TEK discusses the advantages of using specialty units, and some of the design and construction issues that may impact the use of these units SPECIALTY UNIT SIZES Concrete masonry units may be produced with widths, heights, and/or lengths other than the standard sizes listed above. Use of these units produces walls with a scale and aesthetic properties different from those built with standard-sized units. Construction productivity may be impacted by the size, weight and configuration of the units selected. Also, some of the special shapes and sizes may not be available, and may require modification on site by the contractor. One of the most important construction consideration when using specialty-sized units is modular coordination. Modular coordination is the practice of laying out
Keywords: unit shapes, unit sizes, modular coordination, section properties
23 1
and dimensioning structures and elements to standard lengths and heights to accommodate proportioning and incorporating modular-sized building materials. Modular coordination helps maximize construction efficiency and economy by minimizing the number of units that must be cut to accommodate window and door openings, for example. See TEK 5-12, Modular Layout of Concrete Masonry (ref. 4) for information on modular coordination with standard-sized units. In addition to the specialty height units and specialty length units discussed below, veneer units (typically 4 in. (102 mm) thick) may be available in various specialty sizes, up to 16 in. high by 24 in. long (406 x 610 mm).
further information. Veneer anchor spacing requirements remain the same regardless of unit height. For units with a height greater than 8 in. (203 mm), these spacing requirements should be verified and the anchor spacing planned out prior to construction. As an example, consider 12-in. (305-mm) high veneer units installed over a concrete masonry backup wythe. The anchor spacing requirements are: maximum wall surface area supported of 2.67 ft2 (0.25 m2); maximum vertical anchor spacing of 18 in. (457 mm); and maximum horizontal anchor spacing or 32 in. (813 mm) (ref. 11). In this case, anchors need to be installed in every course to meet the requirement for a maximum vertical anchor spacing of 18 in. (457 mm). If the anchors are spaced horizontally at the maximum 32 in. (813 mm), the wall area supported is 2.67 ft2 (0.25 m2), so this veneer anchor spacing meets the code requirements. Veneer anchor spacing requirements are presented in detail in TEK 3-6B, Concrete Masonry Veneers (ref. 8). Another consideration for units with a height exceeding 8 in. (203 mm) is the use of joint reinforcement. Joint reinforcement in concrete masonry can be used to provide crack control, horizontal reinforcement in low seismic categories, and bond for multiple wythes, corners and intersections. Most requirements and rules of thumb for joint reinforcement are based on a specific area of reinforcement per foot of wall height and assume an 8-in. (203-mm) modular unit height. These should be considered prior to construction for units with heights exceeding 8 in. (203 mm). For example, empirical concrete masonry crack control criteria calls for horizontal reinforcement of at least 0.025 in.2/ft of wall height (52.9 mm2/m) between control joints. This corresponds to a maximum vertical spacing of 16 in. (406 mm) when 2-wire W1.7 (9 gage, MW11) joint reinforcement is used. When using 12-in. (305-mm) high units, the joint reinforcement of that size needs to be placed in every horizontal bed joint to meet this requirement. A better alternative is to use 2-wire W2.8 (3/16 in., MW18) joint reinforcement, with a
Specialty Unit Heights Although the most commonly available concrete masonry unit height is 8 in. (203 mm), concrete masonry units may be available in 4-in. ("half-high") or 12-in. (102and 305-mm) high units. Half-high units are gaining in popularity. They provide an aspect ratio similar to brick, but are hollow loadbearing units. See TEK 5-15, Details for Half-High Concrete Masonry Units (ref. 7) for more detailed information. As long as the unit cross-section (i.e., face shell and web thicknesses) is the same as the corresponding 8-in. (203-mm) high unit, these specialty height units can be considered to be structurally equivalent to their corresponding 8-in. (203-mm) high unit. Vertical modular coordination must be adjusted in some cases with these units. Using 4-in. (102-mm) high units provides some additional flexibility in placing wall openings, as the wall is built on a 4-in. (102-mm) vertical module rather than an 8-in. (203-mm) vertical module. With 12-in. high units, the wall height, door opening height and window opening height should ideally be a multiple of 12-in. (305-mm) to minimize cutting units on site (see Figure 1). Note that special door frames may need to be ordered to fit the masonry opening. See TEK 5-12 for
48 in. (1,219 mm)
36 in. (914 mm)
120 in. (3,048 mm) 84 in. (2,134 mm)
48 in. (1,219 mm)
88 in. (2,235 mm)
120 in. (3,048 mm)
32 in. (813 mm)
Figure 1—Vertical Modular Coordination: 12-in. (305-mm) Unit vs. Height 8-in. (203-mm) Unit Height 2
24 NCMA TEK 2-2B
maximum vertical spacing of 24 in. (610 mm), allowing the joint reinforcement to be placed every other course when using 12-in. (305-mm) high units. See TEK 10-2C, Control Joints for Concrete Masonry Walls—Empirical Method (ref. 9) for a discussion of joint reinforcement for crack control, and TEK 12-2B, Joint Reinforcement for Concrete Masonry (ref. 10), for an overview of code requirements for the use of joint reinforcement. Properties of wire for masonry (including steel cross-sectional area) can be found in Table 3 of TEK 12-4D, Steel Reinforcement for Concrete Masonry (ref. 12) Specialty Unit Lengths Specialty concrete masonry unit lengths include 18in. and 24-in. (457- and 610-mm) long units. Concrete masonry units longer than 16 in. (406 mm) are produced with the same equivalent web thickness (i.e., the average web thickness per length of wall) as 16-in. (406-mm) long units, per ASTM C90. As such, these units can be considered to be structurally equivalent to a 16-in. (305mm) long unit of the same width. Horizontal modular coordination should be considered when using these units. For example, wall length and placement of wall openings should ideally be a multiple of the unit length, as shown in Figure 2. Veneer anchor spacing and joint reinforcement considerations are the same as for standard-length units. Specialty Unit Widths In addition to the standard unit widths of 4, 6, 8, 10, and 12 in. (102, 152, 203, 254, 305 mm), specialty widths may include 14 and 16 in. (356 and 406 mm). Because unit width does not affect modular coordination, layout
36 in. (914 mm)
36 in. 36 in. 18 in. 18 in. (914 mm) (457 mm) (914 mm) (457 mm)
considerations are generally the same as for walls constructed using standard concrete masonry units. One construction issue that arises with different unit widths is corner details. TEK 5-9A, Concrete Masonry Corner Details (ref. 13), presents details to minimize cutting of units while maintaining modularity for 4, 6, 8, 10, and 12 in. (102, 152, 203, 254, 305 mm) wide units. Corner details for 14-in. (356-mm) wide units are similar to those for 12-in. (305 mm) wide units, using 8-in. (203-mm) wide units with 2 x 6 in. (51 x 152 mm) pieces of masonry to fill the gaps in the inside corners. Because 16 in. (406 mm) is a modular size, corner details for these units are similar to those for 8-in. (203-mm) wide units. A standard 8-in. (203-mm) wide unit is used in each course at the corner to maintain the running bond. Structural considerations may differ, however, as both the section properties and wall weight varies with wall width. TEKs 14-1B, Section Properties of Concrete Masonry Walls, and 14-13B, Concrete Masonry Wall Weights (refs. 5, 6), list these properties for 14 and 16 in. (356 and 406 mm) wide walls. From a construction standpoint, the larger cores of 14- and 16-in. (356 and 406 mm) wide units accommodate more reinforcement or insulation, when used, and require more grout to fill reinforced cells. SPECIALTY UNIT CONFIGURATIONS Specialty unit configuration refers to units whose crosssection varies significantly from that of a standard two-core concrete masonry unit. In this case, structural properties may be different from standard units. Modular coordination is the same as for standard units, unless the specialty configuration
32 in. (813 mm)
16 in. 40 in. 24 in. 40 in. (1,016 mm) (610 mm) (1,016 mm)(406 mm)
Figure 2—Horizontal Modular Coordination: 18-in. (457-mm) Unit Length vs. 16-in. (406-mm) Unit Length NCMA TEK 2-2B
25 3
is also produced in a specialty size. A variety of concrete masonry units have been developed to address specific performance or construction criteria. For example, units developed for improved energy efficiency may have reduced web areas to reduce heat loss through the webs, a thickened interior face shell for increased thermal storage, and/or additional cavities within the unit to accommodate insulation. Acoustical concrete masonry units provide increased sound absorption and/ or diffusion. These units may have unique construction and/or structural considerations, depending on their configuration. The concrete masonry producer should be contacted for more detailed information on the specific unit under consideration. Units to Facilitate Reinforced Construction Concrete masonry unit shapes have been developed for a wide variety of applications. The shapes illustrated in Figure 3 have been developed specifically to accommodate vertical reinforcement. Bond beam and lintel units have also been developed to accommodate horizontal
reinforcement. Open-ended units allow concrete masonry units to be inserted around vertical reinforcing bars. This eliminates the need to lift units over the top of embedded vertical reinforcement, or to thread the reinforcement through the masonry cores after the wall is constructed. Because all open cells of A- and H-shaped units are grouted and bond beam and lintel units are fully grouted, walls constructed with these units can use the same structural design parameters as for grouted standard units.
Open-ended or
Open end, or unit A-shaped "A" shaped unit
Double-open-ended
Double open end unit or H-shaped unit
Figure 3—Examples of Unit Shapes that Accommodate Reinforcement
REFERENCES 1. Concrete Masonry Unit Shapes and Sizes, TEK 2-1A. National Concrete Masonry Association, 2002. 2. Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-09. ASTM International, 2009. 3. ASTM Specifications for Concrete Masonry Units, TEK 1-1E. National Concrete Masonry Association, 2007, 4. Modular Layout of Concrete Masonry, TEK 5-12. National Concrete Masonry Association, 2008. 5. Section Properties of Concrete Masonry Walls, TEK 14-1B. National Concrete Masonry Association, 2007. 6. Concrete Masonry Wall Weights, TEK 14-13B. National Concrete Masonry Association, 2008. 7. Details for Half-High Concrete Masonry Units, TEK 5-15. National Concrete Masonry Association, 2008. 8. Concrete Masonry Veneers, TEK 3-6B. National Concrete Masonry Association, 2005. 9. Control Joints for Concrete Masonry Walls—Empirical Method, TEK 10-2C. National Concrete Masonry Association, 2010. 10. Joint Reinforcement for Concrete Masonry, TEK 12-2B. National Concrete Masonry Association, 2005. 11. Building Code Requirements for Masonry Structures, TMS 402-08/ACI 530-08/ASCE 5-08. Reported by the Masonry Standards Joint Committee, 2008. 12. Steel Reinforcement for Concrete Masonry, TEK 12-4D. National Concrete Masonry Association, 2006. 13. Concrete Masonry Corner Details, TEK 5-9A. National Concrete Masonry Association, 2004.
NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication. NATIONAL CONCRETE MASONRY ASSOCIATION
13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org
Provided by: To order a complete TEK Manual or TEK Index, contact NCMA Publications (703) 713-1900
4
26 NCMA TEK 2-2B
NCMA TEK National Concrete Masonry Association
an information series from the national authority on concrete masonry technology
ARCHITECTURAL CONCRETE MASONRY UNITS TEK 2-3A Unit Properties (2001)
Keywords: architectural units, burnished, fluted, ground face, glazed, offset face, prefaced, raked, ribbed, sandblasted, scored, slump, split-face, split-rib, striated INTRODUCTION One of the most significant architectural benefits of designing with concrete masonry is its versatility – the finished appearance of a concrete masonry wall can be varied with the unit size and shape, color of units and mortar, bond pattern, and surface finish of the units. The term “architectural concrete masonry units” typically is used to describe units displaying any one of several surface finishes that affects the texture of the unit, allowing the structural wall and finished surface to be installed in a single step. Architectural concrete masonry units are used for interior and exterior walls, partitions, terrace walls, and other enclosures. Some units are available with the same treatment or pattern on both faces, to serve as both exterior and interior finish wall material, increasing both the economic and aesthetic advantages. Architectural units comply with the same quality standards as conventional concrete masonry, Standard
(a) Split Face and Glazed
Specification for Loadbearing Concrete Masonry Units, ASTM C 90 (ref. 3). In some cases, noted below where applicable, additional provisions govern which are more applicable to the specific unit. The units described herein are some of the more common architectural concrete masonry units. However, manufacturers may carry additional products not listed here, and conversely, not all products listed will be available in all locations. Consult a local manufacturer for final unit selection. Architectural Unit TYPEs Split Faced Units Split faced units have a natural stone-like texture produced by molding two units face-to-face, then mechanically splitting them apart after curing, creating a fractured surface. Because coarse aggregate is also fractured and exposed in this process, aggregate selection can alter the final appearance. Split-faced units can also be manufactured with ribs or scores to provide strong vertical lines in the finished wall. Rough textures, like those available with split face units, are often used in areas prone to graffiti, as the texture tends to discourage graffiti vandals.
(b) Fluted Split Face
(c) Split and Ground Face
Figure 1—Examples of Architectural Concrete Masonry Units TEK 2-3A © 2001 National Concrete Masonry Association (replaces TEK 2-3)
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Ribbed Units Ribbed concrete masonry units (often called fluted units) typically have 4, 6, or 8 vertical ribs which align to form continuous vertical elements in the finished wall. The ribs are molded into the unit using a special mold. The ribs may have either a rectangular or circular profile, and may be either smooth or split for added texture. Figure 1b shows an example of a wall using ribbed (fluted) split face units. The ribs can be manufactured to project beyond the overall unit thickness (i.e., the unit thickness including ribs is thicker than a typical CMU), or with the rib projection included in the overall unit thickness. In the first case, the net area, and corresponding section properties, will be larger than those published for non-ribbed units, although the effect of this increase is typically neglected in structural calculations. In the second case, where the rib projection is included in the overall unit thickness, the designer should be aware that the actual bearing area, section modulus, and moment of inertia are less than those published for non-ribbed units. When building concrete masonry walls, mortar is typically placed to all outside edges of the masonry unit. However, with ribbed units, it is difficult to properly tool the mortar due to the projections.
