Sustainability costing to aid bridge management decision making: a case study on bridge deck expansion joint replacements
Date
2016
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Publisher
University of Delaware
Abstract
Many bridges in this country have reached their intended service-life, and are deemed in need of maintenance, rehabilitation, and replacement services. A life cycle inventory collects relevant information about sustainability impacts that can be used to assess the effect of decisions on the economy, environment and society. Sustainability is important because it considers impacts that are externalized from traditional costing systems; so the impacts result in costs but bridge owners do not measure or pay those costs directly. Bridge management sustainability assessment can be thought of as impacting owners, road users, and the environment. As funding for bridge maintenance, rehabilitation, and replacement services dwindle there are greater incentives for sustainable decision making. The development of inventories that assist practitioners in exercising sustainable bridge management techniques are increasingly becoming relevant in bridge management systems (BMS). The bidding process for bridge repair projects illustrates how including sustainable assessment into decision-making can improve upon BMS. Typically, A+B bidding considers both owner costs per item (A) and the costs incurred to the road users as a result of the time to complete the project (B); monetary values are assigned to the time necessary to complete the project and the bidder with the lowest total costs (A+B) is rewarded. The manner at which time is costed is dependent on the agency and can consider road user and vehicle operating costs. However, during traditions construction operations. the costs incurred to society, specifically road users, through travel delays and increased vehicle operation costs are being disregarded. In addition, the environmental costs to human health from pollutant emissions are ignored. These impacts can be greater from specific maintenance, rehabilitation, and replacement service operations and differ from normal traffic patterns. By incorporating the costs incurred to users and the environment, both efficient and sustainable practices can be incentivized, therefore catalyzing contractors to further develop detailed and sustainable plans when bidding for and carrying out a project. For this study, we investigated various maintenance, rehabilitation and replacement actions that are pivotal to the structural health of a bridge. As a case study, the impacts of different deck expansion joint rehabilitation/replacement options measured sustainability impacts in the units of dollars. Thus, costs are associated with impacts incurred by the owner, user, and environment and are summed to provide a total cost to score the overall efficiency and sustainability of each option. Employing the A+B+C costing method, the options with the lowest cost prove to be the most efficient and sustainable. A full-depth replacement of an abutment expansion joint, on a particular bridge, was the primary focus of the case-study conducted. The joint's headers were fully removed as were the armoring and in-place sealant. Using the A+B+C costing method, the most sustainable joint maintenance program, for the particular abutment expansion joint, was determined for the bridge's remaining service life. It was found that the most cost effective joint maintenance program includes a full depth removal of the headers in 2015, and a partial depth replacement of the headers with Class A concrete in 2027. From these findings, the best option is an open compression seal implemented after the full depth replacement in 2015, and replacing the open compression seal with a strip seal in 2030. The lowest cost to the owner, users, and the environment for joint maintenance and replacement for the remaining life of the bridge is approximately $188,000.00. The most expensive joint maintenance program includes a full depth removal of the headers in 2015, and 7 partial depth replacement of the headers with elastomeric concrete; the headers replacement schedule would be supplemented with a new strip seal implemented in 2015 and open compressions seals implemented in 2030 and 2036. The most expensive option would cost approximately $285,000.00, approximately 52% more expensive than the optimized program. Within each program considered the owner costs ranged between 10-15% of the total costs, the societal costs ranged between 80-90% of the total costs while the environmental costs ranged between 2.6 and 2.7% of the total costs.