Lightweight Calcium–Silicate–Hydrate\nNacre with High Strength and High Toughness

Low flexural strength and toughness have posed enduring\nchallenges\nto cementitious materials. As the main hydration product of cement,\ncalcium silicate hydrate (C–S–H) plays important roles\nin the mechanical performance of cementitious materials while exhibiting\nrandom microstructures with pores and defects, which hinder mechanical\nenhancement. Inspired by the “brick-and-mortar” microstructure\nof natural nacre, this paper presents a method combining freeze casting,\nfreeze-drying, in situ polymerization, and hot pressing to fabricate\nC–S–H nacre with high flexural strength, high toughness,\nand lightweight. Poly(acrylamide-<i>co</i>-acrylic acid)\nwas used to disperse C–S–H and toughen C–S–H\nbuilding blocks, which function as “bricks”, while poly(methyl\nmethacrylate) was impregnated as “mortar”. The flexural\nstrength, toughness, and density of C–S–H nacre reached\n124 MPa, 5173 kJ/m<sup>3</sup>, and 0.98 g/cm<sup>3</sup>, respectively.\nThe flexural strength and toughness of the C–S–H nacre\nare 18 and 1230 times higher than those of cement paste, respectively,\nwith a 60% reduction in density, outperforming existing cementitious\nmaterials and natural nacre. This research establishes the relationship\nbetween material composition, fabrication process, microstructure,\nand mechanical performance, facilitating the design of high-performance\nC–S–H-based and cement-based composites for scalable\nengineering applications.