Properties Of Magnesium Phosphate Cement Research Articles

Impact of metakaolin on hydration properties of magnesium phosphate cement

The degradation of mechanical properties in magnesium phosphate cement (MPC) is commonly observed under conditions of rapid heat release and high ambient temperature. To mitigate this phenomenon, the incorporation of metakaolin has been investigated as a means to reduce the hydration heat of MPC and enhance its mechanical properties at elevated temperatures. Experimental findings reveal a pronounced influence of metakaolin on the heat flow behavior of MPC. Specifically, the addition of a small fraction of metakaolin (not exceeding 20wt%) leads to an accelerated heat release rate during the initial 0.13hours, followed by a substantial reduction in the heat release rate with further increments of metakaolin. Furthermore, the inclusion of metakaolin significantly improves the mechanical properties of MPC. For instance, a composition comprising 30% metakaolin yields a notable 79.2% increase in strength after 7 days. It is worth noting that temperatures below 400℃ are found to have an adverse impact on the mechanical properties of MPC, whereas a temperature range encompassing 600℃>T>400℃ enhances these properties due to vitrification at high temperatures. Importantly, MPC incorporating metakaolin exhibits superior mechanical performance compared to its metakaolin-free counterpart across all tested temperatures, which can be attributed to the attainment of a denser microstructure facilitated by metakaolin incorporation.

Early properties of magnesium phosphate cement repairing material used in slab track

Magnesium phosphate cement (MPC) is a high-performance repairing material suitable for the interfacial disease of slab track. In this study, the early properties of MPC were optimized using central composite design (CCD) approach based on response surface methodology (RSM). Three factors with five levels and three responses were considered. The significance of the factors and their interactions were verified by using analysis of variance (ANOVA). The result show that the mass ratio of water-to-binder (W/b) affects fluidity, while the mass ratio of magnesia-to-phosphate (M/P) and borax-to-magnesia (B/M) impact the setting time of MPC. Higher W/b results in higher fluidity, while an increase in M/P reduces the setting time by increasing the neutralization reaction. Borax addition retards the reaction, prolonging the setting time. The three factors significantly affect the early compressive strength of MPC. At M/P = 3.5, the interweaving of MgO and K-struvite (MKP) forms a dense network structure, enhancing the strength. Borax and W/b interact to affect compressive strength, with borax retarding MKP crystal growth and higher W/b reducing compactness. Combined with microscopic property test, the strength generation mechanism of MPC with optimized mixing ratio was revealed, And the feasibility of field application of MPC was verified by strength test.

Properties and reaction mechanism of magnesium phosphate cement modified by calcium lactate

The properties of magnesium phosphate cement (MPC) are studied by measurements of setting time, flowability, compressive strength and by multiple technique analyses of pH values, calorimetry, XRD, TG, MIP and SEM taking calcium lactate (CL) content as variables. Results show that CL can significantly prolong the setting time and promote the synergetic development of compressive strength of MPC, but the addition of CL leads to a decrease in flowability of MPC. Comprehensive consideration on these properties, the optimal dosage of CL is 5%. In this case, the setting time, flowability and 1 day & 28 days compressive strength of MPC are 84 minutes, 185 mm, 40.8 MPa & 54.2 MPa, respectively. Multiple technique analyses show that the addition of CL can decrease the liquid phase pH value and hydration rate of MPC, resulting in the extension of setting time. A low content of CL (3%) can improve the reaction degree and optimize the matrix pore structure of MPC, and thus promoting the strength development (50.90 MPa increased to 65.93 MPa). However, an excessive addition of CL (7%) will lead to the decrease in reaction products and the increase in matrix porosity of MPC, resulting in a decrease in compressive strength (43.30 MPa reduced to 37.36 MPa).

The effect of CaO in fly ash on the hydration mechanism and properties of magnesium phosphate cement

Fly ash (FA) is often used to modify MPC, playing a role in delaying setting time, changing color, enhancing mechanical properties, and reducing costs. Current research mainly focuses on higher quality FA, in which the CaO content is low and mainly of F-type. This type is also widely used to modify traditional cement, leading to a shortage in the supply of F-type FA and limiting its engineering applications. Therefore, this study aims to use FA with a higher CaO content and higher stack volume to solve this problem, systematically studying the effect of high CaO content FA on the hydration mechanism and properties of the MPC system, and comparing it with low CaO content FA. The results show that the CaO in FA undergoes a secondary hydration reaction in the MPC, reacting with the phosphate radical to form Ca3(PO4)2. In addition, Ca(OH)2 is only generated at high CaO content and finally reacts to form CaCO3 with the increase of curing age, while CaHPO4 is generated at low CaO content. As the MPC sets and hardens quickly, the newly generated CaCO3 not only enhances compressive strength but also damages the matrix. However, the addition of FA still enhances the compressive strength of MPC, with the highest increase reaching 14.4%.In addition, the incorporation of FA significantly improves the water resistance of MPC, the compressive strength retention rate of the FA/MPC system after 28d of water immersion is significantly higher than that of MPC. This study provides a theoretical basis for the application of high CaO content FA.

