Properties Of Magnesium Oxychloride Cement Research Articles

Effect of Phosphoric Acid and Soluble Phosphate on the Properties of Magnesium Oxychloride Cement.

This study investigates the effects of phosphoric acid (H3PO4), potassium dihydrogen phosphate (KH2PO4) and sodium dihydrogen phosphate (NaH2PO4) admixtures on the setting time, compressive strength and water resistance of magnesium oxychloride cement (MOC). MOC samples incorporating different admixtures are prepared, and their hydration products and microstructures are studied via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the addition of H3PO4, KH2PO4 and NaH2PO4 reduces the initial and final setting times and decreases the compressive strength. However, the compressive strength of MOC is higher than 30.00 MPa with the addition of 2.0 wt.% phosphoric acid and its phosphate after 14 days of air curing. The water resistance of modified MOC slurries is significantly improved. The softening coefficient of MOC with 2.0 wt.% H3PO4 is 1.2 after 14 days of water immersion, which is 3.44 times higher than that of the neat MOC. The enhancement in water resistance is attributed to the formation of amorphous gel facilitated by H3PO4, KH2PO4 and NaH2PO4. Furthermore, the improvement in water resistance is manifested as H3PO4 > KH2PO4 > NaH2PO4.

EXPERIMENTAL RESEARCH ON MECHANICAL PROPERTIES OF MAGNESIUM OXYCHLORIDE-BASED TITANIUM GYPSUM CONCRETE

To alleviate the environmental pollution, waste of resources of titanium gypsum (TG) and the industrial residue from the production of titanium dioxide by sulfuric acid method, and to develop new building materials, the effects of different dosage on the strength and microscopic properties of magnesium oxychloride cement (MOC) were studied by methods such as unlimited compressive strength, scanning electron microscope (SEM) and X-ray diffractometer (XRD). Results show that the compressive strength of the samples increases first and then decreases with the increase of the amount of titanium gypsum. In the control group, when the dosage was 0%, the compressive strength of the samples was 40.37 MPa. The compressive strength is 34.29 MPa at 50% dosage, which is lower than the compressive strength of the control group by 15.06%. The internal structure changes, and there is an incomplete reaction of SiO2. The addition of titanium gypsum increases the ductility of concrete, but has little effect on its elastic modulus. Therefore, the proper inclusion of TG in the TG-MOC gelling material can improve its deformation ability and maintain a certain strength. This provides a useful reference and guidance for the application of magnesium oxychloride-based titanium gypsum in engineering practice. Keywords: Magnesium oxychloride cement, Titanium gypsum, Mechanical propertie, Microscopic analysis, Compressive strength.

Effect of phytic acid on physiochemical properties of magnesium oxychloride cement as a biomaterial

Magnesium oxychloride cement (MOC) has been selected as a promising material for bone repair materials due to its prominent mechanical properties and non-toxicity towards mesenchymal stem cells. However, the limited water resistance of traditional MOC constrains its application range. Accordingly, this study investigated the impact of phytic acid (PA) on the mechanical properties, water resistance, and handling properties of MOC as a biomaterial, utilizing various macroscopic and microscopic characterization techniques. The results demonstrated that PA can enhance the mechanical strength and water resistance of MOC. Furthermore, multiple microscopic methods were employed to analyze the mechanism underlying the PA modification of MOC. These findings revealed that the insoluble gel-like structure was wrapped on the surface of the phase 5 crystals, which prevented the intrusion of water and improved the water resistance of MOC. Incorporating PA improved the injectability and degradability of MOC. Therefore, the development of this modified MOC provides a promising strategy for its application as a bone repair material.

Study on the mechanism and mechanical properties of magnesium oxychloride cement for blocking pollutants migration from electrolytic manganese residue

Study on the mechanism and mechanical properties of magnesium oxychloride cement for blocking pollutants migration from electrolytic manganese residue

