Date of Award

May 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Committee Member

Amir Poursaee

Committee Member

Thomas Cousins

Committee Member

Qiushi Chen

Abstract

Based on years of experience with reinforced concrete bridge decks it is known that durability can be impacted severely by cracking. Cracks threaten durability by allowing deleterious ions, water, and oxygen to penetrate concrete and reach the reinforcement, and thus accelerate corrosion. Chloride-induced corrosion is widely accepted as one of the most common degradation factors in reinforced concrete structures. Three main objectives will be made in this study regarding the effect of concrete cracking on the corrosion steel reinforcement.

First, an experimental method was developed for evaluating corrosion behavior of steel reinforcement bars in cracked concrete members. In this stage, a reinforced concrete beam specimen of (23.5 cm (9.25 in.) deep x 7.6 cm (3 in.) wide x 81.3 cm (32 in.) long) was developed and implemented. Three nominal crack widths of 0.1, 0.3, and 0.7mm (0.004, 0.012, and 0.028 in) as well as uncracked beams were investigated in this program. The specimens were designed to be portable by hand, have single flexural cracks, have adjustable crack size, receive cracks without the use of specialized equipment, and allow for multiple electrochemical and physical observations.

In the second stage of this study, the effect of crack width on corrosion initiation and propagation was evaluated. The specimens developed for the first stage were subjected 3% wt NaCl solution in two weeks to wet/dry cycles. This stage of the experiment lasted for 550 days, after which some of cracked specimens were repaired and a third stage of study was run for another 200 days. The total duration of both stages was 750 days. In stage three of study, two repair materials (one epoxy and one nitrite based corrosion inhibitor) were used in three different applications: repair using epoxy only, mix of inhibitor and epoxy, and, finally, inject corrosion inhibitor into crack then seal the crack with epoxy. Corrosion data were collected periodically throughout the 750 days using three techniques: half-cell potential (HCP), linear polarization resistance, and potentio-dyamic polarization. In addition some of the specimens were autopsied and visually inspection after 550 days of exposure.

In general more severe corrosion was noted in the steel in specimens of width of 0.7 mm (0.028 in) than steel in specimens with 0.3 mm (0.012 in) width. Corrosion activity in the 0.3mm and 0.7mm crack specimens remained fairly constant prior to repair. However, the corrosion activity in specimens with 0.1 mm (0.004 in) crack opening slowed over course of the experiment. The value of measured potential from HCP was significantly affected by the location of measurement with respect to the location of the crack. HCP measurements were found to be 50% less if they were taken 7.5 in. away from the crack. In terms of repair effect on the corrosion of reinforcement, the results showed that each of the repair techniques significantly reduced the corrosion activity. After repair the effect of crack size on corrosion activity was marginal. In addition, the repair efficiency was lessened by the use of inhibitor. Inhibitors have been shown effective by other researchers as preventative measures, but the current work shows that they were not an effective treatment when cracking and corrosion have been ongoing.

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