Triethanolamine as an accelerator for early hydration of sodium carbonate-activated slag: Effectiveness and underlying mechanisms

Sodium carbonate (SC) has emerged as a promising activator for ground granulated blast-furnace slag. However, engineering application of the SC-activated slag is hindered by its sluggish early hydration. This study investigates the effectiveness of triethanolamine (TEA) in accelerating the early hydration of SC-activated slag and the underlying mechanisms. TEA was added to SC-activated slag paste at dosages of 0, 0.5, 1, and 2 wt% of slag, and its effects on hydration kinetics, strength development, phase evolution, and microstructure were systematically characterized. Results demonstrated that TEA can markedly accelerate the early hydration, especially at higher TEA dosage. While the reference paste could not harden within the first 7 d, the addition of 2% TEA advanced the onset of acceleration period from 7 d to 10 h, achieving rapid early strength development without compromising long-term strength. TEA did not fundamentally alter the overall hydration pathway, but accelerated phase evolution, promoted earlier hydrotalcite formation, and increased the Al incorporation and Ca/Si ratio of C-A-S-H at early age. The accelerating effect of TEA originated from its chelating interaction with Al species, which promoted dissolution of Al units and adjacent Si units from the glassy structure. This resulted in a more leached diffusion layer of slag grains, sustaining their fast dissolution. The increased Ca²⁺ release then rapidly consumed CO₃^2- and raised the pH, thereby triggering earlier main hydration. These findings provide new insight into effective acceleration for early hydration of SC-activated slag.