Effect of nano-SiO2 on the alkali-activated characteristics of spent catalyst metakaolin-based geopolymers

The effects of the nano-SiO2 (NS) addition levels (0.5-2%) and replacement levels of spent catalyst (0-20%) in a geopolymer were analyzed quantitatively. The initial and final setting time of spent catalyst metakaolin-based geopolymers (MKGP) with a 5% spent catalyst substitution at a constant addition of 0.5% NS were 201 and 270 min, respectively. The compressive strength of these geopolymers after 56 days of curing age was 71.10 MPa. Adding 2% NS substantially increased the compressive strength of the samples, and the high energy increases the speed and degree of polymerization. The percentage of mesopores was 84%. The Fourier transform infrared spectra of the geopolymers contained a distinct intensity band at 1300-900 cm−1, associated with the Si-O-T asymmetric vibration. The geopolymer with the optimal spent catalyst replacement level and NS addition level contained more structural dener beneficial to structure development. In summary, the application of NS to a geopolymer enhanced its compactness and strength.