高性能水泥硬化浆体微结构的交流阻抗研究

采用交流阻抗方法对掺有不同辅助性胶凝组分的高性能水泥硬化浆体的微结构进行了研究。从不同龄期时不同品种水泥硬化浆体的交流阻抗响应出发,对掺加辅助性胶凝材料的水泥硬化浆体的微结构进行了分析,并在试验测定的基础上讨论了硬化水泥浆体的结构和性能的关系。     

复合胶凝材料的水化硬化机理

近年来,有关复合胶凝材料的水化硬化机理的研究取得了较大进展。硅酸盐水泥在不同水化阶段的反应机理被广泛深入地探讨,建立了一些水泥基材料水化动力学和浆体微结构形成的预测模型。越来越多的矿物掺合料用于混凝土的制备。本文重点总结了硅酸盐水泥早龄期水化机理、矿物掺合料对硅酸盐水泥水化的影响以及复合胶凝材料反应过程模拟的研究进展。     

粉煤灰对水泥浆体早期水化和孔结构的影响

通过硬化水泥浆体力学性能、交流阻抗和孔结构等性能的测试,以及扫描电镜分析,研究了不同掺量的粉煤灰对硬化水泥浆体早期水化和孔结构的影响。结果表明：随着粉煤灰掺量的增加,水泥的凝结时间增加,抗压强度降低,熟料矿物的水化速率提高,但水泥-粉煤灰体系的水化速率降低,水泥浆体中孔溶液电阻和阻抗相应降低,硬化水泥浆体中大孔数量减少,微孔数量增加。     

硅酸盐水泥对钢渣活性激发的性能研究

试验研究了在硅酸盐水泥体系中通过碱性激发提高钢渣水化活性的方法.研究表明,钢渣掺入量<30%时,硅酸盐水泥对钢渣的活性激发效果最好;复掺矿渣对钢渣活性的激发效果优于粉煤灰,即使掺量为30%时,其早期强度也与相应龄期普通硅酸盐水泥强度持平,而后期强度逐渐超过纯水泥的强度;在普通硅酸盐水泥体系中掺入钢渣可以改善其硬化浆体的性能.     

聚合氯化铝提升矿渣硅酸盐水泥性能及微观机理研究

为了探明聚合氯化铝对矿渣硅酸盐水泥性能影响的规律,同时揭示聚合氯化铝对矿渣硅酸盐水泥性能影响的机理,本研究运用XRD、TG-DSC分析及29 Si NMR技术对水泥水化过程及硬化后力学性能、体积稳定性、浆体微结构进行分析.结果表明:聚合氯化铝掺入矿渣硅酸盐水泥将增加其标准稠度用水量,减小流动度,减小砂浆收缩率;聚合氯化铝可以促进Ca(OH)2的分解,促进C-A-S-H凝胶的形成,促进矿渣的水化,提升硬化水泥浆体的致密度,进而提高强度.     

单掺粉煤灰和矿渣粉对磷酸镁水泥水化进程及强度的影响

以石英粉作为参照,通过监测水化热、悬浮液pH值及凝结时间变化研究了粉煤灰和矿渣粉(GGBS)对磷酸镁水泥水化进程的影响,并测定了砂浆的抗压强度及硬化浆体的孔结构。结果表明,粉煤灰和矿渣粉对磷酸镁水泥的水化具有较强的延缓作用,且矿渣粉的缓凝效果更强。粉煤灰和矿渣粉能够改善硬化浆体的孔结构,其中矿渣粉的改善效果更为显著。在15%(质量分数)掺量下,单掺粉煤灰和矿渣粉的磷酸镁水泥砂浆2 h抗压强度都略高于纯磷酸镁水泥砂浆。掺粉煤灰的磷酸镁水泥砂浆后期抗压强度等于或略高于纯磷酸镁砂浆,掺矿渣粉的磷酸镁水泥砂浆后期抗压强度显著高于纯磷酸镁水泥砂浆。     

粉煤灰对水泥水化与强度的影响

采用测定化学结合水含量的方法反映水泥浆体的水化程度,并通过对水泥硬化浆体强度的分析,评价粉煤灰对水泥水化和力学性能的影响。结果表明,粉煤灰加速了水泥熟料的水化反应,却减缓了水泥-粉煤灰体系的水化进程。掺加粉煤灰虽然降低了水泥浆体的早期强度,但对水泥浆体后期强度的发展有利。     

高温养护下粉煤灰效应机理研究

大体积混凝土施工过程中,为降低水化热而采用大量的粉煤灰替代水泥,故对高掺量粉煤灰水泥的水化硬化机理进行深入系统的研究具有重要的意义.以大掺量粉煤灰胶凝材料硬化浆体为研究对象,结合XRD、FTIR、NMR等测试分析,研究高养护制度下粉煤灰掺量对其水化相C-S-H凝胶硅氧四面体聚合程度的影响规律.结果表明:高温养护的硬化浆体,其水化相C-S-H凝胶硅氧四面体聚合程度和Al原子取代Si原子的程度,在各个养护龄期始终高于常温养护的硬化浆体.     

