# One-Part Alkali-Activated Pastes and Mortars Prepared with Metakaolin and Biomass Ash
## 2 Experimental Program
### Raw Materials Characterization  
As the aluminosilicate precursor, metakaolin (Figure 1a) was synthesized by heating at 700 \({}^{\circ}\)C; a kaolin originating from UK and provided by Imerys Minerals Ltd (Paris, France) was used. The chemical and mineralogical compositions of the kaolin are given in Tables 1 and 2, respectively. The kaolinite and the metakaolinite used in this experimentation are the same used in [PERSON] et al. [24], and the chemical and mineralogical compositions can be found also in their work. As the alkaline activator, a biomass ash (Figure 1b) was chosen. It originated from the Roodenhuyse power plant located in Belgium, which uses wood for electricity generation. Being obtained from wood, the chemical composition shows that the biomass ash is mainly constituted by calcium and potassium oxides (Table 1). The chemical analysis of kaolin and biomass ash was performed by means of semi-quantitative wavelength dispersive X-ray fluorescence (XRF) spectrometry by means of a Philips spectrometer,model PW 2400. The X-ray diffraction (XRD) analysis of kaolin was performed using a Philips PW 1830 diffractometer. The morphology of metakaolin and biomass ash, analyzed by Scanning Electron Microscopy (SEM) in a Philips FEG-ESEM XL30 electron microscope on carbon-coated samples, is reported in Figure 2 and shows the typical plate-like structure of metakaolin and the spherical morphology of biomass ash. The specific density of metakaolin and biomass ash measured with a gas pycnometer was 2.50 g/cm\({}^{3}\) and 2.25 g/cm\({}^{3}\), respectively. The pH of the biomass ash was measured by a HANNA instruments pH-meter by putting 0.5 g of ash in 5 g of distilled water, as reported in the literature [24; 25]. In the present study, the biomass ash has a pH of 12.5, which is higher than the threshold reported in the literature and makes biomass ash a good candidate for producing one-part AAMs. Thermogravimetric analysis (TGA) of metakaolin and biomass ash was carried out by heating samples in nitrogen atmosphere up to 1000 \({}^{\circ}\)C with a heating rate of 20 \({}^{\circ}\)C/min using a Q5000 IR \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Material** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **CaO** & **K\({}_{2}\)O** & **SO\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **MnO** & **Cl** & **Na\({}_{2}\)O** \\ \hline Kaolin & 51.0 & 34.0 & - & 3.0 & - & 1.0 & \(<\)1.0 & - & - & - \\ Biomass ash & 9.0 & 1.7 & 46.1 & 20.9 & 10.7 & 3.6 & 3.7 & 1.8 & \(<\)1.0 & \(<\)1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition (wt%) of kaolin and biomass ash measured by X-ray fluorescence (XRF). Figure 1: Visual aspect of (**a**) metakaolin, (**b**) biomass ash, and (**c**) river sand. Figure 2: SEM images of (**a**) metakaolin and (**b**) biomass ash. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Kaolinite** & **2:1 Clays** & **K-Feldspar** & **Quartz** \\ \hline
68 & 21 & 8 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mineralogical composition (wt%) of kaolin measured by XRD. Thermogravimetric analyzer, TA Instruments. Results obtained by TGA are reported in Figure 3. Concerning metakaolin, a constant mass loss around 2% of the initial mass is registered after 900 \({}^{\circ}\)C. The very low reduction of metakaolin mass is related to the calcination process at 700 \({}^{\circ}\)C to which the starting kaolin has been already submitted ensuring the largest mass loss occurred prior to this test. On the other hand, the biomass ash is subjected to different mass losses at different increasing temperatures. The first one, very limited and of about 1%, occurs around 100 \({}^{\circ}\)C and is caused by the evaporation of water. This is the water adsorbed by the ash when it is stored at environmental conditions, as in the present study. The second one around 350-400 \({}^{\circ}\)C is very small, less than 0.5%, and it is probably related to the oxidation of the lignin and cellulose that remained in the ash [26; 27; 28].