Application of Recycled Polyethylene Terephthalate (PET) Fibers to produce Fiber Reinforced Concrete pipes

R.M.M.P Rathnayaka1, De Silva Sudhira1 and De Silva Subashi1

1Department of Civil and Environmental Engineering Faculty of Engineering University of Ruhuna

Hapugala, Galle Sri Lanka

E-mail:Madushanpri@gmail.com

Abstract: Fiber reinforced concrete is one of the prominent solutions for many problems that concrete had from its early stage. Polyethylene terephthalate (PET) fiber is a sustainable solution for fiber reinforced concrete since it is an eco-friendly material. Manufacturing of the cage form of the conventional reinforcement bars adjusted for concrete pipes requires special bending, welding, and placement machinery, and also it is time-consuming. Objective of this study is to investigate application of PET fibers as a replacement material for steel reinforcement cage in reinforced concrete pipe element. At the initial stage concrete cubes were cast with different fiber compositions (i.e., 0%,1%,2% and 3%) for water cement ratio of 0.3 and 0.45. Three sets of specimens (Plain concrete, Reinforced concrete and PET fiber concrete) were subjected to three-edge-bearing test. It was observed that 2% of PET fiber content contributed to achieve optimum compressive strength of 45.8 MPa for the concrete having 0.3 water cement ratio. In addition, it was found that PET fiber reinforced concrete is the most applicable method for production of concrete pipes. PET-fibre concrete pipes seem to be an economical alternative to the classically-reinforced-concrete pipes. Keywords: Recycled PET, Compressive strength, Cylindrical pipes, Three edge bearing test

1. INTRODUCTION

Fiber reinforced concrete (FRC) has become a prominent solution for the drawbacks of ordinary concrete. For example, pavement laying, shotcrete tunnel linings, blast resistant concrete, overlays, and application to mine construction showed better performance with FRC compared with ordinary concrete (Ochi et al, 2007). In experimental studies, Fraternali (2011) found that FRC has improvement in the compressive strength compared with that of the normal concrete. Further, it has been found that the compressive strength depends on the fiber characteristics: length, diameter and volume.

Cylindrical pipes, which can be manufactured using fiber reinforced concrete, are often manufactured with steel reinforcements and used to convey liquids. However, there are many advantages of using steel fiber reinforced concrete over the ordinary steel reinforcement pipes. Manufacturing of the cage form of the conventional reinforcement bars requires special bending, welding, and placement machinery, and time consuming. Steel fibres of standard sizes, on the other hand, can be added to the pan-mixer of any concrete plant as another aggregate or mineral admixture. Without any extra process for modification, steel-fibre concrete can be produced and cast in the moulds similar to the ordinary plain concrete. Therefore, steel-fibre concrete pipes seem to be an economical alternative to the classically-reinforced-concrete pipes. Most of the times, these cylindrical pipes are used to convey liquid, such as water and waste water. In the process of conveying, steel fiber is exposed to the water. As a result, steel fiber may corrode and durability of the pipe would reduce. To overcome this problem an alternative type of fibers that are not vulnerable to corrosion can be used.

Due to rapid development in technology, the use of PET materials to manufacture containers has been increased. Among them, PET bottles used for beverage containers has become very popular, although PET bottles eventually become an environmental pollutant due to their in proper recycling process (Kim et al, 2010).Use of recycled PET fiber in fiber reinforced concrete pipes would provide a

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mailto:Madushanpri@gmail.com

sustainable solution for the environment pollution while increasing durability of the pipes. Objectives of this study are

• To investigate the optimum mix proportion and strength characteristics of PET fiber reinforced concrete.

• To investigate the mechanical and durability characteristics of short PET fiber reinforced concrete made with short PET fibres.

2. METHODOLOGY

2.1 Pet Fiber Material

PET fibers, used in this study, were collected from Beira Group, Horana, Sri Lanka. PET fibber was added on the volume basis (0%, 1%, 2%, and 3% of total volume), and it would not replace any material in the concrete. Each PET fiber addition was done for two water cement ratios: 0.3 and 0.45.The diameter and the length of the PET fiber was 0.7 mm and 50 mm, respectively (Figure 1).

Figure 1 PET fiber

2.2 Experimental Procedure

2.1.1. Compressive Strength

Cubes having the size of 150 mm x 150mm x 150 mm were cast according to BS 1881 -108 (1988) and cured until the testing day as described in BS1881-111(1988).Concrete was mixed based on the mix design in accordance with BS 5328 .In order to achieve a workable mix, Rheobuild 1000 was added to the concrete mix as a high-range water-reducing admixture. Concrete crushing machine, available in the Buildings Material Laboratory, was used to crush the cubes (Figure 2(a)) at the age of 3, 7, 14, 21, and 28 days. At these ages, the compressive strengths were determined.

