I-129 Missouri River Bridge Deck Condition Assessment Using Non-Destructive Testing Methods RB20-011, November 2012

Field testing using various non-destructive testing (NDT) methods was performed on the reinforced concrete deck of the I-129 Bridge over the Missouri River in Sioux City, Iowa to provide a basis for comparing the NDT techniques and characterizing the current condition of the deck. The NDT techniques employed included visual inspections and sounding, infrared (IR) thermography, ground penetrating radar (GPR), impact echo (IE), and half-cell potential testing. The actual damage in the deck that was used to evaluate the NDT methods was estimated based on the mechanical sounding surveys, with core sampling to confirm these findings. In addition to confirming the NDT testing, core samples were also collected to determine chloride concentrations through the deck thickness. Based on this data and extensive measurements of concrete cover depths obtained using GPR, service life predictions were developed using a statistical model built on a finite difference-based approach for modeling chloride movement through the multi-layer deck of this bridge, which included a low-slump concrete overlay. Delaminations and spalls were observed in 1 to 2 percent of the deck top surface area; this damage was concentrated around transverse cracks and was typically caused by chloride-induced corrosion of the reinforcing steel. The low-slump overlay has effectively protected the reinforcing steel in the deck from chloride infiltration away from cracks, and service life analysis suggests that the service life extension provided by the highly impermeable low-slump concrete may be as high as 80 years when compared to typical bridge deck concrete alone. Repairs for this deck should focus on preventing further chloride ingress at cracked regions and on repairing existing damage. None of the survey techniques employed was wholly accurate. Aside from visual and sounding techniques, the two most accurate techniques, as applied to this bridge, were IE and IR thermography. IE testing was sensitive to misidentifying delaminations, in part due to the epoxy injection work performed previously on this bridge deck. IR thermography is inherently dependent on conducive weather, but was also adversely affected by epoxy residue on the deck top surface