Magnesium Phosphate Cement Research Articles

An Overview of Magnesium-Phosphate-Based Cements as Bone Repair Materials.

In the search for effective biomaterials for bone repair, magnesium phosphate cements (MPCs) are nowadays gaining importance as bone void fillers thanks to their many attractive features that overcome some of the limitations of the well-investigated calcium-phosphate-based cements. The goal of this review was to highlight the main properties and applications of MPCs in the orthopedic field, focusing on the different types of formulations that have been described in the literature, their main features, and the in vivo and in vitro response towards them. The presented results will be useful to showcase the potential of MPCs in the orthopedic field and will suggest novel strategies to further boost their clinical application.

Feasibility of high-magnesium nickel slag-fly ash as precursor of magnesium phosphate cement and its hydration mechanism

The aim of this study was to investigate the process conditions, hydration reaction products and mechanism of high-magnesium nickel slag (HMNS)-fly ash (FA) as a precursor of magnesium phosphate cement (MPC). The relationships between properties, hydration products, hydration processes, and micromorphology were investigated by engineering properties, XRD, TG-DSC, FT-IR, Raman, and SEM/EDS. The results showed that the optimal process (HMNS/FA = 1.0/0, NH4H2PO4 dosing of 25 wt%, water-cement ratio of 0.26, the maintenance condition is air maintenance, and 200 mesh particle size of raw materials) prepared the cementitious material with 28 d compressive strength of 58.00 MPa and linear expansion rate of only 2.5 %. The hydration process was a multi-stage process, including the dissolution of NH4H2PO4 and pre-treated HMNS (WHMNS), the precipitation of intermediate hydration products and the formation of struvite, and the formation of gelling phases such as -Si-O-P-, -Al-O-P-, and -Si-O-Al-O-P-. Eventually, a high-strength gel-crystal phase structure consisting of gelling phases such as struvite wrapped around unreacted raw materials and struvite crystals was formed. FA was harmful for cementitious material, and impurities and high levels of Ca in FA reacted with phosphate to form hydration products with a loose porous structure (e.g., brushite). The optimal process sample complies with the 52.5R grade of ordinary Portland cement (GB175-2007); its embodied energy was reduced by more than 73.4 % compared to magnesium phosphate cement (MPC), and the corresponding CO2 emission was reduced by more than 74.2 %. Therefore, it has the potential to partially replace MPC from the environmental and feasibility point of view.

Evaluation of feasibility and performance of foamed Fire-Resistant coating materials

A preliminary study found high-performance cement mortar, geopolymer mortar, and magnesium phosphate cement mortar (MPCM) have the potential as new fire-resistant materials. In this study, foam was added to these three fire-resistant materials to further improve their rheological, mechanical, and fire-resistant performance and reduce costs. Systematic design and experimental programs were conducted. The results showed the addition of foam enhanced workability, adhesiveness, and fire resistance, allowing the materials to withstand higher temperatures and further delay heat transfer. A mixture of 70% MPCM and 30% foam was identified as the optimum design, which could withstand 1000 °C with low heat transfer rates.

Exploring the potential of magnesium oxychloride, an amorphous magnesium phosphate, and newberyite as possible bone cement candidates.

Magnesium phosphate-based bone cements, particularly struvite (MgNH4PO4∙6H2O)-forming cements, have attracted increased scientific interest in recent years because they exhibit similar biocompatibility to hydroxyapatite while degrading much more rapidly in vivo. However, other magnesium-based minerals which might be promising are, to date, little studied. Therefore, in this study, we investigated three magnesium-based bone cements: a magnesium oxychloride cement (Mg3(OH)5Cl∙4H2O), an amorphous magnesium phosphate cement based on Mg3(PO4)2, MgO, and NaH2PO4, and a newberyite cement (MgHPO4·3H2O). Because it is not sufficiently clear from the literature to what extent these cements are suitable for clinical use, all of them were characterized and optimized regarding setting time, setting temperature, compressive strength and passive degradation in phosphate-buffered saline. Because the in vitro properties of the newberyite cement were most promising, it was orthotopically implanted into a partially weight-bearing tibial bone defect in sheep. The cement exhibited excellent biocompatibility and degraded more rapidly compared to a hydroxyapatite reference cement; after 4months, 18% of the cement was degraded. We conclude that the newberyite cement was the most promising candidate of the investigated cements and has clear advantages over calcium phosphate cements, especially in terms of setting time and degradation behavior.

