Development and evaluation of conductive ultra-lightweight cementitious composites for smart and sustainable infrastructure applications

The stability of electrical conductivity of self-sensing cementitious composites under different environments is the key to the application of structural health monitoring using electrical resistivity/impedance tomography. In addition, the lightweight of concrete is becoming a new requirement for sustainable development. This study aims to develop long carbon fibre (LCF) reinforced ultra-lightweight cementitious composites (ULCC) to address these issues. The mechanical properties and electrical and thermal conductivities of composites were investigated. The conductivity of LCF-reinforced ULCC under different testing methods (AC and DC), frequencies, temperatures, water content in the mixture, and curing ages were examined. The electromechanical properties of LCF-reinforced ULCC under compression (monotonic, cyclic loading under different loading peaks and loading rates) and tension were also tested. Except for the content, the effects of the pre-heating treatment of carbon fibre on the conductivity and electromechanical properties were compared. The experimental results revealed that LCF can remove the polarization effect and maintain the stability of the electrical conductivity of LCF-ULCC under different environments. The LCF can build a complete and continuously 3D conductive pathway, and free electrons can transport stably in the matrix, which can diminish the effect of electrolytic ions on the conductivity. The LCF-reinforced ULCC can show sensitive electromechanical ability where LCF is better used for self-sensing under tension when compared with compression. The conductivity of composites increases with increasing LCF content but initially increases and then decreases with increasing the pretreatment heating temperature of LCF. It is efficient to increase the conductivity and mechanical properties of composites by heating LCF to 300 °C. The composites (Oven-dry density: 990–1100 kg/m³) are a good thermal insulation material and the thermal conductivity is between 0.35 and 0.45 W/mK. Finally, microstructural analysis was conducted and the mechanisms of the improved electrical conductivity and thermal insulation of the composites were discussed.