Influence of Plastic Fibers on the Mechanical Properties of Concrete

The addition of plastic fibers to concrete enhances its tensile strength by approximately 30% to 60%. The compressive strength is either reduced or increased, but the overall effect is negligible. Plastic fibers also improve the flexural tensile strength and bond strength, reduce shrinkage and creep, and increase resistance to chloride penetration. Despite some limitations, such as poor bond and vulnerability to fire and sunlight, plastic fibers are a recommended reinforcement material due to their compactness, ease of pumping and placement, reduced shrinkage, and improved durability.

Behavior of Plastic Fibers in Concrete 1
BEHAVIOR OF PLASTIC FIBERS IN CONCRETE
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Behavior of Plastic Fibers in Concrete 2
Abstract
Fibers exist of very many types and often they are utilized in concrete purposefully to assist in
preventing microcracking which occurs as a result of shrinkage. The most common type of
fibers which are utilized are the polypropylene fibers. These microcracks should be avoided at all
costs since if they are not taken into keen attention they may end up in the growth of steeper
cracks due to the process of drying shrinkage. Theses steeper cracks enable the permeation of
destructive materials from the environment thus limiting the strength and lifespan of structures
which are concrete in nature (Singh, 2016, p. 643).
The main aim of this research is to determine the behavior of plastic fibers in concrete. Fibers
play a significant role in the prevention of deformations in concrete elements. Various roles
played by fibers in concrete have been explained. Besides, the benefits of plastic fibers over
other fibers for the reinforcement of concrete have also been presented. In conclusion, plastic
fiber offers the best characteristics in terms of the following factors and should, therefore, be
conventionally recommended.
Introduction
Various fields including science and construction industry have been greatly attracted by the Use
of plastic fibers to strengthen concrete as compared to other types of steel. This paper has
analytically presented the present state of information and technology of adopting plastic fibers
to reinforce concrete. A detailed review of the effects of plastic fibers on the fresh and hardened
concrete properties have also been covered in this paper (Ozel, 2009, p. 552).
Among the many reasons for the occurrence of cracks, ion concrete elements are the deformation
as a result of shrinkage. The concrete elements vary ranging from pavements, overlays and even

Behavior of Plastic Fibers in Concrete 3
slabs. Polypropylene fibers in most cases help to improve the cement based composites which
are more vulnerable to shrinkage. The deformations may be caused by very many factors such
as restrained shrinkage, autogenously and also increased composite resistance.
In the first 12 hours of concrete shrinkage, the plastic fibers reduce and lessen the presence of
cracks by harnessing the strength and capacity of the cement paste (Mertz, 2008, p. 844).
When these cracks are not controlled, the small tiny cracks formed due to the drying shrinkage
results in the growth of larger cracks. The fibers also help in reducing the width of the cracks
thereby preventing harmful substances from the environment from penetrating. Generally, the
control of cracks is vital for the advancement of more durable and long-lasting structures.
Literature review
Fiber Reinforced Concrete that contains a tough material enhances the structural integrity of the
concrete due to the uniformly distributed fibers. There are two Types of Fibers which include
the;
• Steel Fibers
• Synthetic Fibers- this includes the plastic fibers.
These Fibers are primarily used in concrete for the below purposes;
 For the prevention of cracking which forms as a result of both drying and plastic
shrinkage (béton, 2007, p. 322).
 Besides, the fibers help to enhance the robustness of the concrete.
 Fibers also help to limit the penetrability of the concrete and thereby lessening water
leakage during construction.

Behavior of Plastic Fibers in Concrete 4
Advantages of Fiber
Polypropylene and Nylon Fibers –these type of fibers are mostly applied due to
their property of improving the mixing cohesion and also the ability to pump over longer
distances. They also exhibit the property of increasing the resistance that results from
freeze-thaw or explosive palling during incidents of severe fire .for this reason, these
fibers have been internationally recommended since apart from offering protection to the
concrete it also helps to protect lives and property (Hensher, 2016, p. 985).
Steel Fibers- these type of fibers also are advantageous in terms of Improving
the structural strength of concrete and Reducing the size of the cracks by firmly holding
and in turn promoting its durability •nevertheless, steel fibers Improves abrasion
resistance and freeze-thaw resistance (Paramanantham, 2015, p. 548)
Role of fibers
The process of crack formation in concrete elements plays a key role since it constantly exposes
the structures to a high risk of corrosion. Theses crack lower the quality of the concrete,
therefore, affecting their durability and also their aesthetic value. Hence there is a need to
minimize the size of these cracks and more particularly this is achieved with the addition of
plastic fibers. There are various reasons behind the formation of these cracks including;
Fire damage, plastic shrinkage, freeze-thaw damage and also plastic settlement as discussed
below.

