This study determined the polychlorinated dibenzo-p-dioxins/ dibenzo- furans (PCDD/Fs) and 22 metals contents in ash in the super heater (SH), economizer (EC), semi-dryer absorber (SDA), fabric filter (FF), fly ash pit (FAP) and bottom residue (BR) in a municipal solid waste incinerator (KTMSWI). Experimental results showed that average PCDD/FS contents in ash samples from the SH, EC, SDA, FF, FAP and BR were 0.102, 0.788, 0.210, 1.95, 2.04 and 0.0218 ng I-TEQ /g, respectively. PCDD/Fs content was very low in the SH and BR due to high temperatures (around 461¢XC in the SH and 914¢XC in combustion chamber). Conversely, total PCDD/Fs content was significantly high in ash samples from the EC (around 340¢XC), mainly because the temperature is within the favorable range of 250-400¢XC for PCDD/FS formation due to de nova reformation mechanisms. Although the SDA operated at 245¢XC, the PCDD/FS content decreased very significantly, mainly because the temperature was relatively low and because calcium carbonate was introduced into flue gases to dechlorinate and dilute chlorine-containing species. PCDD/Fs were captured by the active carbon in the FF. Furthermore, the duration that fly ash remained in the FF was longer than that for other incinerator units, and thus causing an increasing trend of PCDD/Fs level downstream (except the SDA). Total PCDD/Fs emission factors (£gg /ton-waste; £gg I-TEQ /ton-waste) in ash samples from different units were: SH (42.3; 0.846), EC (326; 6.12 ), SDA (58.1; 1.10), FF (1540; 61.3), FAP (2950; 107) and BR (537; 4.31). Most PCDD/Fs in ash were contributed by the FF (about 56%), and the generation of PCDD/Fs in ash was significant (about 35%) during the transfer process from different units to the FAP. A strong and positive correlation in a logarithmic form existed between PCDD/Fs and chlorine (Cl-) contents in ash. The results showed that principal metals in the incinerator ash were Al, Fe, Zn, Ba, Pb and Cu. On average, these six metals accounted for 96.6%, 96.8%, 97.0%, 94.2% and 96.7% of the total metals in SH, EC, SDA, FF and BR ash, respectively. The emission factors of individual metals from different units were obtained. Volatile metals, such as Cd, Sn, Sb, Hg and Pb, were mostly in fly ash, while lithophilic metals, such as Al, Fe, Ti, V, Cu, Mn, Fe, Co, Ni, Cu, Sr, Mo, Ag, Ba and Cr+6 were mainly in bottom ash. Distribution ratios for total metals in SH, EC, SDA, FF and BR ash were 4.87%, 4.26%, 2.89%, 8.17% and 79.81%, respectively. That is, about 20.2% of total metals were in fly ash and most metals (about 79.8%) were in bottom ash. The Pb content in EC ash and Hg content in FF ash were between alarm contents and maximum legal limits, while Cd and Pb contents in FF ash exceeded the maximum legal limits. The existing transportation system for transferring fly ash from different units to a fly ash pit should be modified for recycling the valuable metals. Ash with less than the alarm content for metals content, such as ash from the SH, SDA and BR, can be reused. Ash with metals exceeding the alarm contents, such as ash from the EC and FF, should be collected and transferred to a different fly ash pit for further treatment, such as metal recycling.

Most concrete produced today utilizes pozzolans or supplementary cementitious materials (SCMs) to promote better long term durability and resistance to deleterious chemical reactions. While other pozzolans and SCMs are available and provide many of the same benefits, Class F fly ash has become the industry standard for producing quality, durable concrete because of its low cost and wide-spread availability. With impending environmental and safety regulations threatening the availability and quality of Class F fly ash, it is becoming increasing important to find viable alternatives. This research aims to find natural, lightly processed, alternatives to fly ash that perform similarly to Class F fly ash with regards to pozzolanic reactivity and provide comparable compressive strength, workability, drying shrinkage, thermal expansion properties and resistance to alkali-silica reaction, sulfate attack, and chloride ion penetration. Eight fly ash alternatives from the US were tested for compatibility with the governing standard for pozzolans used in portland cement concrete and various fresh and hardened mortar and concrete properties. The results of this research indicate that six materials meet the requirements for natural pozzolans set by the American Society for Testing and Materials and many are comparable to Class F fly ash in durability tests. The primary concern when using these materials in concrete is the increase in water demand. The spherical particle shape of fly ash provides improved workability even at relatively low water-to-cement ratios; however, all of the materials tested for this research required grinding to achieve the appropriate particle size, resulting in an angular and rough surface area that requires more lubrication to achieve a workable consistency. So long as an appropriate water reducing admixture is used, six of the eight materials tested in this study are appropriate and beneficial for use in portland cement concrete. / text

