Development of Non-Proprietary UHPC Mix – Evaluation of the Shear Strength of UHPC

Link to Latest Report: June 2019 Progress Report

Background:

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, which makes it an ideal material for bridge deck joints and other connections. While considerable information has been developed about many characteristics of UHPC, information about shear behavior is sparse. This project investigates experimentally the behavior of UHPC mixes subject to a variety of stress states, focusing on shear.

The testing will be conducted in a special purpose panel testing machine that is capable of applying loads to a 2-D panel in any combination of shear, tension and compression. The variables to be investigated include the mix design, the fiber content and the stress states. The expected outcome is the data on which to base a constitutive model for shear behavior in UHPC in general, and in particular the non-proprietary UHPC materials being developed by the partner universities.

Objective:

The main objective of this project is to improve the understanding and address the lack of fundamental data pertaining to the shear behavior of UHPC elements. The experiments that will be conducted are intended to serve as benchmark experiments and provide the preliminary experimental evidence necessary to formulate general constitutive models for the shear response of UHPC.

Scope:

The proposed research will take advantage of a new wind-wave-current interaction testing facility at the University of Washington. This 18-m long by 1.2-m high by 0.9-m wide facility generates currents with a centrifugal pump that enables quasi-steady flow conditions at a maximum velocity of 1.0 m/s for at maximum depth or 2.0 m at half depth.  Many structures do not experience impact from the wave front of a tsunami; this facility can be used to model the accumulation of debris, and the effect of rising flows on bridges.

The following tasks will be performed to achieve the project objective:

  • Task 1 – Literature Review
    • Conduct a literature review to determine details of other test programs investigating multi-axial states of stress in UHPC.
  • Task 2 – Preparatory companion material tests
    • Conduct compression, tension and bond tests that will act as fore-runners of the companion materials tests that are planned (see Task 3) to accompany each shear panel test.
  • Task 3 – Conduct biaxial in-plane tests on UHPC panels, with different fiber contents. This experimental program will include:
    • One trial panel to verify that the planned methods for connecting the test panel to the loading system will prove effective with UHPC. (The UHPC is expected to have higher shear strength than that of conventional concrete and may require connections that are different and more robust).
    • One reference panel, made from the reference material, reinforced with the reference fiber content (probably 2%) under the reference loading regime (pure shear). The reference UHPC mix will be selected in the light of the materials testing conducted at ISU and OU.
    • Approximately five panels under different bi-axial stress states (e.g. tension + shear with proportional loading, constant tension + variable shear, etc.). This series will include at least one test to simulate a shear key in a panel joint to determine the relative effectiveness of a shear key vs a roughened plane surface.
    • Approximately two tests to investigate the effects of other fiber contents (e.g. 1% and ½%).
    • One panel to be determined.  The properties and testing regime to be decided the light of the prior tests conducted.
  • Task 4 – Data analysis.
    • The experimental data will be analyzed and preliminary constitutive model will be developed for shear stress-strain response of UHPC under biaxial loading. It should be noted that more extensive testing than is possible within this program will be necessary to optimize such a model.
  • Task 5 – Preparation of the Final Report.
    • Although the testing program is aimed at developing fundamental stress-strain data, the report will be prepared with end applications in mind. These include response to vertical shear stresses in the joint caused by wheel loads on deck panels or horizontal shear stresses caused by seismic action, as well as the future possibility of gravity shear stresses in a thin-walled UHPC girder.

Research Team:

Principal Investigator:  Dr. Paolo M. Calvi

Co-Principal Investigators: John Stanton

Research Assistant:  N/A