Polymer Concrete Using Coal Fly Ash

The disposal of coal combustion byproducts wastes has been a pressing issue during the past few decades. In parallel, the formulation of high-performance materials that are stronger and more durable than conventional cement-based materials has emerged as an issue of considerable importance in the construction industry. This paper shows that it is possible to utilize fly ash, a byproduct of coal burning, to produce a high-performance material at a potentially lower cost and without compromising its structural integrity. The high-performance material reported in this study is polymer concrete (PC) made with fly-ash fillers. The PC is investigated for its compressive strength, flexural strength, creep deformation, and bond strength of PC overlay on portland cement concrete under thermal cycling. The use of fly ash as an aggregate in PC is very promising because it enhances the physical properties of the material and particularly its compressive and flexural strength. PC using fly ash could be used as an overlay in pavement, bridges, and runways or in precast applications such as utility, transportation, and hydraulic components.     

Metals Removal from Municipal Waste Incinerator Fly Ashes and Reuse of Treated Leachates

Incinerator fly ash from municipal solid waste is considered as a hazardous waste and can release toxic metals such as Pb and Cd into the environment. This research verifies the performance of a sequential, closed circuit treatment process involving chemical leaching (alkaline washings followed by an acid washings) and precipitation (neutralization at pH = 5 and 7). This method also includes the recirculation of treated leachates during the acid washing steps. In total, ten recirculation loops were executed in laboratory pilot scale. The three alkaline leaching steps effectively solubilized the leachable Pb. Two acid leaching steps were required to solubilize Cd, Al, and Zn. Toxic metals, Cd and Pb, were removed from the fly ash at 72 and 30%, respectively. The toxicity characteristic leaching procedure (TCLP), the synthetic precipitation leaching procedure (SPLP), and a simple test using neutral water were conducted on the treated ash in order to validate the process. The results obtained were below the norm for the TCLP and near 0.01?mg/L of Cd and Pb in solution for the other two tests. The removal efficiency during the precipitation step were 21% Cd, 99% Pb, 100% Al, and 63% Zn. The metallic residue produced at pH = 7 contained 23% Zn which is potentially recyclable in the metallurgical industry. The recirculation of treated leachates reduced water consumption for the decontamination process by 60%.     

Treatment of Arsenic-Contaminated Soils. II: Treatability Study and Remediation

Treatment of sandy soils contaminated with arsenic was investigated at a bench scale and carried through to remediation in the field. The initial treatability study looked at many combinations of cement binders and reagents. Salts of iron, barium, manganese, and magnesium were generally effective at reducing arsenic leachability. The most consistently low potential for leaching [toxicity characteristic leaching procedure (TCLP) and a modified version of the American Nuclear Society's ANS16.1] was observed when the soils were treated with a mixture of Type I portland cement and ferrous sulfate. For instance, the average of arsenic concentrations in TCLP leachates in many treated soil samples from four sites was 0.26 mg∕L. Better protection against leaching was observed when the soil was pretreated with FeSO4?7H2O, then with portland cement. In addition to chemical containment, the mixture should prevent ground-water leaching by physical entrapment, because the permeabilities of the treated soils were in the range of 10?9–10?10 m∕s. Scanning electron microscope micrographs showed a dense mass with minimal void space, and a combination of X-ray diffraction, thermal analysis, and solid-state nuclear magnetic resonance (NMR) spectroscopy indicated the formation of a normal hydrated cement matrix, with some excess ettringite being present due to the extra sulfate being added to the formulation. Results from the bench-scale treatability study were reproduced very faithfully in the field, with permeabilities and compressive strengths being similar to those observed in the laboratory and TCLP leachability being even lower than predicted by the laboratory study.     

外加剂对水泥固化铁矾渣性能的影响

在硅酸盐水泥熟料中加入铁矾渣,制备成胶凝材料.分别以粉煤灰沸石、硫化钠和粉煤灰为外加剂,研究其对水泥固化体强度和浸出毒性的影响.在胶凝材料中铁矾渣加入量为60%时,加入沸石、硫化钠为稳定剂,均可提高重金属离子的稳定性,不同固化体的浸出毒性值均低于国家标准.在胶凝材料中加入粉煤灰,粉煤灰掺量增加,固化体强度下降,不同固化体的浸出毒性值也均低于国家标准.     

