Magnesium Oxysulfate Research Articles

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%.

Durable self-cleaning superhydrophobic coatings based on 5 Mg(OH)2·MgSO4·2H2O whisker-SiO2 nanoparticles composites

Poor mechanical robustness is a major handicap to the practical application of superhydrophobic coatings. It is imperative to design an effective strategy to improve the durability of superhydrophobic coatings. In this work, we prepared a robust superhydrophobic coating using all-in one suspension that contained magnesium oxysulfate whiskers, SiO2 nanoparticles and amino drying varnish via a drop coating method. The suspension was formed through that a mixture of magnesium oxysulfate whiskers and SiO2 nanoparticles modified by tetraethylorthosilicate and octadecyltrichlorosilane was mixed into amino drying varnish diluted with thinner. The results showed that such inorganic–organic composite modification method could effectively improve the modified effect. The prepared coating displayed excellent water repellency not only on the top surface but also at any exposed internal section throughout the coating, and maintained its superior superhydrophobicity even after the top area was scraped off a layer. Notably, the coating exhibited outstanding self-cleaning capability with a contact angle of 168.81° and a very low sliding angle. Further, amino drying varnish as binders replaced by other common commercial paints could also prepare superhydrophobic coatings. This study can not only facilitate the large-scale fabrication and application of superhydrophobic coatings, but also expand the application filed of magnesium oxysulfate whiskers.

Different effects for phosphoric acid and calcium citrate on properties of magnesium oxysulfate cement

Chemical additive is an indispensable component to improve the properties of magnesium oxysulfate cement (MOSc). In this paper, the differences of the effects of chemical additives phosphoric acid (PA) and calcium citrate (CC) on the performance of MOSc were investigated by analyzing the composition and content of MOSc hydration products and characterizing the microstructure. The results manifest that the hydration rate of MOSc with PA is relatively slow, but the crystalline grain of the hydration product 5 Mg(OH)2·MgSO4·7H2O (5·1·7 phase) is coarse, and the composition of the hydration product is excellent, so it has good mechanical strength and water resistance. The hydration rate of MOSc with CC is relatively fast, and the amount of 5·1·7 phase is relatively high, but its crystalline grain is not as coarse as that of MOSc with PA. Therefore, the MOSc with CC has high early strength, but its later mechanical strength and water resistance are not as excellent as that of MOSc with PA. Meanwhiles, it is found that 5·1·7 phase with low crystallinity and 5·1·n phase with high content of crystal water may exist in MOSc, which is another factor affecting the reduction of its mechanical strength after immersion. The research results are of great significance for promoting the progress of chemical additive modification technology and improving the performance of MOSc.

Effects of different waste forestry residues on the property of magnesium oxysulfate cement-based composites

To improve the utilization of forestry wastes and save non-renewable raw materials, new composite materials were prepared by adding five kinds of forestry residues into magnesium oxysulfate cement (MOSC) and cured for 3d to 100d. The flexural and compressive strength, relation of force and displacement before fracture, and the microstructure of composites were studied. The range of flexural strength and compressive strength was 11.30–13.89 MPa and 34.38–55.97 MPa at 100d for the composites, with change rate of − 4.07%∼17.91% and − 31.98%∼− 58.27% comparing to MOSC. The relation of displacement and maximum force before fracture was analyzed with term of quantified energy absorption capacity to characterize the brittleness. All residues improve the capacity by 22.98∼374.77% under flexural force at 100d, while reducing the capacity by 15.96∼48.76% under compressive force. Effects of biomass type on primary functional groups, phase changes, thermal stability and microstructure were analyzed by various techniques. Through a newly proposed method, the optimized composite with the best performance was to replace MgO using 10% locust powder or 10% poplar shaving. This paper proposed an environmental-friendly approach to improve the utilization of forestry wastes and develop new cement-based building materials.

Influence of Citric Acid on the Fundamental Properties of CO2 Cured Magnesium Oxysulfate Paste.

