DURABROADS - Life Cycle Costing Analysis of Road System

Divya Deepankar, Research Engineer, BSRIA Sustainable Construction Group

The objective of the DURABROADS project is to design, develop and demonstrate cost-effective, eco-friendly and optimized long-life roads, by means of innovative designs, and the use of greener materials.

BSRIA has been involved in conducting the life cycle assessment (LCA) and life cycle costing (LCC) 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 and LCC to achieve this. This article discusses the results of the LCC analysis of the road system scenarios developed in the project.

Figure 1 denotes the individual net present values of the costs incurred by the initial construction, road maintenance and relaying of the total road system over its life cycle of 50 years. The order of preference for a LCC analysis is in the order of lowest life cycle cost which implies that the most preferred alternative has the lowest life cycle cost. In all the cases the maintenance and relaying costs are significantly high across the life cycle of the road system over 50 years. The LCC calculations show that with reference to the AC Base Case.

In the analysis, 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 compositions. A bitumen mixture for DURABROADS referred 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, basalt as aggregates. This analysis was carried out for the LCC analysis of six cases where the base case was the asphalt concrete road. The other five pavement alternatives - namely AC Alt, BBTM Base, BBTM Alt, PA Base and PA Alt - were compared against the AC Base case to select the one that maximizes net savings. The LCC Model was calculated as the net present value over a 50 year period using a discount rate of 6% per year. The 50 year period has been selected to match the period used for the environmental impact assessment done in the LCA while the 6% discount rate was selected as it is a typical value used for a private sector construction project undertaken by a trusted investor.

Figure 2 illustrates the results of the total LCC analysis denoting the calculated life cycle cost in each case. It can be observed that in each individual case the DURABROADS alternative was more cost effective compared to its current base case. With reference to the AC Base case, the BBTM Alt gave the best economic advantage to the order of £70,710.32 or a 7.07% saving across its lifetime.

The total life cycle costs include the construction, maintenance and transportation costs. The operation and occupation costs are not considered for analysis as they will be the same in the base case and the alternatives hence can be ignored in a comparative analysis. The residual value of the road at the end of the period of analysis is not assigned as most roads have no end of life, but reconstruction or relaying is done with a new road while the old road continues to remain in place.

It is important to note that the LCC analysis is only an aid to make a choice between the alternative scenarios and does not represent the actual costs incurred at various stages through the project. The analysis reduces all initial and through-life costs to their net present value using a discount rate that has been selected as 6% for all the cases in this project.

Therefore, based on the LCC analysis alone, the BBTM Alt is the best alternative while the PA Base is the worst alternative in comparison with AC Base. It is likely that these alternatives may yield different results for different study periods or different discount rates but these sensitivity analyses haven’t been carried out within the scope of this study.

About DURABROADS and this article

This article has been produced in the context of the DURABROADS Project. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n°605404. All information in this document is provided “as is” and no guarantee or warranty is given that the information is fit for any particular purpose. The user thereof uses the information at its sole risk and liability. For the avoidance of all doubts, the European Commission has no liability in respect of this document, which is merely representing the author’s view.