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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. [ABSTRACT FROM AUTHOR]

To study the durability of magnesium oxychloride cement (MOC) in practical applications, samples from 6 to 80 years in different regions of China, including both north and south China, were collected. Phase composition and microstructure of MOC were analyzed, and phase transition patterns and microstructure characteristics of MOC were explored. The results show that, for MOC material, the main hydration product is 5Mg(OH)2·MgCl2·8H2O (phase 5·1·8), and the carbonation products are Mg(OH)2·MgCl2·2MgCO3·6H2O (phase 1·1·2·6) and 4MgCO3·Mg(OH)2·4H2O (phase 4·1·4). For MOC samples with ages less than 20 years, the content of phase 5·1·8 and the total content of carbonized phases (phase 1·1·2·6 and phase 4·1·4) increases and decreases in turn. The change of the total content of the carbonized phase is opposite to that of the phase 5·1·8 and is affected by phase 5·1·8. A calculation formula for the carbonation degree of MOC material system is proposed. The calculation results show that when the age is less than 14 years, the carbonation rate of MOC samples in the dry environment from north China is slow, but obviously increases when the age exceeds 14 years. Carbonation degree of the MOC samples at 6 years in the high humid environment of south China is close to that of the samples at about 20 years in north China. The crystal morphologies of different phases in MOC are varied. There are needle rod-like and flocculent crystals of phase 5·1·8 , short rod-like crystals of phase 1·1·2·6 , flaky crystals of phase 4·1·4 , and nubbly crystals of MgCO3 in MOC. Phase 5·1·8 ensures the integrity of the glass fiber, while sawdust shows disadvantages on the long-term service of MOC. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) is often recognized as an eco-friendly cement and has found widespread application in various sectors. However, research on its resistance against elevated temperatures including fire is very limited. This paper thoroughly investigated the mechanical performance of fibre reinforced MOC-based cementitious composite (FRMOCC) at ambient and elevated temperatures. A recently developed water-resistant MOC was used as the base matrix which was further reinforced using hybrid basalt and polypropylene fibres at various proportions, and a systematic study on the effect of fibre dosage on compressive and tensile strength of FRMOCC was conducted. The specimens were exposed to elevated temperatures ranging from 200 to 800 °C; mechanical performance and phase composition from a microscale study were analysed. The findings revealed that compressive strength, with the increase in temperature, substantially decreased, with values of 30–87% at 400 °C and over 95% at 800 °C. Specimens with 1.5% basalt and 0.5% PP fibre showed the least reduction possibly due to the vacant channels created as a result of the melting effect of PP fibres. Tensile strength was also completely lost at 600 °C and the specimens suffered substantial mass loss exceeding 30% at this temperature, indicating significant matrix decomposition. Additional analysis using X-ray diffraction (XRD) and scanning electron microscope (SEM) revealed the decomposition stages of the matrix and highlighted the instability of the main hydration phases of FRMOCC at elevated temperatures. [ABSTRACT FROM AUTHOR]

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.

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Magnesium oxychloride cement (MOC) is often recognized as an eco-friendly cement and has found widespread application in various sectors. However, research on its resistance against elevated temperatures including fire is very limited. This paper thoroughly investigated the mechanical performance of fibre reinforced MOC-based cementitious composite (FRMOCC) at ambient and elevated temperatures. A recently developed water-resistant MOC was used as the base matrix which was further reinforced using hybrid basalt and polypropylene fibres at various proportions, and a systematic study on the effect of fibre dosage on compressive and tensile strength of FRMOCC was conducted. The specimens were exposed to elevated temperatures ranging from 200 to 800 °C; mechanical performance and phase composition from a microscale study were analysed. The findings revealed that compressive strength, with the increase in temperature, substantially decreased, with values of 30–87% at 400 °C and over 95% at 800 °C. Specimens with 1.5% basalt and 0.5% PP fibre showed the least reduction possibly due to the vacant channels created as a result of the melting effect of PP fibres. Tensile strength was also completely lost at 600 °C and the specimens suffered substantial mass loss exceeding 30% at this temperature, indicating significant matrix decomposition. Additional analysis using X-ray diffraction (XRD) and scanning electron microscope (SEM) revealed the decomposition stages of the matrix and highlighted the instability of the main hydration phases of FRMOCC at elevated temperatures.

