硝酸铅对磷酸镁水泥水化的影响及浸出毒性

重金属铅污染是重大的环境问题,利用磷酸镁水泥体系可对重金属铅进行稳定/固化。研究了不同硝酸铅掺量对磷酸镁水泥水化进程的影响,并对水化产物的晶体形貌、浸出毒性进行了探讨。研究表明:硝酸铅掺量的增加(最大掺量2.5%)对磷酸镁水泥的凝结时间影响不大,对水化产物种类(MgKPO4.6H2O和Mg3(PO4)2)无影响,但水化产物形貌有所变化。磷酸镁水泥对硝酸铅进行固化的浸出毒性试验结果(0.5mg/L左右)比国家标准要求(5mg/L)低一个数量级。EDS检测出Pb元素存在于水泥水化产物中。     

Zn~(2+)对硫铝酸盐和硅酸盐水泥水化性能的影响

研究了Zn2+对硫铝酸盐及普通硅酸盐水泥的水化和物理力学性能的影响,采用XRD和SEM分析2种含Zn2+水泥水化产物相组成、形貌,采用ICP-AES测定水化产物浸出液中Zn2+的浓度。结果表明:Zn2+可促进硫铝酸盐水泥的早期水化,阻碍普通硅酸盐水泥的水化;掺入Zn2+后,两者的强度都降低,但是降幅有所差别;Zn掺量为1%时,2种水泥水化产物中Zn的浸出浓度均低于国家浸出毒性标准,但是硫铝酸水泥对Zn2+的固化率约为普通硅酸盐水泥的4倍。     

超细CaCO3增强硫铝酸盐水泥强度的研究

在硫铝酸盐水泥硬化体中,钙矾石主要以柱状、棒状而存在,这对水泥的性能产生了不利影响。探讨了超细CaCO3对硫铝酸盐水泥进行改性的研究。试验结果表明,超细CaCO3掺量为3%时,明显改善了硫铝酸盐水泥的强度,其28 d净浆与砂浆抗压强度分别达到100.6 MPa和94.1 MPa,且水泥的28 d砂浆抗折强度高达12.5 MPa。SEM显示掺超细CaCO3硫铝酸盐水泥硬化体中难以发现大颗粒状的水化硫铝酸钙晶体,结构较致密、均匀。     

钛石膏不同方法制备的Ⅱ型硬石膏对硫铝酸盐水泥性能影响

目的 为促进工业固废钛石膏资源再利用,了解硬石膏对硫铝酸盐水泥熟料性能的影响,方法 以钛石膏为原料,采用加压水热法和酸浸法合成Ⅱ型硬石膏,研究不同方法合成的硬石膏对硫铝酸盐水泥熟料性能的影响。结果 加压水热法和酸浸法合成的硬石膏因合成方法不同,对粒径、形貌、孔隙和表面积等微观性能影响也不同;在硫铝酸盐水泥熟料中添加不同方法合成的硬石膏或天然硬石膏,且不同种类的硬石膏掺量为15%时,硫铝酸盐水泥熟料的抗压强度均达到最大值;随着养护时间延长,硫铝酸盐水泥熟料的抗压强度均明显提高;与掺入天然硬石膏相比,掺入酸浸法合成硬石膏的抗压强度较低,但在硬石膏相同掺量和相同水化时间下,掺入加压水热法合成的硬石膏的硫铝酸盐水泥熟料的抗压强度均高于掺入其他两种硬石膏的。结论 加压水热法合成硬石膏在水泥熟料中应用前景广阔,是钛石膏再利用的重要途径。     

纳米C—S—H/PCE对硅酸盐-硫铝酸盐复合水泥凝结硬化的影响

研究了纳米C-S—H/PCE对硅酸盐-硫铝酸盐复合水泥凝结时间、早期水化历程及抗压强度的影响,采用XRD、TG、pH计和SEM等分析测试手段对早龄期水化产物和液相碱度等进行表征,探讨了纳米C-S—H/PCE对硅酸盐-硫铝酸盐复合水泥的增强机理.结果表明:掺加纳米C—S—H/PCE能有效缩短硅酸盐-硫铝酸盐复合水泥浆体初...     

