Influence of Superhydrophobic Coating on the Water Resistance of Foundry Dust/Magnesium Oxychloride Cement Composite

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.

Water-to-Cement Ratio of Magnesium Oxychloride Cement Foam Concrete with Caustic Dolomite Powder

“…Since the m MC in MgCl 2 -H 2 O was the product of the m Br and P, Equations (14) and (20) were substituted into Equation (19) to obtain…”

“…Dolomite calcinated at a lower temperature may generate calcination products of MgO with CaCO 3 [13]. The MgO content in dolomite is one-third of that of magnesite; therefore, the mechanical performance of MOC prepared with dolomite raw material is poor [14], especially magnesium oxychloride cement foam concrete (MOCFC) made from porous material [15]. Dolomite has already been tested as a raw material for producing MgO-based cements such as magnesium oxychloride cement [16], magnesium oxysulfate cement [17] and magnesium phosphate cement [13].…”

“…However, the impurity mass content of bischofite can be 2% or more; see Table 1. The strength of MOC can be reduced with the introduction of waste [14]. The MgCl 2 used in the laboratory or small amounts of MgCl 2 used to study MOC material are obtained as high-purity raw materials [23,24], and some errors may be involved in practical industrial applications when an impure raw material is used [25].…”