Chloride Transport in Interfacial Zone of New-Old Concrete Joints of Precast Prestressed Concrete Bridges under Fatigue Load

The interfacial zone of new-old concrete in precast concrete structure is the natural weak part in durability, and fatigue stress and an aggressive medium will accelerate the durability degradation of the interfacial zone. To study the chloride transport behavior in the interfacial zone of new-old concrete joints of precast prestressed bridges under the combined action of fatigue load and chloride penetration, a set of long-term (90-360 days) and low-frequency (0.3 Hz) experiments was carried out in this paper, where three fatigue stress ranges and four exposure durations were set as the main variables. The results indicated that the chloride content in the interfacial zone is higher than that present elsewhere, which shows the interfacial zone effect (IZE). By introducing the index of IZE, the influence laws of fatigue stress range and exposure duration on the IZE are revealed, namely as the fatigue stress range increases, the IZE first increases and then decreases, and as the exposure duration increases, the IZE decreases invariably. Moreover, the influence mechanism of fatigue stress range and exposure duration on the distribution and evolution of chloride concentration in the interfacial zone is analyzed. Considering the heterogeneous distribution of mesocomposition and internal defects (pores) in the interfacial zone of new-old concrete, the model of the chloride diffusion coefficient is established. Based on the relationship between volume strain and porosity, and the relationship between strain and specific crack area, a revised model of the effective chloride diffusion coefficient in the interfacial zone under fatigue stress is proposed. The accuracy of the revised model was verified by physical experiments.