Cold weather concrete strength 4

[Stumpjumpper8]

Years ago I saw a study that showed the correlation between air temperature and the time it takes fresh concrete to reach various compression strengths. Does anybody know where I can find something similar?

 

[msucog]

probably aci306 (cold weather concrete) fig 6.6.1 (you might search for "Kleiger 1958" if you don't have that aci since it appears to be referenced to Kleiger). here's the name of that reference: "effect of mixing and curing temperature on concrete strength"

 

[concretemasonry]

The real factor is the temperature of the concrete itself as it cures and not the air temperature. Air temperature, air movement and humidity all can effect the heat loss of the concrete, which may reduce the concrete temperature.

Depending on the conditions, the 28 day strength of the actual in place concrete can be above or below the 28 day lab strengths. - Possibly below, but it can also be higher depending on the raw materials, cement type and conditions.

 

[msucog]

as far as strengths, cold weather will slow the first part of curing which quite often effects backfilling a wall since it's still green sort of thing. at 28 days, i'm guessing it will likely be close (perhaps slightly to the low side of normal) unless you're down near the freezing temps. if you are trying to hurry up and backfill a wall, i'd wait longer than you normally would in warm weather (especially for a slag type mix). and yes, keep in might cylinder strength is not the same as field strength. if you actually follow cold weather guideline procedures, the strengths shouldn't be too bad even with cold weather.

 

[concretemasonry]

msucog hit it right - the strength depends on the conditions thta effect the concrete temperature and moisture. If you are stripping forms/removing support or backfilling find out what the actual concrete strength is before proceeding.

If you are concerned about durability, that is a much more complex problem and most likely will already have been established by the conditions the concrete was exposed to before you have any opportunity to do any thing about it. Concrete can be allowed to continue curing, but loss of durability cannot be restored if it is lost.

 

[BigH]

If you want to see the graphs, etc., check out Neville's tome on Properties of Hardened Concrete (I believe that's the "offical" title"

 

[strguy11]

On a related note, I had a contractor call me today saying that the concrete they were pouring set up within 30 min, and did not allow for them to install dowel rods and anchor bolts for columns. They were complaining about the concrete specs, specifically the w/c ratio, which was 0.4.

The mix design they provided had 564# cement, 262# water, and they added accelerator due to cold weather. Slump of 4 was specified

My first thought was that the concrete took too long to get to the site, or they added too much accelerator, but I find it hard to believe that if they sampled the slump on site and got 4", that it would have set up in 30 min. any thoughts?? I dont think that the w/c ratio is an issue, since higher strength concrete is typically limited to this ratio, and also that ACI recommends lower wc ratios for cold weather.

 

[hokie66]

You should be complaining that they had not set the dowels and anchor bolts before casting the concrete. And you are correct, the early set has something to do with how the concrete was handled, and maybe the accelerator, rather than the w/c ratio.

 

[strguy11]

hokie-

Yes, we already had a discussion about setting the dowels and anchor rods prior to the concrete.

Regarding the accelerator, is this typically added at the plant, or on site? Personally I think they added too much, and did not account for the travel time. Can they add it on site?

 

[hokie66]

I will leave the comment about when you can add accelerator to others, as I have never permitted its use on a job.

 

[msucog]

contractor's problem(s)....not w/c ratio.