Microstructure and physical properties of fly ash-based geopolymer with expanded vermiculite addition

Fly ash-based geopolymer paste with expanded vermiculite (EV) powder addition was synthesized and its microstructure, compressive strength, setting time, moisture control, efflorescence extent and thermal conductivity were studied. The results showed that EV addition resulted in the increase of standard consistency water consumption and setting time. As a consequence, its excessive addition caused a larger amount of harmful pores, which was detrimental for compressive strength of geopolymer paste. However, geopolymer pastes with an appropriate amount of EV addition (2-7 wt%) presented a slight increase of compressive strength because of the filler effect. Mg2+ and Fe2+diffused from EV interlayer through ions exchange between EV and geoploymer solution participated in geopolymerization. This was reflected by the formation of N-(M)-A-(F)-S-H evidenced through SEM-EDS and FITR analyis. In addition, Na2+/Mg2+or Na2+/Fe2+ ions exchange reduced the mobility of Na2+and therefore decreased the efflorescence extent. Moreover, EV addition favored the improvement of moisture control and thermal conductivity properties of geopolymer paste.