What is Life Cycle Assessment?
Life cycle assessment is a standard method widely used to assess comprehensively the potential environmental impact of products or systems of products. Life cycle assessment (LCA) considers all life-cycle phases from initial construction to demolition. For roads, this includes the construction, operation, maintenance, and end of life phases, and factors such as traffic delay, lighting demand and future maintenance. The LCA method is described in the international standards ISO 14040 and ISO 14044. LCA consists of four phases that affect one another. These phases are as follows:
- First phase: the goal and scope definition involves the determination of system boundary, functional unit and analysis period.
- Life cycle inventory analysis phase: all relevant materials, energy inputs, and outputs are included in the system.
- Life cycle impact assessment phase: the environmental effects of the system components are assigned to different impact categories. Different materials are weighted according to their damage potential and summarized in total impact indicators.
- Final interpretation phase: the impacts are analyzed and evaluated to draw conclusions or make recommendations.
All environmental aspects of the product life cycle including emissions into the air, water and soil, waste, use of raw material and exploitation of nature are considered. This comprehensive approach avoids the misallocation of environmental effects and provides an overview for possible impact reduction. In this article we focus on the role of materials in LCA by answering these three questions:
- What materials are used in road construction?
- What is the role of materials in life cycle assessment?
- What is the future of life cycle assessment from a material perspective?
What materials are used in road construction?
Materials used in roads depend on what type of road is being constructed. A wide variety of materials are used in the construction of roads these are soils (naturally occurring or processed), aggregates (fine aggregates or coarse aggregates obtained from rocks), binders like lime, bituminous materials, and cement, and miscellaneous materials used as admixtures. Global Road Technology has previously penned a detailed article on 5 different types of road construction and surfaces. The materials used in road construction include:
- Aggregates – fine or coarse obtained from rocks.
- Soils – naturally occurring or processed.
- Cementitious materials – cement, fly ash and lime.
- Recycled materials – recycled asphalt pavements and recycled asphalt shingles.
- Bituminous materials – neat and modified bitumen and bitumen emulsions.
- Miscellaneous materials – admixtures
- Geosynthetics – geotextiles, geogrids and geomats.
The different types of roads that are constructed include:
- Earth (dirt) roads.
- Gravel roads.
- Water bound macadam roads.
- Unbound, sealed surface roads
- Asphaltic concrete roads.
- Cement concrete roads.
What is the role of materials in the life cycle assessment of roads?
At the ‘cradle’ the role of materials in their virgin state from the is to achieve the specifications of the type of the road being designed. There has been tendency, to think in a linear way, especially comparing the use of virgin materials and recycled materials. Material selection is less of a fit for purpose, but more specification driven, and it is complying with the design criteria of the road to be constructed. At the ‘grave’ post its service life, large quantities of waste materials are generated which probably ends up in a landfill somewhere forgetting how at the ‘cradle’ a large quantity of virgin materials was consumed. This then necessitates the need for a circular way of thinking when it comes to the role of materials in life cycle assessments of roads. The current challenges faced with linear role of materials in LCA are because large volumes of waste materials, lack of landfill space and scarcity of natural materials. There is need for recycling of materials to complete the full circle of materials used in roads. LCA quantitatively analyzes the environmental impacts of a given system through its entire life cycle from raw material extraction (cradle) to ultimate disposal (grave). The generic road life cycle includes:
- Material production – extraction, production and transportation.
- Construction – onsite equipment, traffic delay and transportation.
- Use (operation) – rolling resistance, carbonation, leachate, albedo and lighting.
- Maintenance and rehabilitation – maintenance, rehabilitation, reconstruction and transportation.
- End of life – landfilling, recycling and transportation.
In a linear system the end point is at the end of life whereas in a circular system the end-of-life feeds into material production again to start a new life cycle with the recycled material at the end of life. The role of materials in LCA of roads can be best understood from the beginning and end of the life cycle with modern day approaches driven more towards creating a sustainable circular economy system.
What is the future of life cycle assessment from a material perspective?
The future of LCA from a material perspective is complete replacement of virgin materials with recycled materials whilst being able to surpass the performance of virgin materials. This will incentivize the use of recycled materials more especially given the scarcity of virgin resources. The main solid waste streams include (1) pavement by-products (2) industrial by-products and (3) construction and demolition by-products. The potential uses of recycled solid waste materials include:
- Substitute for asphalt binder or cement.
- Replace partial bound or unbound aggregates.
- Substitute virgin binder and aggregate.
For example, in Australia, the National Waste Policy Action Plan provides a comprehensive framework to identify gaps and future challenges for waste and resource recovery. The ban imposed on exporting mixed plastic waste comes into effect in July 2021, while single resins/polymer plastics will be banned from export in July 2022. These policy changes are expected to increase the amount of waste material that is recycled and reprocessed in Australia. Recycling of plastic currently stands at 12%. The incentive for job creation will also be met with challenges of pressure on the recycling industry and associated market of recycled products hence life cycle assessment will come in as key to sustainable transitions in an Australian context.
Linear or circular paradigms?
LCA and sustainability are complex topics but also very interesting in the sense that they give opportunity to understand the full circle of roads using methodologies that focus on a cradle to grave approach. The concept of LCA is a new paradigm for future sustainable road frameworks and in our next article in this 4-part series we will evaluate LCA from a selectin of pavement types. We continue to discuss and add value to the circular economy conversation in the drive to raise awareness on the benefits to incentivize circular economy solutions in response to climate change, carbon footprint and sparing use of virgin materials. Are you implementing life cycle assessment for your road construction? Are you skewed towards a circular or linear way of thinking? What are the types of road construction you are dealing with?
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Li et al. 2019. Life cycle assessment and life cycle cost analysis of recycled solid waste materials in highway pavement: A review. Journal of Cleaner Production.
Milachowski, C., Stengel, T., and Gehlen, C. 2011. Life Cycle Assessment for Road Construction and Use. European Concrete Paving Association.
Santos et al. 2021. Recycling waste plastics in roads: A life-cycle assessment study using primary data. Science of the Total Environment. 751. 141842. 1-13.
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