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.

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.

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.

The Improvement Effects of NaH_(2)PO_(4) and KH_(2)PO_(4) on the Properties of Magnesium Oxysulfate Cement

Sodium dihydrogen phosphate (NaH_(2)PO_(4)) and potassium dihydrogen phosphate (KH_(2)PO_(4)) were selected as additives for magnesium oxysulfate (MOS) cement.The phase composition and the microstructure of MOS cement were characterized using X-ray diffraction (XRD),thermogravimetric analysis (TG-DSC),Flourier transform infrared spectroscopy (FT-IR),mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM).It is found that both NaH_(2)PO_(4) and KH_(2)PO_(4) lead to an increase in the compressive strength and an improvement in the volume stability of MOS cement.The XRD,MIP and SEM results show that the addition of NaH_(2)PO_(4) or KH_(2)PO_(4) does not change the phase composition of MOS cement but promotes the formation of strength phase of 5Mg(OH)_(2)·MgSO_(4)·7H_(2)O (5·1·7 phase).This phase brings a considerable improvement in the microstructure of MOS cement,which has a positive effect on the properties of MOS cement.

MK增强BF-MPC力学性能

针对磷酸镁水泥(MPC)韧性低的问题,采用试验研究的方法制备不同掺量玄武岩纤维(BF)和偏高岭土(MK)的磷酸镁水泥砂浆试件测试其各龄期的强度,并通过扫描电镜(SEM)与X射线衍射(XRD)对试件进行微观分析。结果表明:随着偏高岭土掺量的增大,MPC砂浆的抗折强度与抗压强度相应提升;玄武岩纤维的掺入可明显提高MPC砂浆的抗折强度,对抗压强度的影响不显著。微观分析表明,偏高岭土和粉煤灰(FA)在MPC砂浆中参与反应生成二次水化产物,其有助于改善玄武岩纤维与基体间的粘接性能,提高MPC砂浆的力学性能。

MPC作为无砟轨道底座板修复材料的力学性能试验评价

针对高铁无砟轨道底座板混凝土的不同损伤程度,采用磷酸镁水泥(MPC)作为修补材料,研究了修补厚度(20mm、35mm、50mm)对叠合构件力学性的影响。试验结果表明:修补厚度为20mm时,2h的极限承载力达到整浇构件承载力的87.57%;随着修补厚度的增加,叠合构件的极限承载力逐步降低,修补厚度为50mm时,其极限承载力较比修补厚度为20mm的极限承载力下降了16.64%。同时通过有限元模拟分析,其模拟结果与试验结果基本吻合。

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.

用MPC黏结CFRP布约束混凝土柱轴压试验研究

为了解决传统纤维布(fibre reinforced polymer/plastic,FPR)加固都采用有机胶作为黏结剂,存在容易老化、不耐火等问题,将无机新型黏结材料磷酸镁水泥(MPC)与有机胶(EP)分别黏结碳纤维布(CFRP布)1~3层约束素混凝土柱进行了轴压试验,得出了破坏形态、受压强度模型、应力-应变规律.通过比较研究认为:磷酸镁水泥黏结CFRP约束混凝土柱与有机胶黏结时,受压破坏形态一致,受约束柱强度提高,应力-应变规律一致,且磷酸镁水泥作为黏结剂时,约束构件受压破坏过程中表现了较好的延性.

MPC骨水泥纤维蛋白胶复合BMP人工骨支架材料对山羊松质骨缺损的修复

研制MPC/CPC骨水泥纤维蛋白胶复合BMP新型人工骨的制备及人工骨修复骨缺损的性能。通过对成年山羊双侧股骨髁部分别制备1处直径10mm、深15mm松质骨缺损,制备MPC/CPC/FG/BMP(A组)、MPC/CPC/FG(B组)、CPC/FG(C组)人工骨支架材料,分别植入各组实验观察材料,分别于6周、12周进行影像学、组织学、形态计量学观察骨缺损修复情况。说明新型MPC骨水泥纤维蛋白胶复合BMP新型生物活性人工骨支架材料在促进成骨、加快磷酸钙骨水泥降解速度上优于MPC/CPC/FG、CPC/FG的人工骨,同时新型MPC骨水泥复合纤维蛋白胶的成骨和促骨水泥降解作用优于单纯CPC复合FG的人工骨。

磷酸镁水泥(MPC)及其作为FRP粘结剂的研究进展

对磷酸镁水泥(MPC)的组成及水化机理进行介绍,总结了影响其工作性能的因素,综述国内外应用MPC作为粘结剂粘接FRP加固混凝土结构的研究进展,提出了存在的问题,为今后的研究提供了参考。

