Microbiological Analysis of SURAO Low-pH Concrete (LPC) in repository-like conditions

Low-pH concrete (LPC) is used as one of the main construction components of deep geological repositories (DGR) for radioactive waste. The mechanical and chemical stability of this material is crucial for the long term DGR sustainability. However, the presence of microorganisms in the underground environment and backfill matrices could significantly affect its stability and in turn the safety of DGRs. The buffer and backfill matrix (bentonite) and underground water are potential long-term sources of bacteria in DGR. The WP MAGIC as a part of the European joint program EURAD focuses on studying the chemo-mechanical behavior of concrete under varied conditions. The project compares the effect of three different conditions – air, water and bentonite - on aged SURAO LPC samples. The 2-year experiment is disposed in Czech Underground Research Facility (URF) Bukov. Our aim was to investigate microbial activity in LPC discs and describe the capability of present microorganisms to affect the mechanical properties of LPC in time. The microbiological analysis comprised of both cultivation dependent and independent approach. The microbial activity was also confirmed using epifluorescent microscopy and scanning electron microscopy. Our findings reveal unique microorganisms in each of in-situ condition, highlighting their potential effect on mechanical properties of LPC.