Effect of raw materials and proportion on mechanical properties of magnesium phosphate cement

Magnesium phosphate cement (MPC) cementitious material is a phosphate cement-based material with strengthformed by a serious of acid-base neutralization reactions among magnesium oxide, phosphate retarder and water,which has a high early strength and a broad application prospect in the field of pavement rehabilitation. Thisreview collects and organizes the latest progress in the field of research on the influencing factors of mechanicalproperties of magnesium phosphate cementitious materials worldwide in recent years, and discusses the possibilitiesof application in airport engineering.The type of phosphate has a great influence on the reaction products, and the strength of the reaction productsof ammonium salt is higher. Borax is the most commonly used retarder, and the retarding effect is related to theratio of boron to magnesium. However, borax retarders have an adverse effect on the strength of MPC. In terms ofthe influence of mineral admixtures on the properties of MPC, fly ash, silica fume and metakaolin, as commonmineral admixtures, have a positive influence on the mechanical properties of MPC, but the mechanism anddegree of the influence of the three materials on the strength of MPC are slightly different;Aggregates can alsoimprove the volume stability and mechanical properties of MPC by forming skeleton structure and slowing downthe exothermic reaction. In fiber reinforced MPC matrix, steel fiber is the most widely used and the bondingperformance between special-shaped steel fiber and MPC matrix is higher than that of straight fiber;basalt fiberhas also been proved to be used to improve the mechanical properties of MPC system.

Influence of Water Stability on Bond Performance Between Magnesium Phosphate Cement Mortar and Steel Fibre

The fibre pullout test was conducted to investigate the influence of the water stability on the bond behaviour between the Magnesium phosphate cement(MPC)matrix and the steel fibre.The composition of the MPC-matrix and the immersion age of the specimens are experimentally investigated.The average bond strength and the pullout energy are investigated by analysing the experimental results.In addition,the microscopic characteristics of the interface transition zone are investigated using scanning electron microscopy(SEM).The experimental results showed that the bond performance between the MPC-matrix and the steel fibre decreased significantly with the increase of the duration of immersion in water.The average bond strength between the steel fibre and the MPC-matrix reduced by more than 50%when the specimens were immersed in the water for 28 days.The effect of the water on the interface between the steel fibre and the MPC-matrix was found to be more significant compared to the composition of the MPC-matrix.In addition,the MgO-KH2PO4 mole ratio of the MPC significantly influenced the water stability of the interface zone between the steel fibre and MPC-matrix.

Effects of Calcination Temperature of Boron-Containing Magnesium Oxide Raw Materials on Properties of Magnesium Phosphate Cement as a Biomaterial

A new magnesium phosphate bone cement （MPBC） was prepared as a byproduct of boroncontaining magnesium oxide （B-MgO） after extracting Li2CO3 from salt lakes. We analyzed the elementary composition of the B-MgO raw materials and the effects of calcination temperature on the performance of MPBC. The phase composition and microstructure of the B-MgO raw materials and the hydration products （KMgPO4.6H2O） of MPBC were analyzed by X-ray diffraction and scanning electron microscopy. The results showed that ionic impurities and the levels of toxic elements were sufficiently low in B-MgO raw materials to meet the medical requirements for MgO （Chinese Pharmacopeia, 2O10 Edition） and for hydroxyapatite surgical implants （GB23101.1-2O08）. The temperature of B-MgO calcination had a marked influence on the hydration and hardening of MPBC pastes. Increasing calcination temperature prolonged the time required for the MPBC slurry to set, significantly decreased the hydration temperature, and prolonged the time required to reach the highest hydration temperature. However, the compressive strength of hardened MPBC did not increase with higher calcination temperatures. In the 900-1 000 ~C temperature range, the hardened MPBC had a higher compressive strength. Imaging analysis suggested that the setting time and the highest hydration temperature of MPBC pastes were dependent on the size and crystal morphology of the B-MgO materials. The production and microstructure compactness of KMgPOa＇6H2O, the main hydration product, determined the compressive strength.

