Too much fly ash - never reach design strength?
Too much fly ash - never reach design strength?
(OP)
We had petrography performed on a sample taken from a concrete core that came back with below expected strength. The petro results show the fly ash as being 35% of the cementing material instead of 25% as expected. The sample also showed air content slightly above ACI recommendations. I know that fly ash tends to slow the concrete curing. We're trying to reach 75% target strength and are willing to wait beyond 56days.
My question is with beyond the expected fly ash will this concrete eventually reach design strength, just take a little longer? Will the slightly above air content affect long term strength and/or durability?
My question is with beyond the expected fly ash will this concrete eventually reach design strength, just take a little longer? Will the slightly above air content affect long term strength and/or durability?






RE: Too much fly ash - never reach design strength?
RE: Too much fly ash - never reach design strength?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Too much fly ash - never reach design strength?
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Too much fly ash - never reach design strength?
curious mimes want to know...
Dik
RE: Too much fly ash - never reach design strength?
RE: Too much fly ash - never reach design strength?
RE: Too much fly ash - never reach design strength?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Too much fly ash - never reach design strength?
RE: Too much fly ash - never reach design strength?
Dik
RE: Too much fly ash - never reach design strength?
There are many advantages to using fly ash, but as with any other component of concrete, quality matters, and the quality of fly ash probably varies more than most.
http://www.cement.org/docs/default-source/fc_concr...
RE: Too much fly ash - never reach design strength?
Your second question was about air content. Excessive air content is not recoverable.....air doesn't get stronger with time! Depending on the air content excess, you might not achieve the strength you want.
The combination of excessive air content and high fly ash content will certainly put you in a marginal range for compliance. Let us know how it goes.
Can you post a copy of the mix design?
RE: Too much fly ash - never reach design strength?
If massive concrete pours,...and depending on purpose, maybe you do not need 75% design strength to proceed with live loading to a limited degree for the structure. Say a 6 foot deep large scale generator foundation, size necessary for tuning of frequencies of the operational system,...not it's deadload only, which may sitting for months before the generator operational. So, maybe foundation concrete testing 2,500 psi is okay to set equipment, but not torque anchors or fill bins, silos, or turn on equipment, etc. We have spec'd 4,000 psi foundations regularly with 35% flyash with good long term results. May have records into the 5,000psi range on the 4,000 mix. Weather conditions/curing?
OP Could use more information on the pour size and purpose and yes mix design including that flyash type