Molecular mechanisms responsible for the structural changes occurring during geopolymerization: Multiscale simulation

To date, the fundamental details of the molecular structural changes and associated mechanisms, which take place during the formation of aluminosilicate geopolymer gels, have remained largely elusive. Here, density functional theory-based coarse-grained Monte Carlo modeling, a multiscale simulation technique, is used to simulate the geopolymerization reaction and to determine the molecular mechanisms controlling this process. Silica supplied by the alkaline solution plays a significant role in enhancing the dissolution of the solid aluminosilicate precursor (metakaolin, in this case) and the polymerization of the gel. In the reaction between NaOH and metakaolin, in the absence of initially dissolved silica, the solid precursor completely dissolves and the aluminosilicate gel forms via the percolation of small aluminosilicate clusters. On the other hand, in the presence of dissolved silicate, the metakaolin only partially dissolves, as the aluminosilicate gel precipitates on the surfaces of the metakaolin particle after a period of time.