Evaluation of Durability and Corrosion Behavior of Ultra-High Performance Concrete for use in Bridge Connections and Repair
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Ultra-high performance concrete (UHPC) is one of the new, cutting edge concepts in the world of concrete. Boasting significantly higher compressive and tensile strengths, longer service life, and significantly increased durability, UHPC has a considerable level of appeal over conventional concrete mix designs. This result is accomplished through three main changes to the conventional concrete mix design: an extremely low water-to-cementitious material ratio, elimination of coarse aggregate to allow for dense particle packing, and the addition of steel fibers to significantly increase tensile strength. Unfortunately, these additional advantages come at a significant cost. All commercial UHPC mixtures currently on the market are close to 20 times the price of a traditional concrete mix, pricing most people out of the UHPC market. The Oklahoma Department of Transportation (ODOT), however, is hopeful and looking for a way to be able to use UHPC for both full and partial bridge deck repairs. Currently, the University of Oklahoma has completed extensive research into developing their own nonproprietaryUHPC mix, titled “J3”, and found it to be sufficient for all strength and bonding requirements. Still, there is need for research on the durability of J3 before it can be utilized in the field. Quantifying the durability of J3 in comparison to conventional concrete (ODOT class AA), as well as commercially available UHPC (Ductal®), was the primary goal of this study. Testing was broken up into two parts: durability and corrosion. Durability testing included freeze-thaw resistance in accordance with ASTM C666, scaling resistance in accordance with ASTM C672, and chloride ion penetration in accordance with ASTM C1202. Corrosion testing included both small-scale specimen testing to focus solely on the response of each of the different concrete mixtures due to the “Halo Effect”, as well as large-scale specimen testing on previously corroded slabs (provided by ODOT) to analyze the overall impact of using different concrete mixtures to repair existing concrete structures with previously corroded steel rebar. Durability results for J3 included a Relative Dynamic Modulus (RDM) value of 103% after 350 freeze-thaw cycles, a visual rating of 0 after 50 scaling cycles, and an average chloride penetration rating of very low and negligible at 28 and 90 days, respectively. Corrosion testing resulted in minimal corrosion of steel reinforcing bars in both the small- and large-scale corrosion specimens. Additionally, significant surface corrosion occurred along the joint of the large-scale Ductal® specimen, which was not experienced by the J3 specimen, proving a superior response to the Halo Effect and overall corrosive attack. The results of this study show J3 to have exceptional durability properties and corrosion resistance, making it ready for trial use as a bridge deck or bridge girder repair material in the field.
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