**3.1. Steel fibres**

Many efforts have been made in recent years to optimise the shape of steel fibres to achieve improved fibre-matrix bond characteristics, and to enhance fibre dispersibility in the concrete mix [26]. The classification for four general types is provided by ASTM A 820 on the basis of manufacturing products [22]. These products include cut sheet, melt extracted, cold-drawn wire and other fibres.

**Figure 1** has shown other common types of steel fibres. By cutting and chopping wire, rounded and straight steel fibres, having a diameter between 0.25 and 1.0mm are produced. Furthermore, shearing sheet of flattening wire produces flat and straight steel fibres of 0.15–0.41 mm thickness by 0.25–1.14 mm width. The production of crimped and deformed steel fibres is based on the full-length crimpling or bent or enlarged at each side of the fibres. The bending or flattening process is used to deform fibres to expand bond and allow mixing and handling [28].

The handling and mixing process is facilitated through fibres being collated into bundles. The bundles are distributed into single fibres during the mixing process. Similarly, cold-drawn wire is used to produce fibres that are smooth for making steel wool. In addition, the melt extraction process is used to produce steel fibres [22].

*3.2.1. Polypropylene fibres (micro-synthetic fibres)*

*3.2.2. Structural synthetic fibres (macro-synthetic fibres)*

and fabrics [34].

fibres are applicable.

**curing**

**4.1. Steel fibre**

*4.1.1. Composition and quality*

fication for acquiring steel fibre reinforced concrete [35].

The significance of polypropylene fibres emerged due to their high alkaline resistance and low price of the raw polymer material [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 based on 100% polypropylene. According to

Fibre Reinforced Cement Composites http://dx.doi.org/10.5772/intechopen.75102 35

During the last 7 years, the development of micro-synthetic fibres has expanded comprehensively. The potential of these fibres is evident in providing concrete with significant ductility. These fibres have potential to control cracking resultant from lasting drying shrinkage and thermal movements in concrete floors and slabs [33]. These macro-synthetic fibres vary from polypropylene micro-fibres due to their large and higher polymers even though they typically comprise few polypropylenes [32]. A significant level of post-crack control is provided from synthetic structural fibres to accomplish steel fibres

Steel fibres and polypropylene fibres as well as structural synthetic fibres are the most common types of fibres used in structural members. Therefore, the following section discusses the addition, mixing, placing, finishing and curing of steel, polypropylene and structural synthetic fibres. Also, they present the effect of adding these fibre types on the properties of fresh and hardened concrete. However, using waste fibres is relatively a new practice and it is not limited to one type of wastes. Therefore, there is no clear guidance for the addition, mixing, placing, finishing and curing of such fibres. On the other hand, using hybrid fibres is limited to the use of steel and polypropylene as well as using different types of steel fibres. Thus, the below practices of adding single steel or polypropylene

**4. Fibre reinforced concrete addition, mixing, placing, finishing and** 

Higher cement, smaller aggregates and fine contents are generally combined in the fibre reinforced concrete as compared to plain concrete. The fibre content increases to decrease the extent of the slump [21, 22]. Therefore, a steel wire manufacturer signifies the following speci-

Perry [32], micro-synthetic fibres are usually 12 mm long by 18 μm diameter.

**Figure 1.** Different steel fibre types [27].

Young's modulus is 205 MPa, aspect ratio varies from 30 to 100, ultimate tensile strength of steel fibre varies from 345 to 1700 MPa, and length varies from 19 to 60 mm for respective fibres.

The largest fibre producers offer a statistical analysis to claim the sale of 67% fibre based on the hooked type. Katzer (2006) explained that crimped fibre (8%), straight fibre (9%) and fibre with deformed wire (9%) are other most popular fibre types.

#### **3.2. Synthetic fibres**

Research and development reflect the efforts of man-made fibres in the form of synthetic fibres specifically in the textile and petrochemical industries. Organic polymers derive fibres for synthetic fibre reinforced concrete based on available formulations [22]. Acrylic, polyethylene, polypropylene, nylon, polyester, carbon and aramid are the concrete-based matrices for synthetic fibre types in Portland cement. However, there is a dearth of these fibres, but other fibres are found extensively in commercial applications [22]. Low modulus of elasticity and high elongation properties are found in synthetic and organic fibres. In contrast, high modulus of elasticity is found in steel, glass, carbon and asbestos and fibres [29]. Similarly, structural and polypropylene are emerged as synthetic fibres and extensively found in concrete ground floor-slabs.

### *3.2.1. Polypropylene fibres (micro-synthetic fibres)*

The significance of polypropylene fibres emerged due to their high alkaline resistance and low price of the raw polymer material [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 based on 100% polypropylene. According to Perry [32], micro-synthetic fibres are usually 12 mm long by 18 μm diameter.

#### *3.2.2. Structural synthetic fibres (macro-synthetic fibres)*

During the last 7 years, the development of micro-synthetic fibres has expanded comprehensively. The potential of these fibres is evident in providing concrete with significant ductility. These fibres have potential to control cracking resultant from lasting drying shrinkage and thermal movements in concrete floors and slabs [33]. These macro-synthetic fibres vary from polypropylene micro-fibres due to their large and higher polymers even though they typically comprise few polypropylenes [32]. A significant level of post-crack control is provided from synthetic structural fibres to accomplish steel fibres and fabrics [34].

Steel fibres and polypropylene fibres as well as structural synthetic fibres are the most common types of fibres used in structural members. Therefore, the following section discusses the addition, mixing, placing, finishing and curing of steel, polypropylene and structural synthetic fibres. Also, they present the effect of adding these fibre types on the properties of fresh and hardened concrete. However, using waste fibres is relatively a new practice and it is not limited to one type of wastes. Therefore, there is no clear guidance for the addition, mixing, placing, finishing and curing of such fibres. On the other hand, using hybrid fibres is limited to the use of steel and polypropylene as well as using different types of steel fibres. Thus, the below practices of adding single steel or polypropylene fibres are applicable.