MPC黏结CFRP加固混凝土的抗折性能

为了解决传统有机胶黏结纤维布(fibre reinforced polymer/plastic,FRP)加固存在耐久性和耐火性不佳等问题,采用新型黏结材料磷酸镁水泥(magnesium phosphate cement,MPC)和环氧胶(epoxy adhesive,EP)分别黏结碳纤维增强复合材料(carbon fiber reinforced polymer/plastic,CFRP)加固的混凝土试件并进行了抗折性能研究,分析了各类试件断裂类型、抗折强度等性能,得到了荷载-位移曲线、荷载-应变曲线,通过黏结界面破坏时形态机理的比较研究发现:MPC与CFRP复合加固混凝土抗弯试件能达到EP加固的效果,界面能发挥较好的抗剪黏结效果.

MPC粘结CFRP为阳极对锈蚀钢筋混凝土电化学除氯的研究

采用磷酸镁水泥(MPC)粘结碳纤维布(CFRP)作为电化学阳极,对锈蚀钢筋混凝土柱进行电化学除氯。研究了锈蚀钢筋混凝土柱在不同电流密度下的电化学除氯效率、距钢筋不同距离处氯离子分布。结果表明:同一电流密度下,钢筋锈蚀率15%和30%混凝土柱的除氯效率明显大于自然锈蚀和锈蚀率5%的混凝土柱;对于相同锈蚀率的钢筋混凝土,除氯效率随着电流密度的增大而增大;除氯后,混凝土中距钢筋不同位置处的残余氯离子浓度由内到外呈递增趋势,混凝土中各区域残余氯离子随电流密度的增加而降低。

Study of interfacial transition zones between magnesium phosphate cement and Portland cement concrete pavement

The Portland cement concrete pavement(PCCP)often suffers from different environmental distresses and vehicle load failure,resulting in slab corner fractures,potholes,and other diseases.Rapid repair has become one of the effective ways to open traffic rapidly.In this study,a novel type of rapid repair material,basalt fiber reinforced polymer modified magnesium phosphate cement(BFPMPC),is used to rapidly repair PCCP.Notably,the mechanical properties and characteristics of the repair interfaces which are named interfacial transition zones(ITZs)formed by BFPMPC and cement concrete are focused on as a decisive factor for the performance of the rapid repair.The changing trend of the elastic moduli was studied by nanoindentation experiments in the ITZs with the deconvolution analysis that the elastic moduli of certain kinds of substances can be determined.The experimental results show that the elastic modulus of ITZ-1 with a width of about20μm can be regarded as 0.098 times of the aggregate,and 0.51 times of the ordinary Portland cement(OPC)mortar.The BFPMPC-OPC mortar ITZ has roughly the same mechanical properties as the ITZ between aggregate and BFPMPC.A multi-scale representative two-dimensional model was established by random aggregate and a two-dimensional extended finite element method(XFEM)to study the mechanical properties of the repair interface.The simulation results show that the ITZ formed by the interface of BFPMPC and OPC mortar and basalt aggregate is the most vulnerable to failure,which is consistent with the nano-indentation experimental results.

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.

Nanofiber-induced hierarchically-porous magnesium phosphate bone cements accelerate bone regeneration by inhibiting Notch signaling

Magnesium phosphate bone cements(MPC)have been recognized as a viable alternative for bone defect repair due to their high mechanical strength and biodegradability.However,their poor porosity and permeability limit osteogenic cell ingrowth and vascularization,which is critical for bone regeneration.In the current study,we constructed a novel hierarchically-porous magnesium phosphate bone cement by incorporating extracellular matrix(ECM)-mimicking electrospun silk fibroin(SF)nanofibers.The SF-embedded MPC(SM)exhibited a heterogeneous and hierarchical structure,which effectively facilitated the rapid infiltration of oxygen and nutrients as well as cell ingrowth.Besides,the SF fibers improved the mechanical properties of MPC and neutralized the highly alkaline environment caused by excess magnesium oxide.Bone marrow stem cells(BMSCs)adhered excellently on SM,as illustrated by formation of more pseudopodia.CCK8 assay showed that SM promoted early proliferation of BMSCs.Our study also verified that SM increased the expression of OPN,RUNX2 and BMP2,suggesting enhanced osteogenic differentiation of BMSCs.We screened for osteogenesis-related pathways,including FAK signaing,Wnt signaling and Notch signaling,and found that SM aided in the process of bone regeneration by suppressing the Notch signaling pathway,proved by the downregulation of NICD1,Hes1 and Hey2.In addition,using a bone defect model of rat calvaria,the study revealed that SM exhibited enhanced osteogenesis,bone ingrowth and vascularization compared with MPC alone.No adverse effect was found after implantation of SM in vivo.Overall,our novel SM exhibited promising prospects for the treatment of critical-sized bone defects.

