纳米SiO_2对硅酸盐水泥水化放热特性的影响

以硅灰为对比,利用微量热仪研究了纳米SiO2对硅酸盐水泥24 h内水化历程、水化放热特性的影响.研究结果表明:掺入纳米SiO2的水泥试样24 h内水化历程也可划分为类似于纯硅酸盐水泥水化的5个阶段;纳米SiO2的掺入,促使诱导期、加速期和减速期的出现提前,缩短了诱导期持续的时间;提高了水化开始时的放热速率,使第二放热峰的出现提前,增大了水化放热量.     

Effect of silica fume and fly ash on heat of hydration of Portland cement

Results of calorimeter tests on Portland cement-silica fume-fly ash mixtures are presented. Data indicate that silica fume accelerates cement hydration at high water/cementitious ratios and retards hydration at low water/cementitious ratios. On the other hand, fly ash retards cement hydration more significantly at high water/cementitious ratios. When silica fume and fly ash are added together with cement, the reactivity of the silica fume is hampered and the hydration of the cementitious system is significantly retarded.     

石膏对改性硅酸盐水泥性能的影响

将磷铝酸盐水泥熟料掺入硅酸盐水泥中改性后,运用XRD和SEM等测试技术,研究了石膏对改性硅酸盐水泥性能的影响.结果表明,石膏的掺入可以改善改性硅酸盐水泥的力学性能和抗冻性;在石膏掺量为3.5%时,改性硅酸盐水泥水化速度最快,硬化浆体的结构最致密,强度最高,抗冻性最好.     

粉磨方式对硅酸盐水泥颗粒和早期水化行为的影响

采用同一批熟料,通过辊压机终粉磨、辊压机—球磨机联合粉磨和实验室球磨三种粉磨方式粉磨。试验发现,在细度相同时,不同粉磨方式制成的水泥颗粒特性具有较大的差异。水泥颗粒形状、形貌对水泥的早期水化行为(如:标准稠度、凝结时间、流动度和水化热)影响较大,但1d的水化总放热量却相差不大。     

硅酸盐水泥水化热的研究及其进展

硅酸盐水泥水化硬化过程中会释放大量的水化热,由此而产生的温度应力是导致混凝土出现裂缝的一个主要原因,对大体积混凝土的影响更为显著。因此,水泥混凝土水化热的研究长期以来受到国内外水泥和混凝土科学家及建筑工程界的重视。本文在总结前人关于水泥水化热研究方面提出的一些理论计算公式的基础上,综合分析了影响水泥水化热的因素,介绍了国内外关于水泥水化放热模型的最新研究进展以及水泥生产中降低水化热的技术措施。     

Natural cement as the precursor of Portland cement: Methodology for its identification

When cements appeared in the 19th century, they took the place of traditional binding materials (lime, gypsum, and hydraulic lime) which had been used until that time. Early cements can be divided into two groups, natural and artificial (Portland) cements. Natural cements were introduced first, but their widespread usage was short-lived as they were quickly replaced by artificial cements (Portland), still the most important and predominant today. The main differences between natural and artificial cements arise during the manufacturing process. The final properties of the cements are greatly influenced by differences in the raw materials and burning temperatures employed.The aim of this paper is to assess the efficiency of traditional analytical techniques (petrographic microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR)) used to differentiate natural and artificial cements.     

Impact of sand and filler materials on the hydration behavior of calcium aluminate cement

In earlier work, we have observed discrepancies relating to the early hydration of calcium aluminate cement (CAC) when comparing data from heat flow calorimetry of CAC paste with results from mortar strength tests using the crushing method. Here, we investigated on this phenomenon and found that the sand which is used as a filler exerts a major influence on CAC hydration resulting in acceleration. Furthermore, in particular fine filler materials such as, for example, microsilica, fine limestone powder, and especially α- and γ-Al₂O₃ also produced a strong hydration accelerating effect which is dependent on their specific surface area. The mechanism underlying the acceleration is that under alkaline conditions their negative surface charge attracts calcium ions as was confirmed via inductively coupled plasma atomic emission measurements. Such a layer generates favourable conditions for the nucleation of CAC hydration products (C-A-H phases). The resulting crystalline hydrates which form on the surface of the filler particles submerged in CAC cement pore solution were visualized via SEM imaging. This way, specifically selected fillers can significantly accelerate CAC hydration and save precious lithium salts which are commonly used to boost the early strength of CAC.     

