Stabilization Of Ash Research Articles

Strength Characteristics of Compacted Fly Ash Treated Expansive Soil due to Wetting-Drying Cycles Repetition

Due to high swelling-shrinkage caused by climate change, expansive soil is a significant problem in light construction, road embankments, and slope stability (wet and dry). The physical and mechanical properties of the soil are affected by repeated drying and wetting cycles, particularly changes in volume, negative pore water pressure (suction), and compressive strength. Fly ash is used to increase soil strength and reduce plasticity caused by swelling to address this issue. Because of its chemical properties, fly ash is an excellent choice for low-cost soil improvement. The purpose of this investigation is to determine the static mechanical properties of expansive soil fly ash stabilization under Proctor standard compaction conditions. Mechanical properties were investigated due to changes in soil moisture content, saturation, suction, and compressive strength caused by repeated drying and wetting cycles. The soil's suction was measured using Whatman #42 filter paper, and the soil's compressive strength was tested using a free compression test. According to the findings, the fly ash mixture altered the expansion and shrinkage behavior of expansive soils by lowering the consistency limit. At the same moisture content, the addition of 5% to 15% fly ash increases the compressive strength of the soil significantly. Compressive strength (qu) and stress-strain modulus (Ei) decreased in 1-4 cycle cycles, and after four cycles, changes in compressive strength and stress-strain modulus were very small or insignificant. The proposed method effectively reduces the loss of expansive soil strength caused by environmental changes (wetting-drying). As a result, it contributes significantly to the development of materials to reduce structural damage in expansive soils.

An Evaluation of the Physical and Chemical Stability of Dry Bottom Ash as a Concrete Light Weight Aggregate.

Compared to the bottom ash obtained by a water-cooling system (wBA), dry process bottom ash (dBA) makes hardly any unburnt carbon because of its stay time at the bottom of the boiler and contains less chloride because there is no contact with seawater. Accordingly, to identify the chemical stability of dBA as a lightweight aggregate for construction purposes, the chemical properties of dBA were evaluated through the following process of the reviewing engineering properties of a lightweight aggregate (LWA). Typically, river gravel and crushed gravel have been used as coarse aggregates due to their physical and chemical stability. The coal ash and LWA, however, have a variety of chemical compositions, and they have specific chemical properties including SO3, unburnt coal and heavy metal content. As the minimum requirement to use the coal ash and lightweight aggregate with various chemical properties for concrete aggregate, the loss on ignition, the SO3 content and the amount of chloride should be examined, and it is also necessary to examine heavy metal leaching even though it is not included in the standard specifications in Korea. Based on the results, it is believed that there are no significant physical and chemical problems using dBA as a lightweight aggregate for concrete.

Biomass ash formulations as sustainable improvers for mining soil health recovery: Linking soil properties and ecotoxicity

There is a growing need to recover degraded soils to restore their essential ecosystem services and limit damages of anthropic activities onto these systems. Safe and sustainable solutions for long-term recovery must be designed, ideally by recycling existing resources. Using ash from combustion of residual forest biomass at the pulp and paper industry is an interesting and sustainable strategy to recover mining soils. However, formulations must be found to limit the potential toxicity associated with soluble salts and chloride that ash contains. Here, we assessed the effectiveness of three field ash-based amendments for the recovery of three highly acidic soils from Portuguese abandoned mines. Three amendments were tested: an un-stabilized mixture of ash and biological sludge, granulated ash, and granulated ash mixed with composted sludge. One year after application in open field plots (in the scope of LIFE No_Waste project), soil health restoration was evaluated through (i) soil physico-chemical characterization and (ii) soil habitat functions though standardized ecotoxicological tests.This study highlights that stabilized materials provided nutrients, organic matter and alkalinity that corrected soil pH and decreased metal bioavailability, while controlling the release of soluble salts and chloride from ash. This soil improvement correlated with improved soil model organisms’ reproduction and survival. For similar amendment, the native soil properties studied (as soil native electrical conductivity) affected the level of organism response.This work provides evidence that ash stabilization, formulation and supplementation with organic matter could be sustainable strategies to restore highly degraded mining soils and to recover their ecological functions. It further highlights the importance of analyzing combined effects on soil physico-chemical properties and ecological function recovery to assess restoration strategy efficiencies in complex multi-stressor environments.

