Mechanical properties of sprayable ultra-high ductility magnesium phosphate cement -based composites

Abstract

With the aim to investigate the mechanical properties of sprayable ultra-high ductility magnesium phosphate cement-based composites (UHDMC), the effects of starch ether content, water-solid ratio, quartz powder-binder ratio, borax content, fly ash (FA) content and volume content of polyvinyl alcohol (PVA) fibers on the build-up thickness, compressive strength and tensile properties were studied. The mechanism about the change of mechanical properties was explained by Mercury Intrusion Porosimetry (MIP) test. The results showed that the optimum mixture proportion suitable for sprayable UHDMC was as follows: M/P of 4, starch ether content of 0.15%, water-solid ratio of 0.14, quartz powder-binder of 0.3, borax content of 8%, FA content of 40% and PVA content of 2%, presenting the compressive strength of 35.9 MPa, the ultimate tensile strength of 3.7 MPa and the ultimate tensile strain of 4.1%. A linear relationship was established between pore structure parameters and mechanical properties. The macropores and capillary pores had great influence on the compressive strength, while transition pores mainly affected the ultimate tensile strength. Moreover, similar porosity and pore size distribution were presented between the sprayed and cast UHDMC under the optimum mixture proportion.