1. Introduction to Masonry

1. INTRODUCTION TO MASONRY 1.1 What is MASONRY?

Masonry is one of the oldest forms of construction known to humans. The term masonry refers generally to brick, tile, stone, concrete-block etc., or combination there of, bonded with mortar. However, many different definitions of masonry are in vogue. The International Building Code (IBC 2009): defines masonry as “a built-up construction or combination of building units or materials of clay, shale, concrete, glass, gypsum, stone or other approved units bonded together with or without mortar or grout or other accepted methods of  joining.” ASTM E631: defines masonry as “construction usually in mortar, of natural building stone or manufactured units such as brick, concrete block, adobe, glass, block tile, manufacture stone, or gypsum block.” A commonality in these various definitions is that masonry essentially is an assemblage of individual units which may be of the same or different kind, and which have been bonded together in some way to perform intended function. 1.2 Type of Masonry 

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Rubble stone/ Ashlar stone In rubble stone masonry, the stones are left in their natural state, without any kind of shaping. Stone masonry where the blocks blocks are dressed to flat surfaces is known known as ashlar masonry, whereas masonry using irregularly shaped stones is known as rubble masonry. Both rubble and ashlar masonry can be laid in courses (rows of even height) through the careful selection and cutting of stones, but a great deal of stone masonry is un-coursed. Adobe Adobe is air/sun dried brick from mud composed of inorganic soil and sand. The soil must have minimum clay content of 10%. Adobe houses are normally classified as class A to class B on the EMS scale for vulnerability of masonry structures. Brick These buildings are built with burnt bricks, which suggests a certain quality of the unit and hence a good performance in compression. However, even if a good quality mortar is used, the tensile strength is very limited. The number, size and position of openings will play a major role in the performance of this type of buildings. Large openings, small piers between openings and quoins as well as long walls without perpendicular stiffening are detrimental for the building strength. Confined masonry This category includes various systems in which a significant effort has been made to improve the performance and ductility of masonry construction. In reinforced masonry, bars or steel mesh are embedded (in mortar or grout) in holes or between layers of masonry bricks, creating a composite material acting as a highly resistant and ductile 1

wall or wall system. Such reinforcement will be present in both the vertical and horizontal directions. Confined masonry is characterized by masonry built rigidly between structural columns and beams on all four sides and provides a similar level of resistance. In this case it is not intended that the connecting elements should perform as a moment resistant frame where masonry would only act as non-structural infill. The masonry is rather playing a vital role in the resisting system. 

Concrete block Blocks of ordinary concrete (concrete blocks), or hollow tile are generically known as Concrete Masonry Units (CMUs). They usually are much larger than ordinary bricks and so are much faster to lay for a wall of a given size. Furthermore, cinder and concrete blocks typically have much lower water absorption rates than brick. They often are used as the structural core for veneered brick masonry, or are used alone for the walls of factories, garages and other industrial-style buildings where such appearance is acceptable or desirable.

1.3 Advantages and Disadvantages of Structural Masonry

The durability of masonry when used correctly is excellent. However, as with other materials, the proper use of masonry requires an understanding of its physical characteristics, its strengths and weaknesses, the methods of construction and the availability of various shapes and textures, together with relative costs. The advantages which follow are based on the proper use of masonry. Advantage: 

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Cost Speed of Erection A masonry wall can easily be built in two days, and support a floor load soon after. Compare this with an in-situ reinforced concrete column where the time taken to fix reinforcement, erect shuttering, cast concrete, cure, prop, and then strike the shutter is often more than a week. Aesthetics The aesthetic appeal of a building is a complex amalgam of many factors: form, massing, scale, elevation treatment, color, texture, etc. Masonry provides the human scale, is available in a vast range of colors and textures, and, due to the small module size of bricks and blocks, is extremely flexible in application in that it can be used to form a great variety of shapes and sizes of walls, piers, arches, domes, chimneys, etc. Masonry structures tend to wear well and mellow with time. In our climatic and environmental conditions, many other materials perform conspicuously less well. Durability Many historic buildings and engineering structures provide living proof of this quality. It must be emphasized again, however, that this considerable functional and environmental benefit applies only to properly designed masonry. 2

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Sound Insulation The majority of noise introduction is by airborne sound, and the best defence against this traditionally is mass – the heavier the partition, the less the noise transmitted through it. It is an added bonus if the mass structure is not too rigid.

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Thermal Insulation

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Fire Resistance and Accidental Damage

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Capital and Current Energy Requirements

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Repair and Maintenance

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Ease of Combination with other Materials

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Recyclability

Disadvantage: 

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Lack of Education in Masonry Increase in Obstructed Area over Steel and Reinforced Concrete Although masonry units can be obtained with extremely high crushing strengths, the design compressive strengths of masonry walls are generally lower than for steel or reinforced concrete. It follows, therefore, that for a particular loading condition, masonry will require a greater cross-sectional area.

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Construction of Beams and Slabs

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Construction of large Openings

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Health and Safety Considerations

1.4 Bricks, Blocks and Mortars Bricks: Bricks are walling units not exceeding 337.5 mm in length, 225 mm in width and 112.5 mm in height. They are produced from a range of materials, such as clay, concrete and sometimes a mixture of lime and sand or crushed stone. The standard format of clay bricks is given in BS 3921 ‘Specification for clay bricks’ as 225 × 112.5 × 75 mm. This includes an allowance for a 10 mm mortar joint; thus the work size of the actual brick is 215 × 102.5 × 65 mm. Blocks: Blocks are walling units that exceed in length, width or height the sizes specified for bricks. They are generally produced from concrete.

The shape factor for the unit as laid, given by: Shape factor = Height as laid / Thickness as laid 3

Mortars: Whilst masonry walls may be constructed from bricks, blocks or stone, in each of these the mortar is the common factor. The mortar serves several purposes in the construction, and must satisfy a number of requirements in both the newly mixed and the hardened state. During construction, mortar should have good workability to enable efficient use by the bricklayer. It must spread easily so as to provide a level bed on which to align the masonry units of brick, block or stone. This in turn will ensure that the applied loads will be spread evenly over the bearing area of such units. In the hardened state, mortar must be capable of transferring the stresses developed in the masonry units. Ideally, however, it should not be stronger than the masonry units themselves, so that any movement that occurs will be accommodated in the joints. This should ensure that any cracking that does develop will be in the mortar and not the masonry units. 

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BS 5628-1:2005 - Page 11:

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