The application of magnesium oxychloride cement (MOC) is promising, but its poor water resistance seriously hinders its development and application. In this paper, we describe a new type of MOC with excellent water resistance, prepared using fly ash and hexadecyltrimethoxysilane (HDTMS). SEM, XRD, FTIR, TG/DSC, and other microscopic-scale studies were conducted to investigate the mechanism underlying the water-resistance enhancement of the new MOC. It was found that adding 20% fly ash and 3% HDTMS can strengthen the water resistance of MOC while retaining high mechanical properties. In particular, the residual coefficient remained at 0.91 after 7 days of immersion. This is because these two additives, when used together, can increase the content of the gelling 5-phase of MOC, as well as optimize the pore structure of MOC. [ABSTRACT FROM AUTHOR]

Phosphate ions significantly enhance the water resistance of magnesium oxychloride cement (MOC). In this study, MOC was prepared with a MgO/MgCl 2 molar ratio of 7 and a H 2 O/MgCl 2 molar ratio of 12, while varying the dosage of sodium dihydrogen phosphate. The aim was to observe the microstructural changes in 5Mg(OH) 2 ·MgCl 2 ·8H 2 O (Phase 5) crystals and the macroscopic mechanical properties before and after immersion. The research found that phosphate ions increase the content of air-cured Phase 5 and reduce the formation of Mg(OH) 2 by lowering the required Mg2+ concentration for Phase 5 production. However, excessive phosphate ions can damage the crystal structure of Phase 5, leading to a decrease in MOC strength. An appropriate amount of phosphate ions increases the output of Phase 5, resulting in a highly dense microstructure, which significantly improves the water resistance of MOC. Additionally, this enhances the pore structure of MOC, making the overall structure more compact and resistant to water penetration. This research offers valuable theoretical insights into Phase 5 crystal variations during air curing and water-immersion damage under low Mg2+ concentrations. • MOC with a relatively low molar ratio of MgO/MgCl2 at 7. • Additional 1–2 % Phase 5 crystal formation. • Excessive sodium dihydrogen phosphate depletes Phase 5 quantity. • Dosage of sodium dihydrogen phosphate should be kept below 4 %. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) is a new type of cement with high early strength and good brine corrosion resistance. However, the water resistance of MOC is poor, which limits its current application. Highland barley straw ash (HBSA) contains a large amount of silica and, when calcined and ground under certain conditions, has a higher pozzolanic effect. This study investigated the effect of adding HBSA on the water resistance and pore structure of MOC mortar (MOCM), and the correlation between them. HBSA was mixed with MOCM in different proportions to test the water adsorption and water resistance. Nuclear magnetic resonance technology and the Brunauer–Emmett–Teller method were then used to test the distribution of full pores and micropores, respectively, in MOCM. Finally, the gray entropy theory was used to analyze the correlation between all the pore parameters of MOCM and the water resistance, and the numerical relationship between the softening coefficient reflecting the water resistance of MOCM and the characteristic pore parameters was determined. Results showed that the water adsorption of MOCM with added 10% HBSA decreased by 2.11%, the water resistance increased by 6.80%, and the proportion of harmful pores and more harmful pores decreased by 25.11% compared with that without HBSA. Three pore characteristic parameters—the proportion of less harmful pores, most probable diameter within the range of 20 nm, and accumulated micropore volume—had a good linear correlation with the water resistance of MOCM. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC), a type of special construction material, has drawn much research attention in solid waste utilization and environment protection thanks to its eco-friendly production process. The potential consumption of limestone powder (LSP) in MOC products would further mitigate the environmental pollution. This study investigates the feasibility of using LSP in optimized MOC pastes. By adding 10%–40% by weight LSP, the flowability, mechanical, and microstructure properties of LSP-MOC pastes (MOC pastes mixed with LSP) were experimentally evaluated. Results showed that LSP had an adverse effect on the flowability and retarded the setting process. In terms of mechanical properties, decreases in flexural and compressive strength became significant in the presence of LSP. However, it is noteworthy that expansion was mitigated via free deformation tests, which was also reflected by microstructures. By defining normalized expansion strain, the overall strength-expansion performance was analyzed, resulting in a maximum consumption of 30% by weight LSP at a slight improvement in MOC pastes. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) is a promising binder with many advantageous properties over traditional binders. Its main downfall, restricting large-scale use, is its inherent susceptibility to moisture. However, in recent years, niche applications have developed where MOC has been deployed successfully. These include lightweight wall panels, floor tiles, and decorative panels. This paper investigates the effect of molar ratios (MgO/MgCl2 and H2O/MgCl2) and curing conditions on MOC. Findings illustrate that the use of appropriate molar ratios and the implementation of a suitable curing regime can significantly improve the moisture resistance of MOC. After 28 days of immersion in water, the MOC samples lost between 40% and 90% of their strength depending on the molar ratio, demonstrating the importance of correct proportioning. It was also found that curing MOC at temperatures between 20°C and 50°C provides the most stable MOC in humid conditions. These findings add to the current knowledge available on MOC. They will help end users to improve the performance of MOC in its current applications and work toward broadening the range of applications where MOC can be used successfully. [ABSTRACT FROM AUTHOR]

