Production Of Lightweight Aggregates Research Articles

Use of bauxite tailing for the production of fine lightweight aggregates

The prediction of bloating of lightweight aggregates (LWA) made from waste materials according to the chemical composition of raw material does not provide a good fit with existing theories. To explain the pore formation of LWA more accurately, it is necessary to consider the effect of initial voids due to gas release before the generation of the liquid phase. This study utilized the bauxite tailing and silica fume as raw material and a two-step firing method to produce fine LWA. The basic properties and microstructure of LWA were evaluated. The experimental results showed that bauxite tailing and silica fume played different roles in the pore formation of LWA. Bauxite tailing can provide gas-generating components related to the initial voids. Silica fume can promote the generation of the liquid phase associated with the development of closed pores. The LWA produced from bauxite tailing and silica fume had a bulk density of 931–1100 kg/m3 and water absorption of 1.2–16.6%, which met the specification standard for LWA. Silica fume of above 20% and sintering temperature of above 1100 °C could produce LWA applied in lightweight concrete and insulation wall panels, while silica fume of below 20% and sintering temperature of below 1100 °C could produce LWA for internal curing. In a word, it was possible to achieve the bloating of LWA by controlling the amount of gas released using the two-step firing method. Introducing the concept of initial voids can lead to the successful design and production of functional LWA having desirable engineering properties for different industrial applications.

Recycling municipal solid waste incineration fly ash in super-lightweight aggregates by sintering with clay and using SiC as bloating agent

Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste and requires proper treatments. Sintering of MSWI fly ash for the production of lightweight aggregate (LWA) is a promising treatment technology, while the dependence on natural bloating clay to produce high quality LWA has limited its wide application. In this study, by using SiC as a bloating agent, normal clay could be used to produce super-lightweight aggregate (bulk density <500 kg/m3) with MSWI fly ash. Effects of SiC addition amount, sintering temperature and duration on LWA performance were studied. The results showed that LWA with SiC addition of 0.1–0.5 wt% had significant expansion at sintering temperature of 1120 °C–1160 °C. The optimal conditions were 0.3 wt% SiC addition and sintering at 1120 °C for 30 min, and the bulk density could reach 212 kg/m3 with other properties meeting the LWA standard (GB/T 17431.1-2010). Further, the heavy metal leaching toxicity was significantly decreased after sintering and met the MSWI fly ash utilization standard (HJ 1134–2020). The X-ray diffraction results revealed the formation of a complex diopside-based phase after sintering. This study provides a new approach for recycling MSWI fly ash in LWA without dependence on specific clay resources, and makes this technology wider applicability.

Microwave Fast Sintering Production of Sustainable Lightweight Aggregates with Agroindustrial Waste

Microwave Fast Sintering Production of Sustainable Lightweight Aggregates with Agroindustrial Waste

ANALYSIS OF THE POSSIBILITY OF USING PLASTIC POST-PRODUCTION WASTE IN CONSTRUCTION

This paper presents the possibility of managing plastic post-production waste, i.e. ordinary and heat-shrinkable film, in the construction sector. For this purpose, two types of lightweight 16 mm aggregate were produced from plastics, using proprietary technology (i.e. polyethylene terephthalate (PET) and PET/PVC/OPS (MIX) mixtures). The raw material was sourced from post-production waste, generated during the production of film labels. The results of the experimental testing of aggregate properties (bulk density, grain density, absorbability, compressive strength) are presented, the aggregate being sourced from recycled plastics. This paper presents the physical and mechanical properties of the plastic, as well as other popular lightweight aggregates (Certyd and Kermazyt) used in construction. In addition, the financial efficiency of the production of lightweight aggregate from the by-products of plastic label production was analysed. The economic analysis has shown that the use of plastic waste for the production of lightweight aggregate is rational, not only in terms of environmental protection, but also the financial benefits to companies that generate significant amounts of plastic waste.

