Effect of Thai Kaolin on properties of agricultural ash blended geopolymers

• We used kaolin to synthesize geopolymer cured at 80 °C for 24 h to be solidified.
• Metakaolin, kaolin mixed with bagasse ash and rice husk ash were used to synthesize geopolymers cured at ambient temperature.
• Geopolymers synthesized from kaolin mixed with either bagasse ash or rice husk ash can be solidified at ambient temperature.
• Geopolymers gave quite high compressive strength.

sGeopolymer has been developed as an alternative material to Portland cement. It is based on the polymerization of alkali activators and oxides of silicon and aluminium from pozzolans. Pozzolans are materials mainly SiO2 and/or Al2O3 which reacts with NaOH and Na2SiO3 to generate a three dimentional aluminosilicate structure. The clean and fine kaolin from south of Thailand transforms into metakaolin at 550–600 °C, as determined by DTA. In this research, kaolin was heated at 600 °C, 700 °C and 800 °C for 2 and 6 h to optimize its transformation into metakaolin as pozzolans for geopolymers preparation. Additionally, the as-received kaolin was exploited also as a pozzolan for geopolymers in order to reduce heat energy consumption. However, it was found that kaolin alone did not display sufficient pozzolanic behavior to form geopolymer at 7 days of age unless specimens were slightly warm cured. Therefore, it was blended with more active pozzolans such as bagasse ash and rice husk ash. Finally, the results of compressive strength and microstructures were investigated and discussed.