Abstract
In this work, magnesium oxychloride cement (MOC) was used to realize the resource use of foundry dust (FD). Portland cement (PC)-based superhydrophobic coating was prepared on the surface of FD/MOC composite to improve the water resistance of the composite. First, the FD/MOC composites with different contents of FD were prepared. The phase structure of the composite was analyzed using X-ray diffraction (XRD). The microstructure of the cross-section and surface of the composite was observed using field emission scanning electron microscope (FE-SEM). The mechanical properties of the FD/MOC composites with different FD contents at different ages were tested and analyzed. Secondly, the superhydrophobic coating was prepared on the surface of MOC composite using silane/siloxane aqueous emulsion as the hydrophobic modifier, PC as the matrix and water as the solvent. The microstructure and chemical composition of the PC-based superhydrophobic coating were tested and analyzed. The results show that FD can significantly improve the early strength of the FD/MOC composite. The 28-day compressive strength of the FD/MOC composite decreases with increasing FD content. When the FD content is 30%, the 28-day compressive strength of the FD/MOC composite is as high as 75.68 MPa. Superhydrophobic coating can effectively improve the water resistance of the FD/MOC composite. The softening coefficient of the FD/MOC composite without superhydrophobic coating is less than 0.26, while that of the composite modified by superhydrophobic coating is greater than 0.81.
Highlights
Magnesium oxychloride cement (MOC) was invented by French scientist Sorell and belongs to the category of special cement [1,2,3]
We found that the silane/siloxane-based surface modification method was ineffective for MOC
Where I is the softening coefficient; R0 is the compressive strength of the foundry dust (FD)/MOC composite before soaking in water; R1 is the compressive strength of the FD/MOC composite after soaking in water for 7 days
Summary
Magnesium oxychloride cement (MOC) was invented by French scientist Sorell and belongs to the category of special cement [1,2,3]. Materials 2020, 13, 3431 acid, phosphate, fly ash, rice husk ash, or composite modifier into the MOC [2,7,8,9] These additives usually reduce the strength of MOC, which is not conducive to the resource use of industrial solid waste. The method of adding water-resistant additives will no longer be applicable This is because the strength of MOC has been reduced when introducing waste into MOC [2,7,8,9]. When MOC is combined with waste, it is necessary to use other methods which have no adverse effect on its strength to improve its water resistance. To the best of our knowledge, no studies have reported on the use of superhydrophobic coatings to improve the water resistance of MOC
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