Freeze-thaw damage assessment of engineered cementitious composites using the electrochemical impedance spectroscopy method

The mechanical properties of engineered cementitious composites (ECC) in service in cold regions can be significantly degraded by periodic freezing and thawing. In this work, the damage degree of freeze–thaw of ECC was systematically assessed by using the electrochemical impedance spectroscopy (EIS) technique. In addition, Nuclear Magnetic Resonance (NMR) Relaxometry measurements were also performed to obtain pore structure parameters, and the uniaxial tensile tests were also carried out to analyse the tensile performance after freeze–thaw cycles. From the acquired results, it was demonstrated that the EIS behaviour of ECC varied with the freeze–thaw cycles. The diameter of the Nyquist curve in high-frequency was gradually reduced by increasing the freeze–thaw cycles. Furthermore, the volume resistance of ECC after freeze–thaw gradually decreased with the increase in the number of freeze–thaw cycles. The simplified microstructure and conductive paths were used to describe the freeze–thaw damage mechanism of ECC. An equivalent circuit model of ECC exposed to freeze–thaw cycles was proposed, and the parameters of the equivalent circuit model were thoroughly analysed. The experimental findings clearly indicate that the EIS method is an appropriate technique for evaluating the damage degree of freeze–thaw of ECC.