Concrete Pavement Life Cycle Environmental Assessment & Economic Analysis: A Manitoba Case Study

Life Cycle Assessment (LCA) is recognized as one of the most comprehensive ways to evaluate the environmental impacts of different strategies associated with a physical feature such as highway pavement structures, bridges and vertical structures. Alternatively, life cycle cost analysis (LCCA) is performed by different agencies including Manitoba Infrastructure (MI) to select the most cost-effective construction option or life cycle strategy. Highway agencies started to realize the need to combine the LCA and LCCA in the design, construction and management of roadway assets. This paper presents comparisons of the environmental impacts and life cycle costs of various alternative strategies for a portland cement concrete (PCC) pavement project in Manitoba to demonstrate the opportunity to optimize the cost, pavement performance and environmental impacts. A matrix of 10 different strategies that include alternative PCC mix, pavement design, and maintenance and rehabilitation (M&R) treatments have been used to contrast both the life cycle costs and environmental impacts with MI’s past practice (base case). The presented analysis is expected to assist highway agencies to better understand and weigh not only the economics of alternative strategies, but also the environmental implications of alternative roadway materials, design, construction, and maintenance and rehabilitation practices. 1.2 Objectives and scope The objectives of this paper are to show, using the Athena Pavement LCA tool the environmental impacts of various PCC mixes and pavement design scenarios, and to explain the performance reasons for the current MI specification changes and future considerations. Furthermore, this study evaluates the life cycle costs associated with each material and design scenario. These include the agency cost of initial construction and future M&R activities as well as the user costs from excess fuel consumption due to PVI. This case study uses a concrete pavement section constructed in 2015 on the northbound direction of Provincial Trunk Highway (PTH) 75 divided highway, in Manitoba. This project was the first project where the new MI specification was used (listed as Scenario 6 of this case study). The other analysis scenarios include a matrix of alternative PCC mix designs based on varying cement/aggregate, fly ash and slag compositions, varying reinforcing steel type, size and quantity, and rehabilitation practices based on the expected extension of pavement’s initial service life from the usual initial service life due to the construction of more durable pavement. These variations, alone and in combination, facilitated the comparison of the life cycle environmental impacts and costs for 10 alternative scenarios relative to a base case. The environmental impacts and life cycle costs presented in this paper reflect the total for the entire project i.e., 11.02 km x 2 traffic lanes plus shoulders. It should be noted that the empirical approach of linking PCC proportioning and slab design (10 alternative scenarios) to pavement performance, which in turns affect the M&R and PVI, is intended to demonstrate the potential impact of those concrete mixes and slab design. A more robust assessment will require actual long term field performance data for each of these scenarios which is out of the scope of this paper but could be investigated further in future studies. 2 PAVEMENT LCA SOFTWARE