Loss of freeze–thaw durability of concrete containing accelerating admixtures

Abstract

Rapid freeze–thaw durability tests on air entrained concrete mixes containing a proprietary nonchloride accelerating admixture or CaCl2 show that although early age compressive strength acceleration is achieved, the freeze-thaw durability is reduced when compared with the durability of control concretes of similar mix proportions, but without accelerating admixtures. Although the compressive strength gains were accelerated in mixes containing either the proprietary accelerating admixture or CaCl2, the tensile strengths at 28 days were similar for mixes with and without the admixtures.Petrographic analyses showed air contents and air void spacing factors in concretes with accelerating admixtures, either nonchloride or CaCl2, to be similar to the air systems in the control concrete, though more air entraining agent was required with the mixes containing accelerating admixtures. Local aggregates as well as aggregates from three alternate sources were used. Test results did not show any significant differences in durability on the basis of aggregate source.As the larger reduction measured in freeze–thaw durability for concrete mixes containing either chloride or nonchloride accelerating admixtures could not be attributed to either a deficient air void system in the cured concrete or inferior aggregate, it is believed that the cause is some characteristic or a hydration product in the cement paste microstructure produced by accelerated hydration. Key words: concrete, durability, freeze–thaw testing, strength acceleration, admixtures, air void system.