Hierarchical crystallization under extreme conditions enables self-strengthening in cement hydrates

The intrinsic brittleness of cement-based materials is largely attributed to the disordered and porous microstructure of their primary binding phase, namely calcium silicate hydrates (C-S-H). Overcoming this limitation requires a fundamental shift in the structural organization of hydration products. In this study, we explore the hydration of Ca₃SiO₅ (C₃S) under extreme high-temperature and high-pressure (HTHP) conditions—up to 500 °C and 15 GPa—to induce a transformation from disordered C-S-H gels to hierarchically ordered nanocrystalline phases. This structural evolution yields remarkable mechanical enhancements, including a 490 % increase in indentation modulus, a 2300 % increase in creep modulus, and a 480 % increase in micropillar compressive strength. Through a combined experimental and molecular dynamics simulation approach, we demonstrate that these improvements are directly attributed to the formation of hydrous larnite (HL) and hydrous post-hatrurite (HPH), which form a hierarchical crystalline network. These crystalline domains confer superior stress resistance and effectively suppress crack initiation and propagation, enabling efficient dissipation of strain energy via self-reinforcing mechanisms. Our findings establish hierarchical crystallization under extreme conditions as a promising bottom-up strategy for the intrinsic reinforcement of cement hydrates, opening new avenues for the design of high-performance, next-generation cementitious materials.