Interfacial bonding behavior and microstructure of nano carbon black concrete and roller-compacted concrete composites for dam overwintering layer

The influence of nano carbon black (NCB) dosage on the bonding behavior and interfacial characteristics between NCB concrete for dam overwintering layer and roller-compacted concrete was investigated using splitting tensile tests, three-dimensional laser scanning, and microstructural characterization. Interfacial bond strength decreased from 3.09 MPa to 2.76 MPa as NCB dosage increased from 0% to 6%. Interlayer penetration occurred across the interface, while NCB penetration thickness decreased from 117.80 μm to 51.34 μm as dosage increased from 1.5% to 6%. Moderate NCB dosages reduced the overlay transition zone thickness, and interfacial porosity, whereas excessive NCB caused substantial workability loss and increased interfacial defects. The interfacial response was governed by the combined effects of NCB-induced microscale densification and macroscale defects associated with reduced workability. Considering interfacial bonding, electrothermal performance, and practical application requirements, an NCB dosage of 3–4.5% is recommended for electrothermal overwintering layers in roller-compacted concrete dams in cold regions.