Magnesium Oxysulfate Research Articles

Performance and microstructural analysis of modified magnesium oxysulfate cement with additions: Roles of FA and GGBS

Performance and microstructural analysis of modified magnesium oxysulfate cement with additions: Roles of FA and GGBS

Preparation of green and durable magnesium oxysulfate cement using sewage sludge ash: Physical properties, microstructure, and leaching behavior

The aim of this study was to explore the application of sewage sludge ash (SSA) as a substitute for light-burnt magnesium oxide (LBM) in the preparation of magnesium oxysulfate cement (MOSC), in order to achieve the harmless treatment of SSA and improve the performance of MOSC. By adjusting the SSA dosage, a series of MOSC samples were prepared, and their setting time, compressive strength, water resistance, and heavy metal leaching rates were then systematically evaluated. Additionally, their crystal phase composition, relative content, and microstructure were characterized using XRD, TGA, FTIR, and SEM in order to elucidate the mechanism by which SSA affects the properties of the MOSC. The results indicate that the addition of SSA prolongs the setting time of MOSC and reduces its compressive strength. However, pozzolanic SiO2 in SSA can hydrate with MgO to form magnesium-silicate-hydrate gel, effectively improving the water resistance of MOSC. In particular, when SSA replaces 30 % of LBM, MOSC not only meets the heavy metal leaching standards for Class IV surface water in China, but also has a compressive strength of up to 67 MPa and a significant improvement in water resistance by 44 %. This study not only opens up new avenues for the harmless treatment of SSA, but also provides scientific basis and practical reference for optimizing the water resistance of MOSC.

Performance variations of light burned magnesia under different calcination parameters and its effects on magnesium oxysulfate cement preparation

This study systematically investigated the impact of different calcination temperatures and holding times on MgO reactivity, as well as the influence of varying reactivity and lattice distortion of MgO on the properties of magnesium oxysulfate cement (MOSC). Results indicated that at temperatures of 700–900℃, magnesite underwent decomposition, resulting in increased lattice distortion, and heightened reactivity. At temperatures of 1000–1100℃, magnesia began sintering, nucleating, and experienced reduced crystal distortion, leading to decreased reactivity. Notably, the appearance of the pseudomorphic mother rock at calcination temperatures of 900℃ and 1000℃ was associated with decreased magnesia reactivity. Moreover, the compressive strength of MOSC prepared using MgO calcined at 900℃ for 6 h increased to 77 MPa after 28 d of air curing. The hydration reactivity and lattice distortion of MgO could be regulated through changing the calcining temperature and holding time, which provided a theoretical basis for the preparation of magnesium oxysulfate cement with excellent mechanical properties.

Effects of Dolomitic Limestone on the Properties of Magnesium Oxysulfate Cement.

This study investigated the effects of substituting magnesium oxide (MgO) with dolomitic limestone (DL) on the mechanical and physical properties of magnesium oxysulfate (MOS) cement. Additionally, the hydration formation phases and the influence of the molar ratio on the MOS cement's performance were examined. The corresponding action mechanisms were identified and explored by compressive strength tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), isothermal calorimetry, and a thermogravimetric analysis (TGA). The results showed that replacing MgO with DL decreased the reaction speed and heat release rate generated in the hydration process of the MOS cement. This substitution also reduced the quantity of non-hydrated MgO particles and delayed the formation of Mg(OH)2. The diminished formation of Mg(OH)2 contributed to an increase in the apparent porosity of pastes containing DL, thus alleviating internal stresses induced by Mg(OH)2 formation and enhancing their mechanical strength after 28 days of curing. Conversely, the increased porosity improved the CO2 diffusion within the structure, promoting the formation of magnesium carbonates (MgCO3). Through the characterization of the cement matrix (XRD and TGA), it was possible to identify phases, such as the brucite, periclase, and 318 phases. The obtained results revealed the potential of incorporating mineral fillers like limestone as a promising approach to producing MOS cement with a reduced environmental impact and better properties at higher curing ages.