Split face units are governed by ASTM C 90, which includes an allowance to account for the rough face. ASTM C 90 prescribes minimum faceshell thickness requirements for all loadbearing concrete masonry units, but also contains a variance for split face units where up to 10% of a split faceshell can be less than the minimum specified thickness, but not less than 3/4 in. (19 mm). This 10% limit does not apply, however, when the units are solidly grouted. Walls utilizing a variety of split face units are shown in Figure 1. Soft Split A soft split unit is produced using a special mold which textures the face of the unit as it is removed from the mold. The appearance from a distance is very similar to that of a split face, while a closer inspection shows a surface that is not as well defined as that achieved with a conventional split face. In addition, aggregate is not fractured in a soft split as it is in a conventional split face unit. As a result, the final appearance is not significantly affected by aggregate choice. Scored Units Scored concrete masonry units are manufactured with one or more vertical scores on the face to simulate additional mortar joints in the wall. Scored units reduce the perceived scale of the masonry while still allowing construction using full sized units. The scores are molded into the face of the unit during manufacture. Units with one vertical score are most common, and give the appearance of 8 in. x 8 in. (203 x 203 mm) units laid in stack bond. Units may also be available with 2, 3, 5, or 7 vertical scores. Figure 2a shows units with 3 vertical scores in a standard sized ground face block. It is usually desirable to lay units so that scores or ribs align vertically when the units are placed. This may require different bond patterns, depending on the configuration of the scores or ribs. For example, units with two and five scores can be placed in either stack bond or in a one-third running bond to align scores in adjacent courses. Other appropriate bond patterns are included in Table 1. Note that varying bond patterns can impact how the wall responds to structural loads (see ref. 1).
Ground Face Units (Burnished, Honed) Ground face concrete masonry units are polished after manufacture to achieve a smooth finish which reveals the natural aggregate colors. The units have the appearance of polished natural stone. The finished look of the ground surface can be altered by changing aggregate type and proportions. Often, specific aggregates will be used to enhance the appearance of the polished surface (Figure 1c and 2a), while coatings are sometimes used to deepen the color. Ground face units are often scored to achieve a scale other than the conventional 8 x 16 in. (203 x 406 mm), as shown in Figure 2a. Sandblasted Units Sand (or abrasive) blasting is used to expose the aggregate in a concrete masonry unit and results in a "weathered" look.
(a) Scored and Ground Face
(b) Glazed
(c) Slump Block
Figure 2—Additional Examples of Architectural Concrete Masonry Units
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Striated (Raked) Units Striated units achieve an overall texture by means of small vertical grooves molded into the unit face. The striations are most often random, to achieve a naturally rough look, but are sometimes available in uniform striation patterns. Striation can be applied to scored and ribbed units as well (see Figure 3c). Glazed (Prefaced) Units Glazed concrete masonry units are manufactured by bonding a permanent colored facing (typically compsed of polyester resins, silica sand and various other chemicals) to a concrete masonry unit, providing a smooth impervious surface. The glazed facings must comply with ASTM C 744 (ref. 4), Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units, which contains minimum requirements for facing quality and dimensional tolerances. In addition, the unit to which the facing is applied must comply with ASTM C 90 when used in loadbearing applications. The glazed surface is waterproof, resistant to staining and graffiti, highly impact resistant, as well as being resistant to many chemicals and bacteria. Special admixtures and mortars are available for use with glazed units that provide better stain, bacteria, and water penetration resistance. Glazed units are available in a variety of vibrant colors, pastels, earth tones, and even faux granite and marble patterns. They are often used for brightly-colored accent bands, and in gymnasiums, rest rooms, and indoor swimming pools where the stain and moisture resistant finish reduces maintenance. Kitchens and laboratories also benefit from the chemical and bacteria-resistant surface. Offset Face Units Units with an offset face produce a very highly textured wall, with strong patterns of light and shadow. The offsets make it appear as if adjacent units are staggered. This effect is accomplished by using a unit mold with the desired offsets. Slump Block Units Slump block concrete masonry units have a rounded face that resembles handmade adobe. They are more commonly available in the Southwest United States where adobe is part of the architectural heritage. Conventional concrete masonry units are manufactured using a “no-slump” concrete mix, which holds its shape when removed from the manufacturing mold. Slump units, on the other hand, are manufactured using a concrete mix that slumps within desired limits when removed from its mold (see Figure 2c). Slump unit widths may vary as much as 1 in. (25 mm). For this reason, the structural design should assume the actual width of slump units is 1 in. (25 mm) less than the nominal dimension. COLOR Architectural concrete masonry units are often integrally colored to enhance the appearance or achieve a particular effect. Concrete masonry units are colored by adding mineral oxide pigments to the concrete mix. Mortars can also be integrally colored to blend or contrast with the masonry units. The final unit color varies with the amount and type of
pigment used, cement color, aggregate color, and the amount of water used in the mix (a wetter mix will generally produce lighter and brighter colors). Both white and gray cements are available. The use of white cement results in more vibrant colors, but also increases cost. The aggregates used in the concrete mix also impact the final appearance. Because of these varying factors, there are typically some subtle variations in color among units. When units must be exactly the same color to achieve a particular architectural effect, uncolored units should be used, then painted or stained the desired color. Variegated units provide color variations within each unit, producing a marbled effect. These units are manufactured by mixing two different concrete colors into the same unit mold. Standard Unit Nomenclature As with many construction products and systems, there are often regional differences in terminology for the same type of architectural concrete masonry units: ribbed and fluted, ground and burnished, etc. The National Concrete Masonry Association has developed a standardized nomenclature (see Table 1) which can be used to avoid confusion when specifying and supplying masonry units. (See Figure 3 for examples). Table 1 – Standard Unit Nomenclature (ref. 2) Each unit is described using a three-part code in the following format: XX YYY WWHHLL, where “XX” describes the number of scores or ribs, “YYY” describes the architectural finish, and WWHHLL describes the overall nominal unit dimensions for width, height, and length. The various codes are described below. Scores or Ribs: 00 no scores or ribs, applicable for any running bond 01 one score, applicable for one-half running bond (units overlap the unit above and below by one-half the unit length) 02 2 scores, applicable for one-third running bond 03 3 scores, applicable for one-half or one-quarter running bond 04 4 ribs, applicable for one-half or one-quarter running bond 05 5 scores, applicable for one-half running bond 06 6 ribs, applicable for one-half running bond 07 7 scores, applicable for one-half or one-quarter running bond 08 8 ribs, applicable for one-half or one-quarter running bond Architectural Finish: BN1 bullnose unit with 1 in. (25 mm) radius bullnose BN2 bullnose unit with 2 in. (51 mm) radius bullnose SCV vertically scored unit GRF ground face unit MDC circular ribs, rib projects beyond the overall unit thickness MNC circular ribs, rib projection included in overall unit thickness MDR rectangular ribs, rib projects beyond the overall unit thickness MNR rectangular ribs, rib projection included in unit thickness STR striated unit STS striated unit, 1 in. (25 mm) uniform striation pattern STT striated unit, 1/16 in. (1.6 mm) uniform striation pattern SPF split face unit NPF split face ribbed unit, rib projections included in unit thickness SLP slump block **Q locally provided product
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08 MNR 080816 8 x 8 x 16 Rectangular ribbed unit (rib projection included in overall unit thickness), with 8 ribs
Figure 3a—Rectangular Ribbed Unit
06 MNC 080816 8 x 8 x 16 rounded ribbed unit (rib projection included in overall unit thickness), with 6 ribs
Figure 3b—Rounded Rib Unit
01 STR 080816 8 x 8 x 16 striated corner unit striated patterns are often applied to scored or ribbed units
Figure 3c—Striated Scored Unit
00 BN1 120816 12 x 8 x 16 Bullnose Unit with 1 in. (25 mm) radius bullnose.
Figure 3d—Bullnose Unit
Figure 3—Examples of Standard Unit Nomenclature References 1. Concrete Masonry Bond Patterns, TEK 14-6. National Concrete Masonry Association, 1996. 2. Concrete Masonry Shapes & Sizes Manual, CM 260A. National Concrete Masonry Association, 1997. 3. Standard Specification for Loadbearing Concrete Masonry Units, ASTM C 90-00. American Society for Testing and Materials, 2000. 4. Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units, ASTM C 744-99. American Society for Testing and Materials, 1999.
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To order a complete TEK Manual or TEK Index, contact NCMA Publications (703) 713-1900
30
NCMA TEK National Concrete Masonry Association an information series from the national authority on concrete masonry technology
SEGMENTAL RETAINING WALL UNITS
TEK 2-4B Unit Properties
Keywords: absorption, architectural units, compressive strength, coupon testing, dimensions, durability, erosion control, retaining wall, segmental retaining wall, specifications, testing INTRODUCTION Mortarless segmental retaining walls are a natural enhancement to a variety of landscape projects. Applications range from 8 in. (204 mm) high terraces for erosion control to retaining walls 20 ft (6.1 m) or more in height. The individual concrete units can be installed to virtually any straight or curved plan imaginable. Segmental retaining walls are used to stabilize cuts and fills adjacent to highways, driveways, buildings, patios and parking lots, and numerous other applications. Segmental retaining walls replace treated wood, cast-in-place concrete, steel, and other retaining wall systems because they are durable, easier and quicker to install, and blend naturally with the surrounding environment. Concrete units resist deterioration when exposed to the elements without addition of toxic additives which can threaten the environment.
A variety of surface textures and features are available, including split faced, stone faced, and molded face units, any one of which may be scored, ribbed, or colored to fit any project application. Construction of segmental retaining walls does not require heavy equipment access, nor does the system require special construction skills to erect. Manufactured concrete retaining wall units weigh approximately 30 to 100 lb (14 to 45 kg) each and are placed by hand on a level or sloped gravel bed. Successive courses are stacked dry on the course below in the architectural pattern desired. Mechanical interlocking and/or frictional shear strength between courses resists lateral soil pressure. In low-height walls, overturning forces due to soil pressure are resisted by the weight of the units, sometimes aided by an incline toward the retained soil. Higher walls resist lateral soil pressures by inclining the wall toward the retained
Shoreline erosion control Terracing Figure 1—Examples of Segmental Retaining Wall Installations TEK 2-4B © 2008 National Concrete Masonry Association (replaces TEK 2-4A)
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(2008)
earth, or by other methods such as anchoring to geosynthetic reinforcement embedded in the soil. Further information on the design of segmental retaining walls can be found in Design Manual for Segmental Retaining Walls (ref. 1) and Segmental Retaining Wall Drainage Manual (ref. 2). Segmental retaining wall units are factory manufactured to quality standards in accordance with ASTM C 1372, Standard Specification for Segmental Retaining Wall Units (ref. 3). These requirements are intended to assure lasting performance, little or no maintenance, structural integrity, and continued aesthetic value. Segmental retaining wall units complying with the requirements of ASTM C 1372 have been successfully used and have demonstrated good field performance. Segmental retaining wall units currently being supplied to the market should be produced in accordance with this standard so that both the purchaser and the supplier have the assurance and understanding of the expected level of performance of the product. ASTM C 1372 covers both solid and hollow units which are to be installed without mortar (dry-stacked). Units are designed to interlock between courses or to use mechanical devices to resist sliding due to lateral soil pressure. If particular features are desired, such as a specific weight classification, higher compressive strength, surface texture, finish, color, or other special features, they should be specified separately by the purchaser. However, local suppliers should be consulted as to the availability of units with such features before specifying them. Materials ASTM C 1372 includes requirements that define acceptable cementitious materials, aggregates, and other constituents used in the manufacture of concrete segmental retaining wall units. These requirements are similar to those included in ASTM C 90, Standard Specification for Loadbearing Concrete Masonry Units (ref. 4). Compressive Strength Minimum compressive strength requirements for segmental retaining wall units are included in Table 1. Units meeting or exceeding these strengths have demonstrated the integrity needed to resist the structural demands placed on them in normal usage. These demands include impact and vibration
