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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]

Basic magnesium sulfate cement (BMS) is a new type of magnesium cementitious material, which has similar advantages with magnesium oxychloride cement, such as lightweight, fast setting, high strength, wear resistance, and is not easy to absorb the moisture. It can widely replace magnesium oxychloride cement in the field of building insulation materials. In addition, the BMS has 2.5 times the flexural strength of Portland cement of the same strength grade, and its durability and reinforcement protection performance is similar to Portland cement, which also has a good application prospect in the field of civil engineering. The preparation and hydration process of BMS is reviewed in this paper. The microstructure and properties of BMS, magnesium oxychloride cement and magnesium oxysulfate cement are comparatively analyzed. The effects of content and activity of α‐MgO in the magnesium materials, the type of blending solution, the α‐MgO/MgSO4 ratio, the type and dosage of chemical admixture on the microstructure and properties of BMS were clarified. This paper is helpful for the application of BMS in civil engineering. [ABSTRACT FROM AUTHOR]

Adding mineral admixtures is a green, economic and effective way of improving the properties of magnesium oxysulfate cement (MOSC). Based on MOSC modified with low-calcium fly ash (L-FA), high-calcium fly ash (H-FA) and granulated blast-furnace slag (G-BS), the effects of L-FA, H-FA and G-BS and silica fume (SF) double mixing on the properties of MOSC were studied by characterising the compressive strength, water resistance, hydration heat, hydration products and micropore structure characteristics. The modification mechanism of the mineral admixtures was also investigated. The results showed that L-FA, G-BS and SF double mixing optimised the hydration product composition and the micropore structure of the MOSC, thus improving its compressive strength and water resistance. The hydration reaction rate of MOSC and 5.1.7 phase content in the hydration products was increased by H-FA and SF double mixing, but the micropore structure was not further optimised, which is why the water resistance of MOSC with H-FA and SF was not improved. The research results enrich the basic theory of mineral admixtures for improving the properties of MOSC and provide theoretical guidance for practical applications. [ABSTRACT FROM AUTHOR]

This paper is based on the basic mechanical properties and volume deformation test, as well as the characterization of hydration products and microstructure properties such as x-ray diffraction (XRD), scanning electron microscope (SEM), and mercury injection method (MIP). The effects of CO2 curing on the mechanical properties, hydration product composition, and microstructure of magnesium oxysulfate (MOS) cement were studied. The results show that the carbonation properties of MOS cement are closely related to the standard air curing age after demolding. The CO2 curing immediately after demolding is not conducive to the development of compressive strength of MOS cement, while the compressive strength of MOS cement in standard air curing for 14 or 28 days after demolding is increased during CO2 curing. The CO2 can prevent the continuous hydration of residual MgO to form Mg(OH)2 or 5·1·7 phase, which affects the development of the compressive strength of MOS cement. The appropriate addition of low-calcium fly ash (L-FA) can compensate the effect of CO2 on the mechanical properties of MOS cement. During CO2 curing, some Mg(OH)2 is transformed into an amorphous phase to increase the compactness of its microstructure and a small amount of Mg(OH)2 reacts with CO2 to form MgCO3·3H2O. The results provide an important theoretical and experimental foundation for the further study of the effects of CO2 on the properties of MOS cement and the use of CO2 curing modification. [ABSTRACT FROM AUTHOR]

Magnesium oxysulfate (MOS) cement is often seen as a 'green engineering material in the twenty-first century'. However, low mechanical strength is one of the major drawbacks for large-scale applications of MOS cement. In this paper, MOS cement with desirable strength was prepared by adding phosphoric acid. The effects of phosphoric acid on the hydration process, hydration products and microstructure of MOS cement were studied in detail using isothermal calorimetry, X-ray diffraction, Fourier transform infrared spectrometry, mercury intrusion porosimetry and scanning electron microscopy. It was found that the incorporation of phosphoric acid could retard the hydration process and increase the setting time of MOS cement. Furthermore, the incorporation of phosphoric acid was shown to increase the compressive strength through its effect in promoting the formation of 5Mg(OH)2·MgSO4·7H2O. The space-filling properties and directional growth characteristics of 5Mg(OH)2·MgSO4·7H2O contributed to a more compact and uniform microstructure of the MOS cement formed. [ABSTRACT FROM AUTHOR]

