Strength Recovery Effect of Bisphenol A Epoxy Resin E44 on Rock Masses with Various Crack Widths

As a desirable bonding and repair material, epoxy resin combined with other materials is widely used in civil engineering, but its application in underground rock engineering is still limited compared with the wide use of cement grout. To explore and optimize the effect of room temperature-cured bisphenol A epoxy resin E44 on the strength recovery of rock samples with cracks of various widths, the uniaxial compressive strength (UCS) of epoxy resin was studied and the mass ratio of the curing agent to epoxy resin ( $k_{CE}$ ) was adjusted and optimized. On this basis, the UCS of the selected epoxy resin was investigated by adding diverse amounts of ethanol so that the ratio corresponding to the repair material with better mechanical properties could be selected. Artificial cracks of various widths were filled with the optimized materials, and then, a UCS test was conducted on the repaired rock samples to evaluate the effect on strength recovery and compare it with that of ultrafine Portland cement (UPC). The results show that the UCS of epoxy resin stones increases when $k_{CE}$  ≤ 0.25 and decreases when $k_{CE}$  > 0.25, reaching a peak of 92.41 MPa. Furthermore, as the mass ratio of ethanol to curing agent and epoxy resin ( $k_A$ ) increases, the UCS increases to 94.65 MPa for $k_{CE}$  = 0.25 and $k_A$  = 0.01. The crack width influences the UCS of the repaired rock mass. With increasing crack width, the effect of epoxy resin on recovery continuously improves, whereas that of UPC shows the opposite trend. Compared with UPC, epoxy resin has an overwhelmingly greater effect on strength recovery. For instance, for a 3 mm-wide crack, the recovered UCS for 28 d epoxy resin is 83.48 MPa, with much larger peak strains, and the strength recovery rate ( $k_r$ ) is 77.55%; however, the $k_r$ of UPC is only 15.12%.

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