Four-point bending tests of ECC: Mechanical response and toughness evaluation

This work investigated the mechanical response of engineered cementitious composites (ECC) with high content fly ash by four-point bending tests, and a suitable method was recommended for the flexural toughness evaluation of ECC. The test variables were fiber volume fraction (for polyvinyl alcohol (PVA) fiber), fiber type (PVA and polyethylene (PE)), curing age (56d, 28d and 7d), water-to-binder ratio, sand-to-binder ratio and fly ash content. The results of the tests showed that the crack pattern, deflection-hardening behavior and energy dissipation capacity of ECC were mainly affected by fiber volume fraction, fiber type and curing age. The larger the proportion of fiber pulling out during crack bridging was, the higher the deflection and energy dissipation of ECC exhibited. The commonly used JSCE-SF4 method, ASTM C1609 method and post crack strength (PCS) method for evaluating the flexural toughness of fiber reinforced concrete were not applicable to evaluate the toughness of ECC, because the significant deflection-hardening behavior of ECC could not be considered. An improved method was proposed for flexural toughness evaluation of ECC materials, which included two modified indexes (equivalent initial flexural and post-peak flexural toughness index) and a new index (initial energy factor). The large deformation of ECC was taken into account and the determining the first crack point was eliminated in this new method.