Preparation and Reinforcement Adaptability of Jute Fiber Reinforced Magnesium Phosphate Cement Based Composite Materials

To improve the brittleness characteristics of magnesium phosphate cement-based materials(MPC)and to promote its promotion and application in the field of structural reinforcement and repair,this study aimed to increase the toughness of MPC by adding jute fiber,explore the effects of different amounts of jute fiber on the working and mechanical properties of MPC,and prepare jute fiber reinforced magnesium phosphate cement-based materials(JFRMPC)to reinforce damaged beams.The improvement effect of beam performance before and after reinforcement was compared,and the strengthening and toughening mechanisms of jute fiber on MPC were explored through microscopic analysis.The experimental results show that,as the content of jute fiber(JF)increases,the fluidity and setting time of MPC decrease continuously;When the content of jute fiber is 0.8%,the compressive strength,flexural strength,and bonding strength of MPC at 28 days reach their maximum values,which are increased by 18.0%,20.5%,and 22.6%compared to those of M0,respectively.The beam strengthened with JFRMPC can withstand greater deformation,with a deflection of 2.3 times that of the unreinforced beam at failure.The strain of the steel bar is greatly reduced,and the initial crack and failure loads of the reinforced beam are increased by 192.1%and 16.1%,respectively,compared to those of the unreinforced beam.The JF added to the MPC matrix dissipates energy through tensile fracture and debonding pull-out,slowing down stress concentration and inhibiting the free development of cracks in the matrix,enabling JFRMPC to exhibit higher strength and better toughness.The JF does not cause the hydration of MPC to generate new compounds but reduces the amount of hydration products generated.

Effect of Borax on Hydration and Hardening Properties of Magnesium and Pottassium Phosphate Cement Pastes

Magnesium and potassium phosphate cement （MKPC） sample were prepared by mixing dead burnt MgO powder, potassium phosphate and different dosages of retarder borax to investigate the effect of borax on its hydration and hardening characteristics. The pH value, fluidity, hydration temperature and strength development of MKPC paste were investigated, and the mineralogical composition and microstructural morphology of its hydration products were analyzed. The experimental results indicated that, within a certain dosage, borax caused an endothermal effect for MKPC paste, which decreased the early hydration rate of MKPC paste, increased the fluidity of MKPC paste. Thus, strength and micro-morphology of hardened MKPC are affected. It can be concluded that borax in MKPC paste retards the early hydration rate of MKPC paste by forming a film onto surface of MgO, decreasing the temperature and increasing the pH value of the system. As borax dosage varying, different factors may dorminate the effects.

Effect of coral sand on the mechanical properties and hydration mechanism of magnesium potassium phosphate cement mortar

Damaged structures on coral islands have been spalling and cracking due to the dual corrosion of tides and waves.To ensure easy access to aggregate materials,magnesium potassium phosphate cement(MKPC)and coral sand(CS)are mixed to repair damaged structures on coral islands.However,CS is significantly different from land-sourced sand in mineral composition,particle morphology,and strength.This has a substantial impact on the hydration characteristics and macroscopic properties of MKPC mortar.Therefore,in this study we investigated the compressive strength,interfacial mechanical properties,and corrosion resistance of MKPC CS mortar.Changes in the morphology,microstructure,and relative contents of hydration products were revealed by scanning electron microscope-energy dispersive spectrometer(SEM-EDS)and X-ray diffraction(XRD).The results indicated that the compressive strength increased linearly with the interfacial micro-hardness,and then stabilized after long-term immersion in pure water and Na2SO4 solution,showing excellent corrosion resistance.Compared with MKPC river sand(RS)mortar,the hydration products of CS mortar were an intermediate product 6KPO2·8H2O with a relative content of 3.9%at 1 h and 4.1%at 12 h.The hydration product MgKPO_(4)·6H_(2)O increased rapidly after 7-d curing,with an increased growth rate of 1100%.Our results showed that CS promoted the nucleation and formation of hydration products of MKPC,resulting in better crystallinity,tighter overlapping,and a denser interfacial transition zone.The results of this study provide technical support for applying MKPC mortar as a rapid repair material for damaged structures on coral islands.

