Search Results (125)

The objective of this work is to evaluate how spent catalyst from fluid catalytic cracking (SCFCC) affects the physical, mechanical and durability properties of fly ash (FA) and blast furnace slag (BFS)-based alkali-activated materials (AAMs). Recycling of SCFCC by integrating it in a AAM matrix offers several advantages: valorization of the material, reducing its disposal in landfills and the landfill cost, and minimizing the environmental impact. Mineralogical, physical and mechanical characterization were carried out. The durability of the specimens was studied by performing acid attack and thermal stability tests. Mass variation, compressive strength and porosity parameters were determined to assess the durability. BFS- and FA-based AAMs have a different chemical composition, which contribute to variations in microstructure and physical and mechanical properties. Acid neutralization capacity was also determined to analyse the acid attack results. Porosity, including the pore size distribution, and the acid neutralization capacity are crucial in explaining the resistance of the AAMs to sulfuric acid attack and thermal degradation. Herein, a novel route was explored, the use of SCFCC to enhance the durability of AAMs under harsh operating conditions since results show that the compositions containing SCFCC showed lower strength decay due to the lower macroporosity proportions in these compositions. Full article

Circulating fluidized bed fly ash (CFBFA) stockpiles release alkaline dust, high-pH leachate, and secondary CO₂/SO₂—an environmental burden that exceeds 240 Mt yr⁻¹ in China alone. Yet, barely 25% is recycled, because the high f-CaO/SO₃ contents destabilize conventional cementitious products. Here, we presents a pressurized flue gas heat curing (FHC) route to bridge this scientific deficit, converting up to 85 wt% CFBFA into structural lightweight gravel. The gypsum dosage was optimized, and a 1:16 (gypsum/CFBFA) ratio delivered the best compromise between early ettringite nucleation and CO₂-uptake capacity, yielding the highest overall quality. The optimal mix reaches 9.13 MPa 28-day crushing strength, 4.27% in situ CO₂ uptake, 1.75 g cm⁻³ bulk density, and 3.59% water absorption. Multi-technique analyses (SEM, XRD, FTIR, TG-DTG, and MIP) show that FHC rapidly consumes expansive phases, suppresses undesirable granular-ettringite formation, and produces a dense calcite/needle-AFt skeleton. The FHC-treated CFBFA composite gravel demonstrates 30.43% higher crushing strength than JTG/TF20-2015 standards, accompanied by a water absorption rate 28.2% lower than recent studies. Its superior strength and durability highlight its potential as a low-carbon lightweight aggregate for structural engineering. A life-cycle inventory gives a cradle-to-gate energy demand of 1128 MJ t⁻¹ and a process GWP of 226 kg CO₂-eq t⁻¹. Consequently, higher point-source emissions paired with immediate mineral sequestration translate into a low overall climate footprint and eliminate the need for CFBFA landfilling. Full article

International waste policy promotes the reduction and re-use of waste materials, and in some cases, specifically calls for the use of recycled materials in pavements. In countries like Australia, most of the aircraft pavement network is constructed of flexible pavements. Consequently, understanding the opportunities for recycled materials in flexible aircraft pavements is paramount to increasing the technology uptake. This paper reviews opportunities for the incorporation of recycled materials in flexible airport pavement construction, specifically, their application to particle substitution in unbound and asphaltic layers, use in stabilization treatments, and use as a bitumen modifier. Additionally, environmental product declarations are reviewed to provide a range of typical environmental costs for each recycled material when considering material processing for incorporation into flexible pavements. These materials are compared to virgin material environmental costs to determine which recycled materials provide the highest environmental benefit potential. It was concluded that particle replacement in unbound layers with waste materials had a similar environmental cost to using virgin materials. However, the requirement to dispose of waste material to the landfill can be significantly reduced. For asphaltic layers, recycled asphalt pavement as an asphalt mixture replacement, fly ash as a hydrated lime replacement, and waste plastic and crumbed rubber as a virgin polymer replacement all are effective in reducing the environmental cost. To further increase the technology uptake, a risk-based approach for the implementation of waste materials in airport flexible pavements is recommended, which considers performance testing, the depth of the pavement layer, and the pavement functional area. Full article

