accelerating admixtures in conc S.O.G.

[bjb]

Does anyone have any experience with allowing the use of a non-chloride accelerating admixture in a slab-on-grade? I have an exposed exterior slab that will be poured during cod weather conditions. The slab is 8" thick, and is jointed into roughly 16'X16' panels. The problem that I have is that the accelerator will cause the elastic modulus to achieve higher values ealier in the life of the concrete, just at the time when it is desireable to have a low elastic modulus when the concrete is experiencing drying shrinkage. I see an increased potential for random cracking in what will be a slab exposed to view. Also, it is my undersatanding of ACI 306 that accelerating admixtures are not a substitute for maintaining proper temperature control.

If anyone has experience with this (good or bad) I would appreciate hearing about it. Thanks.

 

[hannis]

bjb,

My own experience in the UK is not to use accelerators unless there is a programme need or a structural reason to attain early strength either way they are not a good means of controlling the rate of hydration. Having a good curing regime(often ignored by engineers and contractors) is the best method of ensuring a crack free slab. If your concerned that the hydration temp will drop off to quickly in cold conditions then raise the temp of the water and specify an aggregate with a low thermal coefficient like Limestone. Depending on the likely drop in temperature you may also need to increase the amount of thermal reinforcement.

Hannis