Magnesium Potassium Phosphate Cement Research Articles

A study on particle size of slag on properties of magnesium potassium phosphate cement

AbstractMagnesium potassium phosphate cement (MKPC) presents a broad application prospect in engineering fast repairing, reinforcement, hazardous material, and national defense construction, due to its good properties such as fast hardening and early strength, high bonding strength, and wide environmental adaptability. In this work, the effect of slag with different particle size on the workability, mechanical properties, and hydration products of MKPC was investigated. The results showed that the compositions of slag in the particle size range 75–300 µm are quite different. A decrease in the particle size of slag resulted in reduction of the fluidity of MKPC from 175 to 108 mm and shortening the setting time from 1300 to 850 s. The compressive strength of MKPC (curing for 3 h) does no change much as the particle size of slag varies, and slag with the particle size in the range of 115–300 µm slightly increase the 3‐h‐compressive strength of MKPC, since the compressive strength values are in the vicinity of 13 ± 2 MPa. As the curing age increases, physical effect and hydration activity of slag concurrently dominate the mechanical properties of MKPC, and when the hydration activity of the slag exceeds the adverse effect caused by fine particles, the compressive strength increases. Slag particle size can significantly improve the long‐term compressive strength of MKPC, which can effectively reduce the cost and can be used as a repair material with better durability.

Novel insights into the amorphous feature of granulated blast furnace slag-supplemented magnesium potassium phosphate cement and its effect on bulk properties

This paper reports the effects of MgO:PO4 (3, 9, and 15) ratio and granulated blast furnace slag dosage (0 wt%, 40 wt%, and 80 wt%) on the phase formation, microstructure, and bulk properties of magnesium potassium phosphate cement (MKPC). Results show that the supplementary of slag and the increment in MgO:PO4 inhibit the formation of K-struvite via X-ray diffraction. While the detections of 29Si magic-angle spinning nuclear magnetic resonance spectroscopy and scanning electron microscope-energy dispersion spectrum further unveil the dissolution of slag and the formation of Q4 amorphous structure in slag supplemented MKPCs. Although the Q4 structure increases the interplanar spacing of K-struvite even leads to its amorphization in MKPCs with high MgO:PO4 (>9), the optimum coexisting of K-struvite and Q4 structure minimizes the porosity and maximizes the compressive strength of MKPCs with MgO:PO4=3 and 40 wt% slag. These results are crucial to developing optimal mixture formulations of MKPC with superior mechanical performance and lower costs associated with their production.

Medical waste incineration fly ash-based magnesium potassium phosphate cement: Calcium-reinforced chlorine solidification/stabilization mechanism and optimized carbon reduction process strategy

The traditional solidification/stabilization (S/S) technology, Ordinary Portland Cement (OPC), has been widely criticized due to its poor resistance to chloride and significant carbon emissions. Herein, a S/S strategy based on magnesium potassium phosphate cement (MKPC) was developed for the medical waste incineration fly ash (MFA) disposal, which harmonized the chlorine stabilization rate and potential carbon emissions. The in-situ XRD results indicated that the Cl− was efficiently immobilized in the MKPC system with coexisting Ca2+ by the formation of stable Ca5(PO4)3Cl through direct precipitation or intermediate transformation (the Cl− immobilization rate was up to 77.29%). Additionally, the MFA-based MKPC also demonstrated a compressive strength of up to 39.6 MPa, along with an immobilization rate exceeding 90% for heavy metals. Notably, despite the deterioration of the aforementioned S/S performances with increasing MFA incorporation, the potential carbon emissions associated with the entire S/S process were significantly reduced. According to the Life Cycle Assessment, the potential carbon emissions decreased to 8.35 × 102 kg CO2-eq when the MFA reached the blending equilibrium point (17.68 wt.%), while the Cl− immobilization rate still remained above 65%, achieving an acceptable equilibrium. This work proposes a low-carbon preparation strategy for MKPC that realizes chlorine stabilization, which is instructive for the design of S/S materials.