An experimental approach to microbial carbonate precipitation in improving the engineering properties of sandy soils

PurposeStabilization of weak soil can be achieved through different methods, some of which include jet column, cement stabilization and fly ash stabilization. Unfortunately, the use of the aforementioned methods of soil improvement affects the environment negatively thereby leading to environmental degradation. With the aforesaid impediment in mind, the need for devising methods of weak soil improvement becomes pertinent.MethodsBacillus sp. — a non-pathogenic organism found abundantly in soil — was investigated in this study as a potential agent of soil improvement. The usability of Bacillus sp. in soil improvement was investigated with direct shear tests and permeability tests under optimum conditions in this study.ResultTime-dependent study on the effect of the ureolytic bacteria Bacillus sp.-induced calcium carbonate precipitation shows reduction in permeability and increase in the strength of the soil under study. On exhaustion of the available nutrients in the soil, however, the strength of the soil is not negatively impacted.ConclusionMicrobially induced calcium precipitation by Bacillus sp. is effective in soil improvement as such it may serve as substitute for conventional soil stabilization techniques. The ability of the bacteria to precipitate calcium carbonate in the soil leads to reduction in the permeability and increase in the shear strength of the soil.

Sustainable Transportation, Leaching, Stabilization, and Disposal of Fly Ash Using a Mixture of Natural Surfactant and Sodium Silicate.

The present study evaluates the transportation, leaching, and stabilization ability of novel saponin extracted from the fruits of Acacia auriculiformis. To enhance the dispersing behavior of the fly ash slurry (FAS) at a lower dosage of sodium silicate, A. auriculiformis was incorporated in FAS. In addition to the rheological study, an attempt has been made to remove heavy metals through leaching for the safe disposal of FAS. Critical factors such as the fly ash (FA) concentration, saponin dosage, surface tension, ζ potential, temperature, and combination of saponin and sodium silicate, affecting the rheology of FAS, were extensively studied. The addition of a nonionic natural surfactant saponin has been proved to enhance the wettability of FA particles by decreasing the surface tension of FAS. The obtained rheology results were compared with the stabilization yield of the previously reported commercial surfactant cetyltrimethylammonium bromide. The incorporation of sodium silicate in the FAS system was found to be phenomenal in the settling and stabilization of FAS, thereby developing reaction products like sodium aluminum silicate (N-A-S). This facilitates the sustainable disposal of FA preventing air pollution after dewatering. The formation of N-A-S was further supported by scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies.

​Nutritional Quality and Storage Stability of Processed Biofortified Pearl Millet Varieties

Background: Poor shelf life and nutrient availability is a limiting factor in adoption of pearl millet. It can be addressed by indigenous processing like malting, blanching and roasting. This study delineates outcome of processing on protein, fat, ash, nutrient digestibility and storage stability of biofortified pearl millet varieties. Methods: Unprocessed, malted, blanched and roasted millet grains’ flour was analysed and compared for protein, fat, ash and nutrient digestibility. To assess storage stability, flours were stored at 25 ± 1°C at 40 ± 2% RH and fat acidity and per oxide values analysed at an interval of 10 days. Result: It was found that the protein and fat contents of flours decreased on processing. Blanched and roasted flours possessed more ash compared to malted flour. The amount of fat and ash in HC-20 was significantly more than that of Dhanshakti variety. Digestibilities of protein and starch, of processed flours improved significantly and maximum improvement was exhibited by malted flours followed by roasted and blanched. The fat acidity and peroxide value of stored flours increased and this increase was more in unprocessed compared to processed flours. The findings of this study can be useful for augmenting the nutritional and keeping quality of pearl millet.