In this paper, the hydration reaction and properties of magnesium oxysulfate (MOS) cement modified with ammonium citrate tribasic are discussed and compared with MOS cement without chemical additives. The hydration reaction characteristics, hydration products, mechanical properties, and microstructures of MOS cement prepared with and without chemical additives were characterized by isothermal calorimetry, quantitative X-ray diffraction (QXRD), mercury intrusion porosimetry (MIP), thermogravimetry (TG), and scanning electron microscopy (SEM), and the mechanism of action of the chemical additives–was investigated. The results show that when the molar ratio of α-MgO:MgSO4·7 H2O:H2O is 8∶1∶11 , the basic salt hydrate 5 Mg(OH)2·MgSO4·7H2O phase (5·1·7 phase) can be formed in MOS cement with and without chemical additives. However, ammonium citrate tribasic is an effective chemical additive that can (1) adjust the concentration of H+ and OH− ions in the liquid phase through buffering to meet the requirements of the H+ or OH− ion concentration (or pH value) required for the neutralization reaction of MgO particles, (2) strengthen the neutralization reaction of MgO particles, and (3) reduce the hydration reaction of MgO particles to form Mg(OH)2 through the complexation of the complex ions. Therefore, a large amount of the 5·1·7 phase and small amounts of Mg(OH)2 and the amorphous phase are formed in MOS cement with ammonium citrate tribasic, which optimizes the micropore structure and improves its mechanical strength and water resistance. [ABSTRACT FROM AUTHOR]

The effects of silica powder (SP) with different fineness values on the properties of magnesium oxysulfate cement (MOSC) were compared with the effects of fly ash (FA). X-ray diffraction, mercury porosimetry and scanning electron microscopy were used to analyse the effects of the particle morphology and fineness of FA and SP on the mechanical properties, hydration products and microstructure of MOSC. The results showed that when the α-MgO/MgSO4.7H2O/H2O molar ratio was constant, the concentration of magnesium sulfate and the uniformity of magnesium oxide particles in the slurry were the main factors determining the composition of the hydration products and the microstructure of MOSC. Spherical FA was found to improve the uniformity of magnesium oxide particles in the slurry and exert a nucleation effect, thereby increasing the formation of the 5.1.7 phase of the hydration products. Polyhedral SP with a certain fineness increased the concentration of magnesium sulfate in the slurry and had a filling effect, thus promoting formation of the 5.1.7 phase and optimising the microstructure. Therefore, with a certain magnesium sulfate concentration and a homogeneous slurry, both active FA and inert SP can improve the water resistance of MOSC by optimising the composition of the hydration products and microstructure. [ABSTRACT FROM AUTHOR]

• Using L-FA and H-FA in MOSC achieves beneficial effects. • The possibility of using H-FA in MOSC is confirmed. • The MOSC with H-FA has good volume stability and a denser microstructure. • Compared with L-FA, the incorporation of H-FA into MOSC increases the 5·1·7/Mg(OH) 2 ratio in the hydration products. Magnesia-based cementitious materials have a reputation for being "green engineering materials in the 21st century". By incorporating fly ash (FA) into magnesium oxysulfate cement (MOSC), a new type of high performance MOSC that achieves energy savings and environmental protection can be produced for industrial construction applications. In this paper, the performance of MOSC with low-calcium fly ash (L-FA) and high-calcium fly ash (H-FA) was investigated, including the setting times, compressive strengths, shrinkages, compositions and microstructures. The results show that adding FA to MOSC can accelerate the hydration reaction and improve the volume stability of the MOSC paste. The high compressive strength of MOSC is derived from the sound composition and compact microstructure of the hydration products. The large water requirement of the fine H-FA particles in H-FM and the resulting filling effect are beneficial to the optimization of the composition of the hydration product and the formation of dense microstructures, respectively, which make the MOSC with H-FA possess excellent setting characteristics, high compressive strength, good volume stability and a compact microstructure. These results confirm the feasibility of applying H-FA in MOSC. Therefore, both types of FA can be used as a major component of MOSC, and the dose can be up to 50% of MgO weight or more, which improves the technological, economic and environmental benefits. [ABSTRACT FROM AUTHOR]

