Nanoindentation on micromechanical properties and microstructure of geopolymer with nano-SiO2 and nano-TiO2

Fly ash-based geopolymers incorporated with 2% nano-SiO2 (NS)/nano-TiO2 (NT) particles were subjected to microstructural and statistical nanoindentation analysis. With the addition of both types of nanoparticles, the compressive strength of geopolymer and the micromechanical properties of N-A-S-H gel were increased. NS exhibited higher reinforcement effect than NT on macro-strength. However, NT more significantly enhanced gel micromechanical properties. NT and especially the NS were found to have a positive effect on the early reaction rate of geopolymer. After 28 days, the gel proportion obtained by Backscattered electron (BSE) images analysis was close values of 49.16%, 55.69% and 54.02% for reference sample and NS, NT reinforced geopolymer, which were more than two times of that from the statistical nanoindentation. The effects of NS and NT on microstructure, gel proportion and gel micromechanical properties were discussed to reveal the macro-strength reinforcement mechanism. The results obtained from different techniques were also compared and discussed.

Automated summary

The addition of nano-SiO2 and nano-TiO2 particles in fly ash-based geopolymers improved compressive strength and micro mechanical properties of N-A-S-H gels. Nano-SiO2 had a greater impact on macro-strength, while nano-TiO2 significantly enhanced gel micro-mechanical properties. Both nanoparticles showed a positive effect on the early reaction rate of geopolymers.