This paper presents a comparative study on the corrosion rate and microstructural characteristics of Portland cement (PC) and calcium aluminate cement (CAC)-based concrete mixtures subjected to microbially-induced sulphuric acid (biogenic H2SO4) attack for 120 months in an outfall sewer. The higher amount of the amorphous AH(x) within the CAC-based concrete matrix provides a higher neutralisation capacity to the attacking acid, thus giving it better performance than PC-based concrete mixtures during biogenic H2SO4 attack. In addition the results show that the biogenic corrosion rate of PC-based concrete mixtures increases with the cement content while that of CAC-based concrete mixtures decreases with the cement content.