Effect of calcium chloride on the durability of pre-tensioned wire in prestressed concrete

Abstract

Summary This paper gives in the first place an account of investigations which were made to determine the extent to which calcium chloride may be present in the free state in concrete at various temperatures, since this will have a bearing on the extent of corrosion of embedded steel. It has been concluded that while there is a tendency for a large proportion of the added calcium chloride to react with the hydrating cement at normal temperatures, the residual small amount of free chloride always retained in solution will give an appreciable chloride concentration in solution and will cause a certain amount of corrosion of embedded steel. The amount of free chloride in solution is influenced by the composition of the cement, and will increase with an increase in the amount of calcium chloride added and with increasing temperature. These conclusions offer a reasonable interpretation of some of the findings of the second part of the paper which covers a direct study of corrosion of high-tensile steel embedded in different concretes containing calcium chloride. The present results indicate that with good concrete practice in mix design, depth of cover, and specification of materials, the additional corrosion induced by the use of flake calcium chloride up to about 2 % by weight of the cement in dense normally cured ordinary Portland cement concrete will have no structural significance. However, corrosion is greater under other conditions, and it appears that the degree of corrosion obtained in the presence of calcium chloride will depend on a number of factors, such as the quality of the concrete and adequacy of the casting procedures, the composition of the cement, the amount of calcium chloride added, the conditions of curing and storage of the concrete, and the diameter and initial surface condition of the steel wires.