Preparation and characterization of MgO-based composites: Analysis of moisture, corrosion, and fungal resistance, and mechanical properties

Magnesium oxide (MgO) composite boards are valued in the construction industry because of their outstanding fire resistance, however, the long-term viability of MgO boards is affected by atmospheric humidity. This research work aims to investigate the environmental impacts and mechanical properties of four types of MgO boards from four different manufacturers under varying relative humidity (RH) levels. Three of them contained a high amount of chlorine known as magnesium oxychloride (MOC) boards, and one of them contained a high amount of sulfur known as magnesium oxysulfate (MOS) boards from their elemental composition observed by EDX. Microscopic images showed a rougher and porous surface for MOC boards, whereas smoother surface for MOS boards. MOS boards exhibited 37 % (average) lower moisture absorbency than MOC boards at 95 % RH and remained dry, while the MOC boards leaked salty water drops under the same condition. As a result, the MOS boards exhibited much better corrosion and fungal protection than the MOC boards. Mechanical properties, for example, tensile strength decreased by 45 % in MOC boards and 31 % in MOS boards at 95 % RH compared to 50 % RH. Therefore, the sourced MOS composite boards outperformed the contemporary MOC boards in all parameters.

Hydration and microstructure formation of magnesium oxysulfate (MOS) cement regulated by sepiolite with high adsorption ability

Magnesium oxysulfate (MOS) cement is a potential low-carbon cementitious material with its characteristic depending on the reaction between light-burned magnesia (LBM) and MgSO4 solution. This work aimed to elucidate the effect of sepiolite with high adsorption ability on regulating the reaction within MOS cement. Replacement levels of LBM by sepiolite at 2 and 5 wt% were adopted. Hydration kinetics, microstructure, phase composition and compressive strength of MOS cement without and with sepiolite were studied. Results showed that adding sepiolite into MOS cement adjusted the ion distribution at the early hydration stage and promoted the reaction with an early onset of heat flow peaks. The presence of sepiolite refined the morphology of formed needle-like 5 Mg(OH)2·MgSO4·7H2O (517 phase) and strengthened the bond water within its structure. The high adsorption ability of sepiolite enabled the nucleation of 517 phase and amorphous phase onto its surface. Sepiolite also densified the poorly hydrated regions by tightly combining with the incompletely hydrated MgO grains. Consequently, compressive strength of MOS cement under air curing was improved after adding sepiolite.

Understanding the positive effects of silica fume on the high-temperature resistance and water resistance of magnesium oxysulfate cement

This study aims to improve the high-temperature resistance and water resistance of magnesium oxysulfate cement (MOSC) through introducing silica fume (SF). The residual strength of MOSC after exposure to high temperatures of 200 °C, 400 °C, 600 °C and 800 °C was tested. The softening coefficient of MOSC after immersion in water for 28 days was used to evaluate the water resistance. The results revealed that SF enhanced the high-temperature resistance of MOSC at temperatures exceeding 200 °C. For SF-MOSC system, prolonged exposure to high temperature of 400 °C could further promote the transformation of partial MgO to M-S-H gel. This phenomenon extremely increased the residual compressive strength of SF-MOSC. Although the residual strength of MOSC and SF-MOSC decreased sharply at 600 °C, the SF-MOSC still displayed a better high-temperature resistance performance. At 800 °C, the MgO in SF-MOSC could have a solid-solid reaction with silicon source to generate forsterite with high melting point. Additionally, SF exhibited favorable filling effects in MOSC and could restrict the conversion of MgO to Mg(OH)2, which also promoted the crystallization of 5Mg(OH)2·MgSO4·7H2O (5·1·7 phase). The decreased Mg(OH)2 after immersion in water and further generation of partial 5·1·7 phase contributed to the enhancement of MOSC’s water resistance in this study.

