Specification for pouring 36" Thick Footings & Heat Of Hydration 2

[BSVBD]

Footing size 18' x 18' x 36" thick. 36 yards of concrete. 4 Trucks.

What special concerns or limitations should be considered when pouring a 36" thick concrete footing when considering heat of hydration?

Fly ash? Pozzolan?

Since I do not want the liability of concrete composition, do I simply specify that the concrete supplier furnish the correct concrete mix to prevent excessive heat of hydration for a 36" thick concrete footing or for any applicable element contained within the bid documents?

Is 36" not thick enough to have a heat of hydration concern?

Please advise.

Thank you.

 

[dik]

36" is the lower end for mass concrete. If concerned, use thermocouples to get temperature differential and I've used insulation to keep heat loss to a minimum for a bit. The mix runs a little hotter, but the thermal difference is minimised. On one dam project I was involved with they used chopped ice in the concrete mix. Use minimum slump and lowest strength needed.

Dik

 

[hokie66]

I've never worried so much about a footing of that size. But if it is in a hot climate, the normal precautions for hot weather concreting should be followed, including limiting the temperature of the fresh concrete when placed. As dik indicated, that can be done by using ice as part of the mixing water.

 

[phamENG]

Structure Magazine had a decent primer on mass concrete last spring. Worth the read and points in a few good directions.

 

[r13]

Consider to use cement with low heat hydration property - Portland Cement Type II (MH) and/or Type IV. The trade off is the slower development of concrete strength in early stage.

 

[phamENG]

Good call, retired. I've spec'd Type IV (Low Heat of Hydration) for some really thick caps on piers and mooring dolphins, especially when being placed in the summer.

 

[dik]

phamENG... good paper, thanks.

Dik

 

[StructEngBrah]

You could specify a maximum internal temperature and a maximum temperature differential for mass concrete elements. You could also require the contractor to submit a thermal control plan if you are really concerned. This provides the contractor some flexibility with the actual concrete mix, but you are still limiting the potential for thermal related issues.

 

[AskTooMuch]

3' does not seem thick enough. I'd put ice or if the batch plant has it use liquid nitrogen.

 

[STrctPono]

3 ft is not a depth that strikes me as having a concern for a high heat of hydration. 5 ft then I would probably run something in Concrete Works. Some finite element analysis software packages have heat of hydration modules built into the program these days.

If heat was a concern.... StructEngBrah is correct. The way we deal with it is providing a mass concrete spec on the job. This basically requires just in time training, pre-testing of the mix, a thermal control plan including how to monitor and control the temperature of the concrete, and curing. The ready mix company has many options for how they want to deal with it and since they are the experts I would not suggest you require them to use a certain type of cement of additions of supplementary cementitious materials. Let them come up with the mix, test it, and submit the plan to you. Your spec should also reference ACI 207.1R.