Life cycle sustainable assessment of natural vs artificial lightweight aggregates

Optimal selection of concrete aggregates can promote sustainable construction practice from the bottom line, which is a feasible strategy to cope with resources crisis and solid waste pollution. In this study, a two-level tree structure framework was thus proposed for the sustainability assessment of lightweight aggregates (LWA) based on the life cycle assessment concept. The evaluation system was divided into four criteria categories marked as society demands, economic costs, environmental impacts and technical performance, and each of them was assigned a number of sub-index. A qualitative questionnaire survey with seven sub-index and a quantitative calculation with eight sub-index were executed in the target system. Sintering fly ash aggregates (SFFAA), cold-bonding fly ash aggregates (CBFAA), waste clay brick aggregates (WCBA) and natural pumice aggregates (NPA) were chosen as typical artificial and natural lightweight aggregates objectives and evaluated in the framework. Impact and sensitivity analyses were conducted to comparably discuss the sustainability of various lightweight aggregates. The impact analyses represented that the waste clay brick aggregate has better sustainability. The sensitivity analysis shows that the supply-demand relationship of raw materials greatly impacts the sustainability of lightweight aggregate, and the transportation distance of raw materials is the critical factor in the production of LWA. At the same time, artificial lightweight aggregates are sensitive to cement binder consumption, and zero cement addition or waste cement powder is an optimistic option. From the sustainable life cycle assessment results, waste clay brick aggregates, sintering fly ash aggregates and cold-bonding fly ash aggregates are suggested as the alternative to the natural pumice aggregates for the lightweight aggregates concrete production. The emphasis on the weight of the social dimension will tend to prefer the selection of SFAA, and the economic or environmental dimension will lead to the preference of CBFAA for sustainable development. The framework proposed in this work could be used in choosing other sustainable construction materials or cleaner products.

Production of Synthetic Lightweight Aggregates from Industrial Sludge.

Industrial sludge continues to increase in quantity with the development of industry. Therefore, how to effectively treat industrial sludge continues to be an environmental focus around the world. Due to the high calorie content of industrial sludge in Taiwan, most of the sludge is incinerated for simplicity and convenience. However, this incineration causes environmental pollution and cannot effectively reuse the industrial sludge. In this study, we investigated the feasibility of lightweight aggregates produced from water treatment sludge (WTS) mixed with industrial sludge. The industrial sludge was obtained from three industrial zones in Taiwan. The lightweight aggregate materials were prepared by mixing WTS with 7.5%, 15.0%, or 22.5% of industrial sludge as a secondary ingredient. The chemical composition analyses revealed that the ternary phase diagrams of the chemical components were within the range recommended by C.M. Moreover, Riley indicated that the ingredients could expand. The sintering experiments were conducted in two stages. Stage I served to determine the optimal sintering temperature, while Stage II produced lightweight aggregates at the optimal sintering temperatures after 5, 10, or 15 min of preheating. The results indicated that an increase in preheating time increased the particle density of the lightweight aggregates but decreased the water absorption ratio, because increasing preheating time causes more gases to escape, resulting in aggregates that could not produce sufficient gas to support expansion during the sintering stage. The sintering results of the lightweight aggregates showed that their particle density was between 0.5 and 1.4 g/cm3, which met the requirements of the specification. Their water absorption rate was below 21%, which was roughly in line with the recommendations of the specification. When the amount of industrial sludge added was less than 22.5%, the lightweight aggregate was sintered successfully, which is suitable for engineering applications. The industrial sludge experienced a loss of between 50% and 70% on ignition, resulting in pores and cracks that were observed on the surfaces of the lightweight aggregate. Based on the energy required to sinter lightweight aggregates, a greater loss on ignition indicates the conversion of more materials into heat energy. Therefore, the use of industrial sludge in lightweight aggregates not only provides ways to reuse industrial sewage waste but also reduces the consumption requirements for sintering lightweight aggregates, thereby achieving energy-saving and carbon-reduction goals.

Artificial Lightweight Aggregates Made from Pozzolanic Material: A Review on the Method, Physical and Mechanical Properties, Thermal and Microstructure.

As the demand for nonrenewable natural resources, such as aggregate, is increasing worldwide, new production of artificial aggregate should be developed. Artificial lightweight aggregate can bring advantages to the construction field due to its lower density, thus reducing the dead load applied to the structural elements. In addition, application of artificial lightweight aggregate in lightweight concrete will produce lower thermal conductivity. However, the production of artificial lightweight aggregate is still limited. Production of artificial lightweight aggregate incorporating waste materials or pozzolanic materials is advantageous and beneficial in terms of being environmentally friendly, as well as lowering carbon dioxide emissions. Moreover, additives, such as geopolymer, have been introduced as one of the alternative construction materials that have been proven to have excellent properties. Thus, this paper will review the production of artificial lightweight aggregate through various methods, including sintering, cold bonding, and autoclaving. The significant properties of artificial lightweight aggregate, including physical and mechanical properties, such as water absorption, crushing strength, and impact value, are reviewed. The properties of concrete, including thermal properties, that utilized artificial lightweight aggregate were also briefly reviewed to highlight the advantages of artificial lightweight aggregate.

