The rapid development of high-speed rail (HSR) infrastructure has played a vital role in fostering regional economic growth and alleviating the existing traffic burden. Significant efforts have been devoted to monitoring the health of these systems to address the growing safety concerns. Current technologies for online and onboard monitoring of the HSR systems, including the vehicles and infrastructure, involve different techniques like those based on acoustic emission. Even though these techniques are promising alternatives to visual inspection, they are expensive, have poor long-term durability and are incompatible with HSR infrastructures. In addition, they are mostly made of cementitious composites that are susceptible to extreme environmental conditions and frequent service loads.
Lately, self-sensing cementitious composites (SSCC) have emerged as an effective alternative/supplement to current sensing technologies owing to their numerous benefits attributed to their superior durability and mechanical properties. With the increasing engineering application of SSCCs in sensing, damage detection and structural monitoring, it is promising for potential application in in-situ monitoring railway concrete infrastructures. To facilitate this, SSCCs should possess the merits of excellent repeatability and durability, high sensitivity, fast response and scalable manufacturing.
Conductive fillers, especially carbon nanotubes (CNTs), have been used to improve the sensing performance of SSCCs for multifunctional benefits. However, the non-uniform dispersion of CNTs inside the SSCCs limits their performance modulation, scale manufacturing and overall practical applications. With recent advancements in nanotechnology, new effective strategies have been developed to overcome these limitations. Among them, in-situ synthesizing of CNTs on cement ([email protected]) is a straightforward, scalable, tunable and versatile approach for efficient synthesis and dispersion of CNTs in one step. By varying the in-situ synthesizing parameters like carbon source, feeding rate and gas composition, it is possible to mediate the distribution, morphology and structures of the CNTs. This strategy can also eliminate the functionalization and ultrasonication steps to retain and optimize the properties, integrity and performance of CNT structures in the cement matrix.
Herein, Dr. Siqi Ding and Professor Jinping Ou from Harbin Institute of Technology, Dr. Yu Xiang and Professor Yi-Qing Ni from the Hong Kong Polytechnic University, Professor Vijay Kumar Thakur from Biorefining and Advanced Materials Research Center, SRUC together with Dr. Xinyue Wang and Professor Baoguo Han from Dalian University of Technology developed the self-sensing nano-engineered cementitious composites with in-situ synthesized [email protected] for smart in-situ monitoring of HSR infrastructures. The work is currently published in the journal, Nano Today.
The research team demonstrated the fabrication of SSCCs with outstanding properties and self-sensing performance for effective smart in-situ monitoring of HSR infrastructures. Due to the inherently containing silicate and ferrite phases, microscale cement particles served as effective substrate-bound catalysts, facilitating high-yield and strongly-anchored CNTs growth. The as-synthesized [email protected] exhibited unique morphology with strong interfacial bonding between the cement particles and CNTs, reinforcing the mechanical properties of the composites. The addition of [email protected] was beneficial in effectively enhancing the electrical conductivity and self-sensing capabilities of the SSCCs. It also promoted early hydration to facilitate the strength development of the SSCCs.
SSCCs with [email protected] attained an ultrahigh sensitivity (i.e., gauge factor) of 748, which outperformed most of the reported SSCCs. They also showed excellent properties, including high repeatability, ultrafast response and recovery, outstanding stability and adaptability to different conditions than those without [email protected].
In summary, a one-step, feasible and robust method for scalable fabrication of the next-generation SSCCs is reported. It comprised [email protected], a hierarchical structured functional filler, to eliminate the limitations associated with the dispersion of CNTs to allow fabrication of SSCCs with remarkable self-sensing performances. The manufactured SSCCs-engineered smart track slab was competent in terms of axle counting and speed detection, suggesting the feasibility of using the presented approach to develop smart HSR infrastructures for in-situ monitoring the train load and environmental action as well as infrastructural damage. In a statement to Advances in Engineering, Professor Baoguo Han, the corresponding author, a pioneer in nanotechnology research in cement and concrete composites said the new findings contribute to sustainable manufacturing of high-performance SSCCs-engineered smart structural elements for low-cost and long-term monitoring of HSR infrastructures.
Ding, S., Xiang, Y., Ni, Y., Thakur, V., Wang, X., Han, B., & Ou, J. (2022). In-situ synthesizing carbon nanotubes on cement to develop self-sensing cementitious composites for smart high-speed rail infrastructures. Nano Today, 43, 101438.