PCC Airfield Pavement Response during Thaw-Weakening Periods

A field study was performed at two regional airports in Wisconsin during spring thaw to determine its effects on portland cement concrete (PCC) airport pavements. This study was part of a research program to model the performance of airfield pavements for the Federal Aviation Administration. Subsurface temperature and falling weight deflection measurements of the pavement structures were taken at both airports and used to calculate the frost penetration depths, the changes in bearing capacity, and the joint and load transfer efficiencies. This paper summarizes the findings of this study and includes several relationships between various engineering properties of the subsurface layers below the PCC layer, along with a procedure for evaluating pavement performance using falling weight deflection data for PCC pavements during spring thaw.     

Bench-Scale Evaluation of Chemically Bonded Phosphate Ceramic Technology to Stabilize Mercury Waste Mixtures

This bench-scale study was conducted to evaluate the stabilization of mercury (Hg) and mercuric chloride-containing surrogate test materials by the chemically bonded phosphate ceramics technology. This study was performed as part of a U.S. EPA program to evaluate treatment and disposal alternatives to the current land disposal restriction (LDR) treatment standards for mercury. The stabilized materials were subjected to a suite of leaching tests: one test characterized the solubility and release behavior of mercury as a function of pH between the pH values of 2 and 12; the second test used the toxicity characteristic leaching procedure (TCLP); and the third leaching test used the TCLP “cage” modification. TCLP results showed that leachability of Hg decreased by approximately two orders of magnitude and a maximum of five orders of magnitude. The three leachability test methods produced similar amounts of leached mercury, but the test that studied mercury solubility as a function of pH released slightly higher levels (at pH 2) compared to the TCLP methods. On comparing the results obtained with the standard TCLP and the TCLP cage modification, we learned that the leachates from stabilized wastes containing 50 wt?% loading of elemental Hg and HgCl2 were within the LDR requirements. However, wastes containing higher loadings (i.e., 70 wt?% loading of Hg and HgCl2) had leachate concentrations exceeding the 0.2 mg/L treatment standard and therefore would not meet the Resource Conservation and Recovery Act disposal requirements.     

Inhibition of interleukin-1beta-converting enzyme in human hematopoietic progenitor cells results in blockade of cytokine-mediated apoptosis and expansion of their proliferative potential

This article describes the stabilization/solidification (S/S) of a steel industry waste, using a common type-F fly ash from a coal power station as the main binder. The waste, which contains hazardous levels of metals, may be stabilized by a conventional S/S to achieve permissible Pb, Cd, and Zn concentrations in the Toxicity Characteristic Leaching Procedure (TCLP) leachates of S/S solids. On the other hand, the stabilization of Cr(VI), also present in the waste, requires a reducing pretreatment stage with ferrous sulfate to attain TCLP leachates within limits. A bibliographic study on the stabilization of Cr(VI)-containing wastes is included in the paper, along with a discussion on the lowest Cr concentration in TCLP and aqueous (DIN) leachates.     

Finite Element Analysis of Concrete Pavements Over Culverts

Accelerated distress of Portland cement concrete pavements (PCCP) over structures such as culverts, pipes, and tunnels beneath roadways is a common occurrence. In this article, finite element analysis is employed to analyze the response of concrete pavements over such structures. The factors that influence the overlying pavement slabs include: (1) cover depth, (2) pavement slab thickness and length, (3) cement concrete elastic modulus, (4) foundation modulus, and (5) backfill soil modulus. The tensile stresses at the bottom and top of the slab induced by wheel loads are predicted. In the traditional pavement design only the tensile stress at the bottom of the slab is considered to be significant. However, this study shows that the tensile stress at the top surface of pavement slabs over culverts may also cause the concrete pavements to fail. A laboratory model was employed to study the mechanical characteristics of Portland cement concrete pavement slabs over culverts and to verify the theoretical analysis.     

