Study on synthesis and water stability of geopolymer pavement base material using waste sludge

Waste sludge is a typical solid waste generated during construction excavation, which needs innocuity treatment and resource utilization. The development of geopolymer pavement base material using waste sludge is an economic and environmental method to realize the utilization of waste sludge. This manuscript aims to develop a geopolymer pavement base material using waste sludge and further evaluate its water stability under water soaking environment. The geopolymer specimens with different slag and waste sludge contents were prepared. The optimum mix proportion of geopolymer was determined by analyzing the effect of slag content on the ultimate compressive strength (UCS) and elastic modulus. The CO2 emissions and energy consumption of geopolymer was analyzed. The water stability of the geopolymer was further evaluated by analyzing the effects of soaking time on the density, wave velocity, mechanical properties and pore structure. The results show that the geopolymer with 50% slag content has the largest UCS and excellent strength development characteristics. The UCS of geopolymer pavement base material reaches 48.4 MPa and the CO2 emissions and energy consumption were reduced by 58.34% and 88.16% compared to C40 ordinary concrete. The results also show that the density, longitudinal wave velocity and porosity remain stable as soaking time increases. During the soaking process, the proportion of gel pores and transition pores decreases, while the proportion of capillary pores and air pores increases. The UCS of geopolymer pavement base material remains above 40 MPa after soaking for 90 days, showing excellent water stability. The geopolymer pavement base material has the potential application prospect in road engineering and emission reduction, which provides a feasible and cost-effective method for the utilization of waste sludge.