硅钙渣制备碱激发胶凝材料的机理研究

以水玻璃为激发剂,硅钙渣、矿渣微粉为原料制备得到了碱激发胶凝材料.分别采用XRD、IR、TG-DSC、ESEM等手段研究了试样不同龄期的反应产物及微观形貌特征.结果表明:主要反应产物为低Ca/Si比的C-(A)-S-H凝胶;这些C-(A)-S-H凝胶粒子相互分叉搭接,形成致密的三维蜂窝状网络结构;随着龄期的延长,硅钙渣中的β-C2S逐渐参与碱激发反应,产物C-(A)-S-H凝胶的聚合程度增大,基体致密程度提高.     

碱矿渣胶凝体系的水化特性及机理分析

通过测定矿渣胶凝材料体系不同龄期的化学结合水含量,结合SEM分析,研究了碱矿渣胶凝材料的水化特性以及水化产物的微观形貌.结果表明:随着水化时间的增加,水化程度呈现不断增长的趋势,水化时间为1d时,水化程度为40.37％;水化初期,小颗粒形状的凝胶体在矿渣周围形成,凝胶间不断组合生长为C-S-H凝胶,随着水化时间的增加,胶凝体系逐渐致密.水化产物的Ca/Si、Ca/(Si+ Al)、Na/(Si+ Al)的质量比比值趋于稳定,表明碱矿渣-钢渣复合胶凝体系已形成稳定的水化产物.     

粉煤灰水泥基材料的水化产物

用热重仪-差示扫描量热仪、扫描电子显微镜、透射电子显微镜、X射线能量散射、高分辩电子显微镜、压汞仪,测定了粉煤灰水泥基材料水化产物的形貌特征、微观结构、化学组成及水泥石的孔结构,讨论了水化产物性质及水泥石孔结构随粉煤灰掺量的变化规律。结果表明：粉煤灰的大量掺加,可以改善凝胶的化学组成。水化后期,粉煤灰与Ca(OH)2及由熟料水化生成的高n(Ca)／n(Si)的水化硅酸钙(C—S—H)凝胶发生二次水化反应,生成低n(Ca)／n(Si)的C—S—H凝胶,此种凝胶的固碱能力强,可减少碱-集料反应的危害性。同时,二次水化产物能够填充那些对水泥石强度和耐久性极为不利的孔隙空洞,使水泥石的结构更加致密,优化水泥石的孔结构,对提高水泥基材料的耐久性作用极大,为进一步提高工业废渣利用的技术水平奠定了基础。     

高炉镍铁渣粉在水泥基复合胶凝材料中的水化特性研究

通过对不同高炉镍铁渣掺量的水泥-高炉镍铁渣粉复合胶凝材料水化放热速率、高炉镍铁渣粉的反应程度、硬化浆体化学结合水含量以及水化产物中C-S-H凝胶Ca/Si的测定,分别研究了水泥-高炉镍铁渣粉复合胶凝材料的早期、中长期水化进程、浆体微观形貌以及水化产物特点等水化特性.研究结果表明:高炉镍铁渣的掺入会降低水化放热速率,并推迟水化加速期放热峰的出现时间;在复合胶凝体系中,随着高炉镍铁渣粉掺量的增大,其反应程度和硬化浆体中化学结合水含量将降低.复合胶凝材料水化生成的C-S-H凝胶的Ca/Si低于水泥,且随着水化的进行呈降低趋势;高炉镍铁渣粉中的Al,在水化过程中会取代部分Si进入C-S-H凝胶中,形成C-A-S-H凝胶.     

