Electrochemical grafting of hydroxyl and amine groups on carbon fibres for improved performance in cementitious composites

The use of electrochemistry to functionalise carbon fibre (CF) surface has proven effective in enhancing the performance of polymer composites, offering benefits of time efficiency and precise control. However, its current application to CFs within cementitious matrices remains limited and confined to laboratory-scale studies, restricting broader implementation in the construction industry. The bond between CF and the cementitious matrix is relatively poor due to the CF surface's chemical inertness and hydrophobic nature, which hinders the effective utilisation of fibre-reinforced cementitious composites (FRCC). This study addresses this issue by functionalising CFs with diazonium aryl salts through an in situ electrochemical modification process. This process applies a reductive potential of 3 V to successfully graft phenolic hydroxyl and amino functional groups onto the CF surface, enhancing the interfacial strength. The debonding force of hydroxyl- and amino-functionalised CF within the matrix increased by 48.33 % and 9.70 %, respectively, compared to the untreated CF specimens. The active polar groups enriched the CF surface, notably enhancing chemical adhesion at the CF-matrix interface. Additionally, the rougher surface improved the mechanical interlocking mechanism and created sites for nucleation and hydration product deposition. Overall, the FRCC specimens incorporating hydroxyl-functionalised CFs outperformed those with amino-functionalised CFs, achieving the highest compressive and flexural increases of 32.30 % and 21.04 %, respectively, compared to the plain mortar. Moreover, this approach also reduced the total porosity of FRCC, proving the formation of a denser microstructure. The results indicated the enhanced interfacial bonding efficacy by large-scale electrochemical treatment and highlighted its promising potential for future applications. • In-situ electrochemical grafting of CFs with hydroxyl and amine groups developed. • Achieved 48 % and 10 % IFSS increases over control for OH- and NH 2 -functionalised CF. • FRCC with OH-functionalised CFs outperformed with up to a 32 % increase in strength. • Functionalised CFs effectively reduced porosity and drying shrinkage in FRCC. • Enhanced chemical adhesion and mechanical interlocking at the CF-matrix interface.