High performance concrete freezing resistance

As it results from the experiences accpiired in Canada and related to the concrete stmctures, the best high performance concrete resistance to freezing and thawing, in the case of air entrainment, is achieved at air content from 4 to 6% and spacing factor from 200 to 350 pm [1]. The non air-entrained concrete contains from 1.5 to 2.5% entrapped air [1]. Simultaneously, the 5% strength decrease corresponds to 1 % air content increase, it means the same relation as in ordinary concrete [1]. Therefore some additional amount of cement should be added to the mixture. On the other hand, air entrainment has a positive impact on woikability. 

The superior resistance to a vari ety of degrad i ng effects was reported by Bonneau etal. [59] for RPC freeze-thaw-durability factor equal or greater than 1 scaling-cumulative mass of scaling residue less than 0.03 kg/m (compared with a maximum of 0.80 kg/m allowed in the standards) chloride permeability (ASTM Cl 202) - less than 10 Coulomb (from a practical point of view this is impermeable concrete a range of 500-1000 Coulomb is considered as high performance concrete). The permeability under load conditions, in which cracks are induced, was evaluated by Charron et ai [60] showing that at strains of up to 0.13% the permeability was as low as that of the matrix. This is an indication of the durability potential of such composites under load. 

Mixes in both low- and high-cement-content classes are more prone to problems than the medium range. In low-cement-content mixes, poor cohesion results in segregation and in high-cement-content mixes thixotropy causes pipeline friction. Admixtures will modify the flow characteristics of the paste, helping to achieve and maintain optimum flow characteristics. Because pumped concrete must not only meet specified job performance criteria (e. g. strength, freeze-thaw resistance) but should also remain stable under a variety of job conditions, particularly in hot and cold weather, it is common to find that concrete to be pumped often contains two or more types of admixtures. 

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