Solid Waste Incineration Bottom Ash Research Articles

The Sequential Extraction of Municipal Solid Waste Incineration Bottom Ash: Heavy Metals Mobility and Sustainable Application of Ashes

This manuscript focuses on the sustainable utilization of municipal waste incineration ashes in construction, taking into account their substantial concentration of beneficial elements and the potential environmental pollution caused by the leaching of toxic elements due to naturally occurring processes. To assess heavy metal mobility in ashes, a sequential extraction method based on the European Community Bureau of Reference (BCR) was applied. It enables the determination of heavy metal fractions and provides valuable insights into their potential environmental impact and bioavailability. More than 80% of Cd, and Zn, and over 75% of Cu, exhibited strong associations with the most mobile exchangeable fraction, while over 60% of Al and Fe were predominantly bound to reducible. The distribution of As and Cr was relatively balanced between exchangeable and oxidizable fractions, whereas 100% of Pb was exclusively associated with oxidizable fractions, indicating immobilization of this element in the ash. The calculated Risk Assessment Codes and Individual Contamination Factors indicated a quite high to very high risk level for the element’s mobility and environmental contamination. For elements like Pb, Cd, Cu, and Zn, higher concentrations in the samples are associated with higher overall environmental risk. For elements like As and Cr, higher concentrations in the samples are associated with lower overall environmental risk. Studied ash exhibits potential as a resource, but equally it demands rigorous environmental management to ensure responsible utilization. The observed metal mobilization underscores the necessity for stringent containment and treatment measures to mitigate the risk of environmental contamination.

Simplified kinetics model for hydrogen gas generation from metallic aluminum in municipal solid waste incineration bottom ash

The reaction of metallic aluminum in the incineration bottom ash (IBA) with an alkaline medium generates hydrogen (H2) gas. The generated H2 has caused severe cracking when IBA is used as construction material. Studies have then explored applications of IBA in aerated concretes where H2 from metallic aluminum can be utilized advantageously and found that the kinetics of H2 generation influence the cellular structure and mechanical properties. However, no kinetics model is available to understand the reaction kinetics of H2 gas generation from IBA. This study presents a simplified kinetics model employing the shrinking core model for H2 generation from metallic aluminum in IBA. The uniform distribution of metallic aluminum in IBA particles and average particle size were considered to make the model simplified for practical applications. The model was calibrated by the hydrogen gas generation from IBA and a known alkaline solution (NaOH). The temperature dependency of the reaction rate was implemented using the Arrhenius equation. The study showed that the hydrogen gas generation in IBA demonstrated reaction control kinetics at higher temperatures (≥ 60 °C) and diffusion control kinetics at lower temperatures (≈ 25 °C). The yield of hydrogen gas generation also decreased with the reduction in reaction temperature. The kinetics model was successfully validated against the experimental data for the local IBA. The presented model is expected to improve the understanding of dynamic H2 gas generation from metallic aluminum in IBA and guide the development of aerated composites with target properties where IBA is used as an aerating agent.

High-performance belite rich eco-cement synthesized from solid wastes: Raw feed design, sintering temperature optimization, and property analysis

In this study, a high-performance eco-cement with excellent CO2 sequestration capacity was synthesized using municipal solid waste incineration bottom ash and recycled concrete fine. The influence of clinkering temperature on the clinkers was assessed by mechanical properties, mineralogy, and microstructure. Optimal sintering at 1100 °C for 1 hour yielded eco-cement rich in β-C2S (44.9%), demonstrating remarkable carbonation reactivity (CO2 uptake of 12.5%) and compressive strength (1-day strength of 113.7 MPa). The presence of carbonation products, including cubic-shaped calcite and low Ca/Si C-S-H, resulted in a densified microstructure contributing to exceptional strength. Furthermore, the eco-cement exhibited latent hydraulic behavior and recorded a 28-day strength of 136.9 MPa. Varying clinkering temperatures to 1000 °C and 1200 °C promoted the formation of γ-C2S and rankinite, respectively, which generated silica gel during carbonation curing and weakened the overall performance. Leaching assessments confirmed the eco-cement's reasonable merit as an alternative, high-performance, sustainable binder.

