Link to Latest Report: September 2020 Progress Report
Deterioration of bridge deck is a major issue for bridge owners. The need for cost-effective and durable rehabilitation methods has been documented by many researchers. The primary causes of deck deterioration include vehicle traffic, environmental effects (i.e. freeze-thaw, salt spray), and maintenance practices (snow plows, de-icing chemical treatments). Deterioration is featured by delamination, cracking, corrosion of reinforcing steel, abrasion, scaling, and other mechanisms.
UHPC overlays are gaining in popularity as a rehabilitation material due to the high compressive strength, higher tensile capacity compared to normal strength concrete, low permeability, and low shrinkage. UHPC also has a high early strength that allows for reduced lane closure and construction time. Current research has shown that UHPC bonds well to normal strength concrete, both in direct tension test and shear test. Shrinkage stresses do not appear to be a significant design concern either. UHPC has also been shown to mitigate corrosion activity.
Almost the entire research conducted on the use of UHPC for bridge deck repair has dealt with placing UHPC as a thin overlay over the top surface. In many instances the bottom of bridge deck also demands repair. This study will look at the use of UHPC for repair of bridge deck both from top and bottom and address other missing knowledge gaps, including the following:
- Determining the section capacity of the composite section between UHPC deck overlay, deck normal strength concrete, and bridge girder.
- Hydro-blasting and other methods of removing deteriorated concrete and surface preparation may result in a varying thickness of overlay to attain design grades. What is the effect of such variation on the overlay performance?
- How does the roughness of the interfacial surface between UHPC and normal strength concrete impact moment capacity? What is the optimum interfacial surface roughness?
- Overlays are typically considered for the top surface of the deck, especially in northern climates where de-icing salts are applied. Deterioration may also be found on the bottom of the deck, particularly in coastal areas where salt-spray occurs. Repair techniques should be developed for the deteriorated bottom face of bridge decks. Can shotcrete be used for repairing the bottom of bridge deck?
- UHPC mix designs typically contain 2% steel fibers, but some applications have been documented with different percentages. What is the effect of iterating steel fiber content?
- Fatigue or cyclic loading research is lacking. Only one study has been identified to date that included cyclic loading . More data is needed for the cyclic loading behavior on UHPC overlays.
- The higher tensile capacity of the UHPC may allow the material to be placed over expansion joints on a single span or as a link slab at intermediate supports. Covering the joints will reduce the level of maintenance needed for the joint. The advantages of reduced joint maintenance would be beneficial to bridge owners.
- What needs to be done to extend the use of shotcrete to the case of UHPC? Very recently limited work has been reported in Europe in shotcrete using UHPC by
The objective of this study is to investigate the various parameters involved in optimizing the design of UHPC overlays and to develop design and construction guidelines for UHPC overlays. The activities listed below will be directed to this objective.
An overview of the study tasks is given below.
- Task 1 – Literature Search
- In this task, a comprehensive literature review will be conducted. The researchers will continue the review of the development of the UHPC deck overlay for a better understanding of design challenges and issues.
- Task 2 – Material Level Testing
- In this task, testing of normal strength concrete/UHPC cylinders and flexural beams will be conducted. The testing will iterate various parameters such as thickness, roughness and, mix design. Static and cyclic loading will be performed on beam sections with various UHPC thickness, interfacial surface roughness coefficients, and mix designs. Load-deflection data will be obtained. Testing UHPC overlays on top and on the bottom of the beam sections will be conducted. This task will also examine material characteristics and application of UHPC using shotcrete.
- Task 3 – Numerical Modelling of Material Testing
- In this task, non-linear finite element models will be developed and calibrated to the results of the testing performed in Task 2. The elements modeling the interfacial surface between the normal strength concrete and UHPC will be carefully considered.
- Task 4 – Large Scale Level Testing
- In this task, testing of full-scale specimens will be conducted to validate the models and incorporate the parameters discussed above. It is envisioned that these test specimens will include zones of varying thickness of overlay, differing roughness at the interfacial surface, and debonded/delaminated sections. The selected specimen may be repaired using a combination of shotcrete and formwork.
- Task 5 – Numerical Modelling of Large Scale Testing
- In this task, finite element models will be developed and calibrated to the results of the testing performed in Task 4. Parametric studies will be conducted to expand the scope of the research topic.
- Task 6 – Final Report
- In this Task, a final report will be prepared to provide a methodology and design procedure.
Principal Investigator: Dr. Islam Mantawy
Consultant to Project: Dr. Atorod Azizinamini
Research Assistant: Morgan Dickinson