Carbon nanotube (CNT) reinforced cement composites (CNTRCC) with self-sensing capability have shown great potential for application in structural health monitoring. In this work, a hybrid micromechanical model is developed to predict the overall electrical conductivity of the CNTRCC considering the effects of pores and the orientation and the curved morphology of the CNT. The developed model is validated by comparing theoretical predictions with the experimental results. The results demonstrate that the electrical conductivity of the CNTRCCs considering pores with aspect ratio being 0.01 agree well with the experimental data. The waviness of the CNTs is characterized by different helix angle. A decrease in the helix angle of the CNT results in a decrease in the electrical conductivity of the cement composites. The alignment of the CNTs slightly enhances the electrical conductivity of the CNTRCCs in this direction compared to value for random and uniform distribution of the CNTs. In addition, the potential barrier height plays an essential role in the overall electrical conductivity of the CNTRCCs. An increase in the potential barrier height results in increased percolation threshold for the electrical conductivity of the composites. However, it has limited effects on the electrical conductivity of the CNTRCCs after percolation.

This study aims to contribute to the growing area of research on enhancing the quality of recycled concrete aggregate (RCA). Specifically, the combined effect of washing and thermo-mechanical treatment (W-TMT) methods was investigated. The efficiency of the treatment method was evaluated through the removal of adhered mortar (AM), physio-mechanical properties of treated RCA and their microstructure observed by X-ray µCT scan. The results show a significant improvement in the quality of treated RCA with the complementary effect of W-TMT. The highest AM removal and aggregate quality were achieved by the combined W-TMT at a heating temperature of 600°C with significant improvement in water absorption, bulk density and particle density. Moreover, the X-ray µCT results show a lower AM content, less porosity and no damage (even at heating temperature of 600°C) in the treated RCA. It was found that concrete using untreated RCA only achieves the compressive strength of 21 MPa for the 32 MPa concrete mix design whilst concrete made with the treated RCA showed 72% increase in compressive strength and reaches the target strength. The findings highlight the potential of W-TMT method in enhancing the quality of RCA, thereby supporting the progress in concrete sustainability and circularity.