阿利特—硫铝酸盐水泥与硅酸盐水泥复合性能的研究

研究了阿利特－硫铝酸盐水泥与硅酸盐水泥复合所制备的水泥的性能。结果表明,复合后水泥的强度性能优于单一品种水泥的性能;凝结时间则由复合体中占比例较多的一种水泥所控制。     

醇胺类助磨剂对硅酸盐水泥水化及胶砂强度影响的研究

研究了C和D两种醇胺类助磨剂对硅酸盐水泥水化过程及胶砂强度的影响。化学结合水、水化热分析、综合热分析及XRD结果表明,C加快了水泥3d水化放热和28d水化速度及水化放热,促进了铁铝酸盐矿物的水化;D加快了水泥3d水化速度和水化放热：C、D复合加快了水泥3d和28d的水化,且复合作用优于两者的叠加效应。胶砂强度结果表明,C对水泥28d胶砂抗压强度提高幅度显著;D的加入有利于提高水泥3d胶砂抗压强度;C和D复合对28d抗压强度的增幅远高于两者的叠加效应。     

亚硫酸钙对水泥水化性能的影响

采用XRD、SEM等测试方法研究了亚硫酸钙(CaSO3.1/2H2O)对水泥水化性能的影响,并与石膏(CaSO4.2H2O)进行了对比.结果表明在水泥中CaSO3.1/2H2O不具有石膏那样的调节水泥凝结时间的作用.掺CaSO3.1/2H2O的水泥试样1d强度比掺CaSO4.2H2O试样显著降低,3d后两者强度相近.60d的抗折、抗压强度与28d相比,增幅很小,有的甚至倒缩.CaSO3.1/2H3O和铝酸盐矿物反应,主要生成片状的C3A.CaSO3.     

Early hydration of white Portland cement in the presence of bismuth oxide

Abstract

Abstract

Mineral trioxide aggregate (MTA) is a clinical product comprising a mixture of 80 wt-% Portland cement and 20 wt-% bismuth oxide, which is used as a root-filling material in dentistry. The influence of bismuth oxide on the hydration reactions of Portland cements is not well understood. In this study, the impact of 20 wt-% replacement of bismuth oxide on the hydration of white Portland cement was monitored by powder X-ray diffraction (XRD), ²⁹Si and ²⁷Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) and transmission electron microscopy (TEM). The findings of this research have confirmed that bismuth oxide is an inert additive in white Portland cement, which does not participate in the hydration reactions.     

铝酸盐水泥熟料对粉煤灰硅酸盐水泥性能的影响

以铝酸盐水泥熟料、硅酸盐水泥熟料和粉煤灰为原料,探讨了掺加少量铝酸盐水泥熟料对硅酸盐水泥及粉煤灰硅酸盐水泥复合体系水化、凝结和硬化性能的影响。结果表明,在硅酸盐水泥及粉煤灰硅酸盐水泥中掺加铝酸盐水泥熟料,可以明显缩短水泥的初、终凝时间,但复合体系的需水量增加;掺加少量铝酸盐水泥熟料(≤3%)可明显提高硅酸盐水泥的早期强度,但后期强度(28d)有所降低;当铝酸盐水泥熟料的掺量达5%时,水泥的各龄期强度均明显降低。少量铝酸盐水泥熟料掺加到粉煤灰硅酸盐水泥中,复合体系的各龄期强度都明显提高,且早期强度的提高幅度较大。     

Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques

Diffuse Reflectance Infrared DR-FTIR spectroscopy is employed to monitor chemical transformations in pastes of Portland limestone cement. To obtain a sufficient time resolution a freeze-dry procedure is used to instantaneously ceasing the hydration process. Rapid re-crystallization of sulphates is observed during the first 15 s, and appears to be complete after ~ 30 min. After ~ 60 min, spectroscopic signatures of polymerizing silica start to emerge. A hump at 970-1100 cm^− 1 in conjunction with increasing intensity in the water bending mode region at 1500-1700 cm^− 1 is indicative of the formation of Calcium Silicate Hydrate, C-S-H. Simultaneously with the development of the C-S-H signatures, a dip feature develops at 800-970 cm^− 1, reflecting the dissolution of Alite, C₃S. Setting times, 180 (initial) and 240 (final) minutes, are determined by the Vicat technique. Combining DR-FTIR, SEM and Vicat measurements it is concluded that the setting is caused by inter-particle coalescence of C-S-H.     

Properties of Portland Cement Pastes Incorporating Nanometer-Sized Franklinite Particles Obtained from Electric-Arc-Furnace Dust

The present work presents preliminary results concerning ordinary portland cement (OPC) blended with electric-arc-furnace dust (EAFD) obtained from steel-smelting plants. The powder obtained after acid treatment of the EAFD consisted basically of nanometer-sized particles of ZnFe₂O₄. Incorporation of the EAFD in the OPC produced retardation of the setting process. Nevertheless, after 7 d, the compressive strength of the OPC/EAFD pastes was superior to undoped OPC, and, after 28 d, the extent of hydration of the OPC/EAFD pastes was equivalent to undoped OPC. A compressive strength of 72 MPa was attained after 42 d for OPC doped with 10 wt% EAFD.     

The role of calcium ions and lignosulphonate plasticiser in the hydration of cement

Experiments involving equilibrium dialysis, conductivity, X-ray diffraction analysis (XRD), differential thermal analysis (DTA) and isothermal titration calorimetry (ITC) have been carried out to investigate the role of calcium ions and polymeric plasticisers in cement/admixture hydration. Results from a study of lignosulphonic acid, sodium salt, acetate as a plasticiser shows that a plasticiser has dual role; one mainly as a kinetic inhibitor (poison) in cement hydration mechanism and the other as a dispersant. Evidence of a weak Ca²⁺ binding to lignosulphonate sulphonic moieties was found at low ionic strengths of 0.1 M using ITC. No evidence of formal Ca²⁺ binding to lignosulphonate sulphonic acid moieties was found using equilibrium dialysis at higher ionic strength of 1 M (ionic strengths of 0.4 M are typically found in Portland cement pore solution), as is often suggested in cement/admixture literature.     

