Experimental Investigations of the Bending Fatigue Performance of TRC-Strengthened RC Beams in Conventional and Aggressive Chlorate Environments

To study the fatigue performance of a reinforced-concrete (RC) beam strengthened with textile-reinforced concrete (TRC), a four-point bending fatigue test was conducted, in which the strengthening forms, reinforcement ratio, textile ratio, static load damage, and sustained load corrosion were considered. The results of this test show that TRC can modify the fatigue failure mode and significantly improve the fatigue life of RC beams. The strengthened beams exhibited better performance than the unstrengthened beams with regard to controlling cracks. TRC can increase the number of cracks and decrease the crack width in RC beams, and the strengthened beams exhibit an increase in midspan deflection that rapidly progresses, while the unstrengthened beams do not exhibit this progression. In terms of improving the fatigue life of beams, the single-sided strengthening form is shown to perform better than the three-sided form, and a beam with a high reinforcement ratio is superior to that with a low ratio. The textile ratio is also shown to influence the fatigue life of the RC beam: when the textile ratio is low, the strengthened and unstrengthened beams have nearly identical fatigue lives; however, when the ratio reaches a given value, the fatigue life of the strengthened beams increases with an increasing textile ratio. Also, TRC performs better when used to strengthen damaged beams, and the damage degree influences the fatigue life of a beam strengthened with TRC. However, the fatigue life of strengthened beams will be reduced if the static-damage degree is high. In addition, in a chlorate environment, corrosion or a sustained load acting alone reduces the fatigue life of strengthened beams, and the initial deformation generated by a sustained load also affects the fatigue life. The effect becomes more evident when corrosion and a sustained load are present concurrently. It was also found that corrosion weakens the bond between the TRC and the original concrete, resulting in damage to the interface between the TRC and the strengthened beams. The ratio of the realistic stiffness to the computed stiffness was proposed to judge the safety of the strengthened beams under a fatigue load.