how long should you wait to load a concrete footing?

[msucog]

i had a question that i've never fully considered pop up today. how long should you wait to begin masonry construction on a concrete footing? most of time it's not a concern because there are at least a few days before masonry construction starts after the footing is poured and then the wall takes a few days to get built. on precast wall footings, i've seen structural engineers require 60%-75%+ prior to loading. for your "typical" masonry wall construction, my opinion is approximately 50% +/- prior to starting "significant" construction (above a few courses of foundation block). That would put you around 3 days old or so.

more importantly, my question is asking if someone can put me on a more-definitive reference guideline (and i am aware that project specific site/loading conditions will dictate). i could not find anything specific in aci, ibc, etc. even though i seem to vaguely recall it somewhere (i think aci318 or aci301). can someone pass along any info or previous thread link to this question?

thanks in advance

 

[csd72]

The short answer is ' until it has sufficient strength to support the proposed loads'.

Sorry but I doubt you will find specific guidance on this, you will probably just have to use engineering judgement.

I would require a higher strength if it was supported in poor soil as opposed to rock. I would also require a higher strength if it was supported on piles. Do the math and see what strength you would be happy with then calculate how long you expectn it to reach that strength.

 

[cvg]

Partially depends on the failure consequences. if this is a fence than a crack in the footing might not be critical. if it is a building or retaining wall than cracked masonry or footing may not be acceptable.

Also depends on the type of concrete and temperature. High early strength concrete can reach 3,000 psi or more in 24 hours.

 

[SlideRuleEra]

Another way to address your question is to look at the curing requirements for the footing. The Portland Cement Association advises:

During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process.

Here is the link, see the third question/answer:

http://www.cement.org/basics/concretebasics_faqs.asp

My "hard-line" interpretation of this guideline is that nothing should be done for at least five days, regardless of concrete strength.

There "may" be some room for negotiations on this depending on slab properties, weather, etc... but I would suggest letting the Contractor provide "proof" for that option.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Teguci]

I wouldn't worry about wet curing a footing. Do a quick analysis on loading and get two extra concrete cylinders to test the compressive strength before placing your loads on the foundation. chances are your loads will be minimal (10% of final design) and you can start putting load on the footing within a day or two. Also consider that your final loading will probably include live loads that won't be put on the structure until after the 28 days.

 

[SteelPE]

I know OSHA has requirements for concrete strength prior to steel erection (must attain 75% without EOR approval), maybe they have something similar for masonry construction.