This paper presents an investigation into the extent and reasons of the observed improvement in performance that ground granulated blast furnace slag (GGBFS) contributes against chloride initiated corrosion. Tests conducted on concretes with blended cement included Rapid Chloride Permeability Test (RCPT), long term ponding, corrosion current monitoring, pore size distribution and X-ray diffraction analyses. Values of the RCPT and corrosion current were significantly reduced as the proportion of GGBFS increased. The results showed only small refinements in pore size distribution, as well as indications of the formation of Friedel’s salt. The tests however, revealed the formation of hydrotalcite as a significant hydration product in GGBFS blends. The results further demonstrated the efficiency of hydrotalcite in binding chloride ions. The authors attribute the reduction in corrosion current to the efficient binding of chloride ions by the hydrotalcite that forms in GGBFS hydration products.