Fly ash-based boroaluminosilicate geopolymers: Experimental and molecular simulations

Geopolymers are cement-free construction materials which are produced by mixing an aluminosilicate source such as fly ash with an alkali activator. Despite their eco-friendly nature, geopolymers suffer the negative impact of the sodium silicate part of the alkali activator on the environment. The use of borax, one of the eco-friendly salts of boric acid, as an activator can potentially lead to the production of more environmentally-friendly geopolymer. However, a better understanding of their theoretical properties could be a milestone to produce new generations of geopolymers with high performance. A growing interest in the prediction of the macroscale properties of geopolymer compounds was the most compelling motivation for this study. Building upon this, the current study focused on both points to apply borax as a potential replacement for silicate-based activators and model all the experiments by molecular dynamics (MD) simulation. Substituting boron with aluminium in the molecular structures of geopolymer was the core idea of the simulation. Compressive strength, density and elastic modulus tests were conducted, and the results were compared with the MD simulation outcomes. Increasing the content of borax in the mixture led to a decrease in all of the properties, although the range of 10-30% of replacement eventuated in acceptable results. A fair agreement between simulation and experimental results was achieved through which the best fitting parameters for atomistic modelling of geopolymers were found.