Nacre-inspired geopolymer cement composite with high flexural strength

The most effective approach to enhance the strength of cementitious materials is by manipulating their structure at the nano and microscale levels. However, although long-pursued, current nano-engineering methods are still challenging or impractical for large-scale applications. Here, we introduce a facile method to nano-engineer geopolymer cement materials with microstructure resembling that of nacre, thereby possessing superior tensile/flexural properties. The pivotal step in our approach was meticulously employing mica microplates and cellulose nano-fibers to guide the layer-by-layer, nacre-like assembly of metakaolin, the raw material of geopolymer cement. Then, through straightforward alkali-activation and lamination techniques, we successfully created nacre-like geopolymer cement composites at the centimeter scale, as extensively validated by microscopy, spectroscopy, and thermogravimetric characterization. Mechanical testing showed that the developed nacre-like geopolymer composites possessed a flexural strength of similar to 38 MPa-10-20 times higher than that of conventional cementitious materials-while maintaining similar stiffness and hardness to conventional geopolymer cement. Further microscopy analysis demonstrated that the superior strength of the composites stemmed from the ordered assembly of clay and cellulose building blocks within the geopolymer matrix, endowing a dense microstructure with crack bridging and deflection capabilities. Given the outstanding mechanical performance of the nano-engineered composites and the feasibility of scaling up the method, these findings represent a significant advancement in crafting novel cement-based materials with unparalleled performance.