In this paper, the effects of metakaolin (MK) on the properties of magnesium oxychloride cement (MOC) such as setting time, hydration process, mechanical properties, compactness, phase composition, and microstructure were investigated by using macroscopic or microscopic testing techniques. It was revealed that the addition of MK decreased the setting time, accelerated the hydration process, and improved the water resistance of MOC. Mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM) results showed that MK did not change the phase composition of MOC before and after water immersion but promoted the formation of 5Mg(OH)2·MgCl2·8H2O (phase 5) before water immersion and inhibited the decomposition of phase 5 after water immersion. Based on the strength retention and relative dynamic elastic modulus, a comprehensive model with which to evaluate water resistance of MOC was proposed. This model could normalize multiple parameters and reduce the test error. For MOC, the optimal amount of MK was 20%. [ABSTRACT FROM AUTHOR]

The application of magnesium oxychloride cement (MOC) is promising, but its poor water resistance seriously hinders its development and application. In this paper, we describe a new type of MOC with excellent water resistance, prepared using fly ash and hexadecyltrimethoxysilane (HDTMS). SEM, XRD, FTIR, TG/DSC, and other microscopic-scale studies were conducted to investigate the mechanism underlying the water-resistance enhancement of the new MOC. It was found that adding 20% fly ash and 3% HDTMS can strengthen the water resistance of MOC while retaining high mechanical properties. In particular, the residual coefficient remained at 0.91 after 7 days of immersion. This is because these two additives, when used together, can increase the content of the gelling 5-phase of MOC, as well as optimize the pore structure of MOC.

Magnesium oxychloride cement (MOC) as a green cement has superior mechanical properties such as high strength and quick gain of early strength, however the inherent brittleness has limited its applications where ductility is crucial. To enhance the strength and ductility, a novel hybrid fibre-reinforced MOC-based composite (FRMOC) is developed for the first time using polyethylene (PE) fibres and basalt fibres (BF) to reinforce the MOC. A systematic investigation of the effect of fibre dosage on the flowability, rheological properties, compressive strength, and tensile properties of the developed FRMOC is conducted in this study. The results revealed that the addition of fibre reduces flowability while increasing the yield stress and plastic viscosity. The 1-day compressive strength of the FRMOC reached 68.2–85.4% of the corresponding value at 28 days, demonstrating its high early strength characteristic. The mix with 1.25% PE and 0.75% BF exhibited the maximum compressive strength at all curing ages. All the mixes consistently demonstrated excellent tensile strength and tensile strain capability (ductility), with the tensile strength and tensile strain capacity of 10.95 MPa and 4.41% achieved for the mix of 2% PE fibre, and 8.49 MPa and 2.43% for the mix of 1.25% PE and 0.75% BF respectively. Moreover, a decline in strength characteristics and strain capacity was observed as BF percentages increased. Scanning electron microscope (SEM) analysis was further employed to investigate the morphological changes in the FRMOC matrix at the microscale to discover the fibre reinforcing mechanism. • Hybrid fibre reinforced MOC (FRMOC) with enhanced strength and ductility is developed. • FRMOC demonstrates high-early-strength characteristic. • Rheological, physical, and mechanical properties were evaluated. • 1.25% PE and 0.75% BF-reinforced FRMOC exhibited maximum tensile strength and strain capacity. • Microstructural analysis is performed to analyse the morphological alterations. [ABSTRACT FROM AUTHOR]

