Calcium Chloride

[cwigg66]

I am in the process of pouring a containment area in Mississippi. The slab (60'x70') is to be poured this week, with temperatures hovering around freezing at night and daytime highs around 45 degrees. My contractor would like to add 2% calcium chloride to the mixture. This slab cannot have construction joints, only contraction joints every 12 feet or so, and a fear that shrinkage cracking will be an issue with the calcium chloride. The slab is reinforced with uncoated rebar (#5). Will the calcium chloride create a corrosion problem in the steel, and if so, what should I substitute instead of the calcium chloride to allow cold weather placement. Thanks all.

C

 

[skiitswitch]

Your supplier should use an NCA (Non-chloride Containing Admixture) instead of simple Calcium chloride due to the corrosion potential with your uncoated #5 bar embedded in the slab. Technically, by following ACI recommendations for embedment depth and assuming that the deck will not be susceptible to the addition of chlorides in service, it would most likely be fine even with CaCl2... but, you never can be too cautious I guess. Bascially everything prior to 1975 or so and placed in the winter was placed with 2 to 3% CaCl2 in it and most of those are still standing...

 

[civilperson]

No chlorides in reinforced concrete.

 

[haynewp]

I always heard don't use chlorides in reinforced concrete but was told that ACI 318 has acceptable amounts based on table 4.4.1.

 

[civilperson]

The maximum percentage in the table for dry, protected from moisture,(not a slab on grade), is one. Again, not necessary or advisable for placing concrete in above freezing temperatures.

 

[DRC1]

If the slab is covered with insulated curing blankets, it should be okay. Lower temperatures require heat. ACI 304 I believe covers cold weather concrete. If temperatues have been below freezing the rebar should be warmed prior to pouring.