Influence of Mix Design Parameters on Geopolymer Mechanical Properties and Microstructure

Abstract

This chapter reports on the influence of the four mix design parameters (Si/Al, water/solids ratio (w/solids), Al/Na and H2O/Na2O) on the mechanical properties and microstructure of metakaolin geopolymers in an experiment. The most commonly used alumino-silicate oxide sources are metakaolin, fly ash and blast furnace slag and their dissolution in alkaline medium leads to formation of individual alumina and silicate species which then copolymerize to form geopolymers. Metakaolin was used as the geopolymer precursor. Fifteen mixes were prepared and evaluated for their compressive strengths and densities. The microstructure of the sample was observed by the scanning electron microscope. Sodium hydroxide solution was prepared by dissolving a calculated quantity of NaOH pellets (99.8% pure, purchased from Schedelco Pte. Ltd) into ultrapure water filtered through a Milli-Q water filtration station. Sodium silicate solution was prepared by dissolving varying amounts of amorphous silica (Fumed Silica- Cabosil M5) into freshly prepared sodium hydroxide solution. Geopolymer specimens were prepared by adding metakaolin to the sodium silicate solution of various concentrations to obtain geopolymers with Si/Al molar ratios ranging from 1.03 to 2.0.