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

#### **4.1. Steel fibre**

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

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

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 con-

with deformed wire (9%) are other most popular fibre types.

fibres.

34 Cement Based Materials

**3.2. Synthetic fibres**

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

crete ground floor-slabs.

#### *4.1.1. Composition and quality*

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 specification for acquiring steel fibre reinforced concrete [35].

#### *4.1.2. Addition and mixing of steel fibre*

It is deemed that 20–40 kg/m<sup>3</sup> is usually the recommended dosage for steel fibres. According to Knapton, [27], the flexural strength of the concrete results in higher dosage rate. In general, the fresh concrete is combined with the fibres and; afterwards, these fibres are moved initially to the mixer. Newman and Choo [21] revealed that these fibres can be incorporated to the aggregated conveyor belt. The fibres might be dispensed directly regardless of any balling risk, when the aspect ratio of the fibre is less than 50. Particular packing techniques are employed by manufacturers for reducing the risk with higher aspect ratios [22]. On the contrary, the satisfactory outcome of visual inspection is evaluated for fibre distribution during pouring [27].

composite slump as reported from the variations of volume fractions included in steel fibre reinforced concrete (0.25–1.5 vol%). Furthermore, the effects of vibration are suggested to assess workability of a SFRC mixture with the VB test because mechanical vibration is suggested in a number of SFRC applications as compared to traditional slump measurement. A good workability is maintained through the inclusion of superplasticiser. In contrast, the fibre

Fibre Reinforced Cement Composites http://dx.doi.org/10.5772/intechopen.75102 37

The addition of polypropylene fibres is at a recommended dosage of approximately 0.9 kg/m<sup>3</sup> (0.1% by volume) [27]; the fibre volume is so low that mixing techniques require little or no modification from normal practice [21]. The fibres may be added at either a conventional

Polyproline fibres are comprised of concrete mixes that can be transformed by normal methods and; therefore, flow easily from the hopper outlet. The essential compaction might be used for providing traditional means of vibration and tamping. The traditional concrete can be considered strictly for curing procedures. The floating and trowelling of fibre-dosed mixes

According to Ramakrishnan [4], proper design and application of fibre reinforced concrete mixes can be essentially considered on the basis of knowledge of the fresh concrete properties. The occurrence of polypropylene fibres is mechanically observed since a comprehensive impact is imparted on the concrete, cement hydration and delaying evaporation by holding water [27]. The polypropylene fibres did not affect the slump of fibre-dosed concrete. The properties of the fresh concrete are modified through the primary role of polypropylene. The movement of solid particles, the bleed of water chemicals and the homogeneity of the mix are stabilised, blocked and increased through polypropylene fibres. The bleed capacity of the concrete and plastic settlement is reduced, and decreases the rate of bleed through polypro-

The plastic concrete is formed due to plastic cracking and drying shrinkage. The formation of plastic cracks took place in the first 24 h, when there is high evaporation rate and the concrete surface dries after the placement of the concrete [27]. The appearance of concrete along with its durability and physical and mechanical properties is affected through this high evaporation rate [41]. The width of plastic shrinkage cracks can be restricted due to the polypropylene fibres. In the initial phases, the post-cracking ductility of the concrete emerged from the fibres,

increasing strain capacity and affecting plastic shrinkage cracking [21].

balling should be ignored when considering above specifications.

batching/mixing plant or by hand to the ready-mix truck on site [27].

**4.2. Polypropylene fibre-reinforced concrete**

*4.2.2. Placing finishing and curing (polypropylene)*

can be used for normal hand and poor tools [27].

pylene fibres.

*4.2.3. Mechanical properties of fresh fibre-reinforced concrete*

*4.2.1. Addition and mixing (polypropylene)*

#### *4.1.3. Placing finishing and curing*

Approved mixing, quality control procedures, and finishing are required for good quality and economic construction of steel fibre reinforced concrete [22]. The placement of concrete through good concrete practice is affective in positioning during curing. The reduced flow characteristics allow positively the final placement of steel fibre reinforced concrete (Unwalla, 1982; [36]).

Placing, curing and finishing steel fibre reinforced concrete are satisfactorily used by traditional tools, procedure and equipment [36–39]. Antiwear products and cement are usually expanded on the concrete surface after levelling and compaction [27]. Same methods and techniques can be used for curing and protecting SFRC. Plastic and shrinkage cracking can be produced through insufficient curing methods in traditional concrete [36, 37, 39].

#### *4.1.4. Mechanical properties of fresh steel fibre-reinforced concrete*

The important problem produced during the steel fibre reinforced concrete is the accomplishment of sufficient workability. Fibres are included in the concrete mix with aspect ratio and fibre volume, which affect the workability [36, 40]. The steel fibres can mitigate the estimated


**Table 1.** Concrete mix design of steel fibre reinforced concrete.

composite slump as reported from the variations of volume fractions included in steel fibre reinforced concrete (0.25–1.5 vol%). Furthermore, the effects of vibration are suggested to assess workability of a SFRC mixture with the VB test because mechanical vibration is suggested in a number of SFRC applications as compared to traditional slump measurement. A good workability is maintained through the inclusion of superplasticiser. In contrast, the fibre balling should be ignored when considering above specifications.

