Search Results (19)

As urbanization progresses rapidly, the pollution of heavy metal wastewater and the disposal of municipal solid waste incineration bottom ash (MSWI-BA) have emerged as significant challenges. MSWI-BA is a porous material recognized as an environmentally friendly adsorbent. To prevent escalating costs in future practical engineering applications, this study employed unmodified, natural MSWI-BA. This research assessed the adsorption capabilities of MSWI-BA for Pb(II) and Zn(II) through static adsorption experiments, which included adsorption kinetics and isotherm studies. The influence of various factors on the adsorption performance of MSWI-BA was investigated through adjusting the solution pH and the amount of ash, competitive adsorption conditions, and regeneration experiments. Advanced techniques, including ESEM-EDS, XRD, and FTIR, were utilized to analyze the adsorption mechanisms. The results indicated that under the conditions of pH values of 4 and 5, a temperature of 318 K, and an ash dosage of 0.1 g/20 mL, the maximum adsorption capacities of MSWI-BA for Pb(II) and Zn(II) were 89.09 mg/g and 33.77 mg/g, respectively. MSWI-BA demonstrates robust regeneration potential over multiple cycles, validating its practical feasibility. The principal mechanisms for removal include chemical precipitation, ion exchange, and surface complexation. By repurposing it as an efficient and low-cost adsorbent, this represents a sustainable strategy. Full article

This study examines the strategic incorporation of various recycled materials into asphalt concrete, specifically focusing on municipal solid waste incineration bottom ash (MSWI BA), recycled asphalt shingle (RAS), and recycled concrete aggregate (RCA). Due to the high porosity of MSWI BA and RCA, and the significant asphalt binder content (30–40%) found in RAS, there is a need to increase the amount of liquid asphalt used. RAS is posited as an efficient substitute for the asphalt binder, helping to counterbalance the high absorption characteristics of MSWI BA and RCA. The research objective is to quantitatively evaluate the effect of the combined use of RAS, MSWI BA, and RCA in Hot Mix Asphalt (HMA). This study encompasses several laboratory evaluations (i.e., rutting and tensile strength tests) and a cost–benefit analysis, which is a life cycle cost analysis. The results indicate that the combined use of these materials results in a higher tensile strength and rut resistance when compared with the control (with virgin aggregate). According to the cost–benefit analysis result, when the three recycled materials are used for an HMA overlay over an existing aged pavement, it could be 60–80% more cost-effective compared to a conventional HMA overlay, thereby offering significant economical savings each year in the field of road construction. Full article

This study investigated the positive effect of the combined use of recycled asphalt shingles (RASs) and municipal solid waste incineration (MSWI) bottom ash (B.A.) in asphalt concrete, which contributes to enhanced sustainability in pavement engineering. In addition, unlike traditional approaches that employ individual recycling material in hot mix asphalt (HMA), the combined use of the two waste materials maximizes the mechanical performance of the asphalt mixture. The addition of RAS (with 30–40% aged binder) as an additive generally enhances the strength/stiffness of the asphalt mixture. The high porosity/absorption of MSWI BA results in an additional amount of liquid asphalt binder in the mixture. As an admixture, RAS could supply the additional asphalt binder in the mixture when MSWI BA is used as an aggregate replacement. This research was conducted in two phases: (1) to examine the effect of MSWI BA alone and its optimal asphalt content (OAC), and (2) to assess the combined effect of B.A. and RAS in HMA. Multiple laboratory testing methods were employed for the mechanical performance investigation, including the Marshall stability test, rutting test, and indirect tensile test. The testing results show that the 20% B.A. replacement exhibits the best performance and that it requires an additional asphalt binder of 1.1%. For the combined use of MSWI BA and RAS, 5% RAS shows the best mechanical performance. All mixtures that contain the B.A. and RAS show greater strength than the control specimen (regular HMA). Full article

The cement sector is the second largest contributor to anthropogenic CO₂ emissions, and several efforts have been made to reduce its environmental impact. One alternative that has gained interest in recent years involves the use of municipal solid waste incineration (MSWI) bottom ash (BA) as clinker/cement replacement. This paper studies the application of MSWI BA in three different ways: (i) aggregate (0 to 100 v/v %), (ii) partial binder substitute (0 to 30 v/v %), and (iii) filler (5 v/v %). It stands out for its approach in characterizing seven distinct BA particle sizes and for the development and analysis of eco-cement mortars with only mechanically pre-treated BA. Hardened state properties showed that the use of BA as aggregate leads to deterioration and efflorescence formation on the surface of the mortars, making this application unfeasible. The replacement of 15 v/v % of OPC (Ordinary Portland Cement) by BA and the use of finer (<63 μm) BA as filler caused a decrease in the compressive strength of the mortar, from 15.8 to 9.3 and 11.0, respectively. However, these materials are suitable for use in walls where the minimum required mechanical resistance is 5 MPa. Furthermore, these mortars demonstrated resilience against freeze–thaw cycles and even exhibited increased compressive strength after 25 cycles. Thus, this work showed that MSWI BA can be used as an OPC substitute (up to 15 v/v %) and as a filler, promoting circular economy principles and reducing CO₂ emissions related to the construction industry. Full article

