共查询到20条相似文献,搜索用时 15 毫秒
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《Cement and Concrete Research》1987,17(5):814-820
It does not seem possible to obtain an accurate correlation between the strength development and the rate of calcium sulfate dihydrate formation in anhydrite binders. Investigations on the hydration and hardening of anhydrite samples from different origins allows us to point out that the representation of strength versus the calcium sulfate dihydrate content of the hardened material leads to a diagramm with very scattered experimental points. That is due to a large variation in both the porosity and the crystal habit of dihydrate crystal which are directly connected to the nucleation rate during the hydration reaction. This observation is certainly not limited to anhydrite binders. 相似文献
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研究了同等P2O5掺量下的磷石膏、硬石膏和二水石膏对超硫酸盐水泥(SSC)水化机理的影响,其中硬石膏与二水石膏中的P2O5以可溶性分析纯P2O5形式掺入.测试了3个系列SSC净浆试件各龄期抗压强度和孔溶液pH值,对比了其早期水化放热过程的差异,采用XRD、SEM分析了其水化产物相及微观形貌.结果表明:外掺分析纯P2O5的硬石膏基和二水石膏基SSC各龄期抗压强度与孔溶液pH值接近;与磷石膏基SSC相比,外掺分析纯P2O5的硬石膏与二水石膏降低了SSC各龄期孔溶液pH值,对SSC早期强度发展有所减缓,明显促进了后期强度的发展;早期水化放热分析结果显示,外掺分析纯P2O5的硬石膏与二水石膏加快了SSC第二放热峰的出现,缩短了凝结时间;XRD和SEM结果表明,外掺分析纯P2O5的硬石膏与二水石膏对SSC的激发效果比磷石膏更好,用其制备的SSC浆体后期形成了更多更密实的水化硅酸钙与钙矾石. 相似文献
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Sebastian Seufert C. Hesse F. Goetz-Neunhoeffer J. Neubauer 《Cement and Concrete Research》2009,39(10):936-941
Technical OPC contains mixed sulfate carriers in varying amounts. Gypsum and anhydrite are added to the clinker during the milling process where the gypsum dehydrates partially to bassanite and anhydrite. Due to different hydration kinetics of these phases, it is crucial to be able to characterize the composition of sulfate in a cement system to reach an optimal and reproducible cement hydration. In the current paper different calcium sulfate compositions are investigated by XRD methods in order to identify phase content. Special focus is put on the discrimination of the hemihydrate (bassanite) and anhydrite III as well as on transformation processes of anhydrite III through ambient humidity. 相似文献
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Christopher R. Wilding Brynmor Mile Arthur T. Vincent 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1984,34(2):80-90
Studies of the effects of the concentration of two additives K2SO4 and Na2SO4 on the hydration of synthetic anhydrite are presented which show the occurrence of broad optimisation maxima. By employing a novel in-situ precipitation technique, substantial increases in the initial rate of hydration have been achieved. 相似文献
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G. Tzouvalas 《Cement and Concrete Research》2004,34(11):2113-2118
The hydration process of cement pastes is of great importance to the physicomechanical properties of the hardened material. Thus, substances that regulate the setting of cement, such as natural anhydrite, have attracted significant scientific interest during the past years. This paper briefly describes the results of utilization of natural anhydrite in cement pastes of CEM-I and CEM-II types. The aim of the study has been to inquire the extent of natural gypsum replacement by natural anhydrite. The result of the hydration process has been expressed by the setting time and the compressive strength development, with respect to the SO3−2 content of each mixture. The experimental data conclude that natural anhydrite can be a very efficient retarder of the setting of cement, with no significant change in the physicomechanical properties of the hardened pastes. 相似文献
