Development of recycled polypropylene plastic fibres to reinforce concrete

Yin, Shi (2015) Development of recycled polypropylene plastic fibres to reinforce concrete. PhD thesis, James Cook University.

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In recent years, macro plastic fibres have widely been used to replace traditional steel reinforcement in the construction of concrete footpaths, precast elements and shotcrete tunnel linings, because of the ease of construction, reduced labour time and lower cost. They can effectively improve the performance of concrete, such as reducing drying shrinkage cracks and improving post-cracking performance of concrete elements. Recycled polypropylene (PP) fibres offer significant environmental benefits over virgin PP fibres or steel mesh. However, the recycled PP fibres have not yet been widely adopted by construction industries due to limited research and understanding on their mechanical properties, alkali resistance, and performance in concrete.

Since reinforcing effects of recycled PP fibres in concrete depend mainly on their tensile strength and Young's modulus, this research firstly explored the feasibility of using an improved melt-spinning and hot-drawing process to produce recycled PP fibres of high mechanical properties in an industrial scale. The 100% recycled PP fibre with high tensile strength (342 MPa) and Young's modulus (7115 MPa) was successfully produced in this research. The melt-spinning and hot-drawing process significantly improved crystallinity of the 100% recycled PP fibre from 51% to 82%. Since the 100% recycled PP fibre had higher crystallinity than that of virgin PP fibre, the recycle PP fibre showed higher Young's modulus. However, the 100% recycled PP fibre showed slightly lower tensile strength than that of virgin PP fibre, due to degradation from its repetitive processing and service life. In spite of the lower tensile strength, the 100% recycled PP fibre still has enough capacity to be used in concrete due to its high Young's modulus. An alkali resistance test was conducted and found that the 100% recycled PP fibre has minimum degradation in the concrete alkaline environment.

Performance of the 100% recycled PP fibre in different grades of concrete was studied and compared with virgin PP fibre. In order to increase bond with the concrete, line indentation was made on the surface of recycled PP fibre. Post-cracking performance of the fibre reinforced concrete was studied through the round determinate panel test (RDPT) and crack mouth opening displacement (CMOD) test. In the 40 MPa concrete reinforced with 6 kg/m³ of either 100% recycled or virgin PP fibre (normally used for precast concrete elements), most of the fibres were broken instead of being pulled out at the failure load. The 100% recycled PP fibre showed slightly lower performance than that of virgin PP fibre in the 40 MPa concrete. In 25 MPa concrete with 4 kg/m³ of line-indent PP fibres (normally designed for concrete footpaths), majority of fibres were pulled out instead of being broken in the CMOD and RDPT tests. As the fibres did not reach ultimate tensile strength, their Young's modulus were more influential. The 100% recycled PP fibre had higher Young's modulus and hence, performed better than virgin PP fibre. The test results showed that the 100% recycled PP fibre has sufficient mechanical properties to be used to reinforce precast concrete elements and concrete footpaths.

In order to further improve fibre bonding with concrete, a new indentation of diamond shape was made on the fibre surface and compared with the commonly used line indentation. In the CMOD and RDPT tests, the diamond indents showed a better bonding with the concrete. Therefore, the diamond-indented 100% recycled PP fibre produced better post-cracking reinforcement in the concrete than that of line-indent 100% recycled PP fibre and virgin PP fibre and hence, can be used to replace steel reinforcing mesh (SRM) in concrete footpaths.

The environmental impacts of using 100% recycled PP fibres were assessed by using cradle to gate life cycle assessment (LCA) based on the Australian context. The LCA methodology is generally considered an excellent management tool for quantifying and comparing the eco-performance of alternative products. To reinforce 100 m² of concrete footpath, 364 kg of SRM and 40 kg of PP fibres can achieve the same degree of reinforcing in concrete. In this research, the environmental impacts of production of 40 kg 100% recycled PP fibres made by industrial PP waste and domestic PP waste were studied, and compared with those of production of 40 kg virgin PP fibre and 364 kg SRM. The LCA results showed that industrial 100% recycled PP fibre offers significant important environmental benefits over virgin PP fibre and SRM. Specifically, the industrial recycled PP fibre can save 93% of CO₂ equivalent, 97% of PO₄ equivalent, 99% of water and 91% of oil equivalent, compared to the SRM.

