Abstract: The development of highly reactive and low-carbon cementitious materials is a critical pathway for reducing CO₂ emissions and promoting green transformation in the cement industry. In this study, the intrinsic origin and formation mechanism of amorphous structural reactivity in low-carbon cementitious materials were systematically elucidated based on ²⁷Al and ²⁹Si solid-state nuclear magnetic resonance spectroscopy. The results reveal that in CaO-MgO-Al₂O₃-SiO₂ glass phases derived from rapidly quenched industrial wastes, the primary source of reactivity stems from the depolymerization of the silicate network induced by Ca²⁺ and Mg²⁺, while the partial substitution of Ca²⁺ by Mg²⁺ leads to local structural perturbations around Al³⁺, representing a secondary reactivity mechanism. In contrast, the reactivity of calcined aluminosilicate clays arises from the presence and transformation of multi-coordinated Al species during thermal activation, with highly distorted five-coordinated Al serving as the main reactive structural unit. Based on these findings, a "reactivity integration" design strategy is proposed by co-calcining calcium carbonate and clay to simultaneously activate the silicate depolymerization and the formation of multi-coordinated Al. The structural evolution underlying this integration mechanism is confirmed by ²⁷Al and ²⁹Si solid-state nuclear magnetic resonance analyses. Complementary rapid-relevant-reliable(R³) reactivity and mechanical performance tests further demonstrate the enhanced early-age reactivity and long-term strength development of the integrated system. This study establishes a coherent design pathway from atomic-scale structural insights to multi-source reactivity integration, offering a new theoretical foundation and practical strategy for the development of low-carbon cementitious materials.

Key words: low-carbon cementitious material, glass phase, calcined clay, reactivity integration, ²⁷Al NMR, ²⁹Si NMR, five-coordinated Al