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Article

Recycling Red Ceramic Waste as a Raw Material for Lightweight Aggregates

by
Maelson Mendonça de Souza
1,2,*,
Normando Perazzo Barbosa
2,3,
Marcos Alyssandro Soares dos Anjos
2,3,4,
João Gabriel Cruz Aguiar
1,
José Anselmo da Silva Neto
3 and
Cinthia Maia Pederneiras
5,*
1
Federal Institute of Education, Science and Technology of Rio Grande do Norte, Academic Directorate of Civil Construction, Natal 59015-000, Brazil
2
Postgraduate Programme in Civil and Environmental Engineering, Department of Civil Engineering, Federal University of Paraíba, João Pessoa 58051-900, Brazil
3
Department of Materials Science and Engineering, Federal University of Paraíba, João Pessoa 58051-900, Brazil
4
Federal Institute of Education, Science and Technology of Paraíba, Coordination of Civil Engineering, João Pessoa 58015-435, Brazil
5
c5Lab Sustainable Construction Materials Association, 2795-242 Linda-a-Velha, Portugal
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2025, 15(10), 5729; https://doi.org/10.3390/app15105729
Submission received: 21 April 2025 / Revised: 15 May 2025 / Accepted: 16 May 2025 / Published: 20 May 2025
(This article belongs to the Special Issue Sustainable Materials and Innovative Solutions for Green Construction)
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Abstract

The growing demand for lightweight aggregates (LWAs) in the construction industry is driving the development of sustainable alternatives based on the reuse of solid industrial waste. The aim of this study was to assess the technical feasibility of using red ceramic waste (RCW) as a partial or total substitute for red clay (RC) to produce lightweight expandable aggregates. Six formulations were made with different proportions of RCW and RC and sintered at four temperatures (1100, 1150, 1200 and 1250 °C). They were characterised using physical, thermal, morphological, chemical and mechanical analyses, according to standard protocols. The results showed that almost all the formulations sintered at 1200 and 1250 °C had a positive bloating index (BI > 0), particle density of less than 2.0 g/cm3, low water absorption of less than 2% and mechanical strength of more than 5.4 MPa, revealing strong potential for use in lightweight structural and non-structural concrete. The main conclusion is that RCW, even used in isolation, has physicochemical and mineralogical properties suitable for the production of lightweight aggregates under optimised thermal conditions, contributing to the development of sustainable materials with a competitive technical performance compared to commercial LWAs.

1. Introduction

Lightweight aggregates (LWAs) are of significant importance within the construction industry. Their utilisation in engineering works and services confers numerous advantages, such as a reduction in the structure’s own weight, thermal and acoustic insulation, high fire resistance and durability [1]. As demonstrated in the preceding studies, the global consumption of aggregates exceeds 50 billion tonnes per year, and there is a significant prospect of growth in the coming years [2]. This demand reinforces the need to manufacture new LWAs. Typically, commercial LWAs have granulometric fractions suitable for use as fine and coarse aggregates [3,4,5,6,7,8,9].
Bernhardt et al. [10] posited that in the manufacture of LWAs, it is essential to produce materials with good mechanical properties, as the mechanical strength of the lightweight aggregate has a strong influence on the final strength of the lightweight concrete. As posited by Ayati et al. [11], a lightweight aggregate with optimal properties for use in mortars and concretes should have the following characteristics: a strongly sintered porous core, a rough and impermeable surface and an approximately spherical shape. Generally speaking, when designing the production of expandable LWAs it is possible to obtain these properties and at the same time modify their density, water absorption and mechanical strength, adapting the material to the most diverse applications [12].
The production of expandable LWAs is typically initiated by subjecting the granules to heating to their respective melting points. At this point, gas formation and pyroplastic deformation must occur simultaneously [13]. In this context, Dondi et al. [12] state that for a given sintering temperature, there are three conditions necessary to achieve swelling in LWAs: (a) the production of a quantity of liquid phase capable of transforming the granule into a viscous mass, (b) the development of gas bubbles occurs and (c) obtaining a liquid phase with adequate viscosity for the retention and growth of gas bubbles.
In the production of LWAs, clay is the raw material that is most frequently employed. According to Ayati et al. [11], clay is commonly used in the manufacture of LWAs mainly due to its availability close to urban areas, its ease of forming into granules and the fact that it results in light and resistant samples when subjected to sintering. However, overconsumption of clay can have significant environmental impacts, such as the depletion of natural resources and the production of waste [14,15].
Consequently, the use of waste as a raw material for manufacturing lightweight aggregates has been frequently analysed in scientific research. According to Dondi et al. [12], interest in this application is growing and is strongly influenced by the search for more sustainable technologies. Successful studies have shown that the production of LWAs has a high potential for incorporating waste [11,16]. As demonstrated in the extant literature, a wide variety of waste materials is already employed in LWAs, including but not limited to fly ash, sewage sludge, mining and quarrying tailings, sawdust, glass waste, coffee grounds and reservoir sediments [11,12,17]. However, there are still no reports on the use of red ceramic waste (RCW) in expandable LWAs.
RCW is often generated during the manufacture of ceramic materials. According to Souza et al. [18], construction and demolition waste (CDW) and materials that do not meet technical specifications are the main sources of RCW. It is estimated that approximately 33 per cent of ceramic production can be wasted every day as a result of the generation of defective bricks, blocks, tiles and other articles [19]. This tends to contribute to environmental degradation, causing, for example, water and soil pollution and the modification of the natural landscape and local biodiversity [20].
The chemical and mineralogical compositions of RCW indicate that this waste has significant potential for making lightweight aggregates. The majority of the studies identified revealed that RCW exhibited the following properties: (a) SiO2 contents considered suitable for liquid phase generation [21,22,23], (b) a sum of the melting oxides (Fe2O3, Na2O, K2O, CaO and MgO) capable of reducing the melting temperature of the samples [24,25,26] and (c) one or more minerals capable of producing gases during viscous melting [27,28,29]. Furthermore, in some cases, RCW has exhibited a chemical composition similar to that of commercial LWAs [30].
Therefore, this study aimed to evaluate the technical feasibility of using red ceramic waste (RCW) as a partial or complete substitute for red clay (RC) in the production of lightweight aggregates (LWAs). The influence of different substitution levels and sintering temperatures on the physical, chemical, and mechanical properties of the LWAs was assessed. In addition, the study explored how the mineralogical and chemical composition of the raw materials affected the expansion phenomenon, and compared the performance of the produced aggregates with commercial standards.

