Fly ash concrete subjected to thermal cyclic loads

The present study describes the behaviour of concrete as well as fly ash concrete when subjected to varying number of high temperature heating cycles. A Concrete mix (1:2.37:2.98) with 340 kg/m³ cement and w/cm ratio 0.45 was prepared. Cement was replaced by varying percentages (0%, 20%, 40%, 50% and 60%) of fly ash by weight of cement. The concrete was subjected to a constant temperature of 200°C for 7, 14, 21 and 28 heating cycles. One heating cycle corresponds to 8 h heating and subsequent cooling in 24 h. Subsequently the effect of temperature on the properties of the concrete was investigated and compared with that of the properties of unheated concrete. The compressive strength of plain as well as fly ash concrete increased when it was subjected to thermal cyclic loads. Moreover, the compressive strength increased with an increase in number of heating cycles. Thermal conductivity of concrete was found to decrease with an increase in the fly ash content.     

Fly ash characterization and application in Al–based Mg alloys

Continuing study in metallurgical field calls for growing reinforcements of which fly ash plays an important role. In this study, Al alloys were reinforced with different solid fly ash particles. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence (XRF) analyses were used to identify the fly ash particles, and they were also applied to the composite alloys. The X-ray diffraction (XRD) results indicated that the crystalline phase of the fly ash was an effective reinforced phase. Meanwhile, the SEM and optical micrographs of the composite samples indicated that fly ash could be reacted or settled in the matrix of the aluminium. The physical, tribological and microhardness analyses were also used to study the Al–fly ash composites. The best wear resistance corresponding to the lowest loss was obtained in the samples with as-received fly ash which were mostly in accordance with the results in the samples containing treated fly ash. Meanwhile, the proportion of the wear results to the hardness of the samples was observed. Finally, the light weight Al alloys was realized, and increasing the strength is a likeness.     

Fly ash as a potential starting reagent for the synthesis of ultramarine blue

The traditional starting reagent for the synthesis of ultramarine blue, namely kaolin, has to be heated before the synthesis to weaken the structure of the kaolin. Two batches of fine fly ash (an aluminosilicate waste product from the combustion of coal) were successfully used to synthesize ultramarine blue. Infrared, Raman and X-ray diffraction results confirmed the formation of the product. Fly ash has the advantage over kaolin of being amorphous. The results further showed that the transition from the green ultramarine species to the blue species coincided with an increase in the ratio of the amount of S₃⁻ species relative to the amount of S₂⁻ species.     

Fly ash reactivity: Extension and application of a shrinking core model and thermodynamic approach

In the present paper a theoretical study is presented on the dissolution (reaction) of pulverised powder coal fly ash. A shrinking core model is derived for hollow spheres that contain two regions (outer hull and inner region). The resulting analytical equations are applied to the dissolution experiments by Pietersen (Mat.Res.Soc.Symp.Proc., Vol. 178, Materials Research Society, 1990, p. 139; Ph.D. Thesis, Delft University of Technology, The Netherlands, 1993), yielding reaction rates at various temperatures and pH for two class F fly ashes. It is revealed that the available amount of reactive fly ash is proportional to the glass content of the fly ash, and that the reaction rate is proportional to this glass content as well. Moreover, it is concluded that the outer region is less reactive than the inner region, and that these reactivities are proportional to a power of the hydroxyl concentration. Subsequently, experimental data and model are used to assess the magnitude of inner and outer region. It seems that the outer hull of solid spheres and cenospheres are having the same thickness, about 2 m. Based on the observed trends a reaction mechanism is proposed which accounts for the glass content and composition of the fly ash (and that is applicable to slags as well). Finally, using the reaction product, thermodynamic properties of the studied fly ashes are derived: the free energy, enthalpy and entropy of reaction.     

燃烧法所得含纳米氧化铁粉煤灰建筑吸波材料

为促进纳米材料的推广应用,研究了量大面广的燃煤工业副产物粉煤灰生产工艺对材料性质的影响,利用扫描电镜、能谱仪、X射线衍射仪等对高铁粉煤灰颗粒微观形貌与性质进行了分析.研究表明：在煤粉燃烧过程中,粘土、石英矿物形成硅酸盐玻璃微珠,矿物中的大部分铁元素在球形玻璃体颗粒表面析晶形成铁氧化物,以二价和三价氧化铁的形式存在,晶粒...     