Renewable energy sources are presented as a key solution to today’s energy needs, but they also generate waste that can have a negative impact on the environment. In particular, fly ash from the incineration of municipal solid waste (MSW), classified as hazardous by European regulations, is often deposited in landfills due to its lack of usefulness. This research proposes its valorisation in geopolymers, combining it with mining to create a sustainable material with a high industrial waste content. Firstly, all the wastes involved were characterised, which allowed for the development of a high-quality geopolymer from mining residue activated with 5% NaOH. This material was enriched with up to 50% fly ash (in increasing percentages) with the aim of making it inert, retaining it in the geopolymer matrix, and observing its effect on the final material. The physical and mechanical properties of the geopolymers obtained were evaluated, demonstrating that they do not produce contaminating leachates. The results indicate the feasibility of developing a geopolymer with up to 20% fly ash, obtaining a building material comparable to traditional ceramics, suitable for commercialisation, with a lower environmental impact and in line with the principles of the circular economy. Full article

Resource depletion and environmental degradation have resulted from the substantial increase in the use of natural aggregates and construction materials brought on by the growing demand for infrastructure development. Road building using mining waste has become a viable substitute that reduces the buildup of industrial waste while providing ecological and economic advantages. In order to assess the appropriateness of several mining waste materials for use in road building, this study investigates their engineering characteristics. These materials include slag, fly ash, tailings, waste rock, and overburden. To ensure long-term performance in pavement applications, this study evaluates their tensile and compressive strength, resistance to abrasion, durability under freeze–thaw cycles, and chemical stability. This review highlights the potential of mining waste materials as sustainable alternatives in road construction. Waste rock and slag exhibit excellent mechanical strength and durability, making them suitable for high-traffic pavements. Although fly ash and tailings require stabilization, their pozzolanic properties enhance subgrade reinforcement and soil stabilization. Properly processed overburden materials are viable for subbase and embankment applications. By promoting the reuse of mining waste, this study supports landfill reduction, carbon emission mitigation, and circular economy principles. Overall, mining byproducts present a cost-effective and environmentally responsible alternative to conventional construction materials. To support broader implementation, further efforts are needed to improve stabilization techniques, monitor long-term field performance, and establish effective policy frameworks. Full article

Reducing carbon dioxide emissions is a key priority in the European Union, which aims to achieve carbon neutrality by 2050. Construction has a key role to play in this effort, as it is responsible for a significant proportion of greenhouse gas emissions, especially due to cement production. At the same time, waste reuse emerges as a key strategy within the circular economy, another pillar of European policies. By valuing byproducts and waste, such as construction and demolition waste (CDW), it is possible to reduce the extraction of natural resources, amount of waste sent to landfills, and emissions associated with the production of new materials. This study, with the main objective of evaluating the possibility of using CDW as supplementary cementitious materials, emerges as a possible solution to reduce these problems. Two CDW treatment methods were used: (i) mechanical grinding and (ii) calcination. The mechanical grinding method, even with the use of laboratory equipment, has shown that it is possible to obtain CDW particles with characteristics suitable for replacing cement. For the calcination process, temperatures between 600 °C and 800 °C were the most suitable. The results proved that the replacement of cement by CDW in pastes resulted in suitable behavior for the construction industry, having revealed an incorporation content of up to 25% CDW, a compressive strength and strength activity index higher than that found for pastes developed with fly ash. Regarding the calcination process, this revealed an improvement in the compressive strength of the developed pastes, resulting in an increase in strength activity index of between 7 and 10%. Full article

