# Preliminary Study of Recycled Aggregate Mortar for Electric Arc Furnace Dust Encapsulation
## 1 Introduction  
The \"Europe 2020\" strategy aims to generate smart, sustainable and inclusive growth by opting for an efficient economy in the use of natural resources. The new paradigm of the \"circular economy\" has as its main objective the sustainable use of resources through the principle of \"closing the lifecycle loop\" of materials--that is, to reintroduce into the production process materials classified as \"waste\" whose destination was the landfill [1]. This practice reduces the volume of waste managed in landfills and reduces the amount of raw materials consumed [2]. One of the main focuses of action of the \"circular economy\" is the construction sector, since it is considered one of the main generators of waste and consumers of natural resources at the European level [3, 4]. Within the construction sector, the mortar and concrete industry has a high impact due to its high consumption of non-renewable natural resources [5]. Construction and demolition waste (CDW) is one of the major waste streams globally; therefore, the use of recycled aggregates from CDW as raw materials in mortars and concretes is a practice to be promoted and is in line with the new paradigm of the \"circular economy\". The coarse fraction of recycled aggregates from CDW has been used successfully in the manufacture of structural and non-structural concrete [3, 6, 7]. The fine fraction ofthese recycled aggregates (0/4 mm) has also been used successfully in the manufacture of masonry mortars [8; 9; 10; 11; 12] and structural concrete [13; 14]. Furthermore, Spain is the third-highest steel producing country in the European Union [15]. More than 75% of its steel is produced through scrap recycling [16]. The scrap is melted in an electric arc furnace at temperatures above 1600 \({}^{\circ}\)C, and in this process occurs the volatilization of elements such as iron, zinc and lead, which react with oxygen and generate waste in the form of dust. This waste is known as Electric Arc Furnace Dust (EAFD), and it is collected and recovered in ventilation filters [17]. Although the composition of the EAFD depends on the scrap melted in the electric arc furnace, it is mainly composed of heavy metals such as zinc and lead [18]. From an environmental point of view, the EU Council Decision 2003/33/EC [19] establishes the criteria for classifying waste according to the concentration of heavy metals and anions detected in accordance with a conformity test (UNE EN 12457-4:2003). The levels of classification of waste based on its deposit in a landfill are inert, non-hazardous and hazardous. EAFDs are classified according to the EU Council Decision 2003/33/EC [19] as hazardous waste due to the high content of heavy metals that can leach [20; 21; 22]. Worldwide, around 70% of the EAFD produced is destined for landfilling after an encapsulation treatment, while the remaining 30% is destined for metal recovery [23; 24; 25]. Occasionally, scrap metal contains radioactive elements that may not be detected when entering the steel mill and then contaminate the steel mill dust during the manufacturing process [26]. Several radioactive incidents have been described in EAF steel mills in Italy, Mexico, Brazil, Thailand and Estonia [27]. In Spain, during the last decade, six incidents of this nature occurred in Andalusia (south of Spain) and the Basque Country (north of Spain). Because of this type of incident, it is necessary to encapsulate the EAFD with cement-based materials prior to transporting and subsequent depositing in storage installations for radioactive waste. The maximization of the ratio of EAFD/mortar is crucial to reduce the volume of storage necessary at this type of installation. EAFD encapsulation techniques aim to create mechanically and chemically stable monolithic blocks. The use of conventional Portland cement in the encapsulation of EAFD is usually the most recommended technique due to the extensive knowledge of this material, its availability and its good long-term physical and chemical stability [28].