Influence of steel slag powder on the characteristics of magnesium phosphate cement

Steel slag is a by-product generated during the steel manufacturing process. Currently, most of the steel slag is disposed of using land-fill rather than being recycled. In this study, we studied the effects of the substitute of magnesium oxide (MgO) with steel slag powder (SSP) on the hydration behavior, mechanical properties, phase composition and microstructure in the preparation of magnesium phosphate cement (MPC). The results showed that the addition of SSP did not lead to the formation of new crystal phases, but that the active part of SSP was activated by the high heat release and involved in the hydration process of the MPC system, generating amorphous phases. It was found that replacing MgO with 5% SSP did not reduce the weight fraction of struvite, while that of amorphous phases was increased by 2%. When 15% MgO was replaced by SSP, the weight fraction of struvite decreased by 2% but the mass fraction of amorphous phase rosed by 5%. These amorphous phases filled pores, patched cracks and connected unreacted particles with struvite to establish a continuous network. This helped to form a compact microstructure, improving the mechanical properties of MPC at a late stage. This study contributes towards a better understanding of the influence of SSP in MPC and provide an alternative for the recycling of SSP.

A Review on Durability of Foam Concrete

Foam concrete is a promising material in building and construction applications, providing such outstanding properties as high specific strength, excellent thermal insulation, and effective acoustic absorption in human-inhabited buildings. However, because the porosity and permeable water absorption properties of foam concrete are significantly higher, its durability is often not comparable to that of ordinary concrete, and so the durability of foam concrete requires significant attention during the life cycle of building applications. Durable materials can greatly reduce the environmental impact of waste from maintenance and replacement and the consumption of natural resources resulting from the production of repair and replacement materials. After hardening, the durability of foam concrete includes freeze-thaw cycle resistance, elevated temperature resistance, carbonation resistance, efflorescence resistance, sulfate resistance, chloride resistance, alkali-silica reaction, and so on. This paper reviews articles on the durability of ordinary Portland cement (OPC) foam concrete, geopolymer foam concrete (GFC), magnesium phosphate cement (MPC) foam concrete, sulphoaluminate cement (SAC) foam concrete, and limestone calcined clay cement (LC3) foam concrete and compares their durability to provide a reference for the life cycle design and service life estimation of foam concrete members.

Can tundish deskulling waste be used as a magnesium oxide source to develop magnesium phosphate cement?

Ordinary Portland cement (OPC) has a significant environmental impact since approximately 0.81 kg of CO2 is generated for every kilogram produced. Thus, it is mandatory to look for sustainable alternative cements. One of the most promising materials in this sense is magnesium phosphate cement (MPC). This study evaluates the possibility of revaluing a waste obtained from the tundish deskulling (TUN) as a raw material for formulating alternative MPC. This approach aims to promote the circular economy and minimizing the environmental impact of MPC. The tundish working lining is a crucial refractory material used in continuous steel casting. An optimal cement formulation was achieved by maximizing the compressive strength (CS) at 7 days, resulting in the combination of 60 wt% of TUN and 40 wt% of KH2PO4, with a water/cement (W/C) ratio of 0.27. The physical and mechanical properties were evaluated at three different stages: after 1, 7, and 28 days of curing. Furthermore, an exhaustive physicochemical characterization was conducted to investigate the feasibility of using it as an alternative cement. This study confirms the feasibility of formulating MPC using TUN as raw material due to the main product obtained, which is K-struvite. The use of TUN implies important economic savings and enhances sustainability criteria avoiding its management in landfills.