2. Materials and Methods

2.1. Materials

The red ceramic waste (RCW) was supplied by Cerâmica do Gato Ltd.a., located in the district of Acauã, municipality of Açu, Brazil. According to Carvalho and Leite [31], a significant proportion of this by-product comes from breakages during the handling, transfer, storage and dispatch of bricks, tiles and slabs. Red clay (RC) was also obtained from Cerâmica do Gato (Açu, Brazil). This clay came from previous research and was applied because it has significant amounts of SiO2, Al2O3 and Fe2O3 and an attractive mineralogy for making LWAs [32]. When collected, the RCW and RC had a coarse grain size composed of particles of varying sizes. In order to obtain materials with a granulometry suitable for manufacturing LWAs, grinding and sieving techniques were applied, similar to the protocols used in previous work [32,33,34]. The RCW and RC were subjected to drying conditions at a temperature of 110 ± 5 °C for a duration of 24 h. Thereafter, they were ground into fine powders with a diameter of less than 150 µm using a ball mill.

2.1.1. Particle Size Composition

The particle size distribution of the raw materials was measured using a high-resolution CILAS 1090 device (Orléans, France), using laser granulometry methodology. The particle size compositions of the RC and RCW are shown in Figure 1. The grey bars represent the frequency histogram, indicating the proportion of particles within each size range, while the red line corresponds to the cumulative passing percentage, illustrating the overall fineness of the material. After processing, the red clay and ceramic residue became well-spread materials, with average particle diameters of 17.60 and 15.77 µm, respectively. In addition, the RC and RCW had the following characteristic diameters: D10 = 1.01 and 0.69 µm, D50 = 8.35 and 6.64 µm and D90 = 49.78 and 45.98 µm, in that order. According to the literature, finer particles can enhance the trapping of gases and the sintering kinetics of the mixture, while coarser grains tend to help the process of homogenising the raw mass [12,33].

2.1.2. Chemical Composition

The analytical technique used to characterise the chemical composition of the raw materials was XRF analysis. The measurements were carried out using a Thermo Scientific Niton XL3T spectrometer, Thermo Fisher Scientific Inc., Waltham, MA, USA. Table 1 shows the results.
According to Table 1, the chemical analyses of the RC and RCW showed that the chemical composition of this waste consisted mainly of SiO2 (41.45 and 46.23%) and Fe2O3 (27.99 and 26.31%). These materials also showed significant amounts of alumina, calcium and potassium oxides. These characteristics are partially similar to those presented by other studies [15,35,36,37]. The values of SiO2, Al2O3 and Fe2O3 allow us to assume that the development of mixtures between RC and RCW has significant potential for the manufacture of expandable LWAs [12] and with excellent mechanical strength and low porosity [38]. In addition, it is hypothesised that the CaO present in RCW may contribute to the generation of carbon dioxide gases during the formation of the liquid phase [39].
The substantial difference in Al2O3 content between the RC (21.02%) and RCW (5.98%) can be attributed to the high-temperature processes involved in the production of ceramic elements, which cause irreversible mineralogical transformations. During firing, aluminium-bearing minerals, such as kaolinite and illite, undergo dehydroxylation, and new phases such as muscovite and haematite are formed. These changes reduce the measurable aluminium content in the fired waste. This trend is consistent with findings reported in the literature, which indicate lower Al2O3 levels in ceramic residues compared to their raw clay counterparts due to thermal alterations in their mineral structures [40]. Additionally, the RCW used in this study had been stockpiled for a long period at the industrial facility, and it is possible that it originated from a different clay deposit than the one used to produce the RC samples. This could also have contributed to the observed compositional differences.

2.1.3. Mineralogical Composition of Raw Materials

The mineralogical characterisation of RC and RCW was conducted through the utilisation of X-ray diffraction. The XRD was carried out using Shimadzu XRD-7000 equipment, Shimadzu Corporation, Kyoto, Japan, with Cu Kα radiation at 40 mA and 40 kV in the 10 to 80° (2θ) range. The scanning speed adopted was 1.20°/min, and the angular step was 0.02°. The XRD analysis of the red clay (Figure 2a) revealed a crystalline composition of biotite, illite and quartz. In turn, the main phases found in the RCW were haematite, illite, muscovite and quartz (Figure 2b). The results found are consistent with the data obtained in the XRF test. However, the characteristics of the RCW were not absolutely identical to those presented in other studies [14,41,42]. According to Lasseuguette et al. [43], this variability in the mineralogical composition of RCW is mainly linked to the origin of the raw material and the manufacturing method of the ceramic element. The findings of this study lend further support to the hypothesis that RC and RCW possess considerable potential for the fabrication of LWAs, as the minerals identified in these materials are often attributed to controlling the viscosity of the liquid phase and the generation of gases during the sintering of light aggregate granules [11,44].

2.1.4. Loss of Mass

Thermogravimetric characterisations of RC and RCW were carried out using an SDT 650 simultaneous thermal analyser in a nitrogen atmosphere. During the test, the temperature was raised gradually from 30 °C to 1200 °C. The heating rate was 8 °C/min. Figure 3 shows the results. The loss of mass noted in the RC at 100 °C (Figure 3a) corresponds to the evaporation of adsorbed water. The TGA of the RC also indicated that a greater loss of mass occurred between 100 and 700 °C, mainly due to the burning of organic material, the dehydroxylation of clay minerals and the decomposition of carbonates [12]. Finally, at around 1200 °C, the RC thermo-analytical curve showed a mass loss of almost 17.0%. This can be attributed to the decomposition of illite and reactions with Fe2O3, phenomena that are normally associated with the formation of gases [12].
As illustrated in Figure 3b, the total mass loss identified in the RCW at 1000 °C was significantly lower than that found in the RC (1.30 per cent by mass). Up to this temperature range, the RCW showed significant thermal stability. This phenomenon can be attributed to the similarity between the temperature conditions employed in the mass loss tests and the manufacturing process of the ceramic components. Consequently, some thermogravimetric phenomena originating from the clay, such as the decomposition of carbonates, occurred during industrial processing. The mass loss analysis also revealed a total reduction in RCW weight of approximately 1.90% when the material was subjected to a temperature range of 1200 °C. This result can be attributed to the dissociation of the crystal structure of muscovite and illite, both found in the mineralogy of RCW (Figure 2b). It is therefore possible to assume that this waste has some potential for producing gases.

