How is 28-day strength used in FDOT acceptance, and what if it fails?

• A. It is used to determine acceptance; if it fails, immediate replacement is required.
• B. It is used as a rough indicator; other tests determine acceptance.
• C. It is used to determine acceptance; if it fails, retest or remedial action per spec.
• D. It has no bearing on acceptance.

Answer: (C)

The main idea is that 28-day compressive strength is the basis for FDOT concrete acceptance. When a lot is tested, the 28-day strength of the cylinders is compared to the specified strength. If the strength meets or exceeds the requirement, the lot is accepted. If it falls short, the FDOT specification directs retesting or remedial action rather than automatic replacement. This creates a controlled path to verify or correct material quality: you may pull additional cylinders for another 28-day test, or take specified corrective steps (such as curing adjustments or replacement of the deficient concrete) per the contract. The 28-day test is used precisely because it reflects the concrete’s long-term strength, so it drives acceptance decisions and defines the steps if it fails.