Study on the mechanical properties, gelling products and alkalization process of alkali-activated metakaolin: From experiment to molecular dynamics simulation

Alkali-activated metakaolin (AAMK), which is rich in aluminosilicate, is considered a green material that can replace ordinary Portland cement with high energy consumption. The exceptional durability of alkali-activated materials (AAMs) is widely recognized, but the research on the molecular-scale alkalization mechanism remains largely unexplored. Here, the mechanical properties, the composition of cementitious materials, and molecular dynamics (MD) simulations of the AAMK are studied to verify the consistency and reliability of the experiment and simulation. Research shows that the flexural strength and compressive strength of AAMK reached 80% and 65.8% respectively after 3 days of hydration. Laumontite and Gismondine with a macromolecular structure similar to zeolite were formed. Moreover, AAMK consumes a large amount of Ca (OH)2 and CaCO3. Molecular insights into the alkalization process of MK have been provided through MD simulations. A systematic study was conducted on the structure, kinetics, and alkalization process of the molecules. The results show that silicate is dissolved in sodium hydroxide (NaOH) solution while the aluminate structure remains stable. Furthermore, the observed result of MK alkalization can be regarded as a precursor to the emergence of AAMs.