Kosei Nakatake

Verification of the Physical Significance of Limit Crack Width in Reinforced Concrete Design

Takumi Shimomura

While current design codes for reinforced concrete (RC) structures primarily limit crack widths to suppress the initiation of steel reinforcement corrosion, the effectiveness of such limits on structural performance after corrosion has progressed remains unclear. It is hypothesized that smaller crack widths lead to slower, more uniform corrosion, resulting in a gradual decline in structural performance. Conversely, larger crack widths may cause severe localized corrosion, leading to a sudden loss of load-bearing capacity and ductility due to concentrated cross-sectional loss. This study experimentally investigates whether crack width control serves a significant role in mitigating structural degradation after the onset of corrosion. RC column specimens with various induced crack widths (w=0.12,0.25,0.60,and1.00mm) were subjected to accelerated electrolytic corrosion, followed by uniaxial tension tests to evaluate changes in their mechanical properties. Post-test, the reinforcement was extracted to perform detailed measurements of the axial corrosion distribution. The experimental results revealed that crack width significantly influences the spatial distribution of corrosion. Larger crack widths led to intensified corrosion directly beneath the cracks, increasing the non-uniformity of the reinforcement's cross-sectional area. The minimum cross-sectional area was identified as the dominant factor determining the member's load-bearing capacity. Notably, the specimen with an average crack width of w=0.25mm exhibited the lowest yield load. This occurred because, despite a low average value, localized large cracks within the specimen caused extreme section loss at specific points, which governed the overall strength. Although a specific threshold for a total collapse of structural performance was not identified, the results clearly demonstrate that wider cracks increase the risk of localized corrosion and catastrophic failure. These findings suggest that current crack width limits are vital not only for delaying corrosion initiation but also for preventing fatal localized defects and sudden drops in the deformation and load-bearing capacity of RC structures.