Location

Leeds University, Leeds, UK

Event Website

https://engineering.leeds.ac.uk/info/201479/conferences/270/sixth_international_conference_on_durability_of_concrete_structures_icdcs2018

Keywords

Residual service life; prestressed concrete; corrosion; chloride threshold, diffusion coefficient, preventive maintenance

Abstract

Many pre-tensioned concrete (PTC) bridges are experiencing premature chloride-induced corrosion. Hence, it is crucial to estimate their residual service life and update it with newer data on a periodic basis - to plan for corrosionpreventionorcontrolmeasuresandensuresafetyofexistingbridges.Criticalchloridethreshold(Cl th) is one of the parameters necessary to estimate the corrosion initiation period. However, quantitative estimates on Clth for prestressing (PS) steel are not well-reported in literature. This paper presents experimental data on the Clth of PS steel, the chloride diffusion coefficient (Dcl), and surface chloride concentration (Cs) of concrete samples obtained from a PTC bridge girder in a coastal city in India. For estimation of Clth, 5 specimens were cast with PS steel wires embedded in ordinary Portland cement (OPC) mortar containing 30% of Class F fly ash (similar composition as that of the bridge girder). They were cured for 28 days and then subjected to cyclic wet-dry exposure using simulated concrete pore solution containing 3.5%sodiumchloride.(Linear polarization resistance (LPR) tests were performed at the end of each exposure cycle, corrosion initiation was detected using statistical methods, and Clth was determined). Using the determined Clth and Dcl, and other relevant parameters, the cumulative distribution functions of time to corrosion initiation was developed. It was found that the average time to corrosion initiation was about 40 years, whereas the structure was designed for 120 years. Also, it was estimated that the corrosion products will accumulate within the interstitial space between the 7 wires in a strand and will not flow through the concrete cover and reach the concrete surface (showing rust stains) until about 5% of strand is corroded (about 10 years). This indicates a dire need for regular data collection, updating the residual life estimates, which will help in developing corrosion prevention strategies for PTC structures.

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Residual Service Life Estimation and its Importance for Pretensioned Concrete (PTC) Bridges in Coastal Cities

Leeds University, Leeds, UK

Many pre-tensioned concrete (PTC) bridges are experiencing premature chloride-induced corrosion. Hence, it is crucial to estimate their residual service life and update it with newer data on a periodic basis - to plan for corrosionpreventionorcontrolmeasuresandensuresafetyofexistingbridges.Criticalchloridethreshold(Cl th) is one of the parameters necessary to estimate the corrosion initiation period. However, quantitative estimates on Clth for prestressing (PS) steel are not well-reported in literature. This paper presents experimental data on the Clth of PS steel, the chloride diffusion coefficient (Dcl), and surface chloride concentration (Cs) of concrete samples obtained from a PTC bridge girder in a coastal city in India. For estimation of Clth, 5 specimens were cast with PS steel wires embedded in ordinary Portland cement (OPC) mortar containing 30% of Class F fly ash (similar composition as that of the bridge girder). They were cured for 28 days and then subjected to cyclic wet-dry exposure using simulated concrete pore solution containing 3.5%sodiumchloride.(Linear polarization resistance (LPR) tests were performed at the end of each exposure cycle, corrosion initiation was detected using statistical methods, and Clth was determined). Using the determined Clth and Dcl, and other relevant parameters, the cumulative distribution functions of time to corrosion initiation was developed. It was found that the average time to corrosion initiation was about 40 years, whereas the structure was designed for 120 years. Also, it was estimated that the corrosion products will accumulate within the interstitial space between the 7 wires in a strand and will not flow through the concrete cover and reach the concrete surface (showing rust stains) until about 5% of strand is corroded (about 10 years). This indicates a dire need for regular data collection, updating the residual life estimates, which will help in developing corrosion prevention strategies for PTC structures.

https://docs.lib.purdue.edu/icdcs/2018/dsm/5