FREEZING AND THAWING RESISTANCE OF CONCRETES WITH SHRINKAGE REDUCING ADMIXTURES

摘要

Repeated exposure to freezing and thawing conditions can result in a significant decrease in concrete performance. The use of entrained air, lower water-to-cementitious ratios (w/cm) and increased strength are recommended to improve resistance to freezing and thawing damage. These design modifications often lead to increases in shrinkage, especially in those applications where the w/cm is lowered to improve durability against chloride ingress or to have high strength concretes. The shrinkage often results in cracking which is detrimental to the durability of the concrete as it can lead to corrosion of embedded reinforcement, chemical attack or damage from ice freezing in the cracks. Shrinkage reducing admixtures (SRA's) are effective in reducing shrinkage induced cracking. However, in many cases when SRA's are used, it is difficult to develop an air-void system that will provide good freezing and thawing resistance. This paper provides guidance on how to develop acceptable air-void systems and documents the improved performance in ASTM C 666, Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing, Method A, in which the freezing and thawing occur in water.