2.1.2. Tensile Strength

Three cylindrical specimens having the standard size (150mm diameter and 300mm height) (BS 1881:144 (1988)) were cast and split tensile strength of concrete was determined. For each specimen, split tensile strength was investigated by using the compression testing machine as shown in Figure 2 (b). In addition, slump of the mixture was measured for each mix proportion.

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Figure 2 Testing of specimens: (a) Compressive strength test, (b) Split tensile strength test.

2.1.3. Cylindrical Culverts

Six cylindrical culverts were cast (Figure 3) using three different mixtures: plain concrete, reinforced concrete and fiber reinforced concrete (Table 1). The fiber reinforced cylindrical culvert was cast using the optimum concrete mixture, which gave the optimum value for compressive strength, tensile strength and slump.

Figure 3 Procedure of casting cylindrical culverts; (a) Assembling of the mould. (b) Steel reinforcement cage, (c) Concreting, (d) Curing

a b

(a) (b)

(c) (d)

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(a) (b)

Figure 4 Schematic diagram of test apparatus (a) Front view, (b) Side view

Table 1 Material composition of cylindrical culvert

Specimen Steel reinforcement PET fibers (Total volume)

Plain concrete - -

Reinforced concrete 6mm mild steel at

120mm c/c spacing

-

Fiber reinforced concrete

-

2%

Testing of cylindrical culverts was performed in accordance with BS5911 Part 100 (1988). According to the standard, three edge bearing test was performed as shown in Figure 4. The proof load was obtained and ultimate load that the culvert can sustain was calculated. Proof load is the line load that a pipe can sustain without the development of cracks width exceeding 0.25 mm or more over a distance exceeding 300mm in a three edge beading test [BS 5911 Part 100 (1988)]. The ultimate load was determined by multiplying the proof load by 1.5. A 50x50mm grid was drawn on the surface of the cylinder in order to locate the crack locations. Crack widths were measured using the filler gauge.

3. RESULTS AND DISCUSSION

3.1 Compressive Strength

The variation of compressive strength of fiber reinforced concrete is shown in Figure 5.It can be observed that for fiber reinforced concrete, the compressive strength increases with the age of the concrete for both water cement ratios of 0.30 and 0.45, the similar behaviour that can be expected for normal concrete. However, at each age, the compressive strength of the fiber reinforced concrete is less compared with that for the normal concrete for both water cement ratios of 0.3 and 0.45.For water

Actuator arm

Top support

Bottom supports

LVD

LVDT

Loading beam

500mm

300mm Diameter

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cement ratio 0.30, strength development in fiber reinforced concrete, at 3,7,14 and 21 day is lesser than that for the normal concrete. However, the compressive strength at 28 day is considerably higher in normal concrete than that in fiber reinforced concrete. Table 2 shows the reduction in 28 day compressive strength with fiber percentage for water cement ratio of 0.45 and 0.30. It can be seen that, for the water cement ratio of 0.45, there is 42.35 % reduction in the compressive strength in 28 day comparing to the control specimen for a fiber 1%. However, for a water cement ratio of 0.3, the variation of 28 day compressive strength with the fiber percentage of 1% is 11.29%. Ochi (2006) conducted similar test and identified that compressive strength of PET FRC is increasing with increasing the fiber content. This deference might be due to the properties of PET fiber used in two studies: Ochi had used fibers which has 40mm length whereas 50mm length PET fiber was used in the current study. Except the length of the PET fibers all other properties were similar PET fibre used in the current study. In is study, the maximum improvement (i.e., 5.98 %.) was recorded for 1% of fiber content using 0.55 water cement ratio. Beyond 1% of fiber, the compressive strength decreases with the increment of fiber content. However, the current study indicates a reduction in compressive strength irrespective of the fiber contents (1%, 2%, & 3%) for both water cement ratios of 0.30 and 0.45.

(a) (b)

Figure 5 Variation of compressive strength with age of the concrete; (a) Water cement ratio 0.45, (b) Water cement ratio 0.30 [please edit the Figure 5(b) as in the Figure 5(a)]

Table 2 Reduction of compressive strength (%) with fiber percentage for different water cement ratios: 0.3 and 0.45

3.2 Tensile Strength

Figure 6 shows the variation of tensile strength with the PET fibre content. It can be found that there is an improvement in the tensile strength in the fiber reinforced concrete for water cement ratio 0.3 and 0.45. With the increment of fiber content the tensile strength increases. Specimens with 0.3 water cement ratio exhibits higher tensile strength than 0.45 water cement ratio.

