Abstract: The active bioslurry, a urease-active slurry mixture composed of calcium carbonate and embedded urease-producing bacteria, is generated using microbial-induced calcium carbonate precipitation (MICP) technology. This study proposes a method for heritage bricks restoration using active bioslurry. Laboratory experiments and PFC^2D numerical simulations were conducted on notched simulated bricks to examine the mechanical response and microstructure of the repaired bricks and evaluate the feasibility of this method. Additionally, the repair and failure mechanisms under load were analyzed. The results show that active bioslurry effectively repairs notched simulated heritage bricks, with effectiveness influenced by curing time and notch depth. Longer curing time and shallower notch result in higher flexural strength of repaired samples. Analysis of the structure of calcium carbonate in the repaired notches indicates that after immersion curing, active bioslurry forms two layers of calcium carbonate: an outer layer of rhombohedral particles (approximately 10−25 μm), and an inner layer of spherical particles (around 5 μm). This two-layer structure likely results from differences in calcium ion and urea concentrations diffusing into the inner and outer layers of bioslurry. After 1, 3, and 5 days of curing, the thickness of the outer calcium carbonate layer was 2−2.5 mm, 3−4 mm, and 4−5 mm, respectively. PFC^2D numerical simulations indicate that the micromechanical parameters of the inner calcium carbonate layer are approximately 0.1 times those of the outer layer. Experimental and numerical simulation results demonstrate that the increase in flexural strength of the repaired simulated bricks is primarily attributed to the outer calcium carbonate layer. PFC^2D simulations further show that when the repaired bricks are subjected to bending loads, cracks initiate in the inner calcium carbonate layer and gradually propagate through the entire calcium carbonate layer and the undamaged brick body. This study not only expands the application scope of microbial reinforcement technology but also provides new insights for the restoration of heritage bricks.

Key words: active bioslurry, heritage bricks, microbial-induced calcium carbonate precipitation (MICP), calcium carbonate, urease-producing bacteria