**5. Effect of using single type of fibres on concrete mechanical properties**

#### **5.1. Steel fibres**

Steel fibre is becoming an important type of concrete reinforcement due to the numerous advantages that it offers for concrete. Compared to traditional fabric reinforcement, steel fibres have a tensile strength typically two to three times greater and a significant greater surface area to develop a bond with the concrete matrix [5]. Over the past three decades, the potential of using steel fibre reinforced concrete (SFRC) to improve the performance of structures has been investigated [43]. The available literature on the subject shows that steel fibre reinforcement can increase significantly the compression, tension, flexure, impact and toughness, shear and punching resistance, as well as the energy dissipation capacity and durability of concrete structures.

The occurrence of fibres affects the compressive strength as it varies from 0 to 15%. In contrast, the order of 30–40% fibres is increased with direct tension. There are little data dealing strictly with the torsion and shear even though they are usually increased [22, 44]. Moreover, steel fibre has a noteworthy effect on the residual tensile strength and flexural strength, with increase of more than 100% being reported [45, 46]. The most important part of the commercial use of steel fibre is the post-crack flexural performance, which is based on the steel fibre concrete and sections subjected to point or flexure load. The flexural behaviour of concrete reinforced with straight and hooked end steel fibres was studied by Pajak and Ponikiewski [26]. It was found that the increase of fibre volume ratio increases the flexural tensile strength. The fracture energy increases with the increase of fibre dosage and is higher for hooked end steel fibres than for straight ones. Steel fibres continue to carry stresses after matrix failure. This is also confirmed by many researchers [9, 11, 12].

**4.3. Structural synthetic fibres**

porated to the concrete at any point.

ity, fracture toughness, impact and fatigue resistance.

**5. Effect of using single type of fibres on concrete mechanical** 

Steel fibre is becoming an important type of concrete reinforcement due to the numerous advantages that it offers for concrete. Compared to traditional fabric reinforcement, steel fibres have a tensile strength typically two to three times greater and a significant greater surface area to develop a bond with the concrete matrix [5]. Over the past three decades, the potential of using steel fibre reinforced concrete (SFRC) to improve the performance of structures has been investigated [43]. The available literature on the subject shows that steel fibre reinforcement can increase significantly the compression, tension, flexure, impact and toughness, shear and punching resistance, as well as the energy dissipation capacity and durability of concrete structures. The occurrence of fibres affects the compressive strength as it varies from 0 to 15%. In contrast, the order of 30–40% fibres is increased with direct tension. There are little data dealing strictly with the torsion and shear even though they are usually increased [22, 44]. Moreover, steel fibre has a noteworthy effect on the residual tensile strength and flexural strength, with increase of more than 100% being reported [45, 46]. The most important part of the commercial use of steel fibre is the post-crack flexural performance, which is based on the steel fibre

from 1.8 to 7 kg/m<sup>3</sup>

38 Cement Based Materials

**properties**

**5.1. Steel fibres**

For synthetic structural fibres, the dearth of available references and design guidelines are the considerable barriers for effective comprehension to add, mix, compact, finish, cure, and place within concrete properties. The information associated to these sources are mentioned in the following paragraph [32, 34, 42]. During the patching or mixing processes, the fibres can be incor-

The particular application and intended properties relied on the additional rate, which differs

procedures and mix design to accomplish optimum consequences. The required workability is accomplished by ensuring the adjustments into the mix design. Afterwards, the fine aggregate contents include a slight increase for coating the fibres comprehensively. The concrete is assisted with efficient finishing and rapid placing. In contrast, medium to high level of workability is accomplished through the inclusion of a superplasticiser. It is evident that the position of structural synthetic fibres is appropriately similar according to the normal concrete. Moreover, concrete must be compacted adequately to assure the surface placement with the easy finishing. An easy float is typically transformed over the concrete for patching the surface after compaction. The fibre reinforced is enabled to cure effective concreting practice once it is levelled, floated and compacted. Structural synthetic fibre mostly relies on surface friction to achieve anchorage across a crack. It controls plastic shrinkage cracking and cracking due to drying shrinkage of the concrete. Moreover, it improves concrete properties including ductil-

. Careful attention is required for their additional rate within both batching

According to Hauwaert et al. [47], impact strength and toughness are significantly increased, which is defined as energy absorbed to failure. Under the load deflection curve, the toughness increases resulting in tension and flexure due to the increase in area [21]. A claim is usually made due to fatigue and increased resistance to dynamic load. The resistance of increased resistance to dynamic loading highly emerged as it is associated with the fibre distribution in concrete [48].

