There is a lack of research on the early plastic deformation and capillary pressure of high-volume fly ash concrete (HVFAC) under varying ambient temperatures. This study aims to investigate the effects of water–binder ratio, fly ash admixture, and ambient temperature on the air entry time T, capillary pressure, and plastic shrinkage of HVFAC. Nine different fly ash concrete materials were designed and analyzed to determine the early plastic deformation and capillary pressure of HVFAC under different ambient temperatures. The dosage of different superplasticizers was adjusted to ensure a slump of 180 mm for all the HVFAC mixtures. The results showed that at 20 °C, T increases with the increase in the water–binder ratio and fly ash admixture, while the effect of T is negligible at 35 °C. The plastic shrinkage of HVFAC increases significantly with the increase in curing temperature, and there is a linear correlation between the air entry time T and the plastic shrinkage value at this time. At low water–binder ratios, the capillary pressure threshold P_a increases with increasing curing temperature, while at high water–binder ratios, there is no significant trend observed for P_a. The findings of the study can provide a theoretical basis for preventing plastic cracking of concrete and optimizing early curing methods.

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.