•Evaluate the performance of BFA when used as cement replacement material in HVFAC.•Evaluate the performance of BFA as an alkalinity reserve material in HVFAC.•HVFAC with BFA fulfil the common ...requirements used for conventional concrete.•BFA0.5 mix seems to be the optimum studied solution.
Sustainable construction is high on the agenda, especially regarding building materials. Using of by-products or waste materials from other economic sectors as cement replacement material in concrete production seems to be a more sustainable option than applying ordinary Portland cement concrete.
The main aim of this work was to evaluate the performance of biomass fly ash (BFA) when used as cement replacement material and as an alkalinity reserve material in high-volume fly ash concrete (HVFAC). Therefore, several compositions of concrete including BFA were tested for compressive strength, water absorption, accelerated carbonation, and chloride penetration resistance. It was noted that when small amounts of BFA were used, HVFAC properties were improved, compared with a high-volume coal fly ash concrete. These new concrete mixtures showed a positive contribution to the quality, durability and sustainability of HVFAC.
Coal fly ash, an industrial by-product, is derived from coal combustion in thermal power plants. It is one of the most complex anthropogenic materials, and its improper disposal has become an ...environmental concern and resulted in a waste of recoverable resources. There is a pressing and ongoing need to develop new recycling methods for coal fly ash. The present review first describes the generation, physicochemical properties and hazards of coal fly ash at the global level, and then focuses on its current and potential applications, including use in the soil amelioration, construction industry, ceramic industry, catalysis, depth separation, zeolite synthesis, etc. Finally, the advantages and disadvantages of these applications, the mode of fly ash utilization worldwide and directions for future research are considered.
Thermal plasma treatment has been considered as one of promising methods for fly ash disposal. In this study, firstly, the characteristics of municipal solid waste incineration (MSWI) fly ash and ...sewage sludge incineration (SSI) fly ash were analyzed, followed by the raw material formulations of low melting temperature determined by thermodynamic equilibrium calculation. Then verified experiments were carried out by thermal plasma system, focused on the formation condition of vitrified slags with various CaO-SiO2-Al2O3 ratios and the influence factors of heavy metals (Cd, Cr, Ni, Pb, Zn, Cu) transference. According to the results: During the co-treatment process of fly ashes, a lower temperature of vitrified slag formation as low as 1230 ℃ was observed. Vitrification is determined by the molten phase content during melting process, the correlation coefficient between the glass phase content of slag and the molten phase content was 0.81 (P < 0.01). CaO content of raw materials was a major element for the volatilization of Cd and Pb. High Al2O3 content can remain more Cr, Cu and Ni in slags, but it is not conducive to the solidification of Zn. The synthetic toxicity index of heavy metals would greatly reduce from 23153.15 to 663.29–820.63 after thermal plasma treatment.
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•The co-treatment of incineration fly ashes is beneficial for vitrification.•The formulation at 20–35% CaO, 20–35% Al2O3, 30–60% SiO2 is more easily vitrified.•CaO and Al2O3 contents are the main influencing factors of heavy metals migration.•The synthetic toxicity index of heavy metals is reduced from 23153.15 to 663.29.
•The carbonation resistance of LVFA and HVFA based SCC made with coarse RCA have been investigated.•Compressive strength for all the SCC mixes has been reported for reference.•The microstructural ...investigation of LVFA and HVFA based SCC has been done by SEM and TGA tests.•Electrical resistivity has also been calculated for all the mixes.•The effect of replacement of NA with RCA has been evaluated in binary and ternary blended SCC mixes.
The present study investigates the carbonation resistance of Low Volume Fly Ash (LVFA) and High Volume Fly Ash (HVFA) based Self Compacting Concrete (SCC) made with Coarse Recycled Concrete Aggregates (RCA). In order to study the carbonation resistance of LVFA and HVFA based SCC mixes made with RCA, accelerated carbonation tests were conducted for an exposure period of 4, 12 and 16weeks. The results indicate that with the increase in RCA content as replacement of Coarse Natural Aggregates (NA), decrease in the carbonation resistance of SCC mixes has been observed. The inclusion of metakaolin (MK) as a mineral admixture has been found to compensate the loss in the carbonation resistance on account of substitution of NA with RCA to some extent. The current investigation also emphasises on the microstructural study performed by Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA) for validation of observed results.