Simulation of the thermal degradation and curing kinetics of fly ash reinforced diglycidyl ether bisphenol A composite

Thermogravimetric Analysis (TGA) is concluding expanding applicability in determination of the thermal stability and degradation nature of materials. The present study investigates the thermal degradation behavior and the kinetics of degradation of epoxy mixed with varying percentages of 0, 2.5, 5, and 7.5 ​wt% fly ash. Thermal stability and degradation behavior of fly ash modified epoxy cast were determined by thermogravimetric analysis. The kinetic parameters of the EF composites were calculated by using Coats–Redfern, Broido and Horowitz–Metzger models under best-fit analysis and further proved by linear regression analysis. The kinetics of thermal degradation was calculated from data scanned at a heating rate of 10 ​°C/min. The obtained results reveal that kinetic parameters and thermal behavior of EF composites were improved with the reinforcement of fly ash. The cure kinetics of the varying content of fly ash reinforced epoxy cast were also studied by using a nonisothermal differential scanning calorimetric (DSC) technique at four different heating rates 5 ​°C/min, 10 ​°C/min, 15 ​°C/min and 20 ​°C/min. The curing kinetics of the EF composite was derived from the nonisothermal differential scanning calorimetry (DSC) data with the three Kissinger, Ozawa, and Flynn–Wall–Ozawa models, respectively.

EFFECTS OF LIME AND WOOD ASH ON GEOTECHNICAL PROPERTIES OF LATERITE

This study is on the effects of lime and wood ash on the geotechnical properties of laterite. Classification tests including Atterberg limit and grain-size analysis were performed on the sample in the natural state and when stabilized with lime and wood ash. Unsoaked CBR tests and compaction tests were carried out to establish the analysis parameters needed for the study. Lime and wood ash were added in 2, 4, 6, 8, and 10% by weight of sample. The natural soil sample had a maximum dry density (MDD) of 1665.0 kgm-3 and optimum moisture content (OMC) of 18.8%, the natural soil has CBR of 25.6%. Controls were made 0% lime and wood ash and another at 2% each of lime and wood ash. The optimum moisture percentage of stabilization was obtained at 6% for both stabilizers while results also indicated that 4% lime sample had the lowest optimum moisture content and 4% wood ash had the lowest maximum dry density. The value of CBR at 2% lime and wood ash was found to be lower than stabilizations at 4% lime and wood ash. The results revealed that the CBR values of the soil sample were generally better when stabilized with lime, while MDD of the sample was better with wood ash stabilization.

Emission Characteristics and Toxicity Effects of Halogenated Polycyclic Aromatic Hydrocarbons from Coal-Fired and Waste Incineration Power Plants

