Municipal solid waste incineration fly ash to produce eco-friendly binders for sustainable building construction

Geopolymer Materials from Fly Ash-A Sustainable Approach to Hazardous Waste Management

This study explores the utilisation challenges of fly ash from municipal waste incineration, specifically focusing on ash from a dry desulphurisation plant (DDS), which is categorised as hazardous due to its high heavy metal content. The ash's low silicon and calcium contents restrict its standalone utility. Laboratory investigations initially revealed that geopolymers derived solely from fly ash after flue gas treatment (FGT), in combination with coal combustion fly ash, exhibited low compressive strength (below 0.6 MPa). However, the study demonstrated significant improvements by modifying the FGT ash through water leaching. This process enhanced its performance when mixed with high-silica and -aluminium fly ash, resulting in geopolymers achieving compressive strengths of up to 18 MPa. Comparable strength outcomes were observed when the modified ash was blended with commercial cement. Leachability tests conducted for heavy metals (HMs) such as copper, zinc, lead, cadmium, and nickel indicated that their concentrations fell below the regulatory limits for landfill disposal: 2, 4, 0.5, 0.04, and 0.4 mg/kg, respectively. These results underscore the effectiveness of water-washing FGT ash in conjunction with other materials for producing geopolymers, contributing to sustainable waste management practices.

Multiple objective energy optimization of a trade center building based on genetic algorithm using ecological materials

It is crucial to optimize energy consumption in buildings while considering thermal comfort. The first step here involved an EnergyPlus simulation on a trade center building located in Tehran, Bandar Abbas, and Tabriz, Iran. A multi-objective optimization was then performed based on non-dominated sorting genetic algorithm II (NSGA-II) in jEPlus + EA to establish the building in the selected city where would benefit the most from implementing the radiant ceiling cooling system. Efforts were undertaken to choose environmentally-friendly materials. The final solution by Pareto charts resulted in a 52% reduction in energy consumption, a 37.3% decrease in cooling load, and a 17.4% improvement in comfort hours compared to the original design. Annual emission of greenhouse gas reduced as 167.67 tone of CO2 equivalent emission, 25.77 ton of CH4, and 0.2 ton of NO2. The mentioned algorithm was conducted for the first time on a trade center, including a DOAS system and radiant ceiling cooling system. Simultaneously, the environmental-friendly materials were dealt with. The procedure holds significant relevance for the design and optimization of buildings in Iran, especially wherever the climate is hot and humid. This approach offers advantages to the environment by reducing the impact on energy resources and utilizing environmentally-friendly materials.

Global perspective of municipal solid waste and landfill leachate: generation, composition, eco-toxicity, and sustainable management strategies

Globally, more than 2 billion tonnes of municipal solid waste (MSW) are generated each year, with that amount anticipated to reach around 3.5 billion tonnes by 2050. On a worldwide scale, food and green waste contribute the major proportion of MSW, which accounts for 44% of global waste, followed by recycling waste (38%), which includes plastic, glass, cardboard, and paper, and 18% of other materials. Population growth, urbanization, and industrial expansion are the principal drivers of the ever-increasing production of MSW across the world. Among the different practices employed for the management of waste, landfill disposal has been the most popular and easiest method across the world. Waste management practices differ significantly depending on the income level. In high-income nations, only 2% of waste is dumped, whereas in low-income nations, approximately 93% of waste is burned or dumped. However, the unscientific disposal of waste in landfills causes the generation of gases, heat, and leachate and results in a variety of ecotoxicological problems, including global warming, water pollution, fire hazards, and health effects that are hazardous to both the environment and public health. Therefore, sustainable management of MSW and landfill leachate is critical, necessitating the use of more advanced techniques to lessen waste production and maximize recycling to assure environmental sustainability. The present review provides an updated overview of the global perspective of municipal waste generation, composition, landfill heat and leachate formation, and ecotoxicological effects, and also discusses integrated-waste management approaches for the sustainable management of municipal waste and landfill leachate.