#### **4.2. Polypropylene fibre-reinforced concrete**

## *4.2.1. Addition and mixing (polypropylene)*

*4.1.2. Addition and mixing of steel fibre*

is usually the recommended dosage for steel fibres. According

to Knapton, [27], the flexural strength of the concrete results in higher dosage rate. In general, the fresh concrete is combined with the fibres and; afterwards, these fibres are moved initially to the mixer. Newman and Choo [21] revealed that these fibres can be incorporated to the aggregated conveyor belt. The fibres might be dispensed directly regardless of any balling risk, when the aspect ratio of the fibre is less than 50. Particular packing techniques are employed by manufacturers for reducing the risk with higher aspect ratios [22]. On the contrary, the satisfactory outcome of visual inspection is evaluated for fibre distribution dur-

Approved mixing, quality control procedures, and finishing are required for good quality and economic construction of steel fibre reinforced concrete [22]. The placement of concrete through good concrete practice is affective in positioning during curing. The reduced flow characteristics allow positively the final placement of steel fibre reinforced concrete (Unwalla,

Placing, curing and finishing steel fibre reinforced concrete are satisfactorily used by traditional tools, procedure and equipment [36–39]. Antiwear products and cement are usually expanded on the concrete surface after levelling and compaction [27]. Same methods and techniques can be used for curing and protecting SFRC. Plastic and shrinkage cracking can be

The important problem produced during the steel fibre reinforced concrete is the accomplishment of sufficient workability. Fibres are included in the concrete mix with aspect ratio and fibre volume, which affect the workability [36, 40]. The steel fibres can mitigate the estimated

produced through insufficient curing methods in traditional concrete [36, 37, 39].

*4.1.4. Mechanical properties of fresh steel fibre-reinforced concrete*

**Element Quantity** Cement 320–350 kg/m<sup>3</sup> Well-graded sharp sand 750–850 kg/m<sup>3</sup>

Continuous aggregate grading 28 mm

**Table 1.** Concrete mix design of steel fibre reinforced concrete.

Crushed stone 14 mm, 15–20% Characteristic compressive strength 25 N/mm<sup>2</sup> Water/cement ratio 0.50–0.55

It is deemed that 20–40 kg/m<sup>3</sup>

*4.1.3. Placing finishing and curing*

ing pouring [27].

36 Cement Based Materials

1982; [36]).

The addition of polypropylene fibres is at a recommended dosage of approximately 0.9 kg/m<sup>3</sup> (0.1% by volume) [27]; the fibre volume is so low that mixing techniques require little or no modification from normal practice [21]. The fibres may be added at either a conventional batching/mixing plant or by hand to the ready-mix truck on site [27].

#### *4.2.2. Placing finishing and curing (polypropylene)*

Polyproline fibres are comprised of concrete mixes that can be transformed by normal methods and; therefore, flow easily from the hopper outlet. The essential compaction might be used for providing traditional means of vibration and tamping. The traditional concrete can be considered strictly for curing procedures. The floating and trowelling of fibre-dosed mixes can be used for normal hand and poor tools [27].

### *4.2.3. Mechanical properties of fresh fibre-reinforced concrete*

According to Ramakrishnan [4], proper design and application of fibre reinforced concrete mixes can be essentially considered on the basis of knowledge of the fresh concrete properties. The occurrence of polypropylene fibres is mechanically observed since a comprehensive impact is imparted on the concrete, cement hydration and delaying evaporation by holding water [27]. The polypropylene fibres did not affect the slump of fibre-dosed concrete. The properties of the fresh concrete are modified through the primary role of polypropylene. The movement of solid particles, the bleed of water chemicals and the homogeneity of the mix are stabilised, blocked and increased through polypropylene fibres. The bleed capacity of the concrete and plastic settlement is reduced, and decreases the rate of bleed through polypropylene fibres.

The plastic concrete is formed due to plastic cracking and drying shrinkage. The formation of plastic cracks took place in the first 24 h, when there is high evaporation rate and the concrete surface dries after the placement of the concrete [27]. The appearance of concrete along with its durability and physical and mechanical properties is affected through this high evaporation rate [41]. The width of plastic shrinkage cracks can be restricted due to the polypropylene fibres. In the initial phases, the post-cracking ductility of the concrete emerged from the fibres, increasing strain capacity and affecting plastic shrinkage cracking [21].

#### **4.3. Structural synthetic 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 incorporated to the concrete at any point.

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.

Fibre Reinforced Cement Composites http://dx.doi.org/10.5772/intechopen.75102 39

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

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

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 struc-

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 perme-

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

This is also confirmed by many researchers [9, 11, 12].

concrete [48].

many researchers [8, 9, 49].

tures. This was also confirmed by [13, 14].

ability of cracks can be reduced from the fibres [22, 50].

ductility of concrete under all modes of loading.

The particular application and intended properties relied on the additional rate, which differs from 1.8 to 7 kg/m<sup>3</sup> . Careful attention is required for their additional rate within both batching 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 ductility, fracture toughness, impact and fatigue resistance.