MECHANICAL PROPERTIES AND MICROSCOPIC MECHANISM OF PAPER MILL SLUDGE-MAGNESIUM OXYCHLORIDE CEMENT COMPOSITES

To make use of industrial solid waste from paper mills, namely paper mill sludge (PMS), and to develop green construction materials, the samples were tested by using these methods that include unconfined compressive strength tests, dry density tests, water absorption tests, scanning electron microscopes (SEM), and X-ray diffractometers (XRD). The effects of different dosages, different particle sizes, and different initial water contents of PMS on the strength and microscopic properties of magnesium oxychloride cement were studied. Results show that the compressive strength of the samples decrease with the increasing of particle size and initial water content, and it first increases before decreasing when PMS content increases. PMS can lessen water absorption while having little impact on the dry density. The compressive strength, which can reach 58.47 MPa, is at its highest when the mixing percentage of PMS is 60%. At this point, the composite material's Phase 5 crystal is longer and the water absorption rate is only 6.8%. The obtained conclusions can provide a reference for the engineering application of paper mill sludge-magnesium oxychloride cement composites. Keywords: Magnesium oxychloride cement, Paper mill sludge, Composite materials, Mechanical properties, Microscopic mechanism, Cemento de oxicloruro de magnesio, Lodos de papelera, Materiales compuestos, Propiedades mecánicas, Mecanismo microscópico.

Preparation of building materials from Bayer red mud with magnesium cement

In this paper, influences of red mud on the properties of magnesium oxychloride cement (MOC) and magnesium oxysulfate cement (MOS) were studied with a 200 day time scale.The results showed that the addition of red mud greatly enhanced the 28d water resistance of MOC cement from 0.84 to 1.10, of MOC cement, significantly increased the compressive strength of MOS cement from 24.12 MPa to 33.31 MPa and water resistance from 0.48 to 0.68. At 200d, the addition of red mud had little effect on MOC cement but greatly increased compressive strength and water resistance of MOS cement. The red mud and magnesium cement produced an amorphous gel, which made the matrix more compact.Meanwhile, magnesium cement played the role of solidification soluble salt in red mud and only slight frosting appeared.The research results show the potential of red mud as a modifier of magnesium cement and its application potential as a building material.

Research and Engineering Application of Salt Erosion Resistance of Magnesium Oxychloride Cement Concrete.

Aiming at the problem that ordinary cement concrete is subjected to damage in heavy saline soil areas in China, a new type of magnesium oxychloride cement concrete is prepared by using the gelling properties of magnesium oxychloride cement in this study, and the erosion resistance of the synthesized magnesium oxychloride cement concrete in concentrated brine of salt lakes is studied through the full immersion test. The effects of concentrated brine of salt lakes on the macroscopic, microscopic morphology, phase composition and mechanical properties of magnesium oxychloride cement concrete are investigated by means of macro-morphology, erosion depth, SEM, XRD and strength changes. The salt erosion resistance mechanism of magnesium oxychloride cement concrete is revealed. The results demonstrate that under the environment of full immersion in concentrated brine of salt lakes, there is no macroscopic phenomenon of concrete damage due to salt crystallization, and the main phase composition is basically unchanged. The microscopic morphology mostly changes from needle-rod-like to gel-like. Due to the formation of a new 5·1·8 phase on the surface layer and the increase in compactness, its compressive strength has a gradual increase trend. Based on the engineering application of magnesium oxychloride cement concrete, it is further confirmed that magnesium oxychloride cement concrete has excellent salt erosion resistance and good weather resistance, which provides theoretical support for future popularization and application.

Effects of fly ash, phosphoric acid, and nano-silica on the properties of magnesium oxychloride cement

This study investigates the effects of fly ash, phosphoric acid, nano-silica additives on the hydration process, setting time, compressive strength, water resistance, and thermal stability of magnesium oxychloride cement (MOC). MOC samples incorporating different combinations of additives are prepared, and their hydration products and microstructures are studied via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TGA-DSC), and scanning electron microscopy (SEM). Results indicate that the addition of nano-silica to MOC containing fly ash and phosphoric acid reduces initial and final setting times, decreases the thermal stability, and increases compressive strength. Furthermore, the water resistance of modified MOC pastes is significantly improved through the combined use of additives. Hydration mechanisms arising in MOC are elucidated, and the remarkable enhancement of water resistance is attributed to secondary hydration of the 5 Mg(OH)2·MgCl2·8H2O (5·1·8 phase) and the formation of amorphous gel facilitated by nano-silica inclusion.

