熟料氧化镁含量对水泥浆水化与收缩的影响

探讨了熟料中MgO含量对水泥收缩和水化的影响。通过X射线衍射和热重分析分别对不同氧化镁含量的熟料A矿晶型、方镁石相对含量和水泥水化产物进行了表征,并测试了3种养护条件下水泥的收缩特性。结果表明:熟料中的方镁石含量随着MgO含量增加而增加,方镁石早期水化速率较快,提高养护温度可以加速方镁石早期水化,方镁石水化膨胀能够降低水泥在干燥环境中的收缩,增加水浴环境中的膨胀。Mg(OH)_2以无定型、六方片状等形态存在于水化后的水泥中,且富集于Ca(OH)_2附近,并与Ca(OH)_2共同碳化生成CaMg(CO_3)_2等晶体。     

掺氧化镁水泥的膨胀规律及其影响因素

掺煅烧氧化镁的水泥具有延迟膨胀的性能,水泥浆体在50℃水化时,水化3天到15天的膨胀速率最大,这正是大坝混凝土温降明显阶段,故可补偿混凝土温降引起的体积收缩,简化温控措施。氧化镁水泥的膨胀性能主要决定于氧化镁膨胀剂的膨胀性能。试验表明,调整氧化镁的煅烧制度,可以改变其膨胀速率、膨胀量及膨胀的终止期。     

答读者问

1.问:水泥用压蒸法测定安定性不合格,而用沸煮法测定安定性合格,此水泥是否为合格水泥。如认为是不合格水泥,但水泥软练胶砂检验法只规定沸煮法是否欠妥? 答:影响水泥安定性的主要因素有三:①熟料中游离氧化钙(f-CaO);②熟料中氧化镁(MgO);③水泥中三氧化硫(SO_3)。三者中任何一项含量过高均可导致水泥安定性不合格。造成安定性不合格的原因是由于它们水化时的体积膨胀。虽然它们水化时体积均可膨胀,但     

熟料细度对硫铝酸盐水泥胶凝膨胀性能的影响

采用XRD和TG/DTG等试验方法,对两种不同细度熟料配制成的硫铝酸盐水泥进行研究,通过Rietveld分析法对水化产物进行定量分析,探讨其膨胀性能与水泥粒径及水化产物的关系。结果表明,减小硫铝酸盐水泥熟料平均粒径对提高抗压强度贡献很大,也可促进硫铝酸盐水泥水化,但并不能显著增加试件膨胀率和膨胀持续时间,二水石膏掺量对于硫铝酸盐水泥膨胀性能的影响要大于熟料粒径的影响。     

水泥熟料煅烧和水泥水化受氧化镁的影响分析

随着社会的快速发展,水泥熟料煅烧和水泥水化受氧化镁的影响十分显著。为了能够让水泥熟料煅烧的效率得到相应的提升,需要对其整体的性质进行全面的分析。本文主要针对水泥熟料煅烧和水泥水化受氧化镁的影响进行分析,并提出了相应的优化措施。     

氧化镁制备方法、活性与水化测定方法综述

氧化镁在水泥、混凝土中的应用自20世纪70年代以来越来越受到重视.氧化镁自身的性质决定了它的水化速率、膨胀速率、膨胀量等因素,这些因素与混凝土性能有关.本文对MgO的制备、活性检测、水化动力学计算方法及其定量热分析进行阐述,用以说明水泥、混凝土中的氧化镁的性能及影响因素.     

氧化镁对水泥熟料煅烧和水泥水化的影响

随着现代水泥行业的快速发展,对水泥生产各工序质量也提出更高的要求。然而现行水泥熟料煅烧过程中,其中存在的氧化物会带来明显的影响,以其中氧化镁影响最为突出,除影响水泥熟料煅烧外,也会对水泥水化产生一定作用。本文将对水泥水化、水泥熟料煅烧中氧化镁的影响进行探析,并提出水泥熟料生产中的相关建议。     

高镁熟料的矿物组成对水泥性能的影响

研究了高镁熟料矿物组成对水泥的膨胀、强度、安定性能的影响.试验研究表明,适当的熟料率值可改善高镁熟料的强度;在利用MgO作膨胀源时,熟料中MgO水化缓慢,90d后才有明显的膨胀.     

