Mechanical, durability, and microstructure properties of geopolymer concrete with nano fly ash and nano slag: a review

Abstract

Geopolymer concrete is a sustainable alternative to ordinary Portland cement concrete. However, challenges remain regarding its mechanical performance, durability, and microstructural stability under various exposure conditions. This review examines the influence of nano fly ash (nFa) and nano slag (nSg) on the mechanical properties, durability, and microstructural characteristics of geopolymer concrete, based on strength tests, ultrasonic pulse velocity, water absorption, permeability, and SEM, FESEM, and XRD analyses. The reviewed findings indicate that nFa can improve compressive, splitting tensile, and flexural strengths by up to 40 %, 56 %, and 25 % respectively, while nSg has been reported to enhance these properties by up to 59 %, 73 %, and 79 %, respectively. Both nanomaterials contribute to matrix densification, pore refinement, and reduced permeability, thereby improving durability performance. Furthermore, the formation of a compact geopolymer gel structure enhances the interfacial transition zones while XRD observations indicate the development of reaction products such as N-A-S-H, C-S-H, and C-A-S-H gels. However, the findings highlight a significant research gap regarding the combined use of nFa and nSg, particularly with respect to the long-term durability of nSg-based and hybrid nano-modified geopolymer systems beyond 90 days. Future studies should focus on optimizing nanoparticle dosages, dispersion methods, and curing regimes, as well as experimentally validation the potential synergistic effects of combining nFa and nSg for sustainable geopolymer concrete applications.