# Binary Mixes of Self-Compacting Concrete with Municipal Solid Waste Incinerator Bottom Ash
## 3 Results and Discussion  
### Characterization of the Materials  
The results of the modified Chapelle test, by titration with 0.1M hydrochloric acid, determined the content of unconsumed Ca(OH)\({}_{2}\) (free content), which were meant to react with the reactive aluminosilicate phases present in the FA and MIBA, during 16 h at 90 \(\pm\) 5 \({}^{\circ}\)C. Two grams of CaO laboratory-grade and one gram of the by-product diluted in distilled water were used in this reaction. The reactions presented in the titration are the following:  
\[\mathrm{CaO}+2\mathrm{HCl}\rightarrow\mathrm{CaCl}_{2}+\mathrm{H}_{2}\mathrm{O} \tag{1}\]  
\[\mathrm{Ca(OH)}_{2}+2\mathrm{HCl}\rightarrow\mathrm{CaCl}_{2}+2\mathrm{H}_{2} \tag{2}\]  
Through Equation (3), it is possible to calculate the mg of Ca (OH)\({}_{2}\)/g of by-product.  
\[\mathrm{(mg\ Ca(OH)_{2})/(g\ by\text{-product})=(28\times(v_{3}-v_{2}\ )\times F_{c})/(m_{2})\times 1.32} \tag{3}\]  
where m\({}_{2}\) is the mass (g) of the pozzolanic material, \(v_{2}\) the volume of HCl consumed by the sample; v\({}_{3}\) the volume of HCl consumed by the blank; F\({}_{c}\), the correction factor for a 0.1 M solution and 1.32 the molecular relationship between Ca (OH)\({}_{2}\)/CaO. Values of 566 mg and 445 mg of Ca(OH)\({}_{2}\) per g of residue for FA and MIBA were respectively obtained. Materials with results higher than 436 mg Ca(OH)\({}_{2}\)/g of addition [37] can be considered as pozzolanic, which is the case for both additions.  
Table 2 presents the XRF characterization for cement, FA and MIBA. The results show that the cement complies with EN 197-1 [15]. According to EN 450-1 [16], FA and MIBA can be classified as category B, with respect to the loss on ignition. However, only the FA met the required sum of aluminium, iron and silicon oxides, exceeding the minimum value established by the norm (i.e., 70%). According to ASTM C618-19 [38], MIBA could be classified as Class C fly ash.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline
**Materials** & **Al\({}_{2}\)O\({}_{3}\)** & **CaO** & **Fe\({}_{2}\)O\({}_{3}\)** & **K\({}_{2}\)O** & **MgO** & **Na\({}_{2}\)O** & **SiO\({}_{2}\)** & **SO\({}_{3}\)** & **Cl-** & **IR** & **LOI** \\ \hline CEM I (\%) & 5.24 & 62.7 & 3.17 & - & 2.23 & - & 19.6 & 3.13 & 0.01 & 1.37 & 2.94 \\ Fly ash (\%) & 24.7 & 2.63 & 5.40 & 1.11 & 1.01 & 0.89 & 54.7 & 1.38 & \textless{}0.01 & - & 5.10 \\ MIBA (\%) & 4.10 & 23.0 & 9.21 & 1.57 & 2.37 & 2.40 & 51.8 & 2.42 & 0.70 & - & 2.40 \\ \hline \end{tabular}
\end{table}
Table 2: Chemical characterization for cement, FA and MIBA (% by mass).  
The XRD of MIBA is presented in Figure 1. The main crystalline phases present correspond to quartz (SiO\({}_{2}\)) and calcite (CaCO\({}_{3}\)).  
The morphology of MIBA can be observed in Figure 2. Most of the particles have a porous microstructure and angular shape, which potentially translates into a greater amount of water required to cover the particles and achieve the desired workability. Likewise, the results of the EDS test are presented, where it is observed that the element found in the highest proportion is oxygen with 23.3%, followed by calcium with 15.2%, 8.7% for silicon, 6.63% of aluminium (Al) and 4.1% of iron.  
The quantification of metallic aluminium in MIBA was possible by means of the stoichiometry of the reaction between the metal and the OH\({}^{-}\) from the NaOH added to the solution. The volume of released hydrogen gas was measured and converted to its corresponding mass. The results showed that 6.3 L of H\({}_{2}\) were released for each kg of MIBA, which meant that there were 4.36 g of Al for each kg of MIBA.