The sorption behavior of phosphorus on marine sediments in the presence of black carbon derived from fly ash (FC) was studied. For both the FC and sediment samples, the kinetic curves could be ...described by a two-compartment first order equation, and the isotherms fit the Freundlich and Langmuir models well. The high specific surface area with abundant acidic functional groups of FC promoted the sorption and make this process more irreversible. The effects were more significant with higher amount of FC added. After sorption, more significant increase in Ex-P, Fe/Al-P and CaP was found in the sediment with FC added, while the organic groups in FC rarely react with phosphorus to form OP. The pH of medium influenced the sorption character, and FC promoted the process significantly at pH < pHPZNPC. The sorption was endothermic with an increase in randomness. The presence of FC had little effects on the thermodynamic parameters.
•High surface area with abundant functional groups of FC enhanced phosphorus sorption.•FC strengthened the irreversibility of phosphorus sorption on sediments.•FC promote Ex-P and FeP increasing that favored phosphorus bioavailability.•Organic groups in FC rarely react with phosphorus to form OP.•FC had little effects on the thermodynamic parameters of the sorption process.
Petcoke generated during bitumen upgrading is a potential source of vanadium for the global market. Recovering vanadium from the fly ash originating from the combustion of petcoke appears to be a ...suitable route for commercial implementation, given its high extraction rate. Although the technical feasibility of the recovery process has been proven, the environmental impact should be addressed. Information on the greenhouse (GHG) emissions from the process is scarce in the public domain. Therefore, a framework was developed for assessment of life cycle GHG emissions for extraction of vanadium from petcoke-based fly ash. This framework was used to perform a life cycle GHG emissions assessment of a water leaching and salt roasting process to extract vanadium from fly ash. For the upstream GHG emissions, we collected direct emissions data and energy consumption from the literature, and, for the process emissions, we developed a model to estimate energy and material balances based on process conditions. The emission factors for electricity production, fuel combustion, production of consumables, and gas treatment were used to obtain the life cycle GHG emissions. The results show that the life cycle GHG emission of vanadium recovery are 26.6−3.9+0.9 kg CO2eq/kg V2O5; 66% of these are direct GHG emissions. The process GHG emissions from fly ash decarbonization contribute the most to the life cycle GHG emissions. The air-to-fuel ratio for roasting and the GHG emission factors for petcoke combustion and the gas treatment operation are the inputs that most effect the model output. Compared with the production of V2O5 from vanadium titano-magnetite ore and bitumen upgrading spent catalyst, the petcoke fly ash pathway generates about twice the life cycle GHG emissions. This study's results can help determine areas of improvement in the upstream operations and the recovery process to reduce the life cycle GHG emissions to levels that can compete with primary and alternative routes to produce vanadium pentoxide. The results of this study can help in decision-making associated with vanadium extract from fly ash produced from combustion of petcoke.
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•The life cycle GHG emission of vanadium recovery are 26.5−3.8+1.0 kg CO2eq/kg V2O5.•67% of the life cycle GHG emissions are due to process emissions.•Fly ash decarbonization contributes the most to life cycle GHG emissions.•GHG emissions doubled those from VTM ore and bitumen upgrading spent catalyst pathways.
Neat fly ash-based alkali activated binders require high activator dosages and high temperature curing in order to develop satisfactory mechanical properties. Blending ground granulated blast furnace ...slag (GGBS) with fly ash can give medium to high strengths without the need for high temperature oven curing. An extensive investigation was carried out for understanding the effects of GGBS substitution of fly ash in mortar. GGBS substitution in the mix has an impact on mix proportions, fresh and hardened properties, and microstructure of reaction products. The strength of fly ash/GGBS blends cured at room temperature increased with the increase of GGBS content, whilst setting time showed an opposite trend. Fly ash/GGBS blends required lower activator dosages for obtaining high compressive strength, which has cost and environmental benefits. XRD, FTIR, TGA, and SEM/EDX results confirmed the presence of C-A-S-H gel as a reaction product with as low as 20% GGBS content.
Sewer wastewater systems pose great threats to OPC-based concretes used for pipes due to the presence of various acids. Phosphoric acid can cause as much damage as sulphuric acid but has been very ...lightly studied. This study focuses on the early stage of the degradation process of different cementitious materials in phosphoric acid. Three types of cementitious materials are compared: OPC (100% cement), slag-blended OPC (slag/cement mass ratio at 65/35) and alkali-activated slag/fly ash pastes (slag/fly ash mass ratio at 50/50). Samples were exposed to phosphoric acid solution with a constant pH at 2.0 ± 0.2 for 44 days. The degradation kinetics, chemical and microstructural properties as well as dissolution rate of these binders are analysed. The results show that the alkali-activated slag/fly ash binder has the lowest degradation rate compared to the other cement-based binders. The intrinsic characteristics of the binders lead to significant changes in the kinetics of degradation. The chemical properties of the binders are the critical influential factor of the early stage behaviour. A conceptual degradation process is proposed to describe the early-stage kinetics of degradation for the cementitious materials studied.
