Basic Magnesium Sulfate Cement Research Articles

Effect of Packaging Method and Storage Environment on Activity of Magnesium Oxide and Mechanical Properties of Basic Magnesium Sulfate Cement.

As one of the raw materials of basic magnesium sulfate cement (BMSC), the activity of light-burned magnesium oxide (MgO) has an important effect on the hydration rate, hydration products, and mechanical properties of BMSC. To reveal the influence of packaging method, storage environment, and storage time on the activity of MgO and the mechanical properties of BMSC, an experiment was conducted by using ordinary woven bags, peritoneal woven bags, and plastic and paper compound bags to store the finished BMSC and the raw materials (light-burned MgO, MgSO4·7H2O, fly ash, and a chemical additive) under the conditions of natural environment, sealed environment, and wet environment, respectively. Comparative analysis of the effects of packaging method, storage conditions, and storage time on the activity of MgO and the mechanical properties of BMSC was performed through the mechanical strength test of mortar specimens. The results showed that in a sealed environment, the loss of a-MgO content in light-burned MgO was minimized, which was more conducive to keeping the mechanical properties of BMSC stable. In the wet environment, the mechanical strength of BMSC was significantly reduced in the early stage (1 day) due to the significant reduction in the activity of MgO, and the mechanical strength of the finished BMSC and prepared BMSC after 120 days of storage was still lost, regardless of the packaging method. However, the storage environment and packaging method had relatively little effect on the late mechanical strength (28 days) of BMSC. It is advisable to use ordinary woven bags for packaging in natural and sealed environments as this is more economical for engineering applications. Plastic and paper compound bags are superior to ordinary woven bags and peritoneal woven bags in wet environments.

Study on the Preparation and Compressive Strength of Boron Mud-Based Basic Magnesium Sulfate Cement.

The direct discharge of boron mud poses significant environmental hazards to soil and groundwater. Despite extensive research efforts, the reprocessing of boron mud has not yielded significant advancements. Recently, the development of magnesium cement has spurred interest in the reutilization of boron mud. However, the direct treatment of boron mud remains challenging, necessitating pre-treatment in most studies to achieve substantial results. Consequently, research on the direct incorporation of untreated boron mud is scarce. This study explores the feasibility of using uncalcined boron mud as a base material in basic magnesium sulfate cement (BMSC), composed of lightly calcined magnesia and magnesium sulfate heptahydrate. The effects of varying boron mud content on the compressive strength of the BMSC system were investigated. The results indicate that the 5·1·7 phase is the primary strength phase of BMSC. When the boron mud content is 30%, the uncalcined boron mud has a minimal impact on the formation of the 5·1·7 phase. Additionally, the 28 days compressive strength of BMSC-B30 showed a slight difference compared to the control group BMSC-C, registering at 66.7 MPa. TG-DSC analysis revealed that the presence of a small amount of boron mud inhibits the micro-expansion trend of the BMSC structure. Furthermore, XRD and SEM analyses confirmed that the addition of uncalcined boron mud does not significantly alter the phase structure of the 5·1·7 phase in BMSC. This study provides a foundational basis for the long-term development of direct boron mud treatment.

Study on mechanical properties of E-glass mat reinforced basic magnesium sulfate cement thin-slab

