Effect of nano-silica on mechanical properties and microstructure of engineered geopolymer composites

Engineered geopolymer composites (EGC) are promising alternatives to highly ductile cement-based composites, whereas effectively balancing the strength and ductility of most developed EGC mixes is challenging. This study systematically evaluated the feasibility of incorporating nano-silica (NS) particles to address the problem of balancing strength and ductility in EGC, aiming to develop EGC with extraordinary mechanical properties. The relationship between microstructure and mechanical properties of NS-EGC was studied via X-ray computed tomography (XCT) and backscattered electron microscopy (BSEM) tests, to gain an in-depth understanding of the obtained properties. Results indicate that NS-EGC mixes with superior compressive and tensile behaviour were successfully fabricated based on micromechanics design theory. The optimal NS content and particle size were 1 % and 15 nm, where the resulting composite outperformed all proposed EGC in terms of compressive strength (94 MPa), tensile strength (9.17 MPa) and tensile strain capacity (9.06 %). The mechanical properties of NS-EGC were strongly dependent on the pore structure, fibre orientation and fibre dispersion, where these microstructural effects can be modified by NS. This study provides a new approach to optimising the strength-ductility balance of EGC through nano-silica incorporation, offering the potential for broadening the application of EGC in high-performance structural materials.