during transportation, the weight of the units above them in the wall, nonuniform distribution of loads between units, and the tensile stresses imposed as a result of typical wall settlement. Segmental retaining wall units will not fail in service due to compressive forces since axial loads are only a result of selfweight. Due to the direct relationship between compressive strength and tensile strength, this minimum requirement is used to ensure overall performance. Compressive strength testing of full size units is impractical due to the large size and/or unusual shape of some segmental retaining wall units. Therefore, compressive strength of these units is determined from testing coupons cut from the units. The results of tests on these smaller coupons will typically yield lower strengths than if the larger, full-size specimen were tested. The reason for the difference is size and aspect ratio. However, it is important to keep in mind that the compression test is not intended to determine the load carrying capacity of the unit, since segmental retaining walls are not designed to carry vertical structural loads. Compressive strength is used solely to determine the quality of the concrete. Because tested strengths are affected by size and shape of the specimen tested, it is important that all retaining wall units be tested using a similar size and shape. ASTM C 140, Standard Method of Sampling and Testing Concrete Masonry Units (ref. 5) requires that specimens cut from full-size units for compression testing shall be a coupon with a height to thickness ratio of 2 to 1 before capping and a length to thickness ratio of 4 to 1. The coupon width is to be as close to 2 in. (51 mm) as possible based on the configuration of the unit and the capacity of the testing machine, but not less than 1.5 in. (38 mm). The preferred size is 2 x 4 x 8 in. (51 x 102 x 203 mm) (width x height x length). The coupon height is measured in the same direction as the unit height dimension. If these procedures are followed, the compressive strength of the coupon is considered to be the strength of the whole unit. Alignment of the specimen in the compression machine is critical. Care should be taken in capping the test specimen to assure that capping surfaces are perpendicular to the vertical axis of the specimen. Saw-cutting is the required method of extracting a test specimen from a full size unit. Proper equipment and procedures are essential to prevent damaging the test specimen as a result of saw-cutting. Water-cooled, diamond-tipped blades
Table 1—Strength and Absorption Requirements (ref. 3) Minimum required net area compressive strength psi (MPa) Average of three units
Individual unit
3,000 (20.68)
2,500 (17.24)
Maximum water absorption requirements lb/ft3 (kg/m3) Weight classification—oven dry density of concrete lb/ft3 (kg/m3) Lightweight Medium weight Normal weight less than 105 (1680) to 125 (2000) 105 (1680) less than 125 (2000) or more 18 (288)
15 (240)
13 (208) 32
on a masonry table saw are recommended. The blade should have a diameter sufficient enough to make all cuts in a single pass. Manufacturers of the unit (or licensors of proprietary shapes) should be consulted about recommended locations for obtaining the compression specimen. Weight Classification Weight classifications for segmental retaining wall units are defined in Table 1. The three classifications, lightweight, medium weight, and normal weight, are a function of the oven dry density of the concrete. Most segmental retaining wall units fall into the normal weight category. Absorption Absorption requirements are also included in Table 1. This value is used to represent the volume of voids in a concrete masonry unit, including voids inside the aggregate itself. The void space is measured by determining the volume of water that can be forced into the unit under the nominal head pressure that results from immersion in a tank of water. Lightweight aggregates used in the production of lightweight and medium weight units contain voids within the aggregate itself that also fill with water during the immersion test. While reduced voids indicate a desired tightly compacted unit, tightly compacted lightweight and medium weight units will still have higher absorption due to the voids in the aggregates. For this reason the maximum allowable absorption requirements vary according to weight classification. Similar to compression testing, it generally is not practical to test full-size retaining wall units in absorption tests due to their size and weight. Therefore, ASTM C 140 permits the testing of segments saw-cut from full-size units to determine absorption and density. Sampling location typically has little effect on tested results. Absorption limits are typically expressed as mass (weight) of water absorbed per concrete unit volume. This is preferred to expressing by percentage which permits a denser unit to absorb more water than a lighter weight unit. As previously discussed, this relationship is opposite of the absorption characteristics of the material. Testing larger specimens requires particular attention to drying times, because it takes a greater length of time to remove all moisture from larger masses. ASTM C 140 requires that specimens be dried for a period of not less than 24 hours at a temperature of at least 212 °F (100 °C). The 24-hour time period does not start until the oven reaches the specified temperature. When placing larger specimens in an oven, it may take several hours for the oven to reach the prescribed temperature. ASTM C 140 then requires that specimen weights be determined every two hours to make sure that the unit is not still losing water weight (maximum weight loss in two hours must be less than 0.2% of the previous specimen weight). This will require 48 hours or more for some specimens. If not dried adequately, reported absorptions will be lower than the actual value. Permissible Variations in Dimensions Mortarless systems require consistent unit heights to
maintain vertical alignment and level of the wall. For this reason permissible variation in dimensions is limited to not more than + 1/8 in. (3.2 mm) from the specified standard dimensions. Regarding dimensions, “width” refers to the horizontal dimension of the unit measured perpendicular to the face of the wall. “Height” refers to the vertical dimension of the unit as placed in the wall. “Length” refers to the horizontal dimension of the unit measured parallel to the running length of the wall. Dimensional tolerance requirements for width are waived for split faced and other architectural surfaces. The surface is intended to be rough to satisfy the architectural features desired and can not be held to a specific tolerance. Finish and Appearance Finish and appearance requirements are virtually the same as those in ASTM C 90 for loadbearing concrete masonry units. Minor cracks incidental to the usual method of manufacture or minor chipping resulting from customary methods of handling in shipment and delivery, are not grounds for rejection. Units used in exposed wall construction are not to show chips or cracks or other imperfections in the exposed face when viewed from a distance of not less that 20 ft (6.1 m) under diffused lighting. In addition, up to five percent of a shipment are permitted to contain chips not larger than 1 in. (25.4 mm) in any dimension, or cracks not wider than 0.02 inches (0.5 mm) and not longer than 25% of the nominal height of the unit. Freeze-Thaw Durability Segmental retaining wall units may be used in aggressive freezing and thawing environments. However, freeze-thaw damage can occur when units are saturated with water and then undergo temperature cycles that range from above to below the freezing point of water. Freezing and thawing cycles and a constant source of moisture must both be present for potential damage to occur. Many variations can exist in exposure conditions, any of which may affect the freeze-thaw durability performance of the units. Such variations include: maximum and minimum temperatures, rate of temperature change, duration of temperatures, sunlight exposure, directional facing, source and amount of moisture, chemical exposure, deicing material exposure, and others. ASTM C 1372 includes three different methods of satisfying freeze-thaw durability requirements: 1. proven field performance, 2. five specimens shall each have less than 1% weight loss after 100 cycles in water using ASTM C 1262 (ref. 6), or 3. four of five specimens shall have less than 1.5% weight loss after 150 cycles in water using ASTM C 1262. Segmental retaining wall units in many areas of the country are not exposed to severe exposures. Therefore, the requirements above apply only to “areas where repeated freezing and thawing under saturated conditions occur.” Freeze-thaw durability tests can be conducted in accordance with ASTM C 1262 using water or saline as the media. For most applications, tests in water are considered sufficient. 33
If the units are to be exposed to deicing salts on a regular basis, consideration should be given to performing the tests in saline. However, no pass/fail criteria has been adopted by ASTM for saline testing. Compliance Guidance regarding compliance is also provided in ASTM C 1372. If a sample fails, the manufacturer can then remove or cull units from the shipment. Then, a new sample is selected by the purchaser from the remaining units of the shipment and tested, which is paid for by the manufacturer. If the second sample passes then the remaining units of the
lot being sampled are accepted for use in the project. If the second sample fails, however, the entire lot represented by the sample is rejected. The specification also provides guidance on responsibility for payment of the tests. Unless otherwise provided for in the contract, the purchaser typically pays for the testing if the units pass the test. However, if the units fail the test, the seller bears the cost of the testing. See TEK 18-10 Sampling and Testing Segmental Retaining Wall Units (ref. 7) for more detailed information on SRW unit sampling, testing, and acceptance.
REFERENCES 1. Design Manual for Segmental Retaining Walls, 2nd edition. National Concrete Masonry Association, 2002. 2. Segmental Retaining Wall Drainage Manual. National Concrete Masonry Association, 2002. 3. Standard Specification for Dry-Cast Segmental Retaining Wall Units, ASTM C 1372-04e2. ASTM International, 2004. 4. Standard Specification for Loadbearing Concrete Masonry Units, ASTM C 90-03. ASTM International, 2003. 5. Standard Methods of Sampling and Testing Concrete Masonry Units and Related Units, ASTM C 140-03. ASTM International, 2003. 6. Standard Test Method for Evaluating the Freeze-Thaw Durability of Manufactured Concrete Masonry Units and Related Concrete Units, ASTM C 1262-07. ASTM International, 2007. 7. Sampling and Testing Segmental Retaining Wall Units, TEK 18-10. National Concrete Masonry Association, 2005.
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Disclaimer: Although care has been taken to ensure the enclosed information is as accurate and complete as possible, NCMA does not assume responsibility for errors or omissions resulting from the use of this TEK. NATIONAL CONCRETE MASONRY ASSOCIATION 13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org
To order a complete TEK Manual or TEK Index, 34 contact NCMA Publications (703) 713-1900
NCMA TEK National Concrete Masonry Association
an information series from the national authority on concrete masonry technology
SPECIFICATIONS FOR CONCRETE MASONRY ROOF PAVERS Keywords: ASTM Standards, absorption, ballasted roofs, compressive strength, durability, flexural strength, interlocking roof pavers, roof ballast, roof pavers, testing
INTRODUCTION Concrete roof pavers provide resistance to wind uplift and surface protection for roofing membranes. Concrete roof paver systems are installed over flat roofs and allow melting snow and ice, or rain water to drain from below the roof paver surface. Ballast weight of the concrete roof paver system is designed to resist uplift forces from the entire range of design wind speeds. Concrete roof pavers also provide a durable wearing surface for roof maintenance and repair operations. Specifications for concrete roof pavers included herein specify the physical requirements to ensure field performance. Also presented are methods of sampling and testing pavers to demonstrate compliance with these requirements. Concrete Roof Paver Systems Concrete roof paver systems are categorized as interlocking or non-interlocking. Interlocking systems distribute uplift forces to adjacent pavers by a tongue and groove edge connection or by a mechanical interlock between units. Noninterlocking systems resist uplift by the ballast weight of individual paver units.
Design and Execution In addition to the physical characteristics of the roof paver units themselves, parameters for design of concrete roof paver systems include the following: • Basic wind speed at building site • Building height • Parapet height • Wind gust factors • Adjacent structures and terrain features to account for obstructions in the area • Load capacity of the roof structure • Roof discontinuities • Roof slope • Weight of the units Roof structures must be designed to support the dead weight of roof paver systems. Where roof pavers are installed over existing roofs, it is important to evaluate the structural adequacy of the existing roof to support the roof pavers. Since modern roof paver systems usually contain integral drainage grooves, consideration should be given to their orientation parallel to the roof slope, min. 1/4" per foot (20 mm/m), towards roof drains. See Figure 1 for a typical concrete paver roof installation.
COUNTERFLASHING IN REGLET
Concrete Roof Paver Units Roof pavers are exposed to severe weather conditions due to their horizontal installation over flat or low slope roofs. In cold weather regions, roof pavers can be routinely subjected to freezing and thawing in a saturated condition. Typically these units will also be required to support foot traffic, loaded wheelbarrows, and other equipment without damaging the roofing membrane and insulation. These conditions require that concrete roof pavers be manufactured to specific criteria. The following specification is recommended to ensure a product of consistent quality.
TEK 2-5A © 1999 National Concrete Masonry Association (replaces TEK 2-5)
TEK 2-5A
Unit Properties
8" MAX.
CLEAT & ANGLE SECURED TO WALL RETAINER ANGLE BASE FLASHING CONCRETE ROOF PAVER MASTIC OR SEALANT
3
/ 8 " MIN. PERIMETER SPACE DECK MEMBRANE ROOFING INSULATION TREATED NAILER AS REQUIRED
Figure 1—Typical Concrete Paver Roof Installation
35
(1999)
Specification for CONCRETE ROOF PAVERS
3.1.2.1 Limestone - Limestone, with a minimum 85% calcium carbonate (CaCO3) content, shall be permitted to be added to the cement, provided the requirements of Specification C 150 as modified are met: (1) Limitation on Insoluble Residue - 1.5% (2) Limitation on Air Content of Mortar - Volume percent, 22% max. (3) Limitation on Loss on Ignition - 7%.
1. Scope 1.1 This specification covers concrete roof pavers made from portland cement, water, and mineral aggregates, with or without the inclusion of other materials, for use as roof ballast and protection of roof membranes. Note 1 – The design of roof ballast systems for resisting wind uplift is beyond the scope of this standard. Building codes and other standards should be consulted in designing for wind uplift resistance. 1.2 Concrete roof pavers covered by this specification are made from lightweight or normal weight aggregates, or both. 1.3 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only. 2. Referenced documents
2.1 ASTM Standards: C33 Specification for Concrete Aggregates C140 Methods of Sampling and Testing Concrete Masonry Units C150 Specification for Portland Cement C331 Specification for Lightweight Aggregates for Concrete Masonry Units C595/C595M Specification for Blended Hydraulic Cements C618 Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete C989 Specification for Ground Granulated BlastFurnace Slag for Use in Concrete and Mortars C1157/C1157M Performance Specification for Blended Hydraulic Cement C1262 Standard Test Method for Evaluating the Freeze-Thaw Durability of Manufactured Concrete Masonry Units and Related Concrete Units
3. Materials 3.1 Cementitious Materials - Materials shall conform to the following applicable specifications: 3.1.1
Portland Cement - specification C 150.
3.1.2 Modified Portland Cement - Portland Cement conforming to specification C 150 modified as follows:
3.1.3 Blended Cements - Specification C 595/C 595M or C 1157/C 1157M. 3.1.4 Pozzolans - Specification C 618 3.1.5 Blast Furnace Slag - Specification C 989 3.2 Aggregates - Aggregates shall conform to the following specifications, except that grading requirements shall not necessarily apply: 3.2.1 C 33.
Normal Weight Aggregates - Specification
3.2.2 331.
