Synergistic effects of triethanolamine and nano-SiO₂ on the hydration and hardening properties of Limestone calcined clay cement

Abstract

This study investigates the synergistic effects of triethanolamine (TEA) and nano-SiO₂ (NS) on the hydration, mechanical properties and microstructure of Limestone Calcined Clay Cement (LC³). Isothermal calorimetry results reveal that NS primarily enhances the hydration degree of the silicate phase, whereas TEA preferentially accelerates aluminate hydration through Al³⁺ complexation and surface adsorption, which modifies ion availability and delays C-S-H nucleation, thereby regulating the timing of the silicate peak. Both NS and TEA can increase the intensity of the aluminate peak, while their combination produces an even stronger synergistic effect. TEA consistently contributes to LC³ strength development at all ages, while NS mainly improves early-age strength. The synergistic effect of NS and TEA is more pronounced than either additive alone, with the LC³-3NS-0.2 %TEA (with 3 % NS and 0.2 % TEA) blend exhibiting the best performance across all ages. TEA leads to a greater consumption of CH compared to NS, while NS-TEA blends yield a higher volume of hydrates, including C-(A)-S-H gel, AFm, and AFt phases. Moreover, TEA primarily influences pore size distribution rather than total porosity, shifting larger, more harmful pores into smaller, less detrimental ones. The NS-TEA synergistic blend achieves the most favourable pore structure, characterised by the lowest content of harmful pores (>100 nm) and the highest proportion of fine pores (4.5–50 nm and <4.5 nm).