A preliminary study on preparation and properties of magnesia based clinker with zeolite and magnesite

Dead burnt magnesia is the main raw material of magnesium phosphate cement, which is widely used in road repair works. However, due to the high energy consumption and high cost in the production and preparation process of dead burnt magnesia, its application is limited to a certain extent. In this work, a magnesia based clinker containing a considerable number of magnesium oxide and magnesium silicates phase was prepared by co-firing of zeolite powder and magnesite at low temperature (1200–1300 ℃). The results show that high temperature than 1200℃ results in less free MgO. Intermediate phases 2CaO·MgO·2SiO2 formed in clinker at 1250℃ and 1300℃. The workability of the pastes made from calcined cement clinker was proved to be better than that of traditional magnesium potassium phosphate cement (MKPC). The compressive strength can reach 30 MPa after curing for 7 days. Compared with the traditional MKPC, the hydration heat of the new magnesia based cement is greatly reduced. Lower calcination temperature on the cement clinker resulted in fewer cracks and pores on the surface of magnesia based cement and denser structure of the hydration products.

MgO/KH2PO4 and Curing Moisture Content in MKPC Matrices to Optimize the Immobilization of Pure Al and Al-Mg Alloys.

Magnesium Potassium Phosphate Cements (MKPCs) are considered a good alternative for the immobilization of aluminium radioactive waste. MKPC composition and moisture curing conditions are relevant issues to be evaluated. The corrosion of pure aluminium (A1050) and AlMg alloys (AA5754) with 3.5% of Mg is studied in MKPC systems prepared with different MgO/KH2PO4 (M/P) molar ratios (1, 2, and 3M) and moisture curing conditions (100% Relative Humidity (RH) and isolated in plastic containers (endogenous curing)). The Al corrosion potential (Ecorr) and corrosion kinetic (icorr and Vcorr) are evaluated over 90 days. Additionally, the pore ion evolution, the matrix electrical resistance, the pore structure, and compressive strength are analysed. The corrosion process of Al alloy is affected by the pH and ion content in the pore solution. The pore pH increases from near neutral for the 1M M/P ratio to 9 and 10 for the 2 and 3M M/P ratio, increasing in the same way the corrosion of pure Al (AA1050) and AlMg alloys (AA5754). The effect of Mg content in the alloy (AA5754) becomes more relevant with the increase in the M/P ratio. The presence of phosphate ions in the pore solution inhibits the corrosion process in both Al alloys. The MKPC physicochemical stability improved with the increase in the M/P ratio, higher mechanical strength, and more refined pore structure.

Effect of K+ Diffusion on Hydration of Magnesium Potassium Phosphate Cement with Different Mg/P Ratios: Experiments and Molecular Dynamics Simulation Calculations.

Magnesium potassium phosphate cement (MKPC) is formed on the basis of acid-base reaction between dead burnt MgO and KH2PO4 in aqueous solution with K-struvite as the main cementitious phase. Due to the unique characteristics of these cements, they are suitable for special applications, especially the immobilization of radioactive metal cations and road repair projects at low temperature. However, there are few articles about the hydration mechanism of MKPC. In this study, the types, proportions and formation mechanism of MKPC crystalline phases under different magnesium to phosphorus (Mg/P) ratios were studied by means of AAS, ICP-OES, SEM, EDS and XRD refinement methods. Corresponding MD simulation works were used to explain the hydration mechanism. This study highlights the fact that crystalline phases distribution of MKPC could be adjusted and controlled by different Mg/P ratios for the design of the MKPC, and the key factor is the kinetic of K+.

