Unravelling the hierarchical conductivity-strengthening mechanism in self-sensing concrete with copper tailings and nano carbon black

In this study, nanocarbon black (NCB)-filled cement-based sensors (CuNCBS) were developed using 20% mechanically activated copper tailings (CuT) by weight of cement. CuNCBS exhibited acceptable mechanical properties and enhanced conductive networks. Superior resistance- and capacitance- based sensing performances were demonstrated across thirteen application configurations with multiple loading conditions and electrodes design. Under low dynamic loads, capacitance-based sensing not only showed greater sensitivity but also enabled clearer differentiation of load magnitudes compared with resistance-based sensing. Microstructural characterisation revealed that the improved sensing performance is primarily governed by a hierarchical conductivity-strengthening mechanism, originating from multiple NCB/C-A-S-H layers formed on CuT surfaces with different NCB loading capacities. The formation of these layers can be explained by two synergistic mechanisms, including early hydration inhibition induced by aqueous Al, followed by continuous Si and Al release that modifies C–A–S–H composition, and the prolonged lifetime and enhanced stability of amorphous globular intermediates during early-stage C–A–S–H crystallization compared with C-S-H crystallization. The NCB loading capacity is closely correlated with the compositional and structural evolution of C-A-S-H, where increasing NCB loading capacity corresponds to a transition from higher Si/Ca and Al/Si ratios to lower ones. These insights are expected to advance the development of low-carbon, tailings-incorporated cement-based sensor for efficient structural health monitoring and practical applications in smart and sustainable mining infrastructure.