When to Use Hot Weather Concreting Methods

Leave it to the folks at the American Concrete Institute to provide a long detailed explanation of when you need to resort to hot weather concreting methods. But when you get to the end of that long detailed explanation, you probably still won't know the answer to the question of exactly what's hot. The Committee Report ACI 305R-99, Hot Weather Concreting, says that hot is "any combination of the following conditions that tends to impair the quality of freshly mixed or hardened concrete by accelerating the rate of moisture loss and rate of cement hydration, or otherwise causing detrimental results:

High ambient temperature
High concrete temperature
Low relative humidity
Wind speed
Solar radiation

So basically Committee 305 says that we should consider it hot whenever the heat might damage the concrete. Not very helpful. In most cases, figure that you should start thinking about hot weather techniques any time the air temperature is over about 85°, although even 80° with sun and a dry wind could be considered hot. For the concrete temperature, anything above 80° requires some extra precautions.

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