碱对粉煤灰的活化和微观结构的影响

用Ｘ－射线、ＳＥＭ研究了粉煤灰在不同碱度环境下的活化机制、水化产物和微观结构。研究表明：粉煤灰硅酸盐水泥在常温下养护，粉煤灰的反应能力较低，这是因为在Ｃａ（ＯＨ）２存在条件下的活化很慢，只有提高养护温度或在复合碱和硫酸盐存在条件下才有利于结构的解体和水化产物的稳定。     

机械力活化粉煤灰制备地聚合物的性能及机理研究

利用机械力球磨激发粉煤灰火山灰活性,研究了机械力活化前后粉煤灰基地聚合物性能变化,并对机械力活化粉煤灰及其地聚合物的形成机理进行分析。结果表明,机械力球磨活化后粉煤灰基地聚合物水化反应速度加快,养护28d后抗压强度提高至79.97MPa,具有更好的抗冻融性能。XRD、FT-IR和SEM分析表明机械力活化前后粉煤灰基地聚合物水化产物主要为无定形凝胶;机械力作用能有效提高粉煤灰活性,使地聚合反应更充分;活化后地聚合物样品结构更加致密,为高性能粉煤灰基地聚合物的工程应用提供理论依据。     

粉煤灰在蒸养条件下的氯离子固化性能

通过模拟粉煤灰在硅酸盐水泥中的水化环境,采用二次等温吸附法研究了标准养护和蒸汽养护条件下粉煤灰水泥体系中粉煤灰氯离子固化能力的变化,采用灰色关联分析法对实验结果进行了分析.研究结果表明:粉煤灰氯离子化学结合能力随恒温温度和恒温时间的增加而降低,而物理吸附能力基本不变;在标准养护条件下粉煤灰水化生成的铝酸盐是C4 AH13,而在蒸汽养护条件下是C3 AH6,C3 AH6氯离子固化能力相对较弱,使得蒸养条件下的粉煤灰氯离子固化能力小于标准养护条件;当以氯离子固化总量为参考数列时,蒸汽养护制度中恒温温度的影响大于恒温时间.     

碱激发烧煤矸石胶凝材料的硬化机理研究

利用XRD,IR,SEM等方法,研究了NaOH、KOH和钠水玻璃激发烧煤矸石的反应进程和水化产物,对其力学性能、微观结构和硬化机理进行了探讨.结果表明:水化产物是类似于沸石类结构的无定形碱-硅铝凝胶,碱溶液、液固比、养护温度和养护时间等因素影响着水化产物及其强度的形成.采用模数为1.23钠水玻璃与烧煤矸石混合(液固比0.3),在90℃养护条件下反应生成无定型的碱-硅铝酸盐凝胶,而在65℃养护时,硬化浆体中还存在有一定量未反应的硅酸钠晶体.     

活化煤矸石对水泥水化的影响

研究了活化煤矸石-氢氧化钙体系的水化热、水化产物成分以及活化煤矸石水泥体系的水化过程、水化产物的微结构,结果表明,在石膏的激发下,活化煤矸石能够发生二次水化,与Ca（OH）2反应形成钙矾石、水化硅酸钙、水化铝酸钙等有利于提高水泥石强度的水化产物;活化煤矸石水泥硬化浆体中Ca（OH）2的含量在水化3d时最多,而后随龄期逐渐减少;阐明了活化煤矸石能够降低水化产物中氢氧化钙的含量、抑制氢氧化钙晶体的生长和聚集,并改善水泥石结构．     

养护条件对次轻混凝土强度及抗盐冻性能的影响

研究了养护条件对不同水胶比次轻混凝土强度及盐冻性能的影响，并通过对其内部相对湿度、孔结构及水化产物的测试分析探究其作用机理。结果表明，自然养护条件下，掺50%体积轻骨料次轻混凝土早期强度较低，而其在7～28 d龄期内增长率高；特别是低水胶比混凝土，其14 d龄期强度超过标准养护与水中养护条件下试件强度。对于低水胶比混凝土，水中养护和标准养护可中止或减缓混凝土内水分向外界迁移，水泥的充分水化导致水泥石结构更致密，混凝土抗盐冻性能较好。对于高水胶比混凝土，自然养护条件下混凝土28 d龄期的内部相对湿度仍有90%,其内部存在充足水分供给水泥水化，水泥石孔结构良好；当处于盐溶液中时，相比于含水率较高的水中养护与标准养护下混凝土，自然养护条件下混凝土的水饱和程度低，故其抗盐冻性能最好。     

