Effect of Na_2O content on durability of geopolymer pastes in magnesium sulfate solution

摘要

An experimental investigation was conducted to study the effect of Na20 content on performance of fly ash based geopolymer pastes in magnesium sulfate solution. A study on changes in physical appearance and weight, residual compres-sive strength along with mineralogical and microstructural changes were made on geopolymer specimens exposed to 10% magnesium sulfate solution for a period of 24 weeks. Microstructural and mineralogical changes were studied using SEM/ EDX and XRD, while porosity was determined by mercury intrusion porosimetry (MIP). White precipitates deposited on surfaces of the specimen were analyzed with XRD and it revealed presence of ettringite and gypsum. It was more in speci-mens having higher Na20 content. Porosity was found to influence the performance of geopolymer specimens. Geopolymer paste specimens gained very little weight. Specimens having higher Na20 content showed better performance against sulfate attack.