Determination of Optimum Ingredients for Phosphogypsum Composite Stability under Marine Conditions-Response Surface Analysis with Process Variables

The construction of mixture designs and the methods of response surface analysis of mixture data are discussed and applied for determining the optimum ingredients for stabilized phosphogypsum (PG) composites conducive to marine application. Of particular importance is the ability of the composites to maintain physical integrity when submerged. Therefore, potential indicators for the survivability of the stabilized PG composites were also screened. The triangular coordinate system was used to present the three ingredient components of the PG composites as well as their dependent variables. The augmented simplex centroid design with pseudocomponents was used in determining mixture ingredient composition. A quadratic model with two process variables was used to analyze the experimental results and predict the optimum ingredient composition. The model predicts that a series of PG: class C fly ash:portland type II cement ingredients, such as 62%:35%:3% PG:class C fly ash:portland type II cement and 65%:31%:4% PG:class C fly ash:portland type II cement composites with class C fly ash content (30.7–36.6%) and portland type II cement content (2.7–4.2%), can survive in marine environments for more than two years. The indicator screening for the survivability of the stabilized PG composites in the marine environment showed that the minimum wet leached surface hardness, minimum wet control surface hardness, and maximum effective diffusion coefficient may serve as indicators.     

TCLP Heavy Metal Leaching of Personal Computer Components

Electronic waste (E-waste), including all obsolete electronic products, has become the fastest growing component in the solid waste stream. Personal computers (PCs)—the most significant component in E-waste stream—were studied for their potential leaching toxicity of contaminants. All the components in a PC that are composed of, or contain printed wire boards (PWBs) including the motherboard, various expansion cards, disk drives, and power supply unit were tested by the toxicity characteristic leaching procedure (TCLP). The total contents of eight heavy metals including arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver in the PWBs and their TCLP leaching from the PWBs were examined. Among these eight heavy metals lead was found to be the predominant element that causes the toxicity characteristic of the PC components. The lead concentrations in the TCLP extracts of the vast majority of the PWBs ranged from 150 to 500?mg/L, which are 30–100 times the regulatory level of 5?mg/L for classifying a waste as hazardous. The motherboard in a PC contributed 50–80% of the total lead that could leach out from all the PWBs in the PC under the TCLP test conditions. The contents of barium and silver were found to be high in some components, but they were not leachable under the TCLP test conditions. The contents of other five elements in all the PC components were hardly detectable. They would not have the potential to cause toxicity characteristic leaching concern.     

Assessment of Fossil Fuel Fly Ash Formulations in the Immobilization of Hazardous Wastes

In this work, a simple and inexpensive method is introduced for the immobilization of the hazardous elements Cd, Pb, and Fe from their aqueous solutions in compressed fossil fuel fly ash formulations, as candidates for waste forms. The molded formulations were prepared by initially mixing the hazardous waste solutions with the fossil fuel fly ash material at a constant ratio (17%). Then the resulting pastes were pressed at the appropriate pressure using a manual hydraulic press. The compressed formulations revealed good water resistance, compression strength, and radiation resistance. Leachability investigations of the molded matrices were performed in terms of the accelerated leach test, the toxicity characteristic leaching procedure (TCLP), and long-term leach tests. The TCLP results obtained for Cd and Pb were well below their TCLP limits. On the other hand, the accelerated and long-term leach tests showed a similar behavior. The properties of the compressed formulations revealed their high performance as an alternative for waste forms as indicated by their durability, compression strength, and leachability. The low leachability of Cd, Pb, and Fe from the compressed fly ash formulations could be attributed to a dual mechanism of microencapsulation and/or chemical fixation.     

