Development of Structural Carbon Nanotube–Based Sensing Cement Composite for Rock Bed Defects

Structural health monitoring is a solution to monitor critical infrastructure components especially, those part of infrastructures that are hidden from visual inspection or difficult to monitor using other methods. This research introduces the concept of a carbon nanotube (CNT) cement-composite specimen placed on rock bed, which is capable of providing rock distribution condition. Rock beds are mostly as a layer between soil and infrastructures with roles of transferring loads to interlayers. Therefore, their role in structures make them hidden from visual inspection such as ballast layers under railway sleepers. This CNT-cement composite sensor forms a continuous conductive skin that is exceptionally sensitive to changes in strain and the distribution of stone particles on rock bed. This sensing information allows to have a picture of hidden rock bed layer condition to avoid unsupported infrastructure problems. Once developed, this sensing skin may be able to give real-time feedback on changes in rock bed surface condition. In this regard, three different percentage of CNT as 0.5%, 0.75% and 1% by cement volume are used to manufacture CNT-cement composite sensor. These sensors are tested in different conditions under flexural bending load, on rock bed with unsupported and fully-supported conditions. Final results show that 0.5% CNT content in CNT-cement composite sensor completely detects the unsupported condition of rock bed and shows higher sensitivity to changes rather than other CNT percentages with 220% sudden change at the maximum in fractional changes (FRs) in disturbed rock support.