碾压混凝土胶凝材料水化热数学模型的建立

国内工程试验结果表明：影响碾压混凝土胶凝材料水化热的因素是龄期和粉煤灰掺量。龄期不同，胶凝材料水化热的发展趋势不同；粉煤灰掺量对水化热起到缩放作用；针对国内工程试验，建立我国碾压混凝土胶凝材料水化热的数学模型。     

活性与惰性掺合料对复合胶凝材料水化性能的影响

采用ESEM、MIP、XRD及SEM等测试技术研究活性(粉煤灰)和惰性(石灰石粉)掺合料对复合胶凝材料强度、孔结构及水化产物等的影响,以此揭示水泥-粉煤灰-石灰石粉胶凝材料体系的水化特性。结果表明:石灰石粉和粉煤灰复掺具有比粉煤灰更好的减水效应,复合胶凝材料的强度也比单掺粉煤灰高;石灰石粉和粉煤灰复掺时,能够很好地填充熟料颗粒间的孔隙,显著改善孔结构,降低孔隙率,使孔隙结构得到细化;石灰石粉在复合胶凝材料中后期水化明显,生成水化碳铝酸钙;SEM照片也证实了石灰石粉水化活性以及对孔结构的改善作用。石灰石粉和粉煤灰复掺能优化复合胶凝材料体系,提高材料的水化性能。     

矿渣-水泥复合胶凝体系低温水化动力学研究

研究了低温下矿渣-水泥复合胶凝体系的水化反应特性和水化反应动力学.研究表明:低温下,复合胶凝体系的水化放热速率随着矿渣掺量的增加和环境温度的降低而下降;非蒸发水含量随着矿渣掺量的增加呈现降低的趋势;对已有水泥水化动力学方程进行计算,得到了低温条件下复合胶凝体系的动力学参数以及不同阶段反应速率和水化度间的关系,通过计算获得的动力学参数,可以对低温条件下复合胶凝体系不同反应阶段水化反应程度进行预测;在水化早期,复合胶凝体系中矿渣水化程度较低,消耗少量Ca(OH)2,使生成C-S-H凝胶的Ca/Si降低较少.在水化后期,复合胶凝体系中矿渣水化消耗较多的Ca(OH)2,使生成C-S-H凝胶的Ca/Si降低较多.矿渣掺量为50％时,硬化浆体C-S-H凝胶的Ca/Si远小于纯水泥体系.     

碱矿渣胶凝材料水化产物的试验研究

本研究旨在较为系统全面地研究分析碱矿渣胶凝材料的水化产物及特性.研究采用不同碱浓度和模数的水玻璃制备碱矿渣胶凝材料,利用X-射线衍射(XRD)、热重-差示扫描热分析(TG-DSC)、能谱仪(EDS)等技术手段研究了碱矿渣胶凝材料水化产物及特性.结果 表明,碱矿渣胶凝材料中水化产物主要为低Ca/Si的C-S-H凝胶和C-A-S-H凝胶,同时也包含了水滑石类物相,但含量所占比例较少.碱矿渣胶凝材料水化产物对碱金属离子有较强的结合能力.以上结果为进一步阐明该材料的水化机理提供了理论依据.     

废弃线路板非金属粉对碱激发矿渣/粉煤灰胶凝材料性能的影响

内掺0%～25%(质量分数)废弃线路板非金属粉末(waste circuit board non-metallic powder, NMP),制备了一种新型碱激发矿渣/粉煤灰胶凝材料，测试了其力学强度、水化放热、物相组成和孔径分布，分析了其微结构特征。试验结果表明：掺入NMP不只降低了胶凝材料的累计放热，并且稍微降低了胶凝材料的7和28 d抗压强度；当NMP掺量小于15%(质量分数)时，因玻璃纤维的存在，胶凝材料28 d抗折强度与NMP掺量成正比，最高增幅达55.5%;掺入NMP降低了胶凝材料中孔径为100～1 000 nm的孔隙比例，增大了100 nm以下的微孔隙比例，且试件总孔隙率增加；NMP中的树脂颗粒与胶凝材料基体结合紧密并填充了纤维与基体之间的空隙，NMP的掺入不会影响原胶凝材料的水化产物类型。     

C_3S-S-H系统水化产物的热力学稳定性

依据高C3S水泥和混合材复合体系的组成特征,用热力学方法分析了C3S-S-H系统在不同n(Ca)/n(Si)组成时的水化反应.结果表明,C3S-S-H系统水化产物的稳定性由系统n(Ca)/n(Si)组成决定,当n(Ca)/n(Si)>1.88时,最稳定的水化产物是C2SH1.17;当1.25相似文献   

