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Originally posted by Beton2
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Curing is a can of worms. When the concrete is at its design strength, it can be in service. When concrete testing (to test design strength) is done they put the cylinders in a sheltered place to prevent the sun from heating the concrete up. They cover the tops and then put a foil insulation over the top. The next morning they pick the cylinders up and put them into optimal curing conditions. Minimal water is lost from the test concrete. And then test the cylinders at the 28 days. The 28 days is just a yardstick. It is a uniform benchmark. You can buy an E (early) mix being E3 or E7 vs an N mix,meaning that an E3 32:20:80 mix has to attain 32MPA in 3 days instead of the required 32MPA in 28 days as required in a normal N32:20:80 mix.
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Engineers can create havoc and burden a build with unnecessary costs. Not long ago I poured a carpark at a retail lot. I had to have an engineers design for council approval. The steel supplier, the contractor and the ready mix supplier all criticised the amount of steel and the depth of concrete. When I took it up with the engineer his answer was " That is what I want. I have to cover my butt when I sign my name." The council said it is up to the engineer.
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