Effect of silt modification on the properties of magnesium phosphate cement

Magnesium phosphate cement (MPC), as a new type of cementitious material, is difficult to be popularized in practical applications due to its short setting time, high cost, and poor water resistance. Dredged silt (DS) is a kind of hazardous waste, which may cause serious damage to the ecological environment if it is not disposed of properly. The treatment of DS and its reuse in building materials is an economical and environmentally friendly treatment method, which not only realizes the recycling of DS but also avoids secondary pollution. Using the treated DS as a mineral admixture for modified MPC not only recycles the DS but also improves the properties of MPC. In this paper, the effect of DS modification on the properties of MPC was investigated by setting time test, mechanical property test, water resistance test, and RCM test, and also compared with the modification effect of common mineral admixtures, such as fly ash (FA) and metakaolin (Mk), and finally analyzed by combining with SEM pictures. With the increase of the dosage of FA, Mk, and DS, the compressive strength of the modified MPC all showed the trend of increasing and then decreasing, and the optimal dosage was 5%, 10%, and 15%, respectively. At the optimum dosage, Mk and FA could improve the resistance of MPC to chloride erosion, but DS could not. The three kinds of admixtures could prolong the setting time of MPC, with DS having the best effect, followed by FA, and Mk having the smallest effect. All three admixtures could improve the water resistance of MPC, and the effect of improvement was Mk > DS > FA. The microstructure of the specimen was denser when the dosage of DS was low, and when the dosage was too much, the hydration reaction of MPC was affected, resulting in incomplete hydration and reduced hydration products. This research has significant guiding significance for the treatment of DS and the modification of MPC.

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.

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.

Static and dynamic mechanical properties of magnesium phosphate cement modified by metakaolin after high-temperature treatment

Magnesium phosphate cement (MPC) is widely used in fields of construction and fire-retardant coatings due to its excellent properties. The hydration properties of MPCs at high temperatures are the points of interests. In this work metakaolin was used to improve workability and mechanical properties of MPC, and static and dynamic mechanical properties and hydration products of the MPC after high temperature treatment were investigated. The results showed that the incorporation of metakaolin in MPC allows extending and importantly tuning the setting time of MPC. Notably, 40% replacement of dead burnt magnesia with metakaolin in MPC could extend the setting time of MPC to about 24 min. While the fluidity of MPC significantly decreased with increasing metakaolin content. Typically, increasing the temperature leads the deterioration of mechanical properties of the MPC. However, static and dynamic strength enhancement was also observed at 600℃. The main hydration products of MPC with metakaolin are struvite (MgNH4PO4·6H2O), unreacted MgO, aluminum phosphate (APH) and possibly amorphous substance containing aluminum. Moreover, the impact resistance of MPC at high temperatures were significantly improved with incorporation of metakaolin.

Effect of Modified Magnesium Oxide on the Properties of Magnesium Phosphate Cement under a Negative Temperature Environment.

As a rapid repair material, magnesium phosphate cement (MPC) can be used under various environmental temperature conditions, but different temperatures significantly impact its strength and working performance. In this study, based on the surface modification of magnesium oxide, the working and mechanical properties of samples were investigated at an ambient temperature of -5 °C, and the hydration properties and microstructure of MPC were investigated using X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury-in-pressure (MIP), and scanning electron microscopy (SEM). The results show that the modified magnesium oxide at a negative temperature prolongs the setting time of MPC from 10 min to more than 30 min, and fluidity can still be maintained or increased after half an hour. From 1 d to 28 d, the compressive strength growth rate of the reference group was 257.0% compared to 723.8% for the 10 wt% water-glass-modified MgO sample. K-struvite transformed from a blocky growth to a needle-like growth with the modified sample filling the pores and cracks inside the matrix. Compared with the unmodified sample, MPC's porosity decreased from 9.62% to 9.23% for 10 wt% water-glass-modified MgO. Therefore, the surface modification of magnesium oxide not only prolonged the setting time but also further benefited mechanical performance, which provides the prerequisites for MPC construction in negative-temperature environments.

