Early Hydration of Tetracalcium Aluminoferrite in Gypsum and Lime-Gypsum Solutions

Based on product compositions and on the compositional changes occurring in the aqueous phase, a mechanism for the early hydration of C₄AF in solutions containing gypsum or lime and gypsum is suggested. According to this mechanism, early formation of AFt is preceded by the formation of alumina gel or C₂AH₈. Early AFt formation occurs through solution, and the early AFt product contains little or no iron. The solution chemistry also suggests that an amorphous, iron-rich gel forms and that calcium is associated with this gel.     

Kinetics of Tricalcium Aluminate and Tetracalcium Aluminoferrite Hydration in the Presence of Calcium Sulfate

Hydration reactions of C₃A and C₄AF with calcium sulfate hemihydrate and gypsum were investigated and the kinetics of the reactions compared. The rates of C₃A and C₄AF hydration, as determined by heat evolution, vary depending on whether the sulfate-containing reactant is gypsum or calcium sulfate hemihydrate. The following sequence of reactions involving C₄AF occurs when hemihydrate is the reactant: gypsum formation during the first hour, ettringite formation between 20 and 36 hours, and the conversion of ettringite to monosulfate over a period of about 12 hours. Monosulfate formation initiates prior to the complete consumption of gypsum. The onset of this conversion occurs at a shorter hydration time when hemihydrate is a reactant and the total amount of heat evolved is lower. The hydration reactions in saturated calcium hydroxide solution occur more slowly than those in water. Based on heat liberation, C₄AF reacts at a much higher rate than C₃A. Ettringite formation occurs during the first 8 to 9 days of C₃A hydration. Once the gypsum is consumed, ettringite converts to monosulfate during two additional days. Compared to gypsum, hemihydrate decreases the rates of hydration of both C₃A and C₄AF. The effects on the hydration characteristics of C₄AF are significant. The hydration of C₃A with gypsum in water, in saturated Ca(OH)₂ solution, and in 0.3 M NaOH solution were compared. Heat evolution is the lowest for hydration in 0.3 M NaOH. The onset of monosulfate formation occurs prior to the complete reaction between gypsum and C₃A in the NaOH solution.     

无水硫铝酸钙在石膏和氢氧化钙水溶液中的水化试验研究

基于无水硫铝酸钙水化固液反应的机理,分别在20℃和60℃恒温条件下研究了不同的n(C4A3S∶C SH2∶CH)对C4A3S的水化程度以及水化产物的影响.利用X射线衍射(XRD)和扫描电子显微镜(SEM)分析表征水化试样的矿物种类和微观结构.研究结果表明,CH对C4A3S的水化有一定的抑制作用,温度的升高都有利于C4A3S的水化.在溶液中有CH存在的条件下,温度的提高使得C4A3S在水化早期形成AFm相;由于C SH2量充足,最终的水化产物为AFt相.(在本文缩写中,C=CaO,A=Al2O3,H=H2O,S=SO3,S=SiO2)     

Hydration of Tricalcium Silicate in the Presence of Lignosulfonates, Glucose, and Sodium Gluconate

Two commercial calcium lignosulfonates were separated into their main constituents, i.e. fractions high in salts of lignosulfonic acids and fractions high in sugars and sugar-acid salts. Hydration of C₃S in the presence of these fractions was studied. The fractions high in sugar acids caused a delay in hydration with a subsequent acceleration of hydration at additions of 0.1%. Fractions high in lignosulfonates caused little delay, whereas additions of 0.5% caused complete inhibition. Hydration was also studied in the presence of glucose and sodium gluconate. Adding 0.1 % glucose delayed hydration for about 11 days, whereas adding 0.1% sodium gluconate caused complete inhibition. The delay in hydration is discussed in terms of poisoning of nucleation sites.     

Kinetics of Slag Hydration in the Presence of Calcium Hydroxide

The reaction between ground granulated blast furnace slag (GGBFS) having an empirical formula of C_7.88S_7.39M₃A and calcium hydroxide (CH) was investigated. The kinetics of the reaction were explored. Thermogravimetric analysis was used to monitor the consumption of CH from which rate constants were determined. Based on Knudsen's kinetic model, activation energies of 14.5, 17.9, and 22.6 kJ/mol were determined for three different mass ratios of slag and CH reacted over a temperature range of 15° to 50°C and hydrated for a period of time from 0 to 32 days. A comparison of the kinetics of the slag/CH reaction was made with slag/portland cement hydration. The basic features of both appear similar.     

改性木质素磺酸钙对水泥早期水化的影响及机理探讨

采用双氧水对木钙进行氧化改性处理,测试了改性前后木钙的减水率和对水泥净浆流动性以及凝结时间的影响.采用XRD、IR和SEM对水化不同时间的水泥净浆进行了微观分析.结果表明,改性后的木钙具有更大的减水率,能增大净浆的流动度,并且缓凝效果比改性前弱.微观分析发现,木钙减水剂能促进钙矾石的结晶析出,但会阻碍C3 S和C2 S的水化,对水泥起到缓凝作用.改性后的木钙具有更强的吸附能力,对钙矾石在水泥颗粒表面的沉淀吸附有抑制作用,所以缓凝效果被削弱.     

