# Alkali-Activated Binders Using Bottom Ash from Waste-to-Energy Plants and Aluminium Recycling Waste
###### Abstract  
Alkali-activated binders (AABs) stand out as a promising alternative to replace ordinary Portland cement (OPC) due to the possibility of using by-products and wastes in their manufacturing. This paper assessed the potential of weathered bottom ash (WBA) from waste-to-energy plants and PAVAL(r) (PV), a secondary aluminium recycling process by-product, as precursors of AABs. WBA and PV were mixed at weight ratios of 98/2, 95/5, and 90/10. A mixture of waterglass (WG) and NaOH at different concentrations (4 and 6 M) was used as the alkaline activator solution. The effects of increasing NaOH concentration and PV current were evaluated. Alkali-activated WBA/PV (AA-WBA/PV) binders were obtained. Selective chemical extractions and physicochemical characterization revealed the formation of C-S-H, C-A-S-H, and (N,C)-A-S-H gels. Increasing the NaOH concentration and PV content increased porosity and reduced compressive strength (25.63 to 12.07 MPa). The leaching potential of As and Sb from AA-WBA/PV exceeded the threshold for acceptance in landfills for non-hazardous waste. M +
Footnote †: journal: Physics Letters B  
1
Footnote 1: email: _Applied_  
Footnote †: journal: Physics Letters B  
1
Footnote 1: email: _Applied_  
through the carbonation of the fresh IBA [11]. The resulting material after the weathering process is known as weathered bottom ash (WBA). The particle size distribution and a composition rich in glass, ceramics, stones, bricks, and melting products [12] make the WBA suitable for cement production [13], as aggregates in road construction, concrete, or mortars [14; 15], or for the manufacture of ceramic-based products [16]. However, the use of WBA in engineering is limited due to its environmental risks and inferior properties compared to natural aggregates and products. Research on the potential applications of WBA must therefore be focused on those that minimize the leaching potential of heavy metalloids [10]. In this sense, WBA can be used as an aluminosilicate precursor in alkali activation technology, since a cementitious matrix can immobilize heavy metalloids. Some recent studies have demonstrated the potential of WBA as a precursor in the synthesis of alkali-activated cements (AACs) [17; 18; 19]. AACs are high-strength binders obtained from the reaction between an aluminosilicate-rich solid precursor and an alkaline activator [20]. One of their main advantages is that they can be formulated from aluminosilicate-rich urban, industrial, agro-industrial, and mining wastes [21; 22]. AACs are an excellent alternative to mitigating the CO\({}_{2}\) emissions and energy consumption associated with the production of ordinary Portland cement (OPC) [23]. Hence, the production of AACs can promote suitable waste management and sustainable cement production. Additionally, the properties of the AACs are very promising and comparable to those of OPC [24]. These properties vary depending on the curing temperature [25], the alkaline activator used [26], the SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) ratio, and the calcium content [27]. The aluminium content plays an essential role in the alkali activation, which affects the nature of the formed products and the strength of the AACs [28; 29]. Therefore, the use of aluminium correctors is necessary when the AACs are obtained from the alkali activation of precursors that have a substantial lack of reactive aluminium compared to reactive silica, as is the case with WBA [17; 30]. In this study, new sustainable alkali-activated binders (AABs) were obtained from the alkali activation of municipal and industrial waste. The least polluted fraction of WBA (8 to 30 mm) was used, given that it has the lowest concentrations of heavy metalloids and the highest SiO\({}_{2}\) availability [17; 31]. Additionally, this fraction allows enhancing the mechanical properties of alkali-activated WBA binders as reported elsewhere by the authors [32]. PAVAL(r) (PV) was also used as a source of reactive aluminium.