Latest Progress Report: November 2017 Progress Report
UHPC is increasingly used in novel ABC designs including bridge deck joints and concrete substructure applications. While it is generally accepted that bulk UHPC can provide enhanced corrosion durability due to its low permeability, many ABC applications of the material incorporate designs where reinforcing steel is embedded in both conventional concrete and UHPC. In these conditions, the dissimilar concrete environments may lead to enhanced corrosion conditions. Among the various material effects on long-term corrosion durability of reinforced concrete, material properties and characteristics such as electrical resistivity, internal moisture availability, oxygen diffusivity, and chloride diffusivity can enhance or mitigate corrosion development. Material considerations of the design such as physical bond and moisture and chemical transport at cold joints of conventional and UHPC can be important. Furthermore, electro-chemical considerations such as macro-cell coupling of steel electrodes, cathodic oxygen reduction efficiency of steel, and critical chloride threshold concentrations for steel should be addressed for ABC designs incorporating conventional and UHPC concretes.
The objectives of the research includes to:
- Differentiate relevant material properties including concrete resistivity, internal moisture presence, oxygen diffusivity, and chloride diffusivity for conventional concrete and UHPC in the various salt exposure conditions including ambient, 100%RH, and immersed conditions.
- Identify the extent of macrocell coupling of steel electrodes embedded in mixed conventional concrete and UHPC environments including the determining the significance of extended cathodes in either the conventional concrete or in UHPC.
- Identify possible aggravation of corrosion conditions due to the cold joint between conventional concrete and UHPC including various physical bond conditions and exposure environments.
- Identify the extent of chloride presence that may lead to premature degradation of steel and concrete of ABC designs incorporating dissimilar concrete presence.
The following tasks will be performed to achieve the project objective:
- Task 1 – Literature Review: A comprehensive literature review will be conducted in order to gather available information related to ABC designs for joints and repairs incorporating UHPC, the material performance of UHPC, corrosion of reinforcing steels at joints and repair applications, and relevant case studies of degradation of bridge joints and repairs utilizing dissimilar concrete materials.
- Task 2 – Comparison of Concrete Material Properties: Small scale lab samples made up of conventional concrete materials and UHPC will be created to identify relevant material properties to corrosion of reinforced concrete. Properties of interest include concrete resistivity, internal moisture presence, oxygen diffusivity, and chloride diffusivity for conventional concrete and UHPC in the various salt exposure conditions including ambient, 100%RH, and immersed conditions.
- Task 3 – Macrocell Coupling: Reinforced concrete prisms using mild steel rebar and cast with mixed conventional concrete with various levels of chloride concentration and UHPC will be instrumented such that microcell corrosion (measured by open-circuit potential and linear polarization resistance) and macrocell corrosion (measured by zero-resistance amperemeter) can be determined. Extended cathode conditions using a ladder-array of rebar electrode will be considered.
- Task 4 – Cold-Joint: Concrete prisms will be cast to include cold-joints with various techniques to improve physical bonding such as surface roughness, moisture content, and bonding agents. Samples from Task 3 may be used to supplement testing here. Sodium chloride will be introduced by conventional ponding or electrical migration techniques. Chloride penetration through the bulk concrete materials as well as at the cold joint will be measured to identify preferential transport. Carbonation effects can be measured by application of phenolphthalein on fractured concrete surfaces after demolition of the samples for autopsy. Electrical characteristics can be addressed as well.
- Task 5 – Chloride Threshold: The results of Tasks 2-4 will be analyzed to examine the extent of chloride presence that may lead to premature degradation. This information can be particularly useful for ABC designs for bridge repair utilizing differential concrete materials. For example, identification of critical residual chloride concentrations in the pre-existing concrete that can exacerbate corrosion after application of the ABC repair can be important to identify repair designs.
- Task 6 – Final Report: A final report will be prepared meeting the RITA requirements for UTC funded projects. The content of the report will contain a detailed summary of the results from the preceding tasks and a recommendation for future phases of the project, if necessary.
Principal Investigator: Kingsley Lau, Atorod Azizinamini, David Garber
Research Assistant: Mahsa Farzad, Bin Li