Ceramics-Silikáty

The incorporation of high volumes of ultrafine fly ash (UFA) and coal gangue into concrete mitigates solid waste pollution but reduces the early-age performance of concrete. The addition of an appropriate amount of triethanolamine (TEA) accelerates cement hydration and enhances early-age strength. This study investigates the effects of varying UFA replacement ratios and TEA dosages on the early-age performance of high-volume UFA–coal gangue concrete, focusing on workability, compressive strength, and stress–strain behavior. Microstructural changes were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that the optimal UFA replacement ratio is 20%, and that a moderate UFA content enhances compressive strength. At a UFA replacement ratio of 50%, the optimal TEA dosage was 0.1%, yielding 3d and 28 d compressive strengths of 20.5 MPa and 42.7 MPa, respectively-representing increases of 33.1% and 16.2% compared with the control group. TEA significantly improved the early-age strength of high-volume UFA-coal gangue concrete. Microstructural analysis further revealed that 0.1% TEA most effectively promoted cement hydration. This improvement is attributed to the rapid establishment of an alkaline environment in the cement paste and the promotion of secondary pozzolanic reactions of the active constituents in UFA, resulting in increased C-S-H gel formation and enhanced compressive strength. This study provides a reference for the application of TEA in high-volume UFA–coal gangue concrete.