To achieve sustainable development and reduce the carbon footprint in building material production, the E-glass fiber mat was impregnated with basic magnesium sulfate cement (BMSC) by lamination impregnation. This process reduces environmental pollution from cement preparation, increases fiber volume content, and enhances the mechanical properties of cementitious composite materials. The study examined axial tensile, four-point bending resistance, drop weight impact resistance and pendulum impact resistance of BMSC thin-slab reinforced with dispersed short glass fiber (SGF), short glass fiber mat (SGFM) and continuous glass fiber mat (CGFM) of varying gram weights. The results show that the mechanical properties of BMSC thin-slab reinforced with fiber mat are much higher than those of SGF reinforced thin-slab. The tensile strength of BMSC thin-slab reinforced with CGFM is higher than that of BMSC thin-slab reinforced with SGFM at the same gram weight, and the tensile strength increases as the weight of CGFM increases. Specifically, the axial tensile strength of BMSC thin-slab reinforced with 450 g of CGFM is nearly 8 times higher than that of SGF reinforced BMSC thin-slab. BMSC thin-slab reinforced with 450 g of CGFM has the maximum proportional limit load and bending strength. The impact strength and toughness indexes of BMSC thin-slab reinforced with CGFM are the highest, followed by SGFM reinforced BMSC thin-slab. The addition of 300 g CGFM significantly enhanced flexural toughness during the early stage of thin-slab cracking, while 450 g CGFM showed significant improvement in flexural toughness during the middle and late stages of cracking. When comparing thin-slabs with the same glass fiber volume ratio, those reinforced with 450 g CGFM exhibited the best impact resistance. SEM results indicated superior adhesion between 450 g CGFM and the cement matrix, as well as between adjacent CGFM layers, with fiber breakage being the main cause of specimen failure.

Chromium immobilization in basic magnesium sulfate cement: Experimental and density functional theory studies

This study investigated the effects of different concentrations of Cr(III) on the properties of basic magnesium sulfate cement (BMSC). In addition, the hydration process of BMSC with different concentrations of Cr(III) was studied using isothermal calorimetry and in-situ pH monitoring. A combined experimental approach and density functional theory simulation was further employed to investigate the solidification mechanism of Cr(III) in BMSC. The results indicated that Cr(III) affected the hydration heat, pH value, compressive strength and setting time of BMSC, and the influence became more obvious with the increase of Cr(III) concentration. In addition, the solidification efficiency of Cr(III) in BMSC was up to 99.9%; the efficient solidification of Cr(III) in BMSC primarily operated through ion exchange interactions, as revealed by density functional theory simulation and phase analysis results. Furthermore, the BMSC matrix after being immersed in simulated acid rain solutions for 28 days had a compressive strength of over 45 MPa, showing remarkable resistance to acids.

Research on and Model Analysis of Flexural Mechanical Properties of Basic Magnesium Sulfate Cement Concrete Beams.

This study presents a comprehensive investigation into the mechanical properties of Basic Magnesium Sulfate Cement Concrete (BMSC) in comparison to Ordinary Portland Cement Concrete (OPC) within reinforced concrete components. The main objective is to evaluate BMSC's applicability for practical engineering purposes, with a focus on its with early high strength, improved toughness, and superior crack resistance compared to conventional concrete. Experimental procedures involved fabricating beam specimens using OPC concrete with a C40 strength grade, alongside BMSC beams with varying strength grades (C30, C40, and C50). These specimens underwent bending resistance tests to analyze crack patterns and mechanical characteristics. The findings reveal that BMSC beams demonstrate enhanced bending and tensile properties at equivalent strength grades compared to OPC beams. Particularly, cracking mainly occurred at the mid-span region of BMSC beams, characterized by narrower cracks, indicating superior crack resistance. However, it was noted that the toughness of BMSC beams decreases as the strength grade increases. The maximum mid-span deflection of the BMSC test beam was smaller than that of the OPC test beam, which was 3.8 mm and 2.6 mm, respectively. The maximum crack width of the OPC beam was 4.7 times that of the BMSC beam. To facilitate practical implementation, the study developed calculation models for estimating the crack bending distance and ultimate bending distance in BMSC beams, offering valuable tools for engineering design and optimization. Overall, this research provides significant insights into the mechanical behavior of BMSC, presenting potential advantages for structural engineering applications.

