Frost resistance of concrete of various strengths under compressive loading

Abstract

1. In concrete without admixtures a constant compressive stress that does not exceed the fissure-formation limit R f 0 increases the frost resistance two times and more (for thawing in sea water). 2. When the stress increases above R f 0 , the frost resistance of the concrete decreases, and for values δ=0.4 to 0.6 Rpr (depending on the strength of the concrete) becomes smaller than the frost resistance of the non-loaded concrete. 3. The constant compressive stresses in constructions should be limited to the value δ=0.4 to 0.6 Rpr for which the frost resistance does not appear to be lower than the standard, since for higher load levels an increase in the microdestructions of the concrete immediately after the loading is taking place, and this process is accelerated under the action of repeated cycles of freezing and thawing. 4. In very important construction exposed to repeated cycles of freezing and thawing the compressive stresses should not exceed the limit R f 0 . An increase of the stresses is admissible in the initial period provided that a thermal protection system is installed during the first winter. 5. The supplementary stresses which are induced in the concrete during freezing by the difference between the thermal expansion coefficients of the concrete and the reinforcing steel must be taken into account when the values of the compressive stresses are determined. 6. The concrete with air-entraining admixtures has an increased frost resistance in all cases, including when it is under compressive stress, and this permits of accepting higher levels of compressive stresses in structures made of this type of concrete than in those made of concrete without admixtures.