Development of Thai Lignite Fly Ash and Metakaolin for Pervious Geopolymer Concrete

Abstract

The study was to use Thai lignite fly ash and metakaolin to produce geopolymer paste as binder material in pervious concrete. The proper ratio of fly ash to metakaolin were varied as 100:0, 70:30, and 50:50. Alkali solution to pozzolan (L/P) ratios viz., 0.5, 0.6 and 0.8 by weight were prepared. The mechanical and characterization of pervious geopolymer concrete (PGC) were carried out. The results presented that the particle of fly ash was sphere with smooth surface, while metakaolin was partly agglomerated and irregular shaped. The increase of fly ash in the ratio of fly ash to metakaolin affected the lower requirement of volume of alkali solution. The compressive strength and of pervious geopolymer concrete at 28 days were 3.74-5.41. The void ratio and water permeability were 28.54-30.74% and 1.90-2.09 cm/sec, respectively. Therefore, geopolymer paste from fly ash and metakaolin could be used for pervious concrete with satisfied properties. However, the price of pervious cement concrete is 1,898-2,168 THB/m3, while the price of pervious geopolymer concrete is 2,123-4,173 THB/m3 due to the energy cost to transform kaolin into metakaolin by an electric furnace. The cost can be reduced by increasing the ratio of fly ash to metakaolin.