Regulation Mechanism of Alkanolamines on Hydration and Microstructural Evolution of Thermally Treated Volcanic Rock Powder–Cement System

Utilizing abundant volcanic rock resources as supplementary cementitious materials is a critical pathway for regional low-carbon construction. However, the high crystallinity of natural volcanic rocks limits their reactivity. This study systematically investigates the regulation mechanisms of Triethanolamine (TEA) and Triisopropanolamine (TIPA) on the hydration kinetics and microstructure of a cement system containing Volcanic Rock Powder (VRP) thermally treated at 700 °C. Dissolution kinetics reveal that both TEA and TIPA inhibit Si release but exhibit distinct structural selectivity in promoting metal ion dissolution: TEA demonstrates superior efficiency in promoting the release of Al and Ca ions due to lower steric hindrance, whereas TIPA exhibits a stronger specific activation capacity for insoluble Fe, which is likely attributed to the electron-donating inductive effect. Macroscopic tests show that TEA at 0.05% dosage significantly improved the 28-day compressive strength by 20.4%, attributed to the synergistic effect of efficient chemical activation and pore structure refinement. In contrast, the stronger surface activity of TIPA introduced substantial detrimental macropores; this deterioration in physical structure severely offset its chemical contributions, leading to slow late-age strength development. The study highlights the critical trade-off between chemical activation and microstructural evolution, confirming that TEA is a more suitable activator than TIPA for the Al/Fe-rich thermally treated VRP.