Investigating the Properties of Foamed Fly Ash and Metakaolin-based Geopolymer Concrete

Abstract

A study has been carried out to produce environmentally friendly lightweight concrete by total replacement of cement with fly ash and metakaolin as binder material by adopting the pre-formed foam method. In this research, a geopolymer paste was produced by mixing fly ash or metakaolin with an alkali solution of sodium silicate and sodium hydroxide. Five mixes were produced at a density of 1000 kg/m³ as four foamed geopolymer concrete and one conventional foamed concrete made with cement paste as a binding medium. During the laboratory work, many trials were carried out to solve the segregation of the cellular structure from the mortar. From the results, it was noticed that the pore merging is more evident in foamed concrete mixes rather than in foamed geopolymer concrete mixes. In addition, the pore structure of fly ash-based geopolymer concrete is finer than that of metakaolin-based concrete geopolymer. The greater degree of pore merging resulted in forming of larger irregular voids and wider distribution of pore sizes and finally reducing strength. In general, the permeation, mechanical and thermal properties of foamed mixes made with geopolymer pastes are better than those of foamed mix made with cement paste. For a geopolymer paste, using metakaolin and fly ash C in combination helped in achieving the best properties i.e. reduction in water absorption by 34%, increasing strength by 78% and decreasing thermal conductivity by 44%.