**3. Results and Discussions**

#### *3.1. Density and Water Absorption Analysis*

In order to examine the pore structure in kaolin-based geopolymer ceramic, the density and water absorption of kaolin-based geopolymer samples were investigated. The densities of the unsintered and sintered kaolin at 900 and 1100 ◦C after 3 days are shown in Figure 2. The densities of the unsintered and sintered samples at all temperatures decreased as time increased. The unsintered samples had the highest density of 1610 kg/cm3, while the samples sintered at 1100 ◦C had the lowest density of 1203 kg/cm3. Therefore, we speculate that the formation of large pores created in the kaolin at 1100 ◦C resulted in the lowest density, while sintering at 900 ◦C resulted in the formation of small pores in the kaolin-based geopolymer samples. In addition, the unsintered samples contained small and open pores, while the sintered samples had large and closed pores, which translated into a high material density. The existence of these larger pores was likely due to the growth of sintered necks, which was reflected in the phase evolution. The details of phase crystallization are discussed in Section 3.6.

**Figure 2.** The density of kaolin geopolymer over 3 days for unsintered and sintered samples at 900 and 1100 ◦C.

Figure 3 shows the percentage water absorption of the kaolin-based geopolymer ceramic samples after sintering at 900 and 1100 ◦C after 3 days. After 3 days, the highest value percentage water absorption occurred with sintering at 1100 ◦C. The percentage water absorption continuously increased with sintering temperature and time. This was in accordance with results published by Faris et al. [15]. The higher sintering temperature resulted in larger pores due to water removal, and the increased pore size increased the water absorption capacity of the kaolin-based geopolymer samples. The high volume of open pores in the samples may have contributed to the high water absorption due to a high surface area, which was reported by Zulkifli et al. [11].

**Figure 3.** The water absorption of kaolin geopolymer over 3 days for unsintered and sintered samples at 900 and 1100 ◦C.