In situ monitoring of the hydration process of K-PS geopolymer cement with ESEM

Environmental scanning electron microscope (ESEM) was used to in situ quantitatively study the hydration process of K-PS geopolymer cement under an 80% RH environment. An energy dispersion X-ray analysis (EDXA) was also employed to distinguish the chemical composition of hydration product. The ESEM micrographs showed that metakaolin particles pack loosely at 10 min after mixing, resulting in the existence of many large voids. As hydration proceeds, a lot of gels were seen and gradually precipitated on the surfaces of these particles. At later stage, these particles were wrapped by thick gel layers and their interspaces were almost completely filled. The corresponding EDXA results illustrated that the molar ratios of K/Al increase while Si/Al decrease with the development of hydration. As a result, the molar ratios of K/Al and Si/Al of hydration products at an age of 4 h amounted to 0.99 and 1.49, respectively, which were close to the theoretical values (K/Al=1.0, Si/Al=1.0 for K-PS geopolymer cement paste). In addition, well-developed crystals could not been found at any ages; instead, spongelike amorphous gels were always been observed.     

环境扫描电镜用于硅酸盐水泥早期水化的研究

采用环境扫描电镜对硅酸盐水泥的早期水化过程进行了连续观察。将硅酸盐水泥早期水化过程分为预诱导期、诱导期、加速期、减速期和稳定期个阶段加以描述。预诱导期阶段水泥开始水解,释放出离子,硅酸三钙(C3S)颗粒表面形成低n(Ca)／n(Si)层,第一批水化产物产生,水泥颗粒表面生成一层水化物的保护膜,使水化反应速度降低。诱导期阶段保护膜逐渐推进直至覆盖整个颗粒表面,膜内外产生渗透压力差。当渗透压力大到足以使薄膜在薄弱处破裂,缺钙的硅酸盐离子就被挤入液相,并和钙离子结合,生成各种不定形的C—C—H。加速期阶段钙离子和硅酸盐离子浓度相对于C—S—H来说达到过饱和,C—S—H高速生长,在颗粒表面附近形成类似于网状形貌的产物(高密度C—S—H),而在颗粒间的原充水空间里形成近球状形貌的产物(低密度C—S—H)。减速期阶段水化产物继续生长,由不定形富水的凝胶状转变为不定形的颗粒状,显微结构继续发展。稳定期阶段水化产物颗粒个数几乎保持不变,但单个颗粒均逐渐生长变大,显微结构逐渐致密化。保护膜的形成和破裂分别可以解释诱导期的产生和结束。C—S—H的生长速度是加速期水化反应速度控制的主要因素。     

卤水侵蚀对水泥粉煤灰浆体微结构影响

采用XRD、29Si和27Al MAS NMR测试技术,研究了粉煤灰掺量和侵蚀龄期对卤水侵蚀下水泥-粉煤灰浆体水化产物相组成、含铝相产物迁移与转变、C-S-H凝胶微结构变化的影响规律.研究结果表明:卤水侵蚀导致浆体Ca (OH)2含量降低,AFm和TAH向AFt转变,同时生成大量Friedel盐,C-S-H凝胶中Al[4]脱出;随粉煤灰掺量增加,浆体中AFt、AFm和TAH生成量降低,C-S-H的MCL和Al[4]/Si增大,Friedel盐生成量先增后减;侵蚀早期,水泥-粉煤灰浆体结构疏松,AFt生成量较纯水泥高,后期浆体致密性提高,抑制卤水侵蚀,AFt生成量较少,C-A-S-H脱铝作用减弱.     

Solubility of silica-alumina gels in different pH solutions Discussion on the hydration of slags and fly ashes in cement

The solubility of silica-alumina gels with different compositions were measured in different pH solutions. The solubilities of a silica-alumina gel is remarkably affected by its composition and the pH of the solution. There is a gel with a composition of Si/Al atomic ratio of about 7/3. When the Al/(Si+Al) ratio of silica-alumina gel is less than 0.7, the composition of the liquid phase is more rich in Al₂O₃ than that of the gel, that is, the surface of gel becomes rich in SiO₂. Conversely, when the Al/(Si+Al) ratio of gel is more than 0.7, the composition of the liquid phase is more rich in SiO₂ than that of the gel, and the surface of gel becomes rich in Al₂O₃. In the hydration of silica-alumina glasses such as slag and fly ash, the reason why the hydration proceeds or not, is whether the surface of reacting glass becomes rich in Al₂O₃ or not.     

