Ultra-high performance concrete (UHPC) has been used in different applications and was explored to be
used for precast elements; however, there was limited research and guidance on the connection between UHPC
elements. General test methods to evaluate interface strength (e.g., direct tension pulloff, shear pushoff) can be
used with the Mohr-Coulomb Friction Approach to determine the cohesion coefficient and coefficient of friction
typically used to estimate interface shear strength. The test program here sought to explore the bond behavior of
matchcast UHPC with various interface surface conditions, such as surface roughness (including smooth faces
cast on plywood formwork, roughened surfaces created by casting on form liners) and exposed steel fibers at the
interface (created by the use of paste retarders) in order to inform design provisions for matchcast UHPC. The
effect of pre-corroded steel fibers and the surface wetting conditions were considered as well. Trends in interface
shear behavior associated with surface conditions were identified. The most evident outcome from testing was
that the presence of exposed steel fibers provided improved performance relative to only roughened surfaces.
Roughened interfaces can improve the friction of the interface, but the presence of the exposed fibers improved
both cohesive strength and provided improvement to the post-crack tensile strength. Additionally, there was
improved cohesive bonding when prolonged wetting by burlap was made. Extended term ponding had reduced
performance. Cohesion coefficient and friction factors for the various test conditions were assessed. Modification
to interface shear strength provisions to include the effect of wetting conditions on cohesion was presented. The
experimental work provided practical experiences that were translated into considerations for construction.

Infrastructure Assets: Bridge, Highway Assets
Resource Types: Research Report
Capabilities: Tools & Technology
Management Processes: Performance Based Planning & Programming