Abstract
Calcined magnesia in a designed formulation was prepared with magnesite tailings below 1100°C to compensate for the autogenous shrinkage of steam-cured Portland cement and fly ash pastes with low water/binder ratios. The morphology and hydration properties of the light calcined magnesite tailings (LCM) were studied by field-emission source scanning electron microscopy (FESEM) and isothermal calorimetry. The hydration of magnesium oxide in paste and the microstructure of the paste were determined by thermogravimetric and differential thermal analysis, mercury intrusion porosimetry, FESEM and backscattered SEM. The results show that the hydration activity of LCM can be easily designed by regulating the calcining temperature. Both early age (7 d) and later age (90 d) autogenous shrinkage of steam-cured cement paste could be partially compensated when adding 4 wt% LCM prepared at 850°C (M85), probably due to the locally restrained continued slow hydration of magnesium oxide in M85.
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