Thermal stability of geopolymer modified by different silicon source materials prepared from solid wastes

Abstract

Cement is a construction material responsible for greenhouse gases and CO2 emissions. As a green building material that replaces cement, geopolymer has received widespread attention. Both glass powder (GP) and rice husk ash (RHA) contain large amounts of active silica, but they are solid waste produced in different fields and their microstructures vary greatly. In this study, the thermal stability of metakaolin-based geopolymer blended GP and rice husk ash RHA was investigated. The prepared samples were subjected to elevated temperatures (T = 300 ℃, 500 ℃, 700 ℃ and 900 ℃), and the compression strength and volume shrinkage tests were carried out after high-temperature calcination to evaluate the thermal stability. X-ray Diffraction (XRD), Fourier Transform Infrared Spectrometer (FT-IR) and Scanning Electron Microscope (SEM) were employed to explore the phase composition and microstructure of geopolymer before and after high-temperature calcination. The rice husk ash with optimum chemical activity can be obtained when calcined at 550 ℃ for 4 h. The properties of preventing morphology cracking, loss of compressive strength and volume shrinkage of the samples are improved. After calcination at various temperatures with the addition of glass powder and rice husk ash, the inner parts of the samples maintain the stable chemical bond and amorphous structure after high-temperature exposure. The doping of glass powder and rice husk ash improves the Si/Al ration and SiO2/Na2O ratio. The introduction of GP is more effective in affecting the unstable Al-O bond, while the introduction of RHA is more effective in increasing the degree of polymerization. Meanwhile, the highly active silica in GP and RHA contributes to the healing of microcracks.