Mechanical properties and water resistance study of basic magnesium sulfate cement-emulsified asphalt composite materials

This study introduces a novel semi-flexible composite material (BMSC-EA), formed by merging the favorable properties of emulsified asphalt (EA), known for its high flexibility and crack resistance, with basic magnesium sulfate cement (BMSC), recognized for its high rigidity, early strength, and toughness. The research systematically explores the impact of varying EA dosages on BMSC properties. Furthermore, the study analyzes the phase composition, pore structure, and microstructure of BMSC-EA materials. Results indicate that an increase in EA dosage leads to a corresponding extension in the setting time of BMSC, accompanied by a gradual decrease in compressive and flexural properties. Interestingly, the flexural compression ratio of BMSC increases, suggesting that EA addition significantly enhances BMSC toughness. The principal hydration product of BMSC comprised crystals of 5Mg(OH)2∙MgSO4∙7 H2O (5∙1∙7 phase). However, the introduction of EA exerted an inhibitory influence on the generation of Mg(OH)2, leading to a scenario where more MgO remained uninvolved in the hydration reaction. The porosity of the BMSC matrix increases with higher EA content. After subjecting the BMSC-EA material to water immersion treatment, a noteworthy observation emerged: exceptional water resistance was evident when the EA dosage reached 10%. This phenomenon was primarily ascribed to the heightened densification (ultrasonic velocity) observed in the BMSC-EA samples under these conditions. Additionally, the study observes further growth of Mg(OH)2 in BMSC after water immersion treatment, but excessive Mg(OH)2 negatively impacts BMSC-EA. These findings serve as both experimental and theoretical foundations for advancing innovative semi-flexible composite pavement materials.

Properties and effective improvement approaches of basic magnesium sulfate cement under high-temperature pre-curing

Basic magnesium sulfate cement (BMSC) cured at room temperature has excellent mechanical properties and is widely used in the production of magnesia-based building materials products. However, BMSC products are often manufactured higher than room temperature. This work examines mechanical properties of BMSC under high-temperature pre-curing (HTPC). Citric acid (CA), selected as additive, content was increased and self-made 5Mg(OH)2·MgSO4·7 H2O seed crystal (517 SC) was added to the BMSC to improve their properties. Compressive strength and water resistance were tested, accompanied with an examination of hydration products, monitoring of electrical conductivity evolution and microstructure analysis. The results suggest that HTPC has negative effects on mechanical properties of BMSC and the main hydration product of the BMSC is transformed from 517 phase to Mg(OH)2. The increase in CA content can improve the mechanical properties of BMSC under HTPC to some extent. The addition of self-made 517 SC can significantly improve the compressive strength and water resistance of BMSC under HTPC, which can be attributed to promoting the in-situ growth of 517 phase without reducing the degree of MgO hydration.

The Influences and Effect Mechanism of Low Temperature Curing on the Performances of Basic Magnesium Sulfate Cement

The Influences and Effect Mechanism of Low Temperature Curing on the Performances of Basic Magnesium Sulfate Cement

Flexural behavior of BMSC beam exposed to the harsh environment

Basic magnesium sulfate cement concrete (BMSC) was invented in 2013, which has many merits: excellent mechanical performance, good toughness and good crack resistance. But the mechanical performance of BMSC beams laid in the harsh weather for a long time is not known. The mechanical properties of six corroded reinforced BMSC beams were studied for applying this new concrete to practical engineering. It can be found that there is no rust crack before loading test. The bearing capacity of corroded reinforced BMSC beam laid in the harsh environment for two years, especially in the weather of long-term freeze-thaw cycles and acid rain, degraded by 11.9 % and the bending rigidity degraded by 17.0 %. Based on the attenuation of steel corrosion and deterioration of BMSC after the harsh exposure, the model of bearing capacity and cracking load of the corrosion-damaged BMSC beam is proposed. This paper is helpful to the application of BMSC members in the area of harsh environments.