Fate of Cl and chlorination mechanism during municipal solid waste incineration fly ash reutilization using thermal treatment: a review

Safe and sustainable treatment of municipal solid waste incineration fly ash (MSWI FA) is urgently needed worldwide because of its high heavy metals, dioxin, and chlorine (Cl) contents. Thermal treatment is widely considered as a promising method for treating MSWI FA owing to its high toxic content removal efficiency and resource recovery; however, residual Cl is a concurrent critical problem faced during reutilisation of thermal treatment products. This review summarises the innovative thermal treatment methods of MSWI FA, such as those employed in production of cement, lightweight aggregates, glass slag, and metal alloys. The characteristics of Cl in MSWI FA, removal rate, transformation of water-soluble Cl into water-insoluble Cl, and the effect of different influencing factors such as temperature, composition, superheated steam, and mechanical pressure were analysed. The volatilization and decomposition of NaCl, KCl and CaClOH dominates Cl removal; however, the degradation of organic Cl and heavy metal chlorination volatilization process that generate HCl and heavy metal chlorides, respectively, also contributed to Cl removal. To promote the reutilisation of MSWI FA-based products, the leaching behaviour of residual Cl in products obtained by different thermal treatments was investigated.

Analysis of heavy metal, rare, precious, and metallic element content in bottom ash from municipal solid waste incineration in Tehran based on particle size

Waste incineration is increasingly used worldwide for better municipal solid waste management and energy recovery. However, residues resulting from waste incineration, such as Bottom Ash (BA) and Fly Ash (FA), can pose environmental and human health risks due to their physicochemical properties if not managed appropriately. On the other hand, with proper utilization, these residues can be turned into valuable Municipal metal mines. In this study, BA was granulated in various size ranges (< 0.075 mm, 0.075-0.125 mm, 0.125-0.5 mm, 0.5-1 mm, 1-2 mm, 2-4 mm, 4-16 mm, and > 16 mm). The physicochemical properties, heavy metal elements, environmental hazards, and other rare and precious metal elements in each Granulated Bottom Ash (GBA) group from Tehran's waste incineration were examined using ICP-MASS. Additionally, each GBA group's mineralogical properties and elemental composition were determined using X-ray fluorescence (XRF) and X-ray diffraction (XRD). The results showed that the average concentration of heavy metals in GBA, including Zn (1974 mg/kg), Cu, and Ba (790 mg/kg), Pb (145 mg/kg), Cr (106 mg/kg), Ni (25 mg/kg), Sn (24 mg/kg), V (25 mg/kg), As (11 mg/kg), and Sb (29 mg/kg), was higher in particles smaller than 4 mm. Precious metals such as gold (average 0.3 mg/kg) and silver (average 11 mg/kg) were significantly higher in GBA particles smaller than 0.5 mm, making their extraction economically feasible. Moreover, rare metals such as Ce, Nd, La, and Y were detected in GBA, with average concentrations of 24, 8, 11, and 7 mg/kg, respectively. The results of this study indicated that BA contains environmentally concerning metals, as well as rare and precious metals, with high concentrations, especially in particles smaller than 4 mm. This highlights the need for proper pre-treatment before using these materials in civil and municipal applications or even landfilling.

Decarbonatization of Energy Sector by CO2 Sequestration in Waste Incineration Fly Ash and Its Utilization as Raw Material for Alkali Activation

In this study, municipal solid waste incineration (MSWI) fly ash was subjected to mineral carbonation with the aim of investigating CO2 sequestration in waste material. The conducted study follows the trend of searching for alternatives to natural mineral materials with the ability to sequestrate CO2. The mineral carbonation of MSWI fly ash allowed for the storage of up to 0.25 mmol CO2 g-1. Next, both carbonated and uncarbonated MSWI fly ashes were activated using an alkaline activation method by means of two different activation agents, namely potassium hydroxide and potassium silicate or sodium hydroxide and sodium silicate. Mineral carbonation caused a drop in the compressive strength of alkali-activated materials, probably due to the formation of sodium and/or potassium carbonates. The maximum compressive strength obtained was 3.93 MPa after 28 days for uncarbonated fly ash activated using 8 mol dm-3 KOH and potassium hydroxide (ratio 3:1). The relative ratio of hydroxide:silicate also influenced the mechanical properties of the materials. Both carbonated and uncarbonated fly ashes, as well as their alkali-activated derivatives, were characterized in detail by means of XRD, XRF, and FTIR. Both uncarbonated and carbonated fly ashes were subjected to TG analysis. The obtained results have proved the importance of further research in terms of high-calcium fly ash (HCFA) utilization.

