10.006 7-Day Concrete Strength Reports

Q Is it required that my laboratory report 7-day break results to the client? The customer often calls back worried that the project requirements are not met.

— Unknown

A 8/25/05 – Response prepared by Jeffry Cannon, Laboratory Manager, Kleinfelder, Inc., Sacramento

There is no requirement in the UBC or ASTM standards that requires reporting concrete test results. Project specifications typically address the required 28-day compressive strength, with some specifications also including a 7-day compressive strength. On projects where the concrete compressive strength is specified at an age of 28 days, a 7-day compressive strength test may provide an indication of the 28-day strength. Many laboratories consider concrete with a 7-day strength of less than 65% of the 28-day strength to be suspect (see FAQ 10.004). Most laboratories consider it good business to notify their clients of 7-day compressive strength results that are less than 65% of the 28-day strength, and to include the 7-day strength when reporting the 28-day results.