2.1.5. Microstructure of Raw Materials

A Tescan Scanning Electron Microscope (SEM) model Vega-3 LMU, Tescan Orsay Holding a.s., Brno, Czech Republic, with 20 kV accelerating voltage was used to study the morphology of the starting materials. The pulverised RC and RCW samples were dried and then impregnated in the equipment’s support bases. Figure 4a shows the micrograph of the surface of the red clay at a magnification factor of 342. In general, RC is made up of fine grains with a rough texture and an irregular shape. The majority of visible particles fall in the approximate size range of 10–60 µm, consistent with the D50 value of 8.35 µm and D90 of 49.78 µm reported in the granulometric analysis. The morphology suggests good packing potential during shaping, which can favour densification during sintering [11].
According to Figure 4b, the red ceramic waste consists of porous particles of varying dimensions, irregular in shape and with a rough, angular surface. This is probably a result of the firing process during ceramic production. The particle sizes visible in this image generally vary between 10 and 50 µm, with some fragments visibly exceeding 80 µm in length. This morphology is very similar to the results found in previous studies [36,42,45]. Thus, it is possible to assume that the use of RCW in the preparation of LWAs tends to hinder lubrication of the mixture, thus impairing the workability of the sample during the homogenisation process [46].

2.2. Methods

2.2.1. Making the Mixtures

During the development of the formulations, we endeavoured to comply with the protocols indicated by Riley [44] and Cougny [33]. However, analysing Table 1, it can be seen that the chemical compositions of the raw materials used did not fully meet the conditions for expandable clay [44]. It was therefore decided to make binary mixtures using red clay and ceramic waste. Recent studies corroborate the chosen technique. Da Silva Neto et al. [40], for example, showed that heat-treated ceramic waste increases gas retention and expansion potential, especially at higher substitution levels. Singh et al. [47] also highlighted the efficiency of expanded clay aggregates due to their low density and thermal performance.
Table 2 shows the six mixtures produced. The composition of the samples varied significantly, with RC being replaced by RCW at 50, 60, 70, 80, 90 and 100 per cent. The water content added to ensure the plasticity required to homogenise the samples was between 30% and 40% by mass.
The chemical characterisation of the prepared mixtures was analysed graphically using the expandable clay protocol proposed by Riley [44]. However, it was decided not to plot the data, since, with the exception of R100, all the other samples were not included in the graph. This is because these samples had a lower SiO2 content than stipulated in the graph in question. These results are presented in Appendix C and help to explain the trends observed in the physical and mechanical performance of the aggregates produced. On the other hand, the microstructure and mass loss data were taken into account in order to assess the workability of the mixtures and the thermal behaviour of the formulations during sintering, respectively. Finally, firing tests were carried out on each of the formulations developed in order to analyse the effectiveness of the dosing protocol developed.

2.2.2. Manufacture of Aggregates

Initially, the raw materials were combined in different proportions and then mixed manually. The amount of water added was adjusted for each formulation in order to obtain a mass with a consistency suitable for moulding. The granules were moulded manually, resulting in small spheres. After moulding and drying for 24 h in a controlled environment, the granules were sintered at different temperatures (1100, 1150, 1200 and 1250 °C), with a heating rate of 8 °C/min and an isothermal plateau of 15 min. Following a period of natural cooling, the samples were stored for subsequent analysis. The experimental apparatus comprised a JUNG three-phase chamber furnace model TB9665, which was employed for the sintering of the samples. It should be noted that the steps described in this process followed, with some adaptations, the methodology described in previous works [48,49].

2.2.3. Characterisation of Lightweight Aggregates

An extensive set of characterisation analyses was carried out on the specimens. The results are shown in Table 3. The determination of water absorption, thermogravimetric behaviour, particle density, real density, swelling index, microstructure, mineralogy, mass loss, porosity and crushing resistance of each of the mixtures made it possible to assess the suitability of the waste tested for the production of lightweight aggregates and the main influences of this waste on each of these properties. In addition, the results of these tests made it possible to identify the samples with the greatest potential for producing lightweight aggregates and the prospects for using the other samples.

2.2.4. Sample Classification

The parameters of particle density (ρd), compressive strength (S) and water absorption (WA24H) were used as performance indicators to identify possible commercial applications for the samples produced. The analysis of the potential of the mixtures considered five different categories of application: (a) high-strength concrete, (b) structural lightweight concrete, (c) non-structural lightweight concrete, lightweight mortars, (d) geotechnical applications and (e) gardening and landscaping ad thermal and acoustic insulation. The methodological approach under discussion is founded upon the findings of preceding studies [6,32].
However, applying these parameters to many samples tends to result in an exhaustive database that is difficult to understand. Therefore, in order to simplify the presentation of the categorisation parameters and the understanding of the results, the graphical representation of the methodology proposed by Souza [8] was redesigned into a diagram of just two parameters: compressive strength (S) versus water absorption (WA24H). This is possible because the particle density criterion is the same for all possible application groups of commercial LWAs (ρd less than 2.00 g/cm3). As illustrated in Figure 5, the diagram provides a visual representation of the potential commercial LWAs and their respective regions of use.

