Role of Glucose as Retarding Agent of Magnesium Phosphate Cement

Magnesium phosphate cements (MPCs) find application as alternative inorganic binders in construction, for crack repair and recycling of hazardous wastes. For the most common formulation, setting occurs through the reaction in water between magnesium oxide and potassium dihydrogen phosphate. The products include MgKPO4·6H2O (MKP) and an amorphous phase. Their use is somehow limited by the short working time and excessive release of heat. In this work, glucose has been introduced in the formulation of MPC to extend the setting time and modulate the rate of heat evolution. This can be considered an inexpensive and sustainable solution. The mechanism of action of the additive has been studied by investigating the reaction with isothermal conduction calorimetry, whereas the microstructure and phase composition of the obtained cements have been studied with scanning electron microscopy and X-ray powder diffraction, respectively. Results indicated that the additive influenced the reaction path thanks to the interaction at the molecular level with the dissolution process of magnesium oxide, as well as with the nucleation and growth of MKP. This has been confirmed by the changes induced in the size and shape of MKP crystals observed after the experiments conducted on diluted systems.