RESULTS OF AN INTERLABORATORY TEST PROGRAM: COMPRESSIVE STRENGTH OF CONCRETE

The American Society for Testing and Materials (ASTM) and the Canadian Standards Association (CSA) have had standards in place for testing the compressive strength of concrete cylinders since the 1920s; however, neither standard includes a statement of the within- and between-laboratory precision of its test method as prescribed by Practice for Use of the Terms Precision and Bias in ASTM Test Methods (ASTM E 177). Sixteen CSA-certified Ontario testing laboratories participated in an interlaboratory study in accordance with Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method (ASTM E 691). The analysis revealed that the variability of the test results increases with the mean strength of the concrete. The authors recommend the inclusion of a precision statement in Test Method for Compressive Strength of Cylindrical Concrete Specimens (ASTM C 39) and Compressive Strength of Cylindrical Concrete Specimens (CSA A23.2-9C) based on the results reported here.