Monitoring treatment of industrial wastewater using conventional methods and impedance spectroscopy

The main aim of this study was to develop and monitor an effective and cost-efficient industrial wastewater treatment system that utilizes sand, fly ash, and hearth ash. The latter two are potentially available and inexpensive industrial waste materials that can be used for filtration. The infiltration percolation method was utilized in a vertical cylindrical column to filter the raw wastewater from a detergent manufacturing plant. The main parameters analyzed before and after treatment included suspended solids (SS), chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), and pH. The system successfully achieved significant reductions, including 89% in COD, 73% in BOD₅, and 54% in suspended solids (SS), along with a 66% to 99% reduction in heavy metals. The COD/BOD₅ rejection ratio decreased from above 4.24 before treatment to below 1.73 after treatment. Furthermore, impedance measurements were carried out across the frequency range of 100 to 1 MHz. The analysis of complex conductivity spectra revealed two Cole-Cole relaxation behaviors, and an equivalent circuit was developed to extract the primary parameters and further investigate both relaxation processes. The results of the electrical parameters deduced from the impedance spectra demonstrated a strong correlation with the parameters obtained through conventional methods.

Synergistic influence of diatomite and MoS2 nanosheets on the self-alkali-activated cementation of the municipal solid waste incineration fly ash and mechanisms

The solidification/stabilization technique recommended for the disposal of municipal solid waste incineration (MSWI) fly ashes in developed countries was inappropriate for the treatment in most developing counterparts. In this study, the diatomite and MoS₂ nanosheets were synergistically employed to activate the self-alkali-activated cementation of the MSWI fly ashes to achieve efficient solidification, the immobilization of heavy metals (HMs), and the inhibition of chloride release. The compressive strength of 28.61 MPa and the leaching toxicities (mg/L) of Zn, Pb, Cu, Cd, and Cr of 2.26, 0.87, 0.5, 0.06, and 0.22 were obtained from the hardened mortars. Diatomite significantly influenced the self-alkali-activated cementation of the MSWI fly ashes while MoS₂ nanosheets played both roles in intensifying the stabilization of HMs and strengthening the binding process by inducing the formation of sodalite and kaolinite, enhancing the growth rates of nucleation, and transforming the layered cementation to the partial and full three-dimensional cementation in the hardened matrix. This study not only verified the feasibility of diatomite and MoS₂ in activating the self-alkali-activated cementation of the MSWI fly ashes but also supplied a reliable technique for the harmless disposal and efficient utilization of MSWI fly ashes in developing countries.

Municipal Solid Waste Incineration Fly Ash: From Waste to Cement Manufacturing Resource

This study investigates the possibility of using municipal solid waste incineration fly ash as a supplementary cementitious material to replace part of the clinker in cement. Life cycle assessment has shown that the partial replacement of clinker with blast furnace slag (CEM III) reduces cement's global warming potential by ~30%, while replacing clinker with fly ash reduces it by up to 55%. When using CEM III as the control binder in cement in which 55 wt% of the clinker was replaced with hydrothermally treated fly ash, the flexural strength decreased by ~60% and the compressive strength by ~65%. When the fly ash was mixed with calcined and vitrified demolition materials, flexural strength decreased by ~30% and compressive strength by ~50%. The hardening of the hydraulic binders fixed the heavy metals in the municipal solid waste incineration fly ash.

Water washing and acid washing of gasification fly ash from municipal solid waste: Heavy metal behavior and characterization of residues

Gasification fly ash (GFA) is a hazardous solid residue generated in the slagging-gasification of municipal solid waste (MSW). GFA contains higher amounts of heavy metals such as Pb and Zn than incineration fly ash (IFA), which increases the difficulty of heavy metal immobilization but simultaneously makes it a potential feedstock for metal recovery. Water washing and acid washing are conventional and economic methods to treat wastes with high heavy metal and chloride contents. However, the research on the effects of such methods in treating GFA is still blank. Hence, in this study, water washing and acid washing of GFA were investigated in detail. Heavy metal behaviors at different time points during the washing processes were studied in a wide pH range and comprehensive characterizations of washed GFAs were also conducted. The results show that different re-precipitates could be identified in washed GFAs depending on different pH conditions. After water washing for 24 h, more than 60% of Zn in GFA would dissolve and re-precipitate into calcium zincate. It is also revealed that the precipitation effect could in turn influence the pH during the washing process. After acid washing with a low-concentration acid, heavy metal leachabilities were found reduced due to the pH and precipitation effect. High-concentration acid washing could effectively extract Zn and Cd with extraction ratios exceeding 90%. Applying 1.2 M-HCl washing, a short washing period of 15 min could realize a Pb extraction ratio of 81.2%, much higher than 53.2% when extending the washing period to 24 h.

