Gas Diffusivity Tunable Magnesium Phosphate Cements With Improved Water Resistance

Magnesium phosphate cements (MPC) are attractive for cementitious repairing and sealing applications because of their rapid setting, high early strength and excellent bonding ability. However, the poor water resistance and unknown diffusivity for releasable moisture (gas) are to be improved or investigated in the thermoelectrical fields. Here the calcined ball clay (BC) and hydrated silica (HS) were incorporated into MPC to improve water/moisture stability as well as retain tunability for the MPC gas‐diffusible sealing materials/layers. The hydration behavior, dimensional shrinkage, gas diffusion, mechanical and structural properties of the composite MPCs were investigated by testing flowability, setting time, pH/conductivity and pore‐size distribution as confirmed by XRD, SEM, aperture analysis, strength measurement and in‐situ stereomicroscopic observation. Results show that both BC and HS effectively restrain the MPC volume change and enhance the water resistance. The BC increases gas diffusion coefficient from 1.26 × 10 −6 to 2.33 × 10 −7 m 2 /s, whereas the HS decreases diffusion coefficient to 9.71 × 10 −7 m 2 /s, suggesting tunability of gas diffusion by external incorporation. Mechanism study reveals that the BC works as dilution, microfilling and particle‐packing fillers, whereas the HS promotes early hydration and formation of M–S–H, refines pore structures, densifies MPC matrix, and strengthens the interparticle bonding. It was demonstrated that both BC and HS are effective for improving moisture stability of MPC, while HS is more advantageous over simultaneous enhancement of water resistance, dimensional stability and moisture diffusible sealers as required by electrothermal devices.