28-day test failed - okay to wait for 56-day?
28-day test failed - okay to wait for 56-day?
(OP)
The results of the 28-day tests aren't meeting the target compressive strength. We believe it's due to the strength retarding properties of fly ash in the mix. Assuming the 56-day test meets the target; are there any implications to long-term durability (40 year service life) with utilizing concrete that met it's target strength late? The foundation won't be loaded until the target strength is met.






RE: 28-day test failed - okay to wait for 56-day?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: 28-day test failed - okay to wait for 56-day?
www.PeirceEngineering.com
RE: 28-day test failed - okay to wait for 56-day?
How far off are the breaks coming in at?
RE: 28-day test failed - okay to wait for 56-day?
RE: 28-day test failed - okay to wait for 56-day?
Dik
RE: 28-day test failed - okay to wait for 56-day?
It is not unusual for the testing lab to do their tasks first, then the concrete crews proceed to work and ask for more water, without further lab testing.
Obviously then the samples do not reflect the actual installed concrete.
When this happens, the truck mix driver (at least here in the NYC area) will ask the foreman to sign the tickets to accept changes in the delivered mix design.
You could ask for copies of the tickets sent back to the supplier and see if this happened.
The other thing to consider is that test samples are cured under ideal ASTM specified curing conditions, while the cores reflect the actual curing conditions which are not the same.
In the end, I would put more trust in the cored samples than the test samples.
RE: 28-day test failed - okay to wait for 56-day?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: 28-day test failed - okay to wait for 56-day?
Looks like you are not meeting these requirements.
RE: 28-day test failed - okay to wait for 56-day?
RE: 28-day test failed - okay to wait for 56-day?
Some fly as may actually decrease final strength.