No abstract

The ball-on-three-ball test method (B3B) is used to measure the flexural strength of cement paste and mortar. This method has the advantage of utilizing small and thin samples requiring less material and improved sensitivity, allowing a large number of samples to be tested for improved variability assessment, and assessing chemical degradation rapidly because of its relatively high surface-to-volume ratio. This paper examines two specific questions that have surfaced with the recent adoption of this test method in ASTM C1904-20, Standard Test Methods for Determination of the Effects of Biogenic Acidification on Concrete Antimicrobial Additives and/or Concrete Products. The first question is whether the mixing technique used in sample preparation impacts the results. It was found that the use of vacuum mixing (ASTM C1904-20) and Hobart mixing (ASTM C227-10, Standard Test Method for Potential Alkali Reactivity of Cement-Aggregate Combinations (Mortar-Bar Method), and ASTM C305-20, Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency), provide comparable results; however, the high-shear mixing (ASTM C1738, Standard Practice for High-Shear Mixing of Hydraulic Cement Paste) indicated that the results were not statistically similar to the other mixing techniques. The second question is related to the timing of the test after the samples are removed from an exposure solution. It was found that the sample should be removed from the exposure solutions and tested within 10 minutes to maintain low variability. These results will provide information needed to evaluate changes for ASTM C1904-20.