Effect of nano-Al2O3/epoxy resin composite on the shear strength recovery of fractured rock masses with various crack widths and SCA interfacial treatments

The mechanical properties of grout and the effect of the bonding between grout and the repaired material are the two main factors affecting the shear strength of the material. To study the effect of repairs carried out with nano-Al2O3/epoxy resin composite (NAEC) on the shear strength of rock masses, cracks with different widths and treatments by silane coupling agent (SCA) solutions with various surface treatment concentrations (kSCA) were considered. The mass percentage ratio of nano-Al2O3 in the composite (kAl) was optimized based on the obtained uniaxial compressive strength (UCS). The selected NAEC was used to fill cracks of different widths, and the bonding effect was analyzed using a bilateral shear strength test that effectively avoids the bending effect. Solutions with diverse kSCA values were used to treat the rock surfaces with the 3-mm-wide cracks. The results showed that the UCS of the NAEC tended to increase with increasing kAl when the mass ratio (kCE) of the curing agent to epoxy resin was 0.25. When kAl= 0.01, the UCS of the composite peaked at 97.82 MPa. With increasing crack width, the shear strength first increased and then decreased. When the crack width was 3 mm, the shear strength reached a maximum of 29.02 MPa. However, without nano-Al2O3, the shear strength was 23.66 MPa, and the shear strength of ultrafine Portland cement (UPC) material was only 8.37 MPa. With increasing kSCA, the shear strength tended to first increase and then decrease. For a kSCA of 2%, the shear strength reached a maximum of 39.40 MPa, corresponding to an increase of 35.8%. Nevertheless, the composite shear strength as degraded at 5% kSCA. In summary, the NAEC exhibited a sound bonding effect, SCA surface treatments effectively improved the shear strength, and the bonding shear strength was related to the crack width.