Abstract
Advances in nanotechnology have provided approaches for the fabrication of new composite materials for sensing. Flexible sensors can make up for the shortcomings of traditional strain sensors in monitoring the surface strain and cracks of concrete structures. Using reduced graphene oxide (RGO) as a conductive filler, cellulose nanofiber (CNF) as a dispersant and structural skeleton, and waterborne epoxy (WEP) as a polymer matrix, a flexible composite material with piezoresistive effect was prepared by the solution blending and solvent evaporation method. The mechanical, electrical, and electromechanical properties of the composite were investigated. The results show that CNF can significantly improve the dispersion of RGO in the WEP matrix and help to form stable reinforcing and conductive networks, leading to great changes in the mechanical properties and resistivity of the composite. The composite film can withstand large deformations (>55% strain), and the resistance change rate demonstrates a high sensitivity to mechanical strain with a gauge factor of 34–71. Within a 4% strain range, the piezoresistive property of the composite is stable with good linearity and repeatability. The performance of the flexible film sensor made of the composite is tested and it can monitor the strain and crack of the concrete surface well.
Highlights
Concrete is the most widely used material in civil engineering structures [1]
The results show that cellulose nanofiber (CNF) solves the dispersion problem of reduced graphene oxide (RGO) well and helps to form stable conductive networks in the waterborne epoxy (WEP) matrix
RGO is added into the WEP matrix in two steps, and the key first step is to obtain a uniformly dispersed RGO aqueous suspension
Summary
Concrete is the most widely used material in civil engineering structures [1]. The service life of a concrete structure lasts for several decades or even longer. In long-term processes, the combined actions of multiple factors, such as the load effect, environmental erosion, and material aging, will lead to damage accumulation and resistance attenuation [2,3,4]. Deformation and cracking are the most direct phenomena of structural damage [5,6]. If the deformation and cracking cannot be effectively monitored and located, the structure cannot be repaired and strengthened in time, which will affect the service performance of the structure, and could even lead to catastrophic accidents. Structural health monitoring is necessary to determine the stress and strain states of key positions and to evaluate the safety and reliability of the structure [7]
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