Designation: C 1150 – 96
Standard Test Method for
The Break-Off Number of Concrete 1,2 This standard is issued under the fixed designation C 1150; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Scope 1.1 This test method covers determinati determination on of the break-off break-off number of hardened concrete in test specimens or structures, by measuring the force required to cause failure of a pre-cast or drilled core specimen loaded as a cantilever. 1.2 The values values stated in SI units are to be regarded regarded as the standard. 1.3 This standard standard does not purport purport to address address all of the safe safety ty conc concer erns ns,, if any any, asso associ ciat ated ed with with its its use. use. It is the the responsibility of the user of this standard to establish appro priate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: E 178 Practice Practice for Dealing Dealing with Outlying Outlying Observatio Observations ns 3 C 670 Practice for Preparing Preparing Precision and Bias Statements Statements for Test Methods for Construction Materials 4 C 823 Practice Practice for Examination Examination and Sampling Sampling of Hardened Hardened Concrete in Constructions 4 3. Summary Summary of Test Test Method 3.1 The principle of the break-off break-off test is illustrated in Fig. 1. A plastic sleeve with an annular annular seating ring is inserted inserted in fresh concrete to form a cylindrical test specimen and a counter bore. After the concrete has hardened, the sleeve is removed and a force is applied at the uppermost section of the cylinder so as to break the cylindrical test specimen from the concrete mass. The test result is reported as a break-off number, which is the maximum pressure recorded by the gage measuring the hydraulic pressure in the loading mechanism. In hardened concrete, in cases where the plastic sleeve has not been installed, a concrete coring machine with a specially shaped coring drill bit may be used to drill a similarly shaped test specimen.
FIG. 1 Schematic of Break-Off Test
4. Significanc Significancee and Use 1
This test method is under the jurisdiction of ASTM Committee C-9 on Concrete and Concrete Aggregatesand is the direct responsibility of Subcommittee C09.64on Nondestructive Testing of Concrete. Current Current editio edition n approv approved ed May 10, 1996. 1996. Publish Published ed July July 1996. 1996. Origin Originally ally published published as C 1150 – 90. Last previous previous edition edition C 1150 – 90 e1 2 The break-off break-off method is covered by a patent held by SINTEF SINTEF, Norwegian Norwegian Institute of Technology, Trondheim, Norway. Interested parties are invited to submit information regarding the identification of acceptable alternatives to this patented item to The Committee on Standards, ASTM Headquarters, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Your comments will receive careful consideration at a meeting of the responsible technical committee which you may attend. 3 Annual Book of ASTM Standards Standards,, Vol 14.02. 4 Annual Book of ASTM Standards Standards,, Vol 04.02.
4.1 The break-off break-off number number determine determined d by this test method method may be used to assess the in-place strength of concrete, and to delineate zones, regions, or areas of varying quality or deteriorated concrete in structures. 4.2 Prior Prior to using this test method method for determini determining ng in-place strength, a correlation relationship between the break-off number and the concrete strength should be established. Since such a correlation may vary with type and size of aggregates and method of specimen preparation, a relationship may be developed oped to take take these these and other variab variables les into accoun account. t. This This
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C 1150 relationship must be established for each new combination of concrete-making materials. In developing such relationships, care must be taken to ensure that the break-off specimens and the strength test specimens undergo similar curing histories up to the time of the test. NOTE 1—Published reports (1-8)5 by different researchers present their experience in the use and evaluation of the break-off test equipment and in establishing break-off strength correlation with compressive strength of concrete.
4.3 The break-off test may be used to evaluate the in-place concrete in order to: 4.3.1 Determine if formwork or reshoring can be removed, 4.3.2 Test if concrete meets break-off number specifications, 4.3.3 Determine when prestressing strands may be cut to release the prestressing force, 4.3.4 Determine if concrete has sufficient strength to allow post-tensioning to proceed, 4.3.5 Estimate efficiency of curing techniques, and 4.3.6 Evaluate the effects of exposure to environmental or chemical attack. 4.4 When planning the break-off test and analyzing test results, consideration should be given to ( 1) the normally expected decrease of concrete strength with increasing height within a given concrete placement in a structural element (see 9-11), and (2) locations with less favorable curing conditions prior to form removal. 4.5 Break-off tests are not recommended for concrete with a nominal maximum aggregate size greater than 25 mm. The within test variability of the break-off test has been found to increase in concrete with larger aggregate size (see (6) and (11)). 4.6 The cylindrical break-off specimens may be kept and used for additional testing. The break-off test shall not be performed on concrete that is at a temperature of less than −5°C. Prior to starting a testing program the break-off tester must be calibrated according to the manufacturer’s procedure (using the calibrator force gage and calibration diagram provided with the test unit) to ensure a consistent relationship between the pressure gage reading and the force applied by the loading mechanism.
