*2.1.3 Sodium silicate (Na2SiO3)*

Usually, sodium silicate is common name of compounds which is expressed by a formula (Na2SiO2)*n*O. It is a semi-viscous solution having sp. gravity of 2.4 g/cm3 . The open chemical structure of sodium silicate is shown in **Figure 1**.

#### *2.1.4 Plasticizer*

In order to improve plasticity of the geopolymer, a SiKA compound is used along with reacting materials during processing of geopolymer. It is a low cost material. In addition, extra water (5–6 mL) is added to SiKA plasticizer solution. In designing

**Figure 1.** *Chemical structure of sodium silicate [Wikipedia.org/wiki/Sodium\_metasilicate].*

the mixtures the parameter "water-to-geopolymer solids ratio" by mass is considered to be important. Thus, the total mass of water is the sum of the mass of water contained in the sodium silicate solution, sodium hydroxide solution, and the mass of extra water [21, 22].
