Exploring microstructure development of C-S-H gel in cement blends with starch-based polysaccharide additives

Calcium silicate hydrate (C-S-H) governs the binding of cement-based materials, influencing various properties through its microstructure. However, understanding C-S-H's microstructure development and morphological evolution mechanisms remains incomplete. This study systematically investigated the microstructure development of both outer and inner C-S-H gel in real cement pastes using high-resolution scanning electron microscopy. For the first time, we reported the evolution of outer C-S-H from one-dimensional needle-like morphology to three-dimensional honeycomb-like morphology after reaching the maximum heat flow, involving interconnection between adjacent C-S-H needles and micro-assembly of bonded structure. Inner C-S-H, formed in confined spaces, mirrors outer C-S-H morphology evolution patterns, but with more distinctive deformation and compaction at later stages. A starch-based polysaccharide additive, temperature rise inhibitor (TRI), was then used to regulate cement hydration and C-S-H precipitation. With distinctive exothermic processes and pore solution environments, we validated the C-S-H morphology-calcium concentration correlation. However, our findings challenge calcium concentration as the sole determinant of C-S-H morphology change; it appears rather as a consequence of increasing degree of cement hydration.