Coal-fired power plants (CFPPs) and waste incineration power plants (WIPPs) represent a large portion of polycyclic aromatic hydrocarbons (PAHs) sources in the environment, among which halogenated PAHs (HPAHs) are more toxic to the human body compared with their corresponding parent PAHs. In the current work, we investigated the occurrence, formation mechanism, and toxicity effects of HPAHs in the coal and waste combustion products from three CFPPs and one WIPP. The results indicate that the contents of chlorinated PAHs (Cl-PAHs) in the fly ash from the CFPPs and WIPP were 1.06-1.67 ng·g-1 and 2.76 ng·g-1, respectively, and the contents of brominated PAHs (Br-PAHs) in the fly ash from the CFPPs and WIPP were 26.4-44.2 ng·g-1 and 6.31 ng·g-1, respectively. The HPAH contents in the fly ash from the WIPP were significantly higher than those from the CFPPs primarily due to the abundant plastics in the domestic waste, represented by polyvinyl chloride, resulting in the formation of Cl-PAHs during combustion. The HPAH contents in the fly ash from the pulverized coal-fired (PC) boiler were significantly higher than those from the circulating fluidized bed (CFB) boiler mostly due to the higher combustion temperature operated in the PC boiler. The HPAHs in the fly ash from coal combustion were predominantly 7-BrBaA and 9-ClPhe, and those from domestic combustion were predominantly 9-BrPhe and 2-ClAnt. In addition, the contents of 7-BrBaA and 9,10-Br2 Ant in the coal combustion fly ash were significantly higher than those in domestic waste combustion fly ash, whereas 2-BrFle exhibited a contrasting profile. The content of Br-PAHs in the fly ash treated by semi-dry deacidification was twice that in dust removal fly ash but significantly increased in the chelating agent stabilization fly ash. The Pearson correlation analysis indicated the the formation mechanism of Cl-PAHs and Br-PAHs were the same but a secondary formation of HPAHs during the chelating agent stabilization of the fly ash was deduced. The TEQ values of the HPAHs in the fly ash (8.87×10-3-15.0×10-3 ng·g-1) from the WIPP were similar to those in the fly ash from the CFPPs (10.0×10-3 ng·g-1), which were significantly reduced in the fly ash treated by semi-dry deacidification due to the removal of 7-BrBaA. Moreover, the TEQ values of the HPAHs in the fly ash increased 5.4 times after the chelating agent stabilization. The ecological risk should be considered for the CFPP fly ash due to their massive amount of discharge and high TEQ values.

Immobilization and stabilization of volcanic ash in soil aggregates in semiarid meadows of Northern Patagonia

Although volcanism may be perceived by the society as a phenomenon with mostly negative consequences, this is not always the case especially for natural systems. There is a limited knowledge on how the deposited pristine ash becomes immobilized and stabilized in the soil after the volcanic event. Here, we studied processes of soil aggregates formation in the buried ash layer in an early stage of the succession as well as the influence of the biological legacy (previous land management history) on these processes after the 2011 volcanic event of the Puyehue–Cordón Caulle Volcanic Complex. 5.5 years after the eruption we collected soil cores to a 10 cm depth in wet and mesic meadows with good and poor grassland conditions induced by light and heavy grazing intensity, respectively, in the East semiarid region of North Patagonia, Argentina. The ash layer was observed down to 5 cm from the soil surface, clearly differentiating a newly developed soil layer formed after the volcanic event. Accordingly, the top 5 cm were examined for the distribution of different size fractions of water-stable soil aggregates and their associated organic carbon (C) and total nitrogen (N) contents. We detected signs of physical and physicochemical changes in respect to the pristine ash collected at these sites in 2011. Soil neoformation processes were detected through the presence of large (4%) and small (21%) macroaggregates, although microaggregates (~45%) and silt + clay fractions (~29%) dominated the soil mass (ash-soil matrix: 0–5 cm depth). C and N contents decreased in a sequence: large macroaggregates ≥ small macroaggregates > microaggregates ≥ silt + clay, highlighting the importance of soil organic matter in the formation of larger-size aggregates and their quality (C and N contents). Biological legacy influenced soil aggregate formation and their quality, as reflected by a higher mass of small macroaggregates and a lower mass of microaggregates (only in mesic meadows) and by higher C and N contents under good grassland conditions. The seasonal hydrological conditions of meadow soils (i.e., soil water content, wetting and drying cycles) via effects on biological and physical processes likely resulted in a reduced aggregation in wet meadows. We noticed an incipient but present soil aggregation processes in these semiarid wetlands translated in the immobilization and stabilization of the buried ashes in the soil. The total C content in the new 0–5 cm soil layer increased at a rate of 1.0 Mg C ha−1 yr−1, on average. This indicates a functional recovery of the ecosystem along with a substantial CO2 mitigation potential in the ashes stabilized with soil organic matter, which might partially counterbalance CO2 emitted during the eruption.

