SHEAR BEHAVIOUR OF SELF COMPACTING CONCRETE BEAMS REINFORCED WITH PALM KERNEL FIBRE

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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Item Type: Ghanaian Postgraduate Material  |  Attribute: 91 pages  |  Chapters: 1-5
Format: MS Word  |  Price: GH50  |  Delivery: Within 30Mins.
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