Effect of Lime on Hydration of Pastes Containing Gypsum and Calcium Aluminates or Calcium Sulfoaluminate

Chemical reactions responsible for ettringite formation in the commercial expansive cements are reviewed. X-ray diffraction analyses of the hydrated expansive compounds showed that in the presence of Ca(OH)₂ and CaSO₄ the tricalcium aluminate hydrated very slowly and the monocalcium aluminate quickly, whereas the calcium sulfoaluminate hydrated at a uniform rate during the early hydration period. Scanning micrographs are presented which show that ettringite formed in the presence of Ca(OH)₂ is colloidal. It is proposed that colloidal ettringite can adsorb large quantities of water, thereby causing slump loss in fresh concrete and expansion in hardened concrete.     

氢氧化钙对硫铝酸盐水泥-粉煤灰复合胶凝材料的水化影响

通过凝结时间、抗压强度和电阻率等分析手段,研究了Ca(OH)2对硫铝酸盐水泥-粉煤灰复合胶凝材料水化过程的影响.结果表明,掺入Ca(OH)2明显缩短了硫铝酸盐水泥-粉煤灰复合胶凝材料的凝结时间;当Ca(OH)2掺量为0.5%时,初凝时间最短,1 d、28 d强度均明显提高;当Ca(OH)2的掺量为2%时,28 d强度相比空白样提高了61.9%;掺入Ca(OH)2后,硫铝酸盐水泥-粉煤灰复合胶凝材料的1 d电阻率减小,随着Ca(OH)2掺量增大,电阻率逐渐减小,电阻率变化率极大值提前,说明Ca(OH)2加快了该复合胶凝材料的早期水化进程.XRD分析表明,掺入Ca(OH)2后,水化1 d时钙矾石的生成量增多,消耗无水硫铝酸钙的量增多;水化28 d时钙矾石的生成量相对变化较小,但强度明显增大,粉煤灰对硫铝酸盐水泥强度的贡献较为明显.     

SO3含量对含三异丙醇胺水泥水化的影响

通过水泥胶砂强度试验、水化热(hydration heat)测量、硬化水泥浆体的热分析(TGA)、X射线衍射分析(XRD)及定量X射线衍射分析(QXRD)、微观形貌扫描电镜(BSE)观察,研究了不同SO3含量对含三异丙醇胺(triisopropanolamine,TIPA)硅酸盐水泥胶砂强度、水化进程和水泥浆体微观结构的影响.结果表明:SO3含量提高有助于提高含三异丙醇胺水泥的早期强度;水化热分析结果表明在含TIPA水泥中额外加入SO3后,水泥水化反应速率增大,水化3 d累积放热量增加,水化程度更大,且AFt-AFm的转化过程受到抑制;与含TIPA水泥水化相比,额外SO3掺量为0.6％时,硫酸盐促进整个硅酸盐相(C3S+C2S)的早期水化生成更多的Ca(OH)2(CH)参与C4AF的水化,在一定程度上促进其反应生成更多的AFt;外掺SO3生成的水泥石更致密.     

木质素磺酸钙对硬化水泥抗压强度的影响

木质素磺酸盐(简称木盐)具有较强缓凝和引气作用,可提高混凝土工作性,但过量使用会导致混凝土抗压强度急剧下降。该文从掺量、相对分子质量、亲水基、金属阳离子和糖分5个方面研究了木质素磺酸钙(简称木钙)对硬化水泥抗压强度的影响规律。结果表明,随木钙掺量增加,硬化水泥的各龄期抗压强度均下降,掺量w(木钙)=0.5%时,硬化水泥的28 d抗压强度仅为空白浆体的63.6%。其中相对分子质量为1万~5万的木钙超滤级分对硬化水泥强度的降低作用较小。木钙中糖分质量分数由12.5%降至2.8%时,硬化水泥的7 d抗压强度比可提高16%。通过氧化将木钙分子中的羟基转化为羧基,硬化水泥的3、7、28 d抗压强度比分别提高22.1%、34.7%和13.0%;通过磺甲基化将木钙的磺化度由1.36 mmol/g提高到2.48 mmol/g,硬化水泥的3、7、28 d抗压强度比分别提高36.2%、41.2%和17.9%。     

Magnetic Resonance In Situ Study of Tricalcium Aluminate Hydration in the Presence of Gypsum

The hydration of tricalcium aluminate, in the presence of gypsum, is investigated using in situ "real-time"¹H NMR spin–spin relaxation, X-ray diffraction, and scanning electron microscope experiments. Aside from rapid ettringite formation within the first 45 min, it is shown that a re-distribution of water within the first 2 h contributes significantly to the retardation of the rate of hydration. From the ¹H NMR component with T ₂ of approximately 20 μs, the continual disappearance of ettringite and the production of the layered monosulfate structure is monitored. In addition, the technique makes possible the monitoring of the change in the quantity of interlayer water in monosulfate, as well as the time scale associated with the decrease in the effective interlayer spacing, resulting from the ionic substitution of SO₄²⁻ for OH⁻. The ionic substitution within monosulfate starts after approximately 9 h. Although it has been believed that the time scale for this reaction is fast, we have shown that it can take days to reach completion.     

