Understanding hydration process and paste viscosity evolution of magnesium potassium phosphate cement

In this study, based on the convenient sampling of rheological testing system, the hydration of MKPC and its relationship with paste viscosity evolution were investigated. Results indicated that under the destruction of shearing, paste viscosity is highly related to the fast precipitation of K-struvite. Amorphous and intermediates, mainly newberyite, cannot effectively agglomerate particles and thus fails to increase the paste viscosity. Three K-struvite formation paths produce three viscosity peaks in time-dependent torque curves: the first one is transformed from newberyite; the second one is directly generated through the reaction among raw materials; and the third one is crystallized from amorphous phase. Massive potassium-deficient magnesium phosphate amorphous form prior to all other hydrates, which act as intermediate but also the final hydrate coexist with Kstruvite, shows endothermic and acidizing characteristics during the precipitation, but opposites characteristics in the subsequent process of crystallization from amorphous to K-struvite.