Reactivity-controlled dual silicon sources drive C-S-H crystallization and property enhancement at low Ca/Si ratios

Reducing the Ca/Si molar ratio is critical for optimizing calcium silicate hydrate (C–S–H) materials and enabling the recycling of silicon-rich waste. However, achieving high-performance crystalline C–S–H at Ca/Si < 0.83 remains challenging. This study proposes and systematically investigates a dual-silicon-source strategy, employing both active and inert silicon sources to regulate hydrothermal synthesis. At Ca/Si = 0.6, experimental results demonstrate that increasing the active silicon source content from 0 % to 60 % enhances tobermorite crystallinity by 275 %, decreases thermal conductivity by 26 %, and improves compressive strength by 7.30 MPa. The optimal performance was obtained at a reactive silicon-to-calcium molar ratio of 1.0. These findings confirm that this strategy significantly enhances C–S–H crystallinity and material performance. Mechanistically, the higher reactivity of the active silicon source drives competitive calcium consumption, facilitating the formation of long-chain crystalline C–S–H. This approach demonstrates a scalable pathway for synthesizing high-performance C–S–H under low Ca/Si conditions, offering promising applications in optimizing C–S–H-based materials and the recycling of silicon-rich waste.