Regulating hydration and microstructure development of the foamed magnesium oxychloride cement composites by sodium citrate

To improve the water resistance, the foamed magnesium oxychloride cement (FMOC) composites were constructed using sodium citrate (SC) as a modifier by the physical foaming strategy. Through a universal testing machine, scanning electron microscope, X-ray diffractometer, and other methods, the properties of the composites before and after being soaked in water for 24 h were tested, while the performance mechanism was investigated. Compared with unmodified FMOC, the compressive strength of FMOC/SC was improved by 266 % to 4.31 MPa, while the softening coefficient was enhanced by 237 % to 0.83. These improvements can be ascribed to the transformation of rod-like phase crystal (5Mg(OH) 2 ·MgCl 2 ·8H 2 O) into gel-like phase crystal caused by induction of Mg 2+ chelation with SC, which attached to MgO surface, thereby delaying the hydration reaction and enhancing the water resistance of FMOC. The use of SC for FMOC significantly promotes its potential for application in wet environments.