Papers by Keyword: Magnesium Oxychloride Cement

Abstract: The present work addresses the powder bed binder jet 3D printing as an additive manufacturing process for cement-based materials in the constructions industry. Features are created through the interaction among the droplets of the liquid binding agent and the layered powder bed. The printhead movement over the powder bed at a given feed rate forms voxels and single-lines from the coalesce of successive droplets and adjacent lines are consolidated to create the designed cross-section. Here, statistical models have been developed to study the effect of printing parameters (aggregate particle size, feed rate, velocity of powder spread, pressure of the fluid and nozzle diameter) on the resultant dimension of a single printed line, using a factorial design of experiment. The hardware of the 3D printer, the physical properties of the powder blend and binder are initial constraints for designing voxels. Linear regression models of significant parameters are presented. Pressure is one of the most significant factors, it has a profound effect on the granule formation mechanism. Cubic samples printed with higher pressure level are characterized by higher residual porosities from crater channels during the printing process. The results demonstrate a fundamental understanding of the binder–powder interaction for cementitious materials which can be leveraged to determine the minimum printable feature with required dimensional accuracy, based on the chosen process parameters.

Abstract: Hemp concrete is a well-known bio-based building material, but due to its relatively low compressive strength is mainly used as an insulation material with a load-bearing wooden frame. There are possibilities to expand hemp concrete application in construction by substituting traditional lime with magnesium cement. Magnesium oxychloride cement is a material already known for some time and nowadays used in building board production. Strength, lightweight, ease of use are advantages that highlight relatively new magnesium oxychloride type boards compared to traditional sheeting materials such as plywood, gypsum plasterboard and fibre-cement board. Therefore, similar parameters are thought to be reached by producing magnesium oxychloride hemp board. In this work, magnesium cement water resistance was studied and possibilities to improve it was examined by adding fly ash and nanosilica. Among the nanomaterials used in building materials, nanosilica has gained significant interest by performing a beneficial effect in improving the mechanical properties of concretes. In addition, due to its ultrafine size and high chemical reactivity, the performance of nanosilica is much better with a lower amount of admixture required. Results show that applied nanosilica slightly reduced the compressive strength of magnesium cement in a dry state, but at the same time significantly increased its water resistance. Hemp magnesium oxychloride cement board prototype samples were produced and demonstrate promising results for further manufacturing of hemp composite boards.

Abstract: Magnesium oxychloride cement (MOC) possesses rapid hardening, high mechanical strength, abrasion resistance, low alkali and low corrosive performances. However, its disadvantages of poor water resistance, easily deformation, moisture absorption and halogenations limit the application. A low cost-effective modifier H₃PO₄/Na₂O·xSiO₂·nH₂O was designed for MOC system. The results showed that the softening coefficient of the modified MOC reaches 0.988 by adding appropriate dosage of the modifier. Gelatinous substances in the modified MOC was produced after soaking in water, which effectively inhibit the hydrolysis of phase 5 (5Mg (OH)₂·MgCl₂·8H₂O) and the formation of Mg (OH)₂, thus improving the water resistance of MOC system. Keywords: Magnesium oxychloride cement; Water resistance; Phosphoric acid

Abstract: Modern economy has a strong demand for higher speed of construction and lower construction costs both achieved by using new efficient materials. Significant climate influence on the construction technology urges to make extensive investigations on hardening the construction composite (concrete and mortar) mixtures under freezing temperatures at the actual construction site. The article focuses on the use of advanced composite materials using magnesium oxychloride cement and mineral aggregates. The results of literature review on the problem are also presented. We have found that the problem of magnesia composites hardening under freezing temperatures hasn’t been thoroughly investigated. The results of laboratory study of the effect of initial magnesia concretes maturing and mortars under the conditions of freezing temperatures on the hardening process and the final strength of the material are presented. The scientific explanation of the speed of magnesium oxychloride cement strength development in concretes and mortars which have initially undergone the influence of freezing temperatures is given.

Abstract: The inhibition effect of fly ash on the deformation of magnesium oxychloride cement is not obvious. With the increase of fly ash, the deformation of magnesium oxychloride cement decreased at first, and then increased. The smallest deformation is the proportion of FA-35. The fly ash can promote the formation of the 5·1·8 phase crystal and slow the speed of 5·1·8 phase changing into Mg (OH)₂. The growing crystals were disordered, like the scattered tree branches. The causes of FA-35 specimen expansion deformation can be explained by the configuration of the crystal.

Abstract: Magnesium oxychloride cement (MOC) has the characteristics of big heat and heat concentration in the hydration process. During the hydration process there is an adverse effect on the formation of hydration products and strength as well as volume stability. The hydration heat method was used to study the hydration process of MOC and analyze the influence of materials ratio on the hydration process in the present investigation. The results show that the hydration process could be divided into five stages, inclding initial stage, induction stage, acceleration stage, retardation stage and stable stage. It has been found that with the increasing of the molar ratio of MgO/MgCl₂, the induction stage and acceleration stage extended, and heat release ratio and total heat of 3 days were reduced. With the increasing of the molar ratio of H₂O/MgCl₂, the induction stage is cut down, acceleration stage is in advance and heat release ratio first rising and then down, and the total heat of 3 days are reduced. It may be concluded that the influence of ratio on the hydration process of MOC is mastered, providing the bases to further improve the properties of magnesium oxychloride cement products.

Abstract: Based on different molar ratio of MgO/MgCl₂, H₂O/MgCl₂, magnesium oxychloride cement (MOC) paste was prepared, and soaked in chloride solutions of different concentration. The compressive strength of different age was measured and the component and microstructure of the hydrate was tested by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the hydration characteristics of MOC soaked in chloride solutions of different concentration (10%, 20%, saturated, super-saturated). The results showed that the MOC paste specimen could hydrate, harden, develop and keep strength in saturated chloride solution, but the strength can not maintain in chloride solution of low concentrations; it is found that MOC could hydrate, harden, develop and keep strength in particular chloride solution owing to the formation, development and stabilization of 518.

Abstract: By using furniture production residues-shavings and magnesium oxychloride cement production environment-friendly cement particle board technology, and the production process of different wood than ash, water-cement ratio, press temperature, pressure and pressing time and other parameters conduct research and determine the best pressing temperature, pressing time, materials, scale and other parameters.

Abstract: The influences of fly ash and phosphoric acid on water-resistant property and the microstructure of magnesium oxychloride cement (MOC) were investigated in this paper. It is found that the improvement of the water-resistance of the MOC incorporated with phosphoric acid can be attributed to the dramatic decrease in the quantity of crystallization points. In addition, the new Mg₂PO₄(OH) phase can also prevent the dissolution of 5-phase. And the mechanism of the water-resistance of the MOC mixed with fly ash is due to the Ca₂MgSi₂O₇ phase and the glass phase which are filled into microscopic cracks and skeleton empty.

Abstract: The influence of dosage of fly ash on the properties of magnesium oxychloride cement was studied in this paper. The results indicated that the compressive strength of magnesium oxychloride cement remained unchanged when the dosage of fly ash was 5%. The compressive strength of magnesium oxychloride cement declined when the dosage of fly ash between 10%-30%. Fly ash can enhance the water-repellency of magnesium oxychloride cement and the softening coefficient was about 0.90.