ABSTRACT
The shear strength of palm-kernel-fibre-reinforced self
compacting concrete (SCC) was investigated by experimental means. The SCC with
palm kernel fibre were cast without web reinforcement. An experimental
programme was designed for twenty fibre reinforced SCC beams incorporating
bottom longitudinal steel bars. The beams were simply supported and subjected
to 4 – point monotonic and cyclic loading tests. The variable parameters used
were two different nominal coarse aggregate sizes 10 mm and 20 mm and different
amounts of fibre reinforcements; 0, 0.25, 0.5 ,0.75 and 1 percentages by weight
of cement. With the beams subject to loading, crack patterns were marked and
cracking and ultimate loads were recorded. The deflection at all load points
were also recorded. Test results indicated that the cracking behaviour with the
addition of fibre was more effective in 10 mm nominal coarse aggregate size
beams than the 20 mm nominal coarse aggregate size beams. This was because all
the 10 mm nominal coarse aggregate size beams had the crack widths under
service loads less than 0.3 mm. On the other hand, some of the 20 mm nominal
coarse aggregate size beams recorded crack widths greater than 0.3 mm under
monotonic and cyclic loading. The shear strength of the 10 mm nominal coarse
aggregate size beams were observed to be more than the 20 mm nominal coarse
aggregate size beams. In terms of the failure modes, all the beams, with the
exception of one beam which failed by crushing at the support, failed by shear
failure mode.
CHAPTER 1: INTRODUCTION
1.1 Background of Study
The Egyptians in 3000 BC built from
mudbricks, and built pyramids from lime and gypsum mortar. Following the
production of Portland cement in 1824 by Joseph Aspdin, the materials used to
produce concrete have undergone various improvements till today. Different
types of concrete have been studied to provide better understanding of the
concrete behaviour and impact on structural performance. Following the
reduction in the number of skilled workers in Japan in the 1980’s,
self-compacting concrete (SCC), which is a self-flowing concrete that achieves
compaction under its own weight without any form of vibration was developed.
Primarily, SCC is obtained by increasing the fine aggregate content in place of
the coarse aggregate to allow for easy movement of aggregates which improves
the flow of the concrete. Consequently, there is a reduction in the aggregate
interlock of the self – compacting concrete. The main shear resistance
mechanisms include the compressive strength in the uncracked concrete, the
aggregate interlock and dowel action of the longitudinal reinforcement (Taylor,
1974). Since there is reduction in the aggregate interlock which contributes to
the shear resistance mechanism of concrete, the study into the shear behaviour
of SCC is warranted. Previous researchers, such as Hassan et al., (2008) and
(2010) and Lachemi et al., (2005), investigated the effect of shear behaviour
of SCC considering the coarse aggregate content and the type of concrete. They
found that the shear strength of normal concrete beams was higher than the SCC
beams. Hence, current research efforts (Hassan et al., 2010; Safan, 2012;
Biolzi et al., 2014) on ways of improving the shear strength of SCC,
investigate the impact of type of coarse aggregates used, the variations in
sizes and the optimum proportions to be used for design. Others (Fritih et al.,
2013), have also advocated the inclusion of fibres to improve upon cracking
behaviour and ductility.
Code-conforming empirical models
for estimating nominal shear capacities of reinforced structural members (CSA,
2004) emphasizes that the maximum coarse aggregate size may be a significant
contributor to the shear strength. More so, research efforts (Lachemi et al.,
2005; Hassan et al., 2013) have shown that there is a positive correlation
between aggregate size and shear strength. The inclusion of fibre has been
found in normal concrete to improve cracking behaviour and mechanical
properties of concrete (Di Prisco et al., 2000; Meda et al., 2005). The fibre
improves cracking behaviour by transferring tensile stresses in the concrete
across cracked sections, and delays the crack propagation. The use of fibre in
concrete is not a new practice as horse hair and straw were used to reinforce
mortar and mudbricks in the prehistoric years. Fibre-reinforced concrete gained
attention in the 20th Century as different materials were used as fibre
reinforcement which included steel, glass, synthetic and natural fibre. Among
these types of fibres, steel fibre is the most beneficial in terms of improving
structural performance of reinforced concrete (Fritih et al., 2013). A typical
example is the work of Furlan et al., (1997), which evaluated the cracking
behaviour of steel and polypropylene fibres as used in normal concrete for improving
cracking behaviour.
However, a major disadvantage is
the rusting of the steel fibre and as such other natural occurring fibres (oil
palm, jute) may be better alternatives in terms of improving and maintaining
typical mechanical properties such as compressive and flexural strength of
concrete (Olaoye et al., 2013). However, structural performance metrics mainly
shear strength has been found to be inadequate for reinforced SCC members.
(Hassan et al., 2008). The current study sought to advance knowledge in the
shear behaviour of reinforced SCC beams under
monotonic and cyclic loading. Parameters investigated are the nominal size of
coarse aggregates and fibre.
1.2 Justification for Study
The use of SCC in large scale
construction projects can be deemed to be beneficial due to a significant
reduction in the cost of labor. In addition, since its usage does not require
any form of mechanical vibration, it becomes advantageous in situations where
highly dense concrete is a crucial requirement. Natural fibre from palm kernel
was used as a result of its abundance and the current situation of it being
used as a waste material in Ghana.
1.3 Objectives
The objective of this study was to
investigate the shear strength of palm-kernel-fibre-reinforced SCC. The
specific objectives were:
To determine the impact of the
different sizes of coarse aggregates on shear behaviour in SCC
To determine the impact of palm
kernel fibre as fibre reinforcement on cracking behaviour of SCC
To determine the variation in
structural performance of SCC under monotonic and cyclic loading.
1.4 Organization of Thesis
The thesis consists of five
chapters. Chapter 1 gives the general introduction, the objectives of the study,
and the thesis organization. Chapter 2, presents literature on the shear
behaviour of SCC. Chapter 3 is the methodology. It gives the details of the
tested beams, test variables, properties
of the material used, concrete mix design, mixing and casting, loading
arrangement, testing and measurement. Chapter 4 presents the test results and
discussions. It gives description of the crack patterns and modes of failure of
the tested beams, including the effect of test variables, and test results
including deflections, cracking and ultimate shear strengths showing the effect
of test variables on measured values. Chapter 5 presents conclusions on the
current study and recommendations for future studies.
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