ABSTRACT
All the building materials contain some lime, several being mostly calcium carbonate (limestone and marble*). Thus these calcareous materials are attacked by acids. Generally any aqueous liquid with a pH less than 6 will exhibit some attack. The corrosion of concrete takes place by the leaching of water-soluble salts that are formed by the reaction of the acid and the calcium-containing compounds of the concrete, Webster and Kukacka 1986. For example, the reaction of calcium carbonate with SO2-containing acids (sulfuric acid has been reported to make up 60-70% of the acidity in acid rain for the northeastern United States) forms calcium sulfate or gypsum (CaSO4 · 2H2O). The gypsum, being much more soluble than the carbonate, is then washed away. Runoff water has been shown to be more important than the pH of the solution for pH > 3. This causes etching of the surface in addition to pitting and scaling. Webster and Kukacka 1986 gave the following mechanisms for the dissolution of concrete:
1. dissolution of hydrated cement compounds, 2. dissolution of anhydrous cement compounds, 3. dissolution of calcareous aggregates in the mix, 4. deposition of soluble sulfate and nitrate salts, 5. formation of new solid phases within pores, and 6. production of stresses from numbers 4 and 5.