Study on the properties of magnesium oxychloride cement prepared by the magnesium-rich byproducts from the production of lithium carbonate from salt lakes

Study on the properties of magnesium oxychloride cement prepared by the magnesium-rich byproducts from the production of lithium carbonate from salt lakes

The effect of nano-silica on the properties of magnesium oxychloride cement

As is well known, nano-particles have received particular attention in various application fields for fabricating materials with novel functionalities. This paper presents the effect of nano-silica on the properties of magnesium oxychloride cement (MOC), such as setting time, the hydration process, compressive strength, composition and microstructure of the paste. Results show that nano-silica can promote the hydration process and shorten the initial and final setting times of MOC, which were shortened by 14% and 8% when 5% nano-silica was incorporated in the MOC. In addition, nano-silica can increase the compressive strengths and make the pore structure of MOC denser. The compressive strengths at 3 days and 28 days increase by 29.5% and 18.0%, respectively, when 5% nano-silica is incorporated in MOC. Compared with the pure MOC paste, nano-silica yields no new hydration products in MOC besides P5 and magnesium hydroxide (Mg(OH)2). The higher compressive strength is mainly attributed to the water absorption and filling effect of nano-silica in MOC slurry.

Effect of fly ash and metakaolin on the macroscopic and microscopic characterizations of magnesium oxychloride cement

In order to reduce the production cost and improve the properties of magnesium oxychloride cement (MOC), this paper studied the influence of single and compound addition of fly ash (FA) and metakaolin (MK) on MOC from two aspects of macroscopic and microcosmic characteristics. Macroscopic characterizations include setting time, compressive strength, mass change, ultrasound velocity, and microscopic characterizations include hydration phases, microstructure, and hydration process. The results showed that FA could delay the setting of MOC, and slow down the hydration process of MOC. However, the effect of MK on MOC was opposite. The single and compound addition of FA and MK did not change the phase composition of the hydration products in MOC, but conducive to the formation of richer, thicker and longer phase 5. The compressive strength, mass change and compactness of MOC decreased with the increase of admixture content. However, when the replacement level of MgO by single-doped FA or MK, and combination of FA and MK is 10%, MOC with the properties of rapid setting time, early and high strength, light weight, and advantage in density was obtained. This may provide a basis for further developing the properties of MOC products.

Investigation on the properties of magnesium oxychloride cement prepared with seawater

Seawater from South China Sea was used instead of freshwater to fabricate magnesium oxychloride cement (MOC). To study the basic performance of the seawater-mixed MOC paste, the setting time, hydration exothermic characteristics, compressive strength, thermal stability, seawater resistance, phase composition and microstructure of the paste were analysed in detail. The results showed that the use of seawater in the MOC paste slightly retarded the setting time and increased the total hydration heat. The compressive strength and thermal stability of the seawater-mixed MOC were slightly lower than those of the MOC paste prepared with freshwater. The main hydration product of both MOC pastes was 5Mg(OH)2.MgCl2.8H2O. The residual strength ratio of the seawater MOC paste was 9·70% higher than that of the freshwater MOC paste after 28 d immersion in seawater. However, the standard deviations suggest that the properties of MOC pastes prepared with seawater or freshwater were not significantly different.

Effects of polycarboxylate superplasticiser on the early hydration properties of magnesium oxychloride cement

Magnesium oxychloride cement (MOC) exhibits better mechanical properties with a faster hydration rate than ordinary Portland cement (OPC). However, the rapid setting property of MOC limits its application in engineering applications. In this work, polycarboxylate superplasticiser (PCE) was used to improve the workability of MOC and its effect on the early hydration properties of MOC paste was investigated. The hydration process for MOC with five different PCE dosages of 0%, 0.4%, 0.6%, 0.8%, and 1% by weight of MgO was analysed using electrodeless resistivity. Optical microscopy was used to obtain the flocculation of fresh MOC paste and its rheological properties were tested to investigate its workability. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyse the effects of PCE on the phases and microstructures of the MOC paste. The results reveal that PCE significantly improves the rheological properties of MOC. The setting time of the MOC paste was retarded due to the PCE adsorbed on the cement particle surface, which prevented MgO particles from reacting with water. Meanwhile, MOC in the presence of certain PCE contents showed excellent mechanical properties due to a mass of formed gel-like 5MgO-MgCl2-8H2O crystals.

Synthesis, Structure, and Thermal Stability of Magnesium Oxychloride 5Mg(OH)2∙MgCl2∙8H2O

