The 7-day test result is used to monitor early strength gain and is often estimated to be about 75% of the 28-day strength.
Regardless of the reliability of the estimate for 28-day strength, 7-day strength test results are useful to the contractor and concrete producer as an early warning signal.
With today's fast-track concrete-placement schedules, it's essential for the contractor and concrete producer to know when 7-day test results are low. Then suitable steps can be taken promptly to adjust batch quantities, improve quality control procedures at the job site, and ensure that sampling, molding, and testing of the cylinders are being done in accordance with ASTM applicable standards.
Placement of concrete