The effect of sulfate ions on the corrosion of concrete on outside walls of buildings was studied. The corrosion rate was very high during the early years and decreased with time. Corrosion-induced cracking of concrete can be simulated by sulfate formation with sulfur dioxide (SO2) at the concrete interface for a long period. Excessive alkali sulfate formation at the concrete surface causes destructive volume expansion. In general, the age of concrete is highly correlated with its sulfate content and water solubility. (C) 2001 Elsevier Science Ltd. All rights reserved.