| Summary: | Geopolymer is considered as green, sustainable and supplementary cementitious binder synthesized by reaction of solid aluminosilicate precursor with monoacidic alkaline activators (NaOH/Na2SiO3 or KOH/ K2SiO3). Nevertheless, their preparation with corresponding diacidic alkaline activators i.e Mg(OH)2 and Ca(OH)2 have been limited reported. Interactions between the positively charged metal ions furnished by the alkali and negatively charged aluminosilicate framework are crucially important for characteristic properties of the material. Contrary to the monovalent counter-cation (Na+), the fundamental chemical species like silicate, aluminate and aluminosilicate and their initial key reactions (deprotonation and dimerization) with divalent counter-cations (Mg2+ and Ca2+) have been rarely investigated and compared computationally. In this work, we have employed a reliable DFT method to derive and compare the equilibrated geometries of fundamental monomers, dimers, and their initial key reactions (deprotonation and dimerization) with Mg2+ and Ca2+ as counter-cations. The calculations have been made highly relevant as it mimics the actual solution environment by considering hybrid solvation model (explicit and implicit). The feasibility of the deprotonation and dimerization reactions with Mg2+ and Ca2+ as counter-cations have been predicted on the basis of Gibbs energy of the reaction.
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