An efficient microbial sealing of rock weathering cracks using bio-carbonation of reactive magnesia cement

Abstract

Bio-carbonation of reactive magnesia cement (RMC) was proposed as a promising strategy to stabilize the weathered stone grains for the efficient sealing of rock weathering cracks near surface. The physical and mechanical properties of the sandstone grains stabilized by bio-carbonation of RMC was first investigated to verify the feasibility of applying the method to the rock weathering cracks when subjected to the condition of compression failure. Except for initial water content, RMC content and urea concentration, two new effects including bacteria concentration and bacteria solution composition on the underlying stabilization mechanism were systematically studied. The experimental results showed that bio-carbonation of RMC can effectively stabilize the sandstone grains. The highest unconfined compressive strength (UCS) of bio-carbonated sample was up to 5.5 MPa, which was 7.8 times higher than that of the sample stabilized by RMC hydration only. UCS increased as the RMC content and bacteria concentration increase, while the effects of initial water content and urea concentration were opposite. The dry density, resistance of water absorption, electrical resistivity and P-wave velocity were in proportion to the UCS. The effect of bacteria solution composition indicated that the well stabilization performance can be attributed to the coupling effect of the biomolecules and bacteria. Biomolecules-induced amorphous brucite can form a dense structure to fill the pore spaces. Bacteria-induced hydrated magnesium carbonates (HMCs) can form a stable spatial network structure with high cementation strength. The bacteria and biomolecules inhibited the air-based carbonation but facilitated the bacteria-based bio-carbonation and made the microstructure denser. A better bio-carbonation effect and stabilization performance can be obtained by increasing bacteria activity, such as increasing bacteria concentration or using low concentration of urea.