Lightweight Aggregates - Specification C
3.3 Other Constituents - Air-entraining agents, coloring pigments, integral water repellents, finely ground silica, and other constituents shall be previously established as suitable for use and shall conform to applicable ASTM Standards or, shall be shown by test or experience satisfactory to the purchaser to be not detrimental to the durability of the units. 4. Physical Requirements 4.1 At the time of delivery to the purchaser, all units shall conform to the requirements prescribed in Table 1 and shall have a minimum net area average compression strength (average of 3 units) of 3000 psi (20.68 MPa) Table 1—Absorption Requirements for Concrete Roof Pavers
Concrete Density lb/ft3/(kg/m3) 95 (1522) or less over 95 to 115 (1522 to 1842) 115 (1842) or more
Maximum Water Absorption lb/ft3/(kg/m3) (average of 3 units) 15 (240) 13 (208) 10 (160)
36
with no individual unit compressive strength less than 2600 psi (17.93 MPa) when tested in accordance with Section 7.2 4.2 Resistance to Flexural Load - The average resistance to flexural load for three paver units shall exceed 350 lb (1557 N) and resistance to flexural load of each individual unit shall exceed 280 lb (1246 N) when tested in accordance with Section 7.2. 4.3 Ballast Weight—Requirements for ballast weight per unit area shall be specified separately. 4.4 Freeze-Thaw Durability—In areas where repeated freezing and thawing under saturated conditions occur, freeze-thaw durability shall be demonstrated by test or by proven field performance that the concrete roof paver units have adequate durability for the intended use. When testing is required by the specifier to demonstrate freezethaw durability, the units shall be tested in accordance with the requirement of Section 7.3. 4.4.1 Specimens shall comply with either of the following: (1) the weight loss of each of five test specimens at the conclusion of 100 cycles shall not exceed 1% of its initial weight; or (2) the weight loss of each of four or five test specimens at the conclusion of 150 cycles shall not exceed 1.5% of its initial weight. Note 2 – This standard does not include criteria for large hail stone impact. Where
required, these criteria should be specified by the purchaser. 5. Permissible Variations in Dimension and Weight 5.1 Overall dimensions for width, height, and length shall not differ by more than ± 1/8 in. (3.2 mm) from the specified standard dimensions. 5.2 Ballast weight shall not differ by more than ± 2.0 lb/ft2 (9.7 kg/m2) from the specified weight. Note 3 - Standard dimensions of units are the manufacturer’s designated dimensions. 6. Finish and Appearance 6.1 All units shall be sound and free of cracks or other defects that would interfere with the proper placement of the unit or would significantly impair the strength or permanence of the construction. Minor cracks incidental to the usual method of manufacture or minor chipping resulting from customary methods of handling in shipment and delivery, are not grounds for rejection. 6.2 Five percent of a shipment containing chips not larger than 1 in. (25.4 mm) in any dimension, or cracks not wider than 0.02 in. (0.5 mm) and not longer than 25% of the nominal height of the unit is permitted. 6.3 The color and texture of units shall be specified by the purchaser. The finished surfaces that will be
TEST FORCE DIRECTION LOAD
CUT STRIP FROM FULL PAVER 1.75" 1.75"
SPECIMEN HEIGHT (EQUAL TO SPECIMEN WIDTH)
SP EC IM EN
CAP THIS SURFACE
LE NG TH
SPECIMEN WIDTH
NEOPRENE PAD
2 X 4 WOOD BLOCK CUT TO WIDTH OF ROOF PAVER UNIT ROOF PAVER
1" DIA. STEEL ROD .90 LENGTH UNIT
NEOPRENE PAD
CAP THIS SURFACE
Figure 2—Compressive Strength Test Set-up
Figure 3—Flexural Strength Test Set-up
37
exposed in place shall conform to an approved sample consisting of not less than four units, represetning the range of texture and color permitted.
8. Compliance
7.2 Sample and test units for compressive strength, flexural load, absorption, and dimensional tolerance in accordance with Test Methods C 140.
8.1 If a sample fails to conform to the specified requirements, the manufacturer shall be permitted to remove units from the shipment. A new sample shall be selected by the purchaser from the remaining units from the shipment with a similar configuration and dimension and tested at the expense of the manufacturer. If the second sample meets the specified requirements, the remaining portion of the shipment represented by the sample meets the specified requirements. If the second sample fails to meet the specified requirements, the remaining portion of the shipment re[resented by the sample fails to meet the specified requirements.
7.3 When required, sample and test five specimens for freeze-thaw durability in water in accordance with C 1262. Freeze-thaw durability shall be based on tests of units made with the same materials, concrete mix design, manufacturing process, and curing method, conducted not more than 24 months prior to delivery.
Note 4 - Unless otherwise spcified in the purchase order, the cost of the test is typically borne as follows: (1) if the results of the tests show that the units do not conform to the requirements of this specification, the cost is typically borne by the seller; (2) if the results of the tests show that the units conform to the specification requirements, the cost is typically borne by the purchaser.
7. Sampling and Testing 7.1 The purchaser or authorized representative shall be accorded proper facilities to inspect and sample the units at the place of manufacture from the lots ready for delivery.
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NATIONAL CONCRETE MASONRY ASSOCIATION 2302 Horse Pen Road, Herndon, Virginia 22071-3499 www.ncma.org
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NCMA TEK National Concrete Masonry Association an information series from the national authority on concrete masonry technology
DENSITY-RELATED PROPERTIES OF CONCRETE MASONRY ASSEMBLIES Keywords: acoustics, aesthetics, compressive strength, concrete density, energy efficiency, fire resistance rating, movement control, productivity, water penetration resistance
INTRODUCTION The versatility of concrete masonry as a construction assembly is well established through the variety of applications and structures it is used to create. Concrete masonry offers almost limitless combinations of color, shape, size, strength, texture, and density. This TEK illustrates the various physical and design properties influenced by the density of concrete masonry units, and provides references to guide the user towards a fuller discussion and more detailed information. Although most of the following discussions use lightweight and normal weight concrete masonry as examples, the properties of medium weight masonry can typically be expected to fall between the two. Note that while some of these density-related properties, such as sound transmission loss, may be directly referenced in building codes such as the International Building Code (ref. 1), other properties or characteristics, such as aesthetics and construction productivity fall outside the scope of the building code. BASICS OF CONCRETE MASONRY UNIT DENSITY The density of a concrete masonry unit is expressed as the oven-dry density of concrete in pounds per cubic foot (lb/ft3 [kg/m3]) as determined in accordance with ASTM C 140, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units (ref. 2). In production, the density of a given concrete masonry unit is controlled in part by the methods used to manufacture the unit, but largely by the type of aggregate used in production. Through the use of lightweight aggregates, normal weight aggregates, or blends of lightweight and normal weight aggregates, the resulting density of concrete masonry units can be varied by the producer to achieve one or more desired physical properties. ASTM C 90, Standard Specification for Loadbearing
TEK 2-6 Unit Properties (2008)
Concrete Masonry Units (ref. 3) defines three density classes for concrete masonry units: • Lightweight – units having an average density less than 105 lb/ft3 (1,680 kg/m3). • Medium Weight – units having an average density of 105 lb/ft3 (1,680 kg/m3) or more, but less than 125 lb/ft3 (2,000 kg/m3). • Normal Weight – units having an average density of 125 lb/ft3 (2,000 kg/m3) or more. When a specific density classification or density range is desired for a project, it should be specified in the project documents along with the other physical properties of the concrete masonry units such as size, strength, color, and texture. Before specifying a specific density range, designers are encouraged to first consult with manufacturers local to the project for availability. As with all physical properties of concrete masonry, minor variation in density from unit to unit and from batch to batch should be expected. In accordance with ASTM C 90, aggregates used to manufacture concrete masonry units must conform to either ASTM C 33, Standard Specification for Concrete Aggregates (ref. 4), or ASTM C 331, Standard Specification for Lightweight Aggregates for Concrete Masonry Units (ref. 5). Whereas normal weight aggregates are typically mined or quarried, lightweight aggregates may be manufactured, mined or quarried from a natural source, or a by-product of another process. Although not all aggregate types are produced in all areas of the country, non-local aggregates may be available. If a concrete masonry unit of a specific aggregate type is desired, potential suppliers should be consulted for availability prior to specifying them. FIRE RESISTANCE Fire resistance ratings of one to four hours can be achieved with concrete masonry of various widths (or thicknesses), configurations and densities. As outlined in TEK 7-1A, Fire Resistance Rating of Concrete Masonry Assemblies (ref. 6), the fire resistance rating of a concrete masonry assembly can be determined by physical testing, through a listing service, or by a standardized calculation procedure. Whether through direct measurement or by cal39
TEK 2-6 © 2008 National Concrete Masonry Association
culation, the fire resistance rating of a given concrete masonry assembly varies directly with the aggregate type and with the volume of concrete in the unit, expressed as the equivalent thickness. Through extensive testing and analysis, empirical relationships have been established between the fire resistance rating of a concrete masonry assembly and the corresponding type of aggregate and equivalent thickness of the unit used to construct the assembly. These relationships are summarized in Figure 1. These relationships between aggregate type/equivalent thickness and the corresponding fire resistance rating are shown graphically in Figure 2. Note that equivalent thicknesses used in Figure 2 are for illustration only, and represent typical equivalent thicknesses for standard hollow concrete masonry units. Actual units may have higher or lower equivalent thicknesses than those shown, with corresponding higher or lower fire resistance ratings. In general, 8-in. (203-mm) and wider concrete masonry units can be supplied with fire resistance ratings up to four hours. For example, a typical hollow 8 in. (203 mm) concrete masonry unit with an equivalent (solid) thickness of 4.0 in. (102 mm), can have a calculated fire resistance rating from 1.8 hours to 3 hours, depending on the type of aggregate used to produce the unit. SOUND CONTROL The control of sound between adjacent dwelling units or between dwelling units and public areas is an important design consideration for user comfort. Sound Transmission Class (STC), expressed in decibels (dB), is a single number rating that provides a measure of the sound insulating properties of walls. The higher the STC rating, the better the assembly can block or reduce the transmission of sound across it. For concrete masonry construction, STC
can be calculated using the installed weight of the assembly, which is a function of the unit density, unit size and configuration, presence of surface finishes, and presence of grout or other cell-fill materials such as sand. See Sound Transmission Class Ratings for Concrete Masonry Walls, TEK 13-1B (ref. 7) for a full discussion. In accordance with Standard Method for Determining the Sound Transmission Class Rating for Masonry Walls (ref. 8), the STC rating for single wythe concrete masonry assemblies without additional surface treatments is determined by the following equation: STC = 19.6W0.230 Eqn. 1. SI STC = 13.6W0.230 Where W = the average wall weight based on the weight of: the masonry units; the weight of mortar, grout and loose fill material in the voids within the wall; and the weight of surface treatments (excluding drywall) and other wall components, lb/ft2 (kg/m2). All other design variables being equal, the STC value of masonry construction increases with increasing unit density. Note that STC values determined by the calculation tend to be conservative. Generally, higher STC values are obtained by referring to actual tests than by the calculation. In addition to the STC rating, the value of the Noise Reduction Coefficient (NRC) can also be influenced to some extent by concrete unit density. NRC measures the ability of a surface to absorb sound (based on a scale of 0 to 1), which can be an important characteristic in some applications, such as concert halls and assembly areas. A higher NRC value indicates that more sound is absorbed by an assembly. NRC values for concrete masonry walls are tabulated according to: the application of any coatings to the wall, the surface texture (coarse, medium or fine) and the density classification (lightweight or normal weight).
Aggregate type in the concrete masonry unit2 Calcareous or siliceous gravel the equi . 4 ) .0 5 in thicknes Limestone, cin7 8 mm (103 4 in. 4 mm particula ders or slag (19 ) solid un Expanded clay, The equivalent thickness of this particular unit (a shale or slate solid unit with the same amount of material) is Expanded slag or 4.04 in. (103 mm). pumice
Minimum required equivalent thickness for fire resistance rating, in. (mm)1 4 hr 3 hr 2 hr 1.5 hr 1 hr 0.75 hr 0.5 hr 6.2 (157) 5.9 (150) 5.0 (130) 4.7 (119)
5.3 (135) 5.0 (127) 4.4 (112) 4.0 (102)
4.2 (107) 4.0 (102) 3.6 (91) 3.2 (81)
3.6 (91) 3.4 (86) 3.3 (84) 2.7 (69)
2.8 (71) 2.7 (69) 2.6 (66) 2.1 (53)
2.4 (61) 2.3 (58) 2.2 (56) 1.9 (48)
2.0 (51) 1.9 (48) 1.8 (46) 1.5 (38)
1
Fire resistance ratings between the hourly fire resistance rating periods listed may be determined by linear interpolation based on the equivalent thickness value of the concrete masonry assembly. 2 Minimum required equivalent thickness corresponding to the hourly fire resistance rating for units made with a combination of aggregates shall be determined by linear interpolation based on the percent by volume of each aggregate used in the manufacture. Figure 1— Calculated Fire Resistance Rating for Single Wythe Concrete Masonry Walls 40
7
6
180
160
Typical equivalent thickness of a hollow 16 in. (406 mm) Typical equivalent thickness of a hollow 14 in. (356 mm) unit
140
Typical equivalent thickness of a hollow 12 in. (305 mm) unit
120
Typical equivalent thickness of a hollow 10 in. (254 mm) unit 4
Typical equivalent thickness of a hollow 8 in. (203 mm) unit 100 Typical equivalent thickness of a hollow 6 in. (152 mm) unit 80
3 Typical equivalent thickness of a hollow 4 in. (102 mm) unit
60
Equivalent thickness, mm
Equivalent thickness, in.
5
2 40 1 20
0
0 0.5
0.75
Calcareous or siliceous gravel
1
1.5 Fire resistance, hr
Limestone, cinders, or slag
2
3
Expanded clay, shale, or slate
4 Expanded slag or pumice
Figure 2—Calculated Fire Resistance Ratings Assuming a similar surface texture and coating, a concrete masonry wall constructed with lightweight units will have a higher NRC than a companion wall constructed with normal weight units, due to the larger pore structure often associated with lower density units. Painting or coating the surface of the concrete masonry assembly reduces the NRC for both lightweight and normal weight concrete masonry. See Noise Control with Concrete Masonry, TEK 13-2A (ref. 9) for a full discussion.
Table 1—Absorption Requirements for Concrete Masonry Units Density Maximum water absorption, lb/ft3 (kg/m3) classification Average of 3 units Individual unit Lightweight 18 (288) 20 (320) Medium weight 15 (240) 17 (272) Normal weight 13 (208) 15 (240) WATER PENETRATION AND ABSORPTION
COMPRESSIVE STRENGTH Regardless of unit density, all loadbearing concrete masonry units meeting the physical properties of ASTM C 90 (ref. 3) must have a minimum average compressive strength of 1,900 psi (13.1 MPa). It is possible to produce concrete masonry units that meet or exceed the ASTM C 90 minimum strength in any density classification, although not all combinations of physical properties may be commonly available in all regions. Therefore, local producers should always be consulted for product availability before specifying. In general, for a given concrete masonry unit mix design, higher compressive strengths can be achieved by increasing the unit density through adjustments to the manufacturing methods. (ref. 16).
