The basement floor and walls of my new house (in Indianapolis) were
poured with a 3500 lb mix = 5.5 bag mix. This sounds normal. So my
question is, what could cause this concrete to be harder and more
brittle than any other concrete I have ever drilled? Moisture starved
while curing? Curing in the winter? Here are 2 phenomena that did
not occur in my last 3 homes:

1) When I drill and install standard wall anchors, and screw in
standard zinc-plated screws, about 40% of the screws break.

2) When I drop something hard and heavy on the concrete, it chips out
a significant chunk.

Thanks,
Jim