Multiscale Response Mechanisms of C–S–H Gel to Self‐Reaction Growth and External Metal Cations

ABSTRACT

The molecular behaviors of C–S–H is of significance to the micro‐/macro‐performances of sustainable cement‐based materials, while their quantitative correlation spanning from molecular to macro is still much elusive. Given that C–S–H gel commonly encounters self‐reaction growth and external metal cations attack (Na ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ , and Al ³⁺ ), this study takes it as a model to investigates its multiscale response mechanisms in terms of molecular structure, microstructure, and micro‐/macro‐mechanical properties, analyzing weightings between multiscale factors. Results show that the crystallinity degree increases with self‐reaction growth age, accompanied by water removal, conversion to OH ⁻ , and OH ⁻ dissociation. Monovalent metal cations enhance C–S–H gel compactness mainly via surface adsorption and its induced agglomeration, whereas multivalent metal cations exhibit both physical and chemical effects, manifested as ion intercalation affecting the molecular interlayer spacing. Notably, the weight of the interlayer spacing of C–S–H, a key molecular‐level feature, on the splitting tensile strength is far greater than that of the mean chain length of C‐S‐H, and even exceeds those of porosity and bulk density. This confirms the importance of molecular interlayer bonding within C–S–H gel for its macroscopic tensile properties.