Comparative Investigation of Effect of Borax and Sodium Gluconate Retarders on Properties of Magnesium Phosphate Cement

Retarder is an important component in magnesium phosphate cement (MPC), which plays a key role in adjusting the workability of the fresh paste. In this research, the effects of borax (BR) and sodium gluconate (SG) retarders on MPC properties, including workability, mechanical properties, and durability, were investigated comparatively. The hydration process, the phase assemblage, and the pore structure were analyzed based on microscopic tests such as hydration temperature, pH, XRD, and MIP. The results indicated that retarders could prolong the setting time, increase the fluidity, and promote the bond strength and the free-thaw cycle resistance. And the combined use of BR and SG retarders had a synergistic effect on improving the properties of MPC paste. The mechanism of action of BR and SG retarders was different: BR was effective in reducing the hydration rate, while SG was effective in improving the pore structure. These findings are expected to provide new insights for the theoretical research and engineering application of MPC retarders.