The alkaline activator using sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was prepared 24 hours before the casting. Two molarities of sodium hydroxide (NaOH) solution of 12 M and 14 M were prepared for each mix proportion. The modulus of sodium silicate (i.e., ratio of SiO2/Na2O) was 2.5 and the specific gravity of liquid Na2SiO3 was 1.50 g/mL at 20°C. The sodium silicate liquid was mixed with NaOH solution by weight proportion of 1 : 2.5 (NaOH solution : liquid Na2SiO3).