**7. Conclusion**

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

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

It is noteworthy to examine that the concrete failure is based on a multi-scale and a gradual process even though the research mentioned above have convinced us that remarkable improvement in mechanical performance can be achieved by using single fibre type in concrete. Therefore, significant attempts are made toward fibre combinations with different functions and constitutive responses and dimensions into cementitious composite. Potential advantages can be offered through hybrid combinations of steel and non-metallic fibres to enhance concrete properties and to reduce the entire cost of concrete production (Bentur and Mindess, 1990). Fibre fractions result in a uniform and a denser fibre distribution within the concrete as it enhances post-crack strength of concrete and reduces shrinkage cracks. This combination of low- and high-modulus fibres can arrest the micro- and macro-cracks, respectively, which could be also achieved by using a combination of long and short fibres as differ-

A number of studies indicated the overall benefits of using combinations of steel fibres and polypropylene fibres (Xu et al., 2011; Sivakumar, 2011; Chi, 2014; Ding et al., 2010; Sahoo et al., 2015), while limited research was carried out on the effect of using steel fibres and other types of fibres such as glass and polyethylene (Banthia et al., 2014) or using a mix of short and long

have similar trend in the post-cracking behaviour.

42 Cement Based Materials

wastes on the mechanical properties of concrete could be investigated.

ent lengths of fibres would control different scales of cracking.

**6. Effect of using hybrid fibres**

steel fibres [11].

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 in enhancing the concrete tensile strength, flexure strength; shear strength, punching shear strength, toughness, energy dissipation capacity, resistance to cracking and durability. The reviewed literature also indicated that, in most cases FRC contains individual type of fibres, which includes steel, polypropylene, glass, carbon, polyolefin and polyvinyl. Although extensive research is conducted on the FRC, the reviewed literature showed a dearth of research conducted on waste fibre. The reviewed literature highlighted that the research conducted on the use of waste fibre in concrete is limited to the effect of waste fibre on toughness, flexural strength, compression strength and post-peak behaviour of concrete elements. In addition, this chapter reported on the use of two or more types of fibres in a suitable combination which has proved the potential to improve the mechanical properties of concrete. Numerous studies on hybrid fibre reinforced concrete have been performed. The reviewed literature showed that combination of fibres is commonly limited to two types of mixes, a mix of steel and polypropylene fibres and a mix of steel fibres with different geometry, shape and size. It is recommended that more mixes should be analysed to identify the degree of enhancement in the mechanical properties associated with various fibre combinations.

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Institute; 1996

### **Author details**

Wafa Abdelmajed Labib

Address all correspondence to: wlabib@psu.edu.sa

Prince Sultan University, PSU, Riyadh, Saudi Arabia
