7 day concrete strength
7 day concrete strength
2
charlierock (Geotechnical)
(OP)
Is there a formula for estimating the 28 day compressive strength of concrete based on the 7 day result?
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Contact USThanks. We have received your request and will respond promptly. Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting Guidelines |
|
Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.
Here's Why Members Love Eng-Tips Forums:
Register now while it's still free!
Already a member? Close this window and log in.
RE: 7 day concrete strength
For a typical "run of the mill" mix we start to get concerned if we see much less than 60% of specified 28 day strength at 7 days. I am accustomed to seeing the 7 day strengths at about 2/3 of the 28 day test as a rule of thumb.
RE: 7 day concrete strength
f'ci= f'c*(t/(4.00+0.85t))
If you don't know the f'c, back into it using the 7-day break value. Then use that f'c value to calculate your 28-day strength. My real world experience is that it is a decent estimate.
RE: 7 day concrete strength
Many spec's set a "specimen age correction factor" to predict the 28-days compressive strength from the results obtained at an older or younger age.
The most commonly used factors are :
Age Factor (Multiply By)
--- ------
3 2.5
7 1.5
28 1.0
90 0.85
360 0.75
Provided that the conditions of curing and testing are kept constant. Interpolation could be made for other ages but this will increase the deviation from the true strength.
I’ve used these correction factors in my day-to-day business and found it to be kind of reliable especially for type I Portland cement. Note that this is only an estimate; nothing will give you the exact 28-days strength as there are too many variables. I’ve seen concrete that failed at 28-days though predicted to pass, there's a reason why it's called MEAN compressive strength.
Also this gives no indication of the true compressive strength at the site and generally will yield a higher strength than the true one (depending on temperature, curing and type of cement)
Drop By !!
www.geocities.com/concretesite
RE: 7 day concrete strength
RE: 7 day concrete strength
If your mix has any proportion of ground blast furnace slag cement in it (NEWCEM or similar), then you can expect the 7-day strength gain to be significantly lower than predicted or expected by correlations for plain Type I. The 28-day strengths will not be significantly affected, but the strength gain is slower than with plain Type I cement.
Fly ash causes a similar slowing of the strength gain, though less pronounced because it is usually used in smaller proportions.
Ask the ready-mix supplier for a strength gain curve for their mixes. This should get you where you want to be in your predictability.
RE: 7 day concrete strength
BUT....I won't totally trust data provided by the concrete supplier .... remember it's their concrete you are testing!
Drop By !!
www.geocities.com/concretesite