The influences of modifier and carbonation on the phase assemblage of magnesium oxychloride cement (MOC) are little concerned in the literature. A thermodynamic modeling approach is employed to explore the influencing mechanisms of two commonly used modifiers (i.e. FeSO 4 and KH 2 PO 4) and phase assemblage of MOC under natural and accelerated carbonation. And quantitatively XRD test of the modified or carbonated MOC samples is used to verify the reliability of thermodynamic modeling results. The results indicate that the addition of FeSO 4 ·7H 2 O has no effect on the phase assemblage of MOC, but can improve the formation of 5 Mg(OH) 2 ·MgCl 2 ·8H 2 O (phase 5), whereas KH 2 PO 4 inhibits the formation of phase 5. FeSO 4 ·7H 2 O and KH 2 PO 4 raise the concentration of Mg2+ in pore solution, hence enhancing the stability of phases in the matrix. The carbonate product (i.e. chlorartinite) typically identified in MOC is metastable. The carbonation of MOC may result in the following evolution of Mg-carbonates: chlorartinite → MgCO 3 ·MgCl 2 ·7H 2 O → nesquehonite → hydromagnesite. [ABSTRACT FROM AUTHOR]

Highlights • MOC/FSPCM composites show good mechanical properties and high heat storage efficiency. • FSPCM absorbs heat, and reduce the hydration reaction temperature and hydration rate. • MOC/FSPCM composites show excellent thermal regulation performance. Abstract To increase the heat storage efficiency of the building enclosure structure, form-stable phase change material (FSPCM) was implanted into the magnesium oxychloride cement (MOC) system to generate MOC/FSPCM composites with both high heat storage efficiency and considerable mechanical strength. The microstructure, mechanical properties, hydration process and thermal properties of MOC/FSPCM composites were investigated. The results indicated the structure of MOC was not destroyed and the hydration rate, hydration temperature and total hydration heat also dropped after adding FSPCM. The compressive strength and flexural strength of the MOC/FSPCM composites with 30 wt% FSPCM can still reach to 52.9 MPa and 5.9 MPa, respectively, and the melting and crystallizing enthalpy of MOC/FSPCM composites were 29.91 J/g and 26.52 J/g, respectively. Thermal performance tests indicated that thermal conductivity of MOC/FSPCM composites decreased with the increase in the mass percentage of FSPCM. Meanwhile, MOC/FSPCM composites show excellent performance of indoor temperature regulate, conserve energy and thermal comfort. [ABSTRACT FROM AUTHOR]

The water resistance of magnesium oxychloride cement (MOC) incorporating glass powder (GP) and pulverized fuel ash (PFA) with and without CO 2 curing was investigated in terms of the strength retention coefficient and the volume stability. The microstructure was studied using quantitative X-ray diffraction (QXRD), thermogravimetry (TG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the effect of incorporating GP on the water resistance is much lower than that of PFA due to the lower pozzolanic activity of GP generating a lower amount of magnesium silica hydrate gel (M-S-H gel). The MOC incorporated with GP or PFA showed high water resistance after CO 2 curing due to the higher quantity of amorphous gel that formed a much denser interlocking network. [ABSTRACT FROM AUTHOR]

In this research, the effects of synthesized 5-phase seed crystals [5Mg(OH) 2 ·MgCl 2 ·8H 2 O] on the compressive strength, reaction process, and microstructure of the two kinds of MOC system were investigated. The results show that the addition of 5-phase seed crystals can significantly increase the formation rate of 5-phase in the MOC, which can improve the compressive strength of MOC, especially in its early stage; The compact microstructure not only improves compressive strength but also increases water resistance. Moreover, the effect of seeds in improving compressive strength and water resistance is more noticeable in the MOC system with phosphoric acid. [ABSTRACT FROM AUTHOR]

• Although MOC's advantages, it has low water resistance. • The needle-like hydration products of MOC's lead to high porosity. • The nano-silica was very beneficial for MOC's matrix performance. • Silica fume and nano-silica enhance the pore structure of hardened MOC. Eco-friendly and energy-saving cement products can be manufactured by adding silica fume into magnesium oxychloride cement (MOC). A previous piece of research investigated the addition of silica fume to increase the compactness of cement and consequently the strength and resistance to water erosion. Unfortunately, the results were not as expected; although the water resistance improved and the compressive strength decreased, the current research aims to thoroughly investigate the reasons behind those results besides investigating the influence of nano-silica addition on the MOC performance. The results revealed that using nano-silica in replacement for the silica fume was very beneficial to improving the matrix performance. The addition of nano-silica increases the amount of produced M−S−H and forsterite phases concerning silica fume and improves the mechanical properties. [ABSTRACT FROM AUTHOR]

