## 3 Results and Discussion
### PP Fiber Effect on Thermal Conductivity of Foamed Geopolymer  
The thermal conductivity of foamed geopolymer is shown in Figure 9. As can be seen from Figure 9, the control geopolymer has a high thermal conductivity along with temperature compared with its porous geopolymer. After introducing the foam, the geopolymer was observed to show a decrease in thermal conductivity. The density seems to have a significant effect on the thermal conductivity of the geopolymer. It is well known that porosity is the main effect of thermal conductivity [29]. The enhancement of porosity in the geopolymer matrix lowers the volume of the framework structure, because the thermal conductivity of the framework is higher compared to the air within the voids, therefore the affecting the high thermal conductivity of the control geopolymer [30; 31; 32]. A similar trend was reported for porous geopolymer with the increased amount of H\({}_{2}\)O\({}_{2}\)[24], which causes an enhancement of the voids inside the material and reduces their density and thermal conductivity.  
The effect of PP fibers on the thermal conductivity of foamed geopolymer are shown in Figures 10 and 11. Both 40% and 60% foamed geopolymer has a different thermal conductivity trend regardless of the similar amount of PP fibers. As shown in Figure 10, when 40% foamed geopolymer contains 0.25% PP fiber at the temperature of 50 \({}^{\circ}\)C, the thermal conductivity increases almost 123% from the foamed geopolymer without reinforcement. This value drops significantly at a temperature of 100 \({}^{\circ}\)C, and has the lowest thermal conductivity when the temperature rises to 200 \({}^{\circ}\)C. Although it only rises about 45% at 50 \({}^{\circ}\)C compared with pure foamed geopolymer, the thermal conductivity of 40% foamed geopolymer with 0.5% PP fiber has the highest thermal conductivity in the temperature range 100-200 \({}^{\circ}\)C. In contrast, Figure 11 show that 0.25% PP fiber gives the highest thermal conductivity throughout the temperature of 60% foamed geopolymer. The increase occurred up to 277%, while 0.5% PP only increases as much as 4.7% compared without the pure foamed geopolymer.  
Figure 9: Thermal conductivity of foamed geopolymer.  
Although PP fiber has a relatively small density (around 0.91 g/cm\({}^{3}\)), the PP fibers amount in this study has a significant effect on the density of foamed geopolymer. Generally, adding the PP fiber into the foamed geopolymer will increase their density, thus resulting in higher thermal conductivity. When the temperature was raised, the PP fiber melted and created an extra void inside the foamed geopolymer matrix. Generally [13], this void can allow the steam to release due to the dehydration process and weaken the internal pore pressure. A similar trend was reported [13] using PP fibers in cement mortar compared to without the fiber-reinforced at temperatures of 150 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 450 \({}^{\circ}\)C, and 600 \({}^{\circ}\)C. Fiber-reinforced cement mortar has greater thermal conductivity compared to plain mortar especially when the temperature is above 200 \({}^{\circ}\)C. The thermal conductivity in this study has the same properties as lightweight concrete (density of 1800 kg/m\({}^{3}\), the thermal conductivity of 0.6-0.8 W/m\({}^{\circ}\)C) and a little higher than gypsum board (density of 800 kg/m\({}^{3}\), the thermal conductivity of 0.2 W/m \({}^{\circ}\)C) [33].