Fluid transport in high volume fly ash mixtures with and without internal curing

The transport of fluid and ions in concrete mixtures is central to many aspects of concrete deterioration. As a result, transport properties are frequently measured as an indication of the durability that a concrete mixture may be expected to have. This paper is the second in a series investigating the performance of high volume fly ash (HVFA) mixtures with low water-to-cementitious ratios (w/cm) that are internally cured. While the first paper focused on strength and shrinkage, this paper presents the evaluation of the transport properties of these mixtures. Specifically, the paper presents results from: rapid chloride migration (RCM), rapid chloride penetration test (RCPT), apparent chloride diffusion coefficient, surface electrical resistivity, and water absorption. The test matrix consisted of mortar samples with two levels of class C fly ash replacement (40% and 60% by volume) with and without internal curing provided with pre-wetted lightweight fine aggregates (LWA). These mixtures are compared to plain ordinary portland cement (OPC) mortars. The results indicate that HVFA mixtures with and without internal curing provide benefits in terms of reduced transport coefficients compared to the OPC mixtures.     

Fly ash cenospheres as multifunctional supports of g-C3N4/N-TiO2 with enhanced visible-light photocatalytic activity and adsorption

The ternary composites of g-C₃N₄/N-TiO₂/FACs (FAC: Fly Ash Cenospheres) were synthesized by an in-situ hydrolysis method to improve the photocatalytic activity and their stability. When TiO₂ was anchored on FAC, it was easily to be separated from the aqueous solution and could be repeatedly utilized. In the present experiments, the degradation rate remained for more than 68% even after the composite reused for seven times. The band gap of g-C₃N₄/N-TiO₂/FAC was 2.75?eV, which might be owing to the synergistic effect between N-TiO₂ and g-C₃N₄. The composite of g-C₃N₄/N-TiO₂/FAC had an ideal activity of 72.2% under visible light illumination for 180?min. It was about 1.3 times of N-TiO₂/FAC and 3.5 times of g-C₃N₄. The synergistic effect of SiO₂, Fe₂O₃ and TiO₂ components resulted to the improvement of photocatalytic performance.     

Synthesis of zeolites NaA and analcime using rice husk ash as silica source without using organic template

Silica was extracted from Fajr rice husk ash (RHA) with approximately 97% purity, converted to sodium and potassium silicate solutions and used as silica source for the synthesis of NaA and analcime zeolites. NaOH and KOH without organic templates were used in the synthesis of NaA and analcime zeolite, respectively. Conventional heating and microwave-assisted hydrothermal were used in zeolite synthesis. Zeolites were characterized with XRD, SEM and IR spectroscopy. Heating time and Si/Al ratio were optimized for the synthesis of zeolites.     

A warning against misuse of quarter-point elements

Quarter-point elements are used very frequently for fracture mechanics computations, because the quarter-point technique yields the required singular interpolation without any modification to existing software. This advantage is particularly significant for three-dimensional stress intensity factor computations because of the difficulty of implementing other techniques. However, in practical 3-D applications, the crack front is usually curved, and this note proves that a crack front distortion leads to a negative Jacobian in the region surrounding the crack front. The numerical difficulties to be expected depend on the aspect ratio of the elements.     

MSW fly ash stabilized with coal ash for geotechnical application

The solidification and stabilization of municipal solid waste (MSW) fly ash for the purpose of minimizing the geo-environmental impact caused by toxic heavy metals as well as ensuring engineering safety (strength and soaking durability) are experimentally evaluated. The mixtures of MSW fly ash stabilized with cement and fluidized bed combustion coal fly ash (FCA) were used for unconfined compressive strength tests, leachate tests, and soaking tests. The behavior of soluble salts contained in the MSW fly ash significantly affects strength development, soaking durability, and the hardening reaction of the stabilized MSW fly ash mixtures. The cement stabilization of the MSW fly ash does not have enough effect on strength development and soaking durability. The addition of cement only contributes to the containment of heavy metals due to the high level of alkalinity. When using FCA as a stabilizing agent for MSW fly ash, the mixture exhibits high strength and durability. However, the Cd leachate cannot be prevented in the early stages of curing. Using a combination of cement and FCA as a MSW fly ash stabilizer can attain high strength, high soaking durability, and the containment of heavy metals. The stabilized MSW fly ash with cement and FCA can be practically applied to embankments.     

