# Granular Material Development Applied in an Experimental Section for Civil Engineering Purposes
)1 Departament de Ciencia de Materials i Quimica Fisica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona, Spain; [EMAIL_ADDRESS] (J.F. ); [EMAIL_ADDRESS] (J.M.C. )1 Departament de Ciencia de Materials i Quimica Fisica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona, Spain; [EMAIL_ADDRESS] (J.F. ); [EMAIL_ADDRESS] (J.M.C. )1 Departament de Ciencia de Materials i Quimica Fisica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona, Spain; [EMAIL_ADDRESS] (J.F. )1 Departament de Ciencia de Materials i Quimica Fisica, Universitat de Barcelona, Marti Franques 1, 08028 Barcelona, Spain; joanformosa@ub. MSWI presents mainly two types of waste, named bottom ash (BA) and air pollution control (APC). BA represents the major solid output stream residue from MSWI, and it is the 85 wt. % of the solid resulting from combustion [5]. This residue is classified as non-hazardous waste (EWC 190101), and it is mainly composed of Si, Al, Ca, and Na oxides as major elements, with traces of metal(loid)s [6]. Regarding the materials' compositions, BA is heterogeneous and contains glass, ceramic, concrete, brick, debris, sand, metal, stone and fused clinker, among others [1]. The current practice of BA utilization in Europe involves its use in relatively simple civil engineering applications or disposal by landfilling. Some of the applications of BA are as (a) a precursor of alkali-activated materials (AAM), (b) adsorbent materials for the removal of hazardous elements from wastewater and landfill gases, (c) a soil replacement in agricultural activities, (d) a raw materials substitute for ceramic-based products manufacturing, (e) landfill cover, and (f) a biogas upgrading and production enhancer [7; 8; 9]. After a combustion temperature of 950 \({}^{\circ}\)C [10], BA is further processed in a conditioning plant to recover some valuable materials (ferrous and non-ferrous metals) and to obtain a homogenized granular material. When BA is stabilized through an outdoor maturation (ageing) treatment for 2-3 months, the obtained by-product is called weathered bottom ash (WBA), which is valorized for engineering purposes. This maturation mainly consists of carbonation and a pH stabilization between 8 and 10 [10], which ensures that metal(loid)s are stabilized. There are different applications for WBA as a secondary raw material, such as in civil engineering purposes as a secondary aggregate for road construction [11; 12], embankments [13] and pavements [14], and as concrete aggregate [15]. WBA is also used in the building sector as a ceramic material, such as in tiles, bricks and glass-ceramics, as reported elsewhere [16; 17]. In the case of Spain (except in Catalonia) and some other EU countries [3], there is no regulation regarding WBA utilization, and disposal via landfill is still the most common MSW management. APC is the other waste generated during the MSWI, which mainly contains a mixture of incinerated fly ashes (IFA), products of the neutralization of acid gases (calcium chloride, calcium sulfate or calcium carbonate, among others) and an excess of lime (in semi-dry scrubbers using lime slurry). Some authors evaluated the stabilization of IFA from MSW using hydraulic binders such as Ordinary Portland cement (OPC), lime, coal fly ash or blast furnace slag [18; 19]. The main concern regarding the APC residues is the high content of heavy metal(loid)s, dioxins, furans and soluble salts [20; 21]. Consequently, APC is currently classified as a hazardous waste [22], and it is handled by landfill disposal after stabilized [23]. Hence, cement-based treatment for formulating mortars [24] is the most employed means of APC stabilization, not only due to economic factors but also because of its ease of handling [15]. This paper aims to present the most relevant findings related to the WBA and APC derived from MSWI in formulating a granular material (GM).