Flexural performance of layered ECC-concrete composite beam

The pseudo strain-hardening behavior of fiber reinforced engineered cementitious composites (ECC) is a desirable characteristic for it to act as a substitute for concrete to suppress brittle failure. The use of ECC in the industry is, however, limited by its high cost. To achieve higher cost/performance ratio, ECC can be strategically applied in parts of a structure that is under relatively high stress. In this paper, layered ECC-concrete beams subjected to flexural load are investigated from both theoretical and experimental aspects. Four-point bending tests are performed on beam members with ECC layer at its tensile side. The application of ECC layer leads to increase in both the flexural strength and ductility, and the degree of improvement is found to increase with the ECC thickness. A semi-analytical approach for modeling the flexure behavior of layered ECC-concrete beams is also developed. In the model, the stress-crack width relation of both concrete and ECC are employed as fundamental constitutive relationships. The model and experimental results are found to be in good agreement with one another. Simulation with the model shows that when the ECC thickness goes beyond a certain critical value, both the flexural strength and ductility (reflected by crack mouth opening and crack length at ultimate load) will significantly increase. The critical ECC thickness is hence an important design parameter, and it can be determined with the theoretical approach developed in the present work.