Kiliswa, Moses Wopicho.Surabhi, SrivastavaIlori, Olasunkanmi.2026-01-212026-01-2120232023https://hdl.handle.net/10413/24236Doctoral Degree. University of KwaZulu-Natal, Durban.Globally, municipal wastewater infrastructure is faced with a common problem known as Microbially Induced Concrete Corrosion (MICC). MICC is deterioration caused by the activities of microorganisms, mainly sulphur-reducing bacteria (SRB) and sulphur-oxidizing bacteria (SOB). Through the activities of SRB, sulphate, contained in wastewater in sewer systems, is anaerobically reduced to hydrogen sulphide (𝐻􀀁𝑆). The H2S is eventually released into the sewer headspace in gaseous form and is absorbed onto the exposed moist concrete walls where it is aerobically oxidised thus establishing acidic environments for growth of SOB. Through the activities of SOB, the absorbed 𝐻􀀁𝑆 is further oxidised to sulphuric acid (𝐻􀀁𝑆𝑂􀀂), which gradually attacks and destroys the acid-soluble components in the concrete matrix. However, the rate of destruction or corrosion depends on several factors, such as the relative humidity in the sewer headspace, the amount of the acid-soluble components in the concrete matrix, and more significantly, the nature of the binder hydrates. The aim of the current research was to study the performance of two binder systems in an aggressive wastewater environment, by exposure of various mortar samples; these systems were calcium aluminate cement (CAC)-based and Portland cement (PC)-based. For this study, the newly built Mahatma Gandhi Wastewater Pump Station (MGWWPS) in Durban, South Africa, was chosen as the exposure site for the samples, since it is categorised as an ‘aggressive’ environment based on the extent of MICC within the first few years of commissioning. To achieve the objectives of study, three different types of mortar samples were produced—CAC-based mortars (CACm), PC-based mortars (PCm), and PC-based mortar with a crystalline waterproofing admixture, (PCAm). The waterproofing was intended to keep the oxygen from SOB, within the concrete matrix, thus suppressing their acid-generating activities. These mortar samples were installed in the MGWWPS, after 28 days of water-curing in the laboratory, and were continually monitored for over twelve months, prior to undertaking further laboratory testing. After a 12-month exposure period, total mass loss of about 0.87%, 2.84% and 25.6% was observed on the CACm, PCm and PCAm samples respectively. This translated into a corrosion rate of approximately 0.02 mm/year, 0.7 mm/year and 0.6 mm/year for CACm, PCm and PCAm samples respectively. In addition, backscattered images were taken using the scanning electron microscopy (SEM) technique, and analysed to reveal the microstructural changes that had taken place due to MICC, such as the decrease in the quantities of the products of hydration in the matrix of the mixtures. Findings from this research showed that of the three cementitious binder systems, CAC-based samples showed the greatest resistance to MICC. Also, the SEM images showed that the binding system of the CAC matrix, which is mainly alumina-based, was still intact, unlike the PC-based samples (PCm), which had its binding system—portlandite, 𝐶𝑎(𝑂𝐻)􀀁 and calcium-silicate-hydroxide gel (C-S-H)—being partially destroyed. Despite incorporating a waterproofing admixture, the modified PC-based samples (PCAm) also had its binding system partially destroyed, although to lesser extent than the PCm. This implies that the corrosion-rate controlling parameter during MICC is the nature of the binder used in concrete mixtures.enCC0 1.0 Universalhttp://creativecommons.org/publicdomain/zero/1.0/Calcium aluminate cement.Portland cement.Mahatma Gandhi Wastewater pump station.Thesis