Improved stabilization of loess soil using magnesium oxysulfate cement-based ecological composite binder

The technology of loess solidification plays a crucial role in addressing issues such as soil erosion, with the key material in this process being the loess stabilizer. To tackle the high energy consumption problem associated with traditional loess stabilizers primarily composed of Portland cement, this study employed a more ecological sustainable alternative by incorporating solid waste coal gangue and magnesium oxysulfate (MOS) cement as a binding agent for consolidating loess. The alterations in bulk density, porosity, mineral structure, and microstructure of the consolidated soil with different MOS content were systematically investigated and validated. The pore size of MOS-solidified loess decreased significantly to a range of 0.04–3.60 μm compared to 0.80–3.88 μm for pure loess. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and thermogravimetric (TG/DTG) analysis revealed that the addition of MOS binder generated hydrated magnesium silicate (M-S-H), Mg(OH)2, and a small amount of 5Mg(OH)2·MgSO4·7H2O phase which filled the gaps between soil particles and bonded them together effectively. When the proportion of MOS binder added reached 11 %, the compressive strength of stabilized loess after curing for 28 days increased up to 9.4 MPa. After immersion in water for 24 h, the strength only decreased by 5.3 %, with a softening coefficient of 94.7 %. The test results consistently indicate that the enhancement in mechanical properties can be attributed to the binding effect facilitated by MOS. The ecological composite binder based on coal gangue and MOS demonstrates great potential in the field of soil stabilization.

Performance of magnesium oxysulfate (MOS) cement prepared by MgCl2·6 H2O replacing MgSO4·7 H2O

Despite the influence of Cl- on the properties of cement-based materials, water containing Cl- is more convenient for manufacturing cement-based materials in special areas such as islands and reef construction, compared to fresh water. However, research on the effects of Cl- on the properties of magnesium oxysulfate (MOS) cement was limited. In this paper, MOS cement was prepared by replacing MgSO4·7 H2O with MgCl2·6 H2O to investigate the effect of Cl- on the evolution of MOS cement properties. The mechanical properties, water resistance, phase composition, and microstructure of MOS cement were analyzed. When the replacement rate of MgSO4·7 H2O with MgCl2·6 H2O reached 5 %, MOS cement achieved its highest compressive strength of 77.5 MPa after curing for 90 days, despite a reduction in flexural strength due to MgO hydration. After immersion in water, the trend of compressive strength change in MOS cement remained insensitive to increasing immersion time. During the curing process, Cl- facilitated the formation of hexagonal Mg(OH)2 by participating in the hydration products formation process of MOS cement. Hexagonal Mg(OH)2 contributed to matrix construction and became connected with the 5Mg(OH)2·MgSO4·7 H2O phase. Additionally, Cl- promoted the formation of the modified 5Mg(OH)2·MgSO4·7 H2O phase, known as Mg-S-O-H-Cl phase. After immersion in water, the Mg-S-O-H-Cl phase displayed stability, showcasing their capacity to maintain compressive strength relative stability despite adverse factors such as ions leaching (including Mg2+, SO42-, and Cl-) and the phase transformation of MgO.

Investigation on the solidification effect and mechanism of loess utilizing magnesium oxysulfate cement as a curing agent

In this study, magnesium oxysulfate cement (MOS) was used as a binder for curing loess. The changes in bulk density, porosity, mineral structure and microstructure of the consolidated loess were systematically studied and verified. The porosity decreased from 40.97 % in pure loess to 28.75 % in 13 % MOS solidified sample. Scanning electron microscopy, energy spectrum analysis and thermogravimetric analysis revealed that the addition of MOS binder resulted in the formation of hydrated products, including Mg(OH)2, MgO·mSiO2·nH2O (M-S-H), and 3Mg(OH)2·MgSO4·8H2O (3·1·8 phase), which effectively filled the voids between the grains and facilitated strong bonding among them. After a curing period of 28 days, the compressive strength of loess stabilized with 13 % MOS exhibited an increase to 7.9 MPa. Moreover, following immersion in water for 24 h, the softening coefficient K remained at 0.66. Furthermore, after undergoing five cycles of freeze-thaw cycling, the rate of change in compressive strength RP was only 6.3 %. All the results indicate that MOS exhibits promising potential as a binder for soil stabilization applications.