Experimental study on the strength and water stability of concentrated solution sludge solidified with sulfoaluminate cement combined with MSWI bottom ash

Concentrated solution sludge (CSS) produced by the submersion combustion technology conducted on the municipal solid waste (MSW) sanitary landfill leachate has special characteristics, such as high water content, low organic matter and heavy metal content and extremely high salt content. In the present work, sulphoaluminate cement (SAC) was used as main curing agent and municipal solid waste incineration (MSWI) bottom ash was collaborated as auxiliary curing agent to solidify the CSS. A series of unconfined compression tests, water stability test and microscopic observation tests were conducted on the solidified CSS samples with various curing agent combinations to quantitatively investigate the influence of different curing agents on the solidification effect of the CSS, and to interpret the physical mechanism of strength improvement and deterioration of the solidified CSS in curing and soaking stage. Research results indicate that: the 7 d unconfined compression strength (UCS) of the CSS solidified with 10% SAC is 168.6 kPa, 162.8 kPa and 158.8 kPa when the water cement ratio is 0.25, 0.30 and 0.35, respectively, which are larger than 50 kPa and can satisfy the strength requirement of landfill. The UCS of the CSS solidified with 50% SAC after soaking in water for 28 days is 329.4 kPa, 276.5 kPa and 202.0 kPa when the water cement ratio is 0.25, 0.30 and 0.35, respectively, and can satisfy the strength requirement of landfill concerning water stability of the solidified CSS; the 28d UCS of the CSS solidified with 40% SAC and an addition of 0%, 5%, 10% and 15% bottom ash is 1483.8 kPa, 2144.4 kPa, 2431.2 kPa and 1537.0 kPa, respectively, and decreased to 0 kPa, 52.9 kPa, 103.9 kPa and 51.0 kPa after soaking in water for 28 days; a reasonable bottom ash content is capable of improving the USC of the cement solidified CSS and there is an optimal dosage of bottom ash for enhancing the 28 d UCS of the cement solidified CSS, which is 5% for SAC content lower than 40% and 10% for SAC content higher than 40%. The improvement effect of the solidified CSS can be achieved by using 10% bottom ash as replacement for 10% SAC. The SEM and XRD test results indicate that: the formation of the spatial interlocking structure composed of the C-S-H gels and ettringite crystals generated by the interaction between SAC and bottom ash in soaking stage is the key factor for improving the water stability of the cement solidified CSS by adding a certain dosage of bottom ash.

Sequential extraction procedure of municipal solid waste incineration (MSWI) bottom ash targeting grain size and the amorphous fraction

Introduction: Bottom ash (BA) constitutes a significant by-product obtained during the incineration of municipal solid waste in waste-to-energy (WtE) plants. BA is a heterogeneous material made of different fractions, glass, minerals, metals, and unburned residual organic matter. Due to the non-hazardous nature of the unburned material, BA can be effectively recycled, becoming a valuable resource. However, BA displays a high content of potentially toxic elements (PTEs) within its finer grain size. The presence of these elements raises concerns regarding the potential toxicity associated with BA.Materials and methods: The release of PTEs in the smaller fraction (0.063–0.2 mm; 0.3–0.5 mm; 2–4 mm; bulk <4 mm) of BA collected from the Parma WtE plant was investigated using a new five-step sequential extraction procedure (SEP). Through this method, both leached solutions and solid residues were analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS), X-ray powder diffraction (XRPD), and X-ray fluorescence (XRF) analysis. This integrated approach provided valuable insights into the mineralogy, chemical composition, and PTEs leachability of BA.Results and discussion: The novelty of this work is the development of a new SEP protocol specifically designed and planned for an anthropogenic material such as BA. The weight reduction recorded after each step is linked to the progressive disappearance of both crystalline and amorphous phases. Water-soluble phases, such as salts, are the first to react, followed by the carbonate fraction in the second step. At the end of the procedure, only quartz, corundum, and Ti-oxide are identified. Among the PTEs, Pb exhibits the highest release, particularly during the acid attack, followed by Zn. The significant release of Ni during the oxidizing and reducing steps can potentially be linked to hydroxides and metallic alloys, respectively. The integration of XRF and Rietveld refinement results on solid residues enabled the identification of several types of amorphous materials and their chemical evolution during the sequential extraction.

