Changes in pore formation, strength characteristics and mineral composition of Portland cement M500 during biofouling under conditions simulating a deep geological radioactive waste repository were evaluated. The biocide polyhexamethylene guanidine (PHMG) was added to inhibit microbial growth. After two years, microbial activity was found to be a key determinant of the cement's strength characteristics due to the dissolution of primary mineral phases (portlandite, C3S, C2S and C2FA) and the formation of calcite. The volume fraction of cracks increased by an average of 25 times in all samples. Notably, the addition of PHMG did not significantly affect the porosity of the cement, and its compressive strength parameters showed no correlation with pore and crack content during long-term storage. The observed strength increase with PHMG is likely attributable to the formation of an additional polymer skeleton within the cement matrix.
Abramova et al. (Mon,) studied this question.