Abstract:
Steel fiber for application in concrete structural and nonstructural members
studied more than 50 years. Despite its renowned improving effect in controlling
microcracks and ductility that is at large dependent on its post cracking residual
strength and toughness, application in construction works yet not as expected.
The reason for such discrepancy is the lack of in-depth experimental research,
which in turn lacks provision in design code and experimental procedures.
Meanwhile, research emerges with the idea of using wasted tyre as a
replacement of industrial steel fiber in an objective both to improve the concrete
behavior and sustain the huge environmental waste extracted from the tyre. As
a result, despite its limitation in addressing essential areas, recycled steel fiber
that is extracted from waste tyre shows comparable improvement as that of the
usual steel fibers in concrete members.
This thesis work, therefore, tries to shed some light on the aspect of
improvements and applicability of recycled steel fiber in plain and or
conventionally reinforced concrete members that are exposed to twisting
action. Besides of identifying the failure patterns and overall behaviors that it
avails in concrete, it is also the major purpose of the thesis work to sustain the
environment from the huge burden of wasted tyres that is prohibited from landfill
disposal because of its nondegradable nature, by making it as an alternative
construction material.
With this intent in mind, a torsional test setup was prepared for a total of 28
beams from which 14 beams are plain concrete and another 14 for
conventionally reinforced concrete beams with recycled steel fibers including
control plain and reinforced beams for comparison purposes. The recycled steel
fibers were produced from a controlled burning process of collected ousted
waste tyres with a length of 25 mm and 50 mm having a 0.87 mm diameter. To
identify the effect of the volume fraction of the fiber, three volume fractions
namely 0.5%, 1.0%, and 1.5% were prepared. Concrete grade C-25/30 were
selected and mix proportioning was also made. Sufficient characterization of its
ingredient according to standards that include the recycled steel fiber was done.
The test revealed that up to 131.43% and 45.33% improvement in the ductility
and torsional strength respectively for the fiber length of 50 mm and a
volumetric percentage of 1.5% in the reinforced concrete samples when
compared to the control samples. In addition, a multi cracking behavior
attributed to the crack arresting performance of recycled steel fiber was also
observed for plain and reinforced samples. The result is significant for the
applicability of steel fiber as an alternative construction material in any concrete
construction works where torsional stress is predominant.