Corrosion Activity in Precast Concrete Elements and Cementitious Closure Pours

Abstract

The use of precast concrete elements in the construction of highway bridges has been a common practice in the United States since the 1950s. These bridges have generally performed well during the initial years after construction, but recent failures in Pennsylvania and Indiana have aroused a nationwide alarm to investigate the causes of failure and find solutions to repair these bridges or develop designs for new replacement bridges. It was found that the stressed and nonstressed embedded reinforcements were severely corroded owing to the ingress of chloride ions in the bridge deck through the surface cracks occurring within the closure pours (shear key) and at the interface of the joints between the precast elements and the closure pours. This paper addresses the corrosion activity of embedded steel bars within the closure pours. The experimental investigation consisted of two types of samples: uncracked and cracked slabs, containing regular precast concrete with different closure pours, namely, Quikrete with polyvinyl acetate (PVA) fibers, Ductal with PVA (polyvinyl alcohol) fibers, and Ductal with steel fibers. These specimens were exposed to 3% NaCl solution for the duration of 2 weeks in alternate cycles of wet and dry periods to accelerate the corrosion process. Electrochemical measurements along with the visual inspection revealed active corrosion at the interface of two materials, closure pour and precast concrete, regardless of the materials used in closure pours. This indicates that the bonding at the interface is not strong enough to prevent chloride penetration. Severe corrosion of reinforcing bars observed in cracked and uncracked specimens with the Ductal with PVA fibers as their closure pours, indicating rapid chloride transport through the PVA fibers.