Production of lightweight aggregates from bauxite tailings for the internal curing of high-strength mortars

The pore structure of lightweight aggregates (LWA) has a direct influence on the performance and application of LWA. In this paper, bauxite tailings were used as the main raw materials for the production of LWA. CaF2 and CaCO3 were used as additives to modify the pore structure of LWA. The internal curing performance of pre-saturated LWA in high-strength mortars was studied. It was found that LWA made from 95% bauxite tailings and 5% silica fume had no expanding capacity despite SiO2/∑Fluxing ratio of 2.39. Its porous structure comes from the voids left by the dihydroxylation of clay minerals. CaF2 and CaCO3 increased the pore size of LWA and this effect became more obvious with the increase of CaF2 and CaCO3 content. LWA with a high water absorption could reduce the autogenous shrinkage of mortars most. LWA reduces the strength of mortars but using LWA with high water absorption can lower the negative effect on the compressive strength of mortars.

Volatilization control of CdCl2 and its solidification mechanism during lightweight aggregate production from Cd-contaminated soil

Lightweight aggregates (LWAs) have potential in the harmless resource utilization of Cd-contaminated soil due to their extraordinary ability to effectively solidify heavy metals, although the negative effects of chlorine in the soil are nonnegligible. This work methodically investigated the influence of KCl and MgCl2 with concentrations ranging from 1% to 5% on the volatilization, and solidification of cadmium in LWAs prepared with contaminated soil and lithium slag. The results indicated that cadmium was discharged out of the LWA in the form of CdCl2 driven by Cl−, and the remaining cadmium was completely solidified in the LWA in the form of CdFe2O4. It was found that the addition of chloride significantly increased the volatilization ratio of cadmium, and the distribution of the pore structure of the LWAs was more uniform. The effect of KCl on the volatilization ratio of cadmium and the physical properties of LWA is significantly better than that with MgCl2. It could mainly due to the differences in the release of chlorine free radicals and the content of metal oxides introduced by chlorides. This work could help to understand the migration and transformation mechanism of cadmium in LWAs and guide CdCl2 emission control technology. Ultimately, it is feasible to realize the resource utilization of Cd-contaminated soil and lithium slag with a cleaner approach.

The use of contaminated soil and lithium slag for the production of sustainable lightweight aggregate

The contaminated soil (CS) and lithium slag (LS) contain amounts of hazardous ingredients which may move into the ground water and local cropland. In order to prevent CS and LS from damaging the environment, an investigation on the utilization of CS and LS for the production of lightweight aggregate (LWA) was presented in this article. The basic properties of LWA were evaluated. Furthermore, the crystalline phases of the produced LWA were analyzed, and the microstructure of LWA was analyzed by X-ray micro-tomography. The experimental results showed that the LWA produced from the CS and LS had good performances with density of 0.5–1.5 g/cm3 and compressive strength of 1.0–8.7 MPa, which met the required standard of LWA. Meanwhile, it can be revealed that the LS can reduce the sintering temperature of LWA, thus exhibiting low energy consumption. The analysis of crystal phases indicated that the mineral compositions of LWA contained spinel phases, which provided a possibility for the solidification of heavy metals. In addition, the evaluation of environmental effect revealed the leaching concentrations of hazardous metals were much lower than the critical limits of nonhazardous materials. Finally, the economic benefits were analyzed in the entire production process of LWA, which indicated that using CS and LS to produce LWA can lower the raw material cost by 85–98%. This work will create a more eco-friendly and economical method for the management of solid wastes (CS and LS). Meanwhile, this study can provide theoretical basis for the sustainable production of LWA.