In studying the effect of steel fibres on the shear capacity of concrete, some investigations were carried out for evaluating the performance of beam–column sub assemblages. Susetyo et al. [10] undertaken experimental investigations on concrete panels based on pure-shear monotonic loading conditions for assessing the steel fibre effectiveness to meet minimal shear reinforcement requirements for concrete elements. Ductile behaviour, good crack control attributes and sufficient shear strength are exhibited through the test results. Minimum extent of traditional shear reinforcement is accomplished through the level of performance. The role of steel fibres in enhancing the shear strength of concrete was also confirmed by many researchers [8, 9, 49].

Labib (2008) conducted experimental investigations on concrete slab-column connections reinforced with hooked end steel fibres failing in punching; it was found that the inclusion of steel fibres significantly increases the load carrying capacity of tested specimens and is strongly dependent on the fibre dosage. Moreover, the crack opening restraint provided by the reinforcement mechanisms of steel fibres bridging the crack surfaces leads to a significant increase in terms of load carrying capacity and energy absorption capability of concrete structures. This was also confirmed by [13, 14].

In particular, steel fibre possesses a positive impact on the shrinkage behaviour of concrete that mitigates the extent and organises the cracks width, as compared to plain concrete [22, 28]. The fibres will corrode quickly in exposed situations, if the concrete compacts the fibre corrosion under the surface. The deterioration caused due to freeze-thaw cycling and the permeability of cracks can be reduced from the fibres [22, 50].

The role of fibres in bridging the crack opening and enhancing the load capacity and postpeak behaviour leads to better concrete durability and structural integrity ([15, 16]; Kunieda et al., 2014). This was also confirmed by the experimental results of Stephen (2001) which showed that the introduction of steel fibres into the concrete can arrest the early spalling of the concrete cover and increase the load capacity as well as the ductility of the columns over that of comparable non-fibre reinforced specimens. Similar observations were reported more recently by Lee et al. [49], Joao (2010), and Röhm and Arnold [51]. Steel fibres improve the ductility of concrete under all modes of loading.

#### **5.2. Synthetic fibres**

Synthetic organic fibres have low modulus of elasticity and high elongation properties [29]. Therefore, they have the potential to provide concrete with significant ductility. As a result, when added to concrete, these fibres are able to control cracking caused by thermal movements and long-term drying shrinkage [33] and improve the performance of concrete by negating its disadvantages such as low tensile strength, low ductility and low energy absorption capacity (Lakshmi et al., 2010; [52]; Mu et al., 2000; [53, 54]). Glass, polyvinyl, polypropylene, polyolefin and carbon are concrete-based matrices used in the synthetic fibre types in Portland cement.

On the other hand, polypropylene fibres can improve not only mechanical properties of concrete but also its durability due to reduced crack width by fibre bridging effect. Therefore, it could be considered as solution to extend lifecycle in terms of improvement of durability (Kunieda et al., 2014). The polypropylene fibres enhance the resistance to frost attack and the surface of abrasion resistance. The protection of the steel reinforcement is increased through these aspects alongside corrosion and mitigates the concrete water permeability. Knapton [27] states that the chemical resistance of concrete is not changed in this process. In particular,

Fibre Reinforced Cement Composites http://dx.doi.org/10.5772/intechopen.75102 41

As stated previously, while polypropylene is extensively used in concrete, other synthetic fibres such as glass, carbon, polyolefin and polyvinyl had little reported research or field experience. Barhum et al. (2012) studied the impact of the dispersed and short fibres of carbon and alkali resistance on the textile-reinforced concrete's fracture behaviour. The strength, fracture behaviour and deformation of the study are performed through a series of deformationcontrolled and uniaxial tension tests. Pronounced enhancement of first-crack stress was achieved due to the addition of glass and carbon fibres. While more and finer cracks were observed on the specimens with short fibres added, a moderate improvement in tensile strength

The formation of polyolefin fibre reinforced concrete is based on the employment of polyolefin fibres since they are lighter and possess a final lower cost and not chemically stable. They have been proved to be suitable for structural uses. Moreover, in some cases, they have substituted steel fibres (Behfarnia et al., 2014; Pujadas et al., 2014; Alberti et al., 2015). On the other hand, polyvinyl alcohol organic fibres and nylon are also effective in mitigating spalling, while others like polyethylene fibres are not so effective. Investigations from Laura et al. (2014) indicated that the use of synthetic fibre reinforced concrete can enhance the ductility

