Polydopamine-assisted carbon black grafting on natural fine aggregates for highly conductive and piezoresistive cement mortar

The inherent electrical insulation of cementitious composites fundamentally limits their application in smart infrastructure requiring self-sensing capabilities. Direct dispersion of conductive nanofillers, while improving conductivity, easily triggers nanoparticle agglomeration and internal defects, causing significant mechanical degradation. Conventional surface modification techniques on aggregates are energy-intensive or environmentally hazardous, posing barriers to scalable implementation. To overcome dual challenges, we hypothesize a mussel-mimetic interfacial engineering strategy, leveraging dopamine's spontaneous polymerization into a polydopamine (PDA) adhesive layer, anchors carbon black (CB) onto fine aggregates (CB + PDA@FA) for the conductive aggregate's fabrication, which is simple, energy-efficient, and environmentally friendly. The optimized cement mortar (M-0.4CF + CFA) containing CB + PDA@FA and carbon fibers achieves an electrical resistivity of 1.8 × 10³ Ω cm (five orders of magnitude reduction), while preserving compressive and flexural strengths. This is attributed to that the utilization of CB + PDA@FA did not significantly compromise the pore structure and ITZ of cement mortar. Moreover, M-0.4CF + CFA exhibits exceptional piezoresistive sensitivity under cyclic loading, attaining a gauge factor of ∼98 and a fractional resistivity change up to 5.2 %. Density functional theory calculations validated the PDA interlayer amplifies the chemisorption energy between CB and aggregates, stabilizing the robust conductive network. This work potentially resolves the conductivity-mechanical property conflict in cementitious materials which provide new insights into bio-inspired interfacial design for smart composites, paving the way for energy-efficient, self-sensing infrastructure systems.