普通硅酸盐水泥(OPC)-铝硫酸盐(CSA)复合水泥砂浆性能的压电信号监测

将硫铝酸盐(CSA)与普通硅酸盐水泥(OPC)以不同比例配制成复合水泥砂浆,通过压电陶瓷传感器测定复合水泥砂浆在24h龄期内的压电信号能量值变化曲线,研究了这2种水泥复合后的材料物理力学性能和压电信号的变化规律.结果表明,压电信号能量值变化曲线可以反映水泥基材料早期水化行为,并与抗压强度变化曲线密切相关.CSA掺量对复合水泥的性能有很大影响,随着CSA掺量增加,复合水泥砂浆抗压强度呈现出先降低后增大的变化趋势;掺加CSA,复合水泥砂浆的水化速率普遍加快.当CSA掺量从60%增加到90%时,复合水泥砂浆早期抗压强度逐渐增大.     

掺混合材和硫酸钠水泥石可溶出Na+的实验

目的 分析在掺加Na2SO4后,粉煤灰、矿粉、水泥以及不同粉煤灰、矿粉掺量的水泥石中不同水化龄期的可溶出Na+量,进而研究Na+对混凝土的潜在破坏性.方法 利用溶出法对不同水化龄期样品进行处理,再利用离子选择性电极法对样品中的可溶出Na+量进行化学分析,以此来研究对水泥石仍有影响的Na+量随水化龄期的变化.结果 Na2SO4掺量超过2%时,水化早期的可溶出Na+量有较大幅度的提高;在水泥、粉煤灰和矿粉中,固化Na+量最大的是粉煤灰;Na2SO4掺量2%时,胶凝材料中掺入粉煤灰可明显降低可溶出Na+量,胶凝材料中矿粉掺量越高可溶出Na+量越高.结论 使用Na2SO4时,应将用量控制在2%以下;水泥中复合粉煤灰可显著提高固化Na+的能力,粉煤灰的适宜掺量为30%;水泥中复合矿粉会降低固化Na+的能力.     

掺混合材和硫酸钠水泥石可溶出SO42-的实验

目的 分析在掺加Na2SO4后,粉煤灰、矿粉、水泥以及不同粉煤灰、矿粉掺量的水泥石中可溶出SO42-的量,进而研究SO42-对混凝土的潜在破坏性.方法 利用溶出法对不同水化龄期样品进行处理,再利用BaSO4重量法对样品中可溶出SO42-的量进行化学分析,以此来研究SO42-量随水化龄期的变化.结果 水化28 d时,Na2SO4掺量低于2%的水泥石中已测不出SO42-,而Na2SO4掺量高于2%的水泥石中仍有可溶出SO42-;在水泥、粉煤灰和矿粉中,固化SO42-速率最快的是矿粉,固化SO42-量最大的是水泥;Na2SO4掺量2%,水化7d之前,水泥中粉煤灰掺量越高可溶出SO42-量越大,矿粉掺量越高可溶出SO42-量越小.结论 普通水泥混凝土中Na2SO4掺量不应高于2%;固化SO42-的速率由快到慢为矿粉、水泥和粉煤灰;固化SO42-的量由高到低为水泥、矿粉和粉煤灰;水泥中复合粉煤灰后固化SO42-的速率变慢;水泥中复合矿粉后固化SO42-的速率变快.     

P·O与R·SAC复合水泥砂浆的强度与电阻率研究

将普通硅酸盐水泥(Ordinary Portland Cement,简称为P·O)和快硬硫铝酸盐水泥(Rapid Hardening Sulphoaluminate Cement,简称为R·SAC)以不同比例混合,并掺入一定量的减水剂配制成自流平砂浆,通过测定砂浆在不同龄期的抗压强度和1440min内的电阻率,研究了这两种水泥的复合使用效果.结果表明,当快硬硫铝酸盐水泥的掺量从10%增加到90%时,砂浆抗压强度表现出明显的先降低后增大的变化趋势.随着掺量的增大,砂浆的初始电阻率也逐渐增大,水泥的早期水化逐渐加快;当掺量从60%增加到90%时,电阻率曲线开始出现峰值,并且峰值的出现时间也逐渐提前,此时砂浆的抗压强度也逐渐增大.     

