Long-term performance of steel reinforcing bars in portland cement concrete and concrete incorporating moderate and high volumes of ASTM Class F fly ash

This paper reports the long-term performance of steel reinforcement in port land cement concrete and concrete incorporating moderate and high volumes o f ASTM Class F fly ash. In 1989, three fly ash concrete mixtures and three control portland cement concrete mixtures were made in Halifax, Canada, and concrete slabs 1220 x 1220 x 150 mm thick were cast. Steel reinforcing bar s were placed in the slabs with concrete covers of 20, 40, 60, and 80 mm. A fter 7 day's of moist curing and 21 days of air drying, the slabs were pond ed with 4% calcium chloride solution. In 1997, eight years after ponding, h alf-cell potential measurements were taken to determine the probability of corrosion of the embedded reinforcing bars. Cores were drilled from the sla bs for the determination of the compressive strength, resistance of the con crete to chloride-ion penetration in accordance with ASTM C 1202, and chlor ide content at various depths in the slabs. The reinforcing bars were then removed from the slabs for visual inspection. Notwithstanding the results of various tests performed and the relative per formance of concrete with or without fly after eight years of exposure to 4 % chloride solution, there were no visible signs of any corrosion products on those portions of the steel reinforcing bars that were embedded in the c oncrete. The only exceptions were the bars with a cover of 20 mm in Slab 5 (25% fly ash water-cementitious materials ratio [w/cm] = 0.57), and with co vers of 20 and 40 mm in control concrete Slab 6 [water-cement ratio (w/c) = 0.57] that showed some evidence of corrosion. In general, thr concrete incorporating moderate and high volumes of fly ash showed superior resistance to the penetration of chloride ions compared to the control concrete.