Drying shrinkage properties of expanded polystyrene (EPS) lightweight aggregate concrete: A review

Expanded polystyrene (EPS) is currently being utilized in sustainable materials owing to its ultra-low density and superior thermal performance. It can be incorporated in concrete mixtures to replace coarse aggregate to produce lightweight aggregate concrete (LWAC). Concerning the high shrinkage development in LWAC, the present study reviews the available published articles regarding the drying shrinkage of lightweight concretes containing expanded polystyrene. According to the previous studies, the drying shrinkage development in expanded polystyrene concrete (EPSC) has been reported to be greater than that in conventional concrete, which must be considered for its application in the construction industry. It is mainly attributed to the low elastic modulus and mechanical properties of the EPS. However, incorporating additives and fibers can improve its shrinkage resistance properties. A comprehensive comparison of drying shrinkage magnitude between various LWAC showed that the drying shrinkage strain of EPSC is not generally higher than other types of LWAC; however, the density of EPSC was measured lower than that in other types of lightweight aggregate concretes.

Production and Evaluation of Synthetic Lightweight Aggregates Based on Mixture of Fluidized Bed Fly Ash and Post-Mining Residues.

This paper presents an attempt to obtain technically valuable lightweight aggregate produced from a mixture of fluidized bed fly ash and post-mining residues. The motivation to take up this study is a problem with the reasonable utilization of huge amounts of ashes produced by power plants in Poland. The ashes still produced and those stored in heaps amount to a tonnage of millions, and new ways to utilize them are desired. A real lack of mineral aggregates (non-renewable resources) demands the search for alternative materials. Using the industrial ashes as aggregates is a possible solution to the two above-mentioned problems. The aim of the study was to produce the lightweight aggregate components and to assess them in terms of their physical and mechanical properties. The components were prepared by mixing, granulation, and sintering at the temperature of over 1170 °C. Evaluation of physical parameters was based on parameters such as bulk density and water absorption. The study of mechanical properties was carried out on the basis of aggregates’ resistance to crushing. The obtained results revealed that using a mixture of the combustion and post-mining residues in the production of a lightweight aggregate is beneficial and results in the formation of a porous and durable structure. The measured resistance to the crushing of the produced aggregates varied from 5.9 MPa to 7.5 MPa. They also showed a high freeze-thaw resistance and good resistance to aggressive environments (bases, acids, salt). The registered properties indicate that the aggregates meet the basic requirements for materials used in construction and road-building. This study has a scientific and didactic value in that it describes the step-by-step process of planning and implementing the production of synthetic mineral aggregates.

Mechanical and Thermal Properties of Shale Ceramsite Concrete: Experimental Study on the Influence Law due to Microencapsulated Phase‐Change Material Content and Phase‐Change Cycle Numbers

The addition of microencapsulated phase‐change materials (MPCM) to concrete will inevitably cause changes in the mechanical and thermal properties of concrete, and this is vitally important for the safety and energy saving of concrete building components. In this research, shale ceramsite and shale ceramics sand were used as the main raw materials to produce lightweight aggregate concrete (LWAC) mixed with MPCM. In order to investigate the effect of MPCM content and phase‐change cycle numbers on the mechanical and thermal properties of MPCM‐LWAC, two groups of MPCM‐LWAC specimens were prepared. One group consists of specimens containing 2.5%, 5.0%, 7.5%, and 10% MPCM, respectively, and they are used to reveal the change law of tensile strength, compressive strength, enthalpy, and specific heat capacity of LWAC integrated into MPCM. The other group includes specimens with the same MPCM content, but the specimens are subjected to different phase‐change cycle numbers of 50, 100, 150, and 200 at the environment temperature of −10–60°C to study the thermal properties of MPCM‐LWAC. Findings from the experimental results include the following: (1)The tensile and compressive strengths of MPCM‐LWAC concrete are negatively correlated with the MPCM content, while the enthalpy and specific heat capacity are positively correlated with the MPCM content. When the MPCM content reaches 10%, the compressive and tensile strengths of MPCM‐LWAC decreased, respectively, by 45.49% and 52.63% than the LWAC without MPCM. (2) Under heating and curing condition, the corresponding maximum specific heat capacity of LWAC with 10% MPCM is 328.35% and 249.50% higher than the LWAC without MPCM, respectively, and the average specific heat capacities increase 71.21% and 44.94%, respectively. (3) The melting enthalpy of MPCM‐LWAC is slightly larger than the curing enthalpy, and the difference is more noticeable with the increase of MPCM content. In addition, when the number of phase‐change cycle is below 200, the compressive strength and splitting tensile strength of MPCM‐LWAC decrease by less than 5%, and the specific heat capacity decreases by less than 1.33%. Hence, it concludes that shale ceramsite concrete with MPCM has promising application prospects.

