## 3 Results and Discussion
### Sensitivity Analysis  
Another analysis that we wanted to create for this research is the sensitivity analysis, which aims to determine how changes in the data collected in the LCI and in the selection of one methodology or another affect the LCA results. For this purpose, two scenarios are proposed, which are identified with typologies of gravel pits in Spain. * **Scenario 1: Use of explosives** This scenario assumes that the production of the virgin material at the gravel pit site is not carried out mechanically by the backhoe excavators, but requires the use of explosives to generate this virgin material. The amount of explosive used is 0.18 kg of explosive per ton of NAs with a variation of (\(\pm\)0.03 kg) [23]. Other authors, such as [PERSON] et al., also identify this same amount of explosive in the production of NAs for the specific case of Spain [1] and similar values are used by [PERSON] et al. [22]. The process chosen to simulate the use of explosive is Blasting {RER} processing | Cut-off, S all other LCI data remain the same. * **Scenario 2: Conveyor transport (gravel pit site NCA-production plant)** In the second scenario, the internal transport is modified, i.e., the virgin material produced at the gravel pit site is transported to the aggregate production plant via conveyor belts. The same distances assessed in the LCI are kept constant (see Table 1). The process chosen for conveyor belt transport is Transport, freight, conveyor Belt {GLO} | transport, freight, conveyor belt | Cut-off, U. The results are shown in Figure 4. As can be seen in this graph, the impact categories of the EPD methodology and the impact category of the ReCiPe Midpoint methodology (E) are shown, with the value 100% set to the reference scenario, i.e., the preliminary values obtained in Section 3.1. Subsequently, the results obtained for both scenario 1 (S-1) and scenario 2 (S-2) are plotted as a percentage comparison with respect to the reference scenario (S-REF). This makes it easy to see in which impact categories the impacts are increased compared to the baseline and in which impact category. If we first analyze the S-2, we can see that the results are very similar or practically the same as the S-REF, with the exception of two impact categories where they are slightly increased, such as the Abiotic Depletion of Elements (increase of 112.9%) and the land use category (increase of 22.26%). This is because if the infrastructure for the transport of virgin material from the quarry site to the aggregate production plant is to be carried out by means of conveyor belts, this infrastructure must be installed along the gravel pit site and consequently has a greater impact on the soil. In addition, conveyor belts consume more lubricant in their maintenance and operation, which results in a higher consumption of the natural resources that produce the lubricant. However, the S-1, in contrast to the S-REF, does show substantial differences in certain impact categories that will be discussed later, but for the categories of Water Depletion (increase of 2.04%), Abiotic Depletion of Fossil Fuels (increase of 5.68%) and Ozone Depletion (increase of 3.17%), the increases are insignificant compared to the S-REF. However, in other categories such as Acidification (168.58% increase), Eutrophication (149.73% increase), Photochemical Oxidation (140.10% increase), Abiotic Depletion of Elements (649.69% increase), and land use (80.91% increase), the increases are exponential with respect to the S-REF. The use of explosive material as an element to produce mechanical breakage of the soil and obtain virgin material for subsequent treatment implies the emission of large quantitiesof substances such as ammonia and NO\({}_{\chi}\) emissions and volatile compounds that directly affect the categories highlighted above [31]. This is identified by previous authors such as [PERSON], where she indicates that the use of explosives for the production of natural aggregates can contribute to impact categories ranging from 18% to 86% [22].