## 3 Results and Discussion  
### Impact-Oriented Analysis of Traditional Lightweight Aggregates  
Table 4 and Figure 3 show the impacts associated with the production of 1 kg of traditional lightweight aggregates made entirely of clay. The three clay samples separately obtained similar results to each other in all stages. A significant difference is observed in the manufacturing stage, due to differences in the sintering conditions of the aggregates according to the type of clay used. With regard to the impact categories, it should be noted that Global Warning Potential shows values very close to 0.37-0.38 kg eq. CO\({}_{2}\)/kg in emissions for SY, PY and PR, respectively. This is in line with other authors [53]. Within this same category, the stage with the lowest contribution to the impact is that of raw materials, representing 2% of the total for all the clays studied. Something similar occurs with the extraction and transport stages, with obtained values of 7% and 3%, respectively, for CO\({}_{2}\) emissions. Undoubtedly, the manufacturing stage is the most responsible for the final impact, with a contribution of 89% (88% for SY). This is due to the long periods of time that kilns must remain at temperatures above 1000 \({}^{\circ}\)C and the consequent economic and environmental cost that this entails, which contributes to the higher combustion of fossil fuels responsible for powering kilns at such temperatures, as reported by authors who have analyzed the ceramics sector [52; 53; 54]. The remaining nine impact categories show variations of less than 1% for the three clays studied in the four stages. The One-Layer Depletion category stands out, where the contribution of raw materials increases up to 10% and 19% in the transport stage. Other authors have also found this effect [54] and have analyzed it [53; 55; 56]. They have found that it is due to emissions corresponding to the fuel consumption required for the operation of the extraction machinery and distribution vehicles, as well as the natural gas and electricity used in the atomization plants. Substances such as methane, bromotrifluoro-, Halon 1301, etc., would be the main culprits. This impact could be partially offset by the installation of on-site cogeneration systems. In the extraction process, the categories with the lowest contribution to the final impact are Acidification and Photochemical Oxidation, with 5%. The Fresh Water Aquatic Ecotox and Marine Aquatic Ecotoxicity categories, with 17% and 15%, respectively, increased to make a significant contribution. The last manufacturing stage maintains all its contributions above the significant margin (>50%), with minimum values for the One-Layer Depletion category (60%) and more extreme values for Photochemical Oxidation and Acidification (92% and 91%, respectively) for the three types of clays. Figure 3: Contribution of characterized impacts associated with 1 kg of lightweight aggregates manufactured without any residue from different stages of production (Scenario 0). The degree of influence for the raw materials stage would have a level B, although it would be possible to add different materials to the mixtures, as we show below. The manufacture of lightweight aggregates depends to a large extent on the physical-chemical properties of clays, so the substitution of this raw material could only be executed if a material with similar characteristics and behavior could be obtained. The extraction and transport phases would have a degree of influence C, since there would be no control, beyond the logistic one, that would allow influencing the performance of the activities. In contrast, the manufacturing stage would have a grade A. It is precisely in this stage with the greatest contribution to the impact where the greatest number of measures could be applied to reduce energy dependence. Some of these modifications could be the reduction in sintering times and temperatures, or more engineering measures where the hot air from the furnaces is stored in heat accumulators for later reuse.