# Low-Grade Clay as an Alkali-Activated Material
## 5 Summary and Conclusions  
The following conclusions can be drawn from the analysis of the results:  
1. The amorphous content of the clay increased from 21.6% to 23.8% at 120 \({}^{\circ}\)C. However, a small decrease in the amorphous content was observed (23.1%) when heated to 750\({}^{\circ}\); this is attributed to recrystallization of the amorphous phase at this temperature. 2. The surface area with calcination decreased from 12.45 m\({}^{2}\)/g in the natural clay to 8.66 m\({}^{2}\)/g at 120 \({}^{\circ}\)C and 6.03 m\({}^{2}\)/g at 750 \({}^{\circ}\)C, but the % passing at both 10 and 50 \(\upmu\)increased. This is attributed to the loss of adsorbed water resulting in shrinkage and disintegration of the soil particles and a reduction in particle size. 3. An increase in strength was observed with calcination of the clay under both 120 \({}^{\circ}\)C for 24 h and 750 \({}^{\circ}\)C for 5 h.
4. At 120 \({}^{\circ}\)C, the specimens with a dosage of 10% demonstrated improved performance compared to a dosage of 15%, with an AM of 1.0 providing the optimal strength at both dosages. 5. The main components in the raw clay are illite, kaolinite, and quartz with small quantities of rutile and chlorite and traces of montmorillonite, albite, and goethite. Following calcination of the clay, there was a significant reduction in illite and kaolinite at 120 \({}^{\circ}\)C, while this was not observed following calcination at 750 \({}^{\circ}\)C. Montmorillonite, albite, and goethite all disappeared following calcination, while rutile and calcite content increased at 120 \({}^{\circ}\)C, but this was not evident after calcination at 750 \({}^{\circ}\)C. The quantity of quartz increased with calcination, while significant quantities of muscovite were observed when calcinated at 750 \({}^{\circ}\)C.
6. Calcination at 120 \({}^{\circ}\)C increased the quantity of Al (VI) from 61% to 67%, while at 750 \({}^{\circ}\)C, all of the Al (VI) was converted to Al (IV). Following the reaction, an increase in Al (IV) was noted for all the mortars, with a higher rate of conversion in the 120 \({}^{\circ}\)C specimens compared to the raw clay. The conversion of Al (IV) is identified as the primary factor for the increased strength in the treated clay mortars. 7. The mortar specimens showed a broadening of the peak in the region of 1080-1000 cm\({}^{-1}\), which was noted together with a shift to lower wavenumbers for all of the 10% and 15% dosage mortars. The peaks in the 500-400 cm\({}^{-1}\) region also broadened and increased in intensity. The shifting of the peaks towards the lower wave number is an indication of aluminum incorporation in the backbone of the silicates matrix, consistent with the increases in strength observed and the conversion of Al (VI) to Al (IV). The results indicate that it is feasible to use low-grade clay as a precursor material for geopolymer synthesis. However, while the compressive strengths achieved are insufficient for application as structural concrete, they may be suitable for concrete masonry bricks where a minimum strength of 5 MPa is required. The low strength may be a function of the two calcination regimes, where a decrease in surface area was observed for both regimes, with minimal increases in the amorphous content. Hence, it is recommended that future research assess calcination regimes between 120 and 750 \({}^{\circ}\)C to minimize the energy use and to optimize performance. Furthermore, for the application as masonry bricks, research is required on the long-term performance and a lifecycle assessment of the environmental impacts of manufacturing clay-based geopolymers. Conceptualization, M.M.R., D.W.L. and I.P. ; methodology, M.M.R. and M.T.Y. ; validation, D.W.L. and C.G. ; formal analysis, M.M.R., D.W.L. and C.G. ; investigation, M.M.R. and M.T.Y. ; resources, I.P. ; data curation, D.W.L. ; writing--original draft preparation, M.M.R. ; writing--review and editing, D.W.L. ; visualization, D.W.L. ; supervision, I.P. and D.W.L. ; project administration, I.P. ; funding acquisition, I.P.