Experimental Study on Rheological Properties and Grout-Rock Shear Strength of Graphene Oxide-Fly Ash Cement-Based Grouting Material

Grouting is one of the effective methods to reinforce the fractured rock mass, and the performance of grouting material directly influences the effect of grouting reinforcement. This paper explores the synergistic effect of graphene oxide (GO)-fly ash (FA) for a green cement-based grouting material. The effects of GO, FA, and GO-FA synergies on the fluidity of cement-based grouts and on the flexural and compressive strength of grouting stones were systematically investigated. Furthermore, the GO-FA grout was subjected to a rheology test to study the influence of GO and FA proportion and time effect on the rheological properties of the grout. GO-0, GO-3, and GO-FA were selected for grouting reinforcement of sandstone fracture surfaces, and direct shear tests of grouting materials and grout-rock interface under different normal stresses were carried out using a self-made shear box. Their shear mechanical properties were analyzed to explore the relationship between the strength of the grouting materials and the shear strength of the grout-rock interface. Through SEM and XRD testing, the microstructure and mineral composition of the grout-rock interface were analyzed, and the microactivity mechanism of the grout-rock interface reinforced by GO-FA grouting was revealed. The results showed that: The fluidity of the grout with 0.03% GO and 20% FA was only 8.2% lower than that of pure cement grout. Compared to the strength of the pure cement grouting stone, the flexural and compressive strengths of the GO-FA grouting stone at 28 d were increased by 28.5% and 30.4%, respectively. The GO-FA grout belonged to Binham fluid, and the rheological parameters of the grout showed an exponential function with time. In addition, GO-FA grouting had the best reinforcement effect on the fractured rock mass. Compared with GO-0 grouting, GO-FA grouting significantly increased the peak shear strength and residual strength of the grout-rock interface, resulting in better resistance to deformation and a 19.8% increase in cohesion. The microstructural model of the grout-rock interface agreed well with the Xie model. In addition to hydration products such as calcium hydroxide and calcite, the interface also produced small amounts of potassium feldspar and kaolinite, as well as the new mineral component calcite.