Curing Time in Winter

[PT999]

I am looking at a foundation wall, about to be poured in winter weather. What percentage of concrete strength is considered adequate, to continue on with the work and add some additional dead load.

 

[dicksewerrat]

70%. It will take more than the 7 days suggested. Make extra test cylinder and break them at 6, 7, 8 and 9 days. Cure them onsite, not in the lab. Protect the concrete from frost until it gains at least 750 psi comp. strength.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Rjeffery]

and the field cured cylinders should (read must) be treated to the same conditions as the concrete they are to represent. If the footing is blanketed then the cylinders should be set on top of the footing and blanketed as well.

 

[archeng59]

this response might be too late for you. what are the expected ambient temperatures during the curing phase? If the temps are expected to be less than 40 degrees, I always request that the concrete be covered with blankets for the first 7 days. After that, the forms and blankets can be removed. It's been my experience that the concrete cures well and there are no problems continuing with construction when the blankets are used.

 

[PT999]

Thanks for your replies. Not too late, work scheduled for tommorrow Dec 15. Project is in New York area. Todays temp is about 20 degrees F now, and maybe 30 deg at noon

Contractor naturally wants to pull blankets and forms after 3 days. While I would like 7 days, the cylinders will stay out there and have to pass. If they fail, I will have them take cores to verify. My thinking on this is that the main concern is initial concrete failure in the first few days.
After that, the concrete can take all the times it needs to reach strength. And better weather is forecast for next week.

(Even getting them to use blankets caused a rucus. One sub was fired for refusing to use blankets, and came back to pull 80% of his in-place rebar out. Police were needed to stop the mayhem - I missed it)


On another project, specs call for 4500 psi and results now after 30 days are 3000 psi. Concrete supplier has pulled his computer tickets for the loads, and sees nothing wrong.

Any thoughts. GC plans to core every week to see if strength improves with time. This work was poured a month ago or so when weather was fine. Flyash was used in the mix. What are the pluses and minus's of flyash

 

[archeng59]

take a look at ACI 306 Cold Weather Concreting, especially section 5.3. perhaps you can work with that and compromise with the contractor on how long to protect the concrete.

 

[henri2]

PT999, I would not have specified fly ash if you are shooting for early strength in cold weather. Besides the fly ash may cause a reduction in the level of air-entrainment desired.

Why was the fly ash specified and what class is it?

For cold weather concreting, increasing cement content and use of a non-chloride water-reducing and accelerating admixture (ASTM Type E) is not a bad idea ...if you want early strength.

 

[dicksewerrat]

Tell the contractor he does NOT have a choice in protecting the concrete for 7 days. And then he can pull the blankets if the tests are good.
Do not use fly ash in cold weather. It does not give you any heat from the hydration reactions. But use it to keep the concrete cooler in July-Aug.
What are you going to do about the project with the low test concrete?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[PT999]

On the low test concrete, GC will be core testing every week or so, to see if results improve. Meanwhile all work is stopped.

 

[Dumitrescu]

Dear All,

According to our code of practice, you may also use heaters, that does not exclude blankets, but there are mainly 2 ways to deal this problem:
1. preserving the hydration heat;
2. heating the element.

I personaly use the both, but, be carefull for the possible cracks that might appear. DO NOT EXCEED A DIFFERENCE OF 40 degrees between the heated element and the environment.

Good luck!

Catalin Dumitrescu,

Bellinghausen Beton SRL
Romania

 

[dicksewerrat]

And if you heat, use heaters with vented combustion chambers. Concrete doesn't like combustion gases

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com