Sorry I didn't check back sooner. Thank you for an excellent answer. I've gotten a copy of the ASTM standard you mention and will make sure the contractor follows it to the letter, then use some judgement on the results to determine whether to drop this issue or not. Thanks again.
I hope someone out there can help me. I'm working as QA for the Corps of Engineers in Iraq at a site where a contractor is building concrete structures. Many of the compressive tests (they use cubes, not cylinders) failed in the lab and the contractor now wants to use a Swiss hammer test to...