It is officially winter and it came early this year. For me, winter officially starts when I receive that first customer complaint of the season about set retardation. “Your product is causing my concrete to be retarded!” they say.
Insert politically incorrect response here about who or what might be retarded.
Okay, I don’t actually say politically incorrect things like that – but that’s often what I’m thinking. Strangely enough, these customers have used our product all summer long and not experienced any set retardation at all. Then a little cold weather comes along and suddenly “our product” is causing an unacceptable set delay. Worse still, I sometimes find myself reminding the customer that we already had this very same conversation – about a year ago.
Actually, a little bit of set delay is good for concrete. With lower heat of hydration and longer hydration times you will generally find that you get better, stronger concrete. Of course you must usually adjust your finishing and/or form stripping schedule to compensate. The real problems start when the temperature falls very low. Not only can setting times can become extreme, but if the concrete is allowed to freeze then it will ultimately lose about 50% of its final strength.
There are many factors that can contribute to set delay. Many common admixtures have a set retarding effect to some degree. The use of fly ash, slag and other supplementary cementing materials will slow hydration times. Even the addition of extra water will extend your setting time. But by far the biggest factor is temperature. For every drop in temperature of 10 C (20oF), you can expect your concrete’s setting time to double. Even readers who work in hot climates should note that the preceding list of factors applies to you too..
The American Concrete Institute (ACI) publishes a document titled ACI 306R – Cold Weather Concreting. This comprehensive document is an excellent guide to successfully completing concrete work in cold temperatures. The National Ready Mixed Concrete Association (NRMCA)publishes their own cold weather document titled CIP 27 – Cold Weather Concreting. While many might find that they can’t be bothered to read the ACI document, the NRMCA document is an absolute must read – especially since it is just 2 pages long, it’s free and it hits all the really important points you need to be aware of when placing concrete in cold weather.
It comes down to simply being aware of cold conditions and planning adequately in order to deal with them. Thanks for reading and please feel free to post any comments, tips or additional references.