Abstract: Enzyme-induced calcite precipitation (EICP) is considered to be the cutting-edge technology with broad development in many fields of geotechnical engineering. However, there are limited studies focused on the mechanism affecting the calcite precipitation. This study conducts a series of test-tube experiments to examine the effects of different substrate concentrations, magnesium ion concentrations, and ammonium ion concentrations on the changes of conductivity, pH, calcium carbonate precipitation and precipitation rate during urease mineralization. In this way, the mechanism of urease mineralization strengthening and deterioration was revealed. The water absorption, air permeability and wind erosion tests were carried out on the brick specimens under the action of individual mechanisms. The results show that with the increase of substrate concentration, the conductivity gradually increases but the evolution trend of the curve remains basically unchanged, the pH value does not change significantly, the precipitation amount first increases and then decreases, and the precipitation rate gradually decreases, among which the urea hydrolysis rate and urease activity is the key to the conversion of carbonate and to increase the amount of precipitation and the rate of precipitation. With the increase of the concentration of magnesium chloride, the amount of precipitation increases first and then decreases, and the precipitation efficiency gradually increases. The ions have a positive effect on enhancing the urease activity to form the optimal mineralization effect. With the increase of the ammonium chloride concentration, the conductivity gradually increases and the pH value gradually decreases. Ammonium radical is the main reason for the deterioration of urease activity, precipitation amount and precipitation efficiency. The water-resisting ability of the produced calcite precipitation is further verified through the water absorption, air permeability, and wind erosion tests respectively. The findings of this study explore the potential use of the EICP technology for the protection of heritage buildings in north-west China

Key words: enzyme-induced calcite precipitation, substrate concentration, strengthening mechanism, degradation mechanism, antique-style clay tiles