| dc.description.abstract | Sisal is a vegetable fibre extracted from the leaves of Agave Sisalana. The fibre is long, bold
and creamy white besides being exceptionally strong. It can be used for making agricultural
and parcelling twines of various kinds as well as ropes, sacks, carpets and upholstery.
Some research has been done to investigate the effects of sisal fibre reinforcement on base
materials such as ordinary portland cement paste, mortar and epoxy resin [1-3]. However
their results on strengths of sisal fibre reinforced epoxy resin composites lacked certain
features accompanying composite failure at high fibre volume fractions. Similarly rice husk
ash pozzolanic cement (RHAC) is a relatively new product in the Kenyan market, and not
much work has been done to investigate the strength aspects of its sisal fibre reinforced
composite. The wide scale use of any material however, requires among other things a
considerable understanding of its mechanical and physical characteristics. It is with this
objective in mind that an experimental programme was carried out on sisal fibre reinforced
RHAC mortar and epoxy resin. The results of this work were compared with theoretical
predictions. Based on the results suitable choices of fibre incorporation techniques, critical
fibre length, optimum and critical fibre volume fractions were identified. The results obtained
from sisallRHAC composites will be of considerable potential in such areas as housing
construction in rice growing developing countries. Components made from epoxy resin may
fmd extensive use in applications requiring high strength-to-weight ratio, artificial limbs,
liquid containers, bodies of domestic appliances and low strength structural members.
The primary purpose of this research was to study and evaluate the use of sisal as a
reinforcing fibre in the form of continuous longitudinally aligned and discontinuous
randomly aligned arrangements in RHAC mortar and epoxy resin matrices. The casting
process employed in composite production involved laying and curing. Principles of
continuum mechanics were used in the analysis of various strength aspects of the resulting
composites. The effects of fibre volume fractions, aspect ratios, reinforcing index and
alignments on the tensile strength, flexural strength, flexural toughness and modulus of
elasticity were investigated. In addition the fibre/matrix interfacial bond strength was
evaluated. Finally the occurrence of multiple matrix fracture (MMF) and fibre pull-out
phenomena were also studied. The mechanical properties of the resulting composites were
examined in direct tension, three point and four point bending tests.
(v)
It was found that the tensile and flexural strength characteristics of sisal/epoxy composites
improved with the increases in reinforcement volume fractions (Vr) from 0 to 45% Vf in continuous
parallel aligned fibres. However no effective reinforcement was observed in chopped sisal/epoxy
composites. Both chopped and continuous reinforcing fibres improved the strength and toughness
in sisallRHAC composites. Maximum ultimate strength values of 8.61 N/mm2 at 9.5% Vf and 3.64
N/mm2 at 9.0% Vf were obtained from flexural and direct tension tests respectively for continuous
parallel-aligned fibre reinforced composites. On the other hand chopped fibre composites gave
relatively lower strength values. In this category peak strengths values of 5.13 N/mm2 at 7.3% Vf
and 2.74 N/mm2 at 8.4% Vf were realised for the Modulus of Rupture and tensile strengths
respectively. The optimum fibre volume fractions in flexural loading occurred at 8.5% and 7.4% Vf
in the case of continuous and chopped fibre reinforcements respectively. However the stiffness of
the composites did not vary appreciably with increasing reinforcement levels.
Both the fibre/matrix interfacial bond strength and the average crack spacing decreased with fibre
additions in the composites. The average fibre/matrix interfacial bond strength computed for 63
continuous parallel aligned sisallRHAC specimens was found to be 0.139 N/mm2 while that of
discontinuous randomly aligned fibres was obtained as 0.121 N/mm2
• Increasing the reinforcement
volume fractions also increased the toughness and toughness indices. The study showed that only
the higher toughness index 110 is sensitive to fibre contents, while the lower toughness index Is
showed very little variation with the fibre volume fractions in the composite. Flexural toughness
has an inverse relationship to the water/cement (W/C) ratio. However the proportional relationship
between W/C and toughness index is not clear. The present results also showed that both the <-
toughness and toughness indices increased with curing age. Finally it was also noted that fibre
additions resulted" in a decreased composite density and a corresponding increase in the amount of
voids present in the composite.
Plain mortar specimens failed without any warning exhibiting a brittle failure, while the fibre
reinforced specimens had a slow ductile failure. Multiple matrix cracking was observed with fibre
pull-out taking place after large visible cracks had appeared. The composites were therefore able to
maintain some residual strength even at large displacements and thus continued to absorb energy
with increasing deformations even long after the/matrix had cracked. Fibres consequently allowed
the composites to retain some post-cracking strength hence withstanding deformations much
greater than could be sustained by the matrix alone. | en |
