Interfacial properties of geopolymer mortar and concrete substrate: Effect of polyvinyl alcohol fiber and nano-SiO2 contents

Geopolymer mortar, which is a new type of green cementitious material, can be used as an alternative to traditional cement mortar in the repair and reinforcement of defective structures, and the addition of polyvinyl alcohol (PVA) fiber and nano-SiO2 (NS) can improve the interfacial properties of geopolymer mortar and concrete substrate. In this study, the influence of PVA fiber and NS on the shear characteristics of geopolymer mortar and concrete substrate was studied through a double-interfaced shear experiment. Based on the results of this experiment, surface-based cohesive contact was utilized to analyze the shear behavior of the PVA fiber and NS-reinforced geopolymer mortar and concrete substrate, and a shear toughness evaluation method was proposed to further evaluate the shear behavior. The results indicated that the optimal bond strength was achieved when the geopolymer mortar was mixed with 0.8% PVA fiber and 2.0% NS; compared with geopolymer mortar without PVA fiber and NS, the bond strength increased by 34.76% and 13.78% respectively. The numerical modeling results were consistent with the mechanical mechanism and damage mode of the experimental results, which indicated that surface-based cohesive contact could accurately describe the shear characteristics of a double-interfaced shear specimen. Using the proposed shear toughness evaluation method, it was found that when the PVA fiber content was 0.8%, f(eq), gamma(p), and T-p reached their respective maximum values with increment of 0.69, 0.61 and 1.66, respectively, indicating that the toughening effect of geopolymer mortar was optimal. The shear toughness of geopolymer mortar first rose and then declined with the increase of NS content. The PVA fiber and NS had a positive synergistic effect on the shear toughness of geopolymer mortar and concrete substrate.