Evaluation of water-repelling additives for use in concrete-based sanitary sewer infrastructure

Laboratory and field investigations were conducted in order to evaluate the effectiveness of water-repelling additives in reducing the microbial-induced corrosion of concrete-based infrastructure in sanitary sewer systems. Water-repellent additives, used together with silica fume were observed to reduce the sorptivity and increase the acid resistance of concrete under laboratory conditions. This finding was expected because water-repelling additives reduce the affinity of capillary pore surfaces to moisture, and silica fume refines the size distribution and connectivity of capillary pores. Silica fume further refines the chemistry of cement hydration products, yielding enhanced resistance to acid attack. However, despite the low sorptivity and high acid resistance of concrete formulation incorporating water-repelling additives and silica fume, the resistance to microbial-induced corrosion in actual field conditions could not be improved with the strategies considered in this investigation. This new finding indicates that laboratory physical and chemical tests are not adequate for assessing the performance of concrete under microbial attack. Microbial attack can overwhelm the physical and chemical barriers against deterioration that are introduced by water-repellent additives.