Direct shear behavior after elevated temperature exposure of epoxy-coated carbon textile-reinforced mortar (TRM) modified with different types of microfibers

In this study, direct shear behavior after exposure to high temperatures of epoxy-coated carbon textile-reinforced mortar (TRM) modified with different types of microfibers was investigated. Three primary test parameters were examined: elevated temperature levels (200 degrees, 250 degrees, and 300 degrees C); different microfiber types (polyvinyl alcohol (PVA) fibers, steel fibers, amorphous metallic (AM) fibers, and hybrid fibers made up of steel and PVA fibers); and heating time periods (2 and 4 h). In total, 88 direct shear test specimens were manufactured and tested. The direct shear tests were performed based on the FIP standard by employing test specimens with a pre-formed notch around the vertical middle plane. From the test results, it was observed that elevated temperatures significantly affected bond performance between the textile reinforcement and the mortar matrix, leading to degradation in shear mechanical properties of the test specimens. Under ambient temperature, the addition of microfibers to the mortar matrix was beneficial to most shear mechanical properties of TRM specimens, compared with TRM specimens without microfibers. However, the benefits of PVA fibers were significantly diminished at elevated temperatures of 200-300 degrees C, while AM or steel fibers adequately maintained benefits at the same temperatures. Heating periods investigated in this study did not significantly affect the shear behavior of the TRM specimens. In addition, an analytical model to predict the ultimate shear stress of TRM specimens with and without microfibers (steel or AM fibers) was proposed, and the prediction results agree with the experimental results.