Ash-flow tuff (ignimbrite) is a general term indicating consolidated deposits of volcanic ash flow; a flow of a mixture of gas and pyroclastic materials as products of explosive volcano eruptions (Smith, 1960). Two different ash-flow tuffs are studied in this research: 1. Topopah Spring Tuff at Yucca Mountain, Nevada and 2. the Bandelier Tuff at Pajarito Plateau, New Mexico. Various dynamic test parameters (e.g. confining pressure, shearing strain, etc) were studied with two existing devices: (1) the combined resonant column and torsional shear (RCTS) device, and (2) the free-free, unconfined, resonant column (URC) device. The effects of these parameters are evaluated for two different types of ash-flow tuffs. In addition, a Large Resonant Column (LgRC) device was developed and used to test the some tuffs from Yucca Mountain at larger strain amplitudes than possible with the RCTS and URC devices. Relationships between the linear and nonlinear dynamic properties and lithostratigraphic features were further investigated. Finally, potential problems related to sample disturbance and specimen size are considered based on comparisons of small-strain shear wave velocity (VS) values measured in the laboratory and in the field. / text

A three-dimensional stochastic numerical inverse model has been developed for characterizing the properties of unsaturated fractured medium through analysis of singleand cross-hole pneumatic tests. Over 270 single-hole [Guzman et al., 1996] and 44 cross-hole pneumatic tests [Illman et al., 1998; Inman, 1999] were conducted in 16 shallow vertical and slanted boreholes in unsaturated fractured tuffs at the Apache Leap Research Site (ALRS), Arizona. The single-hole tests were interpreted through steady-state [Guzman et al., 1996] and transient [Illman and Neuman, 2000b] analytical methods. The cross-hole tests were interpreted by analytical type-curves [Illman and Neuman, 2000a]. I describe a geostatistical analysis of the steady-state single-hole data, and numerical inversion of transient single-hole and cross-hole data. The geostatistical analysis of single-hole steady-state data yields information about the spatial structure of air permeabilities on a nominal scale of 1 m. The numerical inverse analysis of transient pneumatic test data is based on the assumption of isothermal single-phase airflow through a locally isotropic, uniform or non-uniform continuum. The stochastic inverse model is based on the geostatistical pilot point method of parameterization [de Marsily, 1978], coupled with a maximum likelihood definition of the inverse problem [Carrera and Neuman, 1986a]. The model combines a finite-volume flow simulator, FEHM [Zyvoloski et al., 1997], an automatic mesh generator, X3D [Trease et al., 1996], a parallelized version of an automatic parameter estimator, PEST [Doherty et al., 1994], and a geostatistical code, GSTAT [Pebesma and Wesseling, 1998]. The model accounts directly for the ability of all borehole intervals to store and conduct air through the system; solves the airflow equations in their original nonlinear form accounting for the dependence of air compressibility on absolute air pressure; can, in principle, account for atmospheric pressure fluctuations at the soil surface; provides kriged estimates of spatial variations in air permeability and air-filled porosity throughout the tested fractured rock volume; and is applied simultaneously to pressure data from multiple borehole intervals as well as to multiple cross-hole tests. The latter amounts to three-dimensional stochastic imaging, or pneumatic tomography, of the rock as proposed by Neuman [1987] in connection with cross-hole hydraulic tests in fractured crystalline rocks near Oracle, Arizona. The model is run in parallel on a supercomputer using 32 processors. Numerical inversion of single-hole pneumatic tests allows interpreting multiple injection-step and recovery data simultaneously, and yields information about air permeability, air-filled porosity, and dimensionless borehole storage coefficient. Some of this cannot be accomplished with type-curves [Inman and Neuman, 2000b]. Air permeability values obtained by my inverse method agree well with those obtained by steady-state and type-curve analyses. Both stochastic inverse analysis of cross-hole data and geostatistical analysis of single-hole data, yield similar geometric mean and similar spatial pattern of air permeability. However, I observe a scale effect in both air permeability and air-filled porosity when I analyze cross-hole pressure records from individual monitoring intervals one by one, while treating the medium as being uniform; both pneumatic parameters have a geometric mean that is larger, and a variance that is smaller, than those obtained by simultaneous stochastic analysis of multiple pressure records. Overall, my analysis suggests that (a) pneumatic pressure behavior of unsaturated fractured tuffs at the ALRS can be interpreted by treating the rock as a continuum on scales ranging from meters to tens of meters; (b) this continuum is representative primarily of interconnected fractures; (c) its pneumatic properties nevertheless correlate poorly with fracture density; and (d) air permeability and air-filled porosity exhibit multiscale random variations in space.

