# Characterization and Reactivity of Natural Pozzolans from Guatema
## 3 Results and Discussion
### Physico-Chemical Characterization of Volcanic Pozzolans (VPs)
\begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline
**MATERIAL** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **MgO** & **SO\({}_{3}\)** & **K\({}_{2}\)O** & **Na\({}_{2}\)O** & **Others** & **LOI *** & **IR** \\ \hline T & 70.49 & 13.57 & 1.83 & 1.82 & 0.50 & 0.12 & 4.02 & 3.35 & 0.94 & 3.37 & 40.80 \\ R & 72.06 & 12.67 & 1.14 & 1.41 & 0.40 & 0.19 & 4.45 & 3.68 & 0.69 & 3.33 & 42.25 \\ CEM II/A-L & 19.71 & 3.82 & 4.25 & 59.70 & 0.88 & 4.09 & 0.86 & - & 0.90 & 5.80 & - \\ \hline \hline \end{tabular} LOI * loss on ignition; IR insoluble residue.  
\end{table} 
Table 4: Chemical composition (%) for VPs and cement CEM II/A-L.  
Figure 1: Granulometric curves of VP. humidity, and probably with either the hydroxyl groups of a clay-type material that can decompose or the amorphous silica itself (decomposition of the silanol groups). The losses within the 35-1000 \({}^{\circ}\)C range were 2.91% and 2.87% for sample T and sample R, respectively. These losses were very slight, showing that they were stable when the temperature increased, and they fell within the same range as the LOI values obtained in other characterization analyses (see Table 4). Scanning electron microscopy (SEM) was used to study the morphology and texture of the natural pozzolan particles. The micrographs are shown in Figure 3.  
As shown in Figure 3, both pozzolans were composed of different-sized irregular-shaped particles with several fractured faces and smooth textures. Some particles displayed slight roughness. Their structure did not appear porous, and the particles were dense and compact. These images are like those found by other authors who have studied this type of material [29]. Finally, Figure 4 shows the diffractograms for samples T and R. The most notable aspect was the deviation of the baseline within the 20 = 15\({}^{\circ}\)-30\({}^{\circ}\) range, suggesting the presence of a significant quantity of amorphous compounds. Several peaks corresponding to different crystalline substances can be observed. The most important one was quartz (Q, SiO\({}_{2}\)  
Figure 3: SEM micrographs at 1000 magnification: (**a**) Sample T; (**b**) Sample R.  
Figure 2: TGA (dotted lines) and DTG (solid lines) curves of the natural pozzolans. Sample T also had small amounts of cristobalite (C, SiO\({}_{2}\) PDFcard 391425), probably due to the crystallization of silica at a high temperature during the eruption process and tremolite (T, Ca\({}_{2}\)Mg\({}_{5}\)Si\({}_{8}\)O\({}_{22}\) (OH)\({}_{2}\) PDFcard 130 437, a zeolite). It also exhibited small amounts of albite (A, NaAlSi\({}_{3}\)O\({}_{8}\) PDFcard 090466, a feldspar) and wollastonite (W, CaSiO\({}_{3}\) PDFcard 100489, a calcium silicate). In sample R, the baseline deviation was greater and could be interpreted as a higher content of amorphous compounds. However, the IR data shown in Table 4 indicate no significant difference with sample T. In this case, tremolite was not present, and the albite peaks and wollastonite were less intense. The displayed crystalline phases are typical of natural pozzolanas of volcanic origin [28]. In short, it can be concluded that both pozzolanas contained significant amounts of amorphous material, which may be interesting for pozzolanic reactivity development. Because of the chemical composition of volcanic ash, it can also be stated that the amorphous material will consist mainly of silicon oxide. Most of the crystalline material (which is unreactive) of pozzolans is constituted by quartz.