Corrosion performance of reinforcing steel in concrete containing supplementary cementing materials

This paper summarizes the corrosion results of a 5.3 year study on the corrosion performance of reinforcing steel in concrete slabs containing supplementary cementitious materials and exposed to chlorides. Chloride ions were introduced into the reinforced concrete slabs through a natural migration process, i.e. a ponding solution of 3.4% sodium chloride on the top slab surface of the concrete slab. The concrete mix was designed with a 0.32 water-tocementitious materials ratio (w/cm), containing plain Portland cement and additions of fly ash Class C, fly ash Class F, silica fume and blast furnace slag. Concrete slabs with Portlandcement only and different w/c ratios (0.32, 0.43 and 0.55) were also tested. The thickness of concrete cover to the steel reinforcing bars ranged from 13 mm to 76 mm. Corrosion of the reinforcing steel bars was evaluated using the half-cell potential, linear polarization and AC impedance techniques. The test results indicated that the concrete incorporating fly ash Class C had the best performance with respect to chloride induced corrosion followed by the concrete containing silica fume and the control concrete with w/c of 0.32. In these concrete slabs the corrosion rate of the steel bars was relatively low, even with 13 mm concrete cover. The concretes made with Class F fly ash and blast furnace slag performed better than thePortland cement concretes with w/c of 0.43 and 0.55.
NACE Northern Area 2003 Conference, September 14, 2003, Ottawa, Ontario