Controlling Strength and Ductility of Strain-Hardening Cementitious Composites by Nano-Engineering

Considering the hierarchical nature of cracking in cement composites, multi-scale reinforcement bears the potential to enhance the fracture performance of fibre-reinforced cementitious composites. This study shows how nanoscale cellulose filaments (CF) can be used as a novel tool for tailoring the properties of strain-hardening cementitious composites (SHCC) towards improved strength and ductility. SHCC with fly ash-to-cement ratio of 1.2 and incorporating CF at rates 0.03, 0.05 and 0.10% of cement mass were developed following the micromechanical principles for pseudo-ductile cement composites. Results indicate that the incorporation of CF in SHCC allows nanoengineering matrix and interface properties by increasing matrix elastic modulus and imparting a significant slip-hardening effect. Consequently, higher complementary energy and lower crack tip toughness were obtained, thereby leading to enhanced ductility as also validated by tensile and flexural tests. As such, the incorporation of CF enhanced composite tensile strength by up to 23% and increased the ultimate strain capacity in tension by up to 26% and the deflection capacity in flexure by up to 36%. Therefore, nano-engineering SHCC with CF yields multi-scale composites with higher ductility without necessarily increasing the volume fraction of PVA fibres while exhibiting higher strength without necessarily increasing the binder content.