Analysis of Mechanical Properties and Pore Structure of Mortar Prepared from Municipal Solid Waste Incineration Slag

Abstract The disposal of a large amount of bottom ash generated from the incineration of municipal solid waste has become the focus of research in solid waste and environmentalism. Using municipal solid waste incineration bottom ash (MSWI BA) to prepare mortar can not only solve the problem of insufficient natural river sand resources, but also play a role in treating a large amount of MSWI BA to alleviate urban pressures. In this study, macroscopic properties of mortar were systematically investigated by rheological, mechanical, and drying shrinkage tests, and the influence of MSWI BA on the internal pore structure and interfacial transition zone of mortar has been analyzed by mercury intrusion porosimetry (MIP), scanning electron microscope (SEM) and back scattered electron imaging (BSE). The results show that the rheological model of fresh mortar mixed with MSWI BA as fine aggregate is more consistent with the modified Bingham model, and its plastic viscosity decreases and then increases with the increase of MSWI BA, while the yield stress shows an increasing trend. The compressive strength and splitting tensile strength of mortar decrease with the increase of MSWI BA; the smaller the water-cement ratio and aggregate-binder ratio, the greater the strength loss. The incorporation of MSWI BA improves the flexural strength and compression-flexure ratio of M5/M10 mortar, and the splitting tensile strength of M5 mortar at 28 days is increased by 30 % with 20 % MSWI BA. Additionally, the incorporation of MSWI BA reduces the drying shrinkage properties of mortar and improves the volume stability. At the same time, it increases the number of pores above 50 nm inside the mortar and the content of ettringite at the interface.

Closed-loop process for Zn and Cu selective recovery from MSWI bottom ash fine fraction

In 2019, 224 Mt of Municipal Solid Wastes (MSW) were produced in Europe. A significant proportion of this MSW is treated by incineration producing each year 20 Mt of Municipal Solid Waste Incineration (MSWI) Bottom Ashes (BA). While the coarsest fraction (>2mm) can be reemployed in construction field, this is not the case for the finest fraction <2 mm (30% wt.) which is intended to be landfilled. The challenges of the treatment of this solid residue are multiple. The metals of interest are dispersed within this complex matrix and the gangue is composed by a large proportion of carbonate based minerals which reduces the choice of possible leaching agents. Moreover, the large amounts of iron and aluminum imply to choose a highly selective recovery method and the economic constrains steer the process towards low-cost technologies. The aim of this work is to study the feasibility of a selective copper and zinc recovery, whose contents in the bottom ash fine fraction are comparable to low-grade ores. A four-step process was designed consisting of a flushing, a leaching, a precipitation and an electrowinning. A selective leaching step using ammonia-ammonium chloride solution was carried out to avoid an iron co-leaching. After the leaching step, the precipitation of zinc was achieved by addition of aluminum nitrate followed by an electrodeposition of copper from ammonia medium. Up to 70% of Cu and Zn could be recovered with minimal modifications of the leachate composition allowing thus its reuse. The developed process enables the recovery of metallic copper and zinc in a spinel form from a waste originally intended for landfilling.

