Frost and Freeze/Thaw resistant Concrete

Frost and Freeze/Thaw resistant Concrete

Frost and freeze/thaw resistant concrete must always be used when concrete surfaces are exposed to weather (wet) and the surface temperature can fall below freezing.

·     Fair-faced concrete façades

·     Bridge structures

·     Tunnel portal areas

·     Traffic areas

·     Retaining walls

By adding air entrainers, small, spherical, closed air voids are generated during the mixing process in the ultra-fine mortar area (cement, finest grain, water) of the concrete. The aim is to ensure that the hardened concrete is frost and freeze/thaw resistant (by creating room for expansion o any water during freezing conditions).

·     Type, size and distribution of air voids

Air voids contained in a standard concrete are generally too large (>0.3mm) to increase the frost and freeze/thaw resistance. Effective air voids are introduced through special air entrainers. The air voids are generated physically during the mixing period. To develop their full effect, they must not be too far from each other. The “effective spacing” is defined by the so-called spacing factor SF.

·     Production/mixing time

To ensure high frost and freeze/thaw resistance, the wet mixing time must be longer than for a standard concrete and continue after the air entrainer is added. Increasing the mixing time from 60 to 90 seconds improves the content of the air voids by up to 100%.

·     Quantity of air voids required

To obtain high frost resistance, the cement matrix must contain about 15% of suitable air voids. Long experience confirms that there are enough effective air voids in a concrete if the results of the test (air pot) show the following air contents:

-       Concrete with 32 mm maximum particle size 3% to 5%

-       Concrete with 16 mm maximum particle size 4% to 6%

Fresh concrete with an air void content of 7% or over should only be installed after detailed investigation and testing.