Suprastructure Graphene Quantum Dots Promote Dispersion and Enhance Thermal Transport in Metakaolin-Cement Composites

High Resolution Image Download MS PowerPoint Slide Metakaolin (MK) dispersion in highly alkaline cement pore solution is limited by platelet agglomeration and ion-induced flocculation, which suppresses its effective pozzolanic reactivity. In this work, suprastructure graphene quantum dots (supra-GQDs) function as a Ca 2+ -mediated interfacial regulator was introduced. Adsorption of Ca 2+ onto oxygen-functionalized supra-GQD surfaces generates ion-enriched nucleation domains that separate MK platelets and promote heterogeneous nucleation of calcium-silicate-hydrate (C–S–H). Portland cement was partially replaced with 10% MK by weight, while supra-GQDs were incorporated at dosages of 0.2, 0.4, and 0.6% by weight of MK. The aim was to optimize MK dispersion through supra-GQDs from Ca 2+ adsorption and evaluate the resulting impact on fresh, physical, mechanical, and thermal properties. Experimental tests included flowability, density, water absorption, porosity, compressive and flexural strengths, surface temperature, thermal conductivity, and microstructural analysis. The results revealed that supra-GQDs promoted uniform MK dispersion, resulting in a denser matrix, accelerated pozzolanic reactions, and significant performance improvements regarding their heterogeneous nucleation. At the optimum dosage of 0.2% supra-GQDs, compressive and flexural strengths increased by 46.6 and 9.8%, respectively, compared with the control by nanobridging mechanism. Thermal performance also improved, with the maximum surface temperature reaching 42.7 °C and thermal conductivity increasing by 39.3%. These findings demonstrate the potential of nanoengineered carbon materials as dispersing agents for pozzolanic additives, enabling the development of sustainable and high-performance cementitious composites.