Benefits of Recycled Materials in Pavement Construction

Recycling is becoming an integral part of modern infrastructure projects, particularly in road construction. Utilising recycled materials in pavements not only addresses the pressing issue of waste management but also provides a sustainable alternative to conventional materials. This blog delves into the use of seven recycled materials in pavement construction, exploring their engineering performance, health and safety considerations, environmental impacts, and economic benefits.

1. Recycled Crushed Glass

Image Source: The Construction Index

Engineering Risk and Performance: Recycled crushed glass (RCG) is increasingly used in road construction due to its comparable performance to natural aggregates. It provides adequate load-bearing capacity and durability when mixed with other materials. However, the variability in glass composition can affect its performance, requiring stringent quality control measures.

Health, Safety, and Environmental Risks: The primary concern with RCG is the potential for contamination and the risk of harmful glass dust. Proper handling and processing techniques are essential to mitigate these risks. Overall, using RCG helps to reduce landfill waste while conserving natural resources.

Economics: RCG is often cheaper than virgin materials, especially when local recycling facilities are available. The economic viability improves further when considering the reduced landfill costs and the potential for reuse in subsequent projects.

2. Recycled Plastic Waste

Example of asphalt modified cores.

Image source: Marie Enfrin, Rebecca Myszka, Filippo Giustozzi via Science Direct.

Engineering Risk and Performance: Plastics in pavement construction, categorised under various SPI codes, can enhance the durability and flexibility of asphalt mixtures. Specifically, they can improve the pavement’s resistance to cracking and rutting. However, ensuring consistent quality and performance remains a challenge due to the different types of plastics available.

Health, Safety, and Environmental Risks: The use of plastics raises concerns about microplastic pollution and toxic emissions during processing. It is crucial to implement safe handling practices and rigorous environmental assessments to minimise these risks.

Economics: Recycled plastics can be cost-effective, especially when sourced from local waste streams. They offer long-term economic benefits by enhancing the lifespan of pavements and reducing maintenance costs.

3. Industrial Slag

Engineering Risk and Performance: Industrial slag, a by-product of steel and iron manufacturing, is known for its high strength and durability. It performs well in both base and sub-base layers of pavements, providing excellent load distribution and stability.

Health, Safety, and Environmental Risks: The main health concern with slag is the potential presence of heavy metals. Appropriate processing and testing can mitigate these risks. Environmentally speaking, using slag reduces the need for natural aggregates and diverts waste from landfills.

Economics: The cost of slag can be lower than traditional materials, particularly when sourced from nearby steel plants. The economic advantages are further enhanced by its durability and low maintenance requirements.

4. Recycled Tyres

Engineering Risk and Performance: Recycled tyres, often processed into crumb rubber, are used to modify asphalt, enhancing its elasticity and resistance to wear. This material significantly improves the pavement's lifespan and performance under varying temperatures.

Health, Safety, and Environmental Risks: Potential risks include the release of harmful compounds during processing and the leaching of contaminants. Implementing strict processing controls and environmental safeguards is crucial. Using recycled tyres also helps reduce landfill waste and environmental pollution from tyre disposal.

Economics: While the initial cost of rubberised asphalt can be higher, the extended lifespan and reduced maintenance needs offer significant long-term savings. Additionally, it supports the recycling industry and creates a market for waste tyres.

5. Reclaimed Asphalt Pavement (RAP)

Image source: The Constructor

Engineering Risk and Performance: RAP involves reusing old asphalt materials, which can be blended into new pavement mixes. It maintains good performance characteristics, including structural integrity and durability when processed correctly.

Health, Safety, and Environmental Risks: The primary concern with RAP is ensuring that it is free from contaminants. Proper assessment and processing can address these issues. RAP contributes to environmental sustainability since it reduces the need for new asphalt and conserves natural resources.

Economics: RAP offers substantial cost savings by reducing the need for virgin materials and lowering disposal costs. The economic benefits are evident in both initial construction and long-term maintenance.

6. Coal Combustion Products (CCPs)

Engineering Risk and Performance: CCPs, such as fly ash and bottom ash, are by-products of coal power plants. They enhance the strength and durability of pavement materials, especially when used as a cement substitute in concrete.

Health, Safety, and Environmental Risks: The use of CCPs raises concerns about the potential leaching of toxic elements. Thorough testing and adherence to safety guidelines are necessary. From an environmental standpoint, CCPs help reduce landfill disposal and decrease greenhouse gas emissions from cement production.

Economics: CCPs are generally cost-effective and provide economic benefits by enhancing the performance of pavements, thus reducing maintenance costs and extending service life.

7. Recycled Crushed Concrete and Masonry

Engineering Risk and Performance: Recycled concrete and masonry materials perform well as aggregates in pavement construction. They offer sufficient strength and stability for use in base and subbase layers.

Health, Safety, and Environmental Risks: The main concerns include the presence of contaminants and the potential for dust during processing. Proper processing and quality control can mitigate these risks. Recycling concrete and masonry conserves natural resources and reduces landfill waste.

Economics: Using recycled concrete and masonry is often more economical than sourcing new materials. It reduces disposal costs and supports sustainable construction practices.

Conclusion

Incorporating recycled materials into pavement construction is a promising strategy for promoting sustainability and reducing environmental impacts. Each material offers unique benefits and challenges, highlighting the importance of thorough assessment and quality control. Through continuous research and refinement of these practices, the road construction industry can contribute significantly to a more sustainable future.

For more detailed information on the performance, risks, and economics of these recycled materials, you can refer to Austroad’s Guide to Pavement Technology Part 4E: Recycled Materials.