Co-disposal of municipal solid waste incineration bottom ash (MSWIBA) and steel slag (SS) to improve the geopolymer materials properties

In previous studies, municipal solid waste incineration bottom ash (MSWIBA) exhibited low compressive strength when made into geopolymer materials due to the lack of active Ca. The introduction of steel slag (SS) not only supplements MSWIBA with active Ca, but also enables further treatment of SS, an underutilized solid waste. In this study, mechanical properties, XRD, TGA, FTIR and MIP are the means to evaluate this binary geopolymer. The heavy metal leaching concentration of this geopolymer was used as a basis for assessing its environmental impact. The results show that the introduction of SS helps to improve the compressive strength of geopolymers. The introduction of SS supplements the active Ca and promotes the production of C-(A)-S-H gels. Increasing the alkali doping on this basis contributes to the dissolution of active substances in MSWIBA and SS and promotes the generation of silica-aluminate gels, which likewise contributes to the development of compressive strength of geopolymers. The activation of MSWIBA by alkali can be used as an aluminum removal process, which can reduce the volume of harmful pores in the geopolymer. The solidification efficiency of heavy metals after the introduction of SS can be>90%.

The performance and microstructure of alkali-activated artificial aggregates prepared from municipal solid waste incineration bottom ash

In order to reduce the negative environmental impact of municipal domestic waste incineration bottom ash (MSWIBA), it is converted into lightweight aggregates by cold bonding technology. To enhance the utilization of waste materials, minimize cement consumption, and fabricate artificial aggregates with superior comprehensive performance, we designed and synthesized alkali-activated aggregates (AAAs) in this study. This study used MSWIBA and ground granulated blast furnace slag (GGBFS) as precursors for alkali-activated aggregates (AAAs), activated by a mixture of sodium hydroxide solutions and sodium silicate. The physical and mechanical properties of AAAs, including water absorption, apparent density, crushing strength and carbon-resistance, were investigated at different NaOH concentrations. In addition, the microstructure, mineral composition, aggregation, porosity and heavy metal leaching behavior of AAAs were analyzed by SEM, XRD, FTIR, TGA, MIP and ICP techniques. All AAAs exhibited a consistent particle size distribution, characterized by apparent densities spanning the range of 1633–1940 kg/m3. The leaching levels of heavy metals align with the standards established by Chinese regulations. Among the different activator concentrations tested, aggregate (M4) displayed superior single-particle crushing strength (3.90 MPa) and better carbonization resistance. It also used a lower concentration of NaOH, which enabled more cost-effective and eco-friendly production. Overall, the findings suggest that MSWIBA can be a viable precursor for producing sustainable lightweight concrete, with 4 M NaOH being the optimal activator concentration for achieving the best performance.

Experts’ perspectives on the sustainability and risks of freely applicable MSWI bottom ash: a Q-methodology study in the Netherlands

Experts in the Netherlands have lately debated the novel policy idea to freely apply municipal solid waste incineration bottom ash (MSWIBA). In this paper, we map this ambivalent and unforeseeable, subjective, expert debate. This will help policymaking because more knowledge on subjective expert viewpoints and perceptions allows for clustering conflict and consent as well as gaps in common understanding in this complex debate. We applied Q-methodology which resulted in four distinct perspectives in the expert debate that reveal insights into the social licence to operate and into the legitimacy of the novel bottom ash regime. The freely applicable quality of BA itself is accepted in all perspectives. Conflicting views were found about new risks, trust and socio-political acceptance of the novel BA applications. An important practical contribution of this study is that a higher acceptance of the freely applicable MSWI BA quality in the Netherlands within the expert community can be achieved if the new risks of the free application regime are tackled. We are the first to use Q-methodology in this field, and our academic contribution is that we show that this method can be a helpful tool to unravel complex expert debates also related to MSWI BA applications.

Experimental study on solidification/stabilisation of high-salt sludge by alkali-activated GGBS and MSWI bottom ash cementitious materials