Behavior of Plastic Fibers in Concrete 5
Plastic shrinkage
These stakes place when the water present at the surface evaporates prior to the bleeding water
reaching the surface. The addition of the plastic fibers will help minimize the extent of the
shrinkage crack due to their property of flexibility and also ability to fit into form (Pielert, 2011,
p. 646).
Plastic settlement
This occurs when there is a high rate of bleeding and the presence of some resistance when
settling. The plastic fiber when added will help to fix this problem since they are uniformly
distributed and flexible thereby ionizing the resistance experienced (A.E. Naaman, 2014, p. 993).
Freeze-thaw damage
The addition of plastic fibers in concrete helps to limit the flow of water by inhibiting the flow of
water through the small nodes. This implies that there will be an improvement in cement
hydration and also a reduction of the water flow or leakage which results in the cracking (R.N.
Swamy, 2015, p. 763).
Fire damage
The presence of heat or fire creates penetrative ways into the concrete thereby disporting the
moisture which is present on the outer layer. These moisture vapors get back into the cold
interior parts and get reabsorbed. These vapours when accumulates increases the pressure rapidly
and eventually results into palling and concrete racks. The addition of plastic fibers releases the
vapor pressure into new voids thus reducing the extent of spalling (Antonio Nanni, 2014, p. 420).

Behavior of Plastic Fibers in Concrete 6
Properties of Plastic Fiber Reinforced Concrete
Prior to the mixing of concrete, certain variables that are adjusted to inhibit the fibers from
balling. These variables may include the fiber length, amount and design mix variables. Best
mixes typically will comprise of an increased volume of mortar as matched to the conventional
concrete mixes which are normally restricted between 100 and 200 to minimize difficulties that
may arise during construction. Conventionally, plastic fibers are randomly and uniformly
distributed in the concrete; nonetheless, to obtain greater strengths the concrete is placed such
that the fibers get lined up in the direction of applied stress
Below are some of the properties of the plastic fibers

Behavior of Plastic Fibers in Concrete 7
These fibers are applied in two ways i.e.
In thin sheet components where they provide the primary reinforcement and the volume content
of fiber is comparatively high such that it exceeds 5% purposefully to attain both solidification
and strengthening (Yin, 2017, p. 777).
The other way of applications is when the volume content is relatively low such that it less than
0.3% thereby providing the secondary reinforcement for specifically for crack control,
Effects of plastic fibers on concrete
Plastic fibers have various influences on both fresh and hardened concrete as discussed below

Behavior of Plastic Fibers in Concrete 8
Effects on Fresh Concrete
The workability of fresh concrete is normally determined by a parameter known as the slump
test. The value of the slump is influenced by the content of water and its absorption properties.
Also, it is attributed to the texture, shape and the surface characteristics of the components
forming the mixture. The addition of the plastic fibers to the concrete decreases these value
slowly. Thereby resulting in an increase in the bond and cohesiveness of fresh concrete.
The plastic fibers shear apart during the mixing of the components thus creating an
interconnection of the individual fibers and the fiber filaments. As a result of the large surface
area, the fibers mechanically anchor to the cement paste (Clarke, 2009, p. 877).
This mixture has a reduced rate of bleeding and aggregate settlement due to the firm holding of
the concrete by the plastic fibers. As a result of the high tensile strength of the plastic fibers,
early plastic shrinkage cracking is greatly managed by improving the tensile capacity of plain
concrete to provide resistance to the tensile stresses initiated by the typical volume changes.
Moreover, the fibers uniformly distribute these tensile tensions all over the concrete and with the
decrease in plastic shrinkage cracking, concrete cracks get reduced. In the event that shrinkage
cracks get formed, they get managed by the plastic fibers which reduce their size and width
(James Shackelford, 2007, p. 542).
Below is a table of the effect of the plastic fibers

