Concrete Time for Curing

[ChipperB]

We have a two week window to get the project done. We are building a 6-in. thick, 6-ft. X 6-ft. reinf concrete slab on 6-in, compacted crushed stone, to support a small condensor unit. Using 3000 psi concrete. After slab is poured, how many days before we can safely install the unit? Any steps we can take to speed up the curing process?

 

[concretemasonry]

Use high early cement and design for a higher compressive strength (4000 psi would not be costly or unreasonable).

Cover the little slab with an insulated blanket to retain the heat of hydration and will be go to go within 2 days, which is less time to make cylinders, transport and test to verify the short term compressive strength (if testing is necessary).

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Ron]

Compute the stress that the condensor unit will place on the slab, then figure the amount of strength you need in the concrete. Check a strength gain curve for the mix design you intend to use and that will give you your answer. Chances are you will be able to place the unit within a few days of concrete placement.

No need to do anything extraordinary in the curing process; however, I would not use a concrete mix with constituents that tend to delay the strength gain, such as fly ash or ground, granulated blast furnace slag cement. Either will delay the strength gain.

 

[beton1]

Agree with comments. Also, you can check with Ready Mix supplier for a '72 hour mix'. They can usually provide a concrete with very accelerated strength gains. Depends on what you want to spend and how critical your timeline is. May be worth the extra money.

 

[hokie66]

Much ado about nothing. The pad is only 6' square. You can set the unit on it the next day. If anchoring, wait for a couple of days before drilling.

 

[dik]

Don't use calcium chloride as an accelerator...

Dik

 

[Samer87]

You can use a curing compound after you pour the concrete. this will make the curing period shorter

 

[scone38]

@chipper

Order a better performing mix from the producer and make sure you have a quality contractor doing the work. Mix designs can be easily tailored to get the results you want. You get what you pay for... don't cut costs where you shouldn't and cross your fingers.

@samer87

All concrete should be cured. Whether it's using a curing compound or some type of wet cure method. If a contractor is not educated enough to properly cure the concrete you don't want him doing the work.

 

[dicksewerrat]

The largest expense for the placement will be the 'short load' charge.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cvg]

curing compound will not speed up curing, only improve the quality of the concrete.

 

[Samer87]

@cvg

The tradtional method of curing by water takes 7~10 days. However, By using curing compound (Eg, Fosroc concure compound) you can start painting bitumen almost immediately. (3~5 hr to dry)

 

[Ron]

Samer87....I wouldn't recommend your approach. Where did the "painting bitumen" come in?

cvg is correct

 

[Samer87]

@Ron
Wherever the concrete surface will be in touch with soil. like foundation.
I'm sharing my experience here. if you have other opinion, please share.

 

[hokie66]

Samer87,
There are many different curing compounds. "Fosroc Concure" itself is a brand name used for several different products, some very good if used correctly, and some useless.

 

[Ron]

I'm sure this is a moot point by now, or at least should be from a construction standpoint, but concrete gains strength (in the curing process) faster if more moisture is present and the temperature is moderately close to 70F. This aids the hydration process. The drier the concrete, the slower the strength gain. The lower the temperature, the slower the strength gain.

Curing compounds are intended to hold within the concrete the moisture that is latent and present in the concrete after finishing. They add nothing other than to temporarily seal the surface of the concrete to prevent such moisture loss. The rate of strength gain will depend on the amount of latent moisture and the temperature during the curing process.