Assessment of the mineral phase and properties of clay-Ca bentonite lightweight aggregates

This study deals with improving the properties of lightweight aggregate by the addition of Ca-bentonite mineral to expandable clays. The addition of bentonite can result in advanced lightweight aggregate materials which meet international standards. Besides bentonite material, twelve different clays (from Egyptian and Hungarian mines) were studied by X-ray fluorescence (XRF), X-ray powder diffraction (XRD, Rietveld method), and a heating microscope (HM). Aggregates were produced and their physical and mechanical properties were measured. The structure and the chemical composition of the clay-Ca bentonite aggregates were studied by scanning electron microscope (SEM) and with energy dispersive spectroscopy (EDAX). The results showed that the addition of 10 wt% bentonite can reduce the bulk density by up to 20%, can increase the compressive strength by up to 180%, and can increase the height of expansion by up to 68% in some samples. It was found that the high kaolinite content of the clay samples was not beneficial for expanding and decreasing the bulk density of aggregates. According to the Rietveld method from XRD and a statistical correlation model shown, the amorphous contents have a reciprocal relationship with the bulk density and a direct relationship with the height expansion. Bentonite, as a natural additive, to some clays, was suitable for producing lightweight aggregates with far better properties, as well as a more economical means of production.

Light Weight Aggregate Production of Kütahya Region Red Soils by Rapid Sintering Method

Bu çalışmada Çöğürler/Kütahya’dan alınan kırmızı toprak; i) gözenek oluşturmak amacıyla evsel atık arıtma çamuru, ii) sinterleme özelliklerini iyileştirmek için sodyum karbonat ve uçucu kül eklenerek hızlı sinterleme yöntemi ile hafif agrega üretilmiştir. Küçük silindirler şeklinde üretilen hafif agregaların fiziksel ve mekanik özeliklerine; kırmızı toprağın ağırlıkça %’si olarak uçucu kül miktarı (%12 ve %17), presleme kuvveti (1, 3 ve 5 kN) ve sinterleme sıcaklığının (1050 ve 1100°C) etkisi araştırılmıştır. Uçucu kül miktarı arttıkça basınç dayanımda artış gözlenmiştir. En yüksek hafif agrega özgül dayanımı (14,80 MPa / 0,98 ton/m3 = 15,10 kN.m/kg) dikkate alınarak en uygun üretim %17 oranında uçucu kül kullanımı, 1 kN ile presleme ve 1050°C’de hızlı sinterleme ile elde edilmiştir.

Use of ballasted flocculation (BF) sludge for the manufacturing of lightweight aggregates

Ballasted flocculation (BF) is an efficient way to remove the turbidity from surface water. The objective of the present study is to optimize the ballast (magnetite), coagulant (poly aluminum chloride) concentration and pH for efficient turbidity removal from surface water. To do this, the sludge produced from an optimized dose of a BF treatment was utilized for the production of lightweight (LW) aggregates by combining it with hard clay and sewage sludge. The LW aggregates were formed by means of rapid sintering in the temperature range of 1000–1200 °C with an exposure time of 10 min. The physical properties of the LW aggregates, in this case the leaching of heavy metals, the bulk density and the microstructure, were investigated. The results indicated that corresponding ballast and coagulant concentrations of 0.75 g/L and 30 mg/L (poly aluminum chloride (PAC)) resulted in the maximum removal efficiency of ≈95%. Using a mixture of BF sludge (30 wt%), dry sewage sludge (20 wt%), and hard clay (50 wt%), aggregates with a density of around 1.0 g/cm3 could be produced. In addition, it was confirmed that the manufactured aggregate was environmentally stable as the elution of heavy metals was suppressed.