Compressive Strength of Basic Magnesium Sulfate Cement Coral Aggregate Concrete (MCAC) on Non-Destructive Testing

Compressive Strength of Basic Magnesium Sulfate Cement Coral Aggregate Concrete (MCAC) on Non-Destructive Testing

Basic magnesium sulfate cement products exposed to air at various exposure ages: Phase composition, microstructure, and mechanical characteristics

Basic magnesium sulfate cement (BMSC) is a kind of air hardening cementitious material with the advantages of high strength, light weight, fire resistance, low alkalinity. However, the durability of the main binding phase (phase 5) of BMSC should be verified. In this work, the flexural strength of BMSC boards with ages between 0.25 years and 11years was investigated. The phase composition and microstructure of BMSC samples, including BMSC boards and the sample of BMSC beam-column joint that hydrates at low temperature were studied. The results reveal that the flexural strength of glass fiber-reinforced BMSC boards is higher than that of ordinary BMSC specimens, and the higher the content of phase 5 is, the greater the flexural strength is. Phase 5 within BMSC boards exposed to the air shows good environment durability, and the change of its content shows little relationship with the service age of BMSC. The phase composition of BMSC samples with long ages still predominantly consists of phase 5, and the microstructure of BMSC remains dense. Besides, the incorporation of air entraining agent can effectively improve the pore distribution of BMSC and generate numerous capillary pores, which may benefit the frost resistance of BMSC. Additionally, even at low temperatures (around 0 °C), BMSC concrete can be hardened to achieve the design strength and fly ash can be dissolved in the matrix of BMSC to form new gel phases.

Dynamic mechanical properties and failure mechanism investigation of multiscale toughened basic magnesium sulfate concrete

The dynamic impact compressive properties of a novel whisker composite material (i.e., ultra-high toughness basic magnesium sulfate cement concrete, UHTBMSC) is investigated in this study. First, X-CT and scanning electron microscopy are used to characterize the three-dimensional distribution characteristics of two types of fibers in the UHTBMSC, as well as the microstructure. Second, the Hopkinson compression bar technique is used to investigate the dynamic impact compression behavior of UHTBMSC under different strain rates. Finally, a novel 3D random packing model of steel fibers (straight and hooked) is established, and the 3D mesoscopic numerical simulation of the dynamic impact compression behavior of UHTBMSC is performed. The results show that the steel fibers are crossed and evenly distributed in the UHTBMSC matrix, whereas needle-rod-like 5–1–7 whiskers appear in large quantities in the UHTBMSC. Dynamic impact compression results show that UHTBMSC is a rate-dependent material, and a mathematical relationship between strain rate and dynamic increase factor is established for UHTBMSC materials. The numerical simulation results agree well with the test results, indicating that the newly established 3D meso-model can be used to effectively analyze the dynamic compression mechanical behavior of UHTBMSC. In addition, the results confirm that UHTBMSC exhibits excellent resistance to dynamic impact compression, which is primarily attributed to the crack inhibition effects of 5-1-7 whiskers and steel fibers, thereby effectively improving the dynamic mechanical properties of UHTBMSC.

Experimental and numerical studies on the mechanical behaviors of basic magnesium sulfate cement concrete under dynamic split-tension

Dynamic splitting-tensile tests were conducted on basic magnesium sulfate cement concrete (BMSCC) at three different water-cement ratios using a 75 mm diameter split Hopkinson pressure bar (SHPB). The failure process of BMSCC under dynamic splitting loading was simulated using the finite element software LS-DYNA and a random aggregate mesoscopic model. The results demonstrated the strain rate effect in BMSCC, where the dynamic splitting-tensile strength increased with higher strain rates. Furthermore, the strength grade of the material significantly influenced the growth rate of peak stress, with higher strength grades exhibiting faster rates. The dynamic increase factor (DIF), a parameter characterizing the dynamic behavior of brittle materials, exhibited a linear relationship with the logarithm of strain rate. The LS-DYNA software was employed to numerically simulate the dynamic splitting-tensile process at the meso-scale, yielding satisfactory results with relative errors of 12.7%, 6.3%, and 3.3% for the dynamic splitting-tensile strength at different water-cement ratios, respectively.

