Engineering Corner


Maximum temperature limits for hot-weather concreting

Q. What are the ACI building code requirements for placing concrete in a tropical climate? Some people in our office say we should specify a maximum permissible concrete temperature of 90 ºF (32 ºC). Others say a temperature higher than 90 ºF (32 ºC) is allowable if the concrete contains a set-retarding admixture.

A. Either of these groups could be right if they could argue that their approach will provide the required strength or serviceability. Section 5.13 of ACI 318-02, “Building Code Requirements for Structural Concrete,” requires that:

“During hot weather, proper attention shall be given to ingredients, production methods, handling, placing, protection, and curing to prevent 'excessive concrete temperatures or water evaporation that could impair required strength or serviceability of the member or structure.”

Section R5.13 in the ACI 318 commentary cites recommendations for hot-weather concreting that are given in ACI 305R-91, “Hot-Weather Concreting.” That document states that:
"In the more general types of hot-weather construction (as defined in Section 1.2), it is impractical to recommend a maximum limiting ambient or concrete temperature because circumstances vary widely. A limit that would serve a specific case might be unsatisfactory in others. Accordingly, the committee can only point out the effects of higher temperatures in concrete as mentioned in Section 1.3 and 2.2.1, and advise that at some temperature between about 75 and 100 ºF (24 and 38 ºC) there is a limit that will be found to be most favorable for best results in each hot weather operation, and such a limit should be determined for the work."

ACI 305-99 contains similar recommendations regarding limits on maximum concrete temperature.

The Florida Department of Transportation's hot weather concreting requirements allow a maximum as-delivered concrete temperature of 100 ºF (38 ºC), and require the concrete producer to use specialized hot-weather mixture proportioning methods. This requirement has worked well for them.

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