# Low-Grade Clay as an Alkali-Activated Material
## 4 Results and Discussion
### NMR Analysis  
The \({}^{27}\)Al MAS-NMR spectra of the clays and the mortars at 28 days are presented in Figure 4. The NMR spectra were deconvoluted in accordance with the singular value decomposition method [59]. The calculation of the relative areas of deconvolution lines for the samples is shown in Table 5.  
The Al (IV)-fold coordination is assigned to the chemical shifts in the range between 60 and 80 ppm, while Al (VI) coordination is assigned to the chemical shifts observed between 3.5 and 5.0 ppm. For the 10% dosage specimens, the untreated clay/natural clay powder showed a distinct Al (VI) coordination peak at 4.8 ppm. This shifted to 3.5 ppm  
Figure 4: NMR spectra: (**a**) clay; (**b**) 10% mortar and (**c**) 15% mortar. when clay was pre-treated at 120 \({}^{\circ}\)C. No change was noted in the Al (IV) peaks following treatment at 120 \({}^{\circ}\)C. In the clay treated at 750 \({}^{\circ}\)C, all of the aluminum was observed to be in the Al (IV) coordination state, being converted during the calcination process. The deconvoluted data show that the untreated natural clay contained 61.6% Al (VI) and 38.4% Al (IV). Following pre-treatment of clay at 120 \({}^{\circ}\)C, the Al (VI) coordination increased to 67.6%, with a corresponding decrease in the Al (IV) coordination, as shown in Table 5. Following activation, the Al (IV) peaks became sharper, indicating a higher Si content after activation [60]. The resultant natural clay mortar specimens for the 10% dosage contained 45.5% Al (VI) and 54.5% Al (IV), and the 120 \({}^{\circ}\)C treated mortars had 38.5% Al (VI) and 61.5% Al (IV) coordination i.e., the Al (IV) coordination increased by 16.1% and 29.1%, respectively. The 15% mortar specimens displayed increased conversion from Al (VI) to Al (IV), the natural clay had 43.8% Al (VI) and 56.2% Al (IV), and the mortar treated at 120 \({}^{\circ}\)C had 28% Al (VI) and 72% Al (IV) coordination, corresponding to an increase of 17.8% and 40.6%, respectively. It has been reported that the quantity of Al (VI) present in the precursor fly ash--and the conversion of this into Al (IV) units during reaction process--influences the achieved compressive strength. Hence, the additional conversion from Al (VI) to Al (IV) would account for the increase in strength observed in the mortar specimens treated at 120 \({}^{\circ}\)C compared to the natural clay mortar. It is noted that the rate of change of Al coordination from (VI) to (IV) is low compared to that of fly-ash-based geopolymerization [61]. The authors found that the conversion of Al (VI) to Al (IV) coordination was 45% in the case of the Gladstone-Fly Ash-based geopolymer, whereas in this study, conversion is less than 30%, excluding that of the 120 \({}^{\circ}\)C 15% mortar, which is approx. 40%. This low conversion is identified as one of the reasons that clay-based AAM exhibits lower compressive strength than that of the class F fly-ash-based geopolymer. It is also noted that the Al (VI) coordination is at 3.5 ppm in the clay powder and shifts to 3.87 ppm in the resultant mortar. This is also a significantly smaller chemical shift that represents a lower rate of chemical reaction taking place in the reaction. This may also be a reason for the longer duration required for alkali-activated clay to achieve structural integrity. Table 5 shows that natural clay contains 62% Al (VI) coordination and that the pre-treatment of clay at 750 \({}^{\circ}\)C converted all Al (VI) coordination to Al (IV) coordination. [PERSON] et al. noted during thermal activation of clay minerals that the Al tetrahedral peak becomes larger and the octahedral peak becomes lower with increasing temperature. They also observed that in the range of 500-800 \({}^{\circ}\)C, the whole Al (VI)-fold coordination converts into Al (IV) coordination, and with further heating, the octahedral peak disappears [2]. [PERSON] et al. supported this observation, reporting that octahedrally coordinated aluminum decreases with increasing temperature [62].