Investigation on water resistance of basic magnesium sulfate cement containing weak organic acids

Magnesium oxysulfate cement has low strength and poor water resistance, so an additive is essential for the preparation of basic magnesium sulfate cement (BMSC). In this paper, the effects and the mechanisms of three organic weak acids on the water resistance in relation to flexural strength of BMSC are investigated. The results show that malic acid fails to ameliorate the water resistance in relation to flexural strength, but citric acid and tartaric acid are successful. The ionisation constant and molecular formulas of different weak organic acids can affect the performance, such as fluidity, strength and water resistance. Therefore, the effect of citric acid is better than tartaric acid, and the optimal dosage of citric acid is 1.0%.

Experimental and Numerical Simulation on the Penetration for Basic Magnesium Sulfate Cement Concrete.

The penetration resistance of the new material Basic Magnesium Sulfate Cement (BMSC) is studied through comprehensive application of an experimental and numerical simulation method. This paper consists of three parts. The first part introduces the preparation of Basic Magnesium Sulfate Cement Concrete (BMSCC) and the study of its dynamic mechanical properties. In the second part, on-site testing was carried out on both BMSCC and an ordinary Portland cement concrete (OPCC) target, and the anti-penetration performance of the two materials was analyzed and compared from three aspects: penetration depth, crater diameter and volume, and failure mode. In the last part, the numerical simulation analysis was carried out based on LS-DYNA, and the effects of factors, such as material strength and penetration velocity on the penetration depth, are analyzed. According to the results, the BMSCC targets have better penetration resistance performance than OPCC under the same conditions, mainly manifested in smaller penetration depth, smaller crater diameter and volume, as well as fewer cracks.

Effect of seed emulsion on the early hydration behavior of basic magnesium sulfate cement

Basic magnesium sulphate cement (BMSC) has been known as a lightweight and high strength magnesium-based cementitious material. However, the addition of admixtures (e.g. citric acid) significantly retards the early hydration process of cement, which is not conducive to its actual utilization in construction. In this work, BMSC and fly ash (FA, 50 wt%)-BMSC with extremely high early strength were prepared by addition of the seed emulsion (SE) of BMSC obtained by wet grinding. Meanwhile, the influence of SE on the early hydration behavior of BMSC was investigated and the corresponding hydration mechanism was proposed as well. The results demonstrated that wet grinding can effectively reduce the particle size of crystal seeds and increase their specific surface area. The crystal seeds were emulsified after 3 h of wet grinding, with a particle size of 2–6 μm and a specific surface area of 14.36 m2/g. The SE could provide crystal nuclei to directly induce the generation of 5·1·7 phase, which could significantly accelerate the early hydration process at low temperature (15 °C). The 12 h-strength of BMSC was reached to 33 MPa with a sharply shorten initial setting time of 48 min when adding 6% SE. Moreover, the mechanical properties of FA-BMSC with addition of SE were improved by 30% since FA particles can be tightly encapsulated in the reticulated whisker structures of 5⋅1⋅7 phase. This work provides a theoretical and technical support to better understand and properly use of SE in the production of BMSC.

Dynamic compressive behaviour of basic magnesium sulfate cement–coral aggregate concrete (BMSC–CAC) after exposure to elevated temperatures: Experimental and analytical studies

This study investigates the effects of high temperature and strain rate on the dynamic compression behaviour of basic magnesium sulfate cement–coral aggregate concrete (BMSC–CAC). Specimens are exposed to temperatures ranging from 100 °C to 900 °C and then systematically tested using a split Hopkinson pressure bar (SHPB) apparatus. A three-dimensional mesoscale modelling approach is adopted in this study to account for the random shape and position of the aggregate. Results indicate that the dynamic impact damage is due to the coupled effect of high exposure temperature and high strain rate. At lower exposure temperatures, the dynamic compressive strength is similar to that at ambient temperature. However, at exposure temperatures of 500 °C and 700 ℃, the compressive strength is reduces to 50% and 30% of that at ambient temperature, respectively. Additionally, an increase in the exposure temperature increases the strain rate and continuously decreases the elastic modulus of concrete. A dynamic constitutive model is proposed considering the temperature and strain rate as influencing factor. This mesoscale modelling method is highly reliable and provides the best calculation parameters for simulating and predicting the dynamic compressive effect of BMSC–CAC after exposure to high temperatures.

