| Summary: | 碩士 === 逢甲大學 === 土木工程學系 === 105 === Since Taiwan is located at the junction of the tectonic plates with rugged terrain, frequent natural disasters often lead to the damage of structures. Post-installed rebar technique is one of the most common methods to repair and reinforce concrete structures. Although the commercially available anchorage adhesives provide high strength, they are unable to resist the high temperatures associated with fire. Therefore, the main purpose of this study is to evaluate the feasibility of using fly ash cement mortar as the substitute of commercial anchorage adhesives by means of experimental tests. First, six different admixtures of cement mortar were mixed according to the proportion design methods illustrated in the literature. The best admixture was determined by examining the results of flow test and compression test. Then the fire resistance of this admixture was investigated and the appropriate procedures to install rebars was established. The pullout specimens were prepared by implanting # 3 steel bars into concrete cylinders with depths of 9 cm or 12 cm. Pullout tests were conducted after the specimens were heated to 200℃, 400℃ or 600℃. The feasibility assessment was carried out by comparing the pullout test results of this study with those of rebars installed with commercial adhesives from other researchers. The test results indicate that the cement mortar admixture, with water-cement ratio of 0.36, 1% polycarboxylate high-performance water-reducing agent and 15% fly ash, provides the best workability and highest strength. This admixture could retain a residual compression strength higher than the concrete strength even after being heated to 600℃. The pullout strengths of the rebars installed with the cement mortar maintain at a certain level for the heating temperature below 400℃. Although the bonding strength seems to be lower than that of rebar installed with commercial adhesives, it has reached the yield strength of steel bars. In addition, the pullout strength of rebars installed with cement mortar shows a reduction after being heated to 600℃, but the decline is more moderate than the rebars installed with commercial adhesives. After the comprehensive evaluation, we consider the fly ash cement mortar containing water-reducing agent may be used as anchorage adhesive. The steel bars post-installed with the proposed cement mortar could achieve an acceptable bonding effect as long as the users select proportional aggregate carefully, mix all the materials evenly, and use the admixture as soon as possible.
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