Use of high strength, high ductility engineered cementitious composites (ECC) to enhance the flexural performance of reinforced concrete beams

This paper investigated the flexural performance of reinforced concrete beams strengthened with high strength, high ductility engineered cementitious composites (HSHD-ECC). A total of seven reinforced concrete (RC) beams, including one control and six strengthened, were prepared and tested. The test variables included thickness of ECC layer and longitudinal reinforcement ratio. The test results showed that HSHD-ECC can be an ideal construction material for improving the flexural performance of reinforced concrete beams. For the failure mode, localized cracking was not observed in the beams with ECC layer even when the ultimate loading was reached, instead of that, multiple micro-cracks appeared in tensile zone of beams due to the high ductility of ECC. In term of flexural performance, the use of ECC layer to strengthen reinforced concrete beams can not only improve the cracking load, yield load and ultimate load of RC beams, but also improve the ductility and energy absorption capability. Moreover, the ECC layer shows superior synergistic performance with steel bars in tension zone and normal concrete in compression zone of RC beams, and as a result, they have enhanced load-bearing capacity. Based on the equilibrium condition between axial force and bending moment, a simplified method for predicting the flexural capacity is derived. The average ratio of the predicted flexural capacity to the experimental ones of the strengthened RC beams was 0.94 with a coefficient of variation of 0.03.