I had a left over half bag of ready-mix concrete. It's about 2 years
old. It was still powdery but had a few small chunks in it, which
easily broke up with my fingers. I filled a 8" round hole in my
sidewalk where there used to be a wooden post. The weather has been
in the 80s and it should have dried quickly. I mixed it so it was
like thick paste (the way it should be). 24 hours later it was all
sand-like and was not hard. I wet it down. (I know it should be kept
wet) and the whole surface washed off. Now it's all sand looking.
Does old cement go bad? It seems this stuff has.

JWR