Elastic and Electronic Properties of Alkali Charge-Balanced Calcium Aluminosilicate Hydrate Nanocomposites: A...

Graphene-based nanomaterials are regarded as outstanding candidates for enhancing cementitious nanocomposites owing to their superior elastic properties. Using a density functional theory (DFT) simulation approach, this study provides an in-depth analysis of the electronic and elastic behavior of alkali-activated Al-substituted tobermorite 14Å structures, adopted here as representative crystalline analogues based on the experimental structural models proposed in previous studies, forming [C-(Na-)-A-S-H] and [C-(K-)-A-S-H] gels reinforced with hydroxyl- and epoxy-functionalized reduced graphene oxide (rGO) lattices. The simulations reveal that interfacial bonding and elastic properties are strongly governed by the type of rGO functionalization. Hydroxyl-functionalized rGO nanosheets enhance proton mobility and stabilize the alkali C-A-S-H phase through the formation of strong covalent bonds with AlO₄ tetrahedra, whereas epoxy-functionalized rGO structures mainly rely on weaker hydrogen-bond interactions. In addition, Na-based nanocomposites showed greater enhancements in elastic properties and stronger ionic interactions compared to their K-based counterparts, highlighting the influence of alkali type on structural performance. Thus, the C-Na-A-S-H phase achieves improvements of ∼69% (dry) and 23% (hydrated) in Young's modulus, and 96% and 26% in bulk modulus. In comparison, the C-K-A-S-H phase shows increases in Young's modulus of ∼74% and 15%, and in bulk modulus of 85% and 13%, respectively, emphasizing the strong reinforcing effects of rGO functionalization. In summary, both hydroxyl- and epoxy-functionalized rGO act as effective reinforcing agents, significantly improving the structural integrity and mechanical performance of alkali-activated slag (AAS)-derived gels relative to conventional C-S-H-based nanocomposites.