利用固体废弃物生产复合硅酸盐水泥的试验

为了最大限度地利用包钢高炉矿渣微粉和粉煤灰,尽可能地减少熟料用量来配制325复合硅酸盐水泥,对复合水泥的配合比进行试验研究,得出当水渣的掺量小于37%,采用石膏、熟料、水渣、粉煤灰4种原料一起混磨配制复合水泥的各项指标均能达到325复合水泥的标准要求。     

Effects of Weathering on Treatment of Lead Contaminated Soils

Treatment of lead-contaminated material focuses on the reduction of leached lead concentrations in laboratory leaching tests. There has been little study on the chemical stability of treated materials after waste disposal. To investigate the effects of weathering on several solidification/stabilization chemistries, lead-contaminated soil was treated with various agents (cement, phosphates, dithiocarbamate, calcium hydroxide, calcium carbonate, and metallic iron) and subjected to natural weathering for one year. Lead concentrations and pH values in field percolates and leachates from toxicity characteristic leaching procedure (TCLP) and water leaching tests were used to evaluate changes in the treatment effectiveness. Weathering altered the treatment chemistry of several additives—alkaline additives were neutralized, while reduced additives were oxidized. Lead concentrations in field percolates from the untreated soil were around 1.0?mg/L, and did not vary over one year of weathering time. After one year of weathering, lead concentrations in field percolates from most samples were reduced to low levels (<0.15 mg/L). Weathering also affected lead concentrations in the TCLP and water leach test leachates from the treated wastes. Treated wastes in which the alkaline additives were neutralized or reduced additives oxidized gave higher TCLP lead concentrations after weathering than before, in contrast to the decreasing lead concentrations in the field percolates. Water leaching tests on the alkaline treated wastes had lower lead concentrations after weathering than before.     

Contaminant Leaching from Stabilized/Solidified Acid Tars

This work investigates the leachability-related properties of acid tars treated with portland cement (CEM I), with the addition of high carbon fly ash (HCFA), as a novel binder for the immobilization of hydrocarbons. The leachate pH, acid neutralization capacity (ANC), and leaching of metals and sulfates from the treated acid tars were investigated. The effect of acid tar type, CEM I:HCFA ratio, and curing time on hydrocarbon leaching was also studied using factorial design experiment. ANC results show that acid tars had detrimental effect on the formation of cement hydration products. The overall results indicate that metal was not released in high concentration from the stabilized/solidified acid tars; hence their leaching is not of great environmental concern. The amount of leached sulfates was significantly lower than untreated acid tars and was attributed to ettringite formation. Factorial analyses show that all studied factors significantly affected hydrocarbon leaching. HCFA addition resulted in reduction in hydrocarbon leaching but led to an increase in sulfate leaching. This work shows that HCFA improved the immobilization of hydrocarbons and may represent an inexpensive binder for stabilization/solidification of wastes containing organic contaminants.     

垃圾焚烧飞灰预处理后水泥固化实验研究

为实现焚烧飞灰的无害化和资源化,采用对飞灰进行预处理后再与水泥混合固化的方法来处理飞灰,并比较了不同方式的处理效果:(1)用去离子水润湿飞灰再厌氧堆放24h后用水泥固化;(2)用绿矾溶液处理后再用水泥固化;(3)飞灰直接与水泥混合固化。研究3种方式所得水泥固化砌块试件强度的发展和控制重金属浸出的效果与直接固化物的对比,研究结果表明:在飞灰与水泥的质量比相同的条件下,采用先用绿矾处理飞灰再进行固化的处理方式,不但稳定重金属的效果好,而且试件强度最高,有望加以应用。     

Dispersion Modeling of Leachates from Thermal Power Plants

Ground and surface water contamination due to leaching of trace elements from ash ponds is a major environmental challenge for thermal power plants. Leaching of trace elements from the ash ponds indicated significant concentration of nine trace elements (Na, K, Mg, Ca, Fe, Pb, Mn, Cu, and Zn) in the leachates of various thermal power plants. The empirical models developed for the prediction of various trace elements i.e., Mn, Cu, Fe, Zn, and Pb, followed first-order reaction rate kinetics. The empirical models derived from the laboratory scale models were subsequently modified to account for the changes in the chemistry, mineralogy, and morphology of fly ash with respect to time which correlated well with the real field data with regression coefficients varying from 0.93 to 0.98. The modified empirical models predicted concentrations of the trace elements within ±3% of the observed values for four thermal power plants with standard deviation varying from 0.001 to 0.032.     