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In this paper, the influence of curing temperature was studied for supersulfated cements made with two slags having different chemical compositions. Supersulfated cements (SSC) made with low-alumina slag developed lower porosity, higher compressive strength and degree of hydration at higher temperatures. SSC made with high-alumina slag resulted in higher strengths and presented a more complex mechanism of hydration that was strongly influenced by the solubility of anhydrite. 相似文献
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Xiaoping Wang Yuxia Pang Hongming Lou Yonghong Deng Xueqing Qiu 《Cement and Concrete Research》2012,42(11):1549-1554
As a plasticizer and retarder, calcium lignosulfonate (CL) frequently leads to quick set of Portland cement containing anhydrite. For exploring the cause of this problem, the hydration characteristics of the tricalcium aluminate–anhydrite system in the saturated calcium hydroxide solution with and without CL were researched from two aspects: the compositions of liquid phases and the formations of hydration products. Results show that the CL can promote the formation of ettringite, which induces a significant decrease in sulfate ion concentration at the initial time of hydration. The size of ettringite crystals becomes large in the presence of CL, which seems to be related to a decrease in calcium sulfate saturation ratio. It can be deduced that the quick set in the presence of CL is mainly caused by the accelerated reaction between the tricalcium aluminate and the anhydrite at the initial time of hydration. 相似文献
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Na2SO4对硬石膏水化进程及其水化产物形貌的影响 总被引:1,自引:0,他引:1
通过硬石膏水化率、水化温度、液相离子浓度测定和硬化体显微结构分析,研究了Na2SO4对硬石膏水化进程和二水石膏晶体形貌的影响,从二水石膏晶体生长角度探讨了Na2SO4的作用机理.结果表明:Na2SO4可促进硬石膏溶解,使硬石膏水化率提高,水化热集中,水化潜伏期缩短,水化进程加快;Na2SO4还可提高二水石膏的析晶过饱和度,使二水石膏临界晶核半径减少,晶体成核与生长速率加快,晶体尺寸减小:Na2SO4形成富SO2-4液相,有利于二水石膏晶体结构基元形成,高SO2-4浓度改变了晶面在不同轴向生长的相对速率,使c轴方向的生长具有优势,从而改变了二水石膏晶体生长习性,使二水石膏晶体由板状变为针柱状. 相似文献
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以垃圾焚烧(MSWI)飞灰为主要原料,在实验室成功烧制了硫铝酸钙(CSA)水泥熟料,继而着重研究了不同种类和不同掺量的石膏对CSA水泥的抗压强度、水化性能、标准稠度用水量和凝结时间的影响;研究了细度对CSA水泥性能的影响。结果表明:无水石膏和二水石膏均促进C4A3S^-水化,提高CSA水泥的早期强度;无水石膏的最佳掺量是5%,二水石膏可根据实际情况进行调整;掺加无水石膏的CSA水泥其标准稠度用水量较对照水泥C—II低,比对照水泥C—I有所增加;掺加5%无水石膏后水泥的凝结时间与对照水泥C-II接近,当掺量增至10%后出现急凝。本试验中,CSA水泥比表面积在288—580m^2/kg范围时均表现出良好的力学性能。 相似文献
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基于热力学模拟,研究了无水硫铝酸钙-石膏-石灰石三元体系的水化产物组成和含量变化规律。模拟结果表明,在无水硫铝酸钙-石膏-石灰石三元体系中,根据石膏、石灰石的掺量和液相的pH值变化,可将水化产物相和pH值的演变过程分为5个区域(Ⅰ~Ⅴ区)。Ⅱ区与Ⅲ、Ⅳ区的边界为石灰石完全反应的边界,Ⅳ区与Ⅴ区的边界为石膏完全反应的边界。基于模拟结果建立了无水硫铝酸钙-石膏-石灰石三元体系的水化模型,并结合实验数据进行了验证,该研究结果为无水硫铝酸钙-石膏-石灰石三元体系的水化机理研究以及硫铝酸盐水泥的配料设计提供了重要理论依据。 相似文献
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硫硅酸钙-硫铝酸钙水泥是一种新型低碳水泥,硫硅酸钙矿物的水化活性对水泥性能具有积极作用。本文利用离子掺杂制备了硫硅酸钙-硫铝酸钙水泥,研究了硫硅酸钙、硫铝酸钙矿物以及后掺石膏的配比优化。结果表明,硫硅酸钙-硫铝酸钙水泥熟料的实际矿物组成与设计含量较为一致。硫铝酸钙含量的增加有利于提高水泥的早期强度,其适宜含量范围为30%~40%(质量分数);水泥的强度随着硫硅酸钙含量的增加而提高,当其设计含量增加至48%(质量分数)时,水泥强度降低,该矿物的适宜含量范围为40%~55%(质量分数),其优化含量根据硫铝酸钙的含量而有所不同。石膏的添加有利于硫硅酸钙-硫铝酸钙水泥强度的增长,与天然石膏相比,硬石膏更能促进水泥强度的发展;水泥的后掺石膏优选硬石膏,其优化掺量为8%(质量分数),28 d强度达到76 MPa。硬石膏掺量的增加促进了钙矾石的形成,但过高掺量的硬石膏会抑制硫硅酸钙的水化。 相似文献