水浸泡养护对铝酸钙水泥水化行为影响的研究

为研究水浸泡养护对铝酸钙水泥水化行为的影响,以纯铝酸钙水泥Secar71为研究对象,试验温度为20℃,按水灰质量比0.3将水与铝酸钙水泥混合搅拌均匀,采用TG-DSC、XRD、SEM等方法对比研究了铝酸钙水泥在自然养护与水浸泡养护两种条件下分别养护1、7和15 d的水化行为。结果表明:铝酸钙水泥与水混合后,自然养护条件下,在最初的几分钟内有少量的放热,经过诱导期后有大量的放热,形成了一个"一次水化峰",之后进入稳定期;注水浸泡养护后试样内未水化水泥产生一个较"一次水化峰"低的"二次水化峰",之后水化缓慢;浸泡养护结束后试样内水化产物量与自然养护的相比明显增多,生长发育良好的片状CAH10相和絮状或粒状的三水铝石沿试样孔隙分布,填充气孔,试样结构更加致密。     

硫铝酸盐水泥与硅酸盐水泥复配性能研究

基于硫铝酸盐水泥、硅酸盐水泥各自的特点,研究了二者复配后的标准稠度用水量、凝结时间、水化热效应、胶砂强度、膨胀性、水化产物的物相及微观形貌。结果表明,复配水泥的标准稠度用水量因复配比例不同而变化,凝结时间相对于占主导地位的单组分水泥明显缩短;复配水泥的早期水化速率得到提高,1d、7d的水化放热量均低于占主导地位的单组分水泥;28d抗压、抗折强度低于任何单组分水泥;膨胀性的大小取决于两种水泥的复配比例;硫铝酸盐水泥与硅酸盐水泥的复配使二者的水化相互促进,随着硫铝酸盐水泥掺量的增加,Ca(OH)2相的衍射峰减弱,AFt相的衍射峰增强;纯硅酸盐水泥水化后的微观形貌是致密的,而与硫铝酸盐水泥复配后则出现微观裂纹。     

The hydration products of Portland cement in the presence of tin(II) chloride

The hydration products of Portland cement pastes cured using water containing tin(II) chloride have been compared with those using distilled water. In the latter case, the expected products—portlandite, ettringite and calcite—were observed. The X-ray diffraction patterns of the cement pastes cured in the presence of tin(II) chloride showed several additional peaks that have been attributed to the formation of calcium hydroxo-stannate, CaSn(OH)₆, and Friedel's salt (tetracalcium aluminate dichloride-10-hydrate), Ca₃Al₂O₆·CaCl₂·10H₂O. The amount of portlandite formed was reduced in the presence of tin(II) chloride. Calcium hydroxo-stannate contains tin in the +IV oxidation state and equations are presented to account for the oxidation of Sn(II) to Sn(IV) preceding the formation of CaSn(OH)₆ and Friedel's salt.     

A new hydration kinetics model of composite cementitious materials,part 1: Hydration kinetic model of Portland cement

This work is the first part of an overall research project that aims to model the hydration kinetics of modern composite cementitious materials. The aim of this part is to build a hydration kinetic model to characterize the hydration behavior of cement at all ages. In this paper, the nucleation and growth of CSH and the diffusion of water are described by a modified BNG model and a modified Jander's model. The kinetic parameters are obtained by simulative fitting of the model to the experimental data. The linear functions between the nucleation and growth rates and the W/C ratios are given in this paper. The apparent activation energy of the nucleation rate constant, growth rate constant, and generalized diffusion constant are approximately 36.0, 37.5, and 42.0 kJ/mol, respectively. Finally, the phase compositions of hardened cement paste are calculated according to the kinetic model and the reaction formula of cement.     

Microwave-promoted burning of Portland cement clinker

A new method of burning Portland cement clinker is studied. The microwave sintering is adopted after the raw meal is heated to certain temperature in an electric furnace. The experimental results show that after the raw meal is heated at a low electric heating temperature (1000-1200 °C) and then further sintered with microwave for 1 to 2 min, Portland cement clinkers can be formed. The f-CaO contents of the clinkers are 1-2%. It has also been found that the higher the temperature of the samples put into the microwave cavity, the shorter the time needed for microwave burning. When the temperature is up to 1300 °C, the sample needs to be heated by microwave for only 40 s, and the f-CaO content decreases to 0.65%. It has been proved by the experiments that (1) the new burning technique can greatly increase the forming speed of Portland cement clinkers, (2) Fe₂O₃ can enhance the microwave clinkering. XRD patterns of the clinkers show that their mineral compositions and the characteristic XRD peaks are similar to those of clinkers by conventional burning method.