Microbial communities in low-pH concrete: Implications for deep geological radioactive waste repositories

Deep geological repositories (DGRs), i.e., underground engineered structures designed to enclose radioactive waste, require strict safety regulations for long-term maintenance. One of the primary construction materials utilized within DGRs is concrete, which often interfaces with compacted bentonite. Concerns have arisen, however, regarding the potential degradation of bentonite swelling properties over time due to the highly alkaline nature of conventional concrete, prompting an investigation into alternative materials, such as low-pH concrete (LPC; pH 10-11). Nevertheless, questions persist regarding the long-term durability of structures composed of LPC due to the influence of microorganisms, which can be more diverse and more metabolically active in LPC than standard concrete. In this review, we explore and discuss the role of microorganisms in LPC, focusing on their potential positive and negative impacts on concrete durability in both aerobic and anaerobic phases within the DGR environment. We summarize how microbial colonization occurs, the potential sources of microbial migration, and the key microbial groups (e.g., autotrophs, mixotrophs, heterotrophs) that could affect LPC in long-term.