Hydrothermal solidification of alkali-activated clay-slaked lime mixtures

Abstract

Waste clay was converted into non-sintered building materials by hydrothermal solidification technology to improve resource utilization. The effects of curing time, curing temperature, initial dry density and alkaline environment on the strength development of the hydrothermally solidified clay-slaked lime mixtures were evaluated by compressive strength tests, and the microstructural evolution and solidification mechanism were analyzed by X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), scanning electron microscopy (SEM) and low-field nuclear magnetic resonance (NMR). The generated calcium silicate hydrate (C-S-H), katoite, and Al-substituted tobermorite filling pores and cementing mineral particles were the main factors responsible for the improved strength and compactness of the material. The C-S-H gel was transformed into Al-substituted tobermorite crystals in the presence of 4 mol/L NaOH solution, which greatly increased the compressive strength to 45.3 MPa. The transverse relaxation time (T2) distribution was transformed into a pore size distribution curve by combined mercury injection porosimetry (MIP) and NMR, which can effectively characterize the evolution of the pore structure. The synthesis conditions determined the type and quantity of hydrothermal products that affect the pore size distribution and microstructure, thereby exhibiting changes in structural and mechanical properties on the macroscale.