Reactivity and Microstructure of Metakaolin Based Geopolymers: Effect of Fly Ash and Liquid/Solid Contents

Geopolymers are inorganic binders based on mixtures of an aluminosilicate powder with an alkali-silicate solution. Properties of geopolymers are strongly determined by the type of reactive solid, the liquid/solid ratio of paste and, amongst others, the Si/Al ratio of the formed geopolymer network. In this study, fly ash blended metakaolin based geopolymers with varying liquid/solid ratios (l/s), activated by potassium silicate solution, are investigated. Reactivity of metakaolin and fly ash was investigated by powder X-ray diffraction (XRD) and dissolution tests. Reactivity, mechanical properties and microstructure of hardened pastes were analyzed by setting and compressive strength tests, mercury intrusion porosimetry (MIP), capillary water absorption tests, thermogravimetric analysis-differential scanning calorimeter (TGA-DSC), isothermal calorimetry and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The results show that substitution of metakaolin by fly ash as well as variation of l/s brings advantages up to a certain degree, but also has a considerable influence on the pore size distribution, mechanical properties, Si/Al ratio of the geopolymer network and the content of bound water.

Synthesis of Silica-Potassium-Nitrogen from Carbamide and Potassium Silicate by CO2 Precipitator

Potassium silicate is well known as a fertilizer and source of silica for plants growth. This study aims to infiltrate nitrogen from carbamide (urea) into potassium silicate solution to produced silica potassium nitrogen (Si-K-N) matrix by precipitation method using CO2 as precipitator. Potassium silicate in the range of 3-8% SiO2 was obtained by extracting silica from geothermal sludge using potassium hydroxide solution. Carbamide is added to the potassium silicate solution allowed by mixing and flowing of CO2 gas in reactor glass. The result of IR spectra indicated the presence of N-H groups, potassium and silica in the gel matrix produced from precipitation process while no N-H group appears in the gel matrix produced from precipitation in the absence of carbamide. X-ray fluorescence showed the composition of the product Si-K-N in the range of 40 to 50 %SiO2 and in the range of 50 to 60 %K2O.