Nano-scale study on molecular structure, thermal stability, and mechanical properties of geopolymer

The well thermal stability and mechanical properties of geopolymer can be attributed to its predominant adhesive constituent, sodium alumino-silicate hydrate (N-A-S-H). However, the intrinsic relation between molecular structure, stoichiometry, and performance of N-A-S-H is far from being understood. Herein, the structure, thermal stability, and tensile behavior of N-A-S-H at different Si/Al ratio are investigated by means of ReaxFF molecular dynamics. The results show that, after extreme low/high temperature treatment, the atomic configuration can also recover to a large extent. The hydrolysis during high temperature treatment slightly inhibits the structure recovery. Its expansion strain at elevated temperature is much smaller than that of calcium silicate hydrate, the primary component of Portland cement. Aluminum addition diminishes alumino-silicate skeleton’s connectivity and promotes the formation of energetically unstable Al–O–Al bonds, resulting in the drop of thermal stability and mechanical properties. The consistence between simulations and experiments demonstrates the considerable function of molecular structure of N-A-S-H for the macro-performance of geopolymer. Graphical abstract: [Figure not available: see fulltext.] Sodium alumino-silicate hydrate (N-A-S-H), featuring cross-linked glassy structure, exhibits excellent thermal stability. Mechanical properties increase with Si/Al ratio.