The purpose of this research is to assess the yield and reaction rate potential of carbon dioxide (CO₂) sequestration through mineralisation using readily available and inexpensive resources by exploiting waste materials. In this case, a blend of four different kinds of ashes and combustion by-products were used, namely, coal fly ash (CFA), flue gas desulphurization (FGD) residues, municipal solid waste incineration fly ashes (MSWI FA) and bottom ash (MSWI BA), produced at the same location. To highlight the impact of these materials on the carbonation process, various factors were analysed, including particle size distribution, immediately soluble contents, mineralogy, particles’ detailed structure, and chemical composition. After preparing the samples, two carbonation processes were tested: natural carbonation and accelerated carbonation. To evaluate the impact of the water content on the reaction rate and yield of the mineral carbonation, various liquid-to-solid (L/S) ratios were used. The results demonstrate that the water content and pressure play a significant role in the CO₂ sequestration during the accelerated carbonation, the higher the L/S, the greater the yields, which can reach up to 152 g CO₂/kg with MSWI FA, while no substantial difference seems to emerge in the case of the natural carbonation. Full article

Large amounts of municipal solid waste incineration bottom ash (MSWI BA) are formed worldwide, and this quantity is growing because of the establishment of new waste-to-energy plants. This waste is generally kept in landfills but can be used for the manufacturing of cementitious building materials. This article analyzes the use of MSWI BA as a microfiller in cement mortars. The effects of MSWI BA on the properties of cement binder and mortar were analyzed by using them separately or in combination with other microfillers: milled quartz sand, metakaolin, milled glass, and microsilica. This article investigates the flowability of cement-based mixtures, the volume change as a result of the evolution of hydrogen gas, cement hydration, XRD, TG, the physical and mechanical properties of the mortar samples, and leaching. The addition of milled MSWI BA in cement mortars was found to significantly increase slump flow; therefore, MSWI BA can be used as a microfiller. The addition of metakaolin changed the kinetics of H₂, which evolved due to the reaction between Al and alkali, and had a positive effect on the mechanical properties of cement mortar. Full article

Global objectives to mitigate climate change in the construction industry have led to increasing geopolymer development as an alternative to carbon-intensive cement. Geopolymers can have similar mechanical properties and a lower carbon footprint. However, geopolymer production is not as homogeneous as cement because it is produced by synthesizing alkali solutions with different aluminosilicate precursors. This study assessed the feasibility of using conventional (fly ash, blast furnace slag, and metakaolin) and alternative precursors (steel slag, mine tailings, glass waste, sewage sludge ashes, and municipal solid waste incineration bottom ashes (MSWI BA)) in geopolymer mixes for different European regions (Belgium and Finland) from a sustainability perspective, using environmental, economic, and resource availability indicators as the criteria. A multi-objective optimization technique was applied to identify optimal precursors for geopolymer mixes using two scenarios: (1) considering both conventional and alternative precursors; (2) only considering alternative precursors. The results from the first scenario show that one of the most optimal precursor combinations for the geopolymer mix is 50% fly ash, 25% MSWI BA, and 25% sewage sludge ash for Belgium. For Finland, it is 19% fly ash, 27% mine tailings, and 45% MSWI BA. For the second scenario, one of the most optimal precursor combinations for Belgium is 87% MSWI BA and 13% steel slag. For Finland, it is 25% mine tailings and 75% MSWI BA. Subsequently, linear regression analysis was applied to predict the compressive strength of the identified optimal mixes, and the results for Belgium and Finland were between 31–55 MPa and 31–50 MPa for the first scenario and between 50–59 MPa and 50–55 Mpa for the second scenario, respectively. Full article

