Applications of Macro Plastic Fibre Reinforced Concrete

Reinforcing steel is expensive and its placement in concrete is labour and time intensive, often requiring placement in difficult and dangerous locations. Moreover, steel is highly corrosive in nature, which commonly deteriorates concrete. Therefore, macro plastic fibres are increasingly used in concrete and shotcrete industries for construction of footpaths, non-structural precast elements (pipes, culverts, cable pits and other small components), tunnels and underground structures, to partially or totally substitute steel reinforcement.

At mines, some locations, such as bedrock, are very difficult to support and are susceptible to collapse. In these cases, there is a long-standing demand to increase the support by increasing the fiber content. In the case of steel fiber reinforced concrete, difficulty of mixing and formation of fiber balls have prevented the use of higher fiber contents (Yang et al. 2012). However, macro plastic fiber reinforced concrete can be produced with fibre dosage more than 1% within the normal mixing time without any fibre ball formation and pipe clogging issues (Ochi et al. 2007).

Steel reinforcing mesh is conventionally used in the footpath applications to prevent drying shrinkage cracks (Abas et al. 2013). However, some roads, such as passages in tunnels under construction, passages through underground structures, urban alleyways, and bush roads, are commonly narrow, winding, and steep. It is desirable to apply fibre reinforced concrete to the pavement of such narrow sections of road. Unfortunately, traditional steel fibre can puncture tires, corrode and also can reduce workability of concrete. Therefore, macro plastic fibres are now gradually replacing steel reinforcing mesh for such usage, because of ease of construction, and for saving labour and cost (Cengiz and Turanli 2004). Table 2.4 lists some applications of PET fibre in mines and pavements in Japan (Ochi et al. 2007).

Macro plastic fibres are also an appealing alternative to steel for reinforcing precast concrete elements, such as pipes (Haktanir et al. 2007), sleepers (Ramezanianpour et al. 2013) and pits (Snelson and Kinuthia 2010). Fuente et al. (2013) produced fibre reinforced concrete pipes with internal diameter of 1000 mm, thickness of 80 mm and length of 1500 mm. PP fibre with continuously embossed indents (54 mm in length, 0.9 mm in diameter, 10 GPa Young’s modulus and

Table 2.4 Example applications of the PET fibres reinforced concrete in Japan (Ochi et al. 2007)

Prefecture

Location

Concrete

sprayed/placed

Water/cement

(%)

Fibre

length

(mm)

Fibre

content

(%)

Remark

Kagoshima

Mine

gateway

Sprayed

50

30

0.3

Replacement of steel fibre. First trial to use PET fibre in Japan. Found to be very easy to handle

Kanagawa

Bush

road

Placed

64

40

0.75

Replacement of wire mesh. Considerable laboursaving

Ibaragi

Bush

road

Placed

64

40

1

Applied successfully to road with 10% gradient

Ehime

Slope

Sprayed

50

30

0.3

Replacement of steel fibre on the sea front

Fukuoka

Tunnel

Placed

52

40

0.3

Applied to tunnel support for the first time

Tottori

Tunnel

Placed

52

40

0.3

A new fibre content analyser was developed and used

Kanagawa

Bridge

pier

Placed

50

30

0.3

Crack

extension was

substantially

decreased

Shiga

Tunnel

Placed

52

40

0.3

A new fibre injector was developed and used

640 MPa tensile strength) was used at 5.5 kg/m3 dosage to reinforce the pipes. Through a crush test, they found that the peak strength of 50 kPa was achieved at the deflection of 1 mm, with the strength dropping to 30 kPa at the deflection of 2 mm, which kept constant until 10 mm. They reported that the traditional pipe production systems can be adapted while using PP fibre reinforced concrete, and the pipes can meet required strength classes without resorting to conventional rebar reinforcement.

 
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