Fiber percentage (%) Compressive strength reduction (%)

0.45 W/C ratio 0.30 W/C ratio

1 42.35 11.29

2 42.14 8.92

3 37.61 11.12

0

10

20

30

40

50

3 7 14 21 28

Com

pres

sive

Str

ess

(MPa

)

Days Control Specimen 1% PET

2% PET 3% PET

0

10

20

30

40

50

3 7 14 21 28

Com

pres

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Str

engt

h (M

Pa)

Days Control Specimen 1% PET

2% PET 3% PET

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Sandaruwani et al (2012) identified that fiber content can be increased up to 2% with an improvement in the tensile strength in concrete. The tensile strength will reduce as the fiber content increase beyond 2%. However, Arful (2015) observed that the inclusion of PET fiber above 1.0% decreases the tensile strength in concrete. The inclusion of PET fiber improved the tensile property and showed the ability in absorbing energy in the post-cracking state due to the bridging action imparted by the fibers during cracking.

Figure 6 Variation of tensile strength with fiber content for water cement ratio 0.3 and 0.45

3.3 Slump

The variation of the slump values with the fiber content is shown in Figure 7. With increasing the fiber content, slump value of the concrete mixture decreases. In the case of 0.3 water cement ratio,3% of PET fiber content the slump value is 45mm. For domestic applications such a water cement ratio is not recommended, because of low workability.

Figure 7 Variation of slump with the fiber content

3.4 Load Bearing Test

Reinforced concrete cylinder shows an improvement in ultimate load over the plain concrete (Figure7). It was identified that PET fiber concrete performs well in bearing test comparing to the steel reinforced concrete and plain concrete: there is a significant reduction in the crack length and width in the fiber reinforced cylinder.

0.00.51.01.52.02.53.03.54.0

control 1% PET 2% PET 3% PET

Tens

ile S

tren

gth

(MPa

)

0.45 w/c ratio 0.3 W/C ratio

0

50

100

150

200

250

300

Control 1% PET 2% PET 3% PET

Slum

p (m

m)

0.45 W/C Ratio 0.3 W/C Ratio

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Figure 8 Crack patterns (a) Plain concrete, (b) Reinforced concrete, (c) Fiber reinforced concrete

Figure 9 Load vs. deflection curve for cylindrical culverts

Plain concrete pipe do not comply with the BS 5911 Part 100 requirements in terms of ultimate load (Figure 8). Both reinforced concrete culverts and fiber reinforced culverts satisfy the requirement of BS 5911 Part 100.Comparing to a previous study by Tefarul et al (2007) , , current study shows a significant improvement in ultimate load, crack width reduction and also the length of the crack. In addition, PET fiber reinforcement has an advantage over normal steel fibers because corrosion can be eliminated by using PET fiber reinforced concrete to produce cylindrical culverts.

4. CONCLUSIONS

For water cement ratio of 0.3 and 0.45, the workability of fresh concrete decreases with the addition of PET fiber, although the geometry of fibers has a small effect on the workability of concrete.The reduction in 28 day compressive strength in PET fiber reinforced concrete is less for water cement ratio of 0.3 compared to that for water cement ratio of 0.45, indicating that 0.3 water cement ratio can be considered as the optimum water cement ratio. In addition, 2% of PET fiber percentage was identified as the optimum fiber content for PET fiber reinforced concrete.

Load

(kN

/m)

35 30 25 20 15 10 5 0

0 1 2 3 4 5 6

Deflection (mm)

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The tensile strength that is required for cylindrical culverts, increases with the inclusion of PET fiber showing the ability in absorbing energy in the post-cracking state due to the bridging action imparted by the fiber. During cracking there is a significant reduction in the crack length and width in the fiber reinforced cylindrical culverts.

ACKNOWLEDGEMENT

The authors would like to express their gratitude to Faculty of Engineering Research Grant 2015 for providing necessary financial support and Department of Civil and Environmental Engineering, Faculty of Engineering, University of Ruhuna for the supports to carry out the research work successfully. The authors also wish to thank Lal Construction for the support extended in preparation of specimens.

REFERENCES

Kim Sung Bae,Yi Na Hyun,Kim Hyun Young,Kim Jang-Ho Jay,Song Young-Chul, 2010. Material and structural performance evaluation of recycled PET fiber reinforced concrete. Cement and concrete composites, 32(3), pp. 232-240. Ochi T, Okubo S,Fukui K, 2007. Development of recycled PET fiber and its application as concrete-reinforcing fiber. Cement and Concrete Composites, 29(6), pp. 448-455. Tefarul Haktanir, Kamuran Ari, Fatih Altun,Okan Karahan, 2007. A comparative experimental investigation of concrete reinforced-concrete and steel-fibre concrete pipes under three-edge-bea ring test. Construction and Building Materials, Volume 21, pp. 1702-1708. Arful, M. C., 2015. Effects of PET fiber arrangement and dimensions on mechanical properties of concrete. The IES Journal Part A: Civil & Structural Engineering, Issue ahead-of-print, pp. 1-10. Sandaruwini A.H.W.E, Bandara K.A.J.M and De Silva G.S.Y., Investigation on Mechanical Behavior of Concrete with Fibers Made of Recycled Materials, Proceedings of International Conference on Sustainable Built Environment (ICSBE-2012), 14-15 December 2012, paper no. SBE/12/81.

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