Concrete masonry unit specifications typically establish upper limits on the amount of water permitted to be absorbed. Expressed in pounds of water per cubic foot of concrete (kilograms of water per cubic meter of concrete), these limits vary with the density classification of the unit, as shown in Table 1. While the absorption values are not directly related to unit physical properties such as compressive strength and resistance to mechanisms of deterioration such as freezethaw, they do provide a measurement of the void structure within the concrete matrix of the unit. Several production variables can affect the void structure, including degree of compaction, water content of the plastic mix, and aggregate gradation. Due to the vesicular structure of lower density units, there is a potential for higher measured absorption than is typical for most higher density units. Consequently, 41
ASTM C 90 permits lower density units to have a higher maximum absorption value. The higher absorption limits permitted by ASTM C 90 for lower density units do not necessarily correlate to reduced water penetration resistance. One reason is that water penetration resistance is known to be highly affected by workmanship and dependent on detailing for water management. It is generally recognized that these two factors more heavily influence the wall’s water penetration resistance than do other factors, such as unit density. AESTHETIC CONSIDERATIONS One of the most significant architectural benefits of designing with concrete masonry is the versatility afforded by the layout and appearance of the finished assembly, which can be varied with the unit size and shape, color of the units and mortar, bond pattern, and surface finish of the units. The term “architectural concrete masonry unit” (ref. 10) is often used to generically describe units exhibiting any number of surface finishes or colors. Loadbearing single wythe masonry walls constructed with these units uniquely offer the designer structural function, envelope enclosure and the aesthetics of a finished wall surface without the need for additional materials, components or assemblies. In general, the many options available for architectural concrete masonry units can be offered in any of the three unit density classifications. However, with respect to unit appearance, any change in aggregates (whether a change in source or a change in aggregate type) used to manufacture a concrete masonry unit may change its color or texture, particularly for units with mechanically altered features such as split or ground-face surfaces. As a result, when aesthetics are an important consideration, sample units submitted for conceptual design should incorporate the specific aggregate intended to be used in the actual production of the units. Note that various degrees of surface “smoothness” (tight, fine, medium, coarse) can be obtained using the same aggregate by varying the mix design (proportions and moisture), aggregate gradation, aggregate shape, and degree of compaction during manufacture. In addition to production variables, the appearance of the finished masonry is also affected by workmanship, and the mortar color and jointing. Where color, texture and finish are of particular concern, the designer should specify a special sample panel for review and approval during the submittal process (ref. 1, 17). ENERGY EFFICIENCY When selecting masonry for its energy efficiency, two material thermal properties should be considered: • R-value—a material’s ability to resist the transfer of heat under steady-state conditions; and • Thermal mass (heat capacity)—a material’s ability to store and release heat (ref. 11). These physical properties, in combination with a building’s design, layout, location, climate, exposure, use,
or occupancy as required by building codes, influence the energy efficiency and thermal characteristics of the building envelope and of the building. Increasing the unit density, unit thickness, unit solid content, and amount/extent of grout, increases the installed weight of the masonry assembly, which is directly related to its heat capacity. (ref. 11). Conversely, increasing the density or amount of grout used in a concrete masonry assembly decreases its R-value (ref. 12). Because of the multitude of variables that determine the overall energy efficiency of a structure, some projects benefit more by increasing the thermal mass of an assembly while others see more energy efficiency by increasing the R-value. As such, the unique requirements of each project should be considered individually for maximum benefit. STRUCTURAL DESIGN INFLUENCES The structural design of masonry is based on the specified compressive strength of masonry, f'm, which is a function of the compressive strength of the unit and the type of mortar used in construction. It is possible to produce a wide range of compressive strengths within each of the density classes. Therefore, for a given unit compressive strength and mortar type, the strength of the masonry assembly is unaffected by the unit density. As such, the design flexural, shear, and bearing strengths of masonry, some deformational properties such as elastic modulus, and the structural behavior of the masonry assembly determined by contemporary codes and standards are independent of the density of the concrete masonry unit. Unit density, however, can influence other structural design considerations, aside from compressive strength. Reducing the density of a concrete masonry unit can reduce the overall weight of a structure, and potentially reduce the required size of the supporting foundation, slab, or beam. Reducing the weight of a structure or element also reduces the seismic load a structure or element must be designed to resist, because the magnitude of seismic loading is a direct function of dead load. As with thermal mass and sound control, there may be circumstances where increasing the unit density is structurally beneficial. For example, the structural stability against overturning and uplift is increased with increasing structural weight. Hence, while increased structural dead load increases seismic design forces, it also concurrently helps to resist wind loads. Therefore, there may be some structural advantage to using lightweight units in areas of high seismic risk; and normal weight units in areas prone to high winds, hurricanes and/or tornadoes. Structural design considerations, however, are often relatively minor compared to other factors that may influence the choice of unit density. PRODUCTIVITY For a given unit configuration, and with all other factors affecting production being equal, lower unit weights 42
typically enable a mason to lay more units within a given timeframe (ref. 13). Other factors influencing the daily productivity of a mason may include environmental conditions, unit size and shape, building size and configuration, masonry bond pattern, and reinforcement and other detailing (ref. 13). MOVEMENT CONTROL Regardless of the density of a concrete masonry unit, the established movement control recommendations for concrete masonry construction are applicable. See Crack Control in Concrete Masonry Walls, TEK 10-1A, and Control Joints for Concrete Masonry Walls – Empirical Method, TEK 10-2B (refs. 14, 15) for more detailed guidance. ASTM C 90 requires that linear drying shrinkage of all concrete masonry units, regardless of unit density, not exceed 0.065% at the time of delivery to the jobsite. However, despite the fact that not all concrete masonry units exhibit the same linear drying shrinkage within this limit, established movement control recommendations (refs. 14, 15) are independent of the concrete masonry unit density. SUMMARY Issues of masonry design and construction can be influenced and addressed to varying extents through the choice of concrete masonry unit density, but generally the resulting effects of varying unit density on masonry behavior and performance are quite limited. Notwithstanding these effects, the designer can be assured that concrete masonry constructed of any unit density offers sufficient flexibility and alternatives in the choice of materials, design, and construction detailing to satisfy the structural and architectural requirements of the project. REFERENCES 1. International Building Code. International Code Council, 2003 and 2006. 2. Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units, ASTM C 140-06,
ASTM International, 2006. 3. Standard Specification for Loadbearing Concrete Masonry Units, ASTM C 90-06a, ASTM International, 2006. 4. Standard Specification for Concrete Aggregates, ASTM C 33-03, ASTM International, 2006. 5. Standard Specification for Lightweight Aggregates for Concrete Masonry Units, ASTM C 331-05, ASTM International, 2006. 6. Fire Resistance Rating of Concrete Masonry Assemblies, TEK 7-1A, National Concrete Masonry Association, 2006. 7. Sound Transmission Class Ratings for Concrete Masonry Walls, TEK 13-1B, National Concrete Masonry Association, 2007. 8. Standard Method for Determining the Sound Transmission Class Rating for Masonry Walls, TMS 0302-07, The Masonry Society, 2007. 9. Noise Control with Concrete Masonry, TEK 13-2A, National Concrete Masonry Association, 2007. 10. Architectural Concrete Masonry Units, TEK 2-3A, National Concrete Masonry Association, 2001. 11. Heat Capacity (HC) Values for Concrete Masonry Walls, TEK 6-16, National Concrete Masonry Association, 1989. 12. R-Values for Single Wythe Concrete Masonry Walls, TEK 6-2A, National Concrete Masonry Association, 2005. 13. Productivity and Modular Coordination in Concrete Masonry Construction, TEK 4-1A, National Concrete Masonry Association, 2002. 14. Crack Control in Concrete Masonry Walls, TEK 10-1A, National Concrete Masonry Association, 2005. 15. Control Joints for Concrete Masonry Walls – Empirical Method, TEK 10-2B. National Concrete Masonry Association, 2005. 16. Holm, T. A. Engineered Masonry With High Strength Lightweight Concrete Masonry Units. Concrete Facts, Vol. 17, No. 2, 1972. 17. Specification for Masonry Structures, ACI 530.1/ASCE 6/TMS 602. Reported by the Masonry Standards Joint Committee, 2002 and 2005.
Provided by:
NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication. NATIONAL CONCRETE MASONRY ASSOCIATION 13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org
To order a complete TEK Manual or TEK Index, 43 contact NCMA Publications (703) 713-1900
NCMA TEK National Concrete Masonry Association an information series from the national authority on concrete masonry technology
ALL-WEATHER CONCRETE MASONRY CONSTRUCTION Keywords: cold weather construction, construction techniques, grout, hot weather construction, mortar, rain, snow, storage of materials, wet weather construction, windy weather construction INTRODUCTION Masonry construction can continue during hot, cold, and wet weather conditions. The ability to continue masonry construction in adverse weather conditions requires consideration of how environmental conditions may affect the quality of the finished masonry. In some cases, environmental conditions may warrant the use of special construction procedures to ensure that the masonry work is not adversely affected. One of the prerequisites of successful all-weather construction is advance knowledge of local conditions. Work stoppage may be justified if a short period of very cold or very hot weather is anticipated. The best source for this type of information is the U.S. Weather Bureau, Environmental Science Services Administration (ESSA) of the U.S. Department of Commerce which can be accessed at their web site http://www.ncdc.noaa.gov. In the following discussion, ambient temperature refers to the surrounding jobsite temperature when the preparation activities and construction are in progress. Similarly the mean daily temperature is the average of the hourly temperatures forecast by the local weather bureau over a 24 hour period following the onset of construction. Minimum daily temperature is the lowest temperature expected during the period. Temperatures between 40 and 90oF (4.4 and 32.2oC) are considered “normal” temperatures for masonry construction and therefore do not require special procedures or protection protocols. COLD WEATHER CONSTRUCTION When ambient temperatures fall below 40oF (4.4oC), the Specification for Masonry Structures (ref. 3) requires consideration of special construction procedures to help ensure the final construction is not adversely affected. Similarly when the minimum daily temperature for grouted masonry or the mean temperature for ungrouted masonry falls below 40oF (4.4oC) during the first 48 or 24 hours after construction respectively, special protection considerations are required.
TEK 3-1C Construction
(2002)
Mortar and Grout Performance Hydration and strength development in mortar and grout generally occurs at temperatures above 40oF (4.4oC) and only when sufficient water is available. However, masonry construction may proceed when temperatures are below 40oF (4.4oC) provided cold weather construction and protection requirements of reference 3 are followed. Mortars and grouts mixed at low temperatures have longer setting and hardening times, and lower early strength than those mixed at normal temperatures. However, mortars and grouts produced with heated materials exhibit performance characteristics identical to those produced during warm weather. Effects of Freezing The initial water content of mortar can be a significant contributing factor to the resulting properties and performance of mortar, affecting workability, bond, compressive strength, and susceptibility to freezing. Research has shown a resulting disruptive expansion effect on the cement-aggregate matrix when fresh mortars with water contents in excess of 8 %mortar are frozen (ref. 2). This disruptive effect increases as the water content increases. Therefore, mortar should not be allowed to freeze until the mortar water content is reduced from the initial 11% to 16% range to a value below 6%. Dry concrete masonry units have a demonstrated capacity to achieve this moisture reduction in a relatively short time. It is for this reason that the specification requires protection from freezing of mortar for only the first 24 hours (ref. 3). Grout is a close relative of mortar in composition and performance characteristics. During cold weather, however, more attention must be directed toward the protection of grout because of the higher water content and resulting disruptive expansion that can occur from freezing of that water. Therefore, grouted masonry needs to be protected for longer periods to allow the water content to be dissipated. Cement During cold weather masonry construction, Type III, highearly strength portland cement should be considered in lieu of Type I portland cement in mortar or grout to accelerate setting. The acceleration not only reduces the curing time but generates more heat which is beneficial in cold weather. 44
TEK 3-1C © 2002 National Concrete Masonry Association (replaces TEK 3-1B)
Admixtures The purpose of an accelerating type of admixture is to hasten the hydration of the portland cement in mortar or grout. However, admixtures containing chlorides in excess of 0.2% chloride ions are not permitted to be used in mortar (ref. 3) due to corrosion of embedded metals and contribution to efflorescence. While specifically not addressed by the Specification, the use of chloride admixtures in grout is generally discouraged. Noncloride accelerators are available but they must be used in addition to cold weather procedures and not as a replacement for them. Antifreezes are not recommended for use in mortars and are prohibited for use in grouts. Material Storage Construction materials should be protected from water by covering. Bagged materials and masonry units should be protected
from precipitation and ground water by storage on pallets or other acceptable means. Coverings for materials include tarpaulins, reinforced paper, polyethylene, or other water repellent sheet materials. If the weather and size of the project warrant, a shelter may be provided for the material storage and mortar mixing areas. Material Heating When the ambient temperature falls below 40°F (4.4°C) during construction, or mean daily temperature is predicted to fall below 40°F (4.4°C) during the first 24 hours following construction of ungrouted masonry, or the minimum daily temperature is predicted to fall below 40°F (4.4°C) during the first 48 hours for grouted masonry, Specification for Masonry Structures (ref. 3) requires specific construction and protection procedures to be implemented as summarized in Tables 1a and 1b. As indicated in
Table 1a—Cold Weather Masonry Construction Requirements (ref. 3) Ambient temperature o
32 to 40 F (0 to 4.4oC)
Construction requirements Do not lay masonry units having a temperature below 20oF (-6.7oC). Remove visible snow and ice on masonry units before the unit is laid in the masonry. Remove snow and ice from foundation. Heat existing foundation and masonry surfaces to receive new masonry above freezing. Heat mixing water or sand to produce mortar temperatures between 40 and 120oF (4.4 and 48.9oC). Grout materials to be 32oF (0oC) minimum. Do not heat water or aggregates above 140oF (60oC).
