Evaluation of the pozzolanic reactivity of volcanic rock powder at different calcination temperatures and the performance of sodium silicate-activated volcanic rock powder geopolymer

Abstract

This study evaluated the pozzolanic reactivity of volcanic rock powder (VRP) from Xizang, China, calcined at various temperatures. The reactivity was assessed using alkali leaching solubility tests and the R³ method. Results indicate that 700 °C represents the optimal calcination temperature for enhancing VRP reactivity, as it promotes the transformation of quartz and feldspar phases into amorphous phases, significantly improving pozzolanic reactivity. A VRP-based geopolymer was prepared using 700 °C calcined VRP as a precursor and sodium silicate (SS) as an alkali activator. The compressive strength of the resulting mortars was measured, and the hydration process and reaction mechanisms of the SS-activated calcined VRP were investigated by Mercury Intrusion Porosimetry (MIP), X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Isothermal Calorimetry, and Thermogravimetry (TG) analysis. The findings reveal that optimal activation was achieved with an SS modulus of 1.8 and a dosage of 10 %, yielding high early strength and continuous strength development in the later stages, concurrently with the formation of a dense microstructure and a uniform pore size distribution. Furthermore, this research elucidates the critical interplay between the content of chemically bound water and the polymerization degree of N-A-S-H in governing compressive strength, providing a mechanistic understanding of strength development in these geopolymers. These findings not only highlight the potential of Xizang’s VRP as a sustainable precursor for geopolymers but also contribute to the broader understanding of geopolymers.