Magnesium phosphate cement-based engineered cementitious composites with polyethylene fibers: Performance improvement and design method

Abstract

This study aims to improve the performance of magnesium phosphate cement-based engineered cementitious composites (MPC-ECC) and establish a systematic design method. The MPC-ECC with ultra-high ductility was prepared with the polyethylene (PE) fibers. The effect of the magnesium oxide to potassium dihydrogen phosphate mass ratio (M/P), quartz sand particle size (Sd), water to solid mass ratio (W/S), sand to binder mass ratio (S/B), fly ash (FA) content and fiber volume fraction (Vf) on the micro-mechanical properties and macro-mechanical properties of MPC-ECC were explored. The macro-mechanical properties of MPC-ECC with different curing temperatures and curing ages were also tested. And the SEM test was carried out to analyze the morphology of the MPC-ECC. The results showed that the ultimate tensile strain of MPC-ECC with optimal proportion can reach 7.1%. Even curing at −10 °C for 7 days, the ultimate tensile strain can reach 5.6%, and the compressive strength can reach nearly 20 MPa. And the microstructure is characterized by a highly dense morphology. Additionally, with the increase of M/P, the compressive strength of MPC-ECC increases, but the ultimate tensile stress decreases. The MPC-ECC with the Sd of 150–180 mesh shows significant strain hardening performance, and its ultimate tensile strain can exceed 5%. The large W/S is helpful to improve strain hardening performance, especially when the S/B is 0.2. In addition, when the FA content is 30% or 40%, the strain hardening performance of MPC-ECC is significant. The quantitative association model between ultimate tensile strain and pseudo strain-hardening indices was established. According to the association model, the design method of MPC-ECC was established, based on which the MPC-ECC with desired ductility can be realized. Meanwhile, the PSHσ and PSHJ are recommended to reach 2.15 and 25.1, respectively, at the same time for the MPC-ECC with ultimate tensile strain of above 3%.