The effect of SCMs on the corrosion of rebar embedded in mortars subjected to an acetic acid attack

Agricultural effluents are transformed under bacteria effect into organic acids which constitute severe chemical and electrochemical attacks for the reinforced concrete of agricultural structures. Among supplementary cementing materials (SCMs), blast-furnace slag (GBFS) and metakaolin (MK) are classified chemically resistant to the aggressiveness of acidic media and especially organic acids. The objective of this research was to evaluate the effect of GBFS and MK on the corrosion performance of reinforced mortars. Here, electrochemical measurements allow determining the time needed to initiate the corrosion. Mortar cylinders were made with three cement types including ordinary Portland cement (OPC), GBFS and MK cements at a fixed water/cementitious material (w/cm) ratio of 0.65. Corrosion of rebars was simulated by subjecting cylinder specimens to cyclic loading with acetic acid solution (pH 4, 0.5 M) and drying. Concrete resistivity and reinforcing steel potentials were measured up to 429 days of age. At the end of the experiment, all specimens were saw cut split open, and visually inspected. It was found that the drop in the linear polarization resistance and corrosion potential curves reflect the time needed to initiate the corrosion. Blending the cement with 20% of MK is beneficial with regard to delaying the onset of the corrosion by a factor of more than two. However, using high percentage of GBFS (80%) decreases the time to initiate the corrosion for specimen subjected to acetic acid attack.