Multi-Layered Calcium Silicate Hydrate-Based Composites: A Nacre-Mimetic Design for Ultra-High Toughness

Cement-based materials are the most extensively utilized artificial material in the world. The low toughness of cementitious materials has long been a significant constraint in the development of modern concrete, limiting its performance in critical infrastructure applications. As the primary hydration product, calcium silicate hydrate (C-S-H) determines the mechanical properties of cementitious materials, in which optimizing C-S-H presents a promising avenue for toughness enhancement. In this work, a nacre-mimetic design strategy is employed to develop a high toughness C-S-H composite, achieved by the arrangement of inorganic C-S-H "brick" alternated with polyvinyl alcohol (PVA) "mortar". The unique hierarchically soft/hard structure significantly improved the mechanical properties of C-S-H composite, showcasing a substantial improvement on tensile strength, ductility and toughness by 1-2 orders of magnitude compared with fiber/polymer reinforced cementitious composites, especially reaching ultra-high toughness (20.01±3.64 MJ m^-3), which outperforms nacre by a factor of over ten and exhibits the highest performance among reported C-S-H-based materials. The nacre-mimetic C-S-H composite displayed exquisite interface and toughening mechanism revealed by density functional theory (DFT), molecular dynamics (MD), and finite element method (FEM) simulations. These findings provide a prospect for toughening cement-based materials, and broaden the potential applications in advanced functional composite systems.