Dual stimuli-responsive performance of alkali-sulfate-activated slag cemented paste backfill: Role of curing temperature and alkali-sulfate ratio

Abstract

The alkali-sulfate ratio and curing temperature jointly determine the engineering performance of alkali-sulfate-activated slag cemented paste backfill (ASAS-CPB); however, their coupled action remains insufficiently understood. In this study, ASAS-CPB with alkali-sulfate ratios of 1:19 – 6:14 was cured at 5, 20, and 35 °C, and its strength, hydration kinetics, phase composition, pore structure, and microstructure were systematically characterized. The results indicate that temperature primarily functions as a kinetic promoting factor: it significantly accelerates the early hydration and matrix densification, but excessively high temperatures inhibit the later slag reaction and undermine the uniformity of the long-term structure. Additionally, the alkali-sulfate ratio mainly regulates the ASAS-CPB performance by influencing the precipitation of Ettringerite (AFt) / C-(A)-S-H and pore refinement; however, when the alkali-sulfate ratio is low, the long-term pore structure also deteriorates. It is noteworthy that the optimal alkali-sulfate ratio is influenced by both curing temperature and time, and it shifts towards a lower value as the curing temperature increases and the hydration process progresses. Within the testing range, AFt and C-(A)-S-H remain the main hydration products, but their relative contents depend on the combined influence of temperature and alkali-sulfate ratio. This coupling mechanism explains why different temperature environments require different activator ratios, and provides a basis for the design of the ratio of ASAS-CPB in mines with different curing conditions.

Keywords

cemented paste backfill / alkali-sulfate activated slag / curing temperature / alkali-sulfate ratio / strength / microstructure

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