Effect of Low Nesquehonite Addition on the Hydration Product and Pore Structure of Reactive Magnesia Paste

Reactive magnesia cement is considered an eco-efficient binder due to its low synthesis temperature and CO₂ absorption properties. However, the hydration of pure MgO-H₂O mixtures cannot produce strong Mg(OH)₂ pastes. In this study, nesquehonite (Nes, MgCO₃·3H₂O) was added to the MgO-H₂O system to improve its strength properties, and its hydration products and pore structure were analyzed. The experimental results showed that the hydration product changed from small plate-like Mg(OH)₂ crystals to interlaced sheet-like crystals after the addition of a small amount of Nes. The porosity increased from 36.3% to 64.6%, and the total pore surface area increased from 4.6 to 118.5 m²/g. At the same time, most of the pores decreased in size from the micron scale to the nanometer scale, which indicated that Nes had a positive effect on improving the pore structure and enhancing the compressive strength. Combined with an X-ray diffractometer (XRD), a Fourier transform infrared spectrometer (FTIR), and a simultaneous thermal analyzer (TG/DSC), the hydration product of the sample after Nes addition could be described as xMgCO₃·Mg(OH)₂·yH₂O. When Nes was added at 7.87 and 14.35 wt%, the x-values in the chemical formula of the hydration products were 0.025 and 0.048, respectively. These small x-values resulted in lattice and property parameters of the hydration products that were similar to those of Mg(OH)₂.