The use of waste fibres plays an important role in sustainable solid waste management. It helps to save natural resources, decreases the pollution of the environment and saves energy production processes. It has beneficial environmental and economic impacts; therefore, wastes and industrial by-products should be considered as potentially valuable resources merely awaiting appropriate treatment and application [19, 20]. Therefore, the addition of waste to concrete corresponds to a new perspective in research activities, integrating the areas

Steel fibres originated from the industry of tyres and plastic wastes are among these wastes; their disposal has harmful effects on the environment due to their long biodegradation period, and therefore one of the logical methods for reduction of their negative effects is the applica-

Recent research is showing that steel fibres originated from the industry of tyre recycling and can be a valuable reinforcement system to decrease significantly the brittle behaviour of cement-based materials, by improving their toughness and post-cracking resistance. Recycled steel fibre reinforced concrete is therefore becoming a promising candidate for both structural

polypropylene fibres are usually more durable as compared to plain concrete [28].

was recorded.

**5.3. Waste fibres**

and energy dissipation capacity of concrete.

of concrete technology and environmental technology.

tion of these materials in other industries.

Synthetic fibre types that have been tried in Portland cement concrete-based matrices are: polypropylene, glass, carbon, polyolefin and polyvinyl. For many of these fibres, there is little reported research or field experience, while others are found in commercial applications and have been the subject of extensive reporting [22]. Among these materials, polypropylene fibres are one of the most widely used for construction applications such as blast-resistant concrete and pavements (Mwangi, 2001).

Polypropylene fibres are gaining significance due to the low price of the raw polymer material and their high alkaline resistance [30, 31]. Their formation is based on fibrillated or monofilament manufactured in an enduring process through polypropylene homopolymer resin extrusion. Micro-synthetic fibres are used for reducing, plastic settlement cracking and plastic shrinkage cracking in ground-supported slabs as based on 100% polypropylene. Polypropylene fibres are used extensively in concrete for the purpose of reducing, plastic shrinkage cracking and plastic settlement cracking [32].

Mazaheripour et al. (2011) investigate the effect of polypropylene fibre inclusion on fresh and hardened properties of concrete. The results obtained have shown that the polypropylene fibres did not influence the compressive strength and elastic modulus; however, applying these fibres at their maximum percentage volume increased the tensile strength and the flexural strength of concrete.

Fire still remains one of the most serious risks for tunnels, buildings and other concrete structures. Thereby, the risks related with increased temperatures should be considered by engineers when designing concrete structures, including explosive spalling due to adverse concrete deterioration (Phan et al., 2002; Horiguchi et al., 2004).

It has been widely shown that polypropylene fibres are very effective in mitigating spalling in concrete exposed to elevated temperatures. Bangi et al. (2012) conducted an experimental study for investigating the fibre type effect and maximum pore pressure amount in fibre reinforced high-strength concrete. It uses different lengths of steel fibres, polyvinyl and polypropylene. The pore pressure reduction in heated concrete is contributed through pore pressure measurements based on organic fibres. The most effective maximum pore pressure development is polypropylene fibres as compared to polyvinyl alcohol fibres. On the contrary, there is a low effect found on the steel fibres. This result has been proved by studies from different researchers. These studies found that the complex mechanism of porosity variations in concrete at elevated temperatures, enriched with polypropylene fibres (Khoury, 2008; [55, 56]; Zeimi et al., 2006; Muzzucco et al., 2015).

On the other hand, polypropylene fibres can improve not only mechanical properties of concrete but also its durability due to reduced crack width by fibre bridging effect. Therefore, it could be considered as solution to extend lifecycle in terms of improvement of durability (Kunieda et al., 2014). The polypropylene fibres enhance the resistance to frost attack and the surface of abrasion resistance. The protection of the steel reinforcement is increased through these aspects alongside corrosion and mitigates the concrete water permeability. Knapton [27] states that the chemical resistance of concrete is not changed in this process. In particular, polypropylene fibres are usually more durable as compared to plain concrete [28].

As stated previously, while polypropylene is extensively used in concrete, other synthetic fibres such as glass, carbon, polyolefin and polyvinyl had little reported research or field experience. Barhum et al. (2012) studied the impact of the dispersed and short fibres of carbon and alkali resistance on the textile-reinforced concrete's fracture behaviour. The strength, fracture behaviour and deformation of the study are performed through a series of deformationcontrolled and uniaxial tension tests. Pronounced enhancement of first-crack stress was achieved due to the addition of glass and carbon fibres. While more and finer cracks were observed on the specimens with short fibres added, a moderate improvement in tensile strength was recorded.