25 to 32oF (-3.9 to 0oC)
Same as above for mortar. Maintain mortar temperature above freezing until used in masonry. Heat grout aggregates and mixing water to produce grout temperatures between 70 and 120oF (21.1 and 48.9oC). Maintain grout temperature above 70oF (21.1oC) at time of grout placement.
20 to 25oF (-6.7 to -3.9oC)
Same as above, plus use heat masonry surfaces under construction to 40oF (4.4oC) and install wind breaks or enclosures when wind velocity exceeds 15 mph (24 km/hr). Heat masonry to a minimum of 40oF (4.4oC) prior to grouting.
20oF (-6.7oC) and below
Same as above, plus provide an enclosure for the masonry under construction and use heat sources to maintain temperatures above 32oF (0oC) within the enclosure.
Table 1b—Cold Weather Masonry Protection Requirements (ref. 3) Mean daily temperature for ungrouted masonry Minimum daily temperature for grouted masonry Protection requirements 25 to 40oF (-3.9 to 4.4oC)
Protect completed masonry from rain or snow by covering with a weather-resistive membrane for 24 hours after construction.
20 to 25oF (-6.7 to -3.9oC)
Completely cover the completed masonry with a weather-resistive insulating blanket or equal for 24 hours after construction (48 hr for grouted masonry unless only Type III portland cement used in grout).
20oF (-6.7oC) and below
Maintain masonry temperature above 32oF (0oC) for 24 hours after construction by enclosure with supplementary heat, by electric heating blankets, by infrared heat lamps, or by other acceptable methods. Extend time to 48 hours for grouted masonry unless the only cement in the grout is Type III portland cement. 45
Table 1a, the temperature of dry masonry units may be as low as 20oF (-6.7oC) at the time of placement. However, wet frozen masonry units should be thawed before placement in the masonry. Also, even when the temperature of dry units approaches the 20oF (-6.7oC) threshold, it may be advantageous to heat the units for greater mason productivity. Masonry should never be placed on a snow or ice-covered surface. Movement occurring when the base thaws will cause cracks in the masonry. Furthermore, the bond between the mortar and the supporting surface will be compromised. Glass Unit Masonry For glass unit masonry, both the ambient temperature and the unit temperature must be above 40oF (4.4oC) and maintained above that temperature for the first 48 hours (ref. 3).
Additional Recommendations Store masonry materials in a shaded area. Use a water barrel as water hoses exposed to direct sunlight can result in water with highly elevated temperatures. The barrel may be filled with water from a hose, but the hot water resulting from hose inactivity should be flushed and discarded first. Additionally, mortar mixing times should be no longer than 3 to 5 minutes and smaller batches will help minimize drying time on the mortar boards. To minimize mortar surface drying, past requirements contained within Specification for Masonry Structures (ref. 3) were to not spread mortar bed joints more than 4 feet (1.2 m) ahead of masonry and to set masonry units within one minute of spreading mortar. This is no longer a requirement in the current document but the concept still merits consideration. If surface drying does occur, the mortar can often be revitalized by wetting the wall but care should be taken to avoid washout of fresh mortar joints.
HOT WEATHER CONSTRUCTION WET WEATHER CONSTRUCTION High temperatures, solar radiation, and ambient relative humidity influence the absorption characteristics of the masonry units and the setting time and drying rate for mortar. When mortar gets too hot, it may lose water so rapidly that the cement does not fully hydrate. Early surface drying of the mortar results in decreased bond strength and less durable mortar. Hot weather construction procedures involve keeping masonry materials as cool as possible and preventing excessive water loss from the mortar. Specific hot weather requirements of the Specification for Masonry Structures (ref. 3) are shown in Tables 2a and 2b.
Even when ambient temperatures are between 40 and 90°F (4.4 and 32.2°C), the presence of rain, or the likelihood of rain, should receive special consideration during masonry construction. Unless protected, masonry construction should not continue during heavy rains, as partially set or plastic mortar is susceptible to washout, which could result in reduced strength or staining of the wall. However, after approximately 8 to 24 hours of curing (depending upon environmental conditions), mortar washout is no
Table 2a—Hot Weather Masonry Preparation and Construction Requirements (ref. 3) Ambient temperature
Preparation and construction requirements
Above 100oF (37.8oC) or above 90oF (32.2oC) with a wind speed greater than 8 mph (12.9 km/hr)
Maintain sand piles in a damp, loose condition. Maintain temperature of mortar and grout below 120oF (48.9oC). Flush mixer, mortar transport container, and mortar boards with cool water before they come into contact with mortar ingredients or mortar. Maintain mortar consistency by retempering with cool water. Use mortar within 2 hours of initial mixing.
Above 115oF (46.1oC) or above 105oF (40.6oC) with a wind speed greater than 8 mph (12.9 km/hr)
Same as above, plus materials and mixing equipment are to be shaded from direct sunlight. Use cool mixing water for mortar and grout. Ice is permitted in the mixing water as long as it is melted when added to the other mortar or grout materials.
Table 2b—Hot Weather Masonry Protection Requirements (ref. 3) Mean daily temperature Above 100oF (37.8oC) or above 90oF (32.2oC) with a wind speed greater than 8 mph (12.9 km/hr)
Protection requirements Fog spray all newly constructed masonry until damp, at least three times a day until the masonry is three days old.
46
longer of concern. Further, the wetting of masonry by rainwater provides beneficial curing conditions for the mortar (ref. 2). When rain is likely, all construction materials should be covered. Newly constructed masonry should be protected from rain by draping a weather-resistant covering over the assemblage. The cover should extend over all mortar that is susceptible to washout. Recommended Maximum Unit Moisture Content When the moisture content of a concrete masonry unit is elevated to excessive levels due to wetting by rain or other sources, several deleterious consequences can result including increased shrinkage potential and possible cracking, decreased mason productivity, and decreased mortar/unit bond strength. While reinforced masonry construction does not rely on mortar/unit bond for structural capacity, this is a design consideration with unreinforced masonry. As such, the concerns associated with structural bond in reinforced masonry construction are diminished. As a means of determining if a unit has acceptable moisture content at the time of installation, the following industry recommended guidance should be used. This simple field procedure can quickly ascertain whether a concrete masonry unit has acceptable moisture content at the time of installation.
A concrete masonry unit for which 50% or more of the surface area is observed to be wet is considered to have unacceptable moisture content for placement. If less than 50% of the surface area is wet, the unit is acceptable for placement. Damp surfaces are not considered wet surfaces. For this application, a surface would be considered damp if some moisture is observed, but the surface darkens when additional free water is applied. Conversely, a surface would be considered wet if moisture is observed and the surface does not darken when free water is applied. It should be noted that these limitations on maximum permissible moisture content are not intended to apply to intermittent masonry units that are wet cut as needed for special fit. WINDY WEATHER CONSTRUCTION In addition to the effects of wind on hot and cold weather construction, the danger of excessive wind resulting in structural failure of newly constructed masonry prior to the development of strength or before the installation of supports must be considered. TEK 3-4B Bracing Concrete Masonry Walls During Construction (ref. 1) provides guidance in this regard.
REFERENCES 1. Bracing Concrete Masonry Walls During Construction, TEK 3-4B. National Concrete Masonry Association, 2000 2. Hot & Cold Weather Masonry Construction. Masonry Industry Council, 1999. 3. Specification for Masonry Structures, ACI 530.1-02/ASCE 6-02/TMS 602-02. Reported by the Masonry Standards Joint Committee, 2002.
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NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication.
NATIONAL CONCRETE MASONRY ASSOCIATION 13750 Sunrise Valley Drive, Herndon, Virginia 20171-3499 www.ncma.org
To order a complete TEK Manual or TEK Index, contact NCMA Publications (703) 713-1900 47
NCMA TEK National Concrete Masonry Association an information series from the national authority on concrete masonry technology
GROUTING CONCRETE MASONRY WALLS
TEK 3-2A Construction
Keywords: cleanouts, concrete masonry units, construction techniques, consolidation, demonstration panel, grout, grouting, lift height, pour height, puddling, reinforced concrete masonry, reinforcement INTRODUCTION Grouted concrete masonry construction offers design flexibility through the use of partially or fully grouted walls, whether plain or reinforced. The industry is experiencing fast-paced advances in grouting procedures and materials as building codes allow new opportunities to explore means and methods for constructing grouted masonry walls. Grout is a mixture of: cementitious material (usually portland cement); aggregate; enough water to cause the mixture to flow readily and without segregation into cores or cavities in the masonry; and sometimes admixtures. Grout is used to give added strength to both reinforced and unreinforced concrete masonry walls by grouting either some or all of the cores. It is also used to fill bond beams and occasionally to fill the collar joint of a multi-wythe wall. Grout may also be added to increase the wall's fire rating, acoustic effectiveness termite resistance, blast resistance, heat capacity or anchor-
age capabilities. Grout may also be used to stabilize screen walls and other landscape elements. In reinforced masonry, grout bonds the masonry units and reinforcing steel so that they act together to resist imposed loads. In partially grouted walls, grout is placed only in wall spaces containing steel reinforcement. When all cores, with or without reinforcement, are grouted, the wall is considered solidly grouted. If vertical reinforcement is spaced close together and/or there are a significant number of bond beams within the wall, it may be faster and more economical to solidly grout the wall. Specifications for grout, sampling and testing procedures, and information on admixtures are covered in Grout for Concrete Masonry (ref. 1). This TEK covers methods for laying the units, placing steel reinforcement and grouting. WALL CONSTRUCTION Figure 1 shows the basic components of a typical reinforced concrete masonry wall. When walls will be grouted, concrete masonry units must be laid up so that vertical cores are aligned to form an unobstructed, continuous series of vertical spaces within the wall.
Place mesh or other grout stop device under bond beam to confine grout or use solid bottom unit Vertical reinforcement lap and secure as required
Reinforcement in bond beams is set in place as wall is laid up
Flashing Leave this block out to serve as a cleanout until wall is laid up Drip edge Cells containing reinforcement are filled solidly with grout; vertical cells should provide a continuous cavity, substantially free of mortar droppings Place mortar on cross webs adjacent to cells which will be grouted
Figure 1—Typical Reinforced Concrete Masonry Wall Section 48 TEK 3-2A © 2005 National Concrete Masonry Association (replaces TEKs 3-2 and 3-3A)
(2005)
Head and bed joints must be filled with mortar for the full thickness of the face shell. If the wall will be partially grouted, those webs adjacent to the cores to be grouted are mortared to confine the grout flow. If the wall will be solidly grouted, the cross webs need not be mortared since the grout flows laterally, filling all spaces. In certain instances, full head joint mortaring should also be considered when solid grouting since it is unlikely that grout will fill the space between head joints that are only mortared the width of the face shell, i.e., when penetration resistance is a concern such as torm shelters and prison walls. In cases such as those, open end or open core units (see Figure 3) should be considered as there is no space between end webs with these types of units. Care should be taken to prevent excess mortar from extruding into the grout space. Mortar that projects more than 1 /2 in. (13 mm) into the grout space must be removed (ref. 3). This is because large protrusions can restrict the flow of grout, which will tend to bridge at these locations potentially causing incomplete filling of the grout space. To prevent bridging, grout slump is required to be between 8 and 11 in. (203 to 279 mm) (refs. 2, 3) at the time of placement. This slump may be adjusted under certain conditions such as hot or cold weather installation, low absorption units or other project specific conditions. Approval should be obtained before adjusting the slump outside the requirements. Using the grout demonstration panel option in Specification for Masonry Structures (ref. 3) is an excellent way to demonstrate the acceptability of an alternate grout slump. See the Grout Demonstration Panel section of this TEK for further information. At the footing, mortar bedding under the first course of block to be grouted should permit grout to come into direct contact with the foundation or bearing surface. If foundation
Vertical reinforcement, as required
dowels are present, they should align with the cores of the masonry units. If a dowel interferes with the placement of the units, it may be bent a maximum of 1 in. (25 mm) horizontally for every 6 in. (152 mm) vertically (see Figure 2). When walls will be solidly grouted, saw cutting or chipping away a portion of the web to better accommodate the dowel may also be acceptable. If there is a substantial dowel alignment problem, the project engineer must be notified. Vertical reinforcing steel may be placed before the blocks are laid, or after laying is completed. If reinforcement is placed prior to laying block, the use of open-end A or Hshaped units will allow the units to be easily placed around the reinforcing steel (see Figure 3). When reinforcement is placed after wall erection, reinforcing steel positioners or other adequate devices to hold the reinforcement in place are commonly used, but not required. However, it is required that both horizontal and vertical reinforcement be located within tolerances and secured to prevent displacement during grouting (ref. 3). Laps are made at the end of grout pours and any time the bar has to be spliced. The length of lap splices should be shown on the project drawings. On occasion there may be locations in the structure where splices are prohibited. Those locations are to be clearly marked on the drawing. Reinforcement can be spliced by either contact or noncontact splices. Noncontact lap splices may be spaced as far apart as one-fifth the required length of the lap but not more than 8 in. (203 mm) per Building Code Requirements for Masonry Structures (ref. 4). This provision accommodates construction interference during installation as well as misplaced dowels.
