Concrete
Compressive Strength
The maximum load per unit area that concrete can withstand before failure, measured in psi at 28 days after placement.
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In the Field
Cylinders are cast at the pour, cured, and broken at 7 and 28 days. A 7-day break should reach about 70% of design strength. If 28-day breaks miss spec, the engineer decides whether cores are needed or the pour must come out.
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Rule of Thumb
Standard structural concrete is 3,000–4,000 psi. High-rise columns and bridge elements often specify 6,000–12,000 psi.