高岩温隧道下矿物掺合料对混凝土力学性能的影响

通过模拟高岩温隧道条件,研究了高岩温隧道条件下矿物掺合料对混凝土强度的影响。结果表明:高岩温条件下可以提高混凝土的早期强度,但后期强度却有较大幅度的下降,当温度低于50℃时,矿渣粉煤灰复合混凝土的强度更高;当温度超过60℃时,粉煤灰混凝土的强度更高。XRD及SEM分析表明:高岩温条件下胶凝材料水化速度加快,生成的水化产物来不及均匀扩散,相互搭接变差,当温度低于50℃时,水分蒸发较慢,水分充足,矿渣的活性容易被激发,水化产物结构致密;当温度超过60℃时,由于水分蒸发较快,矿渣的活性难以被激发,水化产物结构变疏松。     

磷酸盐生物水泥劈裂强度和硬度改善的研究

本文主要以活性HAP(羟基磷灰石 :Ca5(PO4) 3OH)、磷酸盐生物水泥PBC为基础 ,研究了碳纤维、原蚕丝纤维和养护条件对水化试样的劈裂强度和表面硬度的改善。实验结果表明 ,生物纤维和适宜的养护条件使水化试体的劈裂强度有一定的提高 ,维氏硬度有较大的提高 ;用SEM和IR初步研究了纤维与水化产物之间的界面结构 ,发现纤维与生物水泥水化产物界面可能有不同程度的化学结合。     

粉煤灰粒径分布对硅酸盐水泥水化性能的影响

为研究粉煤灰粒径对硅酸盐凝胶材料水化性能的影响,经球磨仪研磨得到3种不同粒径的粉煤灰,探讨其对硅酸盐水泥水化放热速率、水化放热总量、水化反应程度和粉煤灰自身水化反应程度的影响。结果表明:随粉煤灰粒径的减小,粉煤灰的水化活性明显增大,水化反应程度增大,养护龄期为7 d时,水化程度增加20.7%;粉煤灰粒径分布对硅酸盐水泥水化放热总量的影响较小,主要影响其水化放热速率、水化反应程度,养护龄期为28 d时,胶凝材料水化程度增加3%。     

磷酸盐生物水泥劈裂强度和硬度改善的研究

本文主要以活性HAP（羟基磷灰石：Ca5(PO4)3OH)、磷酸盐生物水泥PBC为基础,研究了碳纤维、原蚕丝纤维和养护条件对水化试样的臂裂强度和表面硬度的改善。实验结果表明,生物纤维和适宜的养护条件使水化试体的臂裂强度有一定的提高,维氏硬度有较大的提高;用SEM和IR初步研究了纤维与水化产物之间的界面结构,发现纤维与生物水泥水化产物界面可能有不同程度的化学结合。     

粉煤灰／海泡石纤维复合沥青混合料的制备与性能研究

从海泡石纤维和粉煤灰纤维的微观结构特性出发，进行粉煤灰，海泡石复合纤维增强沥青复合材料的制备。通过路用性能试验，研究了海泡石纤维和粉煤灰纤维对沥青混合料性能的影响以及结合机理。结果表明，添加适量海泡石和粉煤灰纤维可以制备性能优良的纤维复合沥青混合料。海泡石纤维对沥青表现极强吸持能力，有效调节沥青与胶浆的含量。粉煤灰纤维在沥青中主要起加固和改善混合料的作用。两种纤维的添加，使沥青混合料的高温变形性、水稳定性、低温抗裂性和抗疲劳性等显著提高。     

Hydration of quaternary Portland cement blends containing blast-furnace slag,siliceous fly ash and limestone powder

In this study the hydration of quaternary Portland cements containing blast-furnace slag, type V fly ash and limestone and the relationship between the types and contents of supplementary cementitious materials and the hydrate assemblage were investigated at ages of up to 182 days using X-ray diffraction and thermogravimetric analysis. In addition thermodynamic modeling was used to calculate the total volume of hydrates. Two blast-furnace slag contents of 20 and 30 wt.% were studied in blends containing fly ash and/or limestone at a cement replacement of 50 wt.%. In all cases the experiments showed the presence of C–S–H, portlandite and ettringite. In samples without limestone, monosulfate was formed; in the presence of limestone monocarbonate was present instead. The addition of 5 wt.% of limestone resulted in a higher compressive strength after 28 days than observed for cements with lower or higher limestone content. Overall the presence of fly ash exerts little influence on the hydrate assemblage. The strength development reveals that amounts of up to 30 wt.% fly ash can be used in quaternary cements without significant loss in compressive strength.     