The application of magnesium oxychloride cement (MOC) is promising, but its poor water resistance seriously hinders its development and application. In this paper, we describe a new type of MOC with excellent water resistance, prepared using fly ash and hexadecyltrimethoxysilane (HDTMS). SEM, XRD, FTIR, TG/DSC, and other microscopic-scale studies were conducted to investigate the mechanism underlying the water-resistance enhancement of the new MOC. It was found that adding 20% fly ash and 3% HDTMS can strengthen the water resistance of MOC while retaining high mechanical properties. In particular, the residual coefficient remained at 0.91 after 7 days of immersion. This is because these two additives, when used together, can increase the content of the gelling 5-phase of MOC, as well as optimize the pore structure of MOC.

• Temperature in a lower range has little effect on the phase assemblage of MOC. • Phase 5 is not predicted to form at higher temperatures. • phase 3 and brucite become stable at higher temperatures. • MOC samples with the optimal proportion cured at higher temperatures experience volume shrinkage. • The volume of MOC with a high content of H 2 O or MgCl 2 expands with increasing curing temperature. Magnesium oxychloride cement (MOC) is usually applied in industrial flooring, thermal insulation wall panels, flue pipes and grinding wheels. However, studies on the influence of temperature on the phase assemblage in MOC are limited and inconsistent. A thermodynamic modeling approach is employed to explore the influence of temperature on the stable hydrate assemblage in MOC. The results reveal that at lower temperatures, a variation in temperature has little effect on the hydrate phase assemblage in MOC, and the volume deformation of the samples prepared with the optimal proportion is very small. Phase 3 and brucite become stable phases at relatively higher temperatures. MOC samples prepared with the optimal proportion cured at higher temperatures experience volume shrinkage. [ABSTRACT FROM AUTHOR]

Weak water resistance of magnesium oxychloride cement (MOC), an eco-friendly construction material, has been a notorious and critical issue of MOC, restricting its application to mostly indoor with dry service environment. In this paper, sodium monofluorophosphate (MFP) is innovatively used, the first time, as a modifier to enhance the water resistance of MOC, as the PO 3 F2− ions in MFP solution form amorphous phase in MOC, which helps to improve the water repellence of MOC. The effect of MFP with different content, different mixing and curing methods on water resistance of MOC is studied. The effect of phosphates, including phosphoric acid (H 3 PO 4) and soluble phosphates (KH 2 PO 4) with various content on water resistance of MOC is also investigated and compared with the effect of MFP on the water resistance of MOC. The effects of these additives on the physical and mechanical properties of MOC, such as setting time, fluidity, compressive strength, flexural strength, are studied. To reveal the water resistance mechanism, XRD, FTIR, TG/DSC, MIP and SEM-EDS are conducted on the modified MOC. It is found that MFP has similar effect on the mechanical properties of MOC as H 3 PO 4 and KH 2 PO 4 , and they all significantly increase the flexural strength, slightly decrease the compressive strength, and remarkably increase the water resistance of MOC. The highest compressive strength retention coefficient of 0.84, 0.98, and 0.95 was achieved for 1% KH 2 PO 4 -MOC, 1% H 3 PO 4 -MOC, and 1% MFP-MOC respectively. From the microscale study, it is found that the addition of H 3 PO 4 , KH 2 PO 4 , and MFP changes the growth direction and morphology of the phase 5 crystals, which contributes to the increase of the water resistance of MOC. [ABSTRACT FROM AUTHOR]

