# Low-Grade Clay as an Alkali-Activated Material
## 4 Results and Discussion
### XRD Analysis  
The XRD spectra are illustrated in Figure 3, and the analysis is presented in Table 4. The principal crystalline components in the raw clay are illite, corresponding with the high K\({}_{2}\)O content, kaolinite, and quartz, with small quantities of rutile (TiO\({}_{2}\)) and chlorite (MgO) present, as well as traces of montmorillonite, albite and, goethite. The amorphous phase is composed primarily of silica, consistent with the relatively high SiO\({}_{2}\) content, as shown in Table 1. After pre-treatment at 120 \({}^{\circ}\)C, the kaolinite significantly decreased, and following calcination at 750 \({}^{\circ}\)C, none of these remained, as they were completely decomposed to the amorphous phase [52; 53; 54]. Illite was also not observed after calcination, and it is surmised that it was converted to muscovite during the calcination process due to dihydroxylation [55]. Muscovite is not observed in the natural clay or when only heated to 120 \({}^{\circ}\)C, but the quantity of illite reduced at 120 \({}^{\circ}\)C, with a small increase in rutile and chlorite observed together with that in quartz. Following alkali activation, the primary crystalline phase in all of the mortars was quartz, with similar quantities in all of the 10% and 15% mortar specimens, which can be attributed to the presence of sand in the mortar specimens. The amorphous content was reduced following activation; in the 10% specimens, a significant reduction was observed for the raw clay mortar, with a small 1-2% reduction noted in the pre-treated specimens. In the 15% specimens, a similar trend was observed, but the reduction in the raw clay was slightly less than in the raw clay and slightly greater (approx. 8% lower) in the pre-treated clays. In addition to the increase in the quartz present, the mortar specimens showed the presence of a number of sodium containing crystalline compounds. Sodalite was identified in all the 15% dosage mortars and in the pre-treated 10% specimens, while analcine was evident in the 10% and 16% untreated mortars and the 10% mortar pre-treated at 120 \({}^{\circ}\)C. An increase in the albite content was observed in the untreated clay mortar for both the 10% and 15% specimens, as well as in the 750 \({}^{\circ}\)C mortars but not in the 120 \({}^{\circ}\)C specimens at both dosages of 10% or 15%. Furthermore, illite was observed in the 750 \({}^{\circ}\)C mortars, possibly re-converted from the muscovite observed in the calcinated clay. Reduced quantities of illite were detected in the natural and 120 \({}^{\circ}\)C mortars. All of the mortar specimens showed an increase in crystalline content, suggesting the presence of zeolites rather than an amorphous geopolymeric phase [56; 57]. It is hypothesized that the growth of zeolite crystalline phases is supported by the high water content and the employed high curing temperature [58]. Zeolites generally have poor mechanical properties, which could account for the relatively low compressive strengths achieved and the reduction in strength observed in some mixes. Figure 3: XRD spectra: (**a**) clay, (**b**) 10% mortar, and (**c**) 15% mortar.