Effects of cold weather on concrete compression strength test results

[79ron79]

Civil Folks,

I have run into a re-occuring problem of concrete samples not meeting the required 32MPA strength and was wondering what kind of effect collecting the samples for testing in cold weather (-20 - -35C) can have on the test results. Any input is appreciated.

Ron

 

[dik]

At cold temperatures, the formation of the cement gel is retarded and it may take considerably longer than 28 days to reach specified strength. Concrete is typically heated for a couple of days; this allows the concrete to achieve a strength of 8-10 MPa (usually). This is sufficient strength to prevent the gel from deteriorating due to freezing, but the strength gain is still retarded. In really cold climates, strength may not occur until the spring. It's approx -25C here outside... and in Winnipeg, we're used to cold weather concreting.

Dik

 

[Ron]

There is little or no relationship to the in-place concrete and lab cured concrete for cold weather conditions. As dik noted, actual strength gain is significantly retarded.

As for the laboratory, if the curing temperature dips (even slightly), strength results are affected adversely.

 

[dik]

Thanks, Ron... still -25C... supposed to warm up to -20C next week... I was doing a CMU wall review about 10 years back and the wall was unprotected... I used my pocket knife and had no difficulty embedding it in the plastic mortar joint... I told the general that the wall should be protected and that the mortar was still plastic... I was informed that the wall had been constructed the day before...

Dik

 

[ameyerrenke]

Test cylinders should be stored in insulated storage containers (even a cooler is better than nothing) on site until they are transported to the lab. The concretes own heat will help it with the initial cure but it should be taken back to the lab after the initial cure. Obviously precautions need to be taken for inplace concrete as well.

 

[oldestguy]

I've seen a few cases where some cylinders were stored adjacent to and covered with the pour. Purpose was to break them when the schedule called for using that hardened concrete. To me that would mean more than lab tests when a known strength was needed for the continued production work.

As to mortar, I used the rule that no freezing should be allowed in the first 24 hours to be acceptable work.