Mechanical and piezoresistive performance of polymethyl methacrylate modified with carbon nanotubes for sensitive road surface

Piezoresistive materials, known for their mechanical adaptability and sensing capacity, hold the potential to be used as the materials for the sensitive surface layer in the digital twin of road systems. This study aims to investigate the mechanical and piezoresistive performance of a novel pavement material, a composite that comprises Polymethyl methacrylate (PMMA) as the matrix and carbon nanotubes (CNTs) as the conductive filler. Firstly, the composition and preparation process of CNTs-modified PMMA (CMP) were optimized via investigation on curing time, dispersion methods, and initiator content. Subsequently, the piezoresistive responses of CMP were analyzed within a loading range of 0 to 10 MPa by conducting linear increase compressive stress tests. Additionally, dynamic modulus tests and dynamic creep tests were employed to assess the mechanical and piezoresistive responses of CMP under equivalent vehicle loads. Results show that optimal properties are achieved when using ultrasonic methods to disperse CNTs, with a curing period of 72 h and an initiator content of 1.6 wt%. PMMA exhibits a lower modulus, reduced elasticity recovery and temperature sensitivity after modification with CNTs. And varying the CNTs content from 0.8 wt% to 1.2 wt% does not significantly affect the viscoelastic properties of CMP. The piezoresistive response of CMP under equivalent vehicle loads occurs in the first stage of the fractional change in resistance curve and is exclusively correlated with the tunneling resistance of adjacent CNTs. In this stage, CMP demonstrates higher sensitivity to heavy loads at lower CNTs content. The developed piezoresistive model based on tunneling resistance aligns with the experimental results. This study provides a basis for the performance study of CMP as a piezoresistive material in pavements, contributing to the design and development of sensitive surface layers in road systems.