It is estimated that more than 90% of the 5.2 million kilometers of European paved roads and highways are surfaced with asphalt. Also, about 44% of goods are transported by road in the EU; maintaining their condition whilst in transit is crucial for the economy.
The construction of a new road has a number of implications for the environment, consuming large amount of materials and energy. Also, the price of crude oil, which is the major source of bituminous binder, has significantly increased in recent years (the most noticeably in 2001–2008). This has led to an increase in the total price of asphalt mixtures.
In order to promote sustainable practices and to combat price increase, measures with sound sustainability credentials need to be widely implemented. Developing novel materials and technologies to integrate greener material, waste and recycled materials into the production cycle of asphalt mixtures is a solution that improves both sustainability and cost-efficiency of the asphalt pavement industry.
The main concept presented in this paper is the application of an eco-innovative asphalt pavement designed through partial substitution of greener materials into asphalt mixtures: reclaimed asphalt pavement (RAP), construction and demolition waste (C&DW), lignin (by-product of 2nd generation bioethanol processing) and bio-binder from vegetable oil. This paper discusses a new concept of an asphalt pavement structure with ecologically oriented attributes, achieved whilst maintaining a level of long term performance comparable or greater than that of conventional pavement structures.
The two main components of asphalt mixture – bitumen and aggregates – are focused upon. In relation to bitumen, two methods to ‘green’ the fresh binder fraction are explored: The first investigates bio-fluxing bitumen, which enables part of the petro-chemical binder to be replaced with bio-based products; the second uses a specific industrial waste, also bio-derived, to replace the crude-oil derived polymer in modified bitumen. In relation to aggregates, two different approaches are also explored: The use of high rates of reclaimed asphalt pavement (RAP) in new hot asphalt mixtures, thanks to the addition of bio-fluxing agents which will allow working at lower temperatures, and the use of construction and demolition waste (C&DW). Optimal integration of C&DW as raw material will be established using a selective process for the separation of C&DW to increase the overall quality of the recycled aggregates.
Considering the full pavement structure, the main innovations can be summarized as follows: (A) in surface course is the introduction of green bitumen modifier, derived from recovered waste bioethanol production as an alternative to the traditional additives used for polymer modification; (B) in binder and base course, bio-fluxing agents allow for the integration of higher percentage of reclaimed asphalt; and (C) the lower layers (sub-base and subgrade) are mainly composed of materials derived from construction and demolition waste.
This paper describes the systematic approach for selecting the right combination of these main pavement components in the design of asphalt mixtures, from laboratory tests to real applications. This approach has been developed by a consortium of partners in the FP7 funded Asphalt Pavements for a Sustainable Environment (APSE) project.
It is estimated that in excess of 90% of the 5.2 million kilometers of European paved roads and highways are surfaced with asphalt. Also, about 44% of goods are transported by road in the EU, therefore maintaining the condition of highways, to ensure effective transit of goods, is crucial to the economy.
The construction of a new road has a number of implications for the environment, consuming large amounts of materials and energy. Also, the price of crude oil, which is the major source of asphalt binder, has significantly increased in recent years (the most noticeably in 2001–2008). This has led to an increase in the total price of asphalt mixtures.
4. Conclusions and summary
Road construction is a sector where measures need to be taken in order to reduce the energy demand and environmental impact, and, in particular, to reduce the use of raw materials cost-effectively. The APSE project aims to contribute to sustainable development by adhering to relevant EU policies and reducing the environmental impact associated with the construction of roads. It aims to this by proving technologies that facilitate asphalt recycling, use of waste and novel greener binders, all integrated appropriately into optimal and eco-innovative designs of asphalt pavements, and thereby increasing their commercial viability. Based on the research conducted, it can be concluded that potential measures with sound sustainability credentials, including alternative binders and a wide use of recycled materials (including reclaimed asphalt and recycled materials derived from construction and demolition waste), can be adopted for widespread application in the right situations.