Evaluation of the effect of surface coatings on protection of concrete against sewage-induced degradation based on gray correlation analysis

Abstract

Surface coating is the most widely used measure in engineering projects for protecting concrete against sewage attack. In this study, three types of conventional surface coating, including epoxy coal tar pitch coating (ECTPC), cement-based capillary crystalline waterproofing coating (CCCWC), and cement-based bactericidal coating (CBC) were examined for such purpose, and their performance of resisting sewage, water, acid, abrasion, and microbial erosion was investigated. Moreover, the gray theory method was adopted to find out the primary index of coatings that affected their protection of concrete against sewage-induced degradation (SID). The results revealed that ECTPC provided the best protection for concrete against sewage attack, due to the joint effects of its water resistance, resistance to flow erosion and bactericidal function. For the two inorganic coatings, there was no apparent difference between them in the bond strength and wear time. Although the water resistance of CCCWC was better than that of CBC, its resistance to sewage attack was worse. This was mainly attributed to the bactericide component in CBC, only a small number of cells can be observed in the attached biofilm layer. The gray correlation analysis indicates that the resistance to microbial growth of coating is the most critical factor of the SID of concrete. Also, the coatings acid resistance had the lowest correlation degree with its resistance to SID. Therefore, the effect of killing microorganisms at the origin is better than that of preventing or slowing down the penetration of sewage. These findings can be used to guide the selection of coatings in concrete sewers to control SID.