Behavior of Plastic Fibers in Concrete 9
Effects on Hardened Concrete.
Plastic fibers do not have a significantly greater effect on the compressive strength or elastic
modulus but only on the tensile strength. As discussed below, the Addition of plastic fibers
intensifies the splitting of the tensile strength by approximately 30% to 60%.
Compressive strength
This is a vital factor in concrete since it determines other parameters such as the tension and
flexure among others. It is realized that the addition of plastic fibers will either reduce or
increases the compressive strength of concrete through the overall effect is always negligible.
Flexural tensile strength: it is observed that with an increase in the amount of the added
plastic fiber, the tensile strength increases (AL-GHAMDY, 2012, p. 763).
Bond strength:
Typically, the bond between the matrix and the fiber should be desirable and upon attaining the
strengthening critical fiber volume, multiple racking then gets easier to achieve. These multiple
cracks when loosely spaced reduces the possibility of harmful substances from penetrating. The

Behavior of Plastic Fibers in Concrete 10
plastic fibers offer High bond strength that helps to provide close crack spacing (Singh, 2016, p.
552).
Fracture Properties: the addition of fibers improves the failure behavior of high-strength
concrete.
Creep and shrinkage properties:
Fibers help to minimize the creep strain rate and also concrete shrinkage that is caused by the
removal of water from concrete during drying. Since the fibers do not shrink, they will be able to
delay the process of shrinkage thereby overall reducing the deformation (Jochen Bundschuh,
2010, p. 998).
Chloride penetration:
Apart from the improved mechanical properties, the addition of plastic fibers also reduces the
possibility of penetration by chemical substances such as chloride since the interfacial transition
zone in the direction perpendicular is blocked (Baoguo Han, 2017, p. 620).
Obstacles in Use of Plastic fibers
Despite the use of plastic fibers gaining popularity, there is still need to do some improvements.
Of significant note is the poor bond provided by some plastic fibers which provide a reduced
pull-out strength. Incidents of fire also may result in cracking of greater porosity. The plastic
fibers are also prone to destruction when exposing to too much sunlight and oxygen since they
do not have a well-designed protection system. Further, due to reduced elasticity as compared to
the cement matrix, the fibers sometimes acts as an initiator of the small cracks thus creating more
pores in the cement elements (Berga, 2011, p. 531).

Behavior of Plastic Fibers in Concrete 11
Evaluation Analysis
The recent design and construction of new buildings have taken into recognition the use of
plastic fibers for the purposes of controlling shrinkage cracking and deformation. The application
of these fibers is recommended for concrete structures as a result of the improved performances
and effective cost-benefit ratio. Below are some of the advantages that make the plastic fibers
recommendable for use in concrete structures (Mindess, 2014, p. 332).
 Plastic fibers are compact and easy to pump and place,
 Plastic fibers provides a safer working environment
 Plastic fibers also limit the rebound effect by improving the strength of wet concrete.
 Since the plastic fibers are entirely synthetic, chances of corrosion are greatly reduced.
 Plastic fibers also show enhanced impact resistance when compared to conventionally
reinforce brittle concrete (Gustavo J. Parra-Montesinos, 2012, p. 542).
 Besides, plastic fibers improves the abrasive resistance in concrete floors by regulating
the bleeding during the early stages of concrete cracking
 Also, plastic fibers increase the tensile strength and impact resistance thereby providing a
reduction in the weight and thickness of structural components (Ying-shu Yuan, 2015, p.
833).
Conclusion
In conclusion, the research was based on the determination of the behavior of plastic fiber on
concrete. It has been noted that plastic fibers offer the best reinforcement to concrete as
compared to other reinforcement fibers. Below were some of the reason that demonstrated the
best characteristics of plastic fibers in the prevention of crack formations in concrete elements.

Behavior of Plastic Fibers in Concrete 12
When concrete is reinforced with plastic fiber, there is improved cohesion in the mixture and
also the ability to pump over longer distances. Cases of fire breakouts also are countered by
offering a stronger resistance to the explosive spalling. Besides, apart from improved structural
strength and ductility of the mixture, plastic fiber offers a high resistance to the shrinkage during.
The research also indicates that plastic fibers help to improve the resistance to freezing thaw and
abrasion.
The above properties ensure that the width of the crack formed in the concrete material is greatly
reduced thereby improving the lifespan and the aesthetic value of the concrete.

Behavior of Plastic Fibers in Concrete 13
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