Civil Insight: A Technical Magazine Volume 2 | Page 47

CIVIL INSIGHT 2018
STUDENTS’ SECTION
47
COCONUT FIBER REINFORCED CONCRETE:
OVERVIEW AND FEASIBILITY IN NEPAL
Suraj Subedi
Student
BE in Civil Engineering
(4 th Year)
INTRODUCTION
CONCRETE
Concrete is a composite material which is a mixture of cement, fi ne aggregates, coarse aggregates, water and
admixture. The small stone and gravel (aggregate) on the reinforcement and the cement is the matrix that
cleave it together. Concrete has great strength under compression, but is weak under tension. The amount of
concrete produced and consumed by a nation annually indicates the development of the nation.
REINFORCED CONCRETE
Reinforced Concrete (RC) or commonly termed as Reinforced Cement Concrete (RCC) is a composite material
which is an improvement over Plain Cement Concrete. The relatively low tensile strength and ductility of the
concrete are counteracted by the addition of the reinforcements having higher tensile strength or ductility. The
reinforcing steel rods or bars absorb the tensile, shear, and sometimes the compressive stresses in any concrete
structure.
When the concrete begins to harden around the bars, we get a new composite material that works well in
either tension or compression. The concrete resists extrusion which provides compressive strength, while the
steel resists bending and stretching which provides tensile strength. In effect, reinforced concrete is using
one complex material inside another: concrete becomes the matrix while steel bars or wires provide the
reinforcement.
The steel bars are usually made from twisted strands with ridges on them that anchor them fi rmly inside the
concrete without any risk of slipping around inside it.
FIBER REINFORCED CONCRETE
Fiber Reinforced Concrete is a material consisting of a mixture of cement, mortar or concrete and dispersed
fi bers. The concept of using fi bers as secondary reinforcement is not new. Fibers have been used as reinforcement
since ancient times. In the 1900s, asbestos fi bers were used as secondary reinforcement in concrete mixture.
In the 1950s, the concept of composite materials was introduced and fi ber reinforced concrete was one of
the topics of interest. By the 1960s, steel, glass and synthetic fi bers such as polypropylene fi bers were used in
concrete. Research of new fi ber reinforced concrete still continues with the development in technology. Fibers
are typically used in concrete to control cracking due to plastic shrinkage and drying shrinkage. They also
reduce the permeability of concrete and thus reduce bleeding of water. Some fi bers usually produce greater
impact, scrape and shatter-resistance in concrete. Generally, fi bers do not increase the fl exural strength of
concrete and so it cannot replace moment-resisting or structural steel reinforcement. Some fi bers may actually
weaken the strength of concrete.
The bulk of fi bers added to a concrete mix is expressed as a percentage of the total volume of the composite
(concrete and fi bers), termed “volume fraction” (VF). VF typically ranges from 0.1% to 3%. The aspect ratio
(l/d) is calculated by dividing the length of fi ber (l) by its diameter (d). Fibers with a non-circular cross section
use an equivalent diameter for the calculation of aspect ratio. If the fi ber’s modulus of elasticity is more than
that of the matrix (concrete or mortar binder), they help carry the load by increasing the tensile strength of
the material. Increasing the aspect ratio of the fi ber usually segments the fl exural strength and toughness
of concrete. However, fi bers that are too long tend to “ball” in the mix and build workability problems. The
natural fi ber’s reinforced material which can be used in building materials are mainly those based on coconut,