Assessing the suitability of three Australian fly ashes as an aluminosilicate source for geopolymers in high temperature applications

Fly ash characteristics cannot be assumed to be constant between power stations as they are highly dependent on the coal source and burning conditions. It is critical to understand the characteristics of fly ash in order to produce geopolymers suitable for high temperature applications. We report on the characterisation of fly ash from three Australian power stations in terms of elemental composition, phase composition, particle size, density and morphology. Geopolymers were synthesised from each of the fly ashes using sodium silicate and sodium aluminate solutions to achieve a range of Si:Al compositional ratios. Mechanical properties of geopolymer binders are presented and the effect of the source fly ash characteristics on the hardened product is discussed, as well as implications for high temperature applications. It was found that the twenty eight day strength of geopolymers is largely dependent on the sub 20 μm size fraction of the fly ash. Strength loss after high temperature exposure was found to be dependent on the concentration of iron in the fly ash precursor and the Si:Al ratio of the geopolymer mixture.     

An explanation for the negative effect of elevated temperature at early ages on the late-age strength of concrete

Elevated curing temperature at early ages usually has a negative effect on the late-age strength of concrete. This article aims to study the mechanism of this phenomenon. The results show that elevated curing temperature at early ages has a negative effect on the late-age strength of hardened cement paste, but it has a greater negative effect on the late-age strength of cement mortar. After elevated temperature curing at early ages, the late hydration of cement is hindered, but the late reaction of fly ash is not influenced. Owing to the continuous reaction of fly ash, the late-age pore structure of cement–fly ash paste under elevated curing temperature is finer than that under standard curing temperature, and the late-age strength of cement–fly ash paste under elevated curing temperature is higher. However, the late-age strength of cement–fly ash mortar under elevated curing temperature is lower. Apparently, there are differences between the effects of elevated curing temperature on hardened paste and mortar. It is the deterioration of transition zone between hardened paste and aggregate that makes the negative effect of elevated curing temperature on the mortar (or concrete) be greater than the hardened paste. As the water-to-binder ratio decreases, the negative effect of elevated curing temperature on the transition zone tends to be less.     

Dielectric properties of fly ash

This paper reports the dielectric properties of fly ash. The dielectric measurements were performed as a function of frequency and temperature. The sample of fly ash shows almost similar behaviour in the frequency and temperature range studied. The large value of dielectric constant in the typical frequency range is because of orientation polarization and tight binding force between the ions or atoms in the fly ash. The sample of fly ash is of great scientific and technological interest because of its high value of dielectric constant (10⁴).     

Suppression of solidification of calcium-rich incinerator fly ash during thermal treatment for decomposition/detoxification of dioxins

Dioxins and dioxin-like compounds released from municipal and industrial solid waste incinerators have been a serious problem from the viewpoint of environmental pollution control. Since these compounds are concentrated especially on fly ash, supplemental treatment systems to decompose/detoxify them are required after collecting the fly ash either by a bag filter or an electrostatic precipitator. The present work is aimed at developing a heat treatment technique for fly ash, which contains a large amount of calcium (Ca) derived from hydrated lime, at a temperature higher than 500°C by adding chemical additives to prevent the solidification of Ca-rich fly ash. As calcium hydroxychloride (CaClOH) in the Ca-rich fly ash was found to cause solidification of fly ash at high temperatures, sodium hydroxide, mullite and coal fly ash were added as additives prior to the heat treatment. As a result, the additives studied in the present work are effective for decomposing CaClOH and therefore suppressing the solidification of fly ash, and yet they promoted the decomposition/detoxification of dioxins.     

The performance and application of fly ash modified by PDMDAAC

Fly ash modification by polydimethydiallylammonium chloride (PDMDAAC) in laboratory scale was explored in this work and the adsorption performance of modified fly ash and its application in dyeing wastewater treatment were also studied. The key factors (concentration and temperature) for PDMDAAC to affect the adsorption properties of fly ash (FA) were revealed using the orthogonal test with four factors. The results indicated that the adsorption magnitude of fly ash to PDMDAAC increased due to its favorable specific surface causing the change of the surface charge nature. Hence, adsorption performance of modified fly ash on organic molecules and its ion exchange capacity are strengthened. The maximum color removal efficiency was obtained as 88.2% by modified fly ash with 2.0 g/100 mL dosage in dyeing wastewater, which is much higher than 12.5% color removal efficiency by raw fly ash with the same dosage. And, the used modified fly ash could be used for cement production as additive agent. The intensity of cement produced with 15% the modified fly ash in weight reached the Chinese Cement Standard (GB/T17671-1999), blazing a promising novel way in fly ash utilization.     

