# Alkali-Activated Materials with Pre-Treated Municipal Solid Waste Incinerator Bottom Ash
## 1 Introduction  
According to the International Labour Organization (ILO), essential services are globally understood as those that, if interrupted, lead to a clear and imminent threat to life, personal safety, or health of the whole or part of the population [1]. Although this concept of essentiality has become popular due to the COVID-19 pandemic, giving rise to subjectivities associated with each country and their circumstances [2], an objective and global reality is that the collection of domestic waste is an essential activity that fits perfectly within the guideline defined by the ILO [3]. In 2019, the generation of municipal solid waste (MSW) in the European Union (EU) increased around 1% compared to 2018, which the production of an additional 2 million tonnes [4]. This value was expected to be significantly higher in 2020, considering the numerous quarantines and working from home due to the pandemic, which caused an increase of 6.9% in the 27 EU State Members in 2020 when compared to 2019 (from 5.5% to 12.4%) [5] and could imply a greater amount of waste was generated and disposed of. This upward trend in the amount of generated MSW, also directly associated with population growth [6], raises the importance of the research on the technical feasibility of the waste streams generated from the combustion of solid waste [3, 7, 8]. This process is carried out in order to reduce between 70% and 90% of the volume of domestic waste collected, while its combustion is used to produce energy [9]. One of the sub-products generated in this procedure corresponds to MIBA [10, 11], which has been studied as a precursor of alkali-activated materials (AAM); these types of materials are manufactured by mixing a precursor rich in amorphous aluminosilicates andcalcium with an alkaline solution [12; 13; 14], providing mechanical and durability properties similar or even greater to those of conventional Portland cement composites [15]. These relatively new bound construction materials are considered more sustainable from the use of industrial wastes as raw materials. Although MIBA shows pozzolanicity, which makes it a viable precursor in this type of reaction [16; 17; 18], most researchers agree that this material has two main weaknesses: the presence of metallic aluminum that reacts with the alkaline solution to produce hydrogen gas (i.e., on average 1360 mL H\({}_{2}\)/g of Al is generated [19]); and low content of amorphous aluminosilicates, in comparison with other precursors such as ground-granulated blast-furnace slag (GBFS), FA or metkaoolin, which do not require improvement stages to achieve AAM with an excellent performance [20; 21; 22; 23]. To solve the aluminum issue, [PERSON] et al. [24] proposed in their research a pre-treatment stage, which consisted of immersing MIBA in water, with a liquid/solid ratio of 5/1, and placing it in an oven at 105 \({}^{\circ}\)C for 24 h. With increasing temperature, the reaction rate between the aluminum and water releases all the H\({}_{2}\). [PERSON] et al. [25] proposed a uniform agitation for 4 h of the NaOH solution and the MIBA in order to release all the H\({}_{2}\) possible. These same authors replaced 40% of MIBA for granulated blast furnace slag (GBFS) to improve the mechanical properties. Regarding the low content of amorphous aluminosilicates, [PERSON] et al. [26] found a low quantity of reaction products from activated MIBA, thereby requiring aluminum or silicate correctors to achieve adequate performance. In their work, they used the 8 to 30 mm fraction of MIBA and PAVAL as a source of PV reactive aluminum, which is an industrial waste generated from the secondary aluminum recycling process. Their results showed a decline in the mechanical properties because of the resulting high porosity and decreased compressive strength from 25.6 to 12.1 MPa. [PERSON] et al. [27] evaluated the combination of MIBA with FA, in order to improve the mechanical performance, obtaining specimens that were dimensionally more stable than the others made with MIBA alone as a precursor.