Magnesium oxysulfate (MOS), mainly composed of magnesium oxide and magnesium sulfate, is a kind of gas-hardening cementing material with low energy consumption and CO2 emissions. In order to develop environment-friendly cement-based materials, MOS needs to be studied systematically. The paper mainly investigates the influence of citric acid (a retarder) on the working and mechanical properties of MOS paste. In this study, the setting time of fresh MOS paste is determined. The flexural and compressive strengths of hardened specimens exposed to the environment of water dry-wet (D-W) alternations, freeze-thaw (F-T) cycles, and sulfate D-W alternations are investigated. Furthermore, the drying shrinkage (D-S) rate of MOS paste is tested for 3 days and 28 days. The specimens are cured in standard or CO2 curing environments. A scanning electron microscope energy spectrum (SEM-EDS) is obtained to analyze the morphology of hydration products. Results show that citric acid can increase the setting time of MOS paste. The citric acid and CO2 curing have a positive effect on the mechanical strengths and the resistance to erosion by water, F-T cycles, and sulfate D-W alternations. The D-S rate decreased in relation to the increasing dosages of citric acid and increased with CO2 curing. MOS with 0.3% of the total binder material mass shows the best erosion resistance. As observed in the results of SEM-EDS, the CO2 curing and the citric acid can make the hydration products denser.

Improved mechanical strength of magnesium oxysulfate cement using ferric sulfate

This research investigated the impact of ferric sulfate addition on the mechanical strength of magnesium oxysulfate (MOS) cement. Variations in the fluidity, setting time, hydration reaction, volume stability, water resistance, phase composition, and microstructure of MOS cement were reported. The results show that the addition of ferric sulfate accelerated the dissolution of MgO through reacting with OH− to form Fe(OH)3 gel and promoting the growth of 3 Mg(OH)2·MgSO4·8H2O, which reduced the fluidity and shortened the setting time of MOS cement. Although the growth time for 5 Mg(OH)2·MgSO4·7H2O was extended after adding ferric sulfate, the content and crystallinity of 5 Mg(OH)2·MgSO4·7H2O were increased, improving the mechanical strength and volume stability of MOS cement. The formation of Fe(OH)3 gel in MOS cement densified the matrix and optimized the pore structure, which can further enhance the mechanical strength and water resistance of MOS cement.

Effect of Epsom Salt Concentration and Dry-Mix Composition on Bonding Properties of Magnesium Oxysulfate

Non-hydraulic magnesium oxysulfate cement has many superior properties than ordinary portland cement and it draws much research interest due to energy saving and environment protection considerations. It is formed by the exothermic reaction between lightly calcined MgO and MgSO4·7H2O (epsom salt) solution. This heat is responsible for cracking and makes the product unsound. The incorporation of inert filler can overcome this problem by absorbing the excess heat. In present work, a parametric study was conducted to investigate the effect of dry-mix composition (MgO: inert filler) and gauging solution epson (MgSO4·7H2O) concentration on cementing properties of magnesium oxysulfate cement. The results show that a 1:1 dry-mix composition of MgO and dolomite with 25º Be concentration of magnesium sulfate works best in the cementing action of magnesium oxysulfate

Experimental study on the preparation of magnesium oxysulfate cement-based composites using waste locust powders to replace non-renewable magnesium oxide

Magnesium oxysulfate cement is a new type of environment-friendly cement with low energy consumption and promising development potential. But the raw material MgO is not renewable. To improve the utilization of forestry wastes and save MgO, composites containing locust powders with 0 ∼ 25 % mass of MgO were prepared by mechanical mixing and curing for 3d ∼ 100d. The slurry’s fluidity, mechanical property, water resistance and microstructure were studied. Strength data at 100d were found to be essential for property evaluation. The maximum locust dosage based on fluidity was 25 %, and composites with 10 %∼25 % locust exhibited flexural strength of 13.37 ∼ 15.12 MPa and compressive strength of 56 ∼ 64.3 MPa at 100d. The corresponding flexural strength improvement and compressive strength reduction comparing to cement with no locust were by 13.5 %∼28.35 %, and 21.86 %∼31.95 %, respectively. Regarding relations of flexural force and displacement before fracture at 100d, locust with 10 %∼25 % dosage improved the displacement and energy absorption capacity by 56.88 %∼125.58 % and 52.48 %∼108.49 %, showing lower brittleness. Composites containing 10 %∼25 % locust improved the flexural strength by 14.23 %∼48.82 % when soaking in water, and the softening coefficient was larger than 0.85 if cured for 35d and soaked for 7d, indicating good water resistance. Effects of locust dosage on primary functional groups, phase changes, thermal stability and microstructure were analyzed by various techniques. A new optimization method based on seven indicators is proposed, capturing the optimal locust dosage as 20 % mass of MgO. This paper proposed an environmental-friendly approach to improve the utilization of forestry wastes and develop new cement-based building materials.

