Damage Evolution of Ballastless Track Concrete Exposed to Flexural Fatigue Loads: The Application of Ultrasonic Pulse Velocity, Impact-echo and Surface Electrical Resistance Method

In order to clarify the fatigue damage evolution of concrete exposed to flexural fatigue loads, ultrasonic pulse velocity (UPV), impact-echo technology and surface electrical resistance (SR) method were used. Damage variable based on the change of velocity of ultrasonic pulse (D_u) and impact elastic wave (D_i) were defined according to the classical damage theory. The influences of stress level, loading frequency and concrete strength on damage variable were measured. The experimental results show that D_u and D_i both present a three-stages trend for concrete exposed to fatigue loads. Since impact elastic wave is more sensitive to the microstructure damage in stage III, the critical damage variable, i e, the damage variable before the final fracture of concrete of D_i is slightly higher than that of D_u. Meanwhile, the evolution of SR of concrete exposed to fatigue loads were analyzed and the relationship between SR and D_u, SR and D_i of concrete exposed to fatigue loads were established. It is found that the SR of concrete was decreased with the increasing fatigue cycles, indicating that surface electrical resistance method can also be applied to describe the damage of ballastless track concrete exposed to fatigue loads.