DurabRoads - life cycle costing analysis
The objective of the DurabRoads project is to design, develop and demonstrate cost-effective, eco-friendly and optimised long-life roads, by means of innovative designs, and the use of greener materials.
For more information, see DurabRoads.
This article illustrates the life cycle assessment study of the bitumen mixtures undertaken by BSRIA and shows some of the results obtained so far.
BSRIA has been involved in conducting the life cycle assessment (LCA) analysis of the potential new road layer mixtures formulated by the DurabRoads project partners to quantify their environmental impacts.
For this, an analysis of the road processes was carried out including road construction, road maintenance, road relaying and recycling, using the techniques of LCA to achieve this. In the LCA analysis of DurabRoads, three pavement mixtures- PA (porous asphalt), BBTM (Béton Bitumineux Mince), and AC (asphalt concrete), were taken as the three base cases and the partners set about trying to improve their composition.
A bitumen mixture for DurabRoads (referred to as DurabRoads Bitumen here), was designed to be used with all three cases, following which the overall mixtures were also modified with different additives and steel slag and basalt as aggregates.
The LCA study was first used to gauge the environmental impact of 1kg of the bitumen mix alone for the AC, BBTM, PA and DurabRoads Bitumen mixtures. Then the environmental impact assessment of the material for each of the road systems was carried out for a unit area of 7.4 m x 1,000 m, looking at the environmental impacts for a 50-year lifecycle.
Figure 1: Comparing 1kg each of AC, BBTM, PA Bitumen Mixture and 1kg DurabRoad Bitumen Mixture
The original bitumen mixtures were compared to the new alternative bitumen mixture which is shown in Figure 1 using the IPCC method.
The IPCC method denotes the results by normalising the environmental impact into kg of CO2 equivalent. It can be seen that with the additional additives in the DurabRoads bitumen, the environmental impact of 1kg of the DurabRoads bitumen by the IPCC method is higher, making it appear worse than the currently used bitumen mixtures. However, it must be noted that this doesn’t imply that the DurabRoads bitumen must be discarded citing the higher environmental impacts as the obvious reason.
The additives and aggregates used in the DurabRoads bitumen mixture have caused the 1kg of material to have a greater environmental impact than current mixtures; however, these additives do improve the durability of the road surface, which will be able to withstand high traffic densities and adverse weather conditions for longer.
This has a direct effect on the road’s lifecycle impact. With an increased durability, the road has to be maintained and relayed less often; meaning the total quantity of material used in the lifetime of the road is reduced. As the percentage of bitumen in a road is usually quite low (around 4-5%), with aggregates comprising the highest percentage of total materials, if the durability increases by increasing or altering the bitumen content slightly, the reduction of overall environmental impact of the road is a lot more significant as the number of maintenance and relaying cycles reduces. The following figure explains this.
Figure 2: Total life cycle costing analysis of the road system over 50 years
Figure 2 shows the total environmental impact of the surface layers of each of the road systems over its 50-year lifecycle using the IPCC method where it is assumed that the DurabRoads mixture has a higher durability factor, which is considered as 1.5 times that of the original system for this analysis.
When compared against the lifecycle of the standard bitumen mixtures, the DurabRoads bitumen showed promising results by LCA. Every DurabRoads alternative showed an improvement in terms of environmental impact using the IPCC method on the standard mixtures over a 50-year lifecycle. Based on the LCA model results, the BBTM alternative surface layer has the lowest environmental impacts.
In August 2017, the results of the life cycle assessment and life cycle costing analysis of the warm mix asphalt materials were presented by BSRIA.
Divya Deepankar, Research Engineer, BSRIA Sustainable Construction Group, said:
“Based on the results obtained so far, the road layers composed of the warm mix asphalt materials have better environmental and economic performance across the life cycle of the road system studied.
Going forward, the durability factor obtained from the pilot test results of the pilot road tested in Spain will be incorporated to analyse and infer the best case. These results will be reported and presented soon."
This article was originally published in June 2017 by BSRIA.
Written by Divya Deepankar, Research Engineer, BSRIA Sustainable Construction Group.
--BSRIA
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
A transformative shift in the design, construction and management of built assets.
Apprenticeship announcement by the Prime Minister
Welcomed but with call for more actionable detail.
Heat pump announcements, what homeowners need to know
An 'ultimate guide to heat pumps' from a heating company.
Construction contract awards reach 7.1bn in February
Their highest level in seven months.
The journey to sustainability in heritage
Research is the key to better understanding.
Heritage approaches to adaptation, mitigation and loss.
Bridging the gap between policy, finance and installation.
Development on brownfield land
Definition, background, policy and the latest consultation.
With the Design Framework for Building Services.
Retrofit of Buildings, a CIOB Technical Publication
Pertinent technical issues, measures and the roles involved.
ECA joins HSE campaign to support mental health
Working Minds’ five simple steps based on risk assessment.
Mental health in the construction industry
Mental health issues in brief with related articles.
Transitional arrangements, Building Control and the BSR.
For pre-October buildings with substantial progress by April.
Why quality counts in domestic ventilation systems
From products, to systems to the installation.
Empowering the Future with CIOB Academy
Lifelong learning, upscaling, and reskilling for the built environment.