Today, low-energy and low-carbon footprint alternatives to Portland cement are searched because of huge CO2 emissions coming from Portland clinker calcination. Because of some superior properties of magnesium oxychloride cement (MOC) and the lower carbon footprint of its production, MOC became an intensively studied material with high application potential for the design and development of construction products. In this contribution, magnesium oxychloride with stoichiometry 5Mg(OH)2∙MgCl2∙8H2O (Phase 5) was prepared and characterized. The kinetics of formation and the phase composition of the material were determined using X-ray diffraction and consequent Rietveld analysis. The morphology was studied by scanning electron microscopy, and the chemical composition was determined by both energy-dispersive spectroscopy and X-ray fluorescence. Moreover, the simultaneous thermal analysis in combination with mass spectroscopy and Fourier-transform infrared spectroscopy was employed to study the thermal stability. Using mass spectroscopy, we were able to clarify the mechanism of water and hydrochloric acid release, which was not previously reported. The observed structural and chemical changes induced by exposure of studied samples to elevated temperatures were linked with the measured residual macro and micro parameters, such as bulk density, specific density, porosity, water absorption, compressive strength, and pore size distribution. The Phase 5 revealed a needle-like crystalline morphology which formed rapidly and was almost completed after 96 h, resulting in relatively high material strength. The four-day compressive strength of magnesium oxychloride cement was similar to the 28-day compressive strength of Portland cement. The thermal stability of Phase 5 was low as the observed disruptive thermal processes were completed at temperatures lower than 470 °C.

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

AbstractAs 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.

Effect of Fly Ash on Rheological Properties of Magnesium Oxychloride Cement

AbstractThis paper studies the effect of fly ash on rheological properties of magnesium oxychloride cement (MOC) paste. Six different dosages of fly ash (0%, 15%, 20%, 25%, 30%, and 35% by weight o...

Effect of Citric Acid on the Time-Dependent Rheological Properties of Magnesium Oxychloride Cement

AbstractThis study was intended to evaluate how citric acid influences the time-dependent rheological properties of magnesium oxychloride cement (MOC). For this purpose, rheological parameters, set...

Experimental investigation of thermal and mechanical properties of magnesium oxychloride cement with form-stable phase change material

To increase the heat storage efficiency of the building enclosure structure, form-stable phase change material (FSPCM) was implanted into the magnesium oxychloride cement (MOC) system to generate MOC/FSPCM composites with both high heat storage efficiency and considerable mechanical strength. The microstructure, mechanical properties, hydration process and thermal properties of MOC/FSPCM composites were investigated. The results indicated the structure of MOC was not destroyed and the hydration rate, hydration temperature and total hydration heat also dropped after adding FSPCM. The compressive strength and flexural strength of the MOC/FSPCM composites with 30 wt% FSPCM can still reach to 52.9 MPa and 5.9 MPa, respectively, and the melting and crystallizing enthalpy of MOC/FSPCM composites were 29.91 J/g and 26.52 J/g, respectively. Thermal performance tests indicated that thermal conductivity of MOC/FSPCM composites decreased with the increase in the mass percentage of FSPCM. Meanwhile, MOC/FSPCM composites show excellent performance of indoor temperature regulate, conserve energy and thermal comfort.

Research on the properties of magnesium oxychloride cement prepared with simulated seawater

Simulated seawater (SW) was used to fabricate magnesium oxychloride cement (MOC) pastes. Compressive strength, water resistance, performance under salt attack, thermal stability, mineral composition and microstructure were studied in detail by using a materials testing system, thermogravimetry and differential scanning calorimetry methods, X-ray diffraction and scanning electron microscopy. The results showed that the compressive strength, strength retention in distilled water and thermal stability of MOC pastes made with simulated SW were slightly lower than those of the control MOC pastes. The main hydration product of both the MOC pastes was 5Mg(OH)2.MgCl2.8H2O. The strength retention of the simulated SW MOC pastes was 11·27% higher than that of the fresh water (FW) MOC pastes after 28 d of immersion in raw brine. The properties of the MOC pastes appeared to be unchanged when manufactured using simulated SW instead of FW. Due to its good performance under salt attack, the MOC pastes mixed with simulated SW show potential as salt pan material.

Influence of filler on the properties of magnesium oxychloride cement prepared from dolomite

In this study, the objective was to determine the influence of using expanded perlite or exfoliated vermiculite as filler on the properties of magnesium oxychloride cement (MOC). The starting materials necessary for producing MOC were obtained from dolomite ore. Expanded perlite and exfoliated vermiculite were selected as filler for this study. The microstructure of MOC was imaged by scanning electron microscopy and X-ray diffraction analyses. The experimental results demonstrate that the use of filler in the MOC led to a decrease in its density and thermal conductivity. The workability and fluidity of the MOC were strongly influenced by the amount of the filler. Although the amount of carbon in the MOC decreased with an increase in the amount of the filler, the carbonation of MOC was not totally prevented and it occurred through exposure of its surface to carbon dioxide at ambient temperature after 600 d of curing.