In order to clarify the influence of the municipal solid waste incineration bottom ash (MSWI BA) content on the pavement performance of the cement-stabilized macadam, the MSWI BA with 0%, 25%, 38% and 50% content was used instead of fine aggregates. To explore the feasibility of building pavement base with cement stabilized MSWI BA, the cement-stabilized MSWI BA mixture was prepared by mixing the MSWI BA at the mass fraction of 50%, 75% and 100% with fine crushed stuff. Subsequently, the compaction test and 7 days unconfined compression test were conducted with 4%, 5% and 6% cement dosage. The compaction test, unconfined compressive strength test, splitting strength test, compressive resilient modulus test and frost resistance tests were carried out based on the long-age samples with an optimal cement dosage of 5%. Furthermore, the unconfined compressive constitutive model was established based on the test data. Afterwards, the test road was built to measure the practical effect of MSWI BA on road construction. Meanwhile, energy-saving and emission-reduction analyses were conducted on the MSWI BA road. The results showed that under 5% cement dosage, the mechanical properties and frost resistance of the mixture with different MSWI BA content both satisfied the specification requirements; during the construction, the appropriate MSWI BA content could be selected according to the requirements of different highway grades in the specification. The established segmented constitutive model could well simulate the stress–strain relationship of the mixture in the compressive process. Using cement-stabilized MSWI BA to build the pavement base was feasible, which provided not only an important reference for the engineering design but also had positive significance for promoting carbon peaking, carbon neutrality and sustainable development of highway engineering construction. Full article

Bottom ash (BA) is the main residue left by municipal solid waste incineration (MSWI). As the circular economy is strengthened, the use of BA in civil engineering is increasing, but its successful use is hampered by heavy metal leaching. In this study, we investigated the influence of natural weathering (6 months) on the stabilization of heavy metals (Cu, Zn, and Pb) with different particle sizes in MSWI BA. Natural weathering is the most popular and cost-effective treatment method for BA. During this process, calcium carbonate (CaCO₃) is produced, which causes a reduction in heavy metal leaching. We used the following methods in the analysis: The fractionation of BA, XRF, and XRD; an extraction test (LST EN 12457-2:2003); and AAS. The results showed that the concentrations of all elements in BA decreased during natural weathering. An analysis of the mineralogical composition showed a very high (>20%) content of calcium carbonate (CaCO₃). The calcium carbonate content increased by 3.2% during weathering because the Ca(OH)₂ in fractions <5.6 mm and <40.0 mm was hydrolyzed to CaCO₃. Our analysis showed that the metal concentrations (Cu and Pb) in untreated MSWI bottom ash eluate exceeded the limit values, and thus it cannot be used in civil engineering. After three months of stabilization, the heavy metal concentrations were less than the limit values. Full article

The growing increase in the production of municipal solid waste incinerator (MSWI) ashes has led to the research of new possibilities to reuse these by-products. This work aims to use MSW fly ash (FA) as a flame retardant filler. The FA was stabilized according to a simple stabilization process involving the mixing of only different ashes: bottom ash (BA), flue gas desulphurization (FGD) residues and coal fly ash (CFA). Stabilized FA, calcite and commercial flame retardants were compared as additives in an epoxy resin or polypropylene (PP) matrix. The self-extinguish performance of fillers was evaluated by fire resistance tests: the vertical burning test (UL94-V) and glow wire test (GWT) at 750 °C and 850 °C. A life cycle assessment (LCA) evaluation was also performed to estimate the reduction in environmental impact related to the production of the flame retardant with stabilized FA. The results show that this new filler is a promising alternative to traditional flame retardant. The ignition time of composites with calcite was lower than the corresponding sample with FA. From an environmental point of view, the replacement of calcite in an epoxy resin matrix or commercial flame retardant in a PP matrix with stabilized FA allows for a reduction in the impact of about 24.1% and 49.5%, respectively. Full article

New generations of green concretes are often consuming large amounts of industrial waste, as recycled or manufactured aggregates and alternative binders substituting ordinary Portland cement. Among the recycled materials that may be used in civil engineering works, construction and demolition waste (C&DW), fly ashes, slags and municipal solid waste incinerator bottom ashes (MSWI BA) are those most diffused, but at the same, they suffer due to a large variability of their properties. However, the market increasingly asks for new materials capable of adding some specific features to construction materials, and one of the most interesting is the pozzolanic activity. Hence, this work deals with an experimental study aimed at assessing the technical feasibility of using an industrial waste comprised largely of MSWI BA, with small quantities of C&DW and electric arc furnace slag (EAFS), in green cement-based mixtures (cement paste and mortars). The aim of the work is to achieve the goal of upcycling such waste and avoiding its disposal and landfilling. Particularly, the test methods for assessing the pozzolanic activity of this waste are discussed, analyzing the efficacy of indirect methods such as the strength activity index (SAI), the conductivity test and the efficiency factor (k), together with a direct method based on lime consumption. Full article

