Sewer networks are subjected to degradation, including biodeterioration of materials, in the presence of biogenic sulfuric acid, leading to costly repairs. To ensure durable structures, it is essential to select the best adapted materials. Two cementitious materials based on ordinary Portland cement (OPC) or calcium aluminate cement (CAC), were subjected to biodeterioration in the headspace of an operating sewer network. After a few month OPC materials started to deteriorate whereas CAC materials were still intact. The better durability of CAC materials is due to the presence of alumina providing a combination of protective mechanisms. On-site environmental parameters were monitored and analysed in the context of the biological and chemical mechanisms involved in material degradation. These data will eventually feed into the development of a representative, reproducible and accelerated laboratory test.