# Reutilization of Recycled CDW Sand in Mortars, Paving Blocks, and Structural Concrete
## 3 Results and Discussion
### Properties of Aggregates
#### 3.1.2 Particle Size Distribution of Aggregates, Percentage and Quality of Fine Particles  
The particle size distribution and percentage of fines in the NA and CDW aggregates, determined by sieving according to Standard UNE-EN 933-1 [38], are presented in Figure 9. The recommended particle size distribution range from the previous Structural Concrete Instruction EHE-08, as defined in the comments of Article 28.4.1, is also included in the figure for reference. Although this reference range is not incorporated in the current Spanish Structural Code, it remains a useful granulometric reference for fine aggregates. At the upper limit of the 0.063 mm sieve, a cumulative retained percentage of 16% was considered,  
Figure 8: X-ray diffractogram of CDW and calcareous NA sand. D: dolomite (CaMg(CO\({}_{3}\))\({}_{2}\); L: limestone (CaCO\({}_{3}\)); Q: quartz; A: albite (NaAlSi\({}_{3}\)O\({}_{8}\)). which, according to Article 30.4.1 of the Structural Code, corresponds to limestone crushed aggregates intended for use in structural concrete exposed to general non-aggressive exposure classes (X0 and XC, as defined in Article 27). The particle size distribution of both the NA and CDW aggregates falls within the reference limits established by EHE-08. This indicates that, based on their particle size distribution, both NA and RA would be suitable for use in structural concrete. However, it is important to note that, since the RA used in this study was not sourced from concrete waste and pertains to a fine aggregate fraction rather than a coarse aggregate fraction, it falls outside the scope of the current Spanish Structural Code. The percentage and quality of fine particles, as well as the fineness modulus (FM) of the aggregates, are presented in Table 5. Below 1 mm, the CDW particles were larger than the NA particles (see Figure 9), which was due to the repeated washing to remove sulphates. However, both aggregate types had a similar FM (3.1-3.2), because within the 1-4 mm range, NA particles were coarser than those of the recycled CDW, which balanced the overall modulus value. Slightly higher FM values are reported by [PERSON] et al. [52] for natural sand (3.64) and recycled sand obtained from ceramic tiles (3.76), sanitaryware (3.84), and red clay bricks (4.04) intended for use in structural concrete. Article 30.4.1 of the Spanish Structural Code specifies the environmental conditions under which aggregates can be used based on their maximum fine content. Thus, according to the percentage of fines, the CDW recycled sand is suitable for use in structural concrete exposed to the following classes: X0 (no carbonation risk), XC (carbonation-induced corrosion), XS (chloride-induced corrosion from seawater), XD (chloride-induced corrosion not from seawater), XA (chemical attack), XF (freeze-thaw), or XM (erosion). These classifications correspond to non-calcareous aggregates with a fine content below 6%. In contrast, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **NA** & **CDW** \\ \hline FM & 3.1 & 3.2 \\ Percentage of fine particles, wt.\% & 14.4 & 4.4 \\ Sand equivalent & 53 & 73 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Particle size distribution, percentage, and quality of fine particles. Figure 9: Particle size distribution of natural limestone and CDW aggregates. the calcareous sand is restricted to use in X0 or XC environments because its fines content exceeds 16%, which makes it unsuitable for structural concrete exposed to more severe exposure classes. When assessing the quality of fines by the sand equivalent test (Annex A of Standard UNE-EN 933-8 [39]), certain particles in suspension were identified. Additionally, the observation of black particles during the oven drying of the CDW recycled aggregate suggests the presence of organic matter.