# Preliminary Study of Recycled Aggregate Mortar for Electric Arc Furnace Dust Encapsulation
## 2 Materials and Methods  
### Characterization of Materials  
A commercial siliceous sand (Natural aggregate: NA) was used as a reference, and a fine recycled aggregate from structural concrete waste (RCA) was used as an alternative. The RCA was collected from the 0/4 mm stockpile of a recycling plant located in Cordoba, Spain, where structural concrete waste from different sources was previously crushed and subsequently screened. Figure 1 shows the particle size distribution of NA and RCA calculated according to the standard UNE-EN 933-1:2006. In RCA, approximately 93% of the particles are less than 4 mm, while in NA, 100% are less than 4 mm. In RCA, more than 14% of the particles pass through the 0.063 mm sieve, and in NA, only 1.8% pass through this sieve. The RCA shows a more continuous particle size distribution, with higher compaction capacity than the NA, which presents a more uniform particle size distribution. In order that the results of this research can be applied on a real scale, the aggregates were used without altering their granulometric curves. The NA had a sand equivalent value of 94 calculated according to the UNE-EN 933-8:2000 standard. The dry particle density and water absorption were calculated according to the UNE-EN 1097-6:2014 standard, obtaining a value of 2.60 g/cm\({}^{3}\) and 0.95%, respectively, while the RCA had a sand equivalent value of 90, a dry particle density of 2.27 g/cm\({}^{3}\) and 5.7% of water absorption. The RCA composition, calculated in accordance with the UNE EN 933-11:2009 standard, was concrete particles (98%), asphalt particles (1%) and ceramic particles (1%), so it can be considered a pure recycled concrete aggregate. To achieve higher compactness of the cement-based matrix, a commercial siliceous filler (SF) was used. The SF came from crushing siliceous quarry sands and was supplied by Minas Carmina Palau Saverdera (Gerona, Spain). Portland cement CEMI 42.5 R/SR was used, which was supplied by the Portland Valderrivas S.A. from Alcala de Guadaira (Seville, Spain). The chemical composition of NA and RCA was carried out by X-ray fluorescence (XRF) using 4 kW of power and S4 PIONEER, BRUKER equipment. The cement and SF composition was supplied by their manufacturers. The chemical compositions are shown in Table 1.  
Figure 1: Particle size distribution of NA and RCA. The EAFD was collected from an electric arc furnace steel mill located in the North of Spain (Zumarraga). The specific surface area of EAFD, SF and cement was analyzed by the Brunauer-Emmett-Teller (BET) method, through the absorption of N2 with Micromeritics ASAP 2010 equipment. The dry particle density was also determined according to standard UNE 80103:2013 (Standards used in the experimental work are shown in Appendix A). The results obtained are shown in Table 2.  
The chemical composition of EAFD was determined using the EDAX technique using a Jeol scanning electron microscope with the following characteristics: model JSM-6300 with acceleration potential of 20 kV and working distance of 15 mm. The percentages by weight of the elements identified in the EAFD are indicated in Table 3.  
The metallic elements that showed a higher proportion in the EAFD were Zn and Fe, and to a lesser extent Ca, Pb and Mn. These results were in accordance with those reported by other authors such as [PERSON] and [PERSON] [33] and [PERSON] et al. [34]. The composition of this type of waste varies depending on the quality of the molten scrap. [PERSON] et al. [35] also identified Fe as the main element, and to a lesser extent Zn, Ca and Mn.