Characterization of cost-effective green engineered magnesium oxysulfide cement-based composites (MOSC-ECC) prepared by replacing MgO in magnesium oxysulfate cement with slag

A cost-effective green engineered magnesium oxysulfide cement-based composites (MOSC-ECC) which was prepared with magnesium oxysulfate cement (MOSC) and large-volume solid waste (slag) in this paper. The macro and micro mechanical properties, thermal conductivity, water resistance, evolution of hydration products and microstructure of MOSC-ECC were studied. The energy consumption, carbon emissions, and cost of MOSC-ECC were calculated and compared with traditional ECC. Test results showed that adding slag instead of light-burned MgO can increase the strain-hardening strength and energy indices of MOSC-ECC, and improve the ductility. In addition, the incorporation of slag lowered the proportion of 5Mg(OH)2·MgSO4·7 H2O phase (517 phase), led to a decrease in the strength, density and thermal conductivity of the MOSC-ECC. Compared with traditional OPC-based ECCs, the prepared MOSC-ECC showed a reduction in embodied energy by approximately 32 %, a reduction in CO2 emission of around 60 %, and a reduction in material costs more than 38 %. Therefore, slag can be used as the main component of MOSC-ECC, and the dosage can be up to 50 % by weight of MgO, which has obvious economic and environmental benefits.

Assessment of carbonation as a complementary strategy to increase the durability of Magnesium Oxysulfate (MOS)-based fiber cement boards

Magnesium oxysulfate (MOS)-based fiber cement boards reinforced with lignocellulosic fibers were manufactured using the Hatschek process and cured for 24, 48, and 72 hours before curing in a CO2-rich atmosphere. The boards were rehydrated before the accelerated carbonation process to evaluate changes in carbonation after water addition to the system. The materials showed property changes after accelerated carbonation, which was responsible for an increase of approximately 15 % in the MOR values of the carbonated boards after 48 hours. In contrast, pre-rehydration of the boards increased the Modulus of Rupture (MOR), Limit of Proportionality (LOP), and Modulus of Elasticity (MOE)values of the carbonated materials and favored the production of cementitious composites with specific energy values close to 4.4 kJ/m2. The quantification of mineralized CO2 showed that the rehydrated and carbonated boards after 48 hours presented the highest SCO2(effective) values, which is related to the densification and consequent decrease in voids in the carbonated materials under these conditions. Accelerated aging showed that the carbonated boards had a lower loss of mechanical properties, demonstrating that accelerated carbonation, in addition to increasing mechanical properties, emerges as an alternative to increasing the long-term durability of MOS-based fiber cement boards.

High-value utilization of boron mud waste: preparation of magnesium oxysulfate cement after primary blank roasting and secondary (NH4)2SO4 roasting

Boron mud, as a typical industrial solid waste, calls for value-added use because of environmental problems caused by stockpiling and waste of considerable magnesium resource. In this work, the primary blank roasted boron mud, as well as the secondary (NH4)2SO4 roasted boron mud were used to prepare magnesium oxysulfate (MOS) cement, then, its characterization and mechanical properties were analyzed and compared systematically. Results showed that the primary blank roasted boron mud can replace 45 % of light burned MgO to prepare MOS cement, whose compressive and flexural strength are 59.0 MPa and 8.0 MPa after curing for 28 d. During the secondary (NH4)2SO4 roasting process of boron mud, MgO and Mg2SiO4 in the primary roasted boron mud transform into MgSO4. The secondary roasted boron mud can replace MgSO4 completely, MOS cement rich in 5Mg(OH)2·MgSO4·7 H2O (517) phase can be obtained with compressive and flexural strength of 70.0 MPa and 9.0 MPa after curing for 28 d. When both of the primary blank roasted and secondary (NH4)2SO4 roasted boron mud are used for preparing MOS cement which compressive and flexural strength are higher than the requirements of the national standard, MgSO4 can be completely derived from the secondary roasted boron mud, the primary blank roasted boron mud can replace up to 35 % of light burned MgO at most, and the total utilization ratio of boron mud is 53.3 wt%. This process not only achieves the high-value utilization of boron mud, but also provides a new thought to prepare MOS cement with high mechanical properties.