3. Results and Discussion

3.1. Characterisation of Lightweight Aggregates

3.1.1. Bloating Index (BI)

Table 4 compiles the bloating index values obtained from the mixtures. The results indicate high dispersion in the BI data, with values ranging from −43.5% to 29.4%, both corresponding to sample R100 when sintered at 1150 °C and 1250 °C, respectively. There was a tendency towards volumetric expansion in the set evaluated, since all the formulations showed positive bloating indices (BI > 0) in at least one of the sintering temperatures. Notably, sintering at 1250 °C promoted greater volumetric expansion compared to the other thermal conditions tested.
Although a general trend of increased bloating at 1250 °C was observed, sample R50 showed a lower bloating index than expected. This deviation can be attributed to the high variability typically associated with bloating behaviour, as confirmed by the dispersion of BI values across the tested mixtures. As noted by Chandra and Berntsson [4], the manufacturing parameters of lightweight aggregates play a critical role in expansion performance. Key factors such as the granulation technique, the granulometric, chemical, mineralogical and microstructural properties of the raw materials, the formulation and processing conditions of the raw mixes, the water content used during pellet formation and the sintering protocol can significantly influence the extent of bloating [4,11,49].
By grouping the results in Table 4 from the sets of mixtures made, we can see that: (a) the R100 formulation, made exclusively with RCW, obtained an expansion index of almost 30% when calcined at 1250 °C. This result indicates the potential of this residue for the expansion phenomenon, and (b) with the exception of sample R90 at 1200 °C, all the samples made using a mixture of RCW and RC showed bloating when sintered at 1200 °C and 1250 °C. (c) Invariably, the aforementioned samples did not have a chemical composition within the parameters pre-established by Riley [44]. However, the results found attest to the formation of a liquid phase with adequate viscosity to trap the gases. It is therefore possible to assume that the mineralogical composition of this group of samples acted as a substitute for the aluminosilicate matrix [11] and that the prediction of expansion based on the chemical criteria proposed by Riley [44] is not suitable for RCW [12].
Figure 6 illustrates the morphological aspect of the samples, as well as a representative model of their behaviour after the drying and sintering processes. It should be noted that the interpretation of this figure also allows us to infer the presence of relative bloating. Using the R90 formulation as a reference, dimensional shrinkage of close to 30% was observed when sintering at 1100 °C. However, as the temperature increased, the granular structure progressively grew. This evidence suggests that the expansive capacity of this sample is more expressive than that previously estimated by the bloating index (BI). From this perspective, it can be inferred that all the compositions developed in this study showed a degree of volumetric expansion greater than that indicated by the BI values reported in Table 4.
To improve interpretation of Figure 6, it is important to clarify the parameters represented. The relative bloating index refers to the variation in the average particle volume measured from the point of maximum densification to the stage at which the highest bloating index is observed. The symbol Ø denotes the simulated particle diameter values for each mixture, estimated from the experimentally determined bloating index at each sintering temperature. The bloating index (BI) represents the overall expansion behaviour of the material, calculated as the variation in average particle volume from the initial state to the final state after sintering.
Figure 6 shows that the sample made using only RCW (R100) showed strong contraction when sintered at 1100 and 1150 °C and progressive bloating when calcined at 1200 and 1250 °C. Although the specimen in question did not meet the expansion criteria reported in the literature [44], it can be seen that recycling RCW waste into LWA does not require the addition of other materials for the granules to expand. Similarly, previous studies have identified waste with properties suitable for direct use in LWAs [13,58]. It appears that the mineralogical composition of the RCW strongly influenced the results.
Sample R60, made with 60% RCW, also showed significant bloating indices when sintered at 1200 and 1250 °C (17.0 and 23.4%, respectively). The data found at 1200 °C show that the use of clay as a supplementary bloating material helped to obtain the highest BI in the samples fired at this temperature. On the other hand, this temperature range, apparently suitable for sintering R60, is slightly higher than that used by industry during the manufacture of commercial LWAs. However, this may be related to the type of furnace used in the research [13].
According to Figure 6, in general, the samples showed similar behaviour in terms of surface layer formation. In principle, sintering these samples at temperatures above 1150 °C resulted in granules with shinier surfaces, apparently well vitrified. As previously reported, the formation of glassy phases at high temperatures enhances gas retention. This phenomenon appears to exhibit a robust correlation with the BI identified in these samples. Glass phase formation in these samples can also be attributed to the high iron oxide content identified in the RCW and RC [55,59].
According to Figure 6, the data collected at 1250 °C show a predisposition to an increase in BI with an increase in RCW. It is noteworthy that this temperature range appears to be optimal for sintering the set of samples under consideration. This is evident in the observation that, irrespective of the RCW content applied, the BI values were consistently higher than those identified at the other firing temperatures.

3.1.2. Loss on Ignition (LOI)

The generation of gases during sintering, a factor directly related to the bloating phenomenon, can be favoured by relatively small mass losses. According to Moreno-Maroto et al. [52], in certain circumstances, a reduction of just 0.1% of the sample’s original weight is enough to induce volumetric expansion of the matrix. In this context, the results shown in Figure 7 are particularly relevant. The formulations sintered at 1250 °C showed considerable mass losses, regardless of composition. The loss on ignition (LOI) values ranged from 4.3% to 7.3% and were recorded for samples R100 and R50, respectively, which reinforces the potential of these mixtures for porosity formation via gaseous release.
The difference in mass noted in sample R50 after sintering was approximately 7.3%. Considering that this specimen was composed of RCW and RC, it is possible to assume that, in some of the temperature ranges adopted in this study, the dissociation of the clay minerals present in these materials resulted in the formation of gases. This is consistent with the BI values of 15.7% and 16.0% identified in this sample at 1200 and 1250 °C, respectively.
Generally, the specimens produced with higher levels of RCW exhibited lower mass loss. For example, increasing the ceramic residue content from 50 to 100 per cent resulted in a progressive reduction in LOI from 7.3 to 4.3 per cent. This can be explained by the significant thermal stability noted in the RCW (Figure 3b). As previously reported, a large part of the mass loss of this waste occurred during the manufacturing process of the ceramic components. In turn, the addition of clay seems to favour the loss of mass and consequently the formation of gases due to the decomposition of its minerals.

3.1.3. Particle Density (ρd)

The compliance of the samples with the requirements established by Standard EN 13055-1 [60] for lightweight aggregates, which defines a maximum particle density limit (ρd) of 2.0 g/cm3, was widely observed. All the formulations investigated met this criterion in two of the sintering conditions assessed, totalling 12 specimens in compliance with the normative parameter. The particle density values are shown in Table 5. The data show a wide variation in densities, which ranged from 1.42 to 2.46 g/cm3. This dispersion can be attributed to differences in the proportions of constituent materials and the different heating rates adopted. The analysis confirms the direct influence of composition and thermal conditions on the behaviour of the samples.
The data from the prepared samples showed significant ρd results when sintered at 1200 and 1250 °C, demonstrating a strong correlation with the bloating index results obtained in this grouping. For this temperature range, the results from R100 to R50 varied from 1.42 to 1.78 g/cm3, with R100 at 1250 °C and R90 at 1200 °C. According to Fan et al. [61], these results indicate that these specimens have potential for making lightweight structural aggregates. It has been demonstrated that sintering these mixtures at temperatures of at least 1200 °C is more advantageous for producing LWAs.
According to Table 5, an increase in the density of samples R100, R90, R80 and R70 could be seen during the temperature variation from 1100 to 1150 °C, while a decreasing trend was noted at 1200 and 1250 °C. This variation in the density of the aforementioned samples can be attributed to their respective bloating indices, as shown in Figure 6. In general, it can be assumed that the lack of a vitrified layer resulted in an increase in ρd at 1150 °C. Meanwhile, vitreous formation and mineralogical decomposition, resulting from the increase in temperature, led to an increase in porosity and, consequently, a progressive decrease in density [8,55].
A substantial decrease in ρd was observed at temperatures of 1200 and 1250 °C, in comparison to the data obtained at 1100 and 1150 °C. Regardless of the RCW content added, sintering at the higher temperatures resulted in granules with a particle density of less than 2.0 g/cm3, meeting the criteria required of LWAs [60]. Furthermore, there was a certain similarity between the results obtained for RCW contents of up to 80%. Thereafter, when the RCW content was increased, there was greater dispersion in the results. According to Table 4, sample R100, composed of 100% RCW, showed progressive gains in volume at temperatures of 1200 and 1250 °C. These results are therefore justified by the BI data.

