Long-term performance of silane coupling agent/metakaolin based geopolymer

Abstract

This article reports the effects of different dosages of silane coupling agent (KH-550) on the properties of geopolymer that have been cured for 360 days. The mineral phase formation and microstructure changes of geopolymer were analyzed combined with mechanical properties, XRD, FT-IR, SEM and 29Si NMR. The results show that adding an appropriate amount of silane coupling agent can improve the toughness of geopolymer, and the best performance is obtained when the silane coupling agent content is 0.1 wt%. The highest compressive strength and flexural strength of geopolymer samples containing 0.1 wt% silane coupling agent cured for 90 days reached 51.4 MPa and 12.93 MPa, respectively. The gel phase in the geopolymer is significantly enriched after adding silane coupling agent. Combined with 29Si NMR analysis, it can be seen that the doping of silane coupling agent promotes the polymerization reaction, and gradually develops towards low-aluminum bonded silica and Q4(0Al) structure. The decrease in Q4(0Al) structure of the geopolymer samples cured for 360 days indicates the weakening of the geopolymerization reaction and also explains the decrease in strength after long-term curing.