Suppression on PCDD/Fs formation by a novel inhibition system consisting of phosphorous-based compounds coupled with a chlorine-deactivation material

The SN-containing inhibitors are effective for suppressing the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the post-combustion zone of municipal solid waste incineration systems, but the industrial application of the SN-containing inhibitors is restricted by the high cost and the generation of corrosive by-products (e.g., SOx). To develop cost-effective and environmentally friendly inhibitors, a new inhibition system consisting of P-based compounds (i.e., NH₄H₂PO₄ (ADP) and KH₂PO₄ (PDP)) and a chlorine-deactivation material (CaO) was proposed in this study. Also, the performance of this inhibition system in terms of suppressing PCDD/Fs formation was evaluated in an experimental system which simulated PCDD/Fs generation in the post-combustion zone. Generally, the formation of PCDD/Fs was effectively suppressed by over 95 % by the mixed inhibitors (ADP/CaO and PDP/CaO) and the individual inhibitor of ADP. Based on the observation on PCDD/F-fingerprints and the chemical speciation of Cl and Cu, the mechanisms of inhibitors were identified as: (i) passivating metal catalyst by converting the speciation of Cu from chlorides and Cu²⁺ with high reactivities to phosphates, oxides, and Cu⁺ with low reactivities, and (ii) deactivating Cl by CaO to prevent the formation of organic Cl which was critical for PCDD/Fs formation. In addition, both mechanisms were supported by (i) the better performance of inhibitors on suppressing the PCDD/F-congeners formed via de novo pathway than congeners synthesized from chlorophenols and (ii) lower degrees of chlorination of PCDD/Fs for reaction systems with CaO involved than other systems.

PCDD/Fs and heavy metals in the vicinity of landfill used for MSWI fly ash disposal: Pollutant distribution and environmental impact assessment

This study focused on the syngenetic control of polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs) and heavy metals by field stabilization/solidification (S/S) treatment for municipal solid waste incineration fly ash (MSWIFA) and multi-step leachate treatment. Modified European Community Bureau of Reference (BCR) speciation analysis and risk assessment code (RAC) revealed the medium environment risk of Cd and Mn, indicating the necessity of S/S treatment for MSWIFA. S/S treatment significantly declined the mass/toxic concentrations of PCDD/Fs (i.e., from 7.21 to 4.25 μg/kg; from 0.32 to 0.20 μg I-TEQ/kg) and heavy metals in MSWIFA due to chemical fixation and dilution effect. The S/S mechanism of sodium dimethyldithiocarbamate (SDD) and cement was decreasing heavy metals in the mild acid-soluble fraction to reduce their mobility and bioavailability. Oxidation treatment of leachate reduced the PCDD/F concentration from 49.10 to 28.71 pg/L (i.e., from 1.60 to 0.98 pg I-TEQ/L) by suspension absorption or NaClO oxidation decomposition, whereas a so-called "memory effect" phenomena in the subsequent procedures (adsorption, press filtration, flocculating settling, slurry separation, and carbon filtration) increased it back to 38.60 pg/L (1.66 pg I-TEQ/L). Moreover, the multi-step leachate treatment also effectively reduced the concentrations of heavy metals to 1-4 orders of magnitude lower than the national emission standards. Furthermore, the PCDD/Fs and heavy metals in other multiple media (soil, landfill leachate, groundwater, and river water) and their spatial distribution characteristics site were also investigated. No evidence showed any influence of the landfill on the surrounding liquid media. The slightly higher concentration of PCDD/Fs in the soil samples was ascribed to other waste management processes (transportation and unloading) or other local source (hazardous incineration plant). Therefore, proper management of landfills and leachate has a negligible effect on the surrounding environment.