石灰石粉铝酸盐水泥复合体系的水化反应

石灰石粉具有水化活性,能与硅酸盐水泥中的C₃A、铝酸盐水泥中的CA、CA₂等铝酸盐矿物发生反应,水化产物为水化碳铝酸钙。利用微量热仪法、胶砂强度和X射线衍射（XRD）,研究不同比例的石灰石粉铝酸盐水泥复合体系的水化反应,结果表明：石灰石粉会加快铝酸盐水泥的水化进程,水化过程诱导期缩短,放热速率峰值下降;复合体系中石灰石粉占比越高,早期水化反应速率越快,但水化反应放热量越低;相对而言,复合体系中石灰石粉掺量为20%时石灰石粉参与反应程度最高,且掺量为20%时石灰石粉对复合体系强度有显著贡献。随复合体系中石灰石粉比例增加,铝酸盐水泥水化产物越来越不明显;石灰石粉掺量为20%~40%时,水化碳铝酸钙XRD特征峰相对最明显,复合体系中石灰石粉与铝酸盐水泥存在一个最佳的比例范围。研究表明,石灰石粉与铝酸盐水泥间会发生明显的水化反应,石灰石粉与铝酸盐水泥复合有望制得一种新型胶凝材料。     

Carbonation resistance of sulphoaluminate cement-based high performance concrete

The influences of water/cement ratio and admixtures on carbonation resistance of sulphoaluminate cement-based high performance concrete (HPC) were investigated. The experimental results show that with the decreasing water/cement ratio, the carbonation depth of sulphoaluminate cement-based HPC is decreased remarkably, and the carbonation resistance capability is also improved with the adding admixtures. The morphologies and structure characteristics of sulphoaluminate cement hydration products before and after carbonation were analyzed using SEM and XRD. The analysis results reveal that the main hydration product of sulphoaluminate cement, that is ettringite (AFt), decomposes after carbonation. Funded by the National Natural Science Foundation of China (No.50872043)     

The Pore Structure and Hydration Performance of Sulphoaluminate MDF Cement

1　IntroductionReducingporositycouldimprovethestrengthofma terials ,butitisnotenoughthatthechangeofthestrengthofthematerialsisonlysubjectedtothechangeofporosi ty .Thereforetheporedistributionconceptisintroduced .Weeventhinkthattherelationbetweentotalporos…     

Hydration mechanism of sulphoaluminate cement

The feasibility of sulphoaluminate cement (SAC) utilization in support mortar was studied. Setting time and strength of as-received sulphoaluminate cement (SAC) paste were examined, hydration kinetics behavior was determined through Isothermal Calorimeter, and hydration mechanism was investigated by X-Ray diffraction analysis (XRD) and field emission scanning electron microscopy analysis(FSEM). Results showed that as-received SAC contained 61% of anhydrous calcium sulfate (3CA·CaSO4) and dicalcium silicate (C2S). The strength after 1 day or 3 days grew to 68.6% or 85.7% of that after 28 days respectively, while most of hydration heat was released within 1 day. The emergency of three exothermic peaks at acceleration stage was found and hydration kinetics model was established choosing the terminal time of the first exothermic peak at accelerating stage as the beginning of accelerating stage. XRD analysis suggested that large amount of ettringite (AFt) was produced at early age and FSEM observation revealed that ettringite (AFt) formed in sulphoaluminate cement (SAC) paste was characterized of different morphology which was proved to be caused by different ion concentrations.     

不同CO2养护压力下硫铝酸盐和硅酸盐水泥浆体早期微观结构

研究硫铝酸盐和硅酸盐水泥（CSA-OPC）浆体在不同碳养护压力下的早期碳化过程,通过X射线衍射、红外光谱、热重、压汞和扫描电镜等测试方法,表征碳化前后水泥浆体的物相组成和微观结构. 实验结果表明,CSA-OPC浆体的水化产物主要为钙矾石,碳化作用使钙矾石转变为碳酸钙和硫酸钙晶体;水泥中碳酸钙以3种晶型存在,其中方解石为主要存在形式. 碳化使半碳型的水化硫铝酸钙（Hc-AFm相）逐渐转化为单碳型的水化硫铝酸钙（Mc-AFm相）,碳化程度和碳化深度随着碳化压力的增加而递增. 碳化后CSA-OPC水化产物体积减小,样品总孔隙率增大、孔隙结构变疏松. 研究结果阐明了CSA-OPC浆体在早期碳化养护条件下的微结构变化过程,为制备基于硫铝酸盐水泥的高效碳汇材料提供了技术支撑.     