Effect of surface treatment by mineral admixture-magnesium potassium phosphate cement on the mechanical properties, durability, and microstructure of recycled aggregate concrete

Magnesium potassium phosphate cement (MKPC), a clinker-free cement, was used as the recycled coarse aggregate (RCA) surface strengthening material to enhance the mechanical properties and durability of recycled aggregate concrete (RAC) under two surface treatment methods. The effect of strengthening slurry properties on RAC reinforcement was investigated by adding different types and amounts of mineral admixtures (MA). An interface model was prepared to detect the microscopic characteristics of interfaces. The results indicated that all MA-MKPC slurries improved the RAC macroscopic performances, attributed to the fact that MA-MKPC slurries effectively improved the RCA surface pore structure and promoted a secure connection with RCA or new mortar. MA-MKPC slurry properties significantly affected the performances of modified RAC, and the MA optimal dosage of 10 % was found. Furthermore, the pre-coating without pre-curing method outperformed the pre-coating plus pre-curing method, forming an enhanced new interfacial transition zone within the RAC.

Phase and microstructure evolution of the hydration products of magnesium phosphate cements under sulfuric acid environments

Magnesium phosphate cement is a good canditate of repairing material served under harsh environments and its acid resistivity has drawn a lot of interest, but rare detailed research on the evolution of its physiochemical features has been reported. In this work, the impacts of sulfuric acid solution (pH = 2 – 7) on the hydration products of magnesium potassium phosphate cement and magnesium ammonium phosphate cement. Results showed that the main hydration products, struvite/struvite–K, experienced partial corrosion in the absence of the sulfuric acid solution replacement. The phase transition of struvite–K is clearly visible, leading to the formation of the new crystalline hydration product Mg3(PO4)2•22 H2O. The initial blossoms cluster microstructure transformed into a diffused dispersion that resembled a plate. When the solution was replaced, struvite/struvite–K underwent significant corrosion and even complete decomposition in more acidic (pH = 2, 3) solutions.

Cs+ Promoting the Diffusion of K+ and Inhibiting the Generation of Newberyite in Struvite-K Cements: Experiments and Molecular Dynamics Simulation Calculations.

Struvite-K cements, also called magnesium potassium phosphate cements (MKPCs), are applicable for particular applications, especially the immobilization of radioactive Cs+ in the nuclear industry. This work focuses on how Cs+ affects the hydration mechanism of struvite-K cements because newberyite and brucite in the hydration products are deemed to be risky products that result in cracking. Experiments and molecular dynamics simulations showed that Cs+ promoted the diffusion of K+ to the surface of MgO, which greatly facilitates the formation of more K-struvite crystals, inhibiting the formation of newberyite and brucite. A total of 0.02 M Cs+ resulted in a 40.44%, 13.93%, 60.81%, and 32.18% reduction in the amount of newberyite and brucite, and the Cs immobilization rates were 99.07%, 99.84%, 99.87%, and 99.83% when the ratios of Mg/P were 1, 3, 5, and 7, respectively. This provides new evidence of stability for struvite-K cements on radioactive Cs+ immobilization. Surprisingly, another new crystal, [CsPO3·H2O]4, was found to be a dominating Cs-containing phase in Cs-immobilizing struvite-K cements, in addition to Cs-struvite.

Chemical degradation of magnesium potassium phosphate cement pastes during leaching by demineralized water: Experimental investigation and modeling

The long-term durability of magnesium potassium phosphate cement (MKPC) pastes was investigated by examining their leaching behavior. MKPC comprised magnesium oxide (MgO) and potassium dihydrogen phosphate (KH2PO4) in equimolar amounts and yielded K-struvite (MgKPO4·6H2O) and a nearly neutral pore solution pH upon hydration. Semi-dynamic leaching tests were performed on MKPC paste samples using demineralized water with a pH set at 7, and the leached solids were analyzed using XRD, SEM/EDS, 11B and 31P MAS-NMR spectroscopy. Leaching was mainly governed by diffusion of dissolved species through the pore network of the paste. Three main zones were observed in the leached solids: (i) a poorly cohesive residual layer where K-struvite was fully depleted, (ii) an intermediate zone where K-struvite coexisted with cattiite (Mg3(PO4)2·22H2O), and (iii) a third zone without any cattiite. Reactive transport modeling made it possible to predict the extent of degradation and the phase evolution in the MKPC paste samples.

