Enhancement Performance for Reinforcement Property of the Soil Treated by Phosphogypsum Based on the EICP Principle

Enzyme Induced Carbonate Precipitation (EICP) is a new environment-friendly biological soil reinforcement technology.Phosphogypsum,an industrial solid waste,can also be utilized for soil reinforcement.However,the single reinforcement effect of phosphogypsum on soil is restricted,thus further research could be conducted to strengthen soil treated with phosphogypsum based on the EICP principle.Therefore,7 phosphogypsum contents (0,2%,4%,8%,16%,32% and 64%,mass percentage of the soil) and 5 urea concentrations (0,0.5,1.0,1.5 and 2.0mol/L) were established,and the reinforcement effect of EICP on the phosphogypsum-treated soil was evaluated through analyzing the unconfined compressive strength,stress-strain curves,calcium carbonate content,and damage morphology.Additionally,the microscopic reinforcement mechanism was revealed through the use of scanning electron microscopy.The results indicated that the unconfined compressive strengths of phosphogypsum-treated soil ranged from 48.8~86.58kPa,77.94~94.86kPa,86.39~123.86kPa,114.58~134.34kPa and 91.11~117.11kPa under the urea concentrations of 0,0.5,1.0,1.5 and 2.0mol/L,respectively.The EICP increased the unconfined compressive strengths by 21.83%~110.00% compared to the single phosphogypsum-treated soil.Furthermore,the increase in unconfined compressive strength demonstrated a significantly exponential relationship with the calcium carbonate content induced by EICP (P<0.05).This suggests that the cementation effect of the calcium carbonate is the primary factor contributing to the rise in unconfined compressive strength.Moreover,the EICP can generate granular and spherical CaCO₃ that can encapsulate,fill or bond the soil particles,thereby enhancing the soil unconfined compressive strength.These findings can serve as a theoretical foundation for the comprehensive utilization of phosphogypsum resources.