Improving mechanical characteristics of lightweight geopolymers through mechanical activation of fly ash

Abstract

The present paper investigated the influence of mechanical activation of fly ash and various parameters, such as curing temperature and concentration of foaming agent (Al powder), on physical-mechanical characteristics of lightweight geopolymers. Prior to alkali activation, fly ash was mechanically activated in a high energy planetary ball mill. Lightweight geopolymers were obtained by mixing the mechanically activated fly ash with various amounts of Al powder and sodium silicate solution (SiO2/Na2O mass ratio of 1.5). Geopolymer paste samples were cured covered in plastic either at room temperature for 28 days or at elevated temperature (95 oC) for 4 hours. It was observed that the mechanical activation of fly ash resulted in a drastic increase of geopolymer compressive strength regardless of curing conditions, preserving the lightweight properties at the same time. The lightweight geopolymers based on mechanically activated fly ash might be used both in constructive and insulating applications.