Keisuke SHIKANOUCHI

Elucidation of the mechanism of cracks generated in the repair part of expansion joints of road bridge

Takumi SHIMOMURA

From the viewpoint of maintenance of expressways and early opening of roads in emergencies and disasters, super-hard concrete is widely used as a repair and reinforcement material for road bridges. In recent years, construction methods have been optimized and maintained, but there is a problem that super-hard concrete has a high risk of cracking. However, there are few cases in which the cause of crack generation has been studied in detail. In particular, it is necessary to clarify cracks that occur from the very early stage to the early age (a few minutes to about 3 days) characteristic of ultra-fast hardened concrete, including identification of main factors and examination of related physical properties. This study focuses on the cracks that occur in the joint repair part of the expansion and contraction equipment among the uses of ultra-fast hardening concrete. The purpose of this study is to clarify the causes of cracks in ultra-fast-hardened concrete, focusing on cracks that occur in the joint repair part of the expansion device.
It has been confirmed that the cracks that occur in the joint repair part of the expansion device are divided into two periods: cracks that occur within one day and cracks that occur after three days.
It is considered that the cause of the cracks that occur within one day is a phenomenon similar to the settlement caused by bleeding due to the self-shrinkage of the super-hard concrete near the guide plate. The super-hard concrete immediately above the induction plate has a different amount of settlement from its surroundings due to thin cover, and a tensile force is generated at the stage of hardening shrinkage.
It was thought that the cause of the cracks occurring after 3 days was due to the restraint of the ultra-fast hardening concrete being restrained by the reinforcing steel embedded in the joint repair part of the expansion and contraction device. I couldn't. Since the shrinkage behavior of the self-shrinkage during the observation of the cracks hardly changed, it is probable that the binding force required for the occurrence of the crack did not appear.