Synergistic role of supra-GQDs on the mechanical and durability properties of metakaolin-modified concrete

• Supra-GQDs are used to improve metakaolin dispersion in concrete matrices. • An optimal supra-GQDs dosage leads to the highest overall performance. • Mechanical strength is enhanced while chloride permeability is reduced. • Synergistic effects are associated with improved durability and refined Abstract The growing demand for sustainable concrete has intensified interest in supplementary cementitious materials (SCMs) such as metakaolin (MK) to reduce cement consumption and enhance long-term performance. However, the practical utilization of MK is often limited by particle agglomeration, which hinders its uniform dispersion and pozzolanic reactivity. This study addresses this challenge by investigating the synergistic role of suprastructure graphene quantum dots (supra-GQDs), a zero-dimensional carbon nanomaterial, enhancing the mechanical and durability properties of concrete containing 10% MK as a partial replacement for Portland cement. Supra-GQDs were incorporated at dosages of 0.5%, 1%, 2%, and 3% by weight of MK. The results demonstrate that an optimal dosage of 0.5% supra-GQDs led to the most substantial improvements, resulting in a 46.4% increase in 28-day compressive strength (from 22.6 to 33.1 MPa) and a 54.6% reduction in RCPT charge passed compared to the control mixture. At higher supra-GQD dosages (1–3%), the performance improvement gradually diminished, indicating the importance of dosage optimization for nano-modified cementitious systems. This improvement is attributed to the synergistic effect of supra-GQDs acting as nano-dispersing agents and fillers, which enhance MK reactivity and refine the microstructure. These findings highlight the potential of supra-GQDs as an innovative nanocarbon additive for improving the dispersion and reactivity of pozzolanic materials and providing a practical solution for producing high-durability concrete suitable for chloride-exposed environments.