## 3 Results
### Discussion of the Results  
The results of this work suggest that theoretically, both the valorisation pathways of substitution of feldspar in the ceramic paste and inert filler in the structural concrete mix are technically feasible and environmentally more advantageous than GS landfill. In particular, GS can be considered a complete or nearly complete substitute for feldspar since it is a source of alkaline oxides that can favour the formation of a glassy phase reacting with silica and alumina and acting as a fluxing component, increasing ceramic sinterability [13]. Moreover, according to the literature, the use of GS as a substitute for feldspar in ceramic paste, over the technical beneficial characteristics observed in the previous Section 3.1, is expected to guarantee almost the same bending strength [6], as well as higher flexible strength [5] than equivalent ceramic paste in the absence of GS. Pure GS pellets were fired at different temperatures. Their flexural strength ranged from 33.3 MPa (1100 \({}^{\circ}\)C) to 53.7 MPa (1150 \({}^{\circ}\)C), providing values close to values reported in the literature for the GS-based ceramic formulation [6]. Moreover, increasing the firing temperature from 1100 \({}^{\circ}\)C to 1150 \({}^{\circ}\)C caused a slight increase in the apparent density (from 2.26 g/cm\({}^{3}\) to 2.31 g/cm\({}^{3}\)), while the water absorption decreased from 4.32% to 0.29%, confirming the strong fluxing power of GS above 1100 \({}^{\circ}\)C, as commonly observed for natural Na/K feldspars [51; 52]. At 1200 \({}^{\circ}\)C, the pellets fully melted. The reddish colour acquired during firing can be considered a limit in the case of noble whitish application, but in some cases, an advantage when coloured formulations are required because it allows saving or avoiding pigment additives. Regarding GS as a substitute for fine sand, it must be noticed that the literature data point out that the replacement of natural sand with dried GS up to 15% \(w/w\) is favourable for making concrete without adversely affecting its strength and durability [51]. Moreover, [PERSON] et al. [17] and [PERSON] et al. [52] suggested that 25-40% of river sand could be substituted by the GS with a favourable influence on the mechanical properties of concrete, whereas the review of previous works showed that granite dust concrete exhibits enhanced  
Figure 6: Sensitivity analysis of the production cost considering 0 km, 20 km, and 50 km transport for GS in Scenarios 2 and Scenario 3.  
dense and compact concrete matrix at optimum percentage replacement levels [53]. This evidence is in contrast with the results obtained in the present work and with the direct experience of the author, who observed a quality decrease substituting 5% \(\omega/w\) of fine natural sand with GS. Theoretically, the substitution of fine inert with GS, as in the case of the present work, guarantees almost the same classes of resistance (C30/37) and consistency (S4) of the structural concrete composition used as a reference, even if with a final reduced quality (loss 10% compressive strength), over the increase of W:C ratio, which inevitably reduces the class of exposure of the concrete [53]. In practice, given the reality of the current concrete business, with special regard to Portugal, where the economic margins are very limited, according to the authors' experience, firms will hardly choose to replace a good quality natural fine inert in structural cement mixes with GS, which significantly reduces the final technical characteristics and needs to be dried before use. Based on these results, GS can be considered more suitable as a substitute for fine inert in mortars, which have less stringent quality standards than structural commercial concrete. Table 9 reports the synthesis of the advantages and disadvantages associated with the scenarios analysed.