Impact of Sodium Gluconate Admixture on the Properties of Magnesium Oxysulfate Cement

Impact of Sodium Gluconate Admixture on the Properties of Magnesium Oxysulfate Cement

Innovative MOS-based fiber cement boards: Effect of kraft pulp mills waste and curing by accelerated carbonation

The increasing global waste generated by industrial activities poses significant environmental challenges. Eco-waste management emerges as an economically viable solution for converting, valorizing, and repurposing these byproducts, aligning with circular economy principles, and aiming to reduce greenhouse gas emissions. Construction, known for its unsustainability due to high energy consumption, non-renewable resource utilization, waste generation, and greenhouse gas emissions, particularly from cement production, has led to the exploration of alternative materials. Magnesium oxide (MgO)-based cement, an alternative to Ordinary Portland Cement (OPC), has gained attention, leveraging Brazil's prominence as a major magnesite producer. This study explores the valorization of waste from kraft pulp mills of the paper industry, specifically lime sludge (LS) and lime slaker grits (grits), to produce magnesium oxysulfate (MOS)-based fiber cement boards. The effect of accelerated carbonation on cementitious composites produced with formulations containing grits and LS was investigated. Replacing 25% of the limestone with grits showed no noticeable differences in the properties of the boards, and MOR values close to 11.17 MPa were obtained. However, the physical-mechanical performance showed a decrease with the use of LS and higher concentrations of grits, associated with Na2SO4.XH2O formation in the system and ITZ structure formed around the aggregated particle, respectively. Carbonation in a saturated atmosphere led to the carbonation of the 5–1–7 phase, which was related to the decrease in mechanical strength of the boards after the curing process. The thermal decomposition of the Hydrated Magnesium Carbonates (HMCs) formed during accelerated carbonation corroborated with the changes in the physical properties of the composites, demonstrating that the carbonation products are formed within the voids and pores of the material and contribute to the reduction in water absorption of the boards.

Impact of Cl- on the performance of magnesium oxysulfate (MOS) cement

As magnesium oxysulfate (MOS) cement finds more applications in the engineering field, the influence of Cl- on the mechanical properties of MOS cement has gained more attention. In this paper, MgCl2·6 H2O served as the source of Cl- to investigate its influence on the evolving properties of MOS cement. The results showed that MgCl2·6 H2O extended the formation time of the 5Mg(OH)2·MgSO4·7 H2O phase, reduced the dispersion of the MOS cement system, and decreased the crystalline size of the 5Mg(OH)2·MgSO4·7 H2O phase (200) crystal plane. The addition of MgCl2·6 H2O had a positive effect on improving flexural strength and increasing the content of gel. During the curing process, the presence of Cl- facilitated the dissolution and recrystallization of Mg(OH)2, altering its growth tendency and promoting the formation of hexagonal crystal Mg(OH)2. During soaking in water, the increased content of MgCl2·6 H2O led to a decrease in the softening coefficient due to the dissolution of excess MgCl2. The structure of the 5Mg(OH)2·MgSO4·7 H2O phase underwent changes as Cl- entered the crystal interior, leading to an increase in the d-spacing of the 5Mg(OH)2·MgSO4·7 H2O phase at the (222) crystal plane. The introduction of Cl- endowed the 5Mg(OH)2·MgSO4·7 H2O phase with the potential to transform into 5Mg(OH)2·MgCl2·8 H2O. Following immersion in water, the modified structure of the 5Mg(OH)2·MgSO4·7 H2O phase retained its relative integrity, resulting in a higher softening coefficient of 0.73 after a 90-day soaking period, attributed to the proper introduction of Cl-.

