Effect of fly ash on mechanical properties of magnesium oxychloride cement under water attack

Abstract

As an eco‐friendly construction material, magnesium oxychloride cement (MOC) has attracted much research interest in recent decades, however, its mechanical properties degrade severely under water attack, which has prevented its wide application in engineering structures. As a widely used mineral waste, fly ash has been applied in civil engineering for decades. The active SiO2 in fly ash is considered to be conductive to improve the water resistance of MOC. In this paper, the influence of fly ash on the mechanical properties of MOC is investigated, especially when subject to water attack. First, the basic mix design of the MOC with a suitable combination of the molar ratios of MgO/MgCl2 and H2O/MgCl2 is developed, and the developed basic MOC mix is modified by adding fly ash to improve its water resistance. Second, the physical and mechanical properties of both the basic MOC and the fly ash modified MOC, such as compressive strength, Young's modulus, flexural strength cured at room temperature, and immersed in water for 28 days at room temperature (25°C) are determined. It is found that the incorporation of fly ash decreases the workability or fluidity, retards the setting time, but improves the compressive strength and water resistance of the MOC. The techniques of X‐ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis/differential scanning calorimetry, scanning electron microscopy, and mercury intrusion porosimetry are applied to the MOC specimens to discover the mechanism by which fly ash affects on the water resistance of MOC. The microscale analysis shows that the addition of fly ash optimizes the pore distribution in MOC resulting in a denser structure, which contributes to the water repellence.

MOC-Diatomite Composites Filled with Multi-Walled Carbon Nanotubes

“…This can be achieved by the incorporation of microfillers into a composite mixture. As we confirmed in our previous works, the addition of fine particles results in structures with low porosity with improved mechanical strength, reduced water ingress and increased resistance against water damage [ 9 , 10 , 11 ]. The positive effect of microfiller addition can be further strengthened by the application of reactive particles, which can form stable hydrated products.…”

“…The band intensities between 1715 cm −1 and 1150 cm −1 are stretching and bending vibrations of Mg–O and O–H bonds in MgCl 2 ·8H 2 O and C-S-H or M-S-H phases, respectively [ 3 , 4 ]. The presence of MgCO 3 in light burned magnesia and from the carbonation reaction can be observed as the stretching vibration of C=O in carbonates at 1488 cm −1 [ 11 ]. The series of modes below 1000 cm −1 originated from the lattice translation and bond vibrations Mg–O/Mg–Cl and vibrations of Mg–O/Mg 2+ , O/O–Mg–O/O–Mg 2+ –O bonds, rocking motion of oxygen atoms bridging silicon and aluminium atoms in bonds Si–O–Si and Si–O–AlIV [ 14 ].…”

Foam Glass Lightened Sorel’s Cement Composites Doped with Coal Fly Ash

“…Moreover, to improve the functional and technical parameters of produced composites, fly ash was batched as partial substitute of glass granulate. Although the usage of fly ash was due to the promising results on structural and mechanical parameters of fly ash-doped MOC composites published recently [ 42 , 52 , 53 , 54 ], the MOC-fly ash composites were only scantly studied to date. In this way, ternary MOC composites were designed and tested which represents novel and alternative solution for the development of advanced construction materials for construction practice.…”

Mechanical Properties and Pore Structure Characteristics of Magnesium Oxychloride Cement Modified by Highland Barley Straw Ash

“…It has been studied that adding rice husk ash into MOC might be able to obtain higher density and better mechanical properties, and reduce water absorption and improve durability [19]. According to Guo et al, the incorporation of 30% fly ash in MOC could optimize the pore structure, make the structure more compact, and significantly improve the mechanical properties and water resistance [20]. Recent research has suggested that the cement-based material mixed with 15% wheat straw ash has smaller porosity and higher mechanical properties [21].…”