Physicochemical study of the alteration surface of concrete exposed to ammonium salts

The storage of chemicals in concrete silos often presents durability problems due to chemical attack, the high concentration encountered inevitably causes severe conditions. The aim of this paper is to examine the physicochemical changes that occur in concrete exposed to ammonium salts, notably ammonium sulphate and nitrate, which are noted for their aggressivity. The modification to mortar surfaces is examined with X-ray diffraction (XRD) and with SEM. Mortar immersed in ammonium sulphate is covered with gypsum needle-like crystals and undergoes rapid cracking when removed from the solution and washed. In the case of mortars immersed in ammonium nitrate solutions, there is rapid decalcification, accompanied by strength loss, due to the solubilization of calcium. It is also observed that the mortar surface is covered with rhombic calcite, which is attributed to the reaction between liberated calcium and CO2 in the water. (C) 2003 Elsevier Science Ltd. All rights reserved.