Thanks Ron, I'm located in NC we don't have any chert that I know of. Most of our rock quarries are granite. It is gray/green/white. I'll see if I can clean one of the holes out and look at the apex of the cone.
I have a concrete slab that was poured about 6 months ago. It was cold the day the concrete was poured and Calcium Chloride was added. The slab looks good except there are about 10 bad spots. I tested the concrete with a schmidt hammer and have compressive strengths of 3500 plus psi except for...
