ASTM C42/C42M:13 pdf free download – Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete.
If the ratio of the length to the diameter (UD) of the core exceeds 2.1, reduce the length of the core so that he ratio of the capped or ground specimen is between 1.9 and 2.1. Core specimens with length-diameter ratios equal to or less than 1.75 require corrections to the measured compressive strength (see 7.9.1). A strength correction factor is not required for [ID greater than 1.75. A core having a maximum length of less than 95 % of its diameter before capping or a length less than its diameter after capping. trimming, or end grinding shall not he tested.
7.2.2 If the compressive strengths of cores are to be compared with specified strengths based on standard concrete cubes, cores shall be tested with L/D, after end preparation. in the range of 1 .(X) to 1.05 unless otherwise directed by the specifier of the tests. If the strengths of cores with L/D =1 are to he compared with specified concrete cube strength, do not apply the correction factor in 7.9.1.
7.3 Moisture C’onditioniizg—Test cores after moisture conditioning as specified in this test method or as directed by the specifier of the tests. The moisture conditioning procedures specified in this test method are intended to preserve the moisture of the drilled core and to provide a reproducible moisture condition that minimizes the effects of moisture gradients introduced by wetting during drilling and specimen preparation.
7.3.1 After cores have been drilled, wipe off surface drill water and allow remaining surface moisture to evaporate. When surfaces appear dry, but not later than I h after drilling, place cores in separate plastic bags or nonabsorhent containers and seal to prevent moisture loss. Maintain cores at ambient temperature, and protect cores from exposure to direct sunlight. Transport the cores to the testing laboratory as soon as possible. Keep cores in the sealed plastic bags or nonabsorbent containers at all times except during end preparation and for a maximum time of 2 h to permit capping before testing.
7.3.2 If water is used during sawing or grinding of core ends, complete these operations as soon as possible, but no later than 2 days after drilling of cores unless stipulated otherwise by the specifier of tests. After completing end preparation, wipe oil surface moisture, allow the surfaces to dry, and place the cores in sealed plastic bags or nonabsorbent containers. Minimize the duration of exposure to water during end preparation.
7.3.3 Allow the cores to remain in the sealed plastic bags or nonabsorbent containers for at least 5 days after last being wetted and before testing, unless stipulated otherwise by the specifier of tests.
NOTE 11—The waiting period of at least 5 days is intended to reduce moisture gradients introduced when the core is drilled or wetted during sawing or grinding.
7.3.4 When direction is given to test cores in a moisture condition other than achieved by conditioning according to 7.3.1, 7.3.2, and 7.3.3, report the alternative procedure.
7.4 Sawing of Ends—The ends of core specimens to be tested in compression shall be flat, and perpendicular to the longitudinal axis in accordance with Test Method C39/C39M. If necessary. saw the ends of cores that will be capped so that prior to capping. the following requirements are met.