Self-Sensing Carbon Nanotube-Cement Composite Material for Structural Health Monitoring of Pavements

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Abstract
Self-sensing materials are capable of sensing the occurring strains and damage states present within. Smart concrete pavement made with cement-based self-sensing materials could be used for in situ monitoring of both the structural integrity as well as traffic characteristics. This article studies the electrical resistivity and piezoresistivity of cement enriched with multiwall carbon nanotubes (CNTs) under cyclic loading. The effects of fatigue damage and environmental factors, such as temperature, water content, and freeze-thaw cycles, on the resistivity and piezoresistivity were investigated. The test results show that the resistivity increases with the number of fatigue loading cycles. On the other hand, the resistivity decreases as the water content increases. In contrast, the piezoresistivity increases first and then decreases. The temperature has a significant yet offsetting effect on the electrical resistivity as well as the piezoresistivity. As the temperature increases, the electrical resistivity decreases, whereas the piezoresistivity increases. The major cause of the change in electrical resistivity and piezoresistivity was the change of tunneling conduction under different conditions. Moreover, the freeze-thaw cycles induce damage to the CNT-cement composite material. Therefore, the data collected by self-sensing materials must be calibrated for the water content and temperature before interpretation.

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