MgO对水泥性能的影响研究综述

全面回顾了氧化镁在水泥水化反应中的作用,包括抗压强度,体积稳定性,其他水泥性能等,指出了方镁石形成的条件及其水化动力学机理,讨论了方镁石在水泥混凝土使用中的危害和积极作用,最后得出氧化镁作为硅酸盐水泥熟料中的杂质在研究、使用、标准、新型水泥开发、水泥工业可持续发展与节能减排以及水利水电大坝工程最正确使用历史带给我们的启示等方面的结论和思考。     

吉林白山大坝混凝土自生体积膨胀机理的研究

本文对用于制作白山大坝混凝土的抚顺水泥厂水泥的膨胀性能及机理进行了研究。通过实验说明了抚顺水泥厂水泥具有延迟性微膨胀性能。其原因是由于水泥熟料中含有较多的方镁石,它在50℃养护条件下,一个月内就能水化而使水泥硬化浆体产生体积膨胀。     

Accuracy and precision of phase analysis in portland cement by Bogue,microscopic and X-ray diffraction methods

From the results of an inter-laboratory study the magnitude of the between and within laboratory errors were determined for the analysis of portland cement and clinker by the Bogue, microscopic and X-ray diffraction methods. Neither the Bogue nor X-ray diffraction methods gave accurate analyses of the cement. The Bogue method suffers from systematic errors and it appears that the incorporation of MgO into the alite phase is the major cause of error in the Bogue analysis. X-ray diffraction analyses were, with one exception inaccurate. Microscopic analyses could only be performed on cement clinker which was subject to a large sampling error.It is concluded that, at the moment, the Bogue method is the most suitable for specifying the composition of portland cement.     

氧化镁延迟性膨胀水泥

大体积混凝土常因水泥水化过程的放热而使体内温度升高,在之后的降温阶段混凝土收缩而导致开裂。为了防止这种收缩,研制了延迟性膨胀水泥。其一是生产高镁水泥熟料,其二是在水泥粉磨时掺入煅烧的MgO。试验证明,在适当条件下可制得在7—30天内膨胀的水泥,但这种膨胀在3个月之后即趋于稳定,这就有可能补偿降温引起的收缩,同时又能保证制品的安定性。     

On the role of free calcium oxide in expansive cements

Results of research, tending to elucidate the effect of free CaO content in portland cement clinker upon the expansion of specimens of expansive cements, prepared in semi-commercial scale by intergrinding of portland cement clinker, C₄A₃$\text{S}$-phase containing special clinker and gypsum, by means of examination of liquid phase composition and porosity of mortars, have been presented. Special clinker was obtained by burning a mix of limestone, fly ash with high Al₂O₃ content and gypsum. Obtained results confirm the advantageous effect of free lime upon the hydration process and properties of expansive cements. The concentration of CaO in the liquid phase seems to influence rather the rate of ettringite formation than the size of its crystals.     

水泥浆体—集料界面的结构特性与砂浆抗蚀性的关系

本文从界面出发对以石英砂、硅酸盐水泥熟料和高铝水泥熟料作集料的砂浆的抗蚀性进行了对比实验。结果表明两种水泥熟料砂浆均具有比石英砂浆好得多的抗硫酸盐腐蚀和硫酸腐蚀性能。从扫描电镜和能谱及砂浆的氯离子扩散系数的测定结果对上述砂浆的抗蚀性差异的原因、界面结构特性在砂浆腐蚀过程中的作用机理进行了详细的论述。据此给出了界面的结构特性与砂浆的抗蚀性之间的明确关系。     