Performance of magnesium oxysulfate (MOS) cement with granite powders after combined sulfate and chloride attacks

Salt erosion is one of the main factors affecting the durability of cement and concrete. Magnesium oxysulfate (MOS) cement is regarded as a new type of binder with many good features such as lower carbon dioxide emission, excellent fire resistance, etc. However, the salt erosion resistance of MOS cement is rarely studied. This research investigated the performance of MOS cement, with granite powders (GPs) as mineral admixture, soaked in NaCl and Na2SO4 solutions. X-ray diffraction (XRD) and simultaneous comprehensive thermal analyzer (TG-DSC) were used to detect the phase composition and hydration products of MOS cement. Scanning electron microscope (SEM) and mercury porosimeter (MIP) were used to analyze the pore structure and microstructure of MOS cement. The results showed that the value of the salt attack coefficient of MOS cement with 50 % by weight GPs reached 0.58 and 0.57 after immersion in NaCl and Na2SO4 solutions for 230 days, respectively. The compressive strength of MOS cement with 30 % by weight GPs reached the maximum value of 74.1 MPa after standard curing for 28 days by optimizing the pore structure. Both needle-like and plate-like Na2SO4·xH2O crystals were observed in the hydration products. Gypsum and Na2SO4·xH2O grew in the pores and matrix, generated expansion stress and destroyed the matrix structure of MOS cement. During the soaking period, the decomposition of the 5·1·7 phase and MgSO4·nH2O negatively affected the salt resistance of MOS cement. Physical and chemical erosion leads to a decrease in the value of the salt attack coefficient.

Isothermal calorimetry study of the effect of citric acid on the hydration kinetics of magnesium oxysulfate cement

The hydration kinetics of magnesium oxysulfate cement (MOS) with and without citric acid (CA) was evaluated via isothermal calorimetry. A series of tests were conducted with different MgSO4 solution-to-MgO ratios (r) and MgO with different activities at 15 °C and 25 °C. The test results indicated that the effect of CA on the overall cement hydration rate was determined by the CA dose (w) primarily and can be simulated by a generalized scale factor model. The heat flow and cumulative heat evolution of slurries with different CA dosages could be accurately predicted using the scale factor (f) model. There was a linear relationship between lgf and lg(w/w0), so the individual reaction order in CA could be obtained. The effect of temperature on the hydration kinetics of MOS cement with and without CA was modeled with the original scale factor model developed from the Arrhenius equation, and the apparent activation energy obtained was 66.3 and 74.9 kJ/mol, respectively. This study provided a basis for further in-depth research of the kinetic mechanism of the MOS hydration reaction.

Study of untreated phosphogypsum as a fine aggregate for magnesium oxysulfate cement

Phosphogypsum (PG), an industrial waste containing phosphorus, has resulted in accumulation and environmental pollution because of its shallow utilization rate worldwide. In this paper, unpretreated PG is incorporated into magnesium oxysulfate cement (MOSC) as an insert fine aggregate at different dosing levels. The performance of the resulting mortar is evaluated by testing workability, volume stability, mechanical properties, water resistance, and sustainability. Results show that PG improved the water resistance, the long-term compressive strength, and the microstructure of MOSC. XRD/Rietveld analysis and TG-DSC demonstrated that the incorporation of PG inhibited the crystallization of Mg(OH)2 and promoted the formation of 5 Mg(OH)2·MgSO4·7H2O (5·1·7 phase). Besides, some PG undergoes morphological changes that may disrupt the strength of MOSC. PG-MOSC has the potential for environmental sustainability because of its low carbon emissions and efficient toxic immobilization. The paper provides ideas and a reference for the resource utilization of PG.

A Review on the Application of Circulating Fluidized Bed Fly Ash in Building Materials

Circulating fluidized bed (CFB)-based coal burning technology is a type of clean coal combustion technology. Owing to its characteristics of low temperature combustion and desulfurization in furnace, the CFB fly ash is quite different from ordinary fly ash. Based on the comprehensive understanding of physical and chemical characteristics of CFB fly ash, this review summarizes the research progress of the application of CFB fly ash in Portland cement, magnesium oxysulfate (MOS) cement, solid-waste–based cementitious material (SWCM), concrete, geopolymer, artificial aggregate, and other building materials. The study shows that CFB fly ash can improve the early physical and mechanical properties and reduce the drying shrinkage properties for cementitious materials. Its unique chemical composition endows it with good application performance in the MOS cement, geopolymer, and SWCM. However, unfavorable characteristics of CFB fly ash, such as loose and porous structure, self-hardening behavior, and expansibility greatly hinder its practical applications in building materials. Therefore, some measures, such as addition of rational water-reducing agent, ultrafine grinding, mixing of ordinary fly ash, controlling the dosage of CFB fly ash, and water-cement ratio, must be taken to improve the negative influence of CFB fly ash on the building materials, in order to expand its application range. This article summarizes the application and research status of CFB fly ash in building materials, aiming at further promoting the research studies on CFB fly ash resource utilization in building materials and improving the efficiency of CFB fly ash resource utilization.

