Effect of nanosilica@ chitosan phosphate ester on properties and water resistance of magnesium oxychloride cement

Effect of tartaric acid and phosphoric acid on the water resistance of magnesium oxychloride (MOC) cement

As a solid waste, the amount of residual sludge produced by the municipal wastewater treatment process is escalating. How to dispose it properly is attracting much attention in society. Herein, solidifying residual sludge using magnesium oxychloride cement (MOC) is promising for converting it into building materials. Various factors of mass ratio (RW/S) of liquid to solid, molar ratio (Rn) of MgO to MgCl2 in MOC, mass ratio (Rm) of residual sludge to MOC, the mass concentration of Na2SiO3 (DNa2SiO3), and dosage of fly ash (DF) influenced the unconfined compression strength (RC) of the as–obtained MOC–solidified residual sludge, and it was characterized using SEM and XRD analysis. The results show that the value of RC for MOC–residual sludge solidified blocks increased initially and then decreased as Rn and Rm increased, respectively, for 60–day curing. At 10–day curing, equilibrium RC was reached at all RW/S values except 1.38, and at 60–day curing, RC decreased with RW/S increasing. The maximum RC of 60 days of 20.90 MPa was obtained at RW/S = 0.90, Rn = 5.0, and Rm = 1.00. Furthermore, adding Na2SiO3 or fly ash in the solidifying process could improve RC. The water resistance test showed that SM13 and NF5 samples exhibited good alkaline resistance after immersion for 7 and 14 days in an aqueous solution with pH = 7.0–11.0. The water resistance of MOC–residual sludge solidified blocks decreased with increase in immersion duration in aqueous solutions. The fly ash could also help improve water resistance of MOC–solidified residual sludge in neutral and basic aqueous solutions. This work provides an important theoretical basis and possibility for the efficient disposal and comprehensive utilization of residual sludge through solidification/stabilization technology using MOC from the perspective of mechanics and water resistance.

Long-term phase composition and microstructure characteristics of phosphoric acid modified magnesium oxychloride cement exposed to natural environment

Magnesium oxychloride has excellent early strength, lightweight and environmentally friendly properties, and excellent application value. However, insufficient water resistance affects its engineering application. This paper uses fly ash to improve the water resistance of magnesium oxychloride cement (MOC). The response surface method was used to optimize the ratio of magnesium oxychloride cement. The influence of fly ash content, magnesium oxychloride cement ratio, and their interaction on the water resistance of magnesium oxychloride cement was studied using a response surface experiment. The fly ash content and magnesium oxychloride cement ratio were optimized to form magnesium oxychloride cement with good water-resistance. The experimental results show that the fitting efficiency of the response surface model is R2 = 0.9951; the model reflects the relationship between the factors of magnesium oxychloride cement and water resistance well. The magnesium oxychloride cement has a maximum softening coefficient of 0.898 when the amount of fly ash added is 21.94%, and the molar ratio of magnesium oxychloride cement is 11.49: 1:11.77. The magnesium oxychloride cement has good water resistance by optimizing the ratio based on external fly ash and response surface methodology. The study provides a reference for improving the water resistance of magnesium oxychloride cement.

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

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

Conventional binding materials, such as silicate cement and lime, present high energy consumption, pollution, and carbon emissions. Therefore, we utilize crushed stone as a stabilization material. Magnesium oxychloride cement (MOC) is modified and used as an inorganic admixture owing to its eco-friendly nature and low carbon content. We analysed the control indicators of an integrated design of MOC-stabilized crushed stone by conducting unconfined compressive strength and water-resistance tests. The optimum mixing composition of the MOC-stabilized crushed stone was determined through the response surface methodology. We determined the best approach and dosage for improving the water resistance of MOC-stabilized crushed stone by comparing the effects of four modification methods: fly ash, citric acid + silica fume, phosphoric acid + waterborne polyurethane, and dihydrogen phosphate potassium salt. We also perform a comparison with 5% ordinary silicate cement-stabilized crushed stone. The results indicate that the MOC-stabilized crushed stone exhibits a rapid increase in strength in the early stage, but this rate reduces after 28 days. The mixing design employs the 4-day unconfined compressive strength and 1-day water resistance coefficient as the technical indicators. The best mixing composition includes a 4.27% MOC dosage and a molar ratio of MgO/MgCl2 of 5.85. We use 1% citric acid + 10% silica fume in equal amounts to replace the MOC dopant method for composite modification of the MOC stabilized crushed stone. Consequently, the 1-day water resistance coefficient before water immersion is significantly increased from 0.78 to 0.91 and its 4-day unconfined compressive strength is only reduced by 0.10 MPa. This significantly improves the water resistance of the MOC-stabilized crushed stone and ensures that its strength remains unaffected, which is the optimal modification method. However, this method must ensure that a small amount of citric acid and silica fume are uniformly distributed in the MOC-stabilized crushed stone, which increases the construction difficulty of the road base.

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.

Magnesium oxychloride cement (MOC), an alternative to ordinary Portland cement (OPC), has attracted increasing research interest for its excellent mechanical properties and its green and sustainable attributes. The poor water resistance of MOC limited its usage mainly to indoor applications; nevertheless, recent advances in water-resistant MOC have expanded the material’s potential applications from indoor to outdoor. This review aims to showcase recent advances in MOC, including water-resistant MOC and ductile fiber-reinforced MOC (FRMOC), exploring their potential applications including in sustainable construction for future generations. The mechanism under different curing procedures such as normal and CO2 curing and the effect of different inorganic and organic additives on the water resistance of MOC composites are discussed. In particular, the review highlights the recent developments in achieving over 100% strength retention under water at 28 days as well as advancements in FRMOC, where tensile strength has surpassed 10 MPa with a remarkable strain capacity ranging from 4–8%. This paper also sheds light on the potential applications of MOC as a fire-resistant coating material, green-wood-MOC composite building material, and in reducing solid waste industrial byproduct accumulations. Finally, this study suggests future research directions to enhance the practical application of MOC.

Potential application of highland barley straw ash as a new active admixture in magnesium oxychloride cement

Enhancement of mechanical and microstructural characteristics of magnesium oxychloride cement with metasteatite

Effect of tartaric acid on the early hydration process and water resistance of magnesium oxychloride cement

Effects of alumina-leached coal fly ash residue (ACFAR) on magnesium oxychloride (MOC) cement are comprehensively investigated. The results show that the addition of ACFAR delayed the setting time of MOC paste. The compressive strength, the flexural strength and the water resistance of MOC are improved by the incorporation of ACFAR. Furthermore, the improvement effects of ACFAR are compared with those of raw coal fly ash (RFA) on MOC cement. Scanning electron microscopy analysis of MOC cement reveals that ACFAR decreases the interspaces in MOC cement and facilitates the radial growth of 5Mg(OH)2·MgCl2·8H2O. X-ray diffraction analysis of MOC cement with ACFAR indicates that the addition of ACFAR promotes the production of magnesium silicate, which can improve the compactness of 5Mg(OH)2·MgCl2·8H2O and the water resistance of MOC cement.

Exploration of the effects of electrolytic manganese residue on the environmental, economic, and engineering performance of magnesium oxychloride cement: A possible utilization method of electrolytic manganese residue

Effect of partial MgO replacement on the properties of magnesium oxychloride cement