The formation of polyolefin fibre reinforced concrete is based on the employment of polyolefin fibres since they are lighter and possess a final lower cost and not chemically stable. They have been proved to be suitable for structural uses. Moreover, in some cases, they have substituted steel fibres (Behfarnia et al., 2014; Pujadas et al., 2014; Alberti et al., 2015). On the other hand, polyvinyl alcohol organic fibres and nylon are also effective in mitigating spalling, while others like polyethylene fibres are not so effective. Investigations from Laura et al. (2014) indicated that the use of synthetic fibre reinforced concrete can enhance the ductility and energy dissipation capacity of concrete.

#### **5.3. Waste fibres**

**5.2. Synthetic fibres**

40 Cement Based Materials

Portland cement.

ural strength of concrete.

Zeimi et al., 2006; Muzzucco et al., 2015).

concrete and pavements (Mwangi, 2001).

shrinkage cracking and plastic settlement cracking [32].

concrete deterioration (Phan et al., 2002; Horiguchi et al., 2004).

Synthetic organic fibres have low modulus of elasticity and high elongation properties [29]. Therefore, they have the potential to provide concrete with significant ductility. As a result, when added to concrete, these fibres are able to control cracking caused by thermal movements and long-term drying shrinkage [33] and improve the performance of concrete by negating its disadvantages such as low tensile strength, low ductility and low energy absorption capacity (Lakshmi et al., 2010; [52]; Mu et al., 2000; [53, 54]). Glass, polyvinyl, polypropylene, polyolefin and carbon are concrete-based matrices used in the synthetic fibre types in

Synthetic fibre types that have been tried in Portland cement concrete-based matrices are: polypropylene, glass, carbon, polyolefin and polyvinyl. For many of these fibres, there is little reported research or field experience, while others are found in commercial applications and have been the subject of extensive reporting [22]. Among these materials, polypropylene fibres are one of the most widely used for construction applications such as blast-resistant

Polypropylene fibres are gaining significance due to the low price of the raw polymer material and their high alkaline resistance [30, 31]. Their formation is based on fibrillated or monofilament manufactured in an enduring process through polypropylene homopolymer resin extrusion. Micro-synthetic fibres are used for reducing, plastic settlement cracking and plastic shrinkage cracking in ground-supported slabs as based on 100% polypropylene. Polypropylene fibres are used extensively in concrete for the purpose of reducing, plastic

Mazaheripour et al. (2011) investigate the effect of polypropylene fibre inclusion on fresh and hardened properties of concrete. The results obtained have shown that the polypropylene fibres did not influence the compressive strength and elastic modulus; however, applying these fibres at their maximum percentage volume increased the tensile strength and the flex-

Fire still remains one of the most serious risks for tunnels, buildings and other concrete structures. Thereby, the risks related with increased temperatures should be considered by engineers when designing concrete structures, including explosive spalling due to adverse

It has been widely shown that polypropylene fibres are very effective in mitigating spalling in concrete exposed to elevated temperatures. Bangi et al. (2012) conducted an experimental study for investigating the fibre type effect and maximum pore pressure amount in fibre reinforced high-strength concrete. It uses different lengths of steel fibres, polyvinyl and polypropylene. The pore pressure reduction in heated concrete is contributed through pore pressure measurements based on organic fibres. The most effective maximum pore pressure development is polypropylene fibres as compared to polyvinyl alcohol fibres. On the contrary, there is a low effect found on the steel fibres. This result has been proved by studies from different researchers. These studies found that the complex mechanism of porosity variations in concrete at elevated temperatures, enriched with polypropylene fibres (Khoury, 2008; [55, 56]; The use of waste fibres plays an important role in sustainable solid waste management. It helps to save natural resources, decreases the pollution of the environment and saves energy production processes. It has beneficial environmental and economic impacts; therefore, wastes and industrial by-products should be considered as potentially valuable resources merely awaiting appropriate treatment and application [19, 20]. Therefore, the addition of waste to concrete corresponds to a new perspective in research activities, integrating the areas of concrete technology and environmental technology.

Steel fibres originated from the industry of tyres and plastic wastes are among these wastes; their disposal has harmful effects on the environment due to their long biodegradation period, and therefore one of the logical methods for reduction of their negative effects is the application of these materials in other industries.