Laboratory compaction of fly ash and fly ash with cement additions

The use of power-industry wastes as a material for earthen structures depends on its compactibility. It has been confirmed that a fly ash/bottom ash mix compacted several times in Proctor's moulds are not representative. The relationship between dry density of solid particles and water content for re-used waste samples was determined. The re-compaction effect on grain-size distribution, density of solid particles, specific surface and sand equivalent of wastes was investigated. Tests were conducted on fly ash samples compacted by the Standard and Modified Proctor methods. Another aim of the paper was to investigate the influence of cement additions on the compactibility of a fly ash/bottom ash mix. Waste samples in the natural state and with different percentages of cement additions (2, 5 and 10%) were compacted by both impact compaction methods to obtain compactibility curves rhod(w). It was found that cement addition resulted in an increased rhod max value, while wopt decreased. Linear regression relationships for changes in compaction parameters after cement stabilisation are also given.     

Properties of geopolymer with seeded fly ash and rice husk bark ash

In the present work, compressive strength of inorganic polymers (geopolymers) produced of seeded fly ash and rice husk bark ash has been investigated. Different specimens made from a mixture of fly ash and rice husk bark ash in fine and coarse form were subjected to compressive strength tests at 7 and 28 days of curing. The curing regime was different: one set of the specimens were cured at room temperature until reaching to 7 and 28 days and the other sets were oven cured for 36 h at the range of 40-90 °C and then cured at room temperature until 7 and 28 days. The results indicate that in both 7 and 28 days regimes, the highest strengths are related to the specimens by SiO₂/Al₂O₃ ratio equals 2.99 cured at 80 °C. For these specimens, those contained finer fly ash particles show more compressive strength. Thermogravimetric analysis and Fourier transform infrared spectroscopy both also are in agreement with the obtained results from compressive strength tests. In addition, SEM micrographs of the specimens show that the finer the particle size of the utilized ashes, the denser the microstructure which confirms the results obtained by the strength tests.     

低质高碳粉煤灰制备粉煤灰贝利特水泥及其特性研究

利用含碳量高、火山灰活性较低的堆存粉煤灰为原料,用水热合成-低温煅烧方法制备粉煤灰贝利特水泥,研究了配合料CaO掺量与在97℃±2℃下的蒸养时间、煅烧温度和煅烧时间对前驱物和粉煤灰贝利特水泥的组成及其基本物理力学性能的影响。结果表明:在97℃±2℃蒸养和800℃煅烧,粉煤灰中的莫来石和石英几乎不与CaO发生反应;800℃煅烧的粉煤灰贝利特水泥熟料中主要水硬性矿物为α’L-C_2S和C_(12)A_7,当煅烧温度达900℃或更高时,贝利特以活性较低的β-C2S存在,并且熟料中有水化活性很低的钙铝黄长石形成。CaO掺量为30%的石灰-粉煤灰配合料在97℃蒸养10h后经800℃煅烧1h,制得28d抗压强度达到30.2 MPa的粉煤灰贝利特水泥。粉煤灰贝利特水泥凝结快,可用于快修工程,但其需水量大,硬化浆体结构相对疏松,孔隙率较大。     

Child restraint system use and misuse in six states

This project addressed use and misuse of child restraint systems (CRS) in the nation. CRS use and critical misuse observations were collected in the Fall of 2002 for 5527 children less than 36 kg (80 pounds) in 4126 vehicles in six states: Arizona, Florida, Mississippi, Missouri, Pennsylvania, and Washington. Results showed that 62.3% of these children were restrained in a CRS; 25.9% were restrained in a safety belt (SB); and 11.8% were unrestrained. By weight class, CRS use was 97.1% for children less than 9 kg (20 pounds); 86.4% for children between 9 and 18 kg (20 and 40 pounds); 41.7% for children between 18 and 27 kg (40 and 60 pounds); and 10.9% for children between 27 and 36 kg (60 and 80 pounds). Overall critical CRS misuse was 72.6%. Most common critical misuses were loose harness straps and loose vehicle SB attachment to the CRS. Other types of CRS misuses were also observed and recorded in the study. Recommendations are provided for field observation techniques, periodic monitoring, and research for education and enforcement strategies.     