Competitive encapsulation of multiple heavy metals by magnesium potassium phosphate cement: Hydration characteristics and leaching toxicity properties

Magnesium potassium phosphate cement (MKPC) is increasingly used in the solidification/stabilization (SS) of heavy metal (HM) pollutants. However, research on composite HM pollutants remains limited. In this study, four heavy metals (Pb/Zn/Cu/Cd) were individually and simultaneously introduced into MKPC systems with different magnesium/phosphorus (M/P) molar ratios. The introduction of HMs altered the extent of hydration and morphology of MgKPO4·6H2O. Among the MKPC pastes, those with M/P = 2 and 3 had the highest HM solidification efficiency and strength, respectively. The HM solidification efficiency of all specimens exceeded 99 %. In samples with M/P = 3, the codoping of four HMs slightly increased the M/P ratio, thereby increasing MgKPO4·6H2O content and enhancing strength. Pb could generate additional low-solubility precipitates, such as PbHPO4, Pb3 (PO4)2, Pb5 (OH) (PO4)3, and Pb (OH)2, which easily accumulated in pores and were encapsulated by MgKPO4·6H2O, leading to the highest solidification efficiency of Pb by MKPC. Pb and Cu could also form the composite phosphate products Pb2Cu (PO4)3 (OH)·4H2O, thus promoting the S/S effect of Cu. Therefore, the use of MKPC with M/P ratio of 2–3 for the S/S of complex pollutants containing Pb and Cu is a promising approach.

Efficiency of mineral additive-modified magnesium potassium phosphate cement in solidifying waste sediment as alternative roadbed materials

The development of eco-friendly and efficient alternative binder to conventional Portland cement is a challenging issue that deserves to be paid more attention. The mineral additive-modified magnesium potassium phosphate cement mixture was introduced in sediment solidification recycled as alternative roadbed material. The feasibility of mineral additive-MKPC blend in solidifying sediment and its mechanical performance were probed into deeply through unconfined compressive strength, durability, microstructural and mineralogical tests. The results demonstrated that it existed an optimal mineral additive content where the peak strength was achieved, and an excessive amount caused the strength degradation. The unconfined compressive strength of solidified sediment increased with curing age and exhibited a growing potential. Struvite-k crystals were identified as the major cementing phase in mineral additive-MKPC solidified sediment. C-S-H gels and Ca2P2O7 ċ 2H2O were recognized as secondary phases for fly ash-MKPC blend and MgSiO3 for silica fume-MKPC blend. As the molar ratio of M/P and curing age grew, the total porosity was reduced due to the pore filling of mineral grains and densification of hydrated phases. The strength of solidified sediment after durability tests showed a tendency of first decline and then increase with durability period. Overall, the superior benefits including excellent strength performance, strong resistance to external environmental damage and highly densified microstructure could be expected for mineral additive-MKPC blend in sediment solidification as a promising roadbed filling.

Understanding hydration properties of magnesium potassium phosphate cement with low magnesium-to-phosphate ratio

Magnesium potassium phosphate cement (MKPC) is used for rapid repair works, but is a candidate for encapsulating intermediate level waste due to its low alkaline or neutral environment. This work aims to at giving insights into the hydration process of MKPC with quite low magnesium-to phosphate ratios. The hydration process of MKPC under low M/P conditions was investigated using XRD identification, pH/conductivity, isothermal calorimetry, FTIR, TG/DSC and SEM methods. The results show that low magnesium-to phosphate ratios (M/P = 0.2–1) of MKPC result in low pH values in the range of 6.3–8.5 which is suitable for the applications in low alkaline or neutral environment. No obvious hydration products were observed at M/P ≤ 0.2, and as M/P increases, MgHPO4•3 H2O primarily formed, followed by Mg2KH(PO4)2•15 H2O. As M/P increase up to 1, Mg3(PO4)2•22 H2O was also found at the initial and later stage of hydration except at the mid-stage of hydration. Mg3(PO4)2•22 H2O, MgHPO4•3 H2O and Mg2KH(PO4)2•15 H2O were the primary hydration products of MKPC at low M/P, where the formation sequence and properties of them may offer the research interests for the application in radioactive waste encapsulation.

