An Experimental Study on the Mechanical and Microstructural Properties of Geopolymers

Geopolymer is a new class of inorganic polymer synthesized by activation of an aluminosilicate source with an alkaline hydroxide or silicate solution. In recent years, geopolymeric materials have attracted much more attention because of their excellent mechanical properties, good chemical resistance, low shrinkage, environmentally friendly nature and long-term durability. Fly ash, considered to be a waste substance is an important aluminosilicate source material for geopolymer production since it contains sufficient amounts of reactive alumina and silica. In this experimental study, F type fly ash was activated by 4 M, 8 M and 12 M of sodium hydroxide and sodium silicate solutions and the effects of pH on the properties of geopolymeric samples were investigated. All the pastes were cured at 80 °C for 15 hours. The compressive strength tests were carried out at the ages of 7 and 28 days. The samples aged 28 days were crushed and the degrees of reaction of all samples were determined. The microstructure of geopolymer samples were investigated by Scanning Electron Microscope(SEM)/Energy Dispersive X-Ray(EDX) Spectrometer, X-ray diffractometry (XRD) and Fourier Transform Infrared Spectroscopy(FTIR) techniques. According to results, the compressive strength of samples increased as the molarity of sodium hydroxide increased. It was observed that the workability of the pastes was negatively affected by increase in molarity of sodium hydroxide.