Study on the effect of M/P ratio of magnesium phosphate cement coatings on reducing urban heat absorption

Using reflective coatings to enhance the reflective ability of urban underlying surface can effectively reduce building energy consumption and alleviate urban heat island effect. Magnesium phosphate cement (MPC), which consists of high near-infrared reflectivity magnesium oxide (MgO) and phosphate as the main raw materials, is a potential reflective coating. This paper studied the reflection characteristics and mechanisms of MPC with different mass ratios of MgO to phosphate (M/P). The reflectivity test results indicated that the reflectivity of MPC increased with the increase of M/P ratio, with a near-infrared reflectance of 71.74% at an M/P of 10. This was mainly related to its surface chromaticity and micromorphology. In the matter of color characteristic, it was found that the increase of M/P ratio improved the brightness and weakened the performance of other colors, which was conducive to improving the reflective effect. In the matter of micromorphology, scanning electron microscopy and energy dispersive spectrometer (SEM-EDS) analysis confirmed that there were more unreacted MgO particles and less hydration products on the MPC surface with high M/P ratio, which resulted in higher reflectivity and lower bonding strength. Finally, indoor irradiation experiments were conducted to verify the heat reduction effect of MPC coating on asphalt pavement. The results indicated that the surface temperature of the specimen coated with MPC decreased by 15.3 ℃ compared to the control specimen. Therefore, it could be concluded that MPC is a promising reflective coating that can be used to reduce urban heat absorption.

Waste glass recycling in magnesium phosphate coatings for the fire protection of steel structures

The paper focus on the valorization of soda lime silica waste glass powder in the manufacture of fire protective coatings, for steel structures, based on magnesium phosphate cements (MPCs); waste glass powder is used to substitute part of dead burned magnesia (one of the main components of MPC) or to obtain lightweight aggregate (Gt) by alkali activation with NaOH solution followed by thermal treatment at 900 °C for 1 h. Commercially available expanded perlite is also used in MPCs to replace dead-burned magnesia or as lightweight aggregate. The MPCs mineralogical composition (assessed by XRD), microstructure and adhesion to steel plate (assessed by SEM) as well as the changes which occurs during the thermal treatment (assessed by DTA-TG analyses) are used to explain the fire behaviour and insulation properties of these coatings. The studied MPC coatings adhered very well to the steel plate, even after two consecutive fire tests (direct contact with butane flame for 60 min) and effectively decreased the substrate temperature. The coating thickness plays an important role in decreasing the temperature of the steel substrate; for thinner coatings the rate of temperature increase, in the first 10 min, is 3–4 times higher (depending on the coating composition) as compared with thicker coatings. The presence of lightweight porous aggregates, such as expanded perlite or Gt, combined with the increase of water content of MPC coatings, contributes to the decrease of the steel plate temperature during the fire test.

A rapid-hardening cement emulsified asphalt (CEA) mortar prepared from magnesium phosphate cement

Cement emulsified asphalt (CEA) mortar is the key component material of high-speed railway track slabs, and it is prone to damage under the coupling effect of environment and load. For severely damaged CEA mortar, the strategy of replacing the filling layer is required. However, the daily idle period of high-speed railways is extremely short in China, which makes Portland cement-based CEA mortar unable to meet the time and material performance requirements of high-speed railway maintenance. Therefore, a novel magnesium phosphate cement-based CEA (MEA) mortar is prepared in this study, and the effects of key parameters on its fresh properties, strength, and durability are systematically investigated. A MEA mortar with a setting time within 30 min and a compressive strength of 15–45 MPa is developed. Increasing the emulsified asphalt to cement (EA/C) ratio reduces the strength, water resistance, and frost resistance of MEA mortars, mainly because increasing the EA/C ratio leads to decreased reaction products and increased porosity. Meanwhile, increasing the EA/C ratio also leads to a higher volume expansion of the MEA mortar. In addition, adding an appropriate amount of emulsified asphalt with low water content can increase the setting time and failure strain of the MEA mixture compared with the plain magnesium phosphate cement component, and it performs better than emulsified asphalt with high water content. This study demonstrates acceptable performance of MEA mortar prepared with appropriate EA/C ratio and type of emulsified asphalt, which provides an alternative material for track slab maintenance.