The disposal of combustible wastes by incineration is a controversial issue that is strongly debated by both scientists and environmental activists due to the resulting emissions of noxious compounds, including (inter alia) polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), heavy metals and acid gases like sulfur dioxide. Currently available air pollution control devices are capable of effectively cleaning flue gases, and PCDD/F emissions to air from modern municipal solid waste (MSW) incinerators are low. However, the PCDD and PCDF end up in ash fractions that, in Sweden, are usually deposited in landfills. The European Union has recently set a maximum permitted total concentration of 15 µg TEQ/kg for PCDD/F species in waste. Fly ash from municipal solid waste (MSW) incineration containing PCDD/Fs at concentrations above this limit will have to be remediated to avoid disposing of them in landfills; an expensive and environmentally unfriendly option. Therefore, effective, reliable and cost-effective methods for degrading PCDD/F in fly ash are required, and a better understanding of the behavior of PCDDs and PCDFs during thermal treatment will be needed to develop them. In the studies this thesis is based upon both the formation and degradation of PCDDs and PCDFs in ashes from MSW incineration were studied. The main findings of the investigations regarding PCCD/F formation were: - The concentrations of PCDD and PCDF in fly ash increased with reductions in the temperature in the post-combustion zone. - The homologue profile in the ash changed when the temperature in the post-combustion zone changed. - The final amounts of PCDD and PCDF present were affected by their rates of both formation and degradation, and the mechanisms involved differ between PCDDs and PCDFs. The main findings from the degradation studies were: - The chemical composition of ash has a major impact on the degradation potential of PCDD and PCDF. - The presence of oxygen during thermal treatment can enhance the degradation of PCDD and PCDF. - Thermal treatment is a viable option for degrading PCDD and PCDF in ashes from MSW. - Shifts in chlorination degree occur during thermal treatment. - Rapid heat transfer into the ash is a key factor for ensuring fast degradation of PCDD and PCDF. - Degradation of other chlorinated organic compounds, e.g. PCB and HCB, also occurs during thermal treatment of ash. - Reductions in levels of PCDD and PCDF were not solely due to their desorption to the gas phase. - Differences between the behavior of 2378-substituted congeners of PCDD and PCDF and the other congeners during thermal treatment were observed. - Differences in isomer patterns of both PCDD and PCDF were observed between the ash and gas phases after thermal treatment at both 300 and 500 oC. Overall, the results show that the formation and degradation mechanisms of PCDDs differ substantially from those of PCDFs. Thus these groups of compounds should be separately considered in attempts to identify ways to reduce their concentrations.

The ever-increasing quantity of by-products generated from burning coal in the production of electricity has brought about the need for new areas of utilization. This study examined the use of FGD gypsum and fluidized bed combustion ash along with Class F fly ash in the production of low-energy, 100% by-product cement blends. The cement blends used the advantageous properties of the by-product materials to create cementing properties rather than energy intensive clinker used in ordinary portland cement. The FGD gypsum was converted to hemihydrate which rapidly hydrated to provide the cement with early strength gains, whilst the fluidized bed combustion ash reacted with the Class F fly ash to form pozzolanic cementitious phases which provided the longer-term compressive strength and possibly resistance to weathering. The rate of compressive strength gains and minimizing detrimental expansion were two properties of particular interest in the study. Chemical admixtures were used to improve the compressive strengths of the cement mortars and decrease their solubility.

