Investigation of Cracks Observed in Underwater Bridge Seal Structures and Crack Control by Means of Material Design

Abstract

A large number of cracks were observed in a bridge seal structure during an underwater inspection. The seal is 13.2 m long, 5.9 m wide, and 6.8 m deep and thus is considered mass concrete. The concrete mixture contains a 45% cement replacement with Class F fly ash. The seal is evaluated to identify the causes of cracking. The heat of hydration (HoH) and temperature rise are experimentally evaluated. Subsequently, a finite-element analysis model is developed using input from the experimental study. The modeling approach is validated with results from sizeable specimens. A coupled thermal-structural analysis is performed to evaluate the temperature-time history and extent of cracking. The results indicate internal temperature in the seal slightly exceeds the allowable temperature of 70°C, which is known for exposing concrete to the risk of delayed ettringite formation. The gradient temperature exceeds the allowable limit of 19.4°C, leading to increased tensile strain. A sensitivity analysis indicates that two mixtures that contain a 70% cement replacement with slag, metakaolin, and/or fly ash are recommended for reducing the internal temperature below 70°C. However, it is concluded that the differential temperature requirement (19.4°C) cannot be met by altering material designs alone. Therefore, active cooling is necessary to control temperature when placing underwater seal structures with a volume-to-surface-area ratio greater than 4.0.