Title:
Influence of Cracks on Corrosion Initiation of Corrosion Resistant Reinforcement
Author(s):
Soundar Sriram G. Balakumaran, Michael C. Brown and Richard E. Weyers
Publication:
Web Session
Volume:
ws_S18_InfluenceofCracksCorrosion_Balakumaran.pdf
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
11/16/2018
Abstract:
Cracking of bridge deck concrete remains an important issue relative to bridge deck durability. Cracks may allow an increased rate of ingress of chlorides that result in premature corrosion of the reinforcing steel and subsequent spalling of the deck concrete. It is generally understood that the service lives of bridge decks are affected by concrete cracking; however, to what degree is the question that needs to be addressed. Crack repairs can be expensive and only a few state transportation agencies have developed effective decision-making tools to support engineering decisions about whether and how to repair cracks in bridges. This paper presents quantified influences of cracks on the corrosion initiation in bridge deck reinforcing steel built with different concrete mixtures (containing ordinary Portland cement (OPC) with or without supplemental cementing materials (SCM)) and with different reinforcement types, such as black steel or corrosion resistant steel (CRR). To understand the influence of cracks on corrosion, a total of 38 Virginia highway bridges were selected on the basis of environmental exposure, geographic location, traffic conditions and construction era, where 10 decks were built of 0.47 w/c OPC concrete with black steel between 1968 and 1971, and 28 decks were built of 0.45 w/c concrete with epoxy-coated reinforcement between 1984 and 1991. Of the newer 28 decks, 11 had OPC concrete with SCM (fly ash or slag). This research study included field surveying, sampling, and extensive data collection from the 38 highway bridge decks. In addition, laboratory study of the collected concrete samples was conducted to understand the material properties as well as to determine the chloride contents. Statistical methods were used to analyze the collected data and to form regression models for prediction. The increase in chloride diffusion through cracks when compared to corresponding uncracked locations was found to be statistically significant. No strong correlation was found between surface crack widths and chloride diffusion; however, significant correlation was identified between crack depths and chloride diffusion. Time to corrosion initiation was estimated using a probabilistic chloride diffusion model based on Fick’s Second Law of Diffusion to understand the effects of cracks on the corrosion durability of concrete bridge decks built with black steel and different concrete mixtures. Estimated time for corrosion initiation in the decks built with SCM was significantly higher than the decks with OPC, but only if no cracks were present. The presence of cracks adversely affected the time for corrosion initiation in SCM concrete significantly more than OPC. Times to corrosion initiation of CRR that are used commonly in Virginia, specifically ASTM A1035 (VDOT Class I reinforcement) and ASTM A955 (VDOT Class III reinforcement), were estimated and they were shown to be considerably more durable as compared to the black steel reinforcement.