Optimization of fly ash based soil stabilization using secondary admixtures for sustainable road construction

Fly ash, despite being a suitable cement substitute, is only utilized at a low rate in engineering applications, hence not contributing to its current waste mitigation efforts. Under a five-part comprehensive testing program, this study investigated the efficiency of fly ash stabilized soil when combined with secondary additives (enzymes and lime). Part one explored the suitable fly ash and enzyme dosages. Parts two and three assessed the effect of time and lime on enzymatic fly ash stabilized soil, respectively. Part four unveiled the mechanism of stabilization by secondary additives. Part five analyzed the significance and benefits of these additives in pavement stabilization. The study found that the efficiency of fly ash stabilization can be significantly improved when combined with 1% of 1:500 diluted enzyme. Addition of 2% lime has also supplemented with improved load-bearing capacity. Benefits of this research include enhanced fly ash waste mitigation, saving natural resources used as wearing course materials, and development of an alternative solution for pavement stabilization.

Evaluation of Lime-Cement-Fly Ash Stabilization in Curtailing the Dispersive Potential of Australian Sodic Soil

Evaluation of Lime-Cement-Fly Ash Stabilization in Curtailing the Dispersive Potential of Australian Sodic Soil

Stabilization of Municipal Solid Waste Fly Ash, Obtained by Co-Combustion with Sewage Sludge, Mixed with Bottom Ash Derived by the Same Plant

This study presents an innovative stabilization method of fly ash derived from co-combustion of municipal solid waste and sewage sludge. Bottom ash, obtained from the same process, is used as a stabilizing agent. The stabilization method involved the use of two other components—flue gas desulfurization residues and coal fly ash. Leaching tests were performed on stabilized samples, aged in a laboratory at different times. The results reveal the reduction of the concentrations of heavy metals, particularly Zn and Pb about two orders of magnitude lower with respect to fly ash. The immobilization of heavy metals on the solid material mainly depends on three factors—the amount of used ash, the concentrations of Zn and Pb in as-received fly ash and the pH of the solution of the final materials. The inert powder, obtained after the stabilization, is a new eco-material, that is promising to be used as filler in new sustainable composite materials.

The Potential Use of Clay-Fly Ash Geopolymer in the Design of Active-Passive Liners: A Review

AbstractBecause long-term leachate migration through a hydraulic barrier is inevitable, compacted clay and cementitious liners are commonly used as ‘active-passive’ liners to attenuate percolated leachate. The scarcity of suitable clay and because of the CO2emitted during the production of Portland cement as well as drying shrinkage, flow rate due to consolidation, limited attenuation capacity, and chemical instability may mean that these are not the best choices of materials to use for this purpose. An environmentally friendly method to improve the properties of local clay and provision for a long-term physical and chemical containment are essential. Geopolymers can be environmentally friendly substitutes for Portland cement to improve soil properties, not just because of the reduced carbon dioxide emission, but also because of its superior physical and chemical properties, as well as significant early strength, reduced shrinkage, freeze-thaw resistance, long-term durability, and attenuation capacity. According to previous studies, class-F fly ash-based geopolymers activated with NaOH exhibit superior attenuation capacity and long-term durability. The presence of silica, alumina, and iron oxides and the lack of calcium oxide play pivotal roles in the acceptable attenuation capacity and chemical stability of class-F fly ash. Accordingly, a clay-fly ash geopolymer may also work as a sustainable liner with appropriate physical and chemical performance. Clay can also participate in the geopolymerization process as an alumino-silicate precursor. All components of clay-fly ash geopolymers possess acceptable adsorption capacity. The type and percentage of the constituent raw materials control the attenuation capacity and physical properties of final products, however. The porosity and conductivity of typical geopolymers are related to the activator type and concentration, water content, and curing condition. Furthermore, the properties of liner materials can be adjusted with respect to the target contaminants. The present study aimed to present a comprehensive review of the relevant studies to highlight the properties required.

