ICFs and Cold Weather Concreting Series Part II
December 8th, 2009 | From the Field, Lets Get Technical! | cold weather concreting
For Part two of our Cold Weather Concrete for ICFs series there are some key areas that effect chemical reactions when concrete cures.
Heat of Hydration
Concrete generates heat as it hydrates through a chemical reaction of the cement reacting to the water. The heat generated is affected by the dimensions or mass of the concrete, the air temperature, the initial concrete temperature, the water-cement ratio, the cement composition, the amount of cement and admixtures. The heat of hydration sometimes generates enough heat to provide adequate curing in cold weather.
Concrete Mixture
Concrete mixtures may be adjusted in cold weather to accelerate the curing time by using one or a combination of 1) Type III Portland cement – high-early strength cement; 2) additional Portland cement of 100 to 200 pounds per cubic yard; 3) chemical accelerators such as a maximum of 2% by weight of calcium chloride and 4) air-entrained concrete to help the concrete absorb stresses due to ice formation.
Temperature of Concrete
The recommended temperature of the concrete as mixed and as placed should be not less than what is shown in the table below. Mixing concrete to temperatures higher than 70º F can have adverse effects of shrinkage and cracking.
In order to get the proper concrete mix temperature you are trying to achieve, the aggregate, cement and water temperatures must be known and accounted for.
The concrete should be placed into the forms before the concrete temperature drops below 55º F as indicated in the table above. That temperature should be maintained for the duration of the protection period indicated in the table below. This maintains durability against exposure to freezing and thawing.
For Thursday part III we’ll address how the insulation effects the temperature of the concrete and explain exactly why ICFs are ideal for cold weather applications.