Recent research is showing that steel fibres originated from the industry of tyre recycling and can be a valuable reinforcement system to decrease significantly the brittle behaviour of cement-based materials, by improving their toughness and post-cracking resistance. Recycled steel fibre reinforced concrete is therefore becoming a promising candidate for both structural and non-structural applications [18]. Zamanzadeh et al. [43] compared the characterisation of the post-cracking properties of recycled steel fibre reinforced concrete and industrial steel fibre reinforced concrete, on its use as shear reinforcement. Although the results indicated that the fibre reinforcement mechanisms for relatively small crack width levels were not as effective in the recycled steel fibres as the industrial steel fibres, it was verified that both fibres have similar trend in the post-cracking behaviour.

Xu et al. (2011) found that the tensile strength of steel-polypropylene hybrid fibre reinforced concrete. The results indicated that the tensile strength of conventional concrete can be dramatically improved by mixing with hybrid steel-polypropylene fibres. The enhancing effect of hybrid fibre is better than that of single fibre, and the volume fraction of steel fibre is observed to have a great impact on the tensile strength. The same results were found by Sivakumar (2011) who studied the flexural strength, toughness, and ductility of concrete specimens containing individual steel fibres and hybrid combinations of steel and non-metallic fibres such as glass, polyester and polypropylene. He found that the ability of non-metallic fibres to bridge smaller micro-cracks was suggested as the reason for the enhancement in flexural

Fibre Reinforced Cement Composites http://dx.doi.org/10.5772/intechopen.75102 43

The effect of inclusion hybrid steel-polypropylene fibre reinforced concrete on triaxial compression was developed by Chi (2014). The results showed that the steel fibres mainly contribute to the composite's triaxial strength that was observed to improve significantly when both the volume fractions and aspect ratios of steel fibre were increased. On the other hand, the polypropylene fibres were found to have considerable effect on improving the tensile merid-

Ding et al. (2010) analysed the influence of various fibre types, including steel macro-fibre and hybrid fibre (macro-steel fibre and macro-plastic fibre) on the shear strength and shear toughness of reinforced concrete beams. The results indicated that hybrid fibres can evidently

Sahoo et al. (2015) studied the influence of using both high-modulus (steel) and low-modulus (polypropylene) fibres on the shear strength of reinforced concrete beams. A better post-peak residual strength response is noticed in the case of all FRC beam specimens due to multiple cracking associated with the fibre bridging action. The main parameters investigated are shear strength, failure mechanism and displacement ductility. The FRC specimens with combined steel and polypropylene fibres showed that the shear resistance and deformability values are improved significantly; multiple cracks of smaller crack width are noticed at the failure stage of the specimens indicating the better fibre bridging action of combined metallic and non-

Banthia et al. (2014) used hybrid fibres by using two types of macro-steel fibres and a microcellulose fibre. Flexural and direct shear tests were performed, and the results were analysed to identify the degree of enhancement in the mechanical properties associated with various

This chapter reported on the historical use of fibres; types of fibres; and the addition, mixing, placing, finishing and curing of steel, polypropylene and structural synthetic fibres. This chapter also discussed the potential of using various types of fibres in reinforced concrete to optimise the properties of concrete material as well as to improve the mechanical performance of reinforced concrete members. The reviewed literature highlighted the role of fibres

enhance both the shear toughness and the ultimate shear bearing capacity.

properties compared to individual steel fibre.

ian rather than compressive meridian.

metallic fibres.

fibre combinations.

**7. Conclusion**

Much research effort has focused on reusing waste materials from plastic industries in concrete. Different works have analysed the effect of the addition of recycled polyethylene terephthalate (PET) to the properties of concrete (Choi et al., 2005; Jo et al., 2007; Robeiz, 1995). The reinforced concrete with PET bottles has been analysed by Foti (2011). The study has found that there is a great influence on post-cracking performance of simple concrete elements, when incorporating little amount of recycled fibres from PET bottle wastes. The sample's toughness and the concrete plasticity are enhanced and increased, respectively, through these fibres. Moreover, fibres are used from recycled PET bottles in reinforced mortar by De Oliveira et al. (2011). The findings have shown that a significant enhancement on compressive strength of mortars is shown from these PET fibres on their toughness and their flexural strength. The possibility of recycling PET fibres is explored by Foti (2013) as acquired from waste bodies with assorted shapes. The ductility of concrete is increased through these tests and PET fibres in a concrete mixture. At the end, as limited research has been carried out in this area, therefore, more studies could be carried out on the effect of using the previously mentioned wastes on the mechanical properties of concrete to prove the above results and to further examine different mechanical properties. In addition, the effect of using other types of wastes on the mechanical properties of concrete could be investigated.
