Alkali-reinforced hydrothermal solidification of waste soil

To promote the resource utilization of waste soil, hydrothermal solidification technology was used to convert waste soil into a tough material. The effects of curing conditions (time and temperature), molding conditions and alkaline conditions on the physical-mechanical properties of hydrothermally solidified waste soil were investigated in the CaO–MgO–Al2O3–SiO2–H2O system. The solidification mechanism and microstructure evolution under different synthesis conditions were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and low-field nuclear magnetic resonance (NMR). The strength of waste soil was effectively enhanced under hydrothermal conditions; in particular, the addition of NaOH solution could nearly double the strength. Calcium silicate hydrate (C–S–H) and hydrogarnet formed by the hydrothermal reaction filled the pores and cemented mineral particles to form a dense skeleton structure. The filling of hydrothermal products and the dissolution of mineral particles together affected the pore structure and compactness of the material. The synthesis conditions determined the type and quantity of hydrothermal products that affect the microstructure, consequently reflecting the changes in macroscopic physical-mechanical properties. •The waste soil was converted into tough materials using hydrothermal solidification technology.•The effects of different synthesis conditions on the physical-mechanical properties were investigated.•The solidification mechanism of hydrothermally solidified waste soil was analyzed in the CaO–MgO–Al2O3–SiO2–H2O system.•The possibility of hydrothermal solidification of waste soil at 100 °C was verified.