Effects of Mineral Admixtures on Macrocell Corrosion Behaviors of Steel Bars in Chloride-Contaminated Concrete

Based on the macrocell corrosion theory and by alternating the microcell corrosion state and macrocell corrosion state, the influence of mineral admixtures, such as fly ash, slag, and limestone powder, on the macrocell corrosion behaviors of steel bars embedded in chloride-contaminated concrete were investigated and clarified. The results indicated that the inhibition effect induced by slag on macrocell corrosion and microcell corrosion was obviously better than that induced by fly ash or limestone powder. The presence of slag in chloride-contaminated concrete could remarkably decrease the corrosion area ratios of anodic steel, even if the replacement levels of slag to cement reached 70%. With the addition of mineral admixtures into concrete, the ratio of macrocell current density to microcell current density was decreased to some extent, depending on the types, replacement levels, and replacement ways of mineral admixtures. The use of slag and fly ash in chloride-contaminated concrete can effectively weaken the macrocell corrosion and make the corrosion be dominated by microcell corrosion. The types and replacement levels of mineral admixtures also had a remarkable influence on the control mode of macrocell corrosion. The use of slag was more effective than that of fly ash or limestone to weaken the cathode control mode of macrocell corrosion and made the control mode of macrocell corrosion be dominated by jointed control.