Variation in the Composition of C-S-H Gel in Portland Cement Pastes Cured at Various Temperatures

Variation in the composition of C-S-H gel, the main hydration product of portland cement, cured at various temperatures, was studied using scanning electron microscopy with energy dispersive X-ray spectroscopy. Samples of two cement pastes were cured isothermally under water at 10°, 30°, and 60°C for one year. For the inner-product C-S-H gel of both cement pastes, increased curing temperature decreased the Ca/Si and Al/Ca ratios, but increased the S/Ca ratio. The Al/S and (Al + Fe)/S ratios decreased with increased curing temperature. Sulfur, probably in the form of sulfate ions, could be sorbed by the C-S-H gel at higher temperatures.     

硫酸盐侵蚀对不同养护制度UHPC水化产物微结构的影响

采用29Si和27Al MAS NMR、XRD、SEM等测试技术研究了硫酸盐侵蚀对不同养护制度的超高性能混凝土(UHPC)水化产物微结构的影响.结果表明:标准养护和80 ℃高温蒸汽养护条件下,UHPC水化产物主要为C-S-H、Ca(OH)2、AFt、AFm和TAH;210 ℃、2 MPa蒸压养护8 h后,水化产物主要为tobermorite、Ca(OH)2和TAH.硫酸盐侵蚀对不同养护制度的UHPC抗压强度和水化产物微结构的影响微弱,但可促进210 ℃蒸压养护的UHPC胶凝浆体中TAH向AFm和AFt的转化.同时硫酸盐侵蚀180 d时,C-S-H凝胶MCL和Al[4]/Si略有降低,但降低幅度较小,UHPC具有良好的抗硫酸盐侵蚀能力.     

Surface and Elemental Properties of Mount St. Helens Volcanic Ash

Sized fractions of Mount St. Helens volcanic ash were examined by SEM, EDXA, and ESCA. Particle size distributions, density, and specific surface area were determined. The size distribution was bimodal. Both EDXA and AAS demonstrated the presence of Si, Al, Fe, Na, K, Ca, and Mg. The EDXA demonstrated that Si and Al were present in all particles, except one, which was over 99% Si. Particle-to-particle variation in composition was large. X-ray diffraction demonstrated the presence of labradorite (plagioclase), albite, orthoclase, and anorthite, with a high background from amorphous material. ESCA demonstrated the presence of Na as a surface contaminant. No surface sulfur was detected, nor hydrocarbons at levels exceeding those normally found on air-exposed surfaces. The variation of specific surface area with particle size showed that the surface of the ash has a fractal dimension of 2.23 ± 0.03. Specific surface areas ranged from 1 m² g^?1 to 10 m² g^?1. From our study we estimated that the total surface area of the respirable particles emitted during this eruption equals that of all fly ash emitted from coal combustors worldwide during 1980.     

Aggregate-cement paste transition zone properties affecting the salt-frost damage of high-performance concretes

The influence of the cement paste-aggregate interfacial transition zone (ITZ) on the frost durability of high-performance silica fume concrete (HPSFC) has been studied. Investigation was carried out on eight non-air-entrained concretes having water-to-binder (W/B) ratios of 0.3, 0.35 and 0.42 and different additions of condensed silica fume. Studies on the microstructure and composition of the cement paste have been made by means of environmental scanning electron microscope (ESEM)-BSE, ESEM-EDX and mercury intrusion porosimetry (MIP) analysis. The results showed that the transition zone initiates and accelerates damaging mechanisms by enhancing movement of the pore solution within the concrete during freezing and thawing cycles. Cracks filled with ettringite were primarily formed in the ITZ. The test concretes having good frost-deicing salt durability featured a narrow transition zone and a decreased Ca/Si atomic ratio in the transition zone compared to the bulk cement paste. Moderate additions of silica fume seemed to densify the microstructure of the ITZ.