Retardation mechanisms and microstructure evolution of triclinic tricalcium silicate induced by three different organic phosphonic acids

This paper investigated the inhibition effects and mechanisms of organic phosphonic acids (OPAs) with distinct functional groups on triclinic tricalcium silicate (C₃S) clinker hydration. In particular, the effects of three representative OPAs, namely ATMP, HEDP, and PBTC on adsorption/complexation behavior, hydration products, and microstructure characteristics of C₃S clinker were studied. OPAs retardation of the C₃S clinker hydration was governed by synergistic interactions of electrostatic adsorption, and cationic complexation, potentially involving intermolecular self-polycondensation. ATMP primarily relied on Ca²⁺ complexation through its [–C-PO(OH)₂] groups, forming low-solubility precipitates that inhibited hydration. HEDP combined strong complexation with intermolecular self-polycondensation, driven by its [–C–PO(OH)₂] and (–OH) groups, generating dense three-dimensional polymers that enhanced steric hindrance, while PBTC operated through surface adsorption and self-polycondensation. The revealed retardation efficiency hierarchy (HEDP > PBTC > ATMP) arose from functional group synergy: the maximal inhibition was provided by synergy of [–C–PO(OH)₂] and (–OH) groups, a weaker one-by that of [–C–PO(OH)₂] and (–COOH) groups, while isolated [–C–PO(OH)₂] groups had the minimal retarding capacity.