Effects of Si/Al ratio on the efflorescence and properties of fly ash based geopolymer

Abstract

Efflorescence seriously affects the practical application of geopolymer. In this study, fly ash based geopolymer was prepared by raw materials containing different Si/Al ratios. A test method of the efflorescence degree of geopolymer was proposed and applied. The effects of the Si/Al ratio on products, microstructure, pore structures, compressive strength, water loss rate and efflorescence of geopolymer were systematically investigated. The reaction products and structures of geopolymer were tested by XRD, FTIR, TG-DTA, SEM-EDS and BET. The results showed that the efflorescence degree of different samples can be compared by the test method simply, effectively and quantitatively. The products of geopolymer were mainly amorphous gels N(C)-A-S-H containing large amounts of Si and Al components. The structures, properties and efflorescence degree of the geopolymer were different due to the different Si/Al ratio. When the Si/Al ratio of geopolymer was 1.5, the content of [AlO4]- structures was highest, while the volume and size of pore were relatively small. The dense matrix and [AlO4]- structures of geopolymer can reduce the efflorescence degree significantly. This study can provide a reference for future investigation about efflorescence inhibition and efflorescence test methods of geopolymer.