Effect of Admixtures on Tensile Behavior of Fiber Reinforced Cementitious Composites

To reduce the material cost and understand the modification effects of admixtures on the tensile properties of polyvinyl alcohol fiber-reinforced engineered cementitious composites (PVA-ECCs), PVA-ECCs were prepared with different mass percentages of silica fume(SF), fly ash(FA) and metakaolin (MK) for replacement of cement. Then, tensile tests were carried out to study the tensile properties of the PVA-ECCs before and after modification, including the ultimate tensile strain, the initial cracking load, the ultimate tensile strength, and the crack development. Furthermore, the influence mechanisms of the admixtures were discussed on the basis of the experiment. The results show that the initial cracking load and the ultimate tensile strength of the composite modified by 65.0% of FA were decreased by 25.5% and 26.0%, respectively,but the deformation ability was twofold enhanced. In addition, fly ash improved the crack width and crack distance in the composite, causing the multiple cracking phenomenon happened more easily in the FA modified composite. For the composite admixed with 50.0% of FA and 15.0% of SF compound, the crack width decreased; however, the deformation ability was increased by 7.6% compared to the composite admixed with 65.0% of FA. When MK was incorporated into the composite, the modified materials had better deformation abilities. For the composites with the incorporation of FA, SF and MK and a moderate fiber volume fraction of 2.0%, an ultimate strain exceeding 2.0% as well as an ultimate strength of 3.99 MPa was achieved. In addition, the material exhibited a high ductility and multiple cracking characteristic. The cracks were controlled well by the material itself, in which the maximum crack width in saturation state was less than 175 m and the average crack width was less than 115 m.