Also, van Jaarsveld et al. [29] concluded that the incorporation of high kaolinite content (41 wt.%) in fly ash geopolymers
reduced the strength of the final product. This is because not all kaolinite is taking part in the geopolymerization reaction to
form geopolymer network. If the kaolinite is calcined, the compressive strength increases. Table 1 shows the compressive
strength result obtained by van Jaarsveld et al. [29] with calcined kaolinite.