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Concrete & Masonryaka: f'caka: PSIaka: concrete strength

Compressive Strength

In Plain English

How much crushing force concrete can withstand before it breaks — the primary measure of concrete quality.

Definition

The measured capacity of concrete to resist axial loads that crush or compress it, expressed in pounds per square inch (PSI) or megapascals (MPa). Standard test cylinders are cast from concrete samples and broken at 28 days to verify compressive strength. Typical structural concrete ranges from 3,000 to 5,000 PSI; high-strength mixes can exceed 10,000 PSI.

Why It Matters in Bidding

Specified compressive strength drives concrete mix pricing, because higher-PSI mixes cost more per cubic yard, so estimators must read the structural specs carefully when bidding concrete scope. Strength also gates the schedule: cylinders are broken at 28 days, and failing breaks can force costly remove-and-replace work, making the specified f'c a material risk factor in both the bid and the field.

Example

The parking structure was specified at 5,000 PSI compressive strength to handle the combined live and dead loads.

Related Terms

Slump TestWater-Cement RatioCuringPortland Cement

Frequently Asked Questions

Concrete gains strength as cement hydrates, reaching the bulk of its designed strength by 28 days, which became the industry-standard verification age. Test cylinders cast from the placement are cured and crushed at 28 days to confirm the mix meets specified f'c. Earlier 7-day breaks give a progress indicator before the final result.
A failed break triggers investigation: reviewing curing and sampling, then often core sampling the in-place concrete or load testing the structure. If the concrete still falls short, the engineer may require strengthening, partial removal, or replacement. These remedies are expensive and schedule-disrupting, which is why mix design and field curing are tightly controlled.
Higher specified compressive strength requires more cement or admixtures and tighter quality control, raising the unit price per cubic yard. An estimator pricing a 5,000 PSI structural mix budgets more than for a 3,000 PSI slab-on-grade. Misreading the spec and pricing the wrong strength can erase the margin on the concrete scope.

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