3.1.4. Closed Porosity (Pc)

The data shown in Table 6 indicate that the values of closed porosity (Pc) varied between 4.8% and 43.0%, observed in samples R50 at 1250 °C and R100 at 1250 °C. The results indicate a positive correlation between the increase in sintering temperature and Pc levels, suggesting that thermal parameters such as the heating rate have a direct impact on the development of closed porosity. The data used in the Pc calculations are available in Appendix A and Appendix B.
In general, the samples showed progressive gains in Pc as the temperature rose, regardless of the RCW content applied. In sample R90, for example, the closed porosity increased from 8.4 to 37.3 per cent when the temperature rose from 1100 to 1250 °C. In this same temperature range, the bloating index and particle density of R90 varied from -29.5 to 19.5 per cent and from 2.19 to 1.60 g/cm3, respectively. It is known that increased closed porosity has a strong correlation with granule expansion [52]. Consequently, the outcomes observed in this grouping were in alignment with their respective BI and ρd data.
The open porosity data (available in Appendix B) reveal a tendency for PO to decrease with increasing temperature, indicating an intensification of liquid phase formation during sintering. This behaviour suggests that the closure of pores connected to the surface contributes to increased internal porosity. This effect is further intensified by the retention of gases during sintering. In general, the results obtained show high potential for application in the manufacture of lightweight aggregates (LWAs). Moreno-Maroto et al. [52] reported that increased temperature normally reduces porosity due to sintering densification. However, the opposite effect was observed in most of the tested formulations. The increase in closed porosity in this context seems to be strongly related to the trapping of gases during heat treatment.
The effect of adding RCW on the closed porosity of the mixtures was also analysed. According to Table 6, at 1250 °C there was a positive correlation between the amount of RCW and the Pc result. For example, in this temperature range, the closed porosity rose from 36.6 to 43.0 per cent when the RCW content increased from 50 to 100 per cent, respectively. According to reports by Arriagada et al. [62], it can be assumed that the use of RCW can enhance the thermal insulation of the LWAs manufactured. The authors of the study posited that materials characterised by high Pc typically result in a reduction of thermal conductivity, with instances of even convective heat transfer being diminished.

3.1.5. Water Absorption (WA24H)

According to Table 7, all the specimens analysed showed water absorption of less than 10.0%. This indicates a high degree of surface vitrification, as pointed out in previous studies [59,63]. This behaviour reinforces the technical viability of the formulations developed for high-performance concrete applications.
At temperatures up to 1150 °C, there was a negative correlation between the sintering temperature and the WA24H data. However, there was a certain discrepancy in the behaviour of the formulations at higher temperatures. In the R100 formulation, for example, the material became almost impermeable, with absorption rates of 0.7 and 0.6% when sintered at 1150 and 1200 °C, respectively. This aggregate then showed gains in WA24H, reaching an absorption rate of 1.7% at 1250 °C. Apparently, the decrease in open porosity noted at 1150 and 1200 °C (Appendix B) resulted in a significant decrease in WA24H. Likewise, an increase in Po, even on the surface of R100 at 1250 °C (Figure 6), contributed to the increase in the absorption capacity of this sample.
For temperatures of 1100 °C, there was a strong positive correlation between the percentage of RCW used and the WA24H value obtained. This phenomenon can be attributed to the high thermal stability exhibited by RCW, particularly at temperatures that are proximate to those employed during the manufacturing process of ceramic components. Thus, a low sintering rate obviously results in less liquid phase formation and impairment of its viscosity, resulting in high open porosity and, consequently, high water absorption [11,63]. This thesis gains strength when we realise that at higher temperatures, the water absorption data became relatively lower.

3.1.6. Crushing Strength (S)

The crushing strength results obtained are satisfactory from the point of view of engineering applications. According to Table 8, all the specimens produced exceeded the value of 2.3 MPa, a common reference for light aggregates commercially available in Brazil [30]. Among the highlights is sample R100, sintered at 1200 °C, which obtained the highest S value recorded among the samples that met the density criteria, exceeding 12.0 MPa.
The formulations showed significant crushing resistance indices when sintered at 1100 and 1150 °C. On the other hand, there was a significant drop in S values as the temperature rose. There was a significant drop in S values as the temperature increased. In the R70 sample, for instance, crushing strength rose from 25.65 to 40.52 MPa but then dropped to 10.77 and 8.54 MPa at 1200 and 1250 °C, respectively. These results show a strong correlation with the density and porosity data discussed above. Based on the reports by Bernhardt et al. [64], it is possible to assume that, at temperatures of at least 1200 °C, the high concentration of Fe2O3, present in this cluster increased the degree of expandability of the samples, increasing their porosity and consequently reducing their resistance to crushing.
As demonstrated in Table 8, in the majority of cases, there was a downward trend in resistance as the proportion of RCW increased. For example, at temperatures of 1250 °C, the S of the mixture formulated with 100 per cent RCW was approximately four times lower (2.64 MPa) than the value obtained for the sample made with 50 per cent RCW (10.59 MPa). As previously reported, the increase in RCW favoured the formation of a more porous structure. This consequently resulted in a reduction in the crushing resistance indices seen in the aforementioned temperature range. However, it should be emphasised that, regardless of the RCW content added or the temperature range adopted, all the specimens produced in this set had S values higher than those of an LWA commonly used in the production of structural concrete [30].

3.1.7. Mineralogical Composition of LWA

The X-ray diffraction analysis of the R60 sample sintered at 1250 °C is shown below in Figure 8. In general, this mineralogy is compatible with that observed in porous ceramics described in the literature [65,66].
According to Figure 8, the mineralogical composition of R60 showed the presence of cordierite, magnetite, mullite and quartz. Based on Shuguang et al. [67], it is possible to assume that the formation of cordierite peaks in R60 comes from reactions between MgO, present in RC, and the newly formed mullite. According to the authors, the formation of cordierite tends to prevent the formation of cracks on the surface of the granules, helping to reduce water absorption. This finding is consistent with the low WA24H indices of the aggregate in question (Table 7).
In turn, the formation of characteristic mullite peaks in R60 indicates the high potential of this mixture for making porous ceramics. According to what has been observed in the literature, the thermal transformation of illite and/or biotite minerals into mullite is essential for the release of gases and the formation of a structure with greater resistance [6,68]. Apparently, the high Al2O3 content in red clay favours the generation of an additional source of mullite [69].
In addition, a peak of the magnetite phase was seen in R60. According to Bernhardt et al. [70] and Soltan et al. [54], thermal transformations of haematite into magnetite occur from dissociation reactions at temperatures of up to 1200 °C, resulting in the release of oxygen. It is therefore possible to assume that the RCW content used in R60 had a significant effect on one of the primary conditions for bloating, the generation of gases during pyroplastic deformation [44]. It should also be noted that magnetite, as well as mullite, is sometimes reported in the mineralogy of commercial LWAs [65,66].
Although the chemical compositions of the mixtures (Appendix C) did not meet the conditions required for bloating, as defined by Riley [44], all mixtures exhibited some degree of expansion at specific sintering temperatures. This finding reinforces the crucial role of the mineralogical content of RC and RCW in the expansion behaviour of lightweight aggregates. Apparently, the illite, biotite and muscovite phases identified in the raw materials were responsible for gas generation while also acting as substitutes for SiO2 and Al2O3, aiding in the formation of the liquid phase and the entrapment of gases [11].

