Corrosion resistance of BS 8500 compliant concretes

Corrosion of steel reinforcement in concrete, due to the ingress of chloride ions, is the most significant form of concrete deterioration. Fresh concrete however, provides a highly alkaline environment which facilitates a protective passive oxide layer around the steel reinforcement. Modern engineering standards provide guidance to designers on the specification of concrete mixes to meet a prescribed design life. More than one cement blend may however be available to meet the specific design life for a particular exposure classification, which can occasionally lead to confusion. This work investigated the corrosion resistance of BS 8500 compliant cement combinations for a XS3 environmental exposure in order to identify relative durability performance differences. The concretes investigated contained Portland cement (PC), Fly Ash (FA) and Ground Granulated Blastfurnace Slag (GGBS). FA and GGBS were blended in binary combinations with the PC, at levels of 28% and 51% respectively. Two water/cement (w/c) ratios of 0.35 and 0.40 were investigated, together with total cementitious contents of 380kg/m3, representing typical structural reinforced concrete. Specimens were cyclically exposed to a saline solution and tested for compressive strength, electrochemical potential, resistivity, and chloride ion content with depth.