Open end, or "A" shaped unit
Double open end or "H" shaped unit
Grout, as required
Concrete masonry wall
Dowels may be bent up to 1 in. (25 mm) laterally per 6 in. (152 mm) vertically Concrete foundation
Figure 2—Foundation Dowel Clearance
Bond beam units
Lintel unit
Pilaster units
Open core unit
Figure 3—Concrete Masonry Units for Reinforced Construction 49
Splices are not required to be tied, however tying is often used as a means to hold bars in place. As the wall is constructed, horizontal reinforcement can be placed in bond beam or lintel units. If the wall will not be solidly grouted, the grout may be confined within the desired grout area either by using solid bottom masonry bond beam units or by placing plastic or metal screening, expanded metal lath or other approved material in the horizontal bed joint before laying the mortar and units being used to construct the bond beam. Roofing felt or materials that break the bond between the masonry units and mortar should not be used for grout stops. CONCRETE MASONRY UNITS AND REINFORCING BARS Standard two-core concrete masonry units can be effectively reinforced when lap splices are not long, since the mason must lift the units over any vertical reinforcing bars that extend above the previously installed masonry. The concrete masonry units illustrated in Figure 3 are examples of shapes that have been developed specifically to accommodate reinforcement. Open-ended units allow the units to be placed
2 ft 8 in. (813 mm) pour and 2 ft 8 in. (813 mm) lift
5 ft (1.5 m) pour and 5 ft (1.5 m) lift
around reinforcing bars. This eliminates the need to thread units over the top of the reinforcing bar. Horizontal reinforcement in concrete masonry walls can be accommodated either by saw-cutting webs out of a standard unit or by using bond beam units. Bond beam units are manufactured with either reduced webs or with “knock-out” webs, which are removed prior to placement in the wall. Pilaster and column units are used to accommodate a wallcolumn or wall-pilaster interface, allowing space for vertical reinforcement and ties, if necessary, in the hollow center. Concrete masonry units should meet applicable ASTM standards and should typically be stored on pallets to prevent excessive dirt and water from contaminating the units. The units may also need to be covered to protect them from rain and snow. The primary structural reinforcement used in concrete masonry is deformed steel bars. Reinforcing bars must be of the specified diameter, type and grade to assure compliance with the contract documents. See Steel Reinforcement for Concrete Masonry, TEK 12-4C for more information (ref. 6). Shop drawings may be required before installation can begin. Light rust, mill scale or a combination of both need not be removed from the reinforcement. Mud, oil, heavy rust and
2 ft 8 in. (813 mm) lift
5 ft (1.5 m) lift 12 ft 8 in. (3.9 m) pour
Lap
5 ft (1.5 m) pour and 5 ft (1.5 m) lift
Lap
Grouting without cleanouts: (Low-lift) No cleanouts required Wall built in 3 stages Bars spliced at pour height Three grout lifts
5 ft (1.5 m) lift Lap
Cleanout
12 ft 8 in. (3.9 m) pour and 12 ft 8 in (3.9 m) lift
Lap Cleanout
Grouting with cleanouts: Grouting with cleanouts per (High-lift) MSJC (2005) or grout demonstration panel: Cleanouts required Cleanouts required Wall built full height Wall built full height Bars installed full length (no splicing) Bars installed full length (no splicing) Three grout lifts One grout lift
Figure 4—Comparison of Grouting Methods for a 12 ft-8 in. (3,860 mm) High Concrete Masonry Wall 50
other materials which adversely affect bond must be removed however. The dimensions and weights (including heights of deformations) of a cleaned bar cannot be less than those required by the ASTM specification. GROUT PLACEMENT To understand grout placement, the difference between a grout lift and a grout pour needs to be understood. A lift is the amount of grout placed in a single continuous operation. A pour is the entire height of masonry to be grouted prior to the construction of additional masonry. A pour may be composed of one lift or a number of successively placed grout lifts, as illustrated in Figure 4. Historically, only two grout placement procedures have been in general use: (l) where the wall is constructed to pour heights up to 5 ft (1,520 mm) without cleanouts—generally termed “low lift grouting;” and (2) where the wall is constructed to a maximum pour height of 24 ft (7,320 mm) with required cleanouts and lifts are placed in increments of 5 ft (1,520 mm)—generally termed “high lift grouting.” With the advent of the 2002 Specification for Masonry Structures (ref. 5), a third option became available – grout demonstration panels. The 2005 Specification for Masonry Structures (ref. 3) offers an additional option: to increase the grout lift height to 12 ft-8 in. (3,860 mm) under the following conditions: 1. the masonry has cured for at least 4 hours, 2. grout slump is maintained between 10 and 11 in. (245 and 279 mm), and 3. no intermediate reinforced bond beams are placed between the top and the bottom of the pour height. Through the use of a grout demonstration panel, lift heights in excess of the 12 ft-8 in. (3,860 mm) limitation may be permitted if the results of the demonstration show that the completed grout installation is not adversely affected. Written approval is also required. These advances permit more efficient installation and construction options for grouted concrete masonry walls (see Figure 4). Grouting Without Cleanouts—"Low-Lift Grouting” Grout installation without cleanouts is sometimes called low-lift grouting. While the term is not found in codes or standards, it is common industry language to describe the process of constructing walls in shorter segments, without the requirements for cleanout openings, special concrete block shapes or equipment. The wall is built to scaffold height or to a bond beam course, to a maximum of 5 ft (1,520 mm). Steel reinforcing bars and other embedded items are then placed in the designated locations and the cells are grouted. Although not a code requirement, it is considered good practice (for all lifts except the final) to stop the level of the grout being placed approximately 1 in. (25 mm) below the top bed joint to help provide some mechanical keying action and water penetration resistance. Further, this is needed only when a cold joint is formed between the lifts and only in areas that will be receiving additional grout. Steel reinforcement should
project above the top of the pour for sufficient height to provide for the minimum required lap splice, except at the top of the finished wall. Grout is to be placed within 11/2 hours from the initial introduction of water and prior to initial set (ref. 3). Care should be taken to minimize grout splatter on reinforcement, on finished masonry unit faces or into cores not immediately being grouted. Small amounts of grout can be placed by hand with buckets. Larger quantities should be placed by grout pumps, grout buckets equipped with chutes or other mechanical means designed to move large volumes of grout without segregation. Grout must be consolidated either by vibration or puddling immediately after placement to help ensure complete filling of the grout space. Puddling is allowed for grout pours of 12 in. (305 mm) or less. For higher pour heights, mechanical vibration is required and reconsolidation is also required. See the section titled Consolidation and Reconsolidation in this TEK. Grouting With Cleanouts—"High-Lift Grouting” Many times it is advantageous to build the masonry wall to full height before grouting rather than building it in 5 ft (1,520 mm) increments as described above. With the installation of cleanouts this can be done. Typically called high-lift grouting within the industry, grouting with cleanouts permits the wall to be laid up to story height or to the maximum pour height shown in Table 1 prior to the installation of reinforcement and grout. (Note that in Table 1, the maximum area of vertical reinforcement does not include the area at lap splices.) High lift grouting offers certain advantages, especially on larger projects. One advantage is that a larger volume of grout can be placed at one time, thereby increasing the overall speed of construction. A Table 1—Grout Space Requirements (ref. 3) Grout Max. grout type1 pour height, ft (m) Fine Fine Fine Fine Coarse Coarse Coarse Coarse 1 2 3
4
1 (0.30) 5 (1.52) 12 (3.66) 24 (7.32) 1 (0.30) 5 (1.52) 12 (3.66) 24 (7.32)
Min. width of grout space 2,3, in. (mm) ¾ (19.1) 2 (50.8) 2½ (63.5) 3 (76.2) 1½ (38.1) 2 (50.8) 2½ (63.5) 3 (76.2)
Min. grout space dimensions for grouting cells of hollow units 3,4 in. x in. (mm x mm) 1½ x 2 (38.1 x 50.8) 2 x 3 (50.8 x 76.2) 2½ x 3 (63.5 x 76.2) 3 x 3 (76.2 x 76.2) 1½ x 3 (38.1 x 76.2) 2½ x 3 (63.5 x 76.2) 3 x 3 (76.2 x 76.2) 3 x 4 (76.2 x 102)
Fine and coarse grouts are defined in ASTM C 476 (ref. 2). For grouting between masonry wythes. Grout space dimension is the clear dimension between any masonry protrusion and shall be increased by the diameters of the horizontal bars within the cross section of the grout space. Area of vertical reinforcement shall not exceed 6 percent of the area of the grout space. 51
second advantage is that high-lift grouting can permit constructing masonry to the full story height before placing vertical reinforcement and grout. Less reinforcement is used for splices and the location of the reinforcement can be easily checked by the inspector prior to grouting. Bracing may be required during construction. See Bracing Concrete Masonry Walls During Construction, TEK 3-4B (ref. 7) for further information. Cleanout openings must be made in the face shells of the bottom course of units at the location of the grout pour. The openings must be large enough to allow debris to be removed from the space to be grouted. For example, Specification for Masonry Structures (ref. 3) requires a minimum opening dimension of 3 in. (76 mm). Cleanouts must be located at the bottom of all cores containing dowels or vertical reinforcement and at a maximum of 32 in. (813 mm) on center (horizontal measurement) for solidly grouted walls. Face shells are removed either by cutting or use of special scored units which permit easy removal of part of the face shell for cleanout openings (see Figure 5). When the cleanout opening is to be exposed in the finished wall, it may be desirable to remove the entire face shell of the unit, so that it may be replaced in whole to better conceal the opening. At flashing where reduced thickness units are used as shown in Figure 1, the exterior unit can be left out until after the masonry wall is laid up. Then after cleaning the cell, the unit is mortared in which allowed enough time to gain enough strength to prevent blowout prior to placing the grout. Proper preparation of the grout space before grouting is very important. After laying masonry units, mortar droppings and projections larger than 1/2 in. (13 mm) must be removed from the masonry walls, reinforcement and foundation or bearing surface. Debris may be removed using an air hose or by sweeping out through the cleanouts. The grout spaces should be checked by the inspector for cleanliness and reinforcement position before the cleanouts are closed. Cleanout openings may be sealed by mortaring the original face shell or section of face shell, or by blocking the openings to allow grouting to the finish plane of the wall. Face shell plugs should be adequately braced to resist fluid grout pressure. It may be advisable to delay grouting until the mortar has
been allowed to cure, in order to prevent horizontal movement (blowout) of the wall during grouting. When using the increased grout lift height provided for in Article 3.5 D of Specification for Masonry Structures (ref 3), the masonry is required to cure for a minimum of 4 hours prior to grouting for this reason. Consolidation and Reconsolidation An important factor mentioned in both grouting procedures is consolidation. Consolidation eliminates voids, helping to ensure complete grout fill and good bond in the masonry system. As the water from the grout mixture is absorbed into the masonry, small voids may form and the grout column may settle. Reconsolidation acts to remove these small voids and should generally be done between 3 and 10 minutes after grout placement. The timing depends on the water absorption rate, which varies with such factors as temperature, absorptive properties of the masonry units and the presence of water repellent admixtures in the units. It is important to reconsolidate after the initial absorption has taken place and before the grout loses its plasticity. If conditions permit and grout pours are so timed, consolidation of a lift and reconsolidation of the lift below may be done at the same time by extending the vibrator through the top lift and into the one below. The top lift is reconsolidated after the required waiting period and then filled with grout to replace any void left by settlement. A mechanical vibrator is normally used for consolidation and reconsolidation—generally low velocity with a 3/4 in. to 1 in. (19 to 25 mm) head. This “pencil head” vibrator is activated for a few seconds in each grouted cell. Although not addressed by the code, recent research (ref. 8) has demonstrated adequate consolidation by vibrating the top 8 ft (2,440 mm) of a grout lift, relying on head pressure to consolidate the grout below. The vibrator should be withdrawn slowly enough while on to allow the grout to close up the space that was occupied by the vibrator. When double openend units are used, one cell is considered to be formed by the two open ends placed together. When grouting between wythes, the vibrator is placed at points spaced 12 to 16 in. (305 to 406 mm) apart. Excess vibration may blow out the face shells or may separate wythes when grouting between wythes and can also cause grout segregation. GROUT DEMONSTRATION PANEL
Figure 5—Unit Scored to Permit Removal of Part of Face Shell for Cleanout
Specification for Masonry Structures (ref. 3) contains a provision for “alternate grout placement” procedures when means and methods other than those prescribed in the document are proposed. The most common of these include increases in lift height, reduced or increased grout slumps, minimization of reconsolidation, puddling and innovative consolidation techniques. Grout demonstration panels have been used to allow placement of a significant amount of a relatively new product called self-consolidating grout to be used in many parts of the country with outstanding results. 52
Research has demonstrated comparable or superior performance when compared with consolidated and reconsolidated conventional grout in regard to reduction of voids, compressive strength and bond to masonry face shells. Construction and approval of a grout demonstration panel using the proposed grouting procedures, construction techniques and grout space geometry is required. With the advent of self-consolidating grouts and other innovative consolidation techniques, this provision of the Specification has been very useful in demonstrating the effectiveness of alternate grouting procedures to the architect/engineer and building official. COLD WEATHER PROTECTION Protection is required when the minimum daily temperature during construction of grouted masonry is expected to fall below 40oF (4.4oC). Grouted masonry requires special consideration because of the higher water content and potential disruptive expansion that can occur if that water freezes. Therefore, grouted masonry requires protection for longer periods than ungrouted masonry to allow the water to dissipate. For more detailed information on cold, hot, and wet weather protection, see All-Weather Concrete Masonry Construction, TEK 3-1C (ref. 9).
REFERENCES 1. Grout for Concrete Masonry, TEK 9-4. National Concrete Masonry Association, 2002. 2. Standard Specification for Grout for Masonry, ASTM C 476-02, ASTM International, 2005. 3. Specification for Masonry Structures, ACI 530.1-05/ ASCE 6-05/TMS 602-05. Reported by the Masonry Standards Joint Committee, 2005. 4. Building Code Requirements for Masonry Structures, ACI 530-05/ASCE 5-05/TMS 402-05. Reported by the Masonry Standards Joint Committee, 2005. 5. Specification for Masonry Structures, ACI 530.1-02/ ASCE 6-02/TMS 602-02. Reported by the Masonry Standards Joint Committee, 2002. 6. Steel Reinforcement for Concrete Masonry, TEK 12-4C. National Concrete Masonry Association, 2002. 7. Bracing Concrete Masonry Walls During Construction, TEK 3-4B. National Concrete Masonry Association, 2002. 8. Investigation of Alternative Grouting Procedures in Concrete Masonry Construction Through Physical Evaluation and Quality Assessment, MR 25. National Concrete Masonry Association, 2004. 9. All-Weather Concrete Masonry Construction, TEK 3-1C. National Concrete Masonry Association, 2002.