Traditional landfill cover materials have low strength and poor dry–wet durability. Municipal solid waste incineration fly ash (MSWI FA) can be used to partially replace cement solidification dredging sediment (DS). This article investigates the possibility of using MSWI FA and ordinary Portland cement (OPC) composite cured DS as a covering material. The mechanical properties, permeability, and wet–dry durability of the cured system were investigated under the conditions of MSWI FA content ranging from 0% to 60% and OPC content ranging from 10% to 15%. The microscopic mechanism was analyzed by scanning electron microscopy and X-ray diffraction. The results showed that when the OPC and MSWI FA contents were 15% and 20%, respectively, the comprehensive performance of the cured specimens was best after 28 days of natural curing. The unconfined compressive strength reached 1993.9 kPa, and the permeability coefficient decreased to below 1 × 10⁻⁷ cm/s, fully meeting the requirements for landfill coverage. C-S-H gel is the main strength source of the solidified body, while Friedel salt and ettringite enhance the compactness of the matrix. An excessive moisture environment promotes the water absorption of soluble salts produced by MSWI FA hydration, leading to sample expansion and reduced strength. MSWI FA and OPC cured DS exhibit good compression performance in the intermediate cover system of landfills, and can maintain good engineering performance under periodic dry–wet cycles. This dual strategic synergy solves the hazardous disposal problem of MSWI FA and the resource utilization demand of DS, demonstrating enormous application potential. Full article

Municipal solid waste incineration fly ash (MSWI FA) is a hazardous waste that must be kept in special landfills due to the high amounts of chlorides, sulfates, and heavy metals. The granulation of MSWI FA could be used as a solidification/stabilization (S/S) of fly ash to immobilize hazardous chemical elements and to reduce dust emissions. In this work for granulation, three different binders were used: calcium aluminate cement (CAC), geopolymer (GEO), and Portland cement (PC). Chemical (XRF), mineral (XRD), granulometric compositions, and leaching of prepared granules are presented in the article. Furthermore, the impact of different binders on bulk density, compressive strength, and granule structure was analyzed. The results show that the granules with CAC binder have the best initial compressive strength (about 10 MPa), but these granules were destroyed after the leaching test or connection with water. The geopolymer as a binder did not provide the required compressive strength and immobilization of harmful elements. Granules with a Portland cement binder have a suitable compressive strength, a slight leaching of chemical elements, and good durability in the alkaline and acidic environment; they are also resistant to freezing and thawing cycles. Full article

Red mud (RM), a highly alkaline waste from alumina production, poses severe environmental threats due to massive stockpiling (>350 million tons in China) and groundwater contamination. This study evaluates three scalable strategies to repurpose RM: iron recovery via magnetic separation, sintered brick production using RM–fly ash–granulated blast furnace slag (6:1:3 ratio), and non-calcined cementitious binders combining RM and phosphogypsum (PG). Industrial-scale iron extraction achieved 23.85% recovery of iron concentrate (58% Fe₂O₃ grade) and consumed 3.6 million tons/year of RM, generating CNY 31 million annual profit. Sintered bricks exhibited 10–15 MPa compressive strength, meeting ASTM C62-23 standard while reducing material costs by 30%. The RM–PG binder achieved 40 MPa compressive strength at 28 days without cement or calcination, leveraging RM’s alkalinity (21.95% Na₂O) and PG’s sulfate activation. Collectively, these approaches reduced landfill reliance by 50% and CO₂ emissions by 35%–40% compared to conventional practices. The results demonstrate RM’s potential as a secondary resource, offering economically viable and environmentally sustainable pathways for the alumina industry. Full article

Significant amounts of coal fly and bottom ash are generated globally each year, with especially large quantities of bottom ash accumulating in landfills. In this study, fly ash and bottom ash were used to create fire-resistant materials. A mix of 30 wt% gypsum, 9.5 wt% vermiculite, and 0.5 wt% polypropylene fibers was used, maintaining a constant water-to-solid ratio, with varying fly ash/bottom ash ratios (40/20, 30/30, and 20/40). The density, as well as various mechanical properties (compressive strength, flexural strength, and surface hardness), fire insulation capacity, and leaching behavior of both ashes were evaluated. When comparing the 40/20 and 20/40 compositions, a slight decrease in density was observed; however, compressive strength dropped drastically by 80%, while flexural strength decreased slightly due to the action of the polypropylene fibers, and fire resistance dropped by 8%. Neither of the ashes presented any environmental concerns from a leaching standpoint. Additionally, historical data from various materials with different wastes in previous works were used to train different machine learning models (random forest, gradient boosting, artificial neural networks, etc.). Compressive strength and fire resistance were predicted. Simple parameters (density, water/solid ratio and composition for compressive strength and thickness and the composition for fire resistance) were used as input in the models. Both regression and classification algorithms were applied to evaluate the models’ ability to predict compressive strength. Regression models for fire resistance reached r² up to about 0.85. The classification results for the fire resistance rating (FRR) showed high accuracy (96%). The prediction of compressive strength is not as good as the fire resistance prediction, but compressive strength classification reached up to 99% accuracy for some models. Full article