Geopolymer bricks prepared by MSWI fly ash and other solid wastes: Moulding pressure and curing method optimisation

The preparation of geopolymer from alkaline solid waste instead of strong alkali presents the disadvantage of low early strength. However, improving the early mechanical properties of the geopolymer to meet the engineering requirements is challenging. In this paper, the effects of different moulding pressures and curing methods on the properties of red mud-ground granulated blast furnace slag activated by municipal solid waste incineration fly ash (MSWIFA)-carbide slag (CRMG) were studied and evaluated in terms of compressive strength and XRD, FTIR, SEM, and MIP techniques analysis. The results showed that the moulding pressure of 30 MPa could increase the compressive strength at 3 d by 182% and decrease the porosity from 30.28% to 27.38%. These results are attributable to the fact that the moulding pressure causes the particles to be tightly bound and promotes the geopolymerisation reaction. High-temperature (HT) curing could accelerate the hydration reaction and increase the compressive strength at 3 d by 133.7% and 141.6% compared with those obtained by water curing (WC) and room-temperature (RT) curing, respectively. Microscopic analyses showed that HT curing can promote the generation of C-(A)-S-H gel, geopolymer gel and hydrate calcium chloroaluminate (HCC), fill the pores, and increase the structure's compactness. Finally, the proposed method was verified by synthesising geopolymer pavement bricks (GPB), and the compressive strength at 3 d was found to reach 54 MPa under an optimal curing method (moulding pressure of 30 MPa, 90 °C for 12 h). Compared with concrete pavement bricks, GPB presents broad application prospects for saving economic costs and protecting the environment. The results provide a theoretical basis and technical support for the application of CRMG in rapid demoulding projects such as unfired bricks.

A new co-processing mode of organic anaerobic fermentation liquid and municipal solid waste incineration fly ash

A new co-processing mode of waste liquid from anaerobic fermentation of organic wastes and municipal solid waste incineration fly ash (MSWI-FA) dechlorination is reported in this paper. Taking acetic acid, the most common organic acid in anaerobic fermentation systems, as the representative of anaerobic fermentation organic acids, the improvement of the dechlorination effect and the mechanism of washing MSWI-FA with low concentrations of organic acid lotion were explored. The chlorine content of MSWI-FA was reduced to 0.82% after the optimal process washing pretreatment. Three anaerobic fermentation waste liquids (AFWLs) were used to verify that the chlorine content of MSWI-FA could be reduced to less than 1%, and the dechlorination effect of brewery wastewater, which reduced the chlorine content of MSWI-FA to 0.91%, was the best at this. The influence of the washing process on MSWI-FA pyrolysis was reflected in the whole process. The release of chloride decreased and the weight loss was mainly due to the release of CO₂. The melting point of MSWI-FA, washed by the optimal process, was reduced by nearly 30 ℃, and only 0.06% chlorine remained after calcination at 1100 ℃, which was extremely beneficial in reducing the release of trace elements in MSWI-FA during heat treatment, and for the preparation of cement raw meal.

Removal of harmful components from MSWI fly ash as a pretreatment approach to enhance waste recycling

Municipal solid waste incineration (MSWI) fly ash contains many harmful components that may limit its potential for recycling. An effective pretreatment is therefore required before any recycling can be implemented. In this study, the effects of four pretreatment methods (water washing, CO₂-aided washing, CO₃^2--aided washing, and CO₂ and CO₃^2--aided washing) on the extraction behavior of chloride, sulfate, and heavy metals were evaluated. Water washing was found to be effective for the extraction of all easily and moderately soluble Cl-bearing salts, achieving Cl extraction ratios of 88%, 90%, and 96% for ash from Chongqing (CQ), Qingdao (QD), and Tianjin (TJ), respectively. Injection of CO₂ during washing facilitated decomposition of the hardly soluble Cl-bearing salts, increasing the Cl extraction efficiency by 6% for CQ ash and 9% for QD ash. However, for the TJ ash that contained few insoluble Cl-bearing minerals, CO₂ injection decreased the Cl extraction rate. The addition of CO₃^2- had a negative influence on Cl extraction for all ashes, but it slightly promoted sulfate extraction. Despite the high Cl removal rate, only 23-37% of the sulfate and 0.1-12% of heavy metals were removed. Overall, water-based pretreatment, especially CO₂-aided washing, significantly altered the physical, chemical, and mineralogical characteristics of the fly ash, making it more suitable for recycling. Consequently, the blending ratio of the fly ash for cement clinker manufacture increased from 0.2 to 0.3% in the raw ash to 3.5-5.5% in the treated ash, enabling the extensive use of ash materials.