Influence of Tricalcium Aluminate on the Hydration of Calcium Silicates

The behavior of tricalcium silicate and related alites toward a lignosulfonate retarder (LSA) when tricalcium aluminate (C₃A) is added was studied by X-ray diffraction and by thermal analysis. In the absence of C₃A the hydration of the silicates is retarded indefinitely by LSA at the dosage used in this study. The retarding action of LSA was counteracted by the addition of 5% C₃A, apparently through preferential adsorption of the additive onto C₃A. Any calcium aluminate hydrates formed were detected by DTA. Their formation during the hydration of an alite of Jeffery's formulation confirmed that it does contain C₃A.     

外加剂及掺材对粉刷石膏性能的影响

通过实验研究了缓凝剂、掺材及保水剂对β半水型粉刷石膏性能的影响.缓凝剂对β半水膏的缓凝效果:柠檬酸>柠檬酸钠>酒石酸>酒石酸钾钠>蔗糖>磷酸盐.所加入的矿渣及水泥熟料可以提高粉刷石膏的强度.保水剂的保水率:MC>CMC>钠基膨润土.     

木质素磺酸钙与丙烯酰胺共聚反应的研究

文章测定了木质素磺酸钙的含量、溶解性、及其还原糖含量。对木质素磺酸钙与丙烯酰胺接枝共聚产物进行了红外光谱表征,对反应温度、引发剂浓度、反应时间共聚反应的产率是影前进行了考察。     

The Influence of Various Admixtures on the Calcium Carbonate Precipitation from a Calcium Nitrate and Monoethanolamine Solution

Calcium carbonate was precipitated by carbonation of calcium nitrate and monoethanolamine solution. The influence of various organic admixtures on the crystallization, crystal morphology, and polymorphism of calcium carbonate has been studied using different techniques. Our results show that sucrose and fructose present even at very high concentrations do not affect the duration or mechanism of the carbonation process at a higher degree, what is attributed to the specific quality of the ethanolamine process. At high concentration citric acid and ethylenediamine-tetrakis-N,N,N,N-(methylenephosphonic acid) had some effect on the process mechanism, phase composition, morphology and crystal aggregation of the calcium carbonate precipitated.     

复合矿物掺合料在水泥中水化机理的试验研究

通过比较复合矿物掺合料净浆与基准水泥净浆的SEM形貌差别来研究复合掺合料的水化机理。并采用差示扫描量热法(DSC)通过对其吸热峰的峰高和峰面积的分析进而对体系中水泥水化产物的成分进行了验证,从而揭示胶凝体系的水化反应机理。     

矿物掺合料和减水剂对桥梁混凝土水泥石水化热的影响

采用等温量热法研究高效减水剂对普通、中热水泥掺入不同品种及不同掺量的掺合料后水化热的耦合作用规律,分析了减水剂、矿物掺合料及两者双掺对水泥水化热及放热速率的影响.结果表明:矿物掺合料可减缓水泥水化放热的速率,推迟放热峰值的出现,粉煤灰的缓凝效果和削峰效果较矿渣要显著.外加剂对掺粉煤灰水泥的早期水化热有显著的降低作用.     

钙盐调凝剂对硅酸盐水泥水化性能的影响

本文研究了硫酸钙和氯化钙两种钙盐在不同的掺量下对硅酸盐水泥水化性能的影响,试验发现随着两种钙盐掺量的增大,水泥标准稠度值呈现先减小后增大的趋势,且氯化钙的流动度保持效果没有硫酸钙好,但是氯化钙对水泥强度的发展贡献更大,而掺硫酸钙随着掺量达到2‰后,28 d强度出现倒缩.     

纳米水化硅酸钙的制备及对水泥水化影响的研究进展

随着纳米技术的不断发展,纳米材料逐步开始应用于传统混凝土材料中,以提高混凝土的各项服役性能。纳米水化硅酸钙(纳米C-S-H)是一种新型的早强纳米复合材料,可通过晶核效应加快水泥早期水化速率,显著提高水泥基材料的早期力学性能,从而提高施工效率,满足特殊施工要求。本文系统总结了纳米C-S-H的制备方法,及纳米C-S-H对水泥基材料早期和长期性能的影响规律,探讨了其对于水泥水化过程和水化产物的影响机制,其中重点介绍了采用聚合物分散纳米颗粒制备的C-S-H/PCE(聚羧酸型减水剂,简称PCE)纳米复合材料。