FIG. 2 Sleeve for Creating Test Specimen in Fresh Concrete
which produces a core with a circular counterbore at the surface with dimensions as shown in Fig. 3. 5.3 The loading mechanism shall consist of a tubular shaped fixture that fits into the counterbore, and a hydraulic piston which when actuated applies a force at the top of the core, perpendicular to the longitudinal axis of the core. NOTE 2—The loading mechanism may include both a high and low measuring range capability to permit strength test of concrete over a wider range.A correlation relationship must be developed using the range setting that will be used during strength assessment.
5. Apparatus 5.1 The apparatus consists of a loading mechanism, a load generating device, a load measuring instrument, a tubular sleeve and seating ring of the dimensions shown in Fig. 2, a tubular sleeve remover, and a gage for calibrating or adjusting the loading system. The tubular sleeve shall be of a material that is resistant to chemical attack by concrete. It shall be rigid enough to maintain a reproducible size of test specimen. It shall be coated with a release agent that is not reactive with concrete prior to inserting it in the concrete. Plastic is an acceptable sleeve material and automotive grease is a suitable release agent. 5.2 For applications where tests are to be performed in already hardened concrete, a diamond tipped drill bit is used,
5 The boldface numbers in parentheses refer to the list of references appended to this test method.
FIG. 3 Dimensions of Test Specimen Created by Core Drill
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C 1150 5.4 The load generating device shall consist of a hydraulic pump that is connected to the loading mechanism so that it is possible to apply load (with smooth strokes of the pump) to the core until it breaks off. 5.5 The load measuring device shall consist of a pressure gage to measure the hydraulic pressure applied to the loading mechanism. The pressure gage shall have a maximum value indicator. The pressure gage shall have a pressure range up to 15 MPa (150 bars) and a least dial division not greater than 0.2 MPa (2 bars).
is uniformly seated in the counterbore. Set the maximum pressure indicator on the pressure gage to its zero value. Apply a gradual force to the specimen by means of the hydraulic pump until the core breaks off. Use a loading rate that causes a break-off within 60 6 15 s from the start of loading. On the pressure gage dial, read the maximum pressure required to break off the core and record the maximum reading as the break-off number for the test specimen. In reading the maximum pressure, estimate to the nearest 0.1 MPa (1 bar). 7.3.2 Record the nature of the break at the base of the core. Note whether the fracture surface includes the presence of large aggregate particles, reinforcing steel, and other abnormalities, such as foreign inclusions, soft aggregate particles, or excessive air pockets (honeycombing). Measure the diameter (to the nearest 1 mm) at the base of the core in directions parallel and perpendicular to the loading direction. Measure the approximate average height of the core to the nearest 5 mm.
6. Sampling 6.1 The break-off test locations shall be separated so that the center to center distance between test specimens is at least 150 mm. Clear spacing between the plastic inserts and the edges of the concrete shall be at least 100 mm. 6.2 When the break-off test results are used to assess the in-place strength, in order to allow the start of critical operations such as form work removal or applications of post tensioning, at least five individual break-off tests shall be performed for a given placement for every 100 m 3, or a fraction thereof, or for every 500 m 2, or fraction thereof, of the surface area of one face in the case of slabs or walls. Select test sites that are critical in terms of exposure conditions and required structural capacity. 6.3 When the break-off test is used to evaluate concrete strength in an existing structure, the number and locations of tests shall be established by the investigator. Practice C 823 can be used to assist in planning such an evaluation.
NOTE 4—If the presence of abnormalities is associated with a test result that appears to be an outlier compared with the average, the Dixon criteria in Practice E 178 may be used to test whether the suspected result can be discarded. Another test should be performed to replace the discarded test result.
8. Calculation 8.1 Calculate the average of the break-off test results (to the nearest 0.1 MPa (one bar) pressure). This value is the break-off number for the concrete. 9. Report 9.1 Report the following information: 9.1.1 Location of each test, 9.1.2 Date and the time of the test, identification symbols, and name of the operator who performed the test, 9.1.3 Method of specimen preparation, either by sleeve insertion or core drilling, 9.1.4 Maximum aggregate size, 9.1.5 The load range setting (if the loading mechanism is equipped with high- and low-range settings), 9.1.6 Break-off number for each test specimen and the average break-off number, 9.1.7 Description of the nature of the break at the base of the ruptured test specimen, and whether the fracture surface shows the presence of reinforcement or other abnormalities, and 9.1.8 Approximate average height of each test specimen to the nearest 5 mm and the average diameter at the base of the specimen to the nearest 1 mm.
7. Procedure 7.1 Preparation of Cylindrical Specimens by Tubular Sleeves: 7.1.1 At each test location, carefully insert the tubular sleeve which has been thoroughly coated with a release agent. NOTE 3—Insertion of the sleeve may be aided by simultaneously twisting and pushing the sleeve into the concrete until the top of the sleeve is flush with the concrete surface. For concrete with slump less than 75 mm, a slight depression may occur in the center of the sleeve, which should be filled with concrete, tapped in by fingers, and the surface struck off flush. Sleeves are not recommended for no-slump concrete or when deep surface texturing is to be used. In such cases, test specimens should be prepared by drilling.
