Guide Specification for Service Life Design of Highway Bridges

The performance with regard to chloride penetration of specimens made with three base compositions (supplementary cementitious materials: 20% fly ash, 20% fly ash + 8% silica fume, and 50% slag replacement by weight of cement), and water-to-cementitious ratios of 0.35, 0.41, or 0.47 were investigated here. In this investigation, laboratory experiments were carried out to study the correlation between electrical resistivity and non-steady state chloride ion migration coefficients (Dnssm) of concrete. NT Build 492 was used to determine chloride migration coefficients. Rapid migration tests and resistivity measurements were performed several times over two years, and the non-steady state migration coefficient (Dnssm) vs. resistivity values were correlated. Experimental results show that a good correlation was found between electrical resistivity and Dnssm. Based on the relationships developed from this investigation, it appears that the correlations are age and composition dependent.

Effect of w/cm and Composition on Correlations of Concrete Electrical Resistivity and Chloride Migration Coefficients

Useful corrosion damage forecast and risk evaluation methods for steel in concrete were developed starting about three decades ago and are now being used by increasing numbers of engineers. Much room for improvement remains, however, and the following non-exhaustive selection of issues merit special attention in the next generation of predictive models: incorporation of chloride binding in predicting chloride ion penetration to avoid overly conservative design, resolution by additional mechanistic understanding, and a wider database of uncertainty in the long-term evolution of chloride diffusivity in aged concrete, consideration of geometric chloride transport obstructions at the rebar level, and integration of initiation and propagation stage modeling, in particular accounting for the dependence of the chloride threshold on steel potential. Each feature is discussed with attention to the conservative or non-conservative result of its eventual incorporation, and with indication of practical means for its ...

Some Open Issues in Forecasting Corrosion Risk of Steel in Concrete

In the United States, ~30% of the ~600,000 highway bridges are labeled structurally deficient or functionally obsolete. Approximately 65% of the bridges in the United State are reinforced concrete, of which 40% are classified as structurally deficient or functionally obsolete. Many of these bridges are damaged due to chloride induced corrosion of the reinforcing steel. Structural members damaged by corrosion are typically repaired by removal of delaminated concrete and application of repair patches or jackets, but traditional repair methods have limitations due to the presence of incipient anodes after removal of the damaged concrete and replacement with chloride-free repair material. The development and application of effective repair methods and durable materials aiming at extending the lifetime of both existing and new structures is a critical issue. The enhanced mechanical and low permeability characteristics of ultra-high-performance concrete (UHPC) have been widely reported and make UHPC a material of interest for structural applications including rehabilitation of concrete structures. Application of UHPC can potentially result in both technical and economic advantages, including decreased reinforcement corrosion activity and an increase in service life. Because it is becoming more common to apply UHPC for rehabilitation to improve strength, improved protection against corrosion would serve as a complimentary benefit of this treatment. Experimental research on the corrosion durability of a proposed Accelerated Bridge Construction (ABC) solution to repair reinforced concrete elements in marine environments utilizing UHPC is presented in this report. 17.

https://rosap.ntl.bts.gov/view/dot/42748/dot_42748_DS1.pdf

Corrosion Durability of Reinforced Concrete Utilizing UHPC for ABC Applications

This investigation was performed to gain insight and assist in determining the long-term durability of reinforced concrete structures where the external chloride concentrations are different than those typically observed at the permanently immersed, tidal, and splash zones of partially immersed bridges. Insight into the diffusion properties of the concrete at these locations may lead to changes in the state’s policy on corrosion control of reinforced concrete structures. Structures at locations where the external chloride concentrations may have spatial, let alone time, variation are of interest. Additionally, at elevations above the splash zone, the amount of chlorides deposited would be lower, and the concrete close to the surface not saturated. Similarly, the section of structures that extend inland would be subjected to seawater spray and the concrete close to the surface would usually not be water saturated. The performance in regard to chloride penetration of specimens made with three base compositions (the supplementary cementitious materials were: 20% fly ash; 20% fly ash + 8% silica fume; and 50% slag), and water-to-cementitious ratios of 0.35, 0.41, or 0.47 were investigated here. Experiments investigated the diffusion of chloride ions into concrete samples that were exposed in scenarios that simulated the splash, tidal, and immersed portions of a marine structure, with the solution ranging from brackish water to 10% seawater, to seawater. Bulk diffusion experiments were conducted in solutions that contained 0.6%, 3%, and 16.5% NaCl. Rapid migration tests and resistivity measurements were also performed several times over two years, and the non-saturated migration coefficient vs. resistivity values were correlated. The apparent diffusion values from the bulk diffusion tests were correlated to corresponding equivalent resistivity values. Samples exposed for over 18 years, simulating tidal exposure were also part of this investigation. The field component investigated the chloride concentration as a function of elevation. Other experiments were conducted which involved controlling the degree of saturation and exposing a designated surface to finely ground salt. These apparent diffusion results were compared to the apparent diffusion results from specimens in which the chloride transport was due to natural marine atmosphere.

Diffusion vs. Concentration of Chloride Ions in Concrete

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Diffusion vs. Concentration of Chloride Ions in Concrete