The development of fiber-reinforced inorganic polymer (FRIP) composites for strengthening reinforced concrete (RC) structures has become an active field of research in recent years. Compared with fiber-reinforced polymer (FRP) strengthening systems, a FRIP strengthening system possesses improved fire resistance but its performance depends largely on appropriate inorganic paste selection. This paper presents a comparative study of four typical inorganic pastes, made from the following: (1) magnesium phosphate cement (MPC), (2) magnesium oxychloride cement (MOC), (3) geopolymer (GP) cement (i.e., alkali-activated slag cement), and (4) polymer-modified mortar (PMM). The aim was to investigate their performance both as a matrix and bonding adhesive for FRIP strengthening systems. The evaluated performance included the workability and mechanical properties of inorganic pastes, the bonding strength of these pastes with both a concrete substrate and dry fiber sheets, the tensile properties of the formed FRIP composites, and the flexural strength of FRIP-strengthened concrete beams. The microstructures of the four types of inorganic matrix and the fiber-to-matrix interface were also examined. The MPC-based and MOC-based inorganic pastes exhibit similar structural performance as commercially available PMM and are well-suited for the development of FRIP strengthening technology. Geopolymer seems to be the most brittle among the four studied inorganic pastes. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of an experimental investigation on compressive strength of granite waste fly ash magnesium oxychloride cement (GFMOC). Various GFMOC specimens were prepared with 23°Bé or 25°Bé brine and different proportions of granite fragment (GF) or granite sludge (GS) ranging from 0% (for the control mixture) to 40% of magnesia weight. Compression tests were conducted at the age of 3, 7, and 28days. The hydration products and paste microstructure were analyzed by XRD and SEM, respectively. The results demonstrated that the water absorption and filling role of the fine particles of granite waste in GFMOC slurry are favorable for 5Mg(OH)2⋅MgCl2⋅8H2O (P5) and dense microstructure, respectively. The quantity ratio of P5 to Mg(OH)2 (MH) and microstructure are important factors responsible for the compressive strength of GFMOC. The incorporation of granite wastes as aggregate can increase the compressive strength of fly ash magnesium oxychloride cement (FMOC). [Copyright &y& Elsevier]

• HDTMS gives MOC with the overall hydrophobicity. • The softening coefficient is 0.90 and the water absorption rate is only 7.3%. • After adding P123, the compressive strength is twice that of without P123. In this study, hexadecyltrimethoxysilane (HDTMS) and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) were added to magnesium oxychloride cement (MOC). Using the amphiphilicity of P123 to weaken the effect of HDTMS on the hydration reaction of MOC, the entire hydrophobic MOC material was prepared. Compared with the blank sample, the compressive strength can reach its 63% after 28 days. The softening coefficient can reach 0.90 and the mass water absorption is only 7.3% after 28 days of immersing. [ABSTRACT FROM AUTHOR]

In this paper, a water-resistant magnesium oxychloride cement (MOC), an environment friendly cementitious material, was developed by incorporating silica fume and the hybrid of silica fume and fly ash. The effects of these admixtures on the water repellence of MOC were investigated via comprehensive macroscopic physical and mechanical tests and micro-scale studies. A formula design of MOC blended with 15% silica fume and 15% fly ash retained the compressive strength as high as 100% and 95% after 28 days' and 56 days' immersion in water, respectively. Micro-scale studies, including XRD, FTIR, SEM, MIP, TG/DSC and XRM, were conducted to discover the mechanism of the enhanced water resistance of the new MOC. Besides, a clear and precise distribution of the hydration products in well-cured MOC specimens was demonstrated with the X-ray mapping (XRM) technique. It was found that adding silica fume or the hybrid of silica fume and fly ash optimised the porous structure of MOC and thereby increased the density and compressive strength leading to the enhanced water resistance. The filling effect of fine silica fume and fly ash particles, as well as the formation of Mg–Cl–Si–H gel, was found to be the main reason for the densified microstructure of MOC. The fractional contribution of phase 5, i.e. the main phase of MOC, decreased with the combined silica fume and fly ash, and this helped to relieve the internal stress and improve the stability of MOC, leading to enhanced water repellence. • A water-resistant environment friendly MOC was developed by adding industry by-products including silica fume and fly ash. • 15% fly ash-15% silica fume-MOC retained 100% and 95% of compressive strength after 28 days' and 56 days' water immersion. • The mechanism of increment in water resistance and mechanical strength was studied comprehensively by microscale studies. • Results from microscale study agree and explain well with those from mechanical test. • The research solved the notorious poor water resistance issue of MOC, which has restricted its wide application. [ABSTRACT FROM AUTHOR]

