Investigation on the reinforcing of cementitious materials by nano-hydroxyapatites

The brittleness of cement-based materials is a major obstacle to application in large-scale engineering projects. The structure of natural biological skeletons has inspired research into toughening cement. Here, we report a strategy for reinforcing cementitious materials by controlling its microstructure through two types of nano-hydroxyapatite (HAP). This strategy includes improving the dispersion of nano-HAP using polycarboxylic acid, studying the dosage of composite nano-HAP to enhance the toughness of cement-based materials, and synergistically analyzing the mechanism of action of nano-HAP using a multi-scale research framework. We found that when the content of modified nano-HAP was 0.5%, the bending strength of the specimens increased by 55% and 22% at 3d and 28d, respectively, while the compressive strength remained unchanged. Compared to ordinary cement hydration, nano-HAP drives the ordered growth of calcium hydroxide crystals inside the cement paste, leading the formation of a 'brick-mud' microstructure that alters the direction of crack propagation.