An Accelerated, On-Site Bottom Ash Aging and Washing Treatment and Its Effect for Long-Term Leaching

Ash stabilization is important for realizing safe and reliable disposal sites and promoting MSW bottom ash (BA) recycling. An on-site technology that uses a modified detachable container and stabilizes BA with sprinkling water (watering) and flowing 100% CO2 through the ash layer (carbonation) was developed. Experimental verification of this technology was undertaken (Treatment condition: L/S = 0.6–0.7, 24 h duration, 2.2 t/time). Two treatment methods were investigated using unsieved BA: (1) sprinkling water only (2) sprinkling water combined with carbonation. In the verification test, the chlorine (Cl) content of the BA decreased by up to 72% after the watering treatment. The BA treated by watering and carbonation showed reduction in solubility of Pb by up to 90%. An exothermic reaction due to carbonation was also confirmed. In the lysimeter test (column size: o104 × 400 mmH) conducted to evaluate the long-term leaching performance of the BA treated to promote stabilization, leachate data was acquired over 400 days from both treated and untreated BA. It was confirmed that the leachate of BA treated with watering showed lower EC, cumulative Cl and TOC than untreated BA. The leachate of BA treated with watering and carbonation showed lower pH, Pb concentration and higher cumulative Cl, Ca after 400 days than the one treated with watering alone.

Simulating the impact of heavy rain on leaching behavior of municipal solid waste incineration bottom ash (MSWI BA) in semi-aerobic landfill

In Japan, approximately 64% of municipal solid waste incineration bottom ash (MSWI BA) is landfilled. Because landfills in Japan are operated without capping, the landfill body is directly exposed to climatic events. Increased frequency of heavy rain is predicted to affect the chemical stabilization of bottom ash (BA) landfill, as rainwater seeps into and interacts with landfill components. This study examined the effect of normal rainfall (15 mm/h) and heavy rainfall (25, 50, and 100 mm/h) events on the leaching behavior of ions (Cl−, Na+, K+, and Ca2+) and total organic carbon (TOC) in BA (<10 mm particle size) using a percolation column test. The results showed the decreased leaching of leachate components after heavy rainfall and increased leaching after normal rainfall. In addition, the pH fluctuated around 11–12 after heavy rainfall but decreased to 7–9 after normal rainfall. The carbonation of the leachate and BA layers appears to be the main factor in lowering the pH value. Changes in the TOC and ion concentrations can be explained by dissolution, dilution, and the contact time of water molecules and BA particles. The data showed that the cumulative TOC and ion release rates were not affected by heavy rain intensities. The release rate of leachate components during normal rainfall was higher than that in heavy rainfall in all the scenarios. Significant correlations were found between the leachate components (TOC, Cl−, Na+, K+, and Ca2+ concentrations) and rainfall variation.

Review of the Reuse Possibilities Concerning Ash Residues from Thermal Process in a Medium-Sized Urban System in Northern Italy

This review paper reports a detailed characterization of some combustion or incineration residues and by-products produced in a medium-sized city in Northern Italy. The municipal solid waste incineration (MSWI) generates fly ash, which is a toxic waste. Coal fly ash (CFA) and flue gas desulfurization (FGD) derive from the thermoelectric coal plant located in the same city. Along with these ashes, silica fume and rice husk ash are also considered for the stabilization of fly ash based on their amorphous silica content with the aim to convert them into an inert material. The characterization of all the investigated ashes was performed using different techniques: X-ray diffraction, total reflection X-ray fluorescence, scanning electron microscopy, and transmission electron microscopy. The aim of this work is to describe the reuse possibilities that were proposed for these ashes, which were determined also on the basis of their structural properties. Several possible applications of the investigated ashes are proposed, and the most suitable reuse of stabilized fly ash samples seems to be the production of sustainable plastic composites. This paper shows that the reuse of the by-product materials can allow natural resources to be preserved following the principles of a circular economy.

