EXPERIMENTAL STUDY ON GEOPOLYMER PASTE BLENDED WITH SILICA FUME

Abstract

 Geopolymer (GP) has gained attention as a new and environment-friendly material that can be hardened without using cement which emits large volume of carbon dioxide gas (CO₂) in the manufacturing process.

 GP could be produced through chemical reaction between active filler which is mainly composed of amorphous aluminosilicate, and alkaline solution. Fly ash (FA), metakaolin, blast furnace slag fine powder (BFS), sewage sludge incineration ash and rice husk ash are used as active fillers; while sodium hydroxide solution, potassium hydroxide solution, water glass, sodium carbonate solution and potassium carbonate solution are used as alkaline solution.

 According to previous studies, GP can exhibit the same level of compressive strength compared to that of concrete made from ordinary Portland cement. In addition, GP shows in general high adhesion performance to cement concrete and reinforcing bars, and has high resistance to fire and acid attacks. Therefore, GP is expected to be used effectively as repair material for concrete structures.

 In this study, we aim to further develop GP as a crack repairing material by using silica fume (SF) as one of main powders. SF is an ultrafine particle material whose particle size is from 0.1 to 10 µm in diameter, while sizes of common inorganic materials such as cement, FA, BFS are approximately 10µm. It is expected that producing GP with SF as the main powder can provide good injection properties. As an initial step, investigation was carried out on the basic characteristics of GP using SF, before studying on its characteristics as a crack repairing material, i.e. on mixing performance, fluidity and compressive strength. Then, the characteristics of GP with FA as base material and those replaced with SF and BFS were also compared in the discussion.

 As the results, it was observed when substitution of SF increased, mixing became difficult, the fluidity of GP paste decreased, then the workability was lost. This is considered due to the large specific surface area of SF. In addition, the hardened GP paste containing SF showed volume expansion and lower compressive strength as compared to that of specimens without SF. These phenomena are getting remarkable with the increase in the substitution of SF content and the decrease in BFS substitution to 40% or less. The volume expansion is considered mainly due to the production of H₂ gas in GP.