Curing fresh concrete in cold weather conditions

[sapperDAK]

Your comments are solicited regarding a 12' x 3' x 3' mass concrete element placed within forms in an over-sized excavation 16' x 6' x 6' which filled with groundwater (placement in wetlands near sea level) after placement and then the groundwater froze with overnight temp of 26 degree F. The next morning the element was encased to the top of concrete within a chunk of ice and near-freezing water. Clearly this does not meet the spirit of ACI 306.1 requirements for curing concrete in cold weather conditions. But realistically, what negative impact will this "out-of-spec" curing temperature have on the strength and durability of the element? No additional water was mixed with the concrete as placed so the w/c ratio was not really affected. Does your answer depend upon the type of element (footing, beam, anchor, etc...) and/or the loading? Curious to hear your responses, thanks!

 

[darthsoilsguy2]

the key to concrete freezing is whether initial set occurred. apart from nobody knowing what your application is..... the concrete could be evaluated against some better controlled elements with surface hardness testing techniques like windsor probes or swiss hammer. in combination of good thorough inspection for cracks

 

[sapperDAK]

the element is an anchor for a guyed tower that will ultimately be 2 feet below grade! yep, the key is did any of the concrete freeze before initial set!?!

 

[cvg]

you need to keep the temperature above freezing top and bottom for the entire curing period, not just initial set. and in cold weather, the strength gain will be much slower, so instead of 7 days it might take double that.

 

[darthsoilsguy2]

to clarify... my comment assumes people are doing the right thing after they encountered the problem and just wanted to know how to tell if the game is already lost. the surface should be the hardest hit, if you can establish that the most susceptible is good. if you do have any weak spots, there is always coring... but i would look at surface testing first.

 

[BigH]

Certainly you knew that freezing temperatures were on the way so why did you place the concrete without taking suitable measures? Just playing with quality, eh? Quality is a poor cousin to schedule.

 

[sapperDAK]

Thanks to all for your comments, perspectives, interpretations, etc... I was really just hoping to get what I got - some thoughts from industry colleagues. To clarify from my end though... "I" am not the contractor/sub-contractor who scheduled and placed the concrete during cold weather conditions and then did not take appropriate protection measures. Nor am I the owner or his design engineer who is obviously concerned with ultimate performance of this element. I am an independent inspection agency whose scope of work was to perform foundation inspection, to monitor and test the fresh placed concrete, and to cast and test compressive strength specimens. Failure to adhere to ACI 306.1 has been documented in our reports. Thanks again!

 

[dicksewerrat]

Did you get temps of the concrete as when installed? What was the time lapse from placement a sub freezing? Water temp when concrete placed and what did the air water temp do? Do a test with the mix and a freezer and refrigerator to mimic conditions in the field. Monitor the heat gain in the mix over time.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Ron]

If I understand the post placement conditions, the area around the concrete was flooded and only a cake of ice developed on the water surface while below the ice the water was near freezing but did not freeze. If I understand that correctly, then the detriment to the concrete is likely only delayed strength gain. If the concrete surface did not freeze, then you dodged a bullet!