Abstract: Due to the characteristics of environment protection and economy, microbial remediation technology in concrete industry has attracted much attention nowadays, however, the repair efficiency is greatly affected by the alkaline environment. Therefore, it is of great significance to improve the efficiency of the technology and the quality of repair work. In this paper, the accelerating effect of Al2O3 on microbial calcification in high alkaline environment was investigated. Concrete specimens with different crack widths were repaired by adding Al2O3, during which the pH value and urea content of the leaching solution were monitored. After repairing, the repairing effect was evaluated by acoustic time value, CaCO3 formation efficiency and unconfined compressive strength. The results showed that Al2O3 could reduce the inhibition of alkaline environment on bacteria and enhance the urease activity and calcification efficiency. The addition of Al2O3 reduced the pH of the leaching solution from 12 to 9, while the urea utilization rate increased significantly, up to 81%, thus significantly shortened the repair time. The acoustic time value of specimens with addition of Al2O3 is close to that of specimens without cracks, which is significantly better than that of non-added specimens. After Al2O3 addition, the formation rate of CaCO3 in 2 mm cracked specimens was 77.32%, which is way higher than that of 20.98% specimens without Al2O3 addition. The strength recovery of repaired specimens increases with the decrease of crack width, and the strength recovery of repaired specimens with Al2O3 addition is much higher than those of the specimens without Al2O3. Therefore, the addition of Al2O3 can effectively improve the efficiency in concrete repairing process, reduce the repair time, and provide important reference for the rapid and efficient repair of cracks by microorganisms in future practical projects.

Key words: crack repair, Al2O3, acoustic time value, calcium carbonate production rate, strength recovery