Comparative performance of chloride attenuating and corrosion inhibiting systems for reinforced concrete

This paper reports a laboratory-based study carried out to compare the performance of various proprietary concrete protection systems, designed to reduce chloride ingress and reinforcement corrosion. These include: controlled permeability formwork (CPF), a silane/siloxane hydrophobic surface treatment (S/S), an integral liquid waterproofing admixture (WP) and a corrosion-inhibiting chemical admixture (CI). Tests were carried out on a Portland cement (PC) concrete (40 N/mm² design strength) for chloride diffusion index (using a two-cell compartment accelerated test) and, under cyclic wetting and drying conditions, total chloride content at cover depth (25 mm) and corrosion of carbon steel in reinforced concrete specimens (using half-cell potential and corrosion current density (polarisation resistance) measurements). The results indicate that for all protection systems, resistance to chloride ingress was improved, with the greatest benefits noted for the S/S and CPF concretes. Corrosion levels occurring for these generally followed the ranking of chloride ingress rates. The CI was found to reduce the rate of chloride ingress and to give lowest corrosion current densities in relation to chloride contents. This system appeared to provide best overall performance. The practical implications of the results are considered in terms of equivalence of the systems to an increase in design strength or cover depth, i.e. parameters used for specifying concrete durability in standards, and the wider issues relating to their selection and use are reviewed.