Ablation resistance and mechanical properties of ZrB2 reinforced magnesium phosphate cement composite

In this study, the ablation and mechanical properties of magnesium phosphate cement (MPC) were enhanced by adding ZrB2. The effects of ZrB2 on the microstructure, compressive strength, ablation, and heat insulation performances of MPC were studied. ZrB2 creates nanocrystals in the microstructure of the composites; the compressive strength reaches 25 MPa, the density is improved, and the surface temperature decreases to approximately 100 °C. After ablation for 60 s under an oxyacetylene flame at approximately 2100 °C, the mass and line ablation rates of a 15 mm-thick composite are −20.3 mg/s and 8.5 µm/s, respectively, and the backside temperature is 140 °C. Microstructural observations and thermodynamic calculations suggest that the high thermal conductivity of the ZrB2 additive and the evaporation of boron-containing oxides are key to reducing the surface temperature.

Preparation and properties of magnesium phosphate cement with recycled magnesia from waste magnesia refractory bricks

Waste magnesia refractory bricks (WMRBs) are a high-quality magnesia resource with a MgO content of ＞80%. However, numerous WMRBs are not effectively utilized, leading to the waste of magnesia resources. WMRBs can be transformed into recycled magnesia (RM) with a MgO content of ＞82% by simply crushing and grinding the material. Using RM to prepare magnesium phosphate cement (MPC) can significantly cut the preparation cost of MPC and promote the efficient utilization of WMRBs. Herein, the chemical and mineral composition, hydration activity, and micro-morphology of RM are analyzed, and the physico-mechanical properties of MPC prepared with RM are studied. The results show that the chemical and mineral composition of RM is not significantly different from that of dead-burned magnesia (DM), but its hydration activity is remarkably lower than that of DM owing to the larger grain size of periclase and more regular particle morphology of RM. The setting time of MPC prepared with RM (MPCRM) increases significantly, and the hydration temperature rise decreases significantly, which is more conducive to the application of MPC to large-scale engineering. Although the early strength and long-term strength of MPCRM are lower than those of MPC prepared with DM, the 3 h compressive strength of MPCRM exceeds 25 MPa, while its 28-d compressive strength is close to 60 MPa; furthermore, MPCRM has a small drying shrinkage value and good water resistance, which can meet the requirements of repair construction.

Study on graphene oxide reinforced magnesium phosphate cement composites

Graphene oxide (GO) is an excellent nano reinforcing material. This paper presents the effect of GO addition on the hydration, microstructure and mechanical properties of magnesium phosphate cement (MPC). MPC with GO contents of 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10 % was prepared. The functional groups, mechanical properties, phase composition and reinforcement mechanism of the GO-MPC composites were tested and analysed. The results showed that water adhered to the GO, which led to a decrease in the fluidity of the MPC paste. With increasing GO content, the most probable pore size of MPC first decreased and then increased. By adding 0.04 % GO, the most probable aperture of MPC was reduced from 11.3 μm to 0.9 μm. The proper addition of GO could refine the pore size, densify the microstructure and improve the mechanical properties of MPC. An appropriate dosage of GO promoted the hydration of MPC, resulting in more hydration products, including potassium magnesium phosphate hexahydrate (MKP), better growth of MKP with higher crystallinity.

Effects of sodium dihydrogen phosphate on properties of magnesium phosphate cement

Magnesium phosphate cement (MPC) has attracted much attention in repair materials due to its excellent properties. However, the variability and harshness of the environment put increasing demands on the mechanical properties of materials. Modifying the crystal structures of hydration products is a simple and effective method for improving the mechanical properties. In this paper, the effects of sodium ions on the structures of the hydration products were first investigated at a high water-to-cement ratio, and then the setting time, the heat of hydration, flexural strength and compressive strength were systematically studied for cement at a low water-to-cement ratio. X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, pore structure determination, micromorphology analysis and energy spectrometry was used to investigate the effect of the SDP content on MPC. The results showed that adding SDP could change the crystal structure of the hydration products and cause the formation of more uniform struvite whiskers. The main hydration product is struvite, and sodium ions can promote the hydration reaction and increase the amount of hydration products. In addition, the sodium ions replace some of the potassium ions in struvite to form a more stable crystal structure, from potassium-containing magnesium phosphate to sodium-potassium coexisting struvite whiskers. This promotion can refine the crystal structure of the hydration product, thereby changing the pore structure and improving the mechanical properties of SDP-MPC. Typically, the 1 d flexural strength of MPC with 50 wt% SDP addition is up to 12.7 MPa, and the 1 d compressive strength is up to 78.1 MPa; MPC with 50 wt% SDP was found to have 65% higher flexural strength and 122% higher compressive strength compared to MPC without SDP addition, and the 28 d flexural strength and compressive strength also increased by 58% and 70%, respectively. The results show that incorporating sodium ions changes the crystal structure of struvite and can effectively improve the strength properties of magnesium phosphate cement.

