Evaluation of the Groutability and Diffusion Stability of Excess-Sulfate Phosphogypsum Slag Grouting Material Based on Wet Grinding in Sand Layers

In the field of civil engineering, in which the reinforcement and stabilization of various soil layers are of crucial importance, as an emerging alternative to cement-based grouts, excess-sulfate phosphogypsum slag grouting material (EPSGM) has stood out in stabilizing porous sand layers due to its nonflocculating and easy-to-grind traits. However, due to infiltration effects, its post-wet-grinding grain size characteristics critically affected groutability and the distribution of phosphogypsum (PG), ground granulated blast-furnace slag (GGBS), ordinary portland cement (OPC) and water. This work simulated grouting within 0.3–4.75-mm siliceous sand. Firstly, EPSGM slurry was optimized for different wet-grinding times and water-to-cement ratios (w/c), using bleeding, fluidity, and plastic viscosity. Then, groutability was evaluated using the relationship between the particle size of the slurry and sand (D15/d85), diffusion distance, and California bearing ratio, whereas stability was evaluated using solid retention, actual w/c, grout occupancy ratio, and component distribution with diffusion distances. The experimental results showed that within 30 min after the wet-grinding process, the d90 value of EPSGM decreased from 78.87 to 21.02 μm, and the D15/d85 value increased from 11.37 to 37.79. The actual grouting distance was 147 cm. When the grouting distance reached 125 cm, the CBR remained higher than 15%. The retention rate of EPSGM at different diffusion distances ranged from 27.8% to 25.1%, and the w/c ranged from 1.8 to 3.1. The diffusion capacity of the individual components within the sand layer was ranked from highest to lowest as follows: phosphogypsum (PG), ground granulated blast-furnace slag (GGBS), and ordinary portland cement (OPC). The process of wet-grinding PG considerably decreased the overall particle size of EPSGM, and changed fineness differences of each component, improving the groutability and the diffusion stability of each component within the sand layer. EPSGM, optimized via wet grinding, has remarkable effects in civil engineering projects such as grouting in sandy strata.