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The 3/4 inch slump rule I heard on a Denver pour changed how I finish
I was on a commercial job in Denver about 2 weeks ago, and an older finisher named Ray told me something that threw me. He said for every 1 inch you drop the slump, you gain about 200 psi in strength. I looked it up later in my ACI book and there it was, right in the mix design chapter. I had been pouring at a 5 inch slump for years because it flowed nice and saved my back. Ray said the difference between a 4 and a 5 on a slab means the concrete can be 300 to 400 psi weaker at 28 days. That night I went back and checked my last few tickets from a parking garage job and sure enough, the higher slump loads had lower break numbers. Now I am not saying I never add water, but I am a lot pickier about it. Any of you run into a slump number that made you rethink your mix?
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