Research on the application of phosphogypsum in magnesium oxysulfate cement: A comparison with sand

Phosphogypsum (PG), as an industrial by-product, has historically suffered from challenges in achieving efficient utilization, resulting in enormous accumulation and environmental contamination. In this study, a certain proportion of PG was employed as a substitute for sand in magnesium oxysulfate cement (MOSC). The effects of PG on the properties, pores distribution, phase composition and microstructure of MOSC were investigated. The results showed that the introduction of PG yielded several beneficial effects, including enhanced volume stability and water resistance, alongside reduced apparent density. However, it also entailed several drawbacks, such as decreased paste flowability, prolonged setting time and increased water absorption rate of the specimens. PG incorporation induced no new crystalline phase, but moderate PG could promote nucleation and development of 5Mg(OH)2∙MgSO4∙7H2O (5∙1∙7 phase) and the group at 10% PG substitution has the highest compressive strength of 68.2 MPa. PG demonstrated the capability to hinder precipitation of Mg(OH)2, thereby enhancing the mechanical properties of MOSC. Due to the affordability and favorable environmental sustainability, PG-MOSC displayed considerable potential for various applications. This study elucidates the mechanism by which PG influences MOSC, providing reference and approach for the recycling of PG.

Research on the Performance of Carbon-coated Expanded Perlite-based Magnesium Oxysulfate Cement Composite Thermal Storage Materials

Research on the Performance of Carbon-coated Expanded Perlite-based Magnesium Oxysulfate Cement Composite Thermal Storage Materials

Effects of steel slag on the properties and microstructure of magnesium oxysulfate cement prepared by magnesium desulfurization byproducts

The magnesium oxysulfate (MOS) cement has problems of short setting time, poor water resistance, and volume instability. This paper investigates the potential of steel slag (SS) to modify the properties and microstructure of the MOS cement prepared by magnesium desulfurization byproducts (MDBs). The results showed that SS delayed the setting time, restrained the volume shrinkage, and improved the water resistance of the MOS cement. The hydration products of the MOS cement were the fibrous 318 phase (3 Mg(OH)2•MgSO4•8H2O), lamellar Mg(OH)2, and MgCO3. The addition of SS increased the pH and decreased the overall hydration reaction rate and the amount of Mg(OH)2 in the MOS cement. SS reacted with Mg(OH)2 at the late stage to form an amorphous M–S–H gel, which increased the gel pore volume and the density of the cement. In conclusion, SS enhanced the application potential of MOS cement, through improving its macroscopic properties.

Thermodynamic mechanisms on the effects of mix proportion, and type and dosage of chemical modifier on phase assemblage of magnesium oxysulfate cement

The effects of the type of raw material, mix proportion, and chemical modifier on the mechanical properties and water resistance of magnesium oxysulfate cement (MOS) have been extensively studied. However, the formation mechanism of hydration products remains obscure. This study aims to clarify the hydration mechanism of MOS through a thermodynamic modeling approach and to explore the effects of mix proportion and type and dosage of modifier on the phase assemblage as well as the mechanical properties of hardened paste. The volume fraction of 5Mg(OH)2⋅MgSO4⋅7H2O (5-1-7) is used as a key parameter to establish the relationship between the mix proportion and the compressive strength of the MOS system. The results demonstrate that the thermodynamic modeling method can predict the phase evolution of MOS with various mix proportions. As the molar ratio of reactive-MgO (α-MgO) to MgSO4 increases, both the 5-1-7 volume fraction and compressive strength of hardened paste initially increase and then decrease, while decreasing as water dosage increases. The volume fraction of 5-1-7 is proportional to the compressive strength of MOS. Compressive strength is greatest at molar ratio of nMgO:nMgSO4 = 4–9 and nH2O:nMgSO4 = 9–20. The efficiency of modifiers is: citric acid (CA) > tartaric acid > EDTA > phosphoric acid > acetic acid. The modifying mechanism of CA involves the initial formation of 3Mg(OH)2⋅MgSO4⋅8H2O(3-1-8), followed by its transformation into 5-1-7.