Formation of tannic acid-calcium polymeric network in pore solution: Characterization and kinetics

This study investigates the changes of tannic acid (TA) at varying concentrations in cement pore solution. Interestingly, TA spontaneously forms nanosheet tannic acid-calcium polymeric net-works (TA-Ca) by interacting with Ca2+. Spectral, thermal, ionic and organic carbon analyses determine the composition and structural characteristics of these networks and detail the formation mechanism. The networks are connected via hydrogen bonding, C-C coupling and complexation. Moreover, network composition, structure and formation are closely dependent on TA concentration. At low concentrations, crystalline coordination polymer networks form, following second-order kinetics (key factor: Ca2+ concentration). At high concentrations, amorphous C-C coupled polymer networks form, following first-order kinetics (key factor: catalytic oxidation of Ca2+). This study aims to elucidate the reaction and mechanism of TA in cement paste, providing a novel theoretical basis for applying renewable bio-admixtures in sustainable construction.