Performance of magnesium silicate hydrate cement modified with dipotassium hydrogen phosphate

Magnesium silicate hydrate (M−S−H) cement has been extensively studied in recent years. However, poor fluidity and large drying shrinkage restrict its application. To improve the fresh state and hardening properties, this study investigates the effect of dipotassium hydrogen phosphate (DKP) on the fluidity, setting time, rheological behaviour, compressive strength and drying shrinkage of magnesium silicate hydrate cement. The effect of DKP content on hydration reactions and hydration process was also investigated via pH measurement, XRD, FTIR and TG/DTG. The microstructural analysis was conducted using ESEM. The experimental results indicated that DKP presents a higher water reduction efficiency than sodium hexametaphosphate (SHMP) and can be used as a superplasticizer for magnesium silicate hydrate cement. The compressive strength of M−S−H cement was increased by the addition of DKP, especially at early ages. The maximum compressive strength for specimens containing DKP is 96 MPa at 56 days. Moreover, the cement with the addition of DKP exhibited lower drying shrinkage, and the drying shrinkage value was only 0.085% when a mortar with a water to cement ratio of 0.45 and sand to binder ratio of 3 is prepared. The addition of DKP was shown to improve performance of M−S−H cement for potential construction applications.