Fly ash (FA) is one
of the largest industrial wastes in the world,
and its storage is still accumulating. To meet this challenge, one
of the most effective and promising ways is to increase the dosage
of fly ash in cement-based materials. However, the slow reaction of
FA restricts the high content substitution of cement by FA. Therefore,
a better knowledge for enhancing the reaction of FA is essential toward
achieving a green and sustainable cementitious binder. Previous research
demonstrated the synergistic effect on enhancing the reaction of FA
with the combined application of sodium sulfate (SS) and calcium–silicate–hydrates
(C–S–H) seeds, while the mechanism of the synergistic
effect is unclear. In this study, the effect of SS and C–S–H
seeds on the reaction of FA with different amorphous alumina contents
is systematically investigated. The results show that the effect of
SS and C–S–H seeds on the reaction of FA is closely
related to the amorphous alumina content and the reaction time. Moreover,
the underlying mechanism is revealed and may provide guidance for
the massive utilization of FA and other Al-rich mineral admixtures.
This study proposes an environmental-friendly cementitious material using calcium hydroxide-sodium sulfatecalcined clay based on the idea of ancient Roman cement. The pozzolanic reaction characteristics of calcined clay are studied by adjusting the ratio of calcined clay and calcium hydroxide in both experimental and thermodynamic modeling methods, which demonstrate that 70% calcined clay and 30% calcium hydroxide are the optimal ratio for the pozzolanic reaction of calcined clay to promote the formation of hydration products. Furthermore, the effect of sodium sulfate on the microstructure and mechanical properties of the cementitious materials are also investigated. Results indicate that 5% sodium sulfate (relative to the total mass of the binder) can accelerate the pozzolanic reaction of calcined clay and optimize its mechanical properties. Overall, this study provides a non-clinker cementitious material with high utilization of calcined clay to reduce energy consumption and CO 2 emissions.
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