Carboxymethyl chitosan-alginate enhances bone repair effects of magnesium phosphate bone cement by activating the FAK-Wnt pathway

There is a continuing need for artificial bone substitutes for bone repair and reconstruction,Magnesium phosphate bone cement(MPC)has exceptional degradable properties and exhibits promising biocompatibility.However,its mechanical strength needs improved and its low osteo-inductive potential limits its therapeutic application in bone regeneration.We functionally modified MPC by using a polymeric carboxymethyl chitosan-sodium alginate(CMCS/SA)gel network.This had the advantages of:improved compressive strength,ease of handling,and an optimized interface for bioactive bone in-growth.The new composites with 2%CMCS/SA showed the most favorable physicochemical properties,including mechanical strength,wash-out resistance,setting time,injectable time and heat release.Biologically,the composite promoted the attachment and proliferation of osteoblast cells.It was also found to induce osteogenic differentiation in vitro,as verified by expression of osteogenic markers.In terms of molecular mechanisms,data showed that new bone cement activated the Wnt pathway through inhibition of the phosphorylation ofβ-catenin,which is dependent on focal adhesion kinase.Through micro-computed tomography and histological analysis,we found that the MPC-CMCS/SA scaffolds,compared with MPC alone,showed increased bone regeneration in a rat calvarial defect model.Overall,our study suggested that the novel composite had potential to help repair critical bone defects in clinical practice.

Enhancing the mechanical properties and cytocompatibility of magnesium potassium phosphate cement by incorporating oxygen-carboxymethyl chitosan

Incorporating bioactive substances into synthetic bioceramic scaffolds is challenging.In this work,oxygen-carboxymethyl chitosan(0-CMC),a natural biopolymer that is nontoxic,biodegradable and biocompatible,was introduced into magnesium potassium phosphate cement(K-struvite)to enhance its mechanical properties and cytocompatibility.This study aimed to develop 0-CMC/magnesium potassium phosphate composite bone cement(OMPC),thereby combining the opti-mum bioactivity of O-CMC with the extraordinary self setting properties and mechanical intensity of the K-struvite.Our results indicated that O-CMC incorporation increased the compressive strength and setting time of K-struvite and decreased its porosity and pH value.Furthermore,OMPC scaffolds remarkably improved the proliferation,adhesion and osteogenesis related differ-entiation of MC3T3-E1 cells.Therefore,O-CMC introduced suitable physicochemical properties to K-struvite and enhanced its cytocompatibility for use in bone regeneration.

Stability of K-struvite in High Temperature and Acid-base Environment

K-struvite was prepared by precipitation method,and the stability of K-struvite in high temperature and acid-base environment were investigated by X-ray diffraction(XRD),thermogravimetric analysis(TG/DSC),and infrared spectroscopy(FT-IR).The results show that K-struvite decomposes from 50 to 110℃,and the mass loss begins at 50℃before being completely destroyed at 110℃,then further heating at temperature above 500℃leading to complete loss of the binding water in K-struvite.Moreover,K-struvite is more stable in alkaline environments than acidic environment.

Preparation and characterization of a degradable magnesium phosphate bone cement

A kind of degradable magnesium phosphate bone cement(MPBC)was fabricated by using the mixed powders of magnesium oxide(MgO),potassium dihydrogen phosphate(KH_(2)PO_(4))and calcium dihydrogen phosphate(Ca(H_(2)PO_(4))2.H_(2)O).As MgKPO_(4),the main product of MgO and KH_(2)PO_(4)was alkaline,the Ca(H_(2)PO_(4))2.H_(2)Owas added to neutralize the alkali of the system.And the effects of Ca(H_(2)PO_(4))2.H_(2)Oon the performance of MPBC were discussed.The results showed that the adding of Ca(H_(2)PO_(4))2.H_(2)Oextended the setting time,which was about 6 min to 18 min.The compressive strength increased first and then decreased,and maximum value reached 31.2MPa after setting for 24 h without any additional pressure.The MPBC was degradable in Tris–HCl solution,and the extracts of the cytotoxicity assay showed that the MPBC had good biocompatibility,indicating that the MPBC had good biodegradable and biocompatible properties.

