Date of Award

8-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Civil Engineering

Advisor

Schiff, Dr. Scott D

Committee Member

Rangaraju , Dr. Prasad R

Abstract

The use of prefabricated elements in the construction of highway bridges has been a common practice in the United States since 1950s. Precast concrete adjacent box beam girder bridges are quite popular given that the precast elements not only have structural capacity to span across the supports, but also form the bridge deck. 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 design for new replacement bridges. It was found that the stressed and non-stressed embedded reinforcements were severely corroded due 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 shear key. The primary objective of this research is to find an easy and reliable technique to detect the initiation of corrosion in embedded rebar with minimal disturbance to the moving traffic and to investigate the condition of the rebar (active or passive with respect to corrosion) embedded in Ultra High Performance Fiber Reinforced Concrete (UHPFRC) so that precautionary measures and maintenance can be applied before the failure of more in-service bridges. The experimental investigation considered three different samples; ASTM modified G 109 samples (laboratory samples) which served as a control type specimen and large uncracked and cracked specimens (field samples) which served as an actual prototype of a bridge deck. These samples were exposed to 3% of NaCl solution in the wet condition for duration of two weeks in alternate cycles of wet and dry period to accelerate the corrosion process. Half-cell potential (HCP) tests and linear polarization resistance (LPR) tests were carried out on all the samples. HCP test was able to detect the accurate location of corrosion by measuring the corrosion potential in the rebar and LPR test was able to confirm the active or passive state of the rebar by measuring the corrosion current in the rebar. The results of both these tests were validated by observing the physical condition of the rebar which were obtained from cores extracted from each sample types. It was found that rebar were mainly corroded at the interface of the joints between two different materials and areas of the samples which were cracked from the bottom in case of cracked samples. The corrosion of rebar was most prominently observed in the UHPFRC with PVA fibers even at places without joints and cracks. More intensive investigation is needed which will require more time and applications of more detail electro-chemical techniques to arrive at a more confident conclusion.

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