In response to environmental challenges and primary resource scarcity, sustainable approaches that rely on recycling and reusing waste materials are becoming valuable and highly appealing options in modern society. This paper deals with the usage of porous glass and glass-ceramic products derived from waste in the field of thermal insulation in buildings. After providing an overview of the current state of the art with a focus on existing commercial products and related manufacturing methods (foaming strategies), this review discusses the emerging trends toward greener approaches, including the use of by-products or waste substances as foaming agents (e.g., eggshells or mining residues), the use of vitrified bottom or fly ashes from municipal solid waste incinerators as starting materials, the application of surface treatment to reduce post-processing temperatures, and the promise of additive manufacturing technologies in this field. The increased use and spread of sustainable practices are expected to significantly contribute to glass recycling, to minimize landfilling, and to generally reduce energy consumption as well as greenhouse emissions. Full article

This paper analyzes the effective use of a mixture of fly ash (MSWI-FA) and solid waste from flue gas treatment (MSWI-SW), which are by-products of the municipal waste incineration process. MSWI-FA (19 01 13*) and MSWI-SW (19 01 07*) are classified as hazardous waste due to their toxic metal content and leaching potential, and currently lack practical applications, unlike slag and bottom ash (19 01 12). This study tested these wastes as partial substitutes for natural sand within a range of 0–20% of cement mass. Statistical analysis of the experimental results allowed the creation of good quality models predicting the effect of substitution additives on compressive strength and flexural strength (correlation 0.91 and 0.93, respectively). The mixture with the highest share of substitution additives (40% = 20% + 20%) was characterized by a decrease in compressive strength by 1.3% and flexural strength by 25.8%. Cement mortars synthesized with the waste mixture (up to 20% of each component) showed slightly lower consistency and water absorption than the control mortars. After the frost resistance tests (25 cycles), the flexural and compressive strength showed ambiguous behavior, showing both increases and decreases, indicating that the percentage of waste components alone is an insufficient set of factors for predicting these strength properties. The concentration of metal ions, i.e., Zn, Cu, Pb, Ni, Cu, and Cr, in the eluate after the leaching tests did not exceed the legal levels of pollutants introduced into waters, with the exception of barium. However, its content did not exceed the permissible levels required for waste intended for landfill. Using the mixing plant for this waste in the amount of 20% each, we save about EUR 10 in the cost of purchasing sand (which is 13% of the production costs of 1 m³) and EUR 8 in the cost of environmental fees when producing 1 m³ of mortar. The proposed technology is compatible with the objectives of a sustainable economy. Full article

Fly ash does not contain organic matter to initiate soil-forming processes and the proper development of plant cover. Therefore, in the reclamation of fly ash landfills, an integrated approach is required, including the introduction of exogenous organic matter into the top layer of ash. This study assessed changes in the content and quality of organic matter in soils developing on a reclaimed fly ash landfill. This study included reclaimed areas without the introduction of EOM (RV_1—the direct introduction of plants) and with the introduction of EOM (RV_2—surface humus and RV_3—sewage sludge). In samples taken 15 years after reclamation, the contents of total organic carbon (TOC) and total nitrogen (TN), the fractional composition of organic matter, the susceptibility of organic matter to oxidation, and soil carbon management indices (carbon pool index (CPI), C lability (L), lability index (LI), and carbon management index (CMI)) were determined. The study results showed that the use of EOM in the reclamation of the ash dump significantly increased the content and improved the quality parameters of organic matter and thus influenced the initiation of the process of organic matter accumulation. In RV_1 soil, the accumulation of carbon resources was only found in the topsoil. An increase in carbon resources in the 15–40 cm layer was only noted in the variants in which EOM was introduced (RV_2 and RV_3). Carbon management indices showed that organic matter transformations covered only the top layers of these soils and were closely related to the EOM inflow. The interdependence of the CPI and L was most beneficial in the soil reclaimed with sewage sludge. In the soil of this reclaiming variant, the CMI had a value above 100, which indicates the initiation of the soil-forming process. Significant differences between the assessed reclamation variants were confirmed by means of PCA based on organic matter quality indicators. The organic matter content and quality indicators were the most favorable in the soil of variant RV_3. The obtained results confirmed that the introduction of EOM into the top layer of fly ash has a beneficial effect on the accumulation and quality indicators of organic matter and thus on the development of the soil-forming process in Technosols developing on a reclaimed fly ash landfill. Full article

