Pouring Concrete when temp is 25 F

[WWTEng]

I have not dealt with cold weather concreting too often. Now I have a situation that the contractor want to start pouring early tomorrow (slab on grade) when the temp is supposed to be around 25 F, but then it is supposed to raise up to mid 40s. The next two days look good with low forecasted at 37 and highs in the 50s.

So my question is, other then following the typical guidelines for cold weather concerting (ground not froze, no snow on ground, aggregates and water being heated, using a non-chloride accelerator), should I be concerned about any other issues. The contractor has obviously dealt with similar situation many times in the past so he is experienced with cold weather concreting. Also, is there a minimum temperature below which they should not pour concrete?

 

[WWTEng]

It appears that 55 F is the recommended temperature of placement. For how long should the contractor maintain this temperature? I read 3 days somewhere.

 

[concretemasonry]

I think the basic philosophy of gear everything to the air temperature is a real joke. The subgrade, base and site materials have significant mass and thermal storage/inertia that totally over whelm the fact whether there is a cloud in front of the sun early in the morning.

Follow the guidelines for the condition of the base and the temperatures of the mixed materials. Heated aggregates a somewhat uncommon in most areas and are usually not too warm. Mixing water can be very efficient to trigger the cement heating and generation of the heat of hydration that should be contained, but limited but can easily be reduced in real cold weather, by just removing any insulation. Protection of the finished concrete economical and is critical for it to obtain the strength expected.

I have been on projects where large pours were done at -30F without a problem because of preparation, logistics and control of materials and whatever protection that was required later.

Dick


Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Ron]

Simple answer...don't do it.

 

[MiketheEngineer]

Another simple answer - how important is it?? Is it a driveway or the foundation of a 100 story building???

And keep it covered - you can even use "warm" water spray to maintain temp.

 

[concretemasonry]

Insulated blankets are the most flexible and efficient way for any flat surface. Base protection prior to any pouring, and flat or reasonable level concrete surface or even the hang over walls. They also do a reasonable job of retaining moisture for curing. A foot of snow on them even helps more.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[WWTEng]

Ron,

considering the temps are to drop even further in the coming months, if we don't do it now, we'll have to wait till spring to pour concrete.

Mike,

Its a SOG for a church. The slab will eventually be covered with tiles and carpeting. And yes, they now that they have to keep it covered. I told them that 55 F is placing temp they have to maintain and they have to keep this temp for 3 days after the pour.

 

[WWTEng]

Concretemsry,

The contractor is expereinced in cold weather concreting, the mix design seemed to be geared up for the conditions. Also, the air temp this morning at pour time is 30 F and is supposed to warm up to at least high 40s later today. 50s high over the weekend.

 

[Lemony]

Per ACI 318-08 Chapter 5, temp to be maintained at >50 F for seven days unless high early strength concrete, then >50 F for three days.

 

[PEinc]

"Per ACI 318-08 Chapter 5, temp to be maintained at >50 F for seven days unless high early strength concrete, then >50 F for three days."

Please distinguish between the temperature of the air and the temperature of the concrete during placement and while curing.

http://www.PeirceEngineering.com

 

[ztengguy]

Ive seen the slabs poured over heat tubes, and then blankets on top, this was upstate new york, and slabs came out great.

Make sure the subgrade isnt frozen before, then just follow guidelines.

 

[cvg]

get yourself a concrete maturity meter and a supply of thermocouples and then bone up on ACI 306.

intelliRock II™ - Concrete Maturity, Temperature, and Moisture Measurement System
The unit is about $3,000 and the probes are $55 each. They get embedded in the concrete, so they are one use only. You can get temperature only or maturity probes. Recommend several probes in the concrete and at least one for surface air measurement

http://www.engius.com/web/products/intellirock.asp