Recycling of Waste Materials for Stabilizing Ash from Co-Combustion of Municipal Solid Wastes with an Olive By-Product: Soil Leaching Experiments

In the context of the current environmental policies of the European Union promoting the recycling and reuse of waste materials, this work aimed at investigating the environmental impact of ashes produced from the co-combustion of municipal solid wastes with olive kernel in a fixed bed unit. Lignite fly ash, silica fume, wheat straw ash, meat and bone meal biochar, and mixtures of them were used as stabilizing ash materials. All solids were characterized by physical, chemical and mineralogical analyses. Column leaching tests of unstabilized and stabilized ash through a quarzitic soil were conducted, simulating field conditions. pH, electrical conductivity, chloride, sulphate and phosphate ions, major and trace elements in the leachates were measured. The results showed that alkaline compounds were partially dissolved in water extracts, increasing their pH and thus decreasing the leachability of heavy metals from the ash. Cr leached from unstabilized ash reached a hazardous level. Upon the stabilization of ash, the concentrations of heavy metals in the extracts were reduced between 9% and 100%, and were below legislation limits for disposal, apart from Cr. The latter was achieved only when meat and bone meal biochar was used as stabilizer. Entrapment of ash elements was assigned to the amorphous silica and to the phosphates of the stabilizing materials, as well as complexed silicates formed during the process.

Addressing environmental sustainability of plasma vitrification technology for stabilization of municipal solid waste incineration fly ash

Fly ash from municipal solid waste incineration is considered as a hazardous waste, which would raise great threats on environmental safety due to the inherent toxic heavy metals and organic pollutants. In this study, we applied the life cycle assessment to evaluate the thermal plasma vitrification process for stabilization of fly ash from municipal solid waste incineration. We established four scenarios: (i) plasma vitrification, including centralized and off-site plasma treatment, (ii) fuel-based vitrification, (iii) water-washing treatment followed by a rotary kiln, and (iv) conventional solidification and landfill. We found that the environmental impacts, especially toxicity to ecosystem quality and human health, could be significantly reduced by deploying plasma vitrification technology. We also found that centralized plasma vitrification facilities possessing larger treatment capabilities with clean electricity could further reduce the environmental impacts. In contrast, the water-washing treatment exhibited the highest environmental impacts due to the emissions of vaporized heavy metals. Based on the LCA and sensitivity analysis, we confirmed that the thermal plasma vitrification should be considered as an environmentally-friendly solution to sustainable treatment of fly ash from municipal solid waste incineration. Lastly, we provided several perspectives and prospects of plasma vitrification for realizing the sustainable materials management.

Sustainable reuse of dredged sediments as pavement materials by cement and fly ash stabilization

The process of removing sediments from the bottom of dams generates large amounts of dredged sediments, which are considered waste. The purpose of this research was to present the results of testing conducted on dredged sediment stabilized with ordinary Portland cement (OPC) and fly ash (FA) for reuse as pavement materials. The base sediment was high plasticity silt (MH) based on the Unified Soil Classification System (USCS). The experiments in this study consisted of unconfined compression (UC), California bearing ratio (CBR), and resilient modulus (Mr) tests on stabilized dredged sediment. A combination of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) was used to investigate the microstructures of the stabilized specimens. Finally, a simple comparative cost analysis between roads using conventional earthen materials and stabilized dredged sediment was performed. The results showed that the unconfined compressive strength (qu), CBR, and Mr improved the pavement materials from unsuitable to suitable, and a 10% FA content provided the optimal strength enhancement. The SEM images showed that the calcium silicate hydrate (CSH) product, which was formed by hydration and pozzolanic reactions, attached to the clay clusters and filled the pore spaces between clay particles, resulting in a denser sediment structure. The EDX analyses showed that the calcium weight proportion and the silica-aluminum ratio were important factors in improving the strength of the dredged sediment treated with OPC and FA. These EDX results agreed with the qu, CBR, and Mr results. For the studied situation, roads using stabilized sediment were 1.5 times more economical than roads using conventional earthen pavement materials. Dredged sediments treated with OPC and FA can be sustainably reused as pavement materials based on the Department of Highways of Thailand standard, as well as the recommendations of Austroads (2017). Thus, for suitable sediments, reuse in road and pavement construction may be considered with appropriate treatment and conditioning.