Improvement in water resistance of magnesium oxychloride cement via incorporation of dredged sediment

Dredged sediment (DS) derived from dredging operations poses a potential threat to the ecological environment. The proper disposal and utilization of DS remains a challenge. In this study, magnesium oxychloride cement (MOC) was adopted as a sustainable carrier for effective recycling of DS. MOC pastes incorporated with DS or calcined dredged sediment (CDS) were subjected to multiscale characterization techniques to investigate the feasibility of combining MOC with DS. DS/CDS were found to enhance the water resistance of the MOC pastes despite the negative influence of dilution on their mechanical properties. Strength retention tests revealed that the compressive strength retention rate of MOC pastes blended with 10%–40% DS positively correlated with the DS content, and the modification induced by DS was superior to that by CDS. Multiple microscopic approaches were adopted to mechanistically elucidate the modification of MOC by DS/CDS. The results revealed that the addition of DS increased the porosity of the modified MOC pastes, thereby providing more channels for water intrusion. Interestingly, the improvement in the water resistance of the MOC paste was sustained with increasing DS content. Insoluble gel-like phases were observed throughout the MOC substrate and acicular phase 5 crystals, which impeded the intrusion of water and consequently improved the water resistance of the MOC pastes. Thermogravimetric and energy-spectrum analyses confirmed that the insoluble phases were composed of an amorphous Mg–Al–Si–Cl–H gel. The development of this MOC paste demonstrates a promising strategy for improving the water resistance of MOC products and alleviating the burden of DS on the environment.