Deterioration of bridges can often be related to poor performance of longitudinal connections or transverse deck joints, which can be more frequent when precast panels are used for accelerated bridge construction. Ultra-high performance concrete (UHPC) is a relatively recent advancement in cementitious composite materials with mechanical and durability properties far exceeding those of conventional concrete. It combines a high percentage of steel fibers with an optimized gradation of granular constituents, resulting in a compressive strength in excess of 22 ksi, a high post-cracking tensile strength, and exceptional durability. The short reinforcing bar development lengths and exceptional durability provided by UHPC lead to great potential for use in bridge deck joints, other applications for accelerated bridge construction, and as a repair material. The long-term benefits of using UHPC in a number of applications are evident, but commercially available proprietary mixture formulations are very expensive and mix design using local materials is much more complicated than for conventional concrete. The material characteristics, complicated mix design, and need for specialized mixing procedures require detailed specifications and quality control testing currently not included in most states’ standard specifications. Guidance for UHPC produced with local materials that can achieve the necessary mechanical properties and durability for use in bridge component connections is needed to provide additional options for DOTs.
All ABC-UTC partner institutions are considering the use of UHPC for bridge deck joints and a number of other applications, but coordinated efforts are needed to understand the repeatability and impact of locally available materials on performance of non-proprietary UHPC mixture formulations. A mix design developed in one part of the country may not directly translate to another region of the country if the constituent materials used for the mix are not exactly the same. Examination of material properties for UHPC made with constituent materials from different regions is needed to provide guidance applicable for the entire United States. Furthermore, steel fibers are typically the most expensive component of the UHPC mix and also have a significant impact on structural behavior of UHPC. A more thorough understanding of the impact of different fiber contents on non-proprietary UHPC performance could allow for different mix designs with an optimum fiber content tailored to properties required for specific applications.
The primary objective of the project is to develop guidance for an “ABC-UTC Non-Proprietary UHPC Mix” design made with local materials that can achieve the necessary mechanical properties and durability for use in bridge component connections, thereby providing an additional option for DOTs. The combined efforts of the partner institutions will lead to more significant results than could be obtained by any of the institutions working individually.
This project coordinates the efforts of researchers at the five ABC-UTC partner institutions, with a primary focus on mix design, to investigate material properties, bond strength, shear strength, durability, and full-scale structural performance of non-proprietary UHPC developed by the partner institutions. The project includes extensive material property testing on the final “ABC-UTC Non-Proprietary UHPC Mix” developed by the OU team including all material property tests recommended by FHWA for qualification of UHPC. Reinforcing bar bond and development length tests will be conducted for different bar diameters and fiber contents to develop a relationship between reinforcing bar development length, bar diameter, and fiber content. Durability testing will be performed on composite UHPC/conventional concrete specimens to provide a better understanding of the durability of the UHPC/conventional concrete interface. The other partner institutions will examine shear behavior, full-scale joint behavior, and durability of the “ABC-UTC Non-Proprietary UHPC Mix.” Collaboration with the other ABC-UTC institutions will allow for testing the effects of local materials on performance of the “ABC-UTC Non-Proprietary UHPC Mix” and development of training materials. The project includes the following tasks:
- Task 1 – Comparison of Local Materials Used in Mix Designs
- Effects of UHPC constituent materials locally available to each partner institution and fiber content on behavior of the “ABC-UTC Non-Proprietary UHPC Mix” will be considered using material property tests recommended by FHWA for qualification of UHPC mix designs. Mixtures will be tested with 0%, 1.0%, 2.0%, 4.0% and 6.0% fibers by volume. Locally available constituent materials will be shared between the five ABC-UTC institutions to examine the effects of local materials on performance of the “ABC-UTC Non-Proprietary UHPC Mix.”
- Task 2 – Evaluation of Reinforcing Bar Development Length in UHPC
- Reinforcing bar pullout bond tests and beam splice specimen tests will be conducted to examine the development length of reinforcing bars cast in the “ABC-UTC Non-Proprietary UHPC Mix” using local materials with 1.0%, 2.0%, 4.0% and 6.0% fibers by volume. Reinforcing bar development length will be examined for No. 3, No. 5, and No. 8 reinforcing bars.
- Task 3 – UHPC Durability Property Testing
- Freeze-thaw testing will be conducted on composite UHPC/conventional concrete specimens with 1.0%, 2.0%, 4.0% and 6.0% fiber by volume and the results compared to those for solid specimens.
- Task 4 – Short Course Development
- Materials required for teaching a short course focused on development and use of non-proprietary UHPC will be developed incorporating the results of the project. These materials will include presentation slides, physical models and demonstrations, a plan for limited laboratory testing, and assessment exercises. The PI will teach the course once near the end of the project, but the materials will be designed such that it can be taught for DOTs and other stakeholders after completion of the project as needed.
- Task 5 – Technology Transfer Workshop
- A technology transfer workshop will be held during the fourth-quarter of the project to share performance of the “ABC-UTC Non-Proprietary UHPC Mix” with the ABC-UTC stakeholders. It will be coordinated by OU, but will involve presentations by each partner institution.
- Task 6 – Assembling Reports and “Guide for ABC-UTC Non-Proprietary UHPC”
- Quarterly progress reports will be submitted and a final report will be provided at the end of the project year. A “Guide for ABC-UTC Non-Proprietary UHPC” will be developed incorporating the results of research performed by all partner institutions and described in individual reports submitted to ABC-UTC as part of companion projects by partner universities.
Principal Investigator: Dr. Royce W. Floyd
Co-Principal Investigators: Dr. Jeffery S. Volz, Dr. Musharraf Zaman
Research Assistants: Yana Dyachkova, Cole Walker, Stephen Roswurm, Trevor Looney