In-situ synthesizing carbon nanotubes on cement to develop self-sensing cementitious composites for smart high-speed rail infrastructures

Self-sensing cementitious composites (SSCCs) with carbon nanotubes (CNTs) have attracted extensive attention because of their excellent mechanical and durability properties combined with multifunctional benefits. However, their performance modulation, as well as scalable manufacturing and application, are limited by the uniform dispersion of CNTs inside them. Here, a straightforward approach to in-situ synthesizing CNTs on cement (CNT@Cem) toward alleviating the CNTs' dispersion issue and enhancing their composite efficiency and effectiveness is explored. Due to the inherently containing silicate and ferrite phases, microscale cement particles act as effective substrate-bound catalysts, facilitating high-yield and strongly anchored CNTs growth. The hierarchically structured CNT@Cem integrates the dual functions of reinforcement and conduction, significantly affecting early-age hydration, mechanical, electrical, and self sensing properties of the final SSCCs with CNT@Cem. The CNT@Cem structure can promote early-age hydration while slowing the later hydration rate and hindering the strength development of the SSCCs. The addition of CNT@Cem can be effective in tailoring the electrical microstructures to enhance the electrical conductivity and self-sensing sensitivity of the SSCCs. The SSCCs with CNT@Cem achieved a maximum stress sensitivity of 2.87%/MPa with a gauge factor of 748. They demonstrated excellent repeatability and stability, outstanding adaptability to various applied conditions, and fast response and recovery. The developed SSCCs-engineered smart track slab is competent in axle counting and speed detection. It opens up a new territory to develop high-performance and versatile SSCCs-engineered smart components/structures for long-term, wide distribution, and low-cost monitoring of high-speed rail (HSR) infrastructures.(c) 2022 Elsevier Ltd. All rights reserved.