## 3 Results and Discussion
### Environmental Results
This is because the fuel combustion process generates nitrogen oxides (NO\({}_{\chi}\)), sulfur oxides (NO\({}_{\chi}\)), particulate emissions, and carbon oxides (CO\({}_{\chi}\)) which are highly penalized through the characterization coefficients in these categories. For example, in the Ozone Depletion category, these identified gases increase the degradation of the ozone layer, leading to increased ultraviolet radiation directly affecting humans and vegetation cover. Photochemical Oxidation and Acidification is a category where these gases react with sunlight to lead to the creation of ozone and other oxidizing compounds to form toxic clouds resulting in acid rain. One aspect that can be highlighted is that the use of diesel as a fuel can be an advantage in the gravel pit site operations and in the natural aggregate production plant instead of this energy coming from the electricity grid. For example, in [PERSON] et al. 's research, these mechanical processes are supplemented with energy from the electricity grid, particularly in Sri Lanka, where they have greater impacts on the above-mentioned categories. The electricity grid is a mix of energy sources, and in some countries, power generation can come from conventional sources such as coal that have a considerable impact on the environment [2]. In the global warming category, fuel consumption and combustion activities account for approximately 86.52% (3.72 kg CO\({}_{2}\) eq/t), with the transport process having an impact value of 11.74% (0.51 kg CO\({}_{2}\) eq/t). The transport activity can be very variable as it will depend on the distances evaluated--for example, in the research of [PERSON] et al., when including in their LCA the distance from the NA to the customer, the transport process reaches values in this category up to 40% (1.66 kg CO\({}_{2}\) eq/t) [5], so the impact will therefore depend on the transport process depending on the scenario [28]. This is also observed in the research of [PERSON] et al., where they report emission values of 30.9 kg CO\({}_{2}\)/t, including the production of natural aggregates in a quarry as well as the process of transporting these aggregates to the concrete production plant [6]. All this variability of results between similar investigations can be attributed to differences between the local energy sources used, production methods and extraction methods of NAs according to [PERSON] et al. and [PERSON] et al. [2; 29]. The environmental and economic comparison presented by [PERSON] et al. [21] for different investigations depending on whether it is NAs or RAs and its mineral origin is clearly stated. The activities related to the consumption and use of fuel in the functional unit studied are identified to a lesser extent as having more representative values compared to the values entered--for example, for the process of recycling shredded steel, where it is practically invisible in Figure 2, as its percentage contribution to the impact is less than \(<\)1%. This leads to the conclusion that the value of the impact caused by this activity is non-existent in the environmental assessment of producing NAs and the same would apply to tire recycling and lubricant recycling activities. Although, for the case study, these recycling activities are not representative, this does not imply that they do not have associated environmental impacts. Steel recycling, for example, is commonly carried out by melting the scrap in electric furnaces which consume large amounts of energy from the electricity grid. These impact percentages (\(<\)5%), and in agreement with [PERSON] et al. [30], are considered to have a minimal contribution, so the inclusion of these activities/consumables in the system boundaries of the case study and in the LCI could be obviated. However, this process can be carried out once the results have been preliminarily assessed and this fact has been verified. The category of Abiotic Depletion of Elements expresses the depletion of available non-renewable natural resources such as minerals, metals, and fuels.