Fly ash(FA)was applied to modify magnesium phosphate cement(MPC)mortar by replacing a portion(≤30％)of magnesium oxide,and the reactivity and reaction mechanism of fly ash in the MPC system were investigated,the effect of FA on the physico-mechanical properties and microstructure of MPC was analyzed.The results showed that FA embodied complex physical and chemical effects in the MPC system.The spherical fly ash particles have the function of rolling bearings,which optimizes the fluidity of MPC;FA not only fills the micropores and microc-racks of MPC,but also exhibits the'nucleating effect',which provides nucleation sites for the hydration of MPC,promotes the generation of the hydration product-struvite(MgNH4PO4·6H2O),densifies the microstructure and improves the mechanical properties of MPC.In addition,after the activation of hydration heat,Al2O3 from FA would participate in the reaction and generate amorphous aluminum phosphate gels.
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