Fly ash derived from the incineration of garbage is known to contain hazardous materials that can affect the growth of plants and animals and pose a threat to human health. In this study, we explored how treatment of fly ash leachate with microalgae could alter the properties of dissolved organic matter (DOM). Fly ash leachate samples obtained from a landfill site in Wenzhou were treated with the microalgae Chlorella vulgaris or Scenedesmus obliquus without and with the addition of ammonium ferric citrate (C₆H₈FeNO₇) for 24 days, and changes in DOM levels and types were measured using excitation emission matrix fluorescence technology. The following results were obtained: Analysis of three-dimensional fluorescence spectral indices indicated that the algal treatment process consistently generated new autogenous DOM, with most of the organic matter being newly formed. Additional nutrients had a minor effect on the production and composition of DOM in the system. Using a parallel factor model to analyze the three-dimensional fluorescence spectral matrices of water samples from various systems revealed common components in each group, including arginine, tryptophan-like proteins and fulvic acid-like substances. This study aimed to explore the changes in DOM properties during microalgae treatment of fly ash leachate from the perspective of three-dimensional fluorescence. Full article

The rising population and demand for plastic materials lead to increasing plastic waste (PW) annually, much of which is sent to landfills without adequate recycling, posing serious environmental risks globally. PWs are grinded to smaller sizes and used as aggregates in concrete, where they improve environmental and materials sustainability. On the other hand, PW causes a significant reduction in the mechanical properties and durability of concrete. To mitigate the negative effects of PW, highly reactive pozzolanic materials are normally added as additives to the concrete. In this study, PW was used as a partial substitute for coarse aggregate, and graphene nanoplatelets (GNPs) were used as additives to high-volume fly-ash concrete (HVFAC). Utilizing PW as aggregates and GNPs as additives has been found to enhance the mechanical properties of HVFAC. Hence, this study employed two machine-learning (ML) models, namely Gaussian Process Regression (GPR) and Elman Neural Network (ELNN), to forecast the mechanical properties of HVFAC. The study input variables were PW, FA, GNP, W/C, CP, density, and slump, where the target variables are compressive strength (CS), modulus of elasticity (ME), splitting tensile strength (STS), and flexural strength (FS). A total of 240 datasets were employed in this study and divided into calibration (70%) and validation (30%) sets. During the prediction of the CS, it was found that GPR-M3 outperforms all other models with an R-value equal to 0.9930 and PCC value of 0.9929 in the calibration phase, and R-value = 0.9505 and PCC = 0.9339 in the verification phase. Additionally, during the modeling of FS, it was also noticed that GPR-M3 surpasses all other combinations with R = 0.9973 and PCC = 0.9973 in calibration and R = 0.9684 and PCC = 0.9428 in the verification phase. Moreover, in ME modeling, GPR-M3 is the best modeling combination and shows high accuracy with R = 0.9945 and PCC = 0.9945 in calibration and R = 0.9665 and PCC = 0.9584 in the verification phase. On the other hand, GPR-M3 outperforms all other models during the modeling of STS with R = 0.9856 and PCC = 0.9855 in calibration, and R = 0.9482 and PCC = 0.9353 in the verification phase. Further quantitative analysis shows that, in the prediction of CS, the GPR improves the prediction accuracy of ELNN by 0.49%, while during the prediction of the splitting tensile strength, it was also found that the GPR improved the accuracy of ELNN by 1.54%. In FS prediction, it was also improved by 7.66%, while in ME, it was improved by 4.9%. In conclusion, this AI-based model proves how accurate and effective it was to employ an ML-based model in forecasting the mechanical properties of HVFAC. Full article