f'c < 2500 psi
f'c < 2500 psi
(OP)
I know the ACI 318 states that concrete shall have a minimum f'c of 2500 psi. I have a situation where 28 day, 56 day, and even some cored breaks have come in lower (around 2000 psi). Keep in mind that all concrete is for shallow foundations, no vertical elements. I have checked shear and moment capacities in the footings and everything works ok, even when I set f'c=1500 psi. I also checked epoxied anchorage and "backed into" published values from Hilti for masonry (min. f'c=1500 psi). Is there any other potential problem that I should be aware of? Thanks in advance for any help. Rob





RE: f'c < 2500 psi
RE: f'c < 2500 psi
Have you investigated the sampling, cylinder preparation, handling, curing and testing of the cylinders?
Dick
RE: f'c < 2500 psi
RE: f'c < 2500 psi
RE: f'c < 2500 psi
RE: f'c < 2500 psi
I have at least 36 cylinders that are between 2000 and 2500 psi.
RE: f'c < 2500 psi
Thanks
RE: f'c < 2500 psi
Yes, if the failures involved shear planes through the aggregate, you should investigate the aggregates used. Such low strengths should not occur with competent aggregates.
You stated that there are many buildings. What type of buildings? If they are all just single storey structures with only strip footings involved, the concern would certainly be less than with a more significant structure. But you should still try to get to the bottom of why it happened.
RE: f'c < 2500 psi
RE: f'c < 2500 psi
RE: f'c < 2500 psi
RE: f'c < 2500 psi
It is hard to comprehend the aggregate breaking and not a lot of aggregate particles pulled out is unusual at such a low indicated cylinder strength. The split aggregate is indicative of reasonably decent concrete matrix strength.
Calibration of the testing equipment in addition to the testing procedure (capping method and accuracy, centering on the platen and rate of loading) should be looked at. Also, look at the means to allow the upper plate to a rotate if the capping is not parallel between the top and bottom.
Dick
RE: f'c < 2500 psi
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: f'c < 2500 psi
RE: f'c < 2500 psi
RE: f'c < 2500 psi
In general if you design a mix for durability, the strength will follow.
RE: f'c < 2500 psi