Heat deformations of fly ash concrete

When dealing with concrete resistance to high temperatures it is important for design purposes to know the elastic parameters, such as the temperature–strain curves and the modulus of elasticity.Concretes containing a high volume of fly ash differ from conventional mixes in the cementitious phase. This results in a different behaviour under heating compared to plain Portland cement concretes. To find the elastic response of fly ash concrete four series of concrete mixtures were manufactured: one with cement only, another with 30% by mass partial replacement of cement by fly ash, and two with 30% and 40% by mass replacement of cement by ground fly ash. Tests were carried out on cylinders (150 × 300 mm). A high-calcium fly ash was used.The conditions were selected so that the applied level of stress corresponded to 25% or to 40% of the ultimate compressive strength of concrete, and a transient type of temperature regime was followed. Based on the experiments the critical temperature, the residual deformation and the modulus of elasticity were determined.The results indicate that concretes containing a high volume of fly ash are more sensitive to high temperatures, since they developed greater deformations. The fineness of the fly ash used also seems to influence the degree of deformation in an adverse way.     

Estimation of the risk for early thermal cracking for SCC containing fly ash

Cracking of concrete must be avoided during the hardening phase in order to minimize the risk of durability problems in the future, such as corrosion of the reinforcement, water tightness and damages due to frost. Estimation of the risk of early age cracking requires knowledge of the combined effects from temperature development and mechanical behaviour during the hydration. In the present paper, the influence of fly ash on the young concrete behaviour has been investigated. The concrete is based on a Swedish cement aimed for civil engineering structures, and the fly ash is of class F. A comparison of crack risks between concrete containing fly ash in different amounts with concrete without fly ash is presented. Also a previously tested concrete containing limestone filler is considered. The fly ash was added to replace a part of the aggregate, which gives a higher heat evolution. However, a numerical stress analysis showed that the risk for early age through cracking for a typical civil engineering structure is significantly decreased in the mixes containing fly ash. The denotation typical civil engineering structure is used here for concrete structures such as tunnels, bridges, and ramps of common cross-section dimensions. In the case of fly ash added to concrete by a partial replacement of cement, the crack risk will probably be further decreased. For a self-balancing structure of young concrete there is no restraint from adjacent structures, and the temperature and moisture gradients within the young concrete cause self-stresses governed by equilibrium with zero external forces for any cut. The estimated risk for surface cracking on a self-balancing wall or slab was not improved by an addition of fly ash. It is probably an effect of the increased heat development, which most likely counteracts the positive effect of the increased early age creep for concrete containing fly ash. If the heat evolution decreases when cement is partly replaced with fly ash, the use of fly ash might reduce the risk of surface cracks.     

Investigation of the stability of hardened slag paste for the stabilization/solidification of wastes containing heavy metal ions

We have studied the effect of chromium ions and lead ions on the chemical stability of hardened slag paste with toxic wastes during the stabilization/solidification process. The influences of Cr and Pb ions on the hydration of slag were also investigated. Sodium silicate (Na(2)SiO(3)), 5 wt.% of slag, was used as an alkali activator for slag hydration. The physical stability of hardened paste containing partial replacement of slag with fly ash and gypsum was also examined.When gypsum was added to slag, the compressive strength of hardened slag paste developed, accompanying the activation of alumino-ferrite-tricalciumsulfate (Al(2)O(3)-Fe(2)O(3)-3CaSO(4), AFt) and alumino-ferrite-monocalciumsulfate (Al(2)O(3)-Fe(2)O(3)-CaSO(4), AFm) phase generation. Those phases caused densification of the microstructure. Concurrently, the leaching amount of heavy metal ions was decreased. When fly ash was added to slag, the compressive strength increased and the leaching amount decreased with both active formation of aluminate hydrates and ion substitution. Lead ions were mostly stabilized through physical encapsulation by the hardened slag paste's hydrate matrix. In the case of chromium ions, we observed that it was mainly solidified through the formation of a substitutional solid solution with aluminum atoms in the structure of aluminate hydrates.