"Life cycle assessment of alternative asphalt pavements" – Use of recycled materials in hot-mix asphalts

Abstract

Transport infrastructures such as road are assets for the society as they not only ensure mobility but also strengthen society’s economy, and if well done, also its ecology. Considerable amount of energy and materials, that include bitumen, aggregates and additional additives are required to build and maintain roads. Inadequate use of materials and energy may lead to more waste, higher costs and bigger environmental impacts. There are many approaches to analyze in which degree this aspects are fulfilled. This knowledge is decisive in order to decide where further investigation is needed the most.

Studying the life cycle perspective of roads can help us improve the technology in order to achieve a system that has a lower impact on the environment. Currently, there are a number of LCA tools available. However, the use of these tools is still unknown and they are rarely used in real road projects. This shows that there are still gaps, which are need to be filled in order to bring the environmental aspects into practice.

This thesis chose to make a comparative Life Cycle Assessment (LCA) to make conclusion about the environmental impact of different alternative asphalt pavements compared to a virgin asphalt solution. The framework takes into account the construction, maintenance and end of life (EOL) phases and focuses on human health and environmental impacts.

The investigated alternative asphalts are all based on the idea of using waste materials in the asphalt mixture as a sustainable solution by avoid landfilling and even improving mechanical properties and durability.

In one of recycling solutions for road ways is using reclaimed asphalt pavements (RAP). The approach of using old asphalt to build new road is already widely familiar and used. Even though, the percentage of RAP material in new asphalt roads is yet relatively small. This LCA was observing the technology by pushing it to the limit by using 100%RAP mixture with the addition of rejuvenators.

Another approach of using recycled materials is the use of crumb rubber (CR) from end-of-life tires (ELT’s). CR can be mixed with bitumen by creating a crumb-rubber-modified Binder (CRM-Binder), whose functionality and mechanical properties show enhanced characteristics.

All the pavements were compared to a same functional unit (FU) in order to be consistent on the mass calculations. This thesis and its life cycle inventory (LCI) should serve as a basis for further investigations on the observed topics.

The life cycle impact assessment of this thesis showed significant environmental advantages of both alternative solutions compared to a conventional road. The feasibility of the practical use is given, since many countries around Switzerland are already successfully using these sustainable solutions.