Dimensional stability of repair mortars with carbon-based nanoparticles

Abstract The application of repair materials is essential for maintaining the service life of reinforced concrete structures. Dimensional compatibility with the substrate is crucial for the repair material. This study assesses the impact of graphene and carbon nanotubes on dimensional stability and bond strength. Bulk density and consistency index were analysed in the fresh state, while weight loss, dry shrinkage, coefficient of thermal expansion (CTE) and bond strength were evaluated in the hardened state. Scanning electron microscopy (SEM) was employed to assess the impact of carbon nanoparticles on the microstructure. Graphene particles can mitigate dimensional variation caused by dry shrinkage. However, incorporating carbon nanotubes led to higher shrinkage due to the refinement of the cementitious matrix and an increase in capillary pressure. Furthermore, using nanoparticles combined with superplasticisers enhanced bond strength by increasing adhesion points in the interfacial transition zone between the repair and the concrete substrate. SEM analyses demonstrated the formation of crystals on the graphene surface and the good dispersion of carbon nanotubes into the cementitious matrix.