Carbonation rate and reinforcing steel corrosion rate of OPC/FC3R/FA mortars under accelerated conditions

Carbonation kinetics of mortars of normal Portland cement partially substituted by spent fluidised bed catalytic cracking catalyst (FC3R) and fly ash were studied for accelerated test conditions. It has been noted that the main limiting factor for the penetration of carbonation front is the mortar porosity, and only if this porosity is high, would the mortar alkaline reserve play an important role on the carbonation process. For that reason, even for mortars with such a low alkaline reserve as those with total amount of cement substitution of 45%, the carbonation rate obtained has been very low when a low water/cementitious material ratio and a plasticiser were used. The corrosion rates of steels embedded in these mortars have been measured by the polarisation resistance technique. In the initial curing period it was observed that normal Portland cement–FC3R–fly ash mortars did not provoke a premature depassivation of steels. During the subsequent carbonation attack, it was observed that the combination of FC3R and fly ash in mortars resulted in corrosion rate levels slightly higher than those observed in non-substituted mortars.