3.1.8. Thermal Analysis

Figure 9 shows the thermal behaviour of the R60 mixture as the temperature rose. The sample in question suffered significant mass losses between 15 and 600 °C. These mass losses tend to be related to the evaporation of absorbed water and the dehydroxylation of clay minerals and may be responsible for the generation of gases. However, they did not contribute significantly to the bloating shown by R60, since the formation of a liquid phase with adequate viscosity to encapsulate the gases occurs at much higher temperatures.
At temperatures above 600 °C, there was a slight reduction in the weight of R60 up to 1200 °C, resulting in a total mass loss rate of approximately 5.07%. This fact reinforces the thesis proposed by Moreno-Maroto et al. [52] that low rates of mass loss can cause the release of bloating gases at higher temperatures. In this context, at around 1170 °C, the DTA curve registered a pronounced exothermic peak, indicating the formation of a liquid phase.

3.1.9. Microstructure of LWA

The microstructures obtained from the R60 formulation after sintering at 1150, 1200 and 1250 °C are shown below in Figure 10. According to Figure 10a, it can be seen that at 1150 °C, the sample in question had a strongly densified matrix. This is consistent with the high shrinkage indices (Table 4) and particle density (Table 5) identified in R60 at 1150 °C, and can be attributed to the high content of melting oxides found in RCW and RC. According to Gao et al. [69], the excess of fluxing materials combined with the application of high calcining temperatures also potentiates the formation of a vitrified surface. In fact, the low levels of water absorption noted in R60 at 1150 °C (Table 7) corroborate this statement.
According to Figure 10b,c, when the firing temperature was increased to 1200 and 1250 °C, there was a progressive formation of large, irregularly shaped pores. Apparently, the higher firing temperature favoured the release of gases and resulted in the growth and coalescence of bubbles. This supports the significant bloating index values found in R60 at 1200 and 1250 °C. In general, the behaviour of R60 was very similar to that identified in some LWAs manufactured by Gao et al. [69].

3.2. Commercial Potential of the Formulations

The commercial viability of the samples was analysed by comparing the values obtained for compressive strength (S) and water absorption (WA24H) according to the classification criteria previously established (Figure 5). The classification of the samples based on these parameters is shown in Figure 11. It is important to note that all the formulations represented graphically showed a particle density of less than 2.00 g/cm3, thus meeting the normative limit specified for lightweight structural aggregates, as recommended by Standard EN 13055-1 [60]. Furthermore, to make it easier to identify the thermal processing conditions, suffixes were assigned to the samples according to the sintering temperature adopted, for example, suffix (c) corresponds to sintering at 1200 °C, while suffix (d) indicates sintering at 1250 °C.
As shown in Figure 11, 50.0% of the specimens produced conformed to one of the previously established categories of use. The specimens classified in category “H” demonstrated technical performance compatible with multiple engineering applications, ranging from light non-structural concrete to high-strength concrete. According to the data shown in Figure 11, 11 samples were placed in this category, standing out for their combination of low WA24H and high S, properties that are essential for LWAs used in high- performance structural concretes [32]. Among these formulations, the performance of the R100c composition is particularly noteworthy, as it was manufactured using RCW exclusively. This sample showed water absorption and crushing strength indices of 0.6% and 12.01 MPa, respectively. These values are apparently better than those presented by Franus et al. [71] for some commercial LWAs.
Among the specimens analysed, sample R100d, composed entirely of waste, was classified in category “D”, which includes materials considered suitable for application in structural lightweight concrete, non-structural lightweight concrete and lightweight mortars. The performance of R100d is similar to the main lightweight structural aggregate commercialised in Brazil [30]. The findings of this study demonstrate not only the technical feasibility of the proposed approach, but also its significant environmental and sustainability advantages.
The data found in Figure 11 also allowed us to analyse the influence of the firing method adopted on the commercial suitability of the samples produced. In general, sintering the samples at temperatures of 1200 and 1250 °C favoured the production of samples suitable for use in high-strength concretes, lightweight structural and non-structural concretes and lightweight mortars. On the other hand, firing the formulations at temperatures of 1100 and 1150 °C proved unsuitable for making LWAs. Although these samples showed high crushing strength values and low absorption indices under these conditions, excessive densification exceeded the limit set by the EN 13055-1 standard [60], making them technically unviable for applications that require lightness as a fundamental characteristic.
To increase the relevance of this study, a comparative table is included in Appendix D, summarising the main physical and mechanical properties of the 12 LWA samples that met the commercial requirements in Figure 11. The results were compared with a commercial lightweight aggregate commonly used in Brazil [48]. This comparison highlighted that several of the mixtures performed better than the commercial reference in terms of crushing resistance and water absorption, reinforcing the potential of RCW-based LWAs.
As well as meeting technical criteria and offering potential for various applications, the use of RCW also has environmental advantages that are worth highlighting. The use of industrial waste instead of natural clays can reduce the consumption of natural resources and energy [6]. According to this study, incorporating up to 100 per cent RCW can not only reduce the demand for clay, but also promote the principles of the circular economy by diverting significant volumes of waste from landfill [6]. Although a full life-cycle assessment was not carried out, the results are in line with previous studies that reported a significant reduction in environmental impact indicators when building materials incorporated ceramic or mineral waste [72]. Future research should extend this work by quantifying these environmental gains through a full life-cycle assessment.