混凝土预制构件MPC接缝材料性能研究

在再生橡胶粉颗粒中掺入MPC砂浆,通过测试其流动度、抗压强度、黏结性能与耐水性系统研究橡胶改性MPC砂浆的性能,并采用BSE微观图像表征橡胶粉颗粒对MPC砂浆微观结构的影响。结果表明,少量的橡胶粉颗粒对MPC砂浆工作性能影响较小,掺量>10%时,MPC砂浆流动度显著降低;橡胶粉可降低MPC砂浆抗压强度和黏结强度,且对早期抗压强度影响远大于中后期;橡胶粉对MPC砂浆耐水性能有一定改善作用,掺入10%橡胶粉的MPC砂浆浸水60d后耐水系数可达0.88;橡胶粉颗粒与MPC基材料的胶结十分紧密,同时还能改善MPC基材料与石英砂的界面性能。

椰子纤维MPC复合水泥基材料受压性能试验研究

磷酸镁水泥(Magnesium Phosphate Cement,简称MPC)是一种早期强度高、凝结硬化快、干缩变形小、粘结能力强的胶凝材料,可用于高架桥、机场跑道和市政主干道的快速修补等方面.然而,MPC存在韧性差、抗裂性能差的缺点,严重限制了MPC在实际修复工程中的应用.经前期研究发现,在MPC中掺入椰子纤维(Coconut Fiber,简称CF)能有效提高其抗裂性能,然而,CF对MPC力学性能的影响规律和作用机理尚未清晰,因此,需要对椰子纤维加固磷酸镁水泥(Coir Fiber Reinforced Magnesium Phosphate Cement,简称CF-MPC)这一新型生态复合材料进行系列研究.本文主要研究不同体积掺量(1%、2%、3%、4%)CF在不同养护龄期(7 d、28 d)下对MPC静态受压性能的影响.首先,通过静态压缩试验分析了椰子纤维掺量和养护龄期对CF-MPC试件的破坏形态、抗压强度、应力-应变曲线和能量吸收性能的影响规律;其次,通过扫描电子显微镜(Scanning Electron Microscope,简称SEM)和X射线衍射(X-ray diffraction,简称XRD)分析,测试了不同CF掺量在不同养护龄期下,CF-MPC微观结构和水化组分的变化规律,从本质上探明了CF对上述宏观力学性能的影响机理.结果表明:在7 d、28 d两个养护龄期下,CF掺量对MPC静态抗压性能的影响相似.当CF掺量高于1%时,MPC脆性明显降低,且CF掺量为2%时,试件破坏形态由脆性变为一定的延性;CF-MPC试件抗压强度、弹性模量和割线模量随椰子纤维掺量的增加而略有降低,但随龄期的增长而增大;能量吸收随着CF掺量的增加及龄期的增长均呈增大趋势,且当CF掺量为4%、龄期为28 d时能量吸收达到最大;微观分析中,随着CF掺量的增长,主要水化产物六水磷酸钾镁(MgKPO4·6H2O,简称MKP)逐渐减少,而随着龄期的增长MKP逐渐增加.

高海拔地区低温成型磷酸镁水泥砂浆力学与抗冻性能

磷酸镁水泥(MPC)砂浆因其低温下卓越的强度发展潜力和免于蓄热保湿养护的特性,特别适用于高寒地区破损混凝土结构的修补工作。研究采用现场试验的办法,以成型温度、镁磷质量比、养护制度为变量,跟踪不同龄期下不同条件的磷酸镁水泥砂浆的抗折与抗压强度,厘清了高海拔地区低温成型磷酸镁水泥砂浆力学性能的发展规律。研究又以成型海拔、成型温度、镁磷质量比为变量,以气泡结构和水饱和度为中间指标,以单面盐冻中质量剥蚀和快速冻融循环中相对质量及相对动弹性模量的变化为直接指标,剖析了高海拔地区低温成型磷酸镁水泥砂浆抗冻性能的影响因素。研究结果表明,自然养护相较恒定低温养护对早期强度发展有利,但对后期强度发展有不良影响。低温环境下成型有利于自然养护的磷酸镁水泥砂浆的后期强度。成型海拔、成型温度和镁磷质量比与砂浆的含气量呈负相关,与砂浆的气泡间距系数和水饱和度呈正相关。试验条件下,这三个变量的值越小,砂浆的抗冻性越好。-10℃成型,镁磷质量比为4对砂浆强度最有利;而-10℃成型,镁磷质量比为3对砂浆抗冻性最有利。这些研究成果为高寒地区磷酸镁水泥砂浆的工程应用提供了技术建议与理论支持。