Structure–fracture properties relationship for Polypropylene reinforced with fly ash with and without maleic anhydride functionalized isotactic Polypropylene as coupling agent

The deformation and fracture behavior of PP/ash composites with and without maleic anhydride functionalized iPP (MAPP) as coupling agent was investigated, focusing on the effect of ash content and loading conditions. A decreasing trend of tensile strength and strain at break values with filler content was observed for unmodified composites, whereas these properties were roughly independent of ash content for the composites with MAPP. In quasi-static fracture tests, all materials displayed ductile behavior. Most composites exhibited improved fracture properties with respect to the matrix as a result of the toughening mechanisms induced by the ash particles. Under impact loading conditions, in contrast, all materials displayed fully brittle behavior. Impact critical fracture energy values of the composites were higher than those of PP and they also presented a maximum which was explained in terms of the comprehensive analysis of the crystallinity development in PP. The incorporation of MAPP led to better dispersion of ash particles in the matrix but was detrimental to the material fracture behavior independently of loading conditions. Increased interfacial adhesion promoted by MAPP hindered particle-induced toughening mechanisms.     

The use and misuse of citation analysis in research evaluation

The present paper addresses some of the many possible uses of citations, including bookmark, intellectual heritage, impact tracker, and self-serving purposes. The main focus is on the applicability of citation analysis as an impact or quality measure. If a paper's bibliography is viewed as consisting of a directed (research impact or quality) component related to intellectual heritage and random components related to specific self-interest topics, then for large numbers of citations from many different citing paper, the most significant intellectual heritage (research impact or quality) citations will aggregate and the random author-specific self-serving citations will be scattered and not accumulate. However, there are at least two limitations to this model of citation analysis for stand-alone use as a measure of research impact of quality. First, the reference to intellectual heritage could be positive or negative. Second, there could be systemic biases which affect the aggregate results, and one of these, the “Pied Piper Effect”, is described in detail. Finally, the results of a short citation study comparing Russian and American papers in different technical fields are presented. The questions raised in interpreting this data highlight a few of the difficulties in attempting to interpret citation results without supplementary information. Leydesdorff (Leydesdorff, 1998) addresses the history of citations and citation analysis, and the transformation of a reference mechanism into a purportedly quantitive measure of research impact/quality. The present paper examines different facets of citations and citation analysis, and discusses the validity of citation analysis as a useful measure of research impact/quality.     

Biotoxicity evaluation of fly ash and bottom ash from different municipal solid waste incinerators

Different types of municipal solid waste incinerator (MSWI) fly and bottom ash were extracted by TCLP and PBET procedures. The biotoxicity of the leachate of fly ash and bottom ash was evaluated by Vibrio fischeri light inhibition test. The results indicate the following: (1) The optimal solid/liquid ratio was 1:100 for PBET extraction because it had the highest Pb and Cu extractable mass from MSWI fly ash. (2) The extractable metal mass from both fly ash and bottom ash by PBET procedure was significantly higher than that by TCLP procedure. (3) The metal concentrations of fly ash leachate from a fluidized bed incinerator was lower than that from mass-burning and mass-burning combined with rotary kiln incinerator. (4) The TCLP and PBET leachate from all MSWI fly ash samples showed biotoxicity. Even though bottom ash is regarded as a non-hazardous material, its TCLP and PBET leachate also showed biotoxicity. The pH significantly influenced the biotoxicity of leachate.     

Seat belt misuse among children transported in belt-positioning booster seats

Objective

Observe and report seat belt use among children transported in belt-positioning booster seats.

Design

We conducted a cross-sectional, observational survey of children transported in motor vehicles between 2006 and 2007. While drivers completed a survey reporting the child's age, weight and gender, and the driver's age, gender, race, income, education, and relationship to the child; a child passenger safety technician recorded vehicle seating location, restraint type, and use of the car safety seat harness or seat belt as appropriate for the child.

Setting

Twenty-five fast food restaurants and discount department stores throughout Indiana.

Participants

A convenience sample of drivers transporting children younger than 16 years.

Main exposure

Seat belt use among children transported in belt-positioning booster seats.

Outcome measure

Seat belt misuse.

Results

Overall, 1446 drivers participated, 2287 children were observed with 564 children in belt-positioning booster seats. At least one seat belt misuse was observed for 64.8% of the children transported. Common misuses were the shoulder belt being placed over the booster seat armrest (35.8%); shoulder belt not at mid-shoulder position (28.5%), seat belt was too loose (24.5%), and the shoulder belt was either behind the child's back (9.1%) or under their arm (10.0%).

Conclusion

There is a high frequency of seat belt misuses among children transported in booster seats. Advice to parents on appropriate car seat selection, and encouragement to parents to supervise seat belt use may decrease misuse.