高温养护条件下现代混凝土水化、硬化及微结构形成机理研究进展

高温养护会使水泥基材料水化过程和内部微结构发生显著变化,但由于现代混凝土组分复杂,其高温养护条件下早期水化、硬化及微结构形成机理仍存在众多疑惑.本文首先对纯水泥浆体在不同养护温度条件下的水化速率、水化程度、水化产物、孔结构、强度发展规律进行了回顾;然后针对现代混凝土掺加多种矿物掺合料的特点,分别对粉煤灰、矿渣、硅灰复合水泥基材料在高温条件下的水化机理进行归纳.     

碱对硅酸盐水泥水化硬化性能的影响

系统地研究了以碱含量不同、存在形式各异的熟料所制水泥的水化液相成分、水化程度、水化产物和硬化浆体微观结构,揭示了碱对硅酸盐水泥水化硬化性能影响的机理。水泥水化时,熟料中的碱迅速溶入水化液相,使液相中[OH-]升高、[Ca~(2+)]降低。由此促进水泥早期水化,并阻滞了后期水化的发展。所以,高碱水泥凝结快,1～3d硬化浆体的孔隙少、强度高;7～28d硬化浆体的孔隙多、强度低。     

生物质灰对水泥硬化浆体抗压强度影响的试验研究

对比研究了生物质灰与普通粉煤灰在粒度分布、颗粒形态、化学组成、活性指数等方面的不同,并开展了不同掺量生物质灰对水泥硬化浆体抗压强度的影响研究.结果表明:生物质灰颗粒形状不规则、平均粒径及粒径分布范围较大,具有特有的细长纤维状颗粒,且其活性组分Al2O3不足普通粉煤灰的三分之一;生物质灰的火山灰活性小于普通粉煤灰;相同掺量下,生物质灰-水泥复合胶砂各龄期的抗压强度均小于普通粉煤灰-水泥复合胶砂,生物质灰掺量越大,复合胶砂的强度相比纯水泥组下降程度越大;与普通粉煤灰相比,掺加生物质灰的硬化水泥浆体微观结构更为疏松多孔,特别是其特有的细长纤维状颗粒的存在.     

钢渣对硬化水泥浆体结构形成的影响研究

研究了钢渣对水泥强度及体积膨胀率的影响,采用SEM和EDXA分析了水化产物的形貌和微区化学成分,并用XRD对水化产物的矿物组成进行了分析研究。研究结果表明,钢渣的掺入会降低水泥净浆的早期抗压强度,但随钢渣水化的进行,掺钢渣的水泥浆体7d以后的强度增长较快,至120d时净浆抗压强度已与纯硅酸盐水泥相近。掺钢渣的水泥的体积膨胀率比纯硅酸盐水泥的体积膨胀率大,钢渣水泥的体积膨胀率主要取决于钢渣中的fCaO含量。掺钢渣水泥的主要水化产物组成和形貌与纯硅酸盐水泥无明显差别,所不同的是C-S-H凝胶中有较多的铁相。掺钢渣水泥的水化产物主要有C2SH(C)、AFt和Ca(OH)2。     

The fluidity of fly ash-cement paste containing naphthalene sulfonate superplasticizer

The zeta potential measurement indicated that the surface potential of fly ash was different from ordinary Portland cement (OPC) in both sign and value. Hence, the Derjaguin-Landau-Verway-Overbeek (DLVO) theory for dispersion-flocculation of heterogeneous particles with different surface potentials was applied to explain the influence of fly ash on the rheology of cement paste containing naphthalene sulfonate superplasticizer. For the fly ash-cement paste without superplasticizer, the sign of zeta potential of fly ash was different from OPC. Thus, the extent of the potential energy barrier between particles was small or even showed negative value, and the change in the rheology of the fly ash-cement paste was mainly dependent on the bulk solid volume of fly ash, which was related to available free water for fluidizing paste. For the fly ash-cement paste with naphthalene sulfonate superplasticizer, fly ash and cement had the same sign and dispersed well due to higher potential barrier. The extent of potential energy barrier depended on the absolute value of surface potential, which was represented by a function of the amount of adsorbed superplasticizer. The bulk solid volume of fly ash also affected the change in flow ability, but the effect of potential energy barrier between particles was superior to that of the bulk solid volume of fly ash.     