A method for determining the hydration degree of magnesium potassium phosphate cements

A method for determining the hydration degree of magnesium potassium phosphate cements

The Influence of the Magnesium-to-Phosphate Molar Ratio on Magnesium Potassium Phosphate Cement Properties Using Either Wollastonite or Volcanic Ash as Fillers

The use of the fillers wollastonite and volcanic ash for the formulation of magnesium phosphate cements prepared at magnesium-to-phosphate molar ratios of 2, 3 and 4 has been investigated, with the objective of evaluating these formulations for the encapsulation of aluminium radioactive waste. The workability, mechanical strength, dimensional stability, pH, chemical composition and mineralogical properties of cement pastes and mortars were examined. All cement pastes presented fast setting, and the workability was only good at 3 and 4 M. The cement mortars presented high compressive strength and dimensional stability. K-struvite was confirmed as the sole reaction product of the reaction for all formulations. The pH of the cement pastes, measured in suspensions, achieved values in the range of 7.8 to 9.5 after the first days of setting, exceeding pH 8.5 for the 2 and 3 M formulations. pH values below 8.5 are theoretically preferred to avoid potential aluminium corrosion. Both fillers presented adequate characteristics (good workability, chemical compatibility) to be used in the formulation of magnesium phosphate cements. The increasing magnesium-to-phosphate molar ratio prevented unwanted efflorescence and increased the mechanical stability of the cement.

Surface treatment with nano-silica and magnesium potassium phosphate cement co-action for enhancing recycled aggregate concrete

Surface treatment with nano-silica and magnesium potassium phosphate cement co-action for enhancing recycled aggregate concrete

Simultaneous Immobilization of Heavy Metals in MKPC-Based Mortar-Experimental Assessment.

Heavy metal contamination, associated with the increase in industrial production and the development of the population in general, poses a significant risk in terms of the contamination of soil, water, and, consequently, industrial plants and human health. The presence of ecotoxic heavy metals (HMs) thus significantly limits the sustainable development of society and contributes to the deterioration of the quality of the environment as a whole. For this reason, the stabilization and immobilization of heavy metals is a very topical issue. This paper deals with the possibility of the simultaneous immobilization of heavy metals (Ba2+, Pb2+, and Zn2+) in mortar based on magnesium potassium phosphate cement (MKPC). The structural, mechanical, and hygric parameters of mortars artificially contaminated with heavy metals in the form of salt solutions were investigated together with the formed hydration products. In the leachates of the prepared samples, the content of HMs was measured and the immobilization ratio of each HM was determined. The immobilization rate of all the investigated HMs was >98.7%, which gave information about the effectiveness of the MKPC-based matrix for HM stabilization. Furthermore, the content of HMs in the leachates was below the prescribed limits for non-hazardous waste that can be safely treated without any environmental risks. Although the presence of heavy metals led to a reduction in the strength of the prepared mortar (46.5% and 57.3% in compressive and flexural strength, respectively), its mechanical resistance remained high enough for many construction applications. Moreover, the low values of the parameters characterizing the water transport (water absorption coefficient Aw = 4.26 × 10-3 kg·m-2·s-1/2 and sorptivity S = 4.0 × 10-6 m·s-1/2) clearly demonstrate the limited possibility of the leaching of heavy metals from the MKPC matrix structure.

