Nanoscale analysis of Si/P effects on the bonding and mechanical enhancement of phosphoric acid-based geopolymers

Phosphoric geopolymers are attracting growing interest as environmentally friendly materials since they offer reduced CO 2 emissions relative to traditional cement and exhibit enhanced thermal stability and chemical durability compared to alkali-activated geopolymers. This study employs molecular dynamics (MD) simulations to investigate the role of phosphoric acid concentration on PABG’s nanostructure and mechanical properties, with comparison to conventional alkali activators Na- and K-based geopolymers. Results show that moderate Si/P ratios (1.0–1.5) promote dense Si-O-P/Al-O-P crosslinking, while low or excessive phosphoric acid content induces the structural and bonding formation. Low phosphoric acid amount favors Al 6+ /Al 5+ , while for higher dosage Al 5+ is dominant. At Si/P = 3, a maximum average Young’s modulus of 42.5 GPa is reached, while low and excessively high Si/P ratios deteriorate the mechanical properties of PABG due to insufficient crosslinking or network instability. This work clarifies the Si/P ratio-modulated nanostructure-mechanical property correlation, supporting PABG’s compositional optimization for high-stiffness applications.