Curing Concrete

[Nick Rose]

We just had a new driveway and pathway poured on 5/9 and yesterday 5/13 the contractor told us to water down the the concrete 3 times a day for a week. The concrete mixture is for 4000 PSI. Are we wasting our time watering 3 times a day? Everything that I read is that you have to keep it wet 24/7 for at least a week and to never let it dry out. When we do wet it you can see that the concrete quickly absorbs it.

Nick Rose

 

[dik]

Not wasting your time... but, you can improve the curing with burlap or some kind of cloth to retain water.

Dik

 

[SlideRuleEra]

As soon as possible, completely cover the concrete with polyethylene sheet that can be purchased from a home store.

Don't have to seal the joints in the sheets, just lap the joints about 6" or so.

Don't have to remove the sheets to wet the concrete. Put the end of a garden hose under a sheet and run the water for a couple of minutes twice a day, for 7 days (move the hose as needed to make sure all of the concrete gets water on it, each time).

The polyethylene will keep the concrete damp.

Watering the concrete 3 times a day (but not covering it to prevent drying) is better than nothing, but keeping concrete continuously damp is much better than wetting it... letting it dry out... then wetting it again.

Since 5 days have passed since the concrete was placed, go ahead with the above steps but it will be of limited value. Unfortunate the contractor did not advise you earlier, curing should have started either late on 5/9 or first thing in the morning on 5/10.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Ron]

Agree with dik and SRE.....keep it as wet as possible for as long as possible!

Wetting and drying will exacerbate cracking. Hopefully you have proper control joints in the concrete to mitigate shrinkage cracking occurring in "random" fashion.

 

[BigH]

I will throw a bit of wrench into the discussion - I can't remember where I read it but intermittent wetting and drying is not beneficial - it is like freezing and thawing - will try to find the source. Always keep it wet for at least a week - if fly ash or slag is used in the mix, you would want to extend curing for 10 days.

In Asia, they think sprinkling water on the concrete a few times a day is curing. It can get very hot here - nearly 35 deg C. Concrete is hot. Pour some water on a hot concrete surface and watch it evaporate within 5 to 10 minutes.

Good points about using the burlap and keeping wet - or the plastic sheeting. You can also build a bit of a sand dyke around the edges and flood the slab.

http://civilblog.org/2014/05/09/important-notes-to-remember-while-curing-concrete/

see point 4

http://www.nbmcw.com/articles/concr...of-concrete-for-durability-of-structures.html

http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/pccp/05038/008.cfm

in case the first link doesn't work, point 4 is as:

"Ensure uninterrupted curing. If it is discontinued for any reason, the reaction of the hydrdatio0n will be stopped permanently. The partial hydration makes the capillary pores discontinuous and water can't enter the concreste even if the curing is started again."

 

[dik]

Careful with the poly sheet... if it's in contact with the concrete, it can produce a 'mottled' colour to the concrete surface.

Dik