高胶凝性水泥熟料

总结了以硅酸三钙(C3S)为主要矿物的熟料烧成研究成果和最新研究进展．C3S是硅酸盐系统的水泥熟料中含量最高、胶凝性能最好的矿物。在熟料烧成过程中。C3S是形成温度最高的矿物。因此。C3S的充分形成实际上也就代表了熟料的烧成．提高C3S含量是提高水泥熟料胶凝性能有效途径．采用离子掺杂的方法可以降低熟料烧成过程中的游离氧化钙,使C3S质量分数(下同)在70%以上的硅酸盐水泥熟料在正常温度下烧成。如：在生料中掺加氟硫复合矿化剂,适量磷渣或钢渣等含磷杂质及其与氟离子复合。或者掺入1%CuO,可明显改善熟料的易烧性。但是磷的掺加数量应有一定限制。在硅酸盐水泥熟料中引入适量硫铝酸盐矿物也可以有效提高水泥的胶凝性能。但是应该解决烧成温度范围偏窄的问题。     

Diffusion in Portland Cement Clinker

Experimental data on the interfacial reaction between portland cement clinker and molten coal ash at 1400° to 1500°C are consistent with a mechanism involving diffusion in the melt as the rate-controlling step. The formation and growth of well-defined zones between the reactants are characteristic of the reaction. Equations were solved for diffusion with two moving interfaces. On the basis of these equations and data from the lime-alumina-silica phase equilibrium diagram, the diffusion coefficient for CaO in the interstitial melt in the clinker is about 5±10^-6 cm²/s at 1500°. The results imply that the clinkering reaction in the burning of portland cement clinker is also controlled by diffusion in the melt.     

页岩配料在立筒预热器窖上的应用及其改进

用页岩替代粘土配料可生产出早强型的硅酸盐水泥熟料。用其配制矿渣水泥,凝结时间快,早、后期强度均高。用页岩－砂岩配料,可改变页岩单独配料熟料２８ｄ抗压强度低的问题。对燃烧工艺方面的改进,可使页岩配料引起的窑尾系统结堵问题得到缓解。     

Understanding expansion in calcium sulfoaluminate–belite cements

Calcium sulfoaluminate–belite (CSAB) cements are promoted as sustainable alternatives to portland cement because of their lower energy and CO₂ emissions during production and comparable performance. However, the formation of ettringite, the main hydration product in CSAB cements, can be expansive, sometimes resulting in cracking. The factors controlling expansive behavior in CSAB cements have not been completely elucidated. In this study, three CSAB cements synthesized from reagent-grade chemicals with varied phase compositions were examined for dimensional stability in water and sulfate solutions. The interdependent effects of C₄A₃? (Ye'elimite) content, calcium sulfate content, water-to-cement ratio, and particle fineness on CSAB cement expansion were evaluated. The results show that the expansive behavior can be controlled by altering chemical and physical factors in CSAB clinker, cement, and paste.     

Effect of prolonged heating at elevated temperatures on the phase composition and textures of portland cement clinker

Two kinds of portland cement clinker with widely different MgO and SO₃ content were reheated for a long time at elevated temperature. With the clinker rich in MgO and SO₃, alite increased while belite decreased in quantity after reheating. The alite crystals, overgrown with new precipitates, gave zonal structures. Thin platy hexagonal crystals were occasionally nucleated and grown separately in the bulk liquid. High degree of supercooling produced dismembered dendritic crystals of belite. The C/S ratio of the interstitial phase decreased with reheating. The above changes occur in association with the process in which the interstitial liquid, initially variable in basicity, is transformed to the uniform and most acidic one. This process is controlled by the counterdiffusion of CaO and SiO₂, the rate of which is such that, in normal clinker processing, the clinkering reaction terminates before reaching this stage. Rise in firing temperature increases the concentration of SiO₂ in the interstitial liquid and leads to higher solid C₃S/C₂S ratio in clinker. The presence of MgO and SO₃ in abundance lowers the viscosity of the liquid and hence accelerates the changes. No appreciable change could be recognized for the clinker low in MgO and SO₃ content.     

Utilization of phosphogypsum in portland cement industry

Disadvantages associated with the presence of impurities in phosphogypsum can be overcome when, instead of adding it directly to portland cement as a set-retarding additive, it is added to the raw mix before clinkering. Due to the mineralizing action of phosphogypsum, the clinker can be made at a substantially reduced temperature. Cements made by grinding a clinker containing 2 percent SO₃ derived from phosphogypsum did not need any further retardation and possessed high early strength characteristics.