Effect of recycled oyster shell powder on hydration and strength development of magnesium phosphate cement

Using oyster shell powder (OSP) to prepare magnesium phosphate cement (MPC) not only reduces the pollution caused by the wasted oyster shell disposal, but also benefits the development of more environmentally friendly cement. The effect of OSP on the hydration and strength development of MPC was studied. An axial compression experiment including 45 cuboid specimens was executed to investigate the compressive strength, failure mode, stress–strain relationship, and energy absorption of MPC mixing with different mass contents (0% to 12%) of OSP over the curing times of 7, 14, and 28 days. Scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy were utilized for measuring the variation of MPC microstructure and hydration products caused by OSP. Results indicated that a new reactant CaHPO4·2H2O was formed, which optimized matrix strength. The substitution of OSP could reduce the cost of MPC by 2–9% without decreasing the strength. Compared with MPC without OSP, the compressive strength of the specimen with 3% OSP is increased by 6%. However, with the continuous increase of OSP, the compressive strength gradually decreases. Similarly, the elastic modulus of MPC increases first and then decreases with the increase of OSP.

The influence of calcium sulphoaluminate on the properties of low-cost magnesium phosphate cement mortars

Magnesium phosphate cement (MPC) exhibited many excellent performances, however, the high cost of raw materials of MPC limited its application in construction areas. Calcined dolomite powders containing CaO could not be applied in MPC production. The dolomite-bauxite-gypsum powders after calcination were used to replace dead burned MgO and the free-CaO in dolomite was transferred into calcium sulphoaluminate (ye'elemite, C4A3S‾). This study intends to investigate the performance of the low-cost MPC mortars prepared with calcined dolomite-bauxite-gypsum powders containing C4A3S‾. The setting times, fluidities, hydration temperature developments, compressive strength developments and volume changes of MPC mortars with C4A3S‾ were investigated. Furthermore, the differences in compressive strength, flexural strength and bond strength development of MPC mortars with C4A3S‾ in air and water curing were compared. Phase developments, microstructures and pore diameter distribution of MPC mortars with ye'elemite were also investigated. MPC mortars prepared with the calcined dolomite powders containing 51% C4A3S‾ and 26% MgO showed a setting time of 27 min, free-fluidity of 150 mm, 3-h compressive strength of 41 MPa, 7-d compressive strength of 58 MPa and 180-d compressive strength of 74 MPa. C4A3S‾ in MPC mortars could form some amorphous hydration products and its hydration may be promoted in water curing. The new amorphous phases may have filling and cementitious effects, leading to denser structures and higher strengths.

Preparation and properties of hydrotalcite-foamed magnesium phosphate cement for fire protection of steel structures

Foamed magnesium phosphate cement (MPC) is prepared for the fire protection of steel structures based on the carbonate decomposition reaction of hydrotalcite in acidic MPC paste. Hydrotalcite decomposes in an acidic MPC slurry to generate CO2, and approximately 50% of the theoretical gas generation remains in the MPC slurry to form foamed MPC with an apparent density of < 650 kg/m3 and 1-d compressive strength of > 4.0 MPa. The actual gas production of hydrotalcite in the MPC slurry gradually increases as the hydrotalcite content increases and the M/P ratio decreases. The fine hydrotalcite particles refine the pores and obstruct the paths between them, resulting in closed and uniform pores. When the thickness of the foamed MPC coating on the steel plate surface is only 6.0 mm, the temperature on the steel plate back after being subjected a 60 min fire resistance test is about 400 °C, which is significantly lower than the critical temperature (538 °C) for the steel structure to remain stable after encountering fire. Foamed MPC exhibits excellent fireproofing performance owing to its high porosity, low thermal conductivity, the release of CO2 in the pores, and the dehydration of hydration products, which retards heat transfer in case of fire.