4. Conclusions

The results obtained during this study demonstrate the technical feasibility of producing lightweight aggregates through the partial or complete replacement of clay with red ceramic waste. It is evident from the experimental evidence that the following specific conclusions can be deduced:
Lightweight aggregates with excellent physical and mechanical properties can be made from formulations containing up to 100 per cent RCW in their composition. In samples with high RCW contents, the physical and mechanical characteristics of these LWAs proved to be more suitable for commercial applications during sintering at temperatures of 1200 and 1250 °C. In the LWA made exclusively with RCW, when sintered at 1250 °C, the particle density, water absorption and crushing strength were 1.42 g/cm3, 1.7% and 2.64 MPa, respectively. This enabled the recommendation of the LWA for use in lightweight mortars and lightweight structural and non-structural concretes.
Sintering at 1250 °C resulted in a predisposition to bloating of the LWAs. In many cases, the use of higher RCW contents led to an increase in closed porosity and a reduction in particle density. In this temperature range, an increase in RCW content from 50 to 100 per cent, as a substitute for clay, resulted in an increase of almost 18 per cent in Pc and a reduction of approximately 13 per cent in ρd. Thus, RCW, when sintered at high temperatures, proves to be effective in reducing the ρd of lightweight aggregates, making it attractive for applications requiring LWAs with lower density.
The Riley [44] and Cougny [33] protocols, commonly used to analyse the bloating potential of LWAs, proved to be unsuitable for lightweight aggregates made from the waste used in this study. In many cases, the specimens produced met the conditions necessary to achieve bloating, even though they had physical and chemical characteristics considered inadequate by these theories.
The mineralogical composition of RCW and RC had a strong influence on the bloating phenomenon. The absence of the biotite, illite and muscovite peaks present in these starting materials, combined with the formation of magnetite and mullite and the thermal transformations of haematite into magnetite, resulted in strong gas release. In addition, the mineralogy of RCW and RC also acted as a substitute for the aluminosilicate matrix, making up for the chemical deficiency identified in Riley’s protocol [44].
The comparative analysis of the results obtained with data from existing products on the market demonstrates the quality of the samples produced and their technical viability for use in the main commercial applications of LWAs. Of the 24 samples manufactured, 12 proved to be suitable for use in lightweight structural and non-structural concrete and lightweight mortars. Of these, 11 were also suitable for use in high-strength concrete.
In addition to the conclusions already presented, it is worth highlighting the effect of sintering temperature on closed porosity. A positive correlation was observed between the increase in temperature and the development of closed porosity (Pc), especially at 1250 °C, where the values ranged from 35.8% to 43.0%, depending on the RCW content. This phenomenon was closely linked to the retention of gases and the intensification of glass phase formation, which significantly influenced volumetric expansion and density reduction.

Author Contributions

M.M.d.S.: writing—review and editing, investigation, formal analysis, visualization, validation, data curation, conceptualization. N.P.B.: writing—review and editing, visualization, validation, supervision, formal analysis, data curation, conceptualization. M.A.S.d.A.: writing—review and editing, visualization, validation, supervision, formal analysis, data curation, conceptualization. J.G.C.A.: writing—review and editing, validation, supervision, formal analysis, data curation. J.A.d.S.N.: writing—review and editing, validation, supervision, formal analysis, data curation. C.M.P.: writing—review and editing, validation, supervision, formal analysis, data curation. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A. Real Density (Dt) and Density of Dry Samples Excluding Permeable Pores (ρs) of the Mixtures

SamplesReal Density (g/cm3)Dry Density (Without Permeable Pores) (g/cm3)
1100 °C1150 °C1200 °C1250 °C1100 °C1150 °C1200 °C1250 °C
R1002.662.642.612.602.432.471.791.46
R902.652.652.612.612.412.441.791.62
R802.652.652.612.612.402.401.651.64
R702.642.652.622.612.452.391.681.66
R602.632.652.622.612.482.341.691.64
R502.622.652.622.612.492.241.681.65

Appendix B. Total Porosity (PT) and Open Porosity (Po) of the Mixtures

SamplesTotal Porosity (%)Open Porosity (%)
1100 °C1150 °C1200 °C1250 °C1100 °C1150 °C1200 °C1250 °C
R10021.368.0832.3245.4214.021.761.102.39
R9017.578.9132.0438.419.201.100.721.10
R8016.019.8937.3637.447.520.600.960.89
R7012.3410.1936.5136.805.640.400.861.03
R609.4111.8335.9037.633.830.340.640.73
R506.3215.4936.1237.291.490.180.670.73

Appendix C. Chemical Composition of Mixtures

Applsci 15 05729 g0a1
Applsci 15 05729 g0a1

Appendix D. Comparative Table of Experimental Aggregates and a Commercial LWA Commonly Used in Brazil

SamplesS (MPa)WA24H (%)ρd (g/cm3)
R100c12.010.621.77
R90c9.680.401.78
R80c8.810.581.64
R70c10.770.521.66
R60c9.760.381.68
R50c11.060.401.67
R100d2.641.681.42
R90d5.410.681.60
R80d7.300.551.63
R70d8.540.631.65
R60d9.680.451.63
R50d10.590.451.64
LWAB2.099.441.09
(LWAB) Lightweight aggregate in commercial use in Brazil [48].

