## 3 Results and Discussion  
The Influence of Mixtures and SiO\({}_{2}\)/K\({}_{2}\)O Modulus on the Viscosity, Setting Time and Flexural Strength of Geopolymer Slurry  
Figure 3 shows the influence of raw material (WS powder, CC and MK) mixing ratios and the SiO\({}_{2}\)/K\({}_{2}\)O molar ratio on the apparent viscosity of the geopolymer slurry. It is obvious that specimen G5 MK5 has the highest viscosity. As the MK addition decreases from 10% to 2%, the apparent viscosity also decreases from 11,188 mPas to 3270 mPas for geopolymers prepared with 0.57 SiO\({}_{2}\)/K\({}_{2}\)O alkali solution. [PERSON] et al. indicated that the flow of geopolymer concrete increases with an increase in water-to-geopolymer binder ratio by changing the quantity of water [15]. Since the preparation of alkali solutions with various SiO\({}_{2}\)/K\({}_{2}\)O ratios is controlled by the concentration of KOH, the higher SiO\({}_{2}\)/K\({}_{2}\)O ratio solution (0.82) with low alkalinity is prepared with more water added. Therefore, the SiO\({}_{2}\)/K\({}_{2}\)O ratio of the alkali solution may directly affect the viscosity of geopolymer slurry. Particle size may also be another factor that affects the viscosity of geopolymer slurry. Because the particle size of MK (D\({}_{50}\) = 5.3 mm) is smaller than CC (D\({}_{50}\) = 13.4 mm), MK has a much higher surface area that may result in higher viscosity when the mixture has higher MK content. [PERSON] et al. and [PERSON] et al. suggested that the increase in particle size may result in a decrease of viscosity [16; 17]. [PERSON] et al. indicated that suspension viscosity of fly ash slurries increases with increasing solid fraction and it decreases with increasing average particle size [18]. Figure 4 shows the setting time of geopolymer slurry prepared with different SiO\({}_{2}\)/K\({}_{2}\)O modulus solutions. Specimens G5 MK5, G7 MK3, and G9 MK1 prepared with 0.57 SiO\({}_{2}\)/K\({}_{2}\)O alkali solutions have much lower setting time (45-100 min) than those made with 0.70 (250-300 min) and 0.82 (300-520 min) SiO\({}_{2}\)/K\({}_{2}\)O alkali solutions. This is because the lower SiO\({}_{2}\)/K\({}_{2}\)O modulus solution has higher alkalinity that can dissolve considerable aluminosilicates and form more geopolymer precursors for geopolymeric reaction [19]. The lower alkalinity solutions (0.7 and 0.82 SiO\({}_{2}\)/K\({}_{2}\)O molar ratio) lea  
Figure 2: Wax pattern used for casting practice. A: length; B: width; C: height. and Al\({}^{3+}\) ions from the WS powder and metakaolin [2; 19], and results in low concentration of silicate and aluminate monomers anions during geopolymeric reaction. The long setting time for geopolymer mixtures made with higher SiO\({}_{2}\)/K\({}_{2}\)O alkali solutions can also be caused by the higher water content of the solution owing to longer dehydration during the condensation process. For G5 MK5 geopolymer made with 0.70 and 0.82 SiO\({}_{2}\)/K\({}_{2}\)O alkali solutions also have shorter setting time than those prepared with G7 MK3 and G9 MK1 mixtures. This result can be attributed to the higher MK content in the G5 MK5 mixture, which is considered as a suitable precursor for geopolymeric reaction [20]. If the geopolymer can be used for ceramic shell as binder, the shorter setting time also means faster ceramic shell preparation. Figure 5 shows the green strength of geopolymer slurries prepared with different mixtures and SiO\({}_{2}\)/K\({}_{2}\)O modulus solutions. It is clear that the G5 MK5 has flexural strength of about 2-3 MPa higher than G7 MK3 and G9 MK1. Because MK is considered as a suitable precursor for geopolymeric reaction, the higher MK content can provide more alumino-silicate source to synthesize geopolymer [20]. Several researches have indicated that the geopolymer of metakaolin activation with alkali solution is an amorphous cementitious material [21; 22; 23] with good mechanical properties [24].