Microstructure and micromechanical properties of magnesium phosphate cement

This paper presents a systematic study on the evolution of phase composition, microstructure and micromechanical properties of magnesium phosphate cement (MPC) and their relations to macroscopic mechanical properties. The results indicate that the microstructure of MPC is mainly composed of a crystal region of potassium magnesium phosphate hexahydrate (MKP) and a hybrid region of magnesium oxide and amorphous hydration products. The elastic modulus and hardness of MKP crystals are 20.18 GPa and 1.15 GPa, respectively. Amorphous hydration products may consist of MgKPO4 and Mg3 (PO4)2. The elastic modulus of amorphous MgKPO4 drops gradually from 51.4 GPa to 29.2 GPa with increasing curing age towards the elastic modulus of crystalline MKP, while the elastic moduli of amorphous Mg3(PO4)2 and unreacted MgO are approximately 160 GPa and 300 GPa, respectively. The macroscopic strength of MPC is mainly dependent on its pore structure rather than the micromechanical properties of hydration products.

Magnesium phosphate cement incorporating sheep wool fibre for thermal insulation applications

The increasing use of synthetic fibres in clothing and the high quality of sheep wool fibre (SWF) from the Australian and New Zealand market leads to a decline in the interest in SWFs produced in European countries, considering them as waste that could be valorised within the framework of a circular economy. The use of natural fibre in cement-based composites presents the main issue of durability due to the alkaline pH media of conventional cement. The use of a low-pH cement could improve the viability of combining natural fibres in this low-pH cement as matrix for developing composites. One of these low-pH cements is magnesium phosphate cement (MPC). As a ceramic material the MPC presents high thermal conductivity (∼1 W m−1 K−1) to be used as isolating material. The present work combines MPC formulated with an industrial by-product (low-grade magnesium oxide; LG-MgO) and Spanish SWF, to develop new sustainable cement-based materials (Sust-MPC-SWF) for thermal building insulation applications. The physical, thermal, and mechanical properties of Sust-MPC-SWF were evaluated to determine the optimal formulation through a design of experiments (DoE). Thirteen formulations designed by DoE were conducted with different sheep wool fibre/cement (SWF/C) and sheep wool fibre/extra water (SWF/EW) ratios. A statistical model was obtained and the optimal formulation (SWF/C = 0.36 and SWF/EW = 0.25) was validated. The increase in SWF content led to an enhancement of thermal and acoustic insulation properties of Sust-MPC-SWF, with similar results to other building materials commercialized with these features.

Design and experimental evaluation of reflective grouting asphalt concrete for durable cooling asphalt pavement

Based on grouting asphalt concrete, titanium dioxide (TiO2) and magnesium phosphate cement materials were selected as reflective grouting materials (RGM) to prepare reflective grouting asphalt concrete (RGAC), which was used to improve the reflective capacity, mechanical strength and cooling effect of pavement. The reflectance and mechanical properties of RGM were characterized through color characteristic, mechanical strength, reflectance and bonding strength tests. The results show that the spectral reflectance of RGM was 4.61 times higher than that of asphalt, but the addition of TiO2 reduced its mechanical and bonding strength. The visual and cooling effects of RGAC were analyzed by digital image processing technology and indoor irradiation test. The addition of TiO2 improved the visual uniformity and lightness of the surface, which had a good reflection effect. Compared with conventional asphalt mixture, the maximum surface temperature of RGAC reduced by 20.2 ℃. RGAC is a potential material of thermal reflective asphalt pavement construction.

