Effect of curing temperature on corrosion of steel bars embedded in calcium aluminate mortars exposed to chloride solutions

Abstract

Important corrosion problems have been detected in reinforced concretes made of calcium aluminate cement (CAC). However, very little research has been performed to evaluate the incidence of the use of such cement on the corrosion process. Reinforced mortar specimens, pre-mixed with or without 4% NaCl of weight of cement, cured at 20° C, 40° C and 60° C for two weeks and immersed in either a 0.5 M or a 1.5 M NaCl solution, or kept in plastic bags for 255 days, have been monitored electrochemically. Corrosion potential, corrosion intensity and ohmic drop were recorded over time. The appearance with time of chloroaluminates has been monitored by X-ray diffraction, and its microstructure has been observed by means of back-scattering electron (BSE) microscopy. The reaction of chloroaluminates formation in reinforced concrete deals with the process of immobilising chloride ions which penetrate through the concrete up to the reinforcement. Therefore, the enhancement of such a reaction would be a way to reduce chloride ions in the pore solution contained in the concrete pores. Furthermore, stable chloroaluminates formation could mean a decrease in the risk of corrosion. Thus, corrosion rate measurements were carried out throughout the testing period to evaluate this point. Aluminous hydrates showed a high capacity to react with chloride ions to form chloroaluminates; however, the remaining chloride ions in the pore solution were still in an amount enough to promote reinforcement corrosion over time. Corrosion rate was found to be directly influenced by the curing temperature and, therefore, by the degree of conversion from hexagonal to cubic phases.