Comparative Investigation of Effect of Borax and Sodium Gluconate Retarders on Properties of Magnesium Phosphate Cement

Comparative Investigation of Effect of Borax and Sodium Gluconate Retarders on Properties of Magnesium Phosphate Cement

Effects of steel slag on the microstructure and mechanical properties of magnesium phosphate cement

The effects of steel slag (SS) addition on the strength and water resistance of magnesium phosphate cement (MPC) are investigated, and the hydration mechanism is proposed in this paper. With the addition of SS, the strength and water resistance of MPC were significantly enhanced. The compressive strength of MPC with 10 wt% SS (SS 10) cured in air for 60 d reached 56.7 ± 4.2 MPa. Interestingly, the strength loss rate of the sample cured in water for 14 d was only 6.6%. In addition, the microstructure and hydration products of MPC specimens were investigated via X-ray diffraction and scanning electron microscopy. There was a significant amount of unreacted MgO after MPC curing, and the main hydration product was struvite-K. The amount of struvite-K (KMgPO4·6H2O) of MPC with 0 wt% SS decreased after curing in water. However, no significant changes in the amount of hydration products was evident for SS 10, and the compactness was enhanced. This work provides a new approach for the resource utilization of SS.

Effect of Titanium Slag on the Properties of Magnesium Phosphate Cement

Effect of Titanium Slag on the Properties of Magnesium Phosphate Cement

Properties of magnesium phosphate cement as electrolyte for structural supercapacitor

Properties of magnesium phosphate cement as electrolyte for structural supercapacitor

Influencing mechanism of sodium tripolyphosphate on the rheological properties of magnesium phosphate cement

Magnesium phosphate cement (MPC) has been applied in grouting engineering due to its features of quick setting, high early-strength, and perfect volume stability. The rheological properties (RPs) of MPC, being vitally important for site operation, need to be studied further. Sodium tripolyphosphate (STP) is one type of high-efficiency retarders used in MPC. This study investigated the effects of STP content on the RPs of MPC pastes, and the mechanisms were studied by characterizing the zeta potential, 1H NMR relaxation signal, water film thickness, mineral changes, and electrical impedance. Experimental results indicate that the plastic viscosity (η) increases gradually and the yield stress (τ0) decreases firstly and then increases with increasing the STP content. The influencing mechanisms of STP need to be distinguished by analyzing η and τ0 respectively. The water film thickness and the amount of intermediate hydration products within 15 min of hydration is directly related to the change in η. The porosity and distribution of free water obtained from 1H NMR in MPC slurry are the dominant factor for τ0, and followed by the diffused double layer. It is noteworthy that zeta potential is not an effective measure for studying the RPs of MPC. Results of electrical impedance also explain the mechanisms of STP retarding the hydration and improving the early-term strength of MPC.

Design of polymeric binders to improve the properties of magnesium phosphate cement

In the context of reducing the environmental impact of cement manufacturing, magnesium phosphate cements raise interest as alternative binders in construction, for immobilization of wastes, and recycling purposes. Their use in applications is somehow limited by short setting time, brittleness and low water resistance; this calls for the use of additives. Two polymer additives were designed adopting emulsion polymerization, an environmentally friendly solution to make available polymers as water-based latex dispersions. The composites containing 5 wt% of polymer, exhibited better elastic behaviour, with up to twice the toughness of the reference sample and of a sample produced with commercial styrene-butadiene rubber latex. Moreover, the additives reduced the apparent porosity, promoted phosphate crystallization, modified the size and shape of crystals, and effectively retarded the reaction, extending working time. The acrylic emulsion developing keto-hydrazide self-crosslinking reaction imparted better properties to the composite, thanks to the synergistic effect with the MPC setting reaction.

Rheological properties of magnesium phosphate cement with different M/P ratios

Magnesium phosphate cement (MPC) with unique advantages of quick setting and high early-strength has been used as grouting materials. The rheological properties of MPC, being vitally important for site operation, need to be studied further. Dead burnt magnesia (MgO) and phosphate (ADP) are the main raw materials for preparing MPC. This study measured the rheological properties with different M/P ratios, and the mechanisms of M/P ratio were studied by characterizing the zeta potential, 1H NMR relaxation signal, water film thickness, mineral changes and electrical impedance. Experimental results indicate that both the yield stress (τ0) and plastic viscosity (η) decrease firstly and then increase gradually with increasing the M/P ratio from 2.5:1 to 4.5:1. Higher M/P ratio decreases the interparticle water film thickness and accelerates the initial hydration rate remarkably, which is responsible for the change in rheological parameters. Low field NMR, TG-DTG analysis and Nyquist plots confirm the quicker initial hydration in MPC with higher M/P ratio. The change in hydration products is very slight during the rheological property measurements. Nyquist plots show that the MPC paste with lower M/P ratios has more compact microstructure and lower porosity at several hours. In a word, initial hydration rate is the most important factor influencing the rheological properties of MPC, and the separation distance among solid particles is the secondary factor.