## 1 Introduction  
Municipal solid waste incineration (MSWI) in waste-to-energy (WtE) plants is one of the main processes for municipal solid waste (MSW) management [1]. MSWI contributes to the energy recovery from MSW, and the reduction of its volume (by 90%) and weight (by 75%) [2]. It is extensively applied in many European countries. According to the information provided by the Confederation of European Waste-to-EnergyPlants (CEWEP) [3], 492 WTe plants are operating in Europe [4]. In 2017, around 70 Mt of MSW were incinated in the EU (EU-28) [5]. The main by-product produced during the MSW treatment in WtE plants is the incinator bottom ash (IBA). IBA represents 85% of the solid resulting from combustion [6] and it is classified as a hazardous (EWC 19 01 11*--asterisk means hazardous) or non-hazardous waste (EWC 19 01 12) depending on its concentration of hazardous substances. It is mainly composed of Si, Al, Ca, and Na oxides, and a small amount of heavy metal(loid)s [7]. IBA undergoes previous stabilization through an outdoor maturation treatment of 2-3 months, consisting of its carbonation and pH stabilization at values between 8-10 [8]. The resultant by-product of the IBA maturation treatment is weathered bottom ash (WBA), which is valorized for engineering purposes. The main application fields of WBA as secondary material are civil engineering, chemical engineering, and the building sector as reported elsewhere [9]. However, new applications of WBA have emerged in recent years for its use as a precursor on alkali-activated cements (AACs) [10] due to its composition rich in silicates and aluminosilicates [7]. AACs have become an alternative to ordinary Portland cement (OPC) given that the manufacturing process involves CO\({}_{2}\) reductions, energy-savings, and lower resource consumption. This fact has been certified by the large amount of studies published in the last decade [11; 12]. Their obtention consists of the reaction of a solid powder precursor (based on amorphous aluminosilicates) [13] in an alkaline activate solution (usually NaOH, KOH, and/or Na\({}_{2}\)SiO\({}_{3}\)) of variable concentration. After a suitable activation process, a gel is formed (N-A-S-H, C-A-S-H, or N-(C)-A-S-H), of which the nature and final properties depend on the CaO content of the precursor [14], the alkali activator used [15], and the curing temperature [16]. AACs have good mechanical properties [17], high resistance to chemical attack by aggressive aqueous and acid solutions [18], and resistance to high temperatures and fire [19]. The carbon emission levels generated during AAC production are lower than that of OPC [20], which is beneficial from an environmental point of view. AACs are sustainable materials since these can be formulated from waste materials and industrial by-products [21; 22]. Because of their similar properties to OPC, AAC applications are associated with building and civil engineering [23], as well as for the stabilization and solidification of hazardous and radioactive wastes [24; 25; 26]. For all of the above-mentioned reasons, AACs have shown a high potential to be applied as sustainable cements following the zero waste principle [27] promoted by EU [28]. Most of the published studies that include WBA in their AAC formulations add other precursors such as metakaolin [29], fly ash of thermal power plants [30], granulated blast furnace slag [31], or ladle slag [32] to obtain AACs. In all the cases described above, the reported AACs' strength values were low due to the presence of metallic Al found in WBA samples. Aluminum reacts with the alkali activator by forming hydrogen gas [33; 34], increasing the porosity of AACs and decreasing the mechanical strength. On the other hand, great results were obtained when WBA was also used as a raw material in alkali-activated blended or hybrid cements to increase the AACs' mechanical strength [35; 36; 30; 37]. There are few studies where WBA is used as a sole precursor [38; 39; 40].