Multi-scale effects of tensile properties of lightweight engineered geopolymer composites reinforced with MWCNTs and steel-PVA hybrid fibers

In this paper, the effects of functionalized multi-walled carbon nanotubes (MWCNTs) and hybrid fibers on the flowability, tensile properties, failure modes, and microstructure of lightweight engineering geopolymer com-posites (LW-EGC) were discussed. The results showed that functionalized MWCNTs and hybrid fibers have a negative effect on the flowability of the LW-EGC. The tensile properties of the LW-EGC reinforced by PVA fibers were significantly improved by the functionalized MWCNTs. Compared with LW-EGC-R, the ultimate stress, strain, and strain energy density of LW-EGC-M2 increased by 5.67%, 155.78%, and 151.14%, respectively. The hybrid fiber has large volume fraction and high elastic modulus, which can effectively improve the tensile strength, ductility and crack control ability of LW-EGC. As per results, the optimal proportion of hybrid fibers was 0.15% functionalized MWCNTs, 2.5% PVA fiber, and 1.0% steel fiber. The microscopic observation revealed that the functionalized MWCNTs and hybrid fibers mainly played a role in improving the matrix and bridging cracks such that the LW-EGC exhibited good ductility, tensile strength, and multiple cracking behaviors. This study provides a reference for the design of LW-EGC reinforced by functionalizing MWCNTs and hybrid fibers and further explores the mechanisms of multi-scale reinforcement of LW-EGC.