Investigation of the performance of basic magnesium sulfate cement mortar

Basic magnesium sulfate cement (BMSC) is a kind of magnesium oxide (MgO)–magnesium sulfate (MgSO4)–water (H2O) modified ternary cementitious material prepared from light burned magnesia, magnesium sulfate heptahydrate, water and additives. The effects of α-magnesium oxide/magnesium sulfate ratio (MO/MS), water/magnesium sulfate ratio (W/MS), sand-to-binder ratio (s/b) and superplasticiser dosage (SPD) on the performance of BMSC mortar were studied for the first time in this work. The results showed that for, optimal 28-day flexural strength, α-MO/MS = 10:1, W/MS = 16:1, s/b = 0.8 and SPD = 0.3%. For optimal 28-day compressive strength, α-MO/MS = 8:1, W/MS = 14:1, s/b = 0.6 and SPD = 0.4%. For best water resistance, α-MO/MS = 12.5:1, W/MS = 14:1, s/b = 0.2 and SPD = 0.1%. Based on these results, the basic mix proportion ranges of BMSC mortar should be α-MO/MS = 8:1–12.5:1, W/MS = 14:1–16:1, s/b = 0.2–0.6 and SPD = 0.1–0.4%.

Mechanical properties and microstructure of basalt fiber-biobased- basic magnesium sulfate cement

A low-carbon composite termed basalt fiber (BF)-biobased-basic magnesium sulfate cement (BMSC) is proposed. It utilizes recycled wood fiber (RWF) and BF as lightweight fillers and reinforcements. The microscopic mechanism of the effect of RWF and BF on the fluidity of BMSC paste and the mechanical properties of the hardened samples is discussed. The microstructure, physical phase analysis and image identification semi-quantification demonstrated that RWF enhances the development of the 5·1·7 phase. After further incorporation of BF, the fluidity and dispersion of the paste then decrease. However, the magnesium cement matrix–RWF–BF system form in the BMSC turns the single-fiber reinforcement into a composite reinforcement. It improves the mechanical properties of the composite, especially the flexural strength, even though the addition of RWF made the BMSC composite less dense. In addition, the biobased-BMSC is influenced by the coupling-competition mechanism, which is reflected by the pore structure and mechanical properties. It indicates that the low-carbon composite has the potential for carbon sequestration and the development of environmentally friendly additives for improving the performance of BMSC.

Immobilization of Zn(Ⅱ) and Cu(Ⅱ) in basic magnesium-sulfate-cementitious material system: Properties and mechanism

To solve the environmental problems caused by heavy metal pollution, a new cementitious material (basic magnesium sulfate cement, BMSC) was developed for the solidification of Cu2+/Zn2+. First, the effects of different amounts of Cu2+/Zn2+ on the properties (compressive strength, setting time, pH, and leaching toxicity) of the BMSC were investigated. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) were used to investigate the effects of different amounts of Cu2+/Zn2+ on the phase and microstructure of BMSC. The results showed that Cu2+/Zn2+ inhibited the hydration of BMSC, reduced compressive strength, and prolonged the setting time. The results of the leaching tests showed that the BMSC system exhibited high immobilization efficiency (up to 99%) for Cu2+/Zn2+. Further, the BMSC solidification matrix exhibited excellent acid resistance (compressive strength >40 MPa after 28 days of immersion). The physical phase analysis showed that the main phases of BMSC were the 5Mg(OH)2-MgSO4-7 H2O (5−1−7) phase and Mg(OH)2, and the crystal structure refinement analysis suggested that Cu2+/Zn2+ ions were substituted with Mg2+ in the 5–1–7 phase. It was confirmed that the solidification mechanism of BMSC on Cu2+/Zn2+ is mainly performed by chemical complexation and ionic substitution.