This study utilises alkali-activated ground granulated blast furnace slag (GGBS) as the primary method for solidification/stabilisation, with municipal solid waste incineration (MSWI) bottom ash (BA) as an auxiliary precursor to assist in the solidification/stabilisation (S/S) of high-salt sludge. The results show that the alkali-activated GGBS and MSWI BA cementitious material can effectively realize the S/S of high-salt sludge. However, having early strength of the alkali-activated GGBS solidified sludge at low GGBS content is difficult. In comparison, the addition of MSWI BA enhances the unconfined compressive strength (UCS) of the alkali-activated GGBS solidified sludge to reach 6.35 MPa at 3d curing age, whereas the UCS of the alkali-activated GGBS solidified sludge with 20% GGBS achieves only 0.31 MPa at 14d curing age. The MSWI BA significantly improves the effect of S/S on high-salt sludge by alkali-activated GGBS, and the solidified high-salt sludge with 20% alkali-activated GGBS and MSWI BA cementitious material exhibits good water stability, the UCS of which retain 2.33 MPa after 28d water immersion. The analysis of the mineral composition, chemical bond transformation, thermal stability and microstructure of the solidified sludge samples indicates that the geopolymer cementitious material generated by alkali-activated GGBS and MSWI BA can effectively cement and wrap sludge particles and soluble salts, and reduce the strength loss of the solidified samples after water immersion. Moreover, the addition of MSWI BA accelerates the polymerization of alkali-activated GGBS, leading to rapid solidification/stabilisation of high-salt sludge in early curing age and reduction of the consumption of mineral resources. The heavy metal leaching concentration of the solidified sludge is much lower than that of the raw MSWI BA, and can satisfy the pollution control standard limit of landfill. The immobilization efficiency of the heavy metals of the solidified sludge is larger than 89%. By using MSWI BA as an auxiliary precursor in alkali-activated GGBS, the co-disposal of high-salt sludge and MSWI BA can be achieved, providing insights for realizing the energy conservation and environment protection purposes of solid waste reclamation and GGBS consumption reduction.

Test study on mechanical properties of compound municipal solid waste incinerator bottom ash premixed fluidized solidified soil

In this paper, the municipal solid waste incineration bottom ash (MSW-IBA) is used as the fine aggregate and firming agent component of the premixed fluid stabilized soil (PFSS). Through the mechanical strength test, and the hydration products and microstructure characterization, the effects of the NaOH content for MSW-IBA pre-aging treatment and activator content on the mechanical properties of the PFSS are studied. The results show that the mechanical strength of the prepared PFSS is closely related to the amount of NaOH and the activator. The increase in the amount of NaOH and activator can affectthe formation of early hydration product Aft, and reduce the early strength. However, it can promote the depolymerization of glass phase in MSW-IBA and slag to form C-(A)-S-H and Mg-(A)-S-H gel, increase the microstructure density, and thus improve the late strength. The application of MSW-IBA in PFSS can achieve the recycling of solid waste.

The Influence of Liquid/Solid Ratio and Pressure on the Natural and Accelerated Carbonation of Alkaline Wastes

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.

Processing municipal solid waste incineration bottom ash for integration into cement product manufacture

Municipal solid waste incineration (MSWI) bottom ash (BA) contains the elemental composition necessary for cement and concrete production and is a feasible substitute for high-value markets such as cement kiln feed (CKF) and supplementary cementitious material (SCM), providing an opportunity to recycle materials that are typically landfilled. This study explores the physical and chemical properties of individual components of MSWI BA—glass, ceramic, concrete, and slag—for use in cement product manufacture. Elemental oxide data reveals MSWI BA contains a variable composition of elements necessary for clinker formation. For example, MSWI BA concrete has a calcium content (33–40%) similar to that of limestone (64%) used in CKF. Compressive strength of mortar made with MSWI BA glass and ceramic is about 75% that of the control. Elemental analysis and isothermal calorimetry confirm that MSWI BA glass and ceramic fractions have the strength and elemental composition for use as an SCM compared to slag and concrete.

