If compressive strength is less than 7000psi, what should the capping strength be according to C617?

According to ASTM C617, which addresses the capping of concrete specimens for compressive strength testing, the capping material used must have a specified minimum strength depending on the strength of the concrete being tested. When the compressive strength of the concrete is less than 7000 psi, the standard requires that the capping material must have a minimum compressive strength of 5000 psi. This requirement ensures that the capping material is strong enough to provide a uniform surface for loading the concrete specimen during testing and does not impede the accurate measurement of the concrete's compressive strength.

Using a capping material with a strength lower than 5000 psi could introduce variability in the test results and potentially lead to inaccurate assessments of the strength of the concrete. Therefore, adhering to this guideline is essential for maintaining the integrity of the testing process and ensuring reliable results. As a result, the correct answer is the minimum of 5000 psi for the capping strength when the compressive strength of the concrete is below 7000 psi.