Properties of magnesium phosphate cement reinforced with natural brucite fiber

Magnesium phosphate cement (MPC) is widely utilized owing to its excellent properties. However, MPC is a chemically bonded material; therefore, it has the disadvantage of being highly brittle. The introduction of fibers is a simple and effective way to improve its toughness. Therefore, this study was focused on the effects of brucite fiber (BF) on the working properties, mechanical properties, hydration products, and microstructure of MPC. X-ray diffraction, thermogravimetric (TG) analysis, mercury intrusion porosimetry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy were used to analyze the hydration products and microscopic morphology of the specimens. The results showed that the addition of BF reduced the fluidity of the MPC slurry, slightly prolonged the setting time, and reduced the hydration temperature. BF significantly enhanced the mechanical properties of MPC, particularly its flexural strength, which increased with an increase in BF content. The 7-d and 28-d strengths of the specimens with 20 % BF content increased by 72.5 % and 70.0 %, respectively, compared with the reference group. TG analysis showed that BF promoted the production of the hydration product K-struvite, and K-struvite production was almost saturated at 20 % BF doping. The SEM, EDS, and FTIR spectroscopy results showed that the MPC composite matrix containing BF had a denser structure. Moreover, bonding between the fibers and matrix was enhanced, owing to the involvement of BF in the hydration reaction. Additionally, the structure was more solid, which led to a significant decrease in brittleness and an improvement in other properties of the MPC.

Design and fabrication of high-performance injectable self-setting trimagnesium phosphate

Magnesium phosphate bone cement has become a widely used orthopedic implant due to the advantages of fast-setting and high early strength. However, developing magnesium phosphate cement possessing applicable injectability, high strength, and biocompatibility simultaneously remains a significant challenge. Herein, we propose a strategy to develop high-performance bone cement and establish a trimagnesium phosphate cement (TMPC) system. The TMPC exhibits high early strength, low curing temperature, neutral pH, and excellent injectability, overcoming the critical limitations of recently studied magnesium phosphate cement. By monitoring the hydration pH value and electroconductivity, we demonstrate that the magnesium-to-phosphate ratio could manipulate the components of hydration products and their transformation by adjusting the pH of the system, which will influence the hydration speed. Further, the ratio could regulate the hydration network and the properties of TMPC. Moreover, in vitro studies show that TMPC has outstanding biocompatibility and bone-filling capacity. The facile preparation properties and these advantages of TMPC render it a potential clinical alternative to polymethylmethacrylate and calcium phosphate bone cement. This study will contribute to the rational design of high-performance bone cement.

A novel insight into the interface fracture between magnesium phosphate cement mortar and cement concrete

ABSTRACT This paper focused on fracture problem about interfacial transition zone (ITZ) formed after repairing between magnesium phosphate cement (MPC) mortar and old Portland cement concrete (PCC) pavements. Firstly, the mode Ⅱ cracks on the ITZ were hypothesized and the interface fracture model with dislocation theory was proposed. The stress field at the crack tip was represented by Airy stress potential function and Fourier Transform, and the structural characteristics of the kernel solution of Cauchy were retained. Then, combined with the oscillation term, the Dirac function was replaced by the normal distribution function to obtain stable fracture parameters. Besides, the ϵ about 8 ‰ of the crack length in model was analyzed. Secondly, the elastic moduli of ITZs were obtained by nanoindentation experiments. Results showed the elastic modulus of ITZ between MPC mortar and ITZ-1 (the interface in concrete) was lowest. Such weakest position in repair interface was further verified by finite element analysis (FEA). Finally, a twodimensional model was developed to validate the fracture model. Simulation results were found consistent with the theoretical solution of interface fracture model. The developed interface fracture model can provide insights for evaluating the shear behavior of the interface between MPC mortar and concrete.

Ablation and insulation behavior of magnesium phosphate cement composite in harsh environments

In this study, magnesium phosphate cement composite (MPCC) were prepared by the acid-base reaction between MgO and aluminum chromium phosphate solution, and their ablation and thermal insulation behaviors were studied in an oxyacetylene flame under heat flow up to 2000 ℃, 2200 ℃, and 2400 ℃. The results indicated that with the increase in the ablation temperature, the linear ablation rate first increased from 0.09 × 10−3 mm/s to 0.45 × 10−3 mm/s and then decreased to 0.21 × 10−3 mm/s. The porous structure formed in the sample is the main reason for its excellent thermal insulation performance.