Preparation of Magnesium Oxysulfate Cement with Calcined Phosphate Tailings

Preparation of Magnesium Oxysulfate Cement with Calcined Phosphate Tailings

Effects of CO2 Curing on Properties of Magnesium Oxysulfate Cement

Effects of CO2 Curing on Properties of Magnesium Oxysulfate Cement

Polyethylene reinforced by biomimetic (polydopamine, tannic acid) modified magnesium oxysulfate whisker: Mechanical properties, thermal properties and flame retardancy

Two-dimensional magnesium oxysulfate whisker (MOSw) was modified by polydopamine (PDA) and tannic acid (TA) instead of the traditional inorganic flame retardants activated by silane coupling agent ( γ -methacryloxypropyltrimethoxy silane, KH570) such as Mg(OH) 2 and Al(OH) 3 . Differential scanning calorimeter (DSC) results showed that MOSw could act as heterogeneous nucleation for crystallization of HDPE, and further increased the initial crystallization temperatures of composites treated with PDA and TA. Dynamic mechanical thermal analysis (DMTA) showed that both the storage modules and loss modules of the composites with modified MOSw were significantly increased, which suggested the improved compatibility and dispersion between the modified MOSw and matrix. The tensile strengths of HDPE/MOSw@PDA composite and HDPE/MOSw@TA composite could be 118.0% and 121.2% higher than that of HDPE/MOSw@KH570 composite, and the corresponding impact strengths could be 124.0% and 111.2% higher, respectively. Compared to HDPE, the synergistic effect of PDA- MOSw and TA- MOSw (combustion heat through the dehydration of MOSw, gas-phase flame-retarded effect of MOSw, scavenging of active free radicals) increased the limit oxygen index (LOI) of composites from 19.4% to 23.4% and 23.8%, respectively, which were higher than 20.6% of traditional HDPE/Al(OH) 3 @KH570 composite with the same 30 wt.% filler. Schematic of self-polymerization of dopamine, and chelation of tannic acid with metal ions • MOSw covered with PDA and TA substituted for the traditional inorganic flame retardants activated by silane coupling agent. • Different from traditional inorganic flame retardants such as Mg (OH) 2 and Al (OH) 3 , MOSw modified by PDA and TA could not only improved the flame retardancy of HDPE, but also improved the tensile strength to a certain extent. • The composites with MOSw modified by PDA and TA showed good thermal stability.

Comparison of sawdust bio-composites based on magnesium oxysulfate cement and ordinary Portland cement

This study incorporated sawdust (SD) as a bio-aggregate into magnesium oxysulfate cement (MOSC) and ordinary Portland cement (OPC) for the preparation of composite lightweight materials. The effect of sawdust dosage on the mechanical properties, thermal properties, water absorption, and water resistance of the two bio-composites was investigated. Experimental results revealed that SD-MOSC presented lower density, higher compression strength, and excellent thermal insulation properties than SD-OPC. Thus, MOSC is more suitable as a binder for sawdust aggregates than OPC. Microstructure observation showed that 5 Mg(OH)2·MgSO4·7H2O (5·1·7) phase whiskers preferred to form at the defects of sawdust, indicating that MOSC had better compatibility with sawdust. The increase of sawdust hindered the generation of 5·1·7 phase, resulting in the strength reduction. MOSC-based sawdust bio-composites are a promising material for production of thermal insulation panels and are favorable for environmental protection.

Optimizing 1-hydroxyethylidene-1,1-diphosphonic acid and mechanically-activated iron ore tailings to prepare low-cost and retarded magnesium oxysulfate cement

Industrial solid waste, known as iron ore tailings (IOT) is often generated in mineral processing. Precariously, the output of tailing byproducts is quite large while its utilization is very low, and this has become a vital issue to China's economic and social development. This study is aimed at developing a sustainable composite using IOT. In this paper, the impact of IOT and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) on the magnesium oxysulfate (MOS) cement attributes were studied from the micro and macro aspects. Retardation, high-strength, low-cost MOS cement samples were prepared. The compressive strength, setting time and water resistance of MOS cement were explored by replacing light-burned magnesia powder with activated IOT (by 10%, 20%, and 30% respectively). In this paper, the mechanical properties, water resistance, and retardation mechanism of adding HEDP to MOS cement were thoroughly investigated by XRD, TG-DTA, SEM, MIP and other test methods. HEDP forms a stable chelate with [Mg(OH)(H2O)]+ produced during the hydration of MgO, slowing down the hydrolysis of active MgO to Mg(OH)2, thereby delaying the setting time of MOS cement. The addition of HEDP provides feasibility for the application of MOS cement in practical engineering. Experimental results reveal an optimal HEDP dosage of 0.75% and the addition of 10% of mechanically activated IOT for 1.0 h does not reduce the compressive strength of MOS cement, and the purpose of solid waste treatment can be achieved.

