Bridging Composition, Structure, and Reactivity to Performance in a Wide Range of Supplementary Cementitious Materials

ABSTRACT Supplementary cementitious materials (SCMs) are central to low‐carbon binder design, yet broad variability in chemistry, structure, and physical attributes leads to wide spreads in reactivity and hinders widescale adoption. This study establishes a quantitative, structure‐informed framework that links composition and atomic topology to reactivity and performance in Portland cement (PC) systems. Eighteen SCMs—including fly ashes, natural pozzolan, mine tailing, slags, and raw/calcined clays—were evaluated using a modified R 3 test with isothermal calorimetry, coupled to a thermodynamic framework to quantify a composition‐specific reactivity, revealing indices ranging from 2% to 55% after 7 days of hydration. To bridge chemo‐structural information of SCM and reactivity, molecular rigidity and macroscopic behavior, topological constraint theory was employed to compute the number of constraints ( n C ) based on bulk oxide composition. A strong inverse relationship was observed between n C and reactivity, indicating that less‐constrained (i.e., more amorphous and Ca‐rich) networks react more readily. Calcination transforms clays from well‐ordered crystalline structures to partially disordered structures, thereby significantly enhancing their reactivity. Compressive strength tests at 7 and 28 days for PC binders containing 20% SCM, together with calcium hydroxide consumption from the modified R 3 experiments, showed strong agreement with the derived reactivity indices, demonstrating the reliability and robustness of the proposed framework. Thermodynamic simulations further revealed that SCM incorporation predominantly densifies existing hydrates, consistent with observed strength improvements. The proposed workflow enables rapid screening and selection of SCMs—particularly industrial and nonconventional by‐products—for designing PC binders. Notably, a fast preliminary estimation of reactivity can be achieved using only chemical compositions.