Deflection hardening behaviour of ductile fibre reinforced magnesium phosphate cement-based composite

This study aims to develop the ductile fibre reinforced magnesium phosphate cement-based composite (DFRMC) to address the inherent brittleness of magnesium phosphate cement (MPC). An experimental program was conducted, in which the effects of fly ash substitute (FA) content, PVA fibre volume fraction (Vf), sand to binder mass ratio (S/B) and water to solid mass ratio (W/Solid) on the properties of DFRMC were investigated. The test results revealed that all DFRMCs, except for those with mix of FA content of 0%, 10% and W/B of 0.10, can exhibit deflection hardening behaviour accompanied by multiple fine cracks under bending. The new indexes, flexural strength gap (fg), deflection gap (Dg), and toughness gap (Tg) were introduced in this study to accurately evaluate the deflection hardening capacity. The developed DFRMC with FA content of 20%, Vf of 1.6%, S/B of 0.2 and W/Solid of 0.13 showed the superior deflection hardening capacity as compared to other DFRMCs. Meanwhile, a moderate compressive strength of about 40 MPa, nominal flexural strength of 7.60 MPa and a relatively high slump value (over 250 mm) can be achieved. Furthermore, the denser MPC matrix and rough PVA fibre surface of DFRMC were investigated by using the scanning electron microscope (SEM) method.