Highlights • HPC blended with 20% fly ash and 0.1% polypropylene fibre exhibited superior frost resistance. • The value of the icing pressure had a strong linear correlations with the EG solution concentration. • The value of the icing pressure decreased with the increase in the EG concentration. • EG did not react with the concrete hydration product, but the EG could cause frost damage. Abstract The major aimed at investigating the mechanism of the freeze–thaw damage to high performance concrete (HPC) under ethylene glycol (EG) deicer. In this study, three types of HPC were prepared, as well as the reference concrete (OPC0). Tests were performed to evaluate the ice-formation pressure (I p), determine the impact of rapid freeze–thaw cycles, study the microstructure, and evaluate the compression strength of the HPC and OPC0. The results yielded suggested that the I p and the concentration of the EG solution had a strong linear correlation. The I p of EG solution decreased with its concentration. The freeze–thaw deterioration of OPC0 in 3.5 wt% EG was greater than that of HPC, and the EG did not come into any chemical reaction with concrete hydration product. In this study, HPC blended with 20 wt% fly ash and 0.1% polypropylene fibre addition showed superior frost resistance. This could provide theoretical guidance for the concrete frost-resistance design. [ABSTRACT FROM AUTHOR]

The properties of air-entrained concrete (AEC) subjected to freeze–thaw cycles in various salt lake brines were investigated. The relative dynamic elastic modulus (RDEM) and weight loss of the AEC were measured after different numbers of freeze–thaw cycles. In addition, the microstructure and composition of the AEC under the combined action of freeze–thaw cycles and salt lake brine attack were analysed using X-ray diffraction and scanning electron microscopy. The results showed that the RDEM and weight losses of AEC subjected to freeze–thaw cycles in salt lake brines from Tibet and Inner Mongolia decreased sharply. For AEC immersed in salt lake brines from Qinghai and Sinkiang, the RDEM was slightly reduced and the weight loss was slightly increased. The coupling effect of freeze–thaw cycles and salt lake brine thus had only a slight influence on concrete damage in Sinkiang and Qinghai regions. The X-ray diffraction and scanning electron microscopy results demonstrated that only chemical corrosion occurred in the AEC under freeze–thaw action in the Qinghai and Sinkiang salt lake brines. However, the coupled effects of water frost-heaving force, salt crystallisation and chemical corrosion rapidly led to damage to the concrete under freeze–thaw action in the Tibet and Inner Mongolia salt lake brines. [ABSTRACT FROM AUTHOR]

Magnesium oxysulfate (MOS) cement is a type of green inorganic cementitious material, with the advantages of light weight, low thermal conductivity, binding ability in light-weight panels, high temperature resistance and good fire resistance; however, its application range in practical engineering is limited by its low mechanical strength. In this paper, the influences of sodium citrate and citric acid as additives on the mechanical strength, water resistance, setting time, pH change, composition and microstructure of MOS cement were investigated. The sample properties were examined by means of mechanical strength test, Vicat apparatus, pH meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results revealed that adding sodium citrate or citric acid could promote the large amount of 5 Mg(OH) 2 ·MgSO 4 ·7H 2 O generation and improve the water resistance of MOS cement. The incorporation of sodium citrate or citric acid caused a reduction in the total porosity and the volume fraction of large pores (>100 nm) in MOS cement, as well as an increase in the most probable aperture and the volume fraction of small capillary pores (10 nm–100 nm). In addition, the setting time of MOS cement with sodium citrate or citric acid was longer than that without sodium citrate or citric acid. [ABSTRACT FROM AUTHOR]

The deterioration processes of two types of concrete under chemical corrosion (MgSO 4 ), tensile loading coupled with chemical corrosion or flexural loading coupled with chemical corrosion were investigated in this study. Tensile stress and flexural stress loading devices that were designed by the authors were used. A relative dynamic elastic modulus test using the ultrasonic method was utilized, and through the derivation of empirical equations, a crack density model was obtained to describe the concrete damage process. Furthermore, scanning electron microscopy (SEM) was used to investigate the microstructure changes inside the concrete. The results indicated that the flexural and tensile loads significantly affected the deterioration of concrete when combined with magnesium sulfate. Exposure to magnesium sulfate coupled with tensile loading is a harsh environment for concrete. The rate of concrete deterioration under different stress conditions at the same loading level is ranked as follows: tensile stress coupled with chemical corrosion > flexural stress coupled with chemical corrosion > chemical corrosion. [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]

