Hydration behavior of magnesium potassium phosphate cement and stability analysis of its hydration products through thermodynamic modeling

Magnesium potassium phosphate cement (MKPC) is normally applied in civil engineering because of its short setting time and superior mechanical properties. This study investigates the hydration behavior and hydration products of MKPC influenced by molar ratio between magnesia and phosphate (M/P ratio) through thermodynamic method. Results show that the composition of ultimate hydration products are controlled by concentration of KH2PO4 and MgO, activity of water and pH value of solution. When M/P ratio is lower than 0.64, the hydration product is MgHPO(4)3H(2)O; When M/P ratio is between 0.64 and 0.67, the hydration products are MgHPO4 center dot 3H(2)O and Mg2KH(PO4)(2)center dot 15H(2)O. When M/P ratio is between 0.67 and 1.00, hydration products are Mg2KH(PO4)(2)center dot 15H(2)O and KMgPO4 center dot 6H(2)O; When M/P ratio is higher than 1.00, the hydration product is KMgPO4 center dot 6H(2)O together with unreacted MgO. This study also investigated the effect of additives, namely B(OH)(3), H3PO4, K2HPO4 and KH2PO4.