# Recycling Red Ceramic Waste as a Raw Material for Lightweight Aggregates
## 3 Results and Discussion
### 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 (_WA\({}_{24H}\)_) 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/cm\({}^{3}\), 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 \({}^{\circ}\)C, while suffix (d) indicates sintering at 1250 \({}^{\circ}\)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 _WA\({}_{24H}\)_ 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 [PERSON] 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 \({}^{\circ}\)C favoured the production of samples suitable for use in high-strength concretes, lightweight structural and non-structural con  
Figure 11: Commercial potential of the formulations. cretes 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].