The influence of water removal techniques on the composition and microstructure of hardened cement pastes

The removal of water from hardened cement paste for analysis or to arrest ongoing hydration has been reported to affect the composition of hydrated phases and microstructure. The effect that arresting the hydration of hardened cement paste by replacing the pore water with acetone before drying, and by removing the water by freeze, vacuum and oven drying has on the hardened cement paste has been investigated. Two pastes were studied, a cemented iron hydroxide floc where a high proportion of ordinary Portland cement (OPC) had been replaced by pulverised fuel ash, and a pure hydrated OPC. The results showed that none of the water removal techniques caused any major deterioration in the composition and microstructure of the hardened cement pastes studied, but the pores appeared better preserved after arresting hydration using acetone quenching. Freeze drying appeared to cause more cracking of the microstructure than the other water removal techniques.     

A new way to increase the long-term bond strength of new-to-old concrete by the use of fly ash

The short-term and long-term bond strengths of new-to-old concrete were experimentally investigated with an emphasis on the influence of new concretes and binders. These new concretes included ordinary Portland cement concrete, expansive concrete and high-volume fly ash concrete, while the binders included pure cement paste (C-binder), expansive binder (E-binder) and fly ash mortar (F-binder). The results showed that the short-term bond strength of all specimens with fly ash concrete was lower than that with ordinary Portland cement concrete, which in turn was lower than that with expansive concrete. The bond strength of the specimens with F-binder was the lowest at the age of 7 days. However, the long-term bond strength of all specimens with added fly ash was the highest and strength losses were observed in the specimens repaired with expansive concrete or E-binder at the age of 3 years. The microstructure of the transition zone with F-binder was also studied by using both scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) at the ages of 28 days and 1 year, respectively.     

粉煤灰-水泥水化的核磁共振定量分析

利用高分辨固体核磁共振仪结合去卷积技术,定量分析了粉煤灰水泥浆体中水泥和粉煤灰的水化程度以及C-S-H凝胶中硅氧-铝氧链平均长度,同时研究了粉煤灰火山灰反应对C-S-H结构的影响。结果表明:水化3 d时,系统中约47%的水泥和14%的粉煤灰参与了水化反应,C-S-H平均链长为3.2;水化120d时,水泥和粉煤灰的水化程度分别为89%和33%,C-S-H平均链长约为3.8,远大于纯水泥浆体中C-S-H的平均链长(为2.7)。水化3 d时粉煤灰玻璃相结构中的Si—O—Si,Si—O—和Al—Al共价键断裂,形成了单体硅酸根和单体铝酸根,这些单体结构桥连体系中的二聚体单元进而提高了C-S-H平均链长。粉煤灰掺入并不会因为C-S-H聚合度提高以及ACL增加就能促进粉煤灰水泥浆体强度。     

The fluidity of fly ash-cement paste with superplasticizer

The influence of various fly ashes on the fluidity of fly ash-cement paste with superplasticizer was investigated in connection with the amounts of superplasticizer adsorbed on fly ashes, the change of ζ-potential and the physical properties of fly ashes. Fly ash indicates a high negative ζ-potential, and by adding superplasticizer, an even higher negative ζ-potential is indicated. However, the fluidity of fly ash paste is not improved by addition of superplasticizer as much as in the case of cement. The fluidity of fly ash-cement paste mixed with superplasticizer is influenced by the kinds of fly ashes. The bulk specific gravity of fly ash may be an index for judging the influence of fly ash on the fluidity of fly ash-cement paste.     

聚苯乙烯微球改性水泥耐Na2CO3腐蚀的研究

硅酸盐水泥硬化成水泥石之后,在碳酸盐环境下,水泥中的组成成分氢氧化钙会与碳酸盐发生碳化作用从而引起其结构发生破坏,为改善水泥的抗Na2CO3腐蚀性能,在水泥中加入聚苯乙烯（PS）微球,研究水泥石腐蚀前后质量变化和PS微球与水泥作用的机理,以及采用电子扫描显微镜（SEM）分析改性水泥的微观结构形态。     

水泥熟料-粉煤灰体系中粉煤灰活性的复合激发研究

通过水泥砂浆强度试验方法研究了水泥熟料-粉煤灰体系中添加CaO、Na2SO4、明矾等化学物质对其中的粉煤灰活性的激发效果,同时借助于XRD和SEM分析了水泥硬化浆体的组成和微观结构.研究结果表明:CaO-Na2SO4-明矾复合添加能够很好地激发粉煤灰活性,使粉煤灰水泥早期强度降低程度减小.采用42.5等级硅酸盐水泥熟料,粉煤灰掺量高达50％时水泥强度仍然能够达到42.5等级指标.XRD分析表明,CaO-NaSO4-明矾复合激发剂的加入引起了水泥硬化体样品中石英和Ca(OH)2衍射峰的降低,说明它们在一定程度上促进了水泥水化放出的Ca(OH)2与粉煤灰中酸性氧化物的反应,从而加剧粉煤灰潜在活性的快速释放.水泥硬化体样品的SEM照片显示,CaO-Na2 SO4-明矾的加入,使粉煤灰球体表面腐蚀明显,硬化体结构更加致密化.