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Applsci 15 05729 g001
Figure 1. Particle size distribution of (a) RC and (b) RCW.
Figure 1. Particle size distribution of (a) RC and (b) RCW.
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Figure 2. XRD diffraction pattern of (a) RC and (b) RCW.
Figure 2. XRD diffraction pattern of (a) RC and (b) RCW.
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Figure 3. Simultaneous thermal analysis of (a) RC and (b) RCW.
Figure 3. Simultaneous thermal analysis of (a) RC and (b) RCW.
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Figure 4. Morphology of (a) RC at x342 and (b) RCW at x389.
Figure 4. Morphology of (a) RC at x342 and (b) RCW at x389.
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Figure 5. Diagram of commercial potential for manufactured lightweight aggregates. Adapted from Souza [8].
Figure 5. Diagram of commercial potential for manufactured lightweight aggregates. Adapted from Souza [8].
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Figure 6. Appearance and behaviour of the samples after drying and sintering.
Figure 6. Appearance and behaviour of the samples after drying and sintering.
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Figure 7. Loss on ignition of the mixtures.
Figure 7. Loss on ignition of the mixtures.
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Figure 8. XRD diffraction pattern of R60 at 1250 °C.
Figure 8. XRD diffraction pattern of R60 at 1250 °C.
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Figure 9. Simultaneous thermal analysis (STA) of sample R60.
Figure 9. Simultaneous thermal analysis (STA) of sample R60.
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Figure 10. Microstructures of R60 (x133): (a) at 1150 °C, (b) at 1200 °C and (c) at 1250 °C.
Figure 10. Microstructures of R60 (x133): (a) at 1150 °C, (b) at 1200 °C and (c) at 1250 °C.
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Applsci 15 05729 g011
Figure 11. Commercial potential of the formulations.
Figure 11. Commercial potential of the formulations.
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Table 1. Chemical composition of raw materials.
Table 1. Chemical composition of raw materials.
SampleSiO2Al2O3Fe2O3CaOMgONa2OK2OOthers LOI (%)
RC41.4521.0227.991.172.090.002.963.328.6%
RCW46.235.9826.315.190.000.008.567.731.09%
LOI = loss on ignition.
Table 2. Composition of the formulations (% by mass).
Table 2. Composition of the formulations (% by mass).
MixturesR100R90R80R70R60R50
RCW100.090.080.070.060.050.0
RC0.010.020.030.040.050.0
WATER40.035.031.030.030.030.0
Table 3. Characterisation tests on the samples produced.
Table 3. Characterisation tests on the samples produced.
DeterminationMethodEquation or ParametersReferences
Water absorption (WA24H) Hydrostatic weighing. Sample mass: dry (mA), saturated surface dry (mB) and submerged in water (mC).WA24H = 100 (mB − mA)/mA (%)[50]
Particle density (ρd)ρd = mA/(mB − mC) (g/cm3)[50]
Density of dry samples, excluding permeable pores (ρs)ρs = mA/(mA − mC) (g/cm3)[50]
Real density (Dt)Water pycnometry. Pycnometer mass: empty (P1), plus sample (P2), plus sample plus water (P3), plus water (P4).Dt = (P2 − P1)/[(P4 − P1) − (P3 − P2)] (g/cm3) [51]
Total porosity (PT)Relationships between Particle density (ρd), Density of dry samples excluding permeable pores (ρs) and Actual density (Dt).PT = 100 [1 − (ρd/Dt)] (%)[52]
Open porosity (PO)PO = 100 [1 − (ρd/ρs)] (%) [52]
Closed porosity (PC)Difference between Total Porosity (PT) and Open Porosity (PO).PC = PT − PO (%)[52]
Bloating Index (BI)Variation in the average volume of the particles, from the initial state (V1) to the final state after sintering (V2).BI = 100 (V2 − V1)/V1 (%)[53]
Microstructure (SEM)Scanning electron microscopy. Vega-3 LMU TESCAN microscope.Acceleration voltage of 20 kV.[54]
Mineralogy (XRD)X-ray diffractometry. Shimadzu XRD-7000 diffractometer.Cu Kα radiation at 40 Ma; 40 kV; 10 to 80° (2θ); 0.02° pitch and 1.20°/min speed.[55]
Thermal analysis (TG- DTA)Simultaneous thermogravimetric analysis. Shimadzu DTG-60 analyser.30 °C to 1200 °C, rate of 8 °C/min, nitrogen gas, isotherm for 15 min.[13]
Loss on ignition (LOI)Difference between the mass of the samples before and after sintering.LOI = 100 (Mi − Mf)/Mi (%)[56]
Crushing resistance (S)Average of the individual strength of the granules. Where, load at failure (Pc) and particle diameter (x).S = 2.8Pc/πx2 (MPa)[57]
Table 4. Bloating indices of the mixtures.
Table 4. Bloating indices of the mixtures.
SamplesBloating Index (BI) (%)
1100 °C1150 °C1200 °C1250 °C
R100−22.5−43.53.429.4
R90−29.5−23.2−6.719.5
R80−16.0−24.87.910.7
R70−25.4−27.67.815.4
R60−22.7−22.217.023.4
R50−20.8−13.415.716.0
Table 5. Particle density (ρd) of the mixtures.
Table 5. Particle density (ρd) of the mixtures.
SamplesParticle Density (ρd) (g/cm3)
1100 °C1150 °C1200 °C1250 °C
R1002.092.431.771.42
R902.192.411.781.60
R802.222.381.641.63
R702.312.381.661.65
R602.382.331.681.63
R502.462.241.671.64
Table 6. Closed porosity (Pc) of the mixtures.
Table 6. Closed porosity (Pc) of the mixtures.
SamplesClosed Porosity (Pc) (%)
1100 °C1150 °C1200 °C1250 °C
R1007.36.331.243.0
R908.47.831.337.3
R808.59.336.436.6
R706.79.835.635.8
R605.611.535.336.9
R504.815.335.536.6
Table 7. Water absorption (WA24H) of the mixtures.
Table 7. Water absorption (WA24H) of the mixtures.
SamplesWater Absorption (WA24H) (%)
1100 °C1150 °C1200 °C1250 °C
R1006.70.70.61.7
R904.20.50.40.7
R803.40.30.60.5
R702.40.20.50.6
R601.60.10.40.5
R500.60.10.40.4
Table 8. Crushing strength (S) of the mixtures.
Table 8. Crushing strength (S) of the mixtures.
SamplesCrushing Strength (S) (MPa)
1100 °C1150 °C1200 °C1250 °C
R10010.2929.0712.012.64
R9017.6631.929.685.41
R8019.4231.778.817.30
R7025.6540.5210.778.54
R6032.7836.769.769.68
R5031.7232.5111.0610.59
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MDPI and ACS Style

Mendonça de Souza, M.; Barbosa, N.P.; dos Anjos, M.A.S.; Aguiar, J.G.C.; da Silva Neto, J.A.; Pederneiras, C.M. Recycling Red Ceramic Waste as a Raw Material for Lightweight Aggregates. Appl. Sci. 2025, 15, 5729. https://doi.org/10.3390/app15105729

AMA Style

Mendonça de Souza M, Barbosa NP, dos Anjos MAS, Aguiar JGC, da Silva Neto JA, Pederneiras CM. Recycling Red Ceramic Waste as a Raw Material for Lightweight Aggregates. Applied Sciences. 2025; 15(10):5729. https://doi.org/10.3390/app15105729

Chicago/Turabian Style

Mendonça de Souza, Maelson, Normando Perazzo Barbosa, Marcos Alyssandro Soares dos Anjos, João Gabriel Cruz Aguiar, José Anselmo da Silva Neto, and Cinthia Maia Pederneiras. 2025. "Recycling Red Ceramic Waste as a Raw Material for Lightweight Aggregates" Applied Sciences 15, no. 10: 5729. https://doi.org/10.3390/app15105729

APA Style

Mendonça de Souza, M., Barbosa, N. P., dos Anjos, M. A. S., Aguiar, J. G. C., da Silva Neto, J. A., & Pederneiras, C. M. (2025). Recycling Red Ceramic Waste as a Raw Material for Lightweight Aggregates. Applied Sciences, 15(10), 5729. https://doi.org/10.3390/app15105729

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