Effect of surface coatings in the corrosion of reinforced concrete in acid environments

This study involves the protective effect of organic coatings used on reinforced concrete in an acid environment similar to those existing in certain metallurgic processes, in which the concrete degradation and the steel corrosion cause significant costs to the metal production. A 0.50 w/c concrete was prepared and then characterized through physical and mechanical tests such as electrical resistance, capillary absorption, total absorption, total porosity, chloride permeability, and tensile and compressive strength. The uncoated, acrylic, and epoxy coated concrete cylinders were exposed to an artificial acidic solution for 589 days. The corrosion of the steel reinforcement was evaluated by means of corrosion potential and polarization resistance. The morphology of the corrosive attack was observed using scanning electron microscopy (SEM) and the composition of the corrosion products was determined using an X-ray diffractometer (XRD). The deterioration of the concrete and its level of contamination were evaluated by measuring the concentration profiles of chloride, acidity and sulfate. The results show that the reinforcing steel reached an active state in the uncoated concrete and in the acrylic coated concrete, whereas it remained in a passive state in the epoxy coated concrete. Under the conditions established in this study and based on chemical analyses and on the electrochemical tests, it was determined that the coating which performed better as a barrier in an acidic medium was the epoxy coating.