Characterization of contaminant leaching from asphalt pavements: A critical review of measurement methods, reclaimed asphalt pavement, porous asphalt, and waste-modified asphalt mixtures

In recent years, the pavement industry has been seeking sustainable development through recycling reclaimed asphalt pavement and reusing other waste materials as replacements for asphalt mixture constituents. Incorporating waste material into asphalt mixture and the presence of pollutants such as exhaust fumes and gasoline due to vehicle traffic may lead to contaminants leaching from asphalt pavements to underlying soil layers and groundwater aquifers, posing serious risks to ecosystems and the environment. To cast light on contaminant leaching from asphalt pavements, this article presents a comprehensive review of the literature that is divided into four research areas: evaluation of leaching measurement methods, leaching from recycled asphalt materials, leaching characteristics of porous asphalt pavements, and waste-modified asphalt mixtures. Moreover, a critical discussion of bibliometric data, literature content and knowledge gaps in this domain is provided to help highway agencies and environmental scientists address contaminant leaching from asphalt pavements. Finally, some potential research directions are suggested for future research works.

Chemical stabilization of heavy metals in municipal solid waste incineration fly ash: a review

Sufficient attention should be attached to the large amount of fly ash containing high levels of toxic heavy metals generated after municipal solid waste incineration. Because heavy metals could be leached out of the fly ash under specific conditions, it is necessary to stabilize the heavy metals in fly ash before landfill disposal. Processing technologies of incineration fly ash include solidification/stabilization technology, thermal treatments, and separation processes. This study reviewed the current treatment technologies of municipal solid waste incineration (MSWI) fly ash, with the main focus on the treatment of heavy metals in fly ash with chemical stabilization. Chemical stabilization processes involve chemical precipitation of heavy metal and chelation of heavy metals. In multiple studies, chemical stabilization technology has shown practical feasibility in terms of technology, economy, and effect. In addition, the combination of two or more stabilization agents broadens the general applicability of the agents to heavy metals and reduces the cost. The application of joint processing technology realizes the remove of soluble salt from fly ash. To minimize pollutants while increase their usable value, effective use of waste and co-disposal of several kinds of wastes have gradually become the research hotspots. New developments in chemical stabilization are progressively moving towards the sustainable direction of harmlessness and resource utilization of MSWI fly ash.

Green Deal and Circular Economy of Bottom Ash Waste Management in Building Industry-Alkali (NaOH) Pre-Treatment

This study aims to investigate the possibilities of municipal waste incineration bottom ash (MSWIBA) utilization in the construction sector. MSWIBA development fits into the European Green Deal, Sustainable Development Goals (SDGs), and the Circular Economy (CE). This manuscript describes current MSWIBA treatment such as solidification, ceramization, vitrification, chemical activation (NaOH, CaOH2, NA2SiO3 + NaOH, Na2CO3 + NaOH, NH4OH), acid treatment with diluted solutions (HCl, H2SO4), chemical stabilization (FeSO4, PO43-), chelation, etc. For the purpose of comparative research, MSWIBA before valorization, after valorization, and after NaOH pre-treatment was investigated. In terms of their physico-chemical properties, the tested samples were examined. Three kinds of MSWIBA were used as a substitute for 30% of cement in mortars. The mortars were tested for 28-day strength. Leachability tests were performed in acid, aggressive, alkali, and neutral water environments. Life Cycle Assessment (LCA) analysis was carried out, which presented the environmental benefits of MSWIBA management in construction.

Evaluation of Strength Properties of Sand Stabilized with Wood Fly Ash (WFA) and Cement

The article describes the laboratory evaluation of mixtures of sand modified with wood fly ash (WFA) and additionally stabilized with different amounts of cement. Laboratory research includes determining the California Bearing Ratio (CBR), compressive and indirect tensile strengths of the mixtures, and the resistance of mixtures to freezing/thawing cycles. The aim of the research is to determine if WFA, an alternative material, can improve sand bearing capacity and contribute to strength development while reducing necessary cement amounts and satisfying the technical regulation for use in pavement base courses. The test results obtained show that WFA has a considerable stabilization effect on the sand mixture and improves its load bearing capacity. By adding a small quantity of the cement, the hydraulic reaction in the stabilized mixture is more intense and results in greater strengths and an improved resistance to freezing. The test results show that, by replacement of part of the sand with WFA (in the quantity of 30%), greater strengths can be achieved in relation to the mixture of only sand and cement. Additionally, the content of cement necessary for the stabilization of sand (usually 8–12%) is considerably reduced, which enables cost savings in the construction of pavement structures.

