Temperature Control

Concrete producers and quality control inspectors keep a close eye on temperature during the heat of summer. When cement molecules and water molecules mix in concrete, hydration occurs. Hydration is an exothermic chemical reaction that emits additional heat into the concrete mixture in the heat of summer. Since all of the mix ingredients are naturally warmer when its warmer outside, the additional heat of hydration can result in a concrete mix that hardens before tiny cement molecules hydrate to their fullest extent. The hot concrete will set faster and gain initial strength more quickly, but the desired long-term strength and durability of the concrete may be compromised due to insufficient hydration of the cement.

Mass concrete projects present even greater concerns when internal and external concrete placement temperature differentials are too high. The additional heat of hydration raises temperature in the center of the mass much higher than the concrete temperature near the formwork. This often leads to detrimental thermal cracking that can compromise the structure. It’s crucial that concrete producers adhere to guidelines set forth by the American Concrete Institute to produce quality concrete.

The American Concrete Institute defines Mass Concrete in AC116R as:  “Any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change to minimize cracking.” And ACI301 states, “the maximum temperature in mass concrete after placement shall not exceed 160 °F (70 °C); and the maximum temperature difference between center and surface of placement shall not exceed 35 °F (19 °C).”

The most effective way to meet concrete placement temperature requirements during hot weather is to pre-cool the mix constituents prior to mixing. Concrete only consists of four primary ingredients: cement, sand, stone and water. Water is always the easiest, cheapest and most effective place to start cooling concrete even though it contributes the smallest volume to the concrete mix. When the cooling requires more than an 8-10°F temperature drop, other methods such as aggregate cooling or ice should be used in small doses to supplement the cooling process at a much lower expense.  

Concrete batched with 35°F water results in an 8-10°F temperature drop costing less than $00.20 per cubic yard on average.  

                         35°F Batchwater = $2.00 per 10 cubic yards  

The same temperature drop using ice typically requires 40-50lbs of ice per cubic yard at an average cost of $00.20 per pound. 

                          ICE = $50 - $100 per 10 cubic yards