Recycling of waste glass in lightweight geopolymer using incineration bottom ash as a foaming agent: Towards energy conservation

A large amount of waste glass and municipal solid waste incineration bottom ash (IBA) generated in municipalities is a serious environmental issue. For energy conservation purpose, this study aimed to develop a novel thermal insulating lightweight self-foaming geopolymer (SFG) material using waste glass as the main precursor and IBA as a foaming agent. The microstructure was investigated by XRD, FTIR, NMR, MIP and SEM-BSE techniques to reveal the mechanisms of the foaming process and geopolymerization reaction. The results showed that the use of 100% waste glass powder (WGP) as the precursor led to a connecting-cracked matrix due to silica gel shrinkage. However, the cracking was significantly alleviated when 50% IBA was incorporated as IBA contributed to more stable C-(N)-A-S-H (calcium silicate hydrate substituted with Al and Na) production as well as spherical pores formation to mitigate crack propagation. The SFG prepared with 50% IBA exhibited a geopolymer matrix with more regular and independent pores than that prepared with 100% IBA. This was because the high metallic Al content in IBA generated an excessive amount of hydrogen gas, resulting in the development of irregular and interconnected pores. Given the stability of the reaction products with fewer cracks and a uniform pore structure, the SFG prepared with 50% IBA and 50% WGP exhibited satisfactory functional properties (low density and thermal conductivity as well as desirable compressive strength), indicating a great potential for energy saving and environmental protection.

A study of chloride pretreatment methods for enhancing strength of mortar by recycling Municipal Solid Waste Incineration (MSWI) bottom ash

This study explores four different ways (tap water, deionized water, sodium chloride, and seawater) as the pretreatment methods of Municipal Solid Waste Incineration (MSWI) bottom ash used in mortar. After incorporation of the bottom ash as partial replacement of fine aggregate, the mixtures were evaluated for compressive strength, heat of hydration, chloride content and shrinkage performance. The results reveal that all pretreated samples have comparable compressive strength at early age (day-7) and higher compressive strength at later age (day-120). Meanwhile, the pretreatment in tap water and deionized water can slightly reduce the chloride content, whereas the other two pretreatment methods induce extra chloride ions into the mixtures. The correlation between the chloride content and the peak temperature indicates the acceleration effect of chloride ions during hydration. In addition, all the specimens with pretreated MSWI aggregates have higher shrinkage regardless of pretreatment methods.

Feasibility of producing eco-friendly self-compacting mortar with municipal solid waste incineration bottom ash: A preliminary study

Municipal solid waste incineration bottom ash (MSWI-BA) is a major by-product of municipal solid waste incineration, leading to severe shortages of landfill sites in metropolitan cities. To achieve the resource utilization of MSWI-BA, this study explored the feasibility of producing ecological self-compacting mortar (eco-SCM) with MSWI-BA to realize recycling in building materials. First, it focused on the impact of the MSWI-BA proportion on eco-SCM with regard to workability, physical performance, mechanical performance, and durability. Second, it explored changes in the micro pore structure and micromorphology of eco-SCM under the impact of MSWI-BA. Finally, it evaluated the environmental friendliness and cost-effectiveness of eco-SCM. It was found that, (1) the mechanical strength of eco-SCM added with MSWI-BA was decreased. Eco-SCM added with MSWI-BA had compressive strength, flexural strength, and dynamic elastic modulus within the range of 37.71–54.76 MPa, 13.89–20.93 MPa, and 21.05–35.84 GPa, respectively; (2) Due to the addition of MSWI-BA, the chloride permeability of eco-SCM were deteriorated, but its durability was still satisfactory; (3) The environmental friendliness and economic performance of eco-SCM could be significantly improved, because of the addition of MSWI-BA. The energy consumption, carbon emissions, and costs of eco-SCM added with MSWI-BA at 40 wt % were decreased by 10.26 %, 10.49 %, and 26.50 %, respectively; (4) Considering the changes in the workability, mechanical property, durability, environmental friendliness, and economic performance of eco-SCM added with MSWI-BA, MSWI-BA could be used to prepare eco-SCM and could be recycled in building materials.