Dioxins control as co-processing water-washed municipal solid waste incineration fly ash in iron ore sintering process

Co-processing water-washed municipal solid waste incineration fly ash (WM-FA) in iron ore sintering process is of great prospect. In this paper, the emission characteristics of dioxins during sintering process combined with WM-FA were studied, and the control method for dioxins was proposed. The results showed that adding WM-FA in the form of pellets with diameter 5-8 mm slightly influenced sinter quality. Increasing the diameter of WM-FA from 5-8 mm to 10-12 mm helped to reduce the concentration of PCDD/Fs from 1.0425 ng I-TEQ/N m³ to 0.7720 ng I-TEQ/N m³. However, compared with no WM-FA adding case, adding WM-FA pellets caused the increase of PCDD/Fs concentration in the sintering flue gas. A novel method for dioxin control was proposed through preparing WM-FA into 5-8 mm pellets and coated with CaO-containing additive with its function to adsorb and fix HCl and Cl₂, which were the key components to synthesize dioxin. Due to the inhibiting effect of CaO to the chlorination reaction, the emission concentration of PCDD/Fs was decreased to 0.6240 ng I-TEQ/N m³, which was lower than that of no WM-FA adding case. The research findings lay a foundation for the resource utilization of WM-FA and the harmonious development of city and steel plant.

Pedagogical Approaches for Sustainable Development in Building in Higher Education

Education for sustainable development (ESD) is one of the great challenges that university faculties have to face. Therefore, a multidisciplinary team from the faculty of Engineering of Gipuzkoa (EIG) at the University of the Basque Country (UPV/EHU) has developed pedagogical approaches to apply in construction degrees, namely Civil Engineering and Technical Architecture. Pedagogical tools, such as problem-based learning (PBL) or research-based learning (RBL), and environmental tools, such as the life cycle assessment (LCA) and computational thinking (CT), have been used; in doing so, they acquire a sustainable approach to work “soft-skills” competencies into sustainability. For example, research-based tools have helped to revalorize waste both outside and inside the university; they have contributed to more sustainable industrial processes, collaborative research projects, and participation in conferences and scientific publications. Based on academic results, the designed tools are appropriate for teaching in Technical Architecture and Civil Engineering degrees; however, to demonstrate their potential in terms of sustainable education, holistic rubrics based on in-depth quantitative educational research are required. Thus, to analyze the ability of the students to incorporate sustainability principles in their work, the multidisciplinary team presenting this paper plans to collaborate with psychologists and sociologists within the framework of the Bizia-Lab program of the UPV/EHU.

Analysis of Strength and Microstructural Characteristics of Mine Backfills Containing Fly Ash and Desulfurized Gypsum

The utilization of solid wastes (SWs) as a potential resource for backfilling is not only conducive to environmental protection but also reduces the surface storage of waste. Two types of SWs, including fly ash (FA) and desulfurized gypsum (DG), were used to prepare cementitious backfilling materials for underground mined-out areas. Ordinary Portland cement (OPC) was used as cement in mine backfill. To better investigate the feasibility of preparing backfill materials, some laboratory tests, such as uniaxial compressive strength (UCS), scanning electron microscopy (SEM), and energy dissipation theory, were conducted to explore both strength and microstructural properties of backfilling. Results have demonstrated that the main components of FA and DG in this study are oxides, with few toxic and heavy metal components. The ideal ratio of OPC:FA:DG is 1:6:2 and the corresponding UCS values are 2.5 and 4.2 MPa when the curing time are 7 days and 14 days, respectively. Moreover, the average UCS value of backfilling samples gradually decreased when the proportion of DG in the mixture increased. The main failure modes of various backfilling materials are tensile and shearing cracks. In addition, the corresponding relations among total input energy, dissipated energy and strain energy, and stress–strain curve were investigated. The spatial distribution of oxygen, aluminum, silicon, calcium, iron and magnesium elements, and hydration product are explored from the microstructure’s perspective. The findings of this study provide both invaluable information and industrial applications for the efficient management of solid waste, based on sustainable development and circular economy.