To showcase the industrial application of 100% recycled PP fibre produced in this research, the fibre performance was tested in various real-life applications which included concrete footpaths and precast concrete drainage pits. A 100 metre long footpath was casted in James Cook University by using 4 kg/m³ of the diamond-indent 100% recycled PP fibre instead of traditionally used SRM. The fibre was directly mixed with the concrete in a concrete truck, and the ready-mixed concrete was poured into the formwork, which significantly reduced labour time and cost. Plastic shrinkage cracks did not appear after casting. The footpath has been used for half a year, and there are no drying shrinkage cracks as well. Concrete drainage pits reinforced by using 6 kg/m³ of diamond-indent 100% recycled PP fibre were produced and found to have comparable testing results with the steel mesh reinforced concrete pits in the vertical loading tests.

In summary, this research has developed a methodology of producing recycled PP fibres with optimum mechanical properties for reinforcing concrete. The great potential of using these fibres in various concrete applications such as footpaths and precast concrete elements has been shown. This will not only help reduce consumption of virgin materials like steel or plastic but also provides attractive avenue of recycling plastic waste.

Item ID: 43810
Item Type: Thesis (PhD)
Keywords: concrete reinforcement; design; fiber-reinforced concrete; fibre-reinforced concrete; FRC; mechanics; plastic fibers; plastic fibres; polypropylene; PP; recycled plastics; structure
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For this thesis, Shi Yin received the Dean's Award for Excellence 2016.

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Yin, Shi, Tuladhar, Rabin, Shi, Feng, Shanks, Robert A., Combe, Mark, and Collister, Tony (2015) Mechanical reprocessing of polyolefin waste: a review. Polymer Engineering and Science, 55 (12). pp. 2899-2909.

Chapter 3: Yin, Shi, Tuladhar, Rabin, Shanks, Robert A., Collister, Tony, Combe, Mark, Jacob, Mohan, Tian, Ming, and Sivakugan, Nagaratnam (2015) Fiber preparation and mechanical properties of recycled polypropylene for reinforcing concrete. Journal of Applied Polymer Science, 132 (16). pp. 1-10.

Chapter 5: Yin, Shi, Tuladhar, Rabin, Collister, Tony, Combe, Mark, Sivakugan, Nagaratnam, and Deng, Zongcai (2015) Post-cracking performance of recycled polypropylene fibre in concrete. Construction and Building Materials, 101 (Part 1). pp. 1069-1077

Chapter 6: Yin, Shi, Tuladhar, Rabin, Sheehan, Madoc, Combe, Mark, and Collister, Tony (2016) A life cycle assessment of recycled polypropylene fibre in concrete footpaths. Journal of Cleaner Production, 112 (Part 1). pp. 2231-2242.

Date Deposited: 19 May 2016 00:25
FoR Codes: 09 ENGINEERING > 0912 Materials Engineering > 091209 Polymers and Plastics @ 25%
09 ENGINEERING > 0907 Environmental Engineering > 090701 Environmental Engineering Design @ 25%
09 ENGINEERING > 0905 Civil Engineering > 090503 Construction Materials @ 50%
SEO Codes: 87 CONSTRUCTION > 8703 Construction Materials Performance and Processes > 870301 Cement and Concrete Materials @ 70%
87 CONSTRUCTION > 8798 Environmentally Sustainable Construction > 879899 Environmentally Sustainable Construction not elsewhere classified @ 15%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960599 Ecosystem Assessment and Management not elsewhere classified @ 15%
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