## 4 Conclusions  
This study investigates the potential of South African kaolinite clay for limestone calcined clay cement (LC\({}^{3}\)). Three samples of kaolinite clay were selected at different locations within the Grahamstown region of South Africa. The study characterised the locally obtained limestone and calcined clay samples and examined the mortar made from these calcined clays compared to OPC mortar as a control. Effort was taken to maximise the physico-chemical interaction of the limestone and calcined clay with OPC by ensuring higher or similar fineness to that of the OPC. Emphases were placed on the hydration phase mineralogy/content and the mortars' microstructure, strength, and 3D void structure. The following conclusions can be made from the study. * Varied kaolinite content of raw clay can yield similar pozzolanic oxide (SiO\({}_{2}\) + Al\({}_{2}\)O\({}_{3}\)) content of the calcined clay, the main component of the target metakaolin (Al\({}_{2}\)O\({}_{7}\)Si\({}_{2}\)) from the raw clay calcination. The calcined clay particles tend to be flat, irregular, and elongated, with fibril surface cracks. Pozzolanic activity of the LC\({}^{3}\) is directly proportional to the kaolinite content and can be associated with the consumed portlandite. * Increased kaolinite content of LC\({}^{3}\) tends to increase the consistency of the mortar mixture, thereby reducing the demand for water reducer. Limestone and metakaolin densify the microstructural pores of LC\({}^{3}\) systems by forming carbo-aluminates coupled with filler effects and pozzolanic reaction. It is noted that at 28 days, not all the calcined clay particles are fully hydrated. The limestone can also contribute to pure filler effects. * The results suggest that SEM 2D microstructure evaluation may not be adequate to indicate the overall porous nature of LC\({}^{3}\) mortars. The degree of limestone hydration tends to be more important than kaolinite content for microscale void refinement of LC\({}^{3}\) mortar. Figure 14: Compressive strength development of the mortar specimens. * The observed hydration and microstructure mineralogy of the South African clay samples (LC\({}^{3}\)) seem to correlate well with the existing literature on LC\({}^{3}\) from other regions. Therefore, achieving the designed strength for the control OPC with the LC\({}^{3}\) with a minimum kaolinite content of 40% is possible, and consideration must be given to the intrinsic content of limestone in commercially available Portland cement. It can be concluded from this study that the performance of South African clay for use as LC\({}^{3}\) cement is satisfactory and has the potential to be embraced by the cement industry from an engineering point of view. For on-site LC\({}^{3}\) formulation, it is recommended that the intrinsic content of limestone and gypsum in commercially available Portland cement be considered to achieve equivalent 30% limestone (and 5% gypsum) that guarantees similar strength to the OPC. Further research is required to optimise the binder for early strength (\(\leq\)3 days), investigate the long-term durability, and examine the financial considerations for large-scale production and benefits for carbon footprint reduction. Conceptualization, A.J.B. and H.K. ; methodology, H.K. ; software, H.K. ; validation, A.J.B. and H.K. ; formal analysis, H.K. ; investigation, H.K. ; resources, O.M.O. and N.N.B. ; data curation, H.K. ; writing--original draft preparation, A.J.B. and J.T.K. ; writing--review and editing, A.J.B., J.T.K., S.C.P., M.J.M., O.M.O. and N.N.B. ; visualization, H.K. and J.T.K. ; supervision, A.J.B. ; project administration, A.J.B. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Data Availability Statement: Data shall be made available upon request. The authors acknowledge the Department of Civil Engineering, Stellenbosch University, for access to facilities to conduct the tests and the provision of materials. The authors declare no conflict of interest.