• Industrial waste silica fume (SF) is used to improve the performance of basic magnesium sulfate cement (BMSC). • Incorporation of SF can enhance the mechanical properties of BMSC significantly. • Hydration behavior and process of BMSC influenced by SF are studied. • Microstructure and phase evolution of BMSC are characterized and analyzed. Silica fume (SF) as an important supplementary cementitious material has been widely used in Portland cement, but few published articles have reported on the effect of SF on the performance and hydration mechanism of basic magnesium sulfate cement (BMSC). In the present work, the properties, microstructure and hydration mechanism of BMSC influenced by SF was studied systematically. The results show that the setting time and compressive strength of BMSC may increase with the increase of SF content, while the hydration heat will decrease with the increase of SF content. Mercury intrusion porosimetry (MIP), X-ray computed tomography (X-CT), scanning electron microscope- Energy dispersive spectrometer (SEM-EDS) results show that SF exhibits filling effect in the BMSC matrix, which makes the microstructure of BMSC matrix with SF more compact. In addition, solid-state magnetic resonance (NMR) and SEM-EDS analysis indicate that the activity of SF was excited in the BMSC matrix, resulting in the formation of M−S−H gel. [ABSTRACT FROM AUTHOR]

• The properties of MOSC with L-FA or H-FA during water immersion are studied. • The compressive strength of MOSC decreases first and then increases after immersion. • Restricting the expansion contributes to the densification of the microstructures of MOSC. • A small number of 5·1·7 phases can form after immersion in water. To expand the application range of magnesium oxysulfate cement (MOSC) and the utilization of fly ash, the water resistance of MOSC mixed with low-calcium fly ash (L-FA) or high-calcium fly ash (H-FA) was studied. The softening coefficients and volume stability were tested to evaluate the water resistance of MOSC. The hydration products and microstructures of MOSC prepared without L-FA or H-FA (denoted as C) and MOSC prepared with L-FA (L-FM) or H-FA (H-FM) were characterized by quantitative X-ray diffraction (QXRD), mercury intrusion porosimetry (MIP), thermogravimetry (TG), and scanning electron microscopy (SEM). The results show that the expansion stress and the volume deformation caused by the transformation of residual MgO into Mg(OH) 2 are the main reasons for the decrease in the compressive strength of MOSC after its immersion in water. The formation of few 5·1·7 whiskers and the restraints on the expansion increase the compactness of the MOSC, which makes the compressive strengths and softening coefficients of C, L-FM and H-FM increase gradually with an increase in the immersion time. The softening coefficients of C, L-FM and H-FM immersed in water for 90 days are 0.97, 1.00 and 0.84, respectively. Although the softening coefficient of H-FM is not as good as that of C and L-FM due to the formation of CaSO 4 ·2H 2 O, the compressive strength and the compactness of H-FM immersed in water for 90 days are still higher than those of L-FM, which indicates that H-FA has good application prospects in MOSC. [ABSTRACT FROM AUTHOR]

Highlights • The durability of concrete was evaluated by multiple indicators and methods. • The spalling amount was used to evaluate the durability of concrete instead of mass loss. • OPC and HPC with active admixtures including fly ash, silica fume, and slag, in salt lake brines, were investigated. • The study was based on the actual natural environment of salt lake regions. Abstract In view of the serious erosion of concrete in salt lake regions, the properties (the corrosion resistance coefficient, relative dynamic elastic modulus, and spalling amount) of concrete, including ordinary Portland concrete (OPC) and high-performance concrete (HPC), subjected to dry-wet cycles in a variety of salt lake brines, were investigated. Moreover, the microstructures of the concrete were analyzed by X-ray diffraction and scanning electron microscopy in detail. The results showed that the performance of HPC was notably better than that of OPC in salt lake brines. The corrosion degree of OPC was the largest in the Qinghai salt lake brine, and the corrosion degree of HPC was the largest in the Sinkiang saline lake brine, while the corrosion degree of both OPC and HPC was the smallest in the Inner Mongolia salt lake brine. Additionally, no matter what salt lake brines were used, the deterioration trend of concrete subjected to dry-wet cycles in salt lake brines progressed from the surface to the interior. Furthermore, the active admixture had a positive influence on crack repair and performance improvement of HPC, and HPC with active admixtures could be able to withstand the harsh environment of salt lake regions. [ABSTRACT FROM AUTHOR]

