Compression fatigue and self-heating effect of foamed polyurethane grouting materials for roadbed trenchless rehabilitation

Foamed polyurethane (PU) grouting materials are widely used for road trenchless rehabilitation. However, the temperature-rising under cyclic traffic loads affects fatigue resistance and ambient temperature. Therefore, in this work, the fatigue resistance and self-heating mechanism were revealed by Infrared Thermal Imager-Fatigue Tester Combined Device and SEM considering density and specimen size. The compressive strength increased with increasing density and diameter-to-height ratio but decreased with increasing diameter. The fatigue threshold and fatigue life decreased with increasing density, diameter, and diameter-to-height ratio. Temperature-rising was uneven. The maximum temperature increased and then decreased or kept increasing with increasing stress levels. The temperature-rising rate increased with increasing stress levels. At medium-high stress levels, the energy dissipation and the maximum temperature varied in three stages with cycles. The mean final max. temperature was within the glass transition region at 66.25 degrees C. Fatigue damage was jointly dominated by mechanical and thermal damage. The cell structure is severely deformed characterizing powder and melt fracture. At low stress levels, the energy dissipation and maximum temperature varied in two stages with cycles and stabilized at 1.33 x 10-3 MJ/m3 and 36.12 degrees C. Due to the maximum temperature falling outside the glass transition region, fatigue damage was dominated by mechanical damage. The research results have a significant scientific significance for the performance enhancement and popularisation of PU grouting materials.