Influence of cement composition and content on the corrosion behavior of reinforcing steel in concrete

Performance data based on accelerated corrosion monitoring and exposure site tests indicate that cement type, reflecting particularly the C₃A content, significantly affected concrete durability with respect to corrosion of reinforcing steel. On an average, Type I cement (C₃A:9.5%) performed 1.7 times better than Type V cement (C₃A:2.8%) in terms of time to initiation of corrosion. Further, with respect to corrosion, concretes made with fly ash blended cements performed better than no-fly ash concretes with the best performance shown for 30 per cent cement replacement. The greatest beneficial effect of pozzolan addition was provided in conjunction with low w/c ratios of 0.385 and 0.45. The electrical resistivity for portland-pozzolan concrete made with 25 per cent cement replacement was found to be three times that of straight cement concrete irrespective of w/c ratio in the range of 0.35 to 0.65. Depending on the extent of replacement, pH values for concretes made with fly ash blended cements were observed to be in the range of 12.70 to 12.93 after 600 days of exposure to the outdoor environment at Dhahran in Eastern Saudi Arabia. However, the pH values dropped below that of pure saturated Ca(OH)₂solution (12.50) for chloride contaminated concrete made with fly ash blended cement with observed detrimental consequences for corrosion of reinforcement. Increase in the cement factor with attendant reduction in w/c ratio provided a most beneficial effect on time to initiation of corrosion of reinforcing steel.