2.1. Use of Recycled Plastic in Road Pavements
2.2. Plastic Recycling in Asphalt Mixtures
- Uncontrolled waste disposal. Uncontrolled incorporation of variable plastic with only minimal processing to reduce the particle size to be comparable to asphalt mixture aggregates. This offers minimal return on the investment and a higher performance risk.
- Aggregate extension. Hard plastic does not melt at typical asphalt production temperatures but can partially replace or extend the aggregate in the mixture. However, the aggregate is much less expensive than the bituminous binder, so this approach provides a lower return on the investment. Some performance enhancement is often reported due to the reinforcing nature of the plastic, which is often flexible in nature.
- Binder extension. Soft plastic can be melted into the bituminous binder to partially replace or extend the binder without necessarily enhancing its properties. This provides a greater return on the investment than aggregate extension because the binder is significantly more expensive than the aggregate.
- Binder extension and modification. When soft plastic is used to modify, as well as extend, the bituminous binder, the effects can be similar to those associated with traditional polymers for binder and mixture modification .
2.3. The Products
- Productively consume a portion of waste plastic otherwise destined for landfill.
- Reduce the cost of new road construction and maintenance.
- Increase the strength and durability of local roads.
3. Research Methods
|Title||Focus and Scope||Year||Reference|
|Recycled waste plastic for extending and modifying asphalt binders||Summary of the products and the effect on asphalt mixture performance properties||2018|||
|Evaluating recycled waste plastic modification and extension of bituminous binder for asphalt||The effect on typical asphalt mixture performance properties, as well as environmental and safety issues||2019|||
|Recycled waste plastic modification of bituminous binder||The effect on the Performance Grade (PG) rating of two penetration grade bituminous binders||2019|||
|Objective evaluation of the practical benefits of asphalt binders modified with recycled plastic||The improvement in base and surface mixture modulus and fatigue life and the associated effect on predicted pavement life||2019|||
|Laboratory evaluation of asphalt containing recycled plastic as a bitumen extender and modifier||Effect of common bituminous binder properties and surface mixture performance properties||2019|||
|Comparing wet mixed and dry mixed binder modification with recycled waste plastic||Comparison of the effect of wet and dry production on bituminous binder properties||2020|||
|Recycled plastic as an alternative to conventional polymers for bituminous binder||Summary of the effects on various bituminous binder properties, including those used in the UK, Australia, and the USA||2021|||
|Laboratory comparison of wet-mixing and dry-mixing of recycled waste plastic for binder and asphalt modification||Comparison of the effect of the production process on the binder and mixture properties of a common surface mixture||2021|||
|Property||Used by Research References|
|Mixture type||Dense graded||Stone mastic||Dense graded||Dense graded|
|Binder content (%)||4.8||6.3||4.9||5.2|
|Standard||EN 13108-1||EN 13108-5||BCC Type 3||EN 13108-1|
|Property||Method||Description||Measured in Research|
|Penetration||EN 1426||Penetration by a standard needle, over 5 s, into a binder sample at 25 °C||[23,26,28]|
|Force ductility||EN 13703||Percentage of elongation until separation of a binder sample at 25 °C|||
|Elastic recovery||EN 13398||Percentage recovery of a cut binder sample after elongation by 200 mm at 25 °C||[26,28]|
|Softening point||EN 1427 (UK) and AG:PT/T131 (A)||Softening temperature of a binder sample according to the Ring and Ball method||[23,25,26,28]|
|Viscosity 60||AS 2341.2||Propensity of the binder to flow under load at 60 °C|||
|Torsional recovery||AG:PT/T122||Percentage of torsional recovery of a binder sample after rotating 180° at 25 °C|||
|Property||Method||Description||Measured in Research|
|Stiffness||EN 12697-26 (UK) AS 2891.13.1 (A)||Indirect tensile modulus at 20 °C (UK) or 25 °C (A), an indicator of sample stiffness||[22,24,25]|
|Stiffness||EN 12697-34 (UK) AS/NZS 2891.5 (A)||Marshall Stability of samples prepared by 50 blows to each side by a standard Marshall hammer and tested at 60 °C||[25,26,28]|
|Deformation resistance||EN 12697-22 (UK) AG:PT/T231 (A)||Deformation following 10,000 passes of a Cooper’s wheel tracking wheel of samples at a pre-determined temperature, generally 40–60 °C||[21,22,25,26,28]|
|Cracking resistance||EN 12697-24||Indirect tensile fatigue life of over a range of initial tensile strain magnitudes to develop a relationship between initial strain and cycles to failure, an indicator of sample fatigue life||[22,24,26,28]|
|Cracking resistance||AG:PT/T274||Four-point bending at 20 °C and 200 µε sinusoidal repeated load, an indicator of sample fatigue life|||
|Cracking resistance||EN 12697-44||Semicircular bending of notched samples under monotonic loading and tested at 0 °C, an indicator of sample fracture toughness||[21,22]|
|Cracking resistance||EN 12697-34 (UK) AS/NZS 2891.5 (A)||Marshall Flow of samples prepared by 50 blows to each side by a standard Marshall hammer and tested at 60 °C||[25,26,28]|
|Moisture damage resistance||EN 12697-12 (UK) AG:PT/T232 (A)||Ratio of indirect tensile strength of conditioned and unconditioned samples, where conditioning includes saturation and 72 h in 40 °C water||[21,22,25,26,28]|
4. Effect on Bituminous Binders
4.1. Resistance to Flow
4.2. Elasticity and Ductility
4.3. Temperature Susceptibility
4.4. Performance Grading
5. Effect on Asphalt Mixtures
5.2. Deformation Resistance
5.3. Cracking Resistance
5.4. Moisture Damage Resistance
6. Summary and Conclusions
Conflicts of Interest
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|Resistance to flow||Significant increase in resistance to flow, based on penetration and viscosity|
|Elasticity and ductility||Incorporation of substantial elasticity and ductility that were negligible in the unmodified asphalt|
|Performance grading||Three (MR6) to four (MR10) grade increases based on the MSCR test protocol|
|Stiffness||Two- to three-fold increase across various mixture types, based on various measures of mixture modulus|
|Deformation resistance||Significant 65% (MR6) and 43% (MR10) reduction in wheel tracking rut depths for various mixture types|
|Crack resistance||No significant reduction in fatigue life or fracture prorogation resistance, using various test methods|
|Moisture damage resistance||No significant difference in resistance to moisture damage across various mixture types, based on the Lottman test|
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