Laboratory investigation on mechanical behavior of stone cultural relic fractures using rapid microbially induced calcite precipitation

Biogrouting based on a microbially induced calcite precipitation (MICP) process is a developing technique for the restoration of stone cultural relics, but the efficiency and the potential impact of microorganisms are still the concerns. In order to address these issues, this paper proposes an improved biogrouting method using urease-active suspension for repairing rock fractures. The urease-active suspension refers to bacterial suspension containing tiny CaCO 3 particles preformed in solution. Compared to conventional MICP methods, the proposed method improves cementation efficiency due to the preformed calcium carbonate and reduces microbial impact because the calcium carbonate encapsulates some bacteria. The shear behavior of repaired rock fractures was investigated. Employing 3D scanning and image reconstruction technology, the spatial distribution and quantity of biogrout precipitation within the rock fractures were quantified. Test results indicate that the rock fractures treated with biogrouting using urease-active suspension exhibited twice the calcium carbonate content and four times the shear strength compared to those treated with conventional MICP method. For planar fractures, both peak and residual shear strength increased with rising calcium carbonate content; conversely, for rough fractures, the residual shear strength decreased after biogrouting due to the breakage of calcium carbonate crystals. P-wave velocity measurements across the fractures demonstrated a 30–40 % increase after biogrouting, with only a 5 % decrease observed after shear test. These findings prove that biogrouting using urease-active suspension is an efficient method to seal fractures and enhance the fracture strength of stone cultural relics, while also reducing the impact of microorganisms on the relics compared to the traditional MICP method.