Volcanic eruptions produce a range of hazards which can impact society. The most widespread of these hazards is volcanic ash fall which can impact a range of critical infrastructure. Power systems are particularly vulnerable to ash fall hazards and the resulting impacts may lead to power supply disruption. This can lead to cascading disruption of dependent systems, such as hospitals, water and wastewater treatment plants, telecommunications and emergency services. Typically, large emergency power generator sets are used to provide emergency power supply for essential services during electrical power outages. There has been little study of what impact ash fall exposure will have on generator performance. International experience suggests large generators can experience rapid performance reduction when exposed to high concentrations of suspended or falling ash due to obstruction of air filters and radiators, causing overheating of the engine and shut down of the generator system. However, it is not clear at what ash fall thresholds generators are likely to be disrupted. This research uses custom designed empirical laboratory experiments to investigate the performance of large generators subjected to a range of volcanic ash fall types and intensities, simulating both proximal and distal ash fall exposure from a range of eruptive styles. It also investigates the application of temporary external filters to minimise the ingestion of volcanic ash into generator housings. The results are used to inform recommendations on the likely impacts of ash to generators and the most effective type of mitigation, which maximises filtration whilst maintaining generator performance. Control tests recorded high particle concentrations (~0.006 mg/m3) which indicate substantial ash contamination is possible. Multiple factors were considered to determine the best mitigation measure including the lowest particle concentration, highest air speed and the ease with which the measure could be fitted. The study found material filtration to be the most effective measure; however as the quality of filtration increased, the air speed was reduced and thus so was the volume of air available to the generator engine. Therefore, the type of filtration required is dependent the ash fall intensity. The study also found that a deflection hood is an effective mitigation measure; maintaining airspeed while reducing particle concentrations within the generator. This research informs risk management strategies for critical infrastructure organisations to reduce the risk of generator disruption during volcanic ash falls.

Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 222-238).

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 174-181).

Varieties of masonry units such as burnt clay bricks, stones and concrete products are used for masonry construction. Even though these materials are durable, they are considered as unsustainable options because of the issues concerning energy, environment and conservation of natural resources. The walling materials are consumed in bulk quantities and hence large quantities of natural resources are depleted. There is a need for energy efficient and environment friendly alternative materials for masonry. Fly ash is an industrial by-product from the coal based thermal power plants which can be exploited for manufacturing of masonry units such as fly ash blocks/bricks, which are an alternative for conventional masonry units. Fly ash-Lime-Gypsum (FaL-G) bricks can be manufactured by compaction of a mixture of fly ash-lime-gypsum and water. The behaviour of FaL-G brick masonry is inadequately explored area and hence the thesis is focused on understanding the flexural behaviour of FaL-G brick masonry and bond development phenomenon at FaL-G brick-mortar interface. A brief introduction to the fly ash-based masonry units and literature review with respect to utilizing fly ash in manufacturing masonry units are presented. Characteristics of raw materials used and the procedure followed in casting of masonry units/compacts, mortar and their assemblages including testing methods have been discussed. Characteristics of FaL-G brick, mortars, FaL-G brick masonry are presented. Apart from determining the stress-strain relationships for these materials shear strength parameters of FaL-G compact, mortar and brick-mortar joint were determined. Mohr-Coulomb failure envelopes for FaL-G compact and mortar are presented. The mechanism of bond development in masonry is discussed. FaL-G brick masonry shows considerably higher bond strength when compared with the bond strength of conventional brick masonry. Results of micro-structure analysis (SEM, XRD and TGA) of the FaL-G brick-mortar interfaces confirm the formation of chemical bond in addition to mechanical interlocking of cement hydration products into brick pores. Flexural behaviour of FaL-G brick masonry wallettes in the two orthogonal directions was studied. The flexural strength, displacement profiles and load-displacement curves were determined, and moment-curvature relationships were established. Linear elastic analysis performed closely predicted the cracking flexural stress in FaL-G brick masonry. A brief introduction to the computational modelling of masonry using different approaches has been presented. Literature review with respect to simplified micro-modelling approach has been discussed. The flexural behaviour of FaL-G brick masonry panels under lateral loads was predicted using a non-linear 3D finite element analysis. The finite element model reasonably predicted the flexural behaviour of FaL-G brick masonry panels. The thesis ends with summary of research work with a note on scope for further research.