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Disclaimer: Although care has been taken to ensure the enclosed information is as accurate and complete as possible, NCMA does not assume responsibility for errors or omissions resulting from the use of this TEK. NATIONAL CONCRETE MASONRY ASSOCIATION 13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org
To order a complete TEK Manual or TEK Index, 53 contact NCMA Publications (703) 713-1900
An
information
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national
authority
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masonry
technology
Prepared in cooperation with the International Masonry Institute
HYBRID CONCRETE MASONRY TEK 3-3B CONSTRUCTION DETAILS Construction (2009) INTRODUCTION Hybrid masonry is a structural system that utilizes reinforced masonry walls with a framed structure. While the frame can be constructed of reinforced concrete or structural steel, the discussion here includes steel frames with reinforced concrete masonry walls. The reinforced masonry infill participates structurally with the frame and provides strength and stiffness to the system. It can be used in single wythe or cavity wall construction provided the connections and joints are protected against water penetration and corrosion. The hybrid walls are constructed within the plane of the framing. Depending on the type of hybrid wall used, the framing supports some or all of the masonry wall weight. Hybrid masonry/frame structures were first proposed in 2006 (ref. 1). There are several reasons for its development but one primary reason is to simplify the construction of framed buildings with masonry infill. While many designers prefer masonry infill walls as the backup for veneers in framed buildings, there is often a conflict created when structural engineers design steel bracing for the frame which interferes with the masonry infill. This leads to detailing and construction interferences trying to fit masonry around braces. One solution is to eliminate the steel bracing and use reinforced masonry infill as the shear wall bracing to create a hybrid structural system. The concept of using masonry infill to resist lateral forces is not new; having been used successfully throughout the world in different forms. While common worldwide, U.S. based codes and standards have lagged behind in the establishment of standardized means of designing masonry infill. The hybrid masonry system outlined in this TEK is a unique method of utilizing masonry infill to resist
Related TEK: 14-9A NCMA TEK 3-3B
lateral forces. The novelty of the hybrid masonry design approach relative to other more established infill design procedures is in the connection detailing between the masonry and steel frame, which offers multiple alternative means of transferring loads into the masonry—or isolating the masonry infill from the frame. Prior to implementing the design procedures outlined in this TEK, users are strongly urged to become familiar with the hybrid masonry concept, its modeling assumptions, and its limitations particularly in the way in which inelastic loads are distributed during earthquakes throughout the masonry and frame system. This system, or design methods, should not be used in Seismic Design Category D and above until further studies and tests have been performed; and additional design guidance is outlined in adopted codes and standards. CLASSIFICATION OF WALLS There are three hybrid wall types, Type I, Type II and Type III. The masonry walls are constructed within the plane of the framing. The classification is dependent upon the degree of confinement of the masonry within the frame. Type I walls have soft joints (gaps that allow lateral drift at the columns or vertical deflection at the top) at the columns and the top of the wall. The framing supports the full weight of the masonry walls and other gravity loads. Type II walls have soft joints at the columns and are built tight at the top of the wall. Type III walls are built tight at the columns and the top of the wall. For Type II and III walls, the masonry walls share the support of the vertical loads, including the wall weight, with the framing.
Keywords: frame structures, infill, hybrid, shear walls, tie-down, reinforced masonry 1
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CONSTRUCTION Type I Hybrid Walls Practically speaking, the concept of Type I walls is that the masonry wall is a nonloadbearing shear wall built within the frame which also supports out-ofplane loads (see Figure 1). The details closely match those for current cavity wall construction where the infill masonry is within the plane of the frame, except that the vertical reinforcement must be welded to the perimeter framing at supported floors. Since the walls are generally designed to span vertically, the walls may not have to be anchored to the columns. The engineer’s design should reflect whether anchors are required but only for out-of-plane loads. The masonry does have to be isolated from the columns so the columns do not transmit loads to the walls when the frame drifts. In multi-story buildings, each wall is built independently. Walls can be constructed on multiple floors simultaneously. Because the steel framing is supporting the entire wall weight, Type 1 walls are more economical for lower rise buildings. It is possible with Type 1 walls to position the walls outside the framing so they are foundation supported as in caged construction (ref. 1), providing a more economical design for the framing. Type II Hybrid Walls With Type ll walls, the masonry wall is essentially a loadbearing shear wall built within the frame: it supports both gravity and out-of-plane loads (see Fig. 1). There are two options: Type IIa and Type IIb. The engineer must indicate which will be used. For Type IIa walls, the vertical reinforcement (dowels) must be welded to the perimeter framing to transfer tension tiedown forces into the frame. The vertical dowels also transfer shear. For Type IIb walls, vertical reinforcement only needs to be doweled to the concrete slab to transfer shear forces because tie-down is not required. This simplifies the construction of multi-story buildings. The top of the masonry wall must bear tight to the framing. Options include grouting the top course, using solid units, or casting the top of the wall. The top connectors must extend down from the framing to overlap with the vertical wall reinforcement. Since the walls generally span vertically, the engineer must decide whether column anchors are needed similar to Type I walls. These anchors only need to transmit out-of-plane loads. The design must take into account the construction phasing. In multi-story buildings, each wall may be structurally dependent on a wall from the floor below which is very similar to a loadbearing masonry building.
Type III Hybrid Walls This wall type is fully confined within the framing—at beams and columns. Currently, there are no standards in the United States that govern Type III design. Standards are under development and research is underway to help determine structural and construction requirements. Therefore, no details are provided at this time. DETAILS Sample construction details were developed in conjunction with the National Concrete Masonry Association, International Masonry Institute (IMI), and David Biggs. They are hosted on the NCMA web site at www.ncma.org and the IMI web site at www. imiweb.org. Alternate details for hybrid construction are continually under development and will be posted on the web sites. There are several key details that must be considered, including: the wall base, the top of the wall, at columns, and parapets.
Type I Hybrid Wall
Type II Hybrid Wall Figure 1—Hybrid Wall Types I and II
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NCMA TEK 3-3B
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Base of Wall As previously noted for Type I and Type IIa walls, vertical reinforcement must be anchored to either foundation or frame to provide tension-tie downs for the structure. Figure 2 shows the reinforcement anchored to the foundation with a tension lap splice, and also shows the reinforcement anchored at a floor level and tension lap spliced. For Type IIb walls, the vertical reinforcement does not have to be anchored for tension forces because it only transfers shear forces. Figure 3 shows the reinforcement anchored to the foundation. Figure 4 shows the reinforcement anchored at a floor level. The designer must determine if the dowel can be effectively anchored to the slab for shear or if it must be welded to the framing as shown for Type I and Type IIa walls.
connectors at the top of the wall. Since the top course could be a solid unit, the connector should extend down to a solid grouted bond beam. Top of wall construction raises the most concern by designers. Constructability testing by masons has been successfully performed. The design concept for the connectors is: 1. Determine the out-of-plane loads to the wall top. 2. Design the top bond beam to span horizontally between connectors. Connector spacing is a designer's choice but is generally between 2 and 4 ft (6.09 and 1.22 m) o. c. 3. Using the in-plane loading, analyze the connector and design the bolts. 4. If the design does not work, repeat using a smaller connector spacing.
Top of Wall For all wall types, the top of the wall must be anchored to transfer in-plane shear loads from the framing to the wall. It also accommodates out-of-plane forces. This is accomplished by a connector. Figures 5 and 5A show an example with bent plates and slotted holes. For Type I walls, the gap at the top of the wall must allow for the framing to deflect without bearing on the wall or loading the bolts. For Type II walls, the gap is filled tight so the framing bears on the wall. The vertical reinforcement must overlap with the
Figure 3—Type IIb Foundation Detail
Figure 2—Type I and IIa Foundation and Floor Detail NCMA TEK 3-3B
Figure 4—Type IIb Floor Detail 3
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Note: For Type I walls, provide soft joint (gap to allow for movement. For Type II walls, fill gap tight.
Figure 5—Top of Wall Details 4
NCMA TEK 3-3B
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Figure 5—Top of Wall Details (continued)
Figure 5A—Connector Plate Detail NCMA TEK 3-3B
5
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Figure 6—Column Details
Option 1 Figure 7—Parapet Details 6
NCMA TEK 3-3B
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Option 2
Option 3 Figure 7—Parapet Details (continued) NCMA TEK 3-3B
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The steel framing is affected by out-of-plane load transfer to the beam's bottom flange. Beam analysis and flange bracing concerns for the steel are identical to those for any infill wall. Column For Type I and IIa walls, the wall must be kept separated from the columns so that when the frame drifts it does not bear on the wall. Lightweight anchors can be used to support out-of-plane loads if desired. Figure 6 shows a possible anchor. Parapet Parapets can be constructed by cantilevering off the roof framing. Details vary depending on the framing used but are similar to Figure 2. Figure 7 shows three variations for: concrete slab, wide flange framing, and bar joist framing. There is a plate on the beam's top flange for the bar joist and wide flange framing options. QUALITY ASSURANCE
of the quality assurance plan. Besides verifying the vertical reinforcement is properly installed as required by Building Code Requirements for Masonry Structures (ref. 2), the connector must be checked as well. If Type I walls are used, the bolts from the connector to the wall must allow for vertical deflection of the framing without loading the wall. CONCLUSIONS Hybrid masonry offers many benefits and complements framed construction. By using the masonry as a structural shear wall, the constructability of the masonry with the frames is improved, lateral stiffness is increased, redundancy is improved, and opportunities for improved construction cost are created. For now, Type I and Type II hybrid systems can be designed and constructed in the United States using existing codes and standards. Criteria for Type III hybrid systems are under development. Design issues for hybrid walls are discussed in TEK 14-9A and IMI Tech Brief 02.13.01 (refs. 3, 4).
Special inspections should be an essential aspect REFERENCES 1. Biggs, D.T., Hybrid Masonry Structures, Proceedings of the Tenth North American Masonry Conference. The Masonry Society, June 2007. 2. Building Code Requirements for Masonry Structures, ACI 530-08/ASCE 5-08/TMS 402-08. The Masonry Society, 2008. 3. Hybrid Concrete Masonry Design, TEK 14-9A. National Concrete Masonry Association, 2009. 4. Hybrid Masonry Design, IMI Technology Brief 02.13.01. International Masonry Institute, 2009.
NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication. NATIONAL CONCRETE MASONRY ASSOCIATION
13750 Sunrise Valley Drive, Herndon, Virginia 20171 www.ncma.org To order a complete TEK Manual or TEK Index, contact NCMA Publications (703) 713-1900
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NCMA TEK 3-3B
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NCMA TEK National Concrete Masonry Association an information series from the national authority on concrete masonry technology
BRACING CONCRETE MASONRY WALLS DURING CONSTRUCTION
TEK 3-4B Construction
(2005)
Keywords: backfilling, basement walls, bracing walls, construction loads, lateral loads, plain concrete masonry, restricted zone, unreinforced concrete masonry, wind loads Figure 1. When the wind speeds exceed those allowed during the Initial and Intermediate Periods, there is a chance that the masonry wall could fail and the Restricted Zone must be evacuated in order to ensure life safety.
INTRODUCTION Various codes and regulations relating to buildings and structures place responsibility on the erecting contractor for providing a reasonable level of life safety for workers during construction. Until the recent development of the Standard Practice for Bracing Masonry Walls During Construction (ref. 3) by the Council for Masonry Wall Bracing, there were no uniform guidelines for masonry wall stability. The Standard only addresses strategies to resist the lateral loading effects of wind during construction. When other lateral loads such as impact, seismic, scaffolding, and lateral earth pressure are present, they need to be considered and evaluated separately. A section is provided at the end of this TEK regarding bracing and support of basement walls during backfilling operations.
Initial Period The Initial Period is the time frame during which the masonry is being laid above its base or highest line of bracing, limited to a maximum of one working day. During this period, the mortar is assumed to have no strength and wall stability is accomplished from its self weight only. Based on this assumption and a wind speed limit of 20 mph (32.2 km/hr), walls can be built to the height shown in Table 1 without bracing during the Initial Period. If wind speeds exceed 20 mph (32.2 km/hr) during the Initial Period, work on the wall must cease
WALLS SUBJECT TO WIND FORCES Recognizing that it may be impracticable to prevent the collapse of a masonry wall during construction when subjected to extreme loading conditions and that life safety is the primary concern, the Standard includes a procedure whereby the wall and the area around it is evacuated at prescribed wind speeds. Wind speeds as defined in the Standard are five-second gusts measured at the job site. The critical wind speed resulting in evacuation is dependent on the age of the wall being constructed and involves three new terms. They are “Restricted Zone,” “Initial Period,” and “Intermediate Period.” Restricted Zone The Restricted Zone is the area on each side of a wall equal to the length of the wall and extending a distance perpendicular to the wall equal to the height of the constructed wall plus 4 ft. (1.22 m), as shown in
Restricted zone
h ngt Le
Height
He igh t+
4f
t (1 .22
Restricted zone m)
He igh t+
4f t (1 .22
m)
Le
h ngt
Figure 1—Restricted Zone for Masonry Walls 62
TEK 3-4B © 2005 National Concrete Masonry Association (replaces TEK 3-4A)
scaffolding and evacuate the restricted zone. Table 3 lists bracing points determined by the bracing method previously described and Figure 2 shows a wood brace detail for support Density of Masonry Units, γ , lb/ft3 (kg/m3) Nominal wall Lightweight Medium Weight Normal Weight heights up to 14'-4" (4.37 m) maximum. Proprithickness, Units Units3 Units etary pipe bracing systems and cable systems in (mm) 95 < γ < 105 105 < γ < 115 115 < γ < 125 125 < γ are also available for all heights shown in Table (1522
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