Waste management is a vital environmental issue in the world today. Municipal solid wastes (MSWs) are discarded in huge quantities on a daily basis and need to be well controlled. Incineration is a common method for reducing the volume of these wastes, yet it produces ashes that require further assessment. Municipal solid waste incineration bottom ash (MSWI-BA) is the bulk byproduct of the incineration process and has the potential to be used in the construction sector. This paper offers a review of the use of MSWI-BA as aggregates in cementitious materials. With the growing demand of aggregates in cementitious materials, MSWI-BA is considered for use as a partial or full alternative. Although the physical and chemical properties of MSWI-BA are different than those of natural aggregates (NA) in terms of water absorption, density, and fineness, they can be treated by various methods to ensure suitable quality for construction purposes. These treatment methods are classified into thermal treatment, solidification and stabilization, and separation processes, where this review focuses on the techniques that reduce deficiencies limiting the use of MSWI-BA as aggregates in different ways. When replacing NA in cementitious materials, MSWI-BA causes a decrease in workability, density, and strength. Moreover, they cause an increase in water absorption, air porosity, and drying shrinkage. In general, the practicality of using MSWI-BA in cementitious materials is mainly influenced by its treatment method and the replacement level, and it is concluded that further research, especially on durability, is required before MSWI-BA can be efficiently used in the production of sustainable cementitious materials. Full article

Municipal waste incinerator bottom ashes contain copper contents comparable to those of low-grade ores in addition to other valuable metals. While the processing of coarse fractions (>2 mm) is state of the art, the fines with their residual metal content are landfilled. This paper presents the results from a mineralogical characterization of fine fractions from the processing of municipal solid waste incinerator bottom ashes. From the results, possible approaches for a recovery of copper from the fine fraction are derived. Spatially resolved phase analysis reveals that the material contains a very heterogenic mixture of naturally occurring compounds as well as particles of alloys, metals, artificial oxides, and sulfides. The most interesting element to recover is copper. Copper can be found in the form of alloys, simple sulfides (XS), and oxides (XO). During the incineration process, new phases are generated that differ from natural ones and therefore can be called artificial minerals. Additionally, several components are partially altered due to oxidation, especially after the prolonged outside storage of the bottom ash. Crystalline silicate and glass particles are only sporadically enriched in Cu. Based on these results, different processing techniques are discussed. Due to the small particle size distribution and the physical and physico-chemical properties of the particles, flotation seems to be the most promising technique for the enrichment of copper from municipal solid waste incineration bottom ash (MSWI-BA) fine fractions. Full article

Production of artificial lightweight aggregate (LWA) from industrial by-products or abundant volcanic mud is a promising solution to prevent damaging the environment due to the mining of natural aggregate. However, improvements are still needed in order to control the high water absorption of LWA and strength reduction in resulting concrete or mortar. Hence in this research, fly ash, municipal solid waste incineration bottom ash (MSWI BA), and Sidoarjo volcanic mud (Lusi) were employed as a precursor and activated using NaOH 6 M and Na₂SiO₃ in producing LWA. The influence of the type of the precursors on the physical properties of resulting LWA was investigated. The effect of replacing natural fine aggregate with the resulting LWA on the compressive strength and volume density of mortar was also determined. Finer particles, a high amount of amorphous phase, and low loss on ignition (LOI) of the raw material improved the properties of resulting LWA. Mortar compressive strength was decreased by 6% when replacing 16% by volume of natural fine aggregate with fly ash based LWA. Compared to the expanded clay LWA, the properties of alternative LWAs in this study were slightly, but not significantly, inferior. Alternative LWA becomes attractive when considering that expanded clay LWA requires more energy during the sintering process. Full article

Municipal solid waste incineration (MSWI) is a major element of modern waste management and produces annually around 5.7 million tonnes of bottom ash (BA) in Germany. In order to save natural resources and protect the environment, utilisable materials need to be recovered from BA. It was the aim of the present study to determine metal and mineral resource potentials of MSWI BA based on a characterisation study of raw and aged BA of the MSWI plant in Kassel (Germany). The BA investigated consisted of 82.2% mineral materials, 16.3% metals, and 1.5% unburnt organic matter. Overall, 12.1% and 3.6% of the MSWI BA were theoretically recoverable as native ferrous (Fe) and non-ferrous (NFe) metals, respectively. Assuming state-of-the-art recovery technology, 10.7% and 2.0% of the BA were actually extractable as Fe and NFe metals. The processed BA, as a mixture, did not comply with current German limit values for use as a construction material mainly due to excessive soluble salt contents. Coarser grain size fractions were less contaminated, resulting in a utilisable potential of less than 30% of the BA as a construction material. Hence, grain-size specific processing routes need to be developed for MSWI BA to fully exploit its mineral resource potential. Full article