Comparison of chloride-induced corrosion between alkali-activated slag concretes and Portland cement concretes

It is reported that the diffusion of chlorides in Alkali-activated slag (AAS) concretes is lower than that in Portland cement (PC) counterparts and is comparable to concretes containing high volumes of supplementary cementitious materials. This is considered to be due to its dense calcium silicate hydrate structure and relatively better chloride binding capacity due to its high alumina content. However, a critical review of the literature indicated that both the resistance to chloride ingress and chloride-induced corrosion of steel in AAS concretes are not found uniformly in all publications. Further, less is known about the effect of mix proportions, including binder content, water-binder ratio, role of activator, etc. on the rate of chloride transport through AAS concretes. As a consequence, there is conflicting information on the ability of AAS concretes to delay both the onset and the rate of corrosion of embedded steel in such concretes. Therefore, a thorough investigation was carried out focusing on their permeation properties and the corrosion behaviour in them. The results obtained from this research has illustrated that AAS concretes could achieve lower non-steady state diffusion coefficient and higher degree of chloride binding, resulting in improved corrosion resistance. However, there is a need to optimise mix proportions as there was a significant influence and interaction between both Na2O % and Ms of water glass used as activator for the AAS binder