A novel magnesium potassium phosphate chemically bonded ceramic (MKPCBC) was prepared as a byproduct of boron-containing magnesium oxide (B-MgO) after extracting Li 2 CO 3 from salt lakes. In this work, the influence of glucose on the properties of MKPCBC, such as the setting time, compressive strength and hydration heat, was investigated. In addition, we studied the effect of the magnesium-phosphate ratio (M/P) and liquid-solid ratio (L/S) on the injectability of MKPCBC. The pH change in glucose modified MKPCBC paste was also investigated. The phase composition and microstructure were studied in detail by using X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS). The results show that the optimal content of glucose is 6 wt%. The optimum proportions of M/P and L/S for MKPCBC are 1.5 and 0.25, respectively. The properties of the novel MPCBC can meet the requirements of biomaterials. In addition, the retardation mechanism of glucose on MKPCBC and the hydration mechanism of novel MKPCBC were studied in detail through the continuous monitoring of the phase composition and microstructure. [ABSTRACT FROM AUTHOR]

A new magnesium-calcium oxysulfate cement (MCOSC) was proposed by replacing MgSO4 in magnesium oxysulfate cement (MOSC) with untreated flue gas desulfurization gypsum (FGDG) at levels of 25%, 50%, 75% and 100%. The synergistic effect of FGDG and chemical additives, including citric acid, ammonium citrate tribasic and ammonium dihydrogen phosphate on the mechanical performance and hydration mechanism of MCOSC was investigated. The results showed that three additives all promoted the formation of 5 Mg(OH)2·MgSO4·7H2O (5·1·7) phase and hindered Mg(OH)2 precipitation, improving mechanical properties of MCOSC. FGDG incorporation induced no new crystalline phase, but gypsum crystal provided the space for nucleation of 5·1·7 phase. FGDG also reacted with MOSC to form amorphous phase, which was identified as a magnesium-sulfide-calcium-hydrate gel. Moreover, it affected the morphology of 5·1·7 phase and lowered the temperature of endothermic peaks in the paste during the heating process. The additive-incorporated specimens with 25% FGDG replacement presented a superior compressive strength, water resistance and volume stability. This confirmed the effective application of FGDG in preparing MCOSC, and it also provided an approach for recycling waste gypsum. • Magnesium-calcium oxysulfate cement is prepared by replacing MgSO 4 with untreated FGDG. • The synergistic effect of FGDG and additives on mechanical performance and hydration mechanism of MCOSC is studied. • CA, ACT and ADP all induce the formation of needle-like 5·1·7 phase. • FGDG provides the space for nucleation of 5·1·7 phase and reacts to form a magnesium-sulfide-calcium-hydrate gel. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of two chemical additives on the performance of MOSC was compared. • The mechanism of the different effects of two chemical additives on the properties of MOSc was analyzed. • The decrease of hydration rate of MOSc is beneficial to the crystallization development of 5·1·7 phase. • The 5·1·7 phase with low crystallinity or 5·1·n phase may be another factor for the reduction of compressive strength of MOSc after immersion. 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 ·MgSO 4 ·7H 2 O (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. [ABSTRACT FROM AUTHOR]

Herein, to reduce CO 2 emissions and energy consumption and to promote the recycling of waste resources, two types of boron-containing MgO by-products, which were obtained by lithium extraction from Qarhan Salt Lake, China, were used as substitutes for dead-burned MgO to prepare magnesium phosphate potassium cement (MKPC) as a rapid repair material. First, the phase composition and particle-size distribution of the MgO by-product were investigated. The effects of different MgO sources, molar ratio of MgO to KH 2 PO 4 (M/P), and curing age on the setting time and mechanical properties of MKPC were then studied. Based on the results, the mix proportion of MKPC was optimized. Finally, X-ray diffractometry, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), differential thermogravimetric (DTG) analysis, and mercury intrusion porosimetry were used to characterize the phase and microstructure evolution of MKPC prepared with different MgO contents. The results demonstrated that the by-product MgO prolonged the setting time of MKPC to more than 40 min. In addition, in the initial stage of hydration, the compressive strength of the MgO by-product was slightly lower than that of the dead-burned MgO; however, with increasing age, the mechanical properties of MKPC prepared by by-product MgO were excellent (up to 60 MPa). The phase and microstructure results revealed that the main hydration product of MKPC prepared using the three types of MgO was MgKPO 4 ·6H 2 O. Combined with the physical and chemical properties of the raw materials, it was confirmed that the larger particle size and the coexisting impurities from the salt lake were the main reasons for the longer setting time of the MKPC prepared by the by-product MgO. We believe that this research will be of great significance for the preparation of low-carbon, low-cost, and high-performance MKPC materials. [Display omitted] [ABSTRACT FROM AUTHOR]