Found out my mix design was way off after a core test came back

Pulled a core from a driveway I poured 2 months ago in Austin and it tested at 2800 psi instead of 3500. Lab said my water-cement ratio was too high from the batch ticket. Any of you guys run into this with a pump mix?

3 comments

3 Comments

marydavis1mo ago

Did you run the break test yourself or just trust the lab? I've had pump mixes come in a bit loose before in the Houston heat. 2800 psi is rough for a driveway in Texas though, that sun will cook the surface fast. Might be worth pulling a second core just to double check.

blake7921mo ago

Did you wet cure any test cylinders from that same batch?

kimfisher1mo ago

Yeah, I read somewhere that ACI 306 says you're supposed to wet cure for at least 7 days in hot weather, but half the time nobody does it because the schedule is too tight. I had a neighbor who poured a slab in July and they just sprayed it once with a hose then left it. That thing was dust by the end of the month. The heat really does mess with the surface hydration, so even if the mix design is fine, the top inch can end up weak if you don't keep it damp. I've also heard that pump mixes can have a bit more air in them sometimes, which might explain the low numbers. Pulling another core sounds like a smart move before you make any decisions about ripping it out.