In situ magnesium calcium phosphate cements formation: From one pot powders precursors synthesis to in vitro investigations

Calcium phosphate cements are of great interest for researchers and their applications in medical practice expanded.Nevertheless,they have a number of drawbacks including the insufficient level of mechanical properties and low degradation rate.Struvite(MgNH4PO4)-based cements,which grew in popularity in recent years,despite their neutral pH and acceptable mechanical performance,release undesirable NH4+ions during their resorption.This issue could be avoided by replacement of ammonia ions in the cement liquid with sodium,however,such cements have a pH values of 9–10,leading to cytotoxicity.Thus,the main goal of this investigation is to optimize the composition of cements to achieve the combination of desirable properties:neutral pH,sufficient mechanical properties,and the absence of cytotoxicity,applying Na2HPO4-based cement liquid.For this purpose,cement powders precursors in the CaO-MgO-P2O5 system were synthesized by one-pot process in a wide composition range,and their properties were investigated.The optimal performance was observed for the cements with(Ca+Mg)/P ratio of 1.67,which are characterized by newberyite phase formation during setting reaction,pH values close to 7,sufficient compressive strength up to 22±3 MPa(for 20 mol.%of Mg),dense microstructure and adequate matrix properties of the surface.This set of features make those materials promising candidates for medical applications.

MPC混凝土制备及其力学性能试验研究

为了解决现有加固材料加固施工周期长、与旧混凝土结构黏结差等问题,利用改性磷酸镁水泥(magnesium phosphate cement,MPC)作为胶凝材料,制备3种不同骨料类别的MPC混凝土,研究其与普通混凝土力学性能的差异以及不同骨料对其力学性能的影响.以普通混凝土作为对照,制作4组棱柱体试件进行单轴抗压试验.结果表明:MPC混凝土的峰值应变明显高于普通混凝土,轻骨料的加入使其峰值应变进一步升高;其弹性模量明显低于普通混凝土,轻骨料使其弹性模量进一步降低;4组混凝土试件弹性阶段泊松比均为0.2左右,但MPC混凝土峰值时的泊松比明显高于普通混凝土,进入塑性阶段后MPC混凝土内部裂隙发展比例更高,最终破坏现象更加突然,试件破坏后更加松散.因此,MPC混凝土与普通混凝土相比脆性更强.

Bioactive calcium and mangnesium phosphate bone adhesive for enhanced vascularization and bone regeneration

Bone adhesive is a promising material for the treatment of bone fractures,which is helpful for the fast and effective reduction and fixation of broken bones.However,the existing adhesives bond weakly to bone tissues,and are non-absorbable,or hard to cure under wet conditions.Herein,inspired by the cement-based adhesive used in the industry field,we report a bioactive calcium and magnesium phosphate bone adhesive(MPBA)with the properties of facile preparation,robust adhesion,and bioactive.MPBA is equipped with similar strength to cancellous bones and shows reliable bonding performance for various interfaces,such as Ti6Al4V,Al2O3,and poly(ether-ether-ketone).MPBA achieves excellent bonding ability for the above interfaces with the bonding strengths of 2.28±0.47,2.32±0.15,and 1.44±0.38 MPa,respectively.Besides,it also shows reliable fixation ability for bovine bone surfaces.The bonding behavior to materials and bones suggests that MPBA could be used for both fracture treatment and implant fixation.Meanwhile,MPBA possesses good biological activity,which could promote the vascularization process and osteogenic differentiation.Finally,in vivo experiments confirmed MPBA can effectively restore bone strength and promote bone regeneration.

The Comparative Study of Gelatin/CNT-contained Mg-Ca-P Bone Cement with the Plain and CNT-reinforced Ones

Mimicking compositional and constructional features of the extracellular matrix(ECM)is an effective parameter in improving the biological response of biomaterials.In this regard,carbon nanotube(CNT)and gelatin were added to magnesium-calcium phosphate cement(CNG)to mimic fibrillar construction and organic composition of ECM,respectively,besides the CNG performance was compared with the plain and CNT-reinforced cement.Cementation behavior of the cements was investigated by evaluating their setting time,cement composition variation during setting,and viscosity fluctuation.Furthermore,compressive strength,degradation,and cell response of the cements were compared.Adding 5 wt.%gelatin reduced setting time about 60%,because of gel formation,not due to struvite precipitation.Moreover,the gelatin decreased compressive strength by about 20%.Although gelatin decreased compressive strength,the strength remained in the range attributed to trabecular bone.All the types of cement indicated shear thinning behavior that made their injectability feasible.Compared to other types of cement,CNG enhanced proliferation and differentiation of mesenchymal stem cells besides faster degradation,nontoxicity and suitable cell adhesion.Hence,mimicking features of CNG enhanced osteoconductivity and osteoinductivity of the cement compared to the plain one.