• High-strength, high-ductility MOC-SHCC is developed. • MOC-SHCC demonstrates high-early-strength characteristic. • Addition of PE fiber increases the water-resistance of MOC mortar. A new category of magnesium oxychloride cement-based strain-hardening cementitious composites (MOC-SHCC) with high-strength and high-ductility is developed in this research. The eco-friendly and high-strength MOC mortar is used as the matrix and ultra-high-molecular-weight polyethylene (PE) fiber is deployed as reinforcement. The development of mechanical properties of the MOC-SHCC with the curing ages varying from 12 h (h) to 28 days (d) is fully investigated and the high-early-strength characteristic of MOC-SHCC is demonstrated. The compressive, flexural, and tensile strength of the MOC-SHCC at 1d reach 71.4 MPa, 25.2 MPa, and 8.28 MPa respectively, accounting for 56%, 84%, and 75% of the corresponding values at 28d. The tensile capacities of the MOC-SHCC decrease slightly with the curing age, while all the values are beyond 6% accompanying with the evenly distributed microcracks. Additionally, water resistance of the MOC-SHCC is systematically investigated by using an accelerating method through immersing specimens into 60 °C hot water for 7d and 28d at the curing ages of 1d, 3d and 28d, respectively. The developed high-performance MOC-SHCC features with high early strength, high ductility, and satisfactory water resistance, which would have a strong potential application in practical engineering. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement-based composites (MOC) with silica sand/porcelain waste blended fillers were designed and tested. The objective of the presented research was to design and test low carbon, eco-friendly and viable alternatives to Portland cement-based materials. To make new materials environmentally acceptable and sustainable, silica sand applied in the reference composite material was partially substituted by ground porcelain waste (PW) coming from used electrical insulators. The sand substitution ratio was 5, 10, and 15 vol.%. The chemical and mineralogical composition, morphology, and particle size distribution of porcelain waste were measured. For silica sand, porcelain waste, and MgO, specific density, loose bulk density, and Blaine fineness were determined. The effect of porcelain waste on the workability of fresh composite mixtures was characterized by spread diameter. The composites were characterized by their basic structural, mechanical, hygric, and thermal properties. The phase composition and thermal stability at high temperatures of MOC/porcelain waste pastes were also analyzed. Fourier-transform infrared spectroscopy (FT-IR) analysis helped to indicate main compounds formed within the precipitation of MOC phases and their reaction with porcelain waste. The usage of porcelain waste greatly decreased the porosity of composite matrix, which resulted in high mechanical resistance and reduced and decelerated water imbibition. The 10% sand substitution with porcelain waste brought the best mechanical resistance and the lowest water absorption due to the formation of amorphous phases, water-insoluble aluminosilicates. In case of the thermal performance of the examined composites, the low thermal conductivity of porcelain waste was the contradictory parameter to porosity and the high thermal stability of the phases present in porcelain slightly decreased the thermal decomposition of composites with porcelain waste dosage. Based on the results emerged from the experimental tests it was concluded that the partial substitution of silica sand in MOC composites enabled the development of materials possessing interesting and advanced function and technical parameters. [ABSTRACT FROM AUTHOR]

This study is the first in the literature to systematically assess the environmental impacts of magnesium oxychloride cement (MOC) samples, which are regarded as a more eco-friendly construction material than Portland cement. The environmental impacts of MOC samples prepared with various molar ratios of MgO/MgCl2∙6H2O and sources of reactive magnesia were obtained via a life cycle assessment (LCA) approach (from cradle to grave), and the obtained outcomes were further compared with the counterparts associated with the preparation of Portland cement (PC) samples. Meanwhile, a sensitivity analysis in terms of shipping reactive magnesia from China to Europe was performed. Results indicated that the preparation of MOC samples with higher molar ratios led to more severe overall environmental impacts and greater CO2 sequestration potentials due to the difference of energies required for the production of MgO and MgCl2∙6H2O as well as their various CO2 binding capacities, whereas in terms of CO2 intensities, the molar ratios in MOC samples should be carefully selected depending on the strength requirements of the applications. Furthermore, various allocation procedures and MgO production processes will greatly influence the final outcomes, and allocation by mass is more recommended. Meanwhile, the environmental impacts associated with the transportation of reactive magnesia from China to Europe can be ignored. Finally, it can be concluded that MOC concrete is no longer a type of 'low-carbon' binder in comparison with PC concrete in terms of CO2 emissions, and in view of the single scores and mixing triangles for weighing, MOC concrete can only be identified as a type of more sustainable binder than PC concrete when the main component MgO in MOC samples is obtained through the dry process route rather than the wet process route. [ABSTRACT FROM AUTHOR]