What I'm trying to find more information about, is: just how badly does the CaCl2 rust out the rebar? Is it just a crumbly rust pocket in 6 months or is it an accumulated-damage phenomenon over 50 years? Some of the reading I did suggests it is affected by moisture bathing the concrete (as in the case of a roadway or bridge)...in a garage slab with independent walls, it would seem to be mostly from underneath, hence a thick crushed rock layer and well-sealed vapor barrier to be directional pluses.
I don't understand if CaCl2 is instant doom for mesh or rebar, why is it still used all over? On one hand, the tradespeople placing and finishing the concrete, are going to call in the chloride every time because they don't want to be standing around all day for it to setup....
Also, per yard, what's the additional cost of the NCA (non-chloride accelerator)? Is it ~$10 per yard...or more...I don't have any handle on what the CaCl2 costs initially?
I can't offer too much direct experience to actual failures from CaCl on my own jobs relative to steel re-inforcement, as I've never tracked it. My assumption is that it takes years with little coverage to be an issue. CaCl produces much darker, and often "blotchy" finishes also, which is one of the reasons we limit it's use. Generally, we use a small dosage of CaCl, complimented by a varying degree of NCA. Just yesterday, we needed to pour a tiny sidewalk, and first warmed the ground well, requested the warmest concrete we could get with the dispatcher (74 degree concrete on-site), and used 1% CaCl with 1.5% NCA. Poured at 1 pm and covered with straw and blankets at 6 pm. 22 degrees and sunny at placement, 14 degrees and dark at covering. If I checked this morning, the concrete would probably be at 45-50 degrees under the straw.
As for costs, here's what the accelerators cost me approx:
CaCl : ~$3.00 per yard for 1% dosage, maximum allowable of 2%.
NCA : ~$6.50 per yard for 1% dosage, I've yet to hear a maximum allowable dosage, but have heard of contractors using up to 7% dosage for extreme cases.
TO complicate things, you generally need to use more NCA to equal setting times o CaCl, the general thought is 1.5% NCA is roughly equivalent to 1% CaCl in enitial set times. So, realistically, NCA would cost nearly $10.00 per yard to achieve similar results of $3.00 of CaCl.
Also, many finishers don't care for large amounts of NCA, as it has increasing effects on finishing of concrete (it get's much stickier the more you use), which I'm sure leads to many contractors swaying away from it as well......
