Life cycle assessments

Life cycle assessments (LCA) on innovative pavement designs incorporating the 3 key recycled materials was performed using the Sustainability Assessment Tool (SAT).

• Crumb rubber
• Recycled plastics
• Recycled crushed glass

The SAT was developed through a joint Western Australian Road Research and Innovation Program and the National Assets Centre of Excellence program in a collaboration between the Australian Road Research Board, Main Roads Western Australia, and the Queensland Department of Transport and Main Roads.

SA-specific data was generated and incorporated into the SAT. This state-specified data recognises SA’s unique energy mix compared with the rest of Australia. Data used for the LCA was sourced from AusLCI and modified using SimaPro software to calculate emissions based on the SA energy market.

The assessment basis and design scenarios are shown below.

Crumb rubber

An LCA was undertaken for crumb rubber in dense graded asphalt (CR-DGA) as wearing course with the following criteria:

• Crumb rubber (1 wt.% of asphalt) was added into the wearing course as a binder modifier (wet method). 
• It was assumed that the crumb rubber requires 3 routine and 2 periodic maintenances over a 40-year period (base case asphalt assumes 4 routine and 3 periodic maintenances over a 40-year period).

Figure 4.5 shows the contribution analysis of pavement containing crumb rubber compared with a base case. The key findings include:

• Fewer maintenance interventions decrease the overall greenhouse gas emissions of CR-DGA. 
• The highest emission saving is from using fewer maintenance materials (embodied) followed by maintenance processes and maintenance materials (manufacturing). 
• CR-DGA requires less bitumen binder compared to a conventional DGA, therefore the overall emissions are significantly reduced by using crumb rubber. 

Recycled plastics

An LCA was undertaken for recycled plastics in DGA as wearing course. The following criteria were used:

• Recycled plastic (0.5 wt.% of asphalt) was added to the wearing course as a binder modifier. 
• Recycled plastic was assumed to be polyethylene. 
• It was assumed that the recycled plastic requires 3 routine and 2 periodic maintenances over 40 years (base case asphalt assumes 4 routine and 3 periodic maintenances over 40 years).

Figure 4.7 shows the contribution analysis of pavement containing recycled plastics compared with conventional pavements. The key findings include:

• The overall greenhouse gas emissions of RP-DGA is lower compared to conventional DGA. This is due to the higher emissions savings linked to the maintenance activities.
• Both recycled plastics and crumb rubber are used as binder modifiers to enhance the performance of asphalt, however, RP-DGA has higher overall emissions compared to CR-DGA. This is due to:
  • the recycled plastics sorting process producing higher emissions compared to crumb rubber sorting processes
  • recycled plastics being added in lower percentages to the asphalt mix compared to crumb rubber, and therefore more bitumen (which has high embodied emissions) is used.

Recycled crushed glass 

An LCA was undertaken for recycled crushed glass in DGA as wearing course asphalt. The following criteria were used:

• 5% recycled crushed glass was incorporated into the wearing course as partial aggregate replacement. 
• Maintenance types and frequencies for pavements containing recycled crushed glass were assumed to be the same as a base case.

Figure 4.3 shows the contribution analysis of greenhouse gas emissions during different stages of the life cycle. The key findings include:

• Use of 5 wt.% recycled crushed glass in wearing course has no significant impact on overall emissions as compared to conventional materials. 
• Recycled crushed glass has slightly higher embodied emissions as compared to conventional aggregates.