Effects of LiAl-layered double hydroxides on early hydration of calcium sulphoaluminate cement paste

As a 3D micro-nano material, layered double hydroxides have been widely used in many fields, especially for reinforced composite materials. In this paper, LiAl-LDHs was obtained by a hydrothermal method. In order to investigate the effects of LiAl-LDHs on the early hydration of calcium sulphoaluminate (CSA) cement paste, compressive strength, setting time and hydration heat were tested while X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scaning electron microscopy (SEM) and differential scanning calorimetry (DSC) analysis were employed. The results indicated that LiAl-LDHs could significantly improve the early compressive strength and shorten the setting time of calcium sulphoaluminate cement paste with 3wt% concentration. Besides, the hydration exothermic rate within 5 h was accelerated with increasing LiAl-LDHs content. Moreover, the addition of LiAl-LDHs did not result in the formation of a new phase, but increased the quantity of hydration products providing higher compressive strength, shorter setting time and denser microstructure.     

The Cement Solidification of Municipal Solid Waste Incineration Fly Ash

The chemical composition, the content and the leachability of heavy metals in municipal solid waste incineration （ MSWI） fly ash were tested and analyzed. It is shown that the leachability of Pb and Cr exceeds the leaching toxicity standard, and so the MSWI fly ash is considered as hazardous waste and must be solidifled. The effect of solidifying the MSWI fly ash by cement was studied, and it is indicated that the heavy metals can be well immobilized if the mass fraction of the fly ash is appropriate. The heavy metals were immobilized within cement hydration products through either physical fixation, substhtaion, deposition or adsorption mechanisms.     

Analysis of Hydration Mechanism and Microstructure of Composite Cementitious Materials for Filling Mining

To obtain the compositions and microstructure of hydration products of cementitious material in different hydration ages and its growth law of filling strength, the optimal proportion of composite cementitious material was determined according to the chemical composition of cement clinker which was composed of the Portland cement 32.5R, CSA 42.5 sulphoaluminate cement and two gypsum(CS). The characterization of composite cementitious materials in different hydration ages was conducted by NMR, XRD and SEM techniques. The mechanism of hydration was explored. It is shown that the compressive strength of the test block increases gradually with the increase of hydration age. The microstructure of composite cementitious material can be changed from Al-O octahedron into Al-O tetrahedron in the hydration process. The hydrated alkali alumi niumsilicate formed with Si-O tetrahedron and Al-O tetrahedron. The degree of polymerization of Si-O tetrahedron gradually increased, and the structural strength of cementitious materials continued to increase. The diffraction peak of clinker minerals gradually decreased with the extension of hydration age. The CaSO_4 completely hydrated to produce Aft during hydration which resulted in high early strength of cementitious material. The early hydration product of composite cementitious materials was Aft with a needle bar structure. The main middle and last hydration products were CSH gel and CH gel with dense prismatic shape. The microscopic pore of composite cementitious material gradually decreased and improved the later strength of filling block. The strong support was provided for mined-out area.     

Retention of clay-solidified grouting curtain to Cd~(2 ), Pb~(2 ) and Hg~(2 ) in landfill of municipal solid waste

1　INTRODUCTIONIntheseyears ,innocuitytreatmentofmunicipalsolidwaste (MSW )hasincreasedgreatlyand 95 %isattributedtosanitaryandsemi sanitarylandfillswiththelandfillsbeingconstructedinarapidprogressinChina.Itisveryimportantforlandfillsto preventseepageofleachateincludingheavymetalsfromlandfillsintotheenvironment.Manyresearchershavestudiedtheanti seepagetechnology .Forexample ,Philip[1 ] investigatedcontaminationtransportprocessthroughsingle phasecement bentoniteslurrywallbytriaxialcelle…     

Hydration mechanism of silica fume-sulphoaluminate cement

Setting time and strength of sulphoaluminate rapid hardening cement （SAC） incorporated in the presence and absence of silica fume （SF） were determined. Combined with the techniques of＂ isothermal calorimeter, XRD and FSEM, the hydration kinetics of the two systems and the effect mechanism of SF on SAC were investigated. The experimental results showed that SF was proved to be beneficial for SAC system, in terms of setting time and late strength gain. Evidence of accelerator effect of silica fume was found during the first 8 hours of hydration. The formation of AFt was accelerated and the microstructure of the hydration products grew denser with incorporation of SF. SF was proved to play the role of dispersion and setting control at early age and had a greater contribution to later strength due to the increment of crystal nucleation point and the pozzolanic activity. Therefore, SF can be used to not only control the hydration kinetics of SAC, but also develop the late strength and improve the microstructure.