Improved low-carbon magnesium oxysulfate cement pastes containing boric acid and citric acid

The dominant form of cement used worldwide is Portland cement with annual output of approximately 4 billion tons and emissions of approximately 8% of total global anthropogenic greenhouse gas emissions. One of inorganic binders being developed to relieve this negative effect relates to the use of low-carbon magnesium oxysulfate (MOS) cement. This research investigated the hydration process and mechanical properties of low-carbon MOS cement containing citric acid and boric acid. A boric acid-citric acid gel precursor is formed in MgSO4 solution, changing the hydration behavior of MOS cement due to electrostatic and steric stabilization. As a result, 3 Mg(OH)2·MgSO4·8H2O destabilizes to Mg(OH)2·MgSO4·5H2O and forms the phase 517 (5 Mg(OH)2·MgSO4·7H2O). This reduces the hydration rate of MOS cement and provides more time for the nucleation and growth of the phase 517 crystals, resulting in an optimization in pore structure and a decrease in total porosity, which improves the mechanical properties and produces a low-carbon MOS cement with characteristics that are more suitable for use in construction industry.

Synthesis and characterization of superhydrophobic magnesium oxysulfate whiskers

Superhydrophobic materials have attracted much attention for their special wettability. In this study, magnesium oxysulfate (MOS) whiskers were surface modified by vinyltrimethoxysilane (VTMS) and prepared as superhydrophobic materials, which are expected to be widely used in self-cleaning, corrosion prevention, and oil-water separation. The factors of silane concentration, hydrolysis time, reaction temperature, and reaction time were investigated. The superhydrophobic MOS whiskers were synthesized. SEM and XRD turned out that there were no apparent changes in the morphology and crystallization behavior of whiskers before and after modification, while the surface was uniformly coated with a layer of non-crystal material, and the surface of the whiskers employed a chemical bond Si–O–Mg covalently connected. The thermogravimetric analysis ultimately demonstrated that surface modification was beneficial to the improvement of the thermal stability of MOS whiskers. Superhydrophobic MOS whiskers showed good compatibility with organic solvents through oil-water separation experiments, and demonstrated excellent self-cleaning performance. The methodology for the surface treatment of MOS whiskers to prepare superhydrophobic whiskers in this work may be extended for other whiskers or fillers, which may be promising for the preparation of superhydrophobic materials.

Carbon-negative cement-bonded biochar particleboards

Biochar from bio-waste pyrolysis presents excellent CO2 sequestration capacity. This study innovated the design of cement-bonded particleboards utilizing a substantial amount of 50–70 wt.% pre-soaked biochar to render the products carbon-negative. We investigated the roles of biochar in magnesium oxysulfate cement (MOSC) system and demonstrated good mechanical and functional properties of biochar cement particleboards. In the presence of biochar, the amounts of hydration products were enriched in the cement systems as illustrated by the thermogravimetric analyses (TGA) and X-ray diffraction (XRD). We further incorporated supplementary cementitious materials (SCMs) and generated 5 Mg(OH)2⋅MgSO4·7H2O (5–1–7) phase in the MOSC system. As a result, our designs of biochar particleboards satisfied the standard requirements for flexural strength (> 5.5 MPa) and thickness swelling (< 2%). Moreover, our biochar particleboards presented a low thermal conductivity as the biochar pores disrupted thermal bridging within particleboards. We illustrated that the high dosage ratio of biochar could significantly offset the CO2 emissions of the particleboards (i.e., carbon-negative) via life cycle assessment. Noticeable economic profits could also be accomplished for the biochar particleboards. For instance, the 50BC-MOSC bonded particleboard (with 50 wt.% pre-soaked biochar as aggregate, 50 wt.% MOSC as binder) with promising mechanical properties could store 137 kg CO2 tonne−1 and yield an overall economic profit of 92 to 116 USD m−3 depending on the carbon prices in different countries. In summary, our new designs of carbon-negative biochar particleboards could curtail carbon emissions in the construction materials and promote the realization of carbon neutrality and circular economy.Graphical