7.1.2 Tap on the concrete surface adjacent to each sleeve to reconsolidate the concrete and close any visible voids next to the sleeve. Clean off excess mortar from the tops of the sleeves and allow specimens to cure within the concrete mass. 7.1.3 At the time of test, remove the sleeve using the sleeve removal tool. Remove all loose concrete or other materials from the cylindrical slit before testing. 7.2 Preparation of Cylindrical Specimens by Coring : 7.2.1 Select test locations. Set up drilling equipment (using a vacuum plate or bolts to ensure rigidity) so that core drill is perpendicular to the concrete surface. Drill core into concrete using a suitable diamond core drill to produce a test specimen having the dimensions shown in Fig. 3. 7.3 Testing: 7.3.1 At each test location, place the loading mechanism into the counterbore so that the ring of the loading mechanism
10. Precision and Bias 10.1 Precision—Based on the data summarized in ACI 228.1R-95 (12), the average coefficient of variation for break-off tests made on concrete with maximum aggregate size of 19.0 mm (3 ⁄ 4 in.) or 25.4 mm (1 in.) by a single operator using the same test device is 9 %. 6 Therefore, the range of individual test results (see Note 5), expressed as a percentage of the average, should not exceed the following:
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3
This number represents the (1s %) limit as described in Practice C 670.
C 1150 Number of tests 5 7 10
disregard those tests for which reasons for the outlying results can be identified positively. If there are no obvious causes of the extreme values, it is probable that there are real differences in concrete strength at the different test locations. These differences could be due to variations in mixture proportions, degree of consolidation, or curing conditions.
Acceptable range (percentage of average) 35 % 38 % 40 %
NOTE 5—If the range of test results exceeds the acceptable range, further investigation should be carried out. Abnormal test results could be due to faulty test specimens, improper procedures, or equipment malfunction. The user should investigate the potential causes of the outliers, and
10.2 Bias—The bias of this test method cannot be determined because the break-off number can only be obtained by the use of this test method.
REFERENCES (1) Carlsson, M., Eeg, I. R., and Jahner, P., “Field Experience in the Use of the Break-off Tester,” ACI SP82-14, In Situ/Nondestructive Testing of Concrete, V. M. Malhotra, Ed., American Concrete Institute, Detroit, MI, 1984, pp. 277–292. (2) Dahl-Jorgenson, E., and Johansen, R.,“ General and Specialized Use of the Break-off Concrete Strength Test Method,” ACI SP82-15, In Situ/Nondestructive Testing of Concrete, V. M. Malhotra, Ed., American Concrete Institute, Detroit, MI, 1984, pp. 293–308. (3) “Early Strength Measuring Test for Offshore Oil Platform,” Concrete Products, September 1985. (4) Naik, T. R., Hassaballah, A. A., and Salameh, Z., “The Break-off Test Method,” Department of Civil Engineering, the University of Wisconsin-Milwaukee, Milwaukee, WI, 1988. (5) Yener, M., and Chen, W. F., “Evaluation of In-Place Flexural Strength of Concrete,” American Concrete Institute Journal, Vol 82, No. 6, Nov./Dec. 1985, pp. 788–796. (6) Barker, M. G., and Ramirez, J. A., “Determimation of Concrete Strength Using the Break-off Tester,” American Concrete Institute Journal, Vol 85, No. 4, July/Aug. 1988, pp. 221–228. (7) Dahl-Jorgenson, E., “In Situ Strength of Concrete, Laboratory and
Field Test,” SINTEF Report No. STF 65A82032, 1982-06-04, Norwegian Institute of Technology. (8) American Concrete Institute Committee 228 Report, “In-Place Methods for Determination of Strength of Concrete,” ACI 228-IR-89, American Concrete Institute, Detroit, Michigan, 1989. (9) Murphy, W. E., “The Interpretation of Tests on the Strength of Concrete in Structures,” ACI SP-82, In Situ/Nondestructive Testing of Concrete, V. M. Malhotra, Ed., American Concrete Institute, Detroit, MI, 1984, pp. 377–392. (10) Munday, J. G. L., and Dhir, R. K., “Assessment of In Situ Concrete Quality by Core Testing,” ACI SP-82, In Situ/Nondestructive Testing of Concrete, V. M. Malhotra, Ed., American Concrete Institute, Detroit, MI, 1984, pp. 393–410. (11) Haque, M. N., Day, R. L., and Langan, B. W., “Realistic Strength of Air-Entrained Concrete with and without Fly Ash,” American Concrete Institute Journal, Vol 85, No. 4, July/Aug. 1988, pp. 241–247. (12) ACI 228.1R-95, “In-Place Methods to Estimate Concrete Strength,” Report of ACI Committee 228 on Nondestructive Testing, American Concrete Institute, Farmington Hills, MI.
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