Immobilization and characteristics of potassium magnesium phosphate on copper ions

Potassium magnesium phosphate cement (MKPC) can be used in the fields of solidification of heavy metal ions in hazardous waste. Scholars have demonstrated that MKPC has a good curing effect on Cu2+. However, Cu2+ can lead to a significant decrease in the mechanical properties of solidified matrix, resulting in a decrease in compressive strength and even fragility. In view of the existing problems in the current research, a method of MgKPO4·6H2O strengthening MKPC solidifying Cu2+ is proposed to solve the problem of significant mechanical property loss of solidified matrix in the later stage, while also ensuring excellent solidifying effect. The evolution process and morphology of MKPC products after solidifying Cu2+ are studied. In addition, the long-term solidifying effect of MKPC is also tested. The results shows that MKPC with MgKPO4·6H2O has a relatively stable 180d solidifying effect on Cu2+, with a leaching concentration of 7.64 mg/L, which meet the standard requirements. The products of MKPC solidified Cu2+ include Mg.95Cu.05O and Cu3(PO4)2. The process of strengthening and solidifying Cu2+ by MKPC with MgKPO4·6H2O includes adsorption, chemical bond and physical encapsulation. MgKPO4·6H2O provides an auxiliary alkaline environment for the solidification of Cu2+ and has adsorption properties, improving the immobilization effect of Cu2+ and achieving long-term immobilization stability. This study provides a new idea for the solidification of other waste containing divalent heavy metal ions using MKPC with MgKPO4·6H2O.

Reactivity of MSWI-fly ash in Mg-K-phosphate cement

In this study, the behaviour and reactivity of Municipal Solid Waste Incineration Fly Ash (MSWI-FA), introduced in the formulation of magnesium potassium phosphate cement (MKPC), was investigated by considering the waste either as fully inert or reactive. MSWI-FA induced structural and compositional modifications in MKPC as a consequence of dissolution/precipitation processes which involved many MSWI-FA elements (e.g., Ca, Mg, Al, Si, Zn) and led to the formation of mostly amorphous phosphate secondary products. The reaction path has been described in terms of the early fast dissolution of MSWI-FA, with precipitation of very low solubility phases, and subsequent late precipitation due to pH changes and water subtraction during MKPC gelification. The increase in amorphous content peaked to 50 wt.% and it has been related to the improved behaviour with respect to the leaching of heavy metals (reduced by 70-99%), pointing to this cement as an excellent matrix for their chemical stabilization. The obtained MKPC microstructure exhibited better mechanical performance, with an improvement of up to 60% in compressive strength. All in all, the results indicated that the incorporation in MKPC is a viable recycling opportunity for MSWI-FA, although, for an effective cement formulation, its reactivity must be taken into account.

Dynamic properties of steel fiber-reinforced potassium magnesium phosphate cement-based materials after high-temperature treatment

Potassium magnesium phosphate cement (MKPC) demonstrates remarkably high-temperature resistance and exhibits ceramic-like characteristics above 1000 °C. When micro steel fibers (MSF) are introduced, the resulting micro steel fiber-reinforced potassium magnesium phosphate cement-based (MSF-MKPC) material displays superior impact resistance even at high temperatures. Besides that, it is non-toxic and environmentally friendly. To investigate the impact resistance of MSF-MKPC at high temperatures, the split Hopkinson pressure bar test was conducted to analyze its dynamic mechanical properties under varying conditions, including MSF content, temperature, and strain rate. Mechanism analyses were carried out using scanning electron microscopy, mercury intrusion porosimetry, and X-ray diffraction testing. The experimental findings revealed the following key points: (1) MSF content has a more significant impact on enhancing the dynamic compressive strength of MSF-MKPC after high-temperature exposure compared to room temperature. Additionally, as the temperature increases, the residual dynamic compressive strength of MSF-MKPC initially decreases and then rises. (2) In contrast to room temperature conditions, the overall dynamic toughness index of MSF-MKPC shows an upward trend with increasing MSF content after high-temperature exposure. As the strain rate increases, the overall dynamic toughness index of MSF-MKPC also increases. (3) A dynamic impact constitutive regression equation is proposed for MSF-MKPC after high temperature, and the predicted results align well with the experimental findings. The analysis of the dynamic performance of MSF-MKPC after high temperatures can serve as a theoretical basis for the design of MSF-MKPC in future engineering applications, as well as for advancing the environmental sustainability and mechanical properties of fiber-reinforced cement-based composite materials.