Schematic diagram showing the early stage degradation processes of AASF and OPC-based pastes exposed to the phosphoric acid. ADD-Apparent degradation depth; DD-Dissolved/detached depth. Display omitted
This study was aimed at the synthesis of pure phase zeolite 4A from coal fly ash sourced from Nishat power plant in the Punjab province of Pakistan. Analysis of fly ash (FA) demonstrated that it can ...be used to produce low silicate type zeolites specifically zeolite 4A due to its Si/Al molar ratio of ∼2. The current investigation emphasized on the addition of induction time (before and after crystallization) to the fly ash extract of Si-Al-Na species that was extracted from fly ash. The induction time helped in catalysing primary and secondary gel formation during the synthesis leading to controlled formation of single phase with high crystallinity and small crystallite size. The physiochemical investigations of synthetic zeolite 4A by using various analytical techniques made the proposed process justified on comparison with commercial zeolite 4A. The X-Ray Diffraction (XRD) analysis for synthesize zeolite 4A confirmed only one crystallographic phase and small crystallite size with 82% crystallinity compared to reference zeolite with 75% crystallinity. Fourier-Transform Infrared spectroscopy (FTIR) spectra revealed the structural aspects of synthesis and reference zeolite by indicating the presence of identical structural units with same height and width of peaks. Morphological analysis by Scanning Electron Microscope (SEM) showed a well-defined cubic shape of synthesis zeolitic crystals. Surface area analyses by Brunauer–Emmett–Teller (BET) showed that synthesized zeolite possessed 122 m2/g surface area that is 3 times higher than reference zeolite of 36.3 m2/g. The synthesized zeolite was also found to have smaller particle size than reference zeolite. Thermal stability comparison of both zeolites was studied by non-isothermal Thermo Gravimetric Analysis-Differential Thermal Analysis (TGA-DTA) thermograms from 25 to 800 °C temperature and both the samples were found to be stable at 800 °C.
•Pakistani Coal Fly ash for synthesis of zeolite 4A and waste into useful material.•New step of induction time in the conventional two-step hydrothermal synthesis.•Pure, single-phase crystals with high crystallinity and small crystallite size.•Comparative physiochemical analysis of the synthesized and reference zeolite 4A.•Analytical techniques employed were XRD, SEM, BET, FTIR, PSA, EDX and TGA.
On combustion, coal produces fly ash (FA) and spheroidal carbonaceous particles (SCP) at high temperatures. Airborne particles like FA and SCP can be transported over long distances by wind, leading ...to the pollution of air and water resources. Concern mainly arises from various toxic metals loosely bound to the surface of FA and SCP. Here, we trace the provenance of SCP in soil samples collected upwind and downwind from two coal-fired thermal power plants (TPP) in central Nagpur (Khaperkheda and Koradi) that have been operational for over four decades. The samples showed morphological similarities between SCPs from soil samples and FA collected from the Khaperkheda power plant. The SCP distribution shows a sharp increase in the soil profiles coinciding with the expansion of the power plants between 2010 and 2015. Backward trajectories of winds were calculated to ascertain whether the sampling locations downwind of the TPPs were potentially affected by FA emissions. The results from the back trajectories indicate that emissions from the TPP are directed toward the sampling sites. Finally, leaching experiments were conducted in FA to assess the release of elements. Leaching experiments at 30, 40, and 50 °C and at a given pH or extraction time did not show any notable differences in elemental concentrations of Al, As, Ca, Cr, Co, Cu, Fe, Mn, Mo, Se, Ni, Ti, V, and Zn. The concentration of different elements mobilized from FA was high at pH 3, with rapid leaching occurring within the first 30 min of the experiment. Hence, disposal, reclamation, and management of FA need to be regulated and monitored correctly to ensure the safety of its use.
•Surface soils around coal-fired power plants indicate contamination risks.•Fly ash and spheroidal carbonaceous particles (SCP) can be traced in soils.•SCP numbers correspond well with expansion of the power plant capacity.•The leaching potential of metals was high at low pH.•High temperature or exposure had no effect on leaching capacity of metals.
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