The deterioration of mortar in sulphate environments

摘要

The skin of concrete plays an important role in the durability of cementitious materials. In a sulphate environment this surface reaction can cause deterioration or in some cases protection. Surface properties of mortars, which arc exposed to sulphate environments, have been studied using SEM, microanalysis, X-ray diffraction and Vickers' hardness testing. When cement mortar is exposed to sulphuric acid a dense layer of gypsum is formed, this is capable of retarding the deterioration process by acting as a surface sealing layer. Gypsum also exists in pores and fissures in the surface zone, indicating that the attack is due to expansive crystallisation. In ammonium sulphate the surface deposit of gypsum is sparse and the damage to the concrete occurs to a greater depth. The lack of sulphur found in the surface zone indicates that the mechanism of deterioration is due to the dissolution of Ca~2+.