Development and characterization of lightweight aggregate recycled from construction and demolition waste mixed with other industrial by-products

The amount of construction and demolition waste and industrial by-products are increasingly high in Vietnam recently. The recycling of these wastes as new construction materials is an effective solution for sustainable development. This paper presents a method for the recycling of construction and demolition waste and other industrial by-products, such as fly ash and slag in Vietnam to produce lightweight aggregate . Experimental results show that masonry wastes including brick and mortar as well as fly ash are suitable materials for producing lightweight aggregates with a granule density of less than 1000 kg/m3 with the optimum sintering temperatures and the residence time in the range from 1220 °C to 1250 °C and, 6 to 9 min, respectively. These recycled lightweight aggregates can be used as valuable substitutes for natural aggregates to make lightweight concrete for new structures and therefore contribute to the construction industry's sustainability.

Determination of the expansion capacity by calcination of the clays from San José de Cúcuta, Colombia

Viscoplasticity and pyroplasticity of clays are important characteristics to control in production processes of lightweight concrete aggregates. When clay is calcined under temperatures above 1,000 °C, its volume increases. For this reason, it is important to investigate how much volume can gain a given clay before using it in production of lightweight aggregates. This research work has evaluated the expansive capacity of some Colombian clays, applying to them static heat treatment in furnaces at temperatures above 1,000°C. The theoretical background of this work is based on the state of the art of production processes of lightweight clay-based aggregates, which were used to determine if the available clay is a precursor of lightweight aggregate. Also, chemical characteristics were determined using X-ray fluorescence tests. Raw material was chosen from several clays existing in San José de Cúcuta, Colombia. The clays were processed until particles’ diameters resulted smaller than 75 µm. Using these particles, pellets with diameter varying from 10 mm to 15 mm were formed. To determine the expansion capacity and the reduction of volumetric density, volume and weight of pellets were measured before and after applying the heat treatments. When the clay presented a low expansion capacity, technological nutrients were added to the mixtures attempting to maximize the expansion capacity of the pellets. A swelling of up to 3.24 times the initial size of pellets was observed. technological nutrients based on organic matter were chosen and applied in a proportion of 1: 4, i.e., one gram of technological nutrients was added to 4 g of clay. The density of manufactured aggregates resulted to be between 0.50 g/cm3 and 1.93 g/cm3. Clay mixtures added with technological nutrient showed density lower than 1 gram per cubic centimeter, this means that they could float on water.

STUDY OF SHRINKAGE OF CONCRETE USING NORMAL WEIGHT AND LIGHTWEIGHT AGGREGATE

Drying shrinkage can be a major cause of deterioration of concrete structures. Aggregate sizes, curing period and water-cement ratio imparts a great impact on shrinkage of concrete. This paper represents the observed effects of water-cement ratio, curing period and aggregate sizes on shrinkage of concrete using normal weight and lightweight aggregate. Structural lightweight aggregate concrete offers several benefits as compared to the normal weight concrete. This paper checks the suitability of using lightweight concrete instead of normal concrete in case of susceptibility to shrinkage. Though the cost of the production of the lightweight aggregate is high due to energy and raw material consumption, economy can be achieved by using locally available waste materials to produce lightweight aggregates. The experiments were carried out according to ASTM C157 and ASTM C490. The variations of aggregate sizes, curing period and the water-cement ratio were applied and their effects were observed on shrinkage of concrete. This paper also recommends the proper type of concrete owing to minimal shrinkage.

A Metallurgical Approach Toward Bloating of Canal-Dredging Sediments

The similarity of the fine fraction of dredged freshwater sediments to natural clays stimulates the valorization in a product similar to expanded clay aggregates, obtained by bloating at high temperature. The impact of the ratios between different flux elements (Fe2O3 + CaO + MgO + K2O + Na2O) on the melting behavior is quantified using thermodynamic modeling and validated with experiments. The total content of alkalis is found to be key in controlling melting and bloating. Increased alkali content triggers the formation of alkali feldspars that start to melt at low temperature and give rise to a gradual increase of the amount of melt with temperature. The ratio (CaO + MgO + K2O + Na2O)/Al2O3 should preferably be smaller than or close to 1 to avoid excessive pyroxene formation, which causes complete meltdown of the granules around 1150 °C. The chemical composition has a complex influence on the melting behavior, even when on the same location on the SiO2–Al2O3–flux diagram. The conventional approach of trying to modify the composition towards a certain range in the ternary diagram does not work for all materials, and therefore, the understanding of the melting behavior using the phase composition at high temperature (= the metallurgical approach) provided in this work is shown to be crucial to produce lightweight aggregates from materials with a higher chemical variability.Graphical Abstract