## 3 Case Study: Description and Technical Assessment  
Implementation of the circular model used wastes (dregs and grits) as alternative aggregates in the bituminous mixture, but also avoiding landfill disposal of wastes in the pulp and paper industry. Hence, three mixtures of the AC14 surface type (named reference, dregs, and grits) were produced for application as a top layer in a 250 m road stretch, with the formulations shown in Table 1.  
The implementation of this industrial real-scale trial involved the following steps (Figure 1): In the linear case (reference), the natural raw materials were transported directly to the mixing plant from the extraction sites. For the mixtures with wastes (dregs and grits), they were first dried in a solar greenhouse oven, sieved, and placed in big bags for transportation to the bituminous mixture process central. There, they were inserted as aggregates, replacing the natural crushed limestone (0/4 mm) in the reference formulation  
CE marking of construction products is mandatory for products that are covered by a harmonized standard [39], which, in the case of bituminous mixtures aggregates, follows EN 13043 [40]. It identifies the minimum requirements that aggregates must meet (particle size analysis) and the properties to be characterized (density and quality of fines) [10]. Table 2 shows that dregs, grits, and natural limestone powder characteristics are quite similar and comply with the quality limit of fine particles they should contain (10 g/kg) as an AC14 surface type mixture. Figure 2 shows the particle size distribution (EN 933-2) [41] of dregs, grits, and limestone (0/4 mm) and, although finer, both wastes show a size grading comparable to the natural limestone used as fine aggregate. Figure 3 shows the fitting of the aggregate mixture in the formulations under test. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Standard** & **Grits** & **Dregs** &
\begin{tabular}{c} **Crushed** \\ **Limestone (0/4)** \\ \end{tabular} & **Units** \\ \hline Particle density & EN 1097-6 [42] & 2630 & 2630 & 2640 & mg/m\({}^{3}\) \\ Fines quality & EN 933-9 [43] & 0.2 & 3.6 & 4 & g/kg \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics for dregs, grits, and crushed limestone (0/4 mm). Figure 1: Implementation steps of bituminous mixtures with and without wastes (dregs and grits) on a road surface: 1. Waste transportation from producer (NVG) to waste manager (WM) in an open truck; 2. Drying process at solar drying (greenhouse); 3. Grits drying process; 4. Grits transportation to the bituminous central; 5. Dregs drying; 6. Dregsieving process after drying; 7. Dregs transportation to the bituminous central; 8. Mixing dregs and grits in the bituminous mixtures; 9. Bituminous mixtures production; 10. Discharge of bituminous mixture to the truck; 11. Bituminous mixture truck arriving at road location; 12. Surface treatment for roughness; 13. Track coat asphalt emulsion application; 14. Mixtures application equipment; 15. Dregs bituminous mixture application; 16. Grits bituminous mixture application; 17. Standard (reference) bituminous mixture application; 18. Final road stretches (reference, dregs, and grits). Figure 2: Particle size distribution of dregs, grits, and crushed limestone (0/4 mm). During implementation, the features gathered in Table 3 were characterized. All the parameters of the different bituminous mixtures comply with the required limits in the specifications of an AC14 surface type layer, except for a small deviation in the porosity and conserved strength of the bituminous mixture with dregs.