不同胶凝材料对氰化废渣的固化性能研究

采用胶凝材料固化技术,以不同类型胶凝材料为固化剂,对氰化废渣进行固化处理。结果表明：与硅酸盐水泥（PC）、铝酸盐水泥（AC）和硫铝酸盐水泥（SAC）相比,改性硫氧镁水泥（MOC）固化剂所得固化体的强度性能最优;固化体中CN-的浸出率大小顺序为RAC＞RSAC＞RPC＞RMOC,固化体中CN-的累积浸出分数AC＞SAC＞PC＞MOC;在MOC固化体系中,部分氰化废渣还参与了胶结反应,一方面促进了强度的增长,另一方面阻碍了CN-的浸出。     

Autoclaved Aerated Concrete Produced with Low NOx Burner∕Selective Catalytic Reduction Fly Ash

Electric utility coal combustion processes employing low NOx burner and high-dust selective catalytic reduction (SCR) emission control technologies produce fly ash that is high in carbon and ammonium salt content. Such ash is considered undesirable for use as admixture in standard concrete because of its decreased compressive strength and ammonia odor. This research investigates the use of low NOx burner∕SCR fly ash for production of autoclaved aerated concrete (AAC). For this study, samples were obtained from the Orlando Utility Commission's Stanton Power Generation Plant Unit 2, which contained 6% carbon and 28 mg of ammonium ion∕kg fly ash. A number of AAC recipes were developed with this ash, producing blocks with compressive strength values ranging from 2.268 to 4.435 kPa and densities ranging from 560 to 812 kg∕m3. During block production, carbon particles in the ash exhibited hydrophobic properties and separated from water at the AAC slurry∕gas bubbles boundary that is produced in the rising cake. Separated carbon was unable to physically interfere with calcium silica hydrate gel formation occurring in the slurry. In addition, the alkaline environment inside the reactive AAC slurry was sufficiently high to cause the release of ammonia gas. Consequently, ammonia odor was not observed during the later setting of an undisturbed block or during curing stages of the finished block. The toxicity characteristic leaching procedure and synthetic precipitation leaching procedure were found to be below the appropriate toxicity thresholds. In general, toxicity characteristic leaching procedure concentrations were higher than synthetic precipitation leaching procedure concentrations for all samples and all analytes (As, Ba, B, Cd, Cr, Ni, and Pb). It is concluded that the high carbon, ammonia bearing fly ash from the Stanton Unit 2 Low NOx burner∕SCR pulverized coal combustion process is a suitable source of siliceous material for the production of AAC prototype block, from physical, environmental, and aesthetic perspectives.     

Performance and Leaching Assessment of Flowable Slurry

This project was conducted to evaluate the performance and leaching of controlled low strength materials (CLSM) incorporating fly ash and foundry sand. Two different CLSM (or flowable slurry) reference mixtures (equivalent to available production CLSM mixtures) were proportioned for unconfined compressive strength levels in the range of 0.3–0.7 MPa (50–100 psi), at 28 days, using two sources of ASTM Class F fly ash. For each reference mixture, other mixtures were proportioned using two sources of foundry sand (molten metal-casting mold sand) as a replacement for fly ash in the range of 30–85%. The ingredients of the slurry mixtures—fly ash, clean foundry sand, and used foundry sand—were tested for their physical and chemical properties and their leachate characteristics. Portland cement used as the primary binder was also tested for its properties. All CLSM mixtures made with and without foundry sand were evaluated for settlement, setting and hardening characteristics, compressive strength, permeability, and leachate characteristics. The leachate results of these CLSM-making materials were below the enforcement standards (ES) of the Wisconsin Department of Natural Resources (WDNR) ground-water quality standards (GWQS). They also met practically all the parameters of the drinking water standards. A number of CLSM mixtures incorporating fly ash and foundry sand are recommended for construction applications.     

蒸养混凝土掺粉煤灰的试验研究

本文通过正交试验,以工业废渣-粉煤灰代替部分水泥研制蒸养粉煤灰砼.结果给出了常用的不同强度等级蒸养砼的粉煤灰适宜掺量,并在实践中得到应用.该成果对于综合利用工业废渣和保护环境具有十分重要的意义.