Mechanism of macro- and microscopic performance of cement mortars influenced by municipal solid waste incineration bottom ash as sand substitution

With growing construction work, natural sand has turned out an endangered resource for building materials, leading to a research hotspot for alternative materials as natural sand substitutes. In this paper, we investigated the effect of municipal solid waste incineration (MSWI) bottom ash replacing natural sand on macro- and microscopic performance of cement-based materials after wet treatment. The viability of bottom ash in the mortar was explored instead of conventional fine aggregates. The fluidity, flexural strength, and compressive strength of different water-cement ratios in the mortar with substitution of 0%, 25%, 50%, and 75% were investigated by using the macro-experimental method. We examined the components and micro-morphology of hydration products by using thermogravimetry–differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results demonstrated that a large substitution amount slightly effects the strength of cement mortar, while the early strength became stronger with the increase of the substitution rate. Notably, MSWI bottom ash showed a certain pozzolanic activity, which reduces the formation of Ca(OH)2 and can improve the early strength of the mortar. Additionally, the leaching concentrations of heavy metals (Cu, Zn, Pb, Cr, etc) in the mortars containing bottom ash were all less than the identification value of solid waste leaching toxicity. The carried out research confirmed that MSWI bottom ash can successfully replace conventional sand as building materials. The proposed work enables the reuse of MSWI bottom ash and also provides a reliable and effective method for solving the shortage of conventional aggregate resources.

Durability-related performance of recycled aggregate concrete containing alkali-activated municipal solid waste incinerator bottom ash

The increasing demand for sustainable construction materials has led to a growing interest in the use of recycled materials in concrete production. The main motivation for this research is to explore sustainable alternatives to conventional concrete mixes that can reduce the environmental impact of construction activities and address the growing issue of waste accumulation. For this reason, this study intends to evaluate the performance of alkali-activated concrete with different contents of fly ash (FA) and municipal solid waste incinerator bottom ash (MIBA). For this purpose, five compositions were considered, where the binder ratios were 100% cement, 100% FA, 75% FA/25% MIBA, 50% FA/50% MIBA and 25% FA/75% MIBA, all of which were produced with natural aggregates. Five additional mixes were produced by fully replacing the natural aggregate with recycled aggregate from mixed construction and demolition waste. A mix with 100% FA, fine natural aggregates and coarse recycled aggregates was also produced to understand the difference between the full use of recycled aggregates and their partial use. The conducted tests include compressive strength, water absorption by capillarity and immersion, chloride penetration, carbonation, and shrinkage (autogenous and total). The results showed that the substitution of FA with MIBA led to progressively worse durability-related performance, though manageable in given proportions. The incorporation of recycled aggregates led to an unexpectedly steep decline of ∼80% in compressive strength and overall durability performance in comparison with equivalent cement-based recycled aggregate concrete mixes. Nevertheless, the trend reverted in terms of shrinkage, wherein recycled aggregate-containing mixes presented the least dimensional variations. In the mechanical strength test, the curing of the alkali-activated concrete mixes in a CO2 chamber led to a considerable improvement (i.e. 5–15 MPa) in all tested mixes.

Engineered cementitious composites using powder regenerated from municipal solid waste incineration bottom ash as supplementary cementitious material

Ecotype Engineered Cementitious Composites (ECC) can not only consume a huge amount of solid waste, reduce environmental pollution and human damage, but also reduce the high production cost of such materials. In this research, municipal solid waste incineration (MSWI) bottom ash was used to develop economical and applicable ecotype ECC. Firstly, the physical and chemical properties of MSWI bottom ash with different particle sizes were analyzed, and the bottom ash particles with high reactivity were screened out and ground into powder. Then the uniaxial tensile and four-point bending tests were used to study the mechanical strength and strain-hardening properties of ECC containing bottom ash powder. The results present that the powder milled by bottom ash particles with the size of 2.36–9.5 mm has finer particles and higher reactivity. The optimal ratio of bottom ash powder to cement for ECC can be determined as 2.2:1. Here ECC not only has high mechanical strength but also exhibits wonderful strain-hardening properties and multiple micro-cracking capacities. The increase in fiber content and water-binder ratio is beneficial to the development of excellent ductility. This study provides a strategy to produce low-cost ecotype ECC by using MSWI bottom ash powder as supplementary cementitious materials.