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The hydration of an anhydrite of gypsum (CaSO4.II) in a ball mill was studied as a function of time and temperature. The amount of gypsum formed at different intervals of time was determined by weight loss method and powder X-ray diffraction technique. Specific surface area at different time intervals was determined by LASER granulometric method. The results showed that the maximum rate of formation of gypsum was at a longer time than the time for the development of maximum specific surface area. In the presence of activators, the time for maximum rate of gypsum formation and maximum specific surface area shifted towards lower hydration time. Morphological changes during the course of hydration have been studied by the scanning electron microscopic (SEM) technique. A mechanism of hydration has been proposed. 相似文献
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The hydration and transformation of Ca-rich kerogenous oil-shale (kukersite) ashes, formed in circulating fluidized bed (CFB) combustion furnaces, were investigated during a one-year experiment. During the first stages the process was characterized by rapid hydration of free lime hydration into portlandite and dissolution of anhydrite and periclase, whereas the formation of (crystalline) ettringite was somewhat delayed. During the final process, ettringite and portlandite that are unstable under atmospheric conditions were replaced by stable calcite and Ca-sulphate. 相似文献
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The phase formation, heat of hydration and dilatation in a blended cement consisting of 50 wt.% calcium aluminate cement, 25 wt.% Portland cement and 25 wt.% calcium sulfate were studied (w/c=1). The calcium sulfate was β-hemihydrate, anhydrite and mixes of the two. Kinetic expressions describing the ettringite formation in the pastes with the pure calcium sulfates were found. Hydration reactions were suggested and the phase development was compared to the hydration heat by mass and heat balances. When the calcium sulfate was 75 and 50 wt.% β-hemihydrate, the systems behaved as a linear combination of the 100 and 0 wt.% blends. At 25 wt.%, the hydration kinetics differed from the other blends. With only β-hemihydrate, the last 50% of ettringite formation was accompanied by expansion, mainly caused by interaction of crystals growing radially on cement grains. In the paste with only anhydrite, ettringite crystals grew in solution and produced no expansion. 相似文献
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粉煤灰改性无水石膏胶结材的研究 总被引:11,自引:2,他引:11
以脱硫石膏与粉煤灰两种工业废渣为主要原料制得的粉煤灰无水石膏胶结材(以下简称FAB),具有比石膏制品高的强度与耐水性。本文对该胶结材的配制原理与方法,养护方式及材料性能进行了研究。初步分析了该胶结材水化硬化特点,结构及其与性能的关系。 相似文献
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N. B. Singh 《Journal of the American Ceramic Society》2005,88(1):196-201
The effect of K2 SO4 activator on the hydration of chemical anhydrite obtained from burned FGD-gypsum has been studied by different experimental techniques. Results obtained show that the degree of hydration increases when the K2 SO4 concentrations increase from 0.5 to 3.3 wt%. Their heat evolution rate and maximum value also increase with the increase of K2 SO4 concentration. The highest values were obtained when the hydration degree was about 50%. Also a correlation between the hydration degree and the total heat evolved was obtained. The X-ray and SEM/EDX studies have shown that K2 SO4 is adsorbed at the surface of CaSO4 even within 5 min of hydration and a syngenite—a double salt K2 SO4 ·CaSO4 ·H2 O is formed (even in the presence of 1.0 wt% K2 SO4 ). Also, important changes in the morphology of the dihydrate crystal are detected. Finally, in the presence of 1.0 wt% K2 SO4 (water/anhydrite ( W / A ) ratio=0.33), it was found that the resonance frequency, modulus of elasticity, compressive strength, and tensile strength increase with the degree of hydration whereas the total porosity decreases. 相似文献