Effect of fiber shape on mechanical behavior of steel fiber in fiber reinforced concrete FRC

Abstract

Fiber pull-out process is the main micro-mechanism that governs post-cracking behaviour of short steel fiber
reinforced concrete structural beams. A detailed analysis of the fiber pull-out process provides understanding
about the role of different micro-mechanisms involved in the pull-out process and leads to conclusions about the
optimal fiber shape as well as the optimal properties of the matrix. Different steel fiber shapes involve different
micro-mechanisms in the pull-out process. Initially fibers and the surrounding concrete matrix deform elastically.
The linear elastic behaviour of the fiber-matrix system is interrupted by interface debonding which occurs due to
overall weak bonding between the concrete matrix and the surface of the steel fiber. Shear crack propagates and
the interface debonding continues untill whole length of the fiber has parted from the surronding concrete matrix.
At that point the further applied pull-out load is resisted only by friction forces resulting from fiber sliding out of the
concrete matrix. In some cases, if steel fibers have sophisticated form (e.g., end hooks or corrugated form) , much
of the pull-out resistance can be achieved from straightening of the fibers. Straightening of steel fibers can only be
possible if the surrounding concrete matrix has sufficiently enough strength to resist stress concentration at fiber
edges. If surrounding concrete matrix is weak, the stress concentration causes failure of the brittle matrix and no
pull-out resistance is obtained. Concrete matrix failure (spalling) is more likely to happen for cases with larger fiber
diameters. This paper introduces experimental study relevant to impact of fiber shape on mechanical behavior of
steel fiber in fiber reinforced concrete FRC using three femouse steel fiber types and different cases of embedded
length into concrete matrix.