Increasing service life of concretes in sewage treatment plants using silica fume and natural zeolite

Microbiological attacks cause concrete structures used in wastewater collection and treatment facilities to deteriorate and degrade rapidly in short service lives. Hence, it is more cost-effective to produce concrete resistant to chemical and sulfuric acid corrosion. In the present study, a total of six concrete mixtures incorporating 7.5% silica fumes (SF) and 10% natural zeolite (ZE) were immersed in 0.5% and 1% sulfuric acid solutions with a maximum pH threshold of 2 and 1 respectively for 70 weeks to enhance concrete resistance to acid attack. The specimens were regularly monitored for surface deterioration, mass changes, and crushing load changes. To better understand the relationship between the pore structure of concrete mixtures and resistance to sulfuric acid, various durability tests such as rapid chloride penetration, water absorption, electrical resistivity, and chloride diffusion coefficient were performed. Based on the results obtained, it was concluded that converting calcium hydroxide (CH) into CSH gel through pozzolanic reactions and then refining the porosity of concrete with silica fume and natural zeolite was effective in enhancing the resistance of concrete to attack by sulfuric acid of relatively low concentration. As a result, using SF and ZE is a lower-cost method for reducing corrosion rates to extend the service life of facilities, particularly in lower concentrations.