Categories: Issue 77 July/August 2014

Julie Buffenbarger, FACI, LEED AP, Lafarge

Fig. 1. Nearly 80 years after it was first constructed, the Hope Memorial (Lorain-Carnegie) Bridge is “complete.” The $4.5 million investment is consistent with the Cleveland’s Complete and Green Streets law, which requires sustainable transportation options be incorporated into new road projects.
Photo By Erik Drost (Flickr: Hope Memorial Bridge) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

(Part II of a two-part series)

Design Selection with Life Cycle Analysis

For several decades, researchers interested in the relationship between building materials, construction processes, and their environmental impacts have studied embodied energy in building materials. Embodied energy is divided into two main areas, namely the initial embodied energy and the operational energy. Simply put, initial embodied energy is the total energy consumed during resource extraction, transportation, manufacturing, and fabrication of a material/product; and is typically calculated within the boundaries of Cradle-to-Gate (factory gate) or Cradle-to-Site (site of use) to separate it from operational impacts. Operational energy is non-renewable energy consumed to maintain, repair, restore, refurbish or replace materials, components or systems during the structure’s life span. Operational energy is heavily influenced by the durability and maintenance of construction materials, systems and components installed in the structure, and the life span of the structure.

Life Cycle Assessment (LCA) is a method to evaluate all the aspects connected with bridge construction and the associated environmental impacts during its entire life span, including such phases like materials acquisition, creation, transportation, use, and finally disposal of the product(s). Three reporting strategies to support impact reduction predominate: Reduced net embodied energy; Environmental Product Declarations (EPDs); or specific parameters from EPDs. An EPD, is a comprehensive, internationally harmonized, verified document that reports environmental data of products, materials or processes based on life cycle assessment (LCA) and other relevant information in accordance with the international standard ISO 14025 (Type III Environmental Declarations). Specific parameters of EPDs may include global warming potential (GWP), ozone depletion, acidification, eutrophication, photochemical smog, ecotoxity, resource depletion, and reduced net embodied energy.

Collings1 studied embodied energy and CO2 emissions data from different forms of bridge construction in the United Kingdom (Figure 2). Data was gathered on a moderate river bridge with a width of approximately 394 feet (120 m) and 217 feet (66 m) approaches on each side and a total deck area was approximately 46,285 ft2 (4300 m2). The main river span and shorter approach span structure were evaluated.

Fig. 2. Three Bridge Forms Considered in the Study: a) girder; b) arch; and c) cable stay.
Fig. 2. Three Bridge Forms Considered in the Study: a) girder; b) arch; and c) cable stay.

Three commonly used construction materials were considered: steel; concrete; and a steel–concrete composite.

The concrete type used an in situ deck on a reusable shuttering system. The composite type was of steel girders supporting a concrete deck slab with permanent formwork. For the composite bridge the towers of the cable stay form were concrete and the arch steel. The steel bridge used an orthotropic deck on girders.

The embodied energy and carbon dioxide emissions generated during construction are shown in Table 1. The data illustrates that across the range of bridge forms, concrete construction consumes the least energy and produces the least CO2 emissions. It additionally implies that a well-engineered, longer span bridge using regional materials, recycled steel and eco-friendly concrete is similar to shorter less sustainable spans.2 Subsequent LCA studies by others conducted on bridges have also shown concrete to be a favorable environmental building material in comparison to wood and steel alternatives.3, 4, 5

Table 1. Embodied Energy and CO2 emissions data for different forms of bridge construction21
Table 1. Embodied Energy and CO2 emissions data for different forms of bridge construction21

LCAs of structures are greatly impacted by service life. Bridges should be designed to maximize the life of the existing infrastructure. Proper structural design and detailing, material composition, high quality construction practice, and preplanned operation and maintenance routines, including durability monitoring of the structure will significantly extend service lives and offer much lower predictable operational energy.6, 7

It is the responsibility of the bridge engineer to consider both the mechanical and environmental loads effects, including future climatic conditions, and potential deterioration mechanisms and durability risks to ensure safety and serviceability over the bridge structure’s entire service life.8, 9 Qualitative service life prediction models should be used to link material property improvements and infrastructure life cycle analysis. By coupling materials and structural deterioration models, a quantitative service life maintenance model and full life-cycle impact assessment can be created.10 Evaluation of environmental factors, loads, materials, service life prediction models during the analysis and design stages coupled with life cycle assessment and life cycle cost optimization should become an integral part of a sustainable infrastructure design. Figure 2 shows a flow chart of durability design.

Fig. 3. Flow Chart of the Durability Design Procedure11
Fig. 3. Flow Chart of the Durability Design Procedure11

Life Cycle Balance: Life Cycle Costing Analysis and Service Life Performance Requirements

The design of long life structures and effective life cycle management of existing structures will enable the construction of bridge infrastructure that contribute to the protection of the environment, as well as ensuring public safety, health, security, serviceability and life cycle cost-effectiveness.12, 13 Development of performance-based approaches and employment of appropriate maintenance strategies is critical to ensure adequate safety, serviceability and extended service life that minimizes the risk of failure for concrete infrastructure.

The increased emphasis on life cycle cost analysis (LCCA) for projects requires that attention be focused on the service life and durability of concrete structures including costs of initial construction, continued maintenance, and eventual demolition or deconstruction. The initial selection of bridge construction materials may depend on a number of complex and often intangible factors, but the total initial and long-term costs of using any construction material system is one of the most important parameters for planners and budgeters. LCCA is a necessary component in bridge management systems (BMSs) for assessing investment decisions and identifying the most cost-effective improvement alternatives. The LCCA helps to identify the lowest cost alternative that accomplishes project objectives by providing critical information for the overall decision-making process.

When used in combination with service life performance requirements, LCCA modeling provides a balanced importance of economics, environmental and societal impacts for material or system selections for infrastructure (Figure 3).

Fig. 4. Macroscale Life Cycle Modeling of Infrastructure Systems14

Sustainable Bridge Engineering Tools

CEEQUAL, Envision™, INVEST and the National Cooperative Highway Research Program’s “Guidebook for Sustainability Performance Measurement for Transportation Agencies” are some recently developed rating systems and guidance tools providing similar goals; objectives; evaluation, measurement and assessment tools; as well as, design and project implementation strategies to improve the sustainable design and performance of infrastructure.15, 16, 17, 18, 19

Future Considerations

The use of innovative design and practices such as: complementary cementing materials, ultra-high performance concretes,20 high-performance fiber reinforced cementitious composites, recycled concrete aggregates, internal curing, photovoltaic and LED lighting, vertical wind turbines, and accelerated bridge construction can all impact LCA and LCCA. In addition, high-speed and high-resolution, nondestructive evaluation (NDE) technologies for inspection, evaluation, and performance monitoring feedback to deterioration mechanisms that allow for timely preventive, corrective, and improvement measures to preserve good structural and functional performance with extended service life. Considerations should also include maintenance management programs with inclusion of non-invasive devices and sensors (e.g., smart sensors, embedded sensors and systems) that permit both periodic and continuous performance evaluation and accurate condition assessment.21 Finally, designing for adaptability and deconstruction provide strategies for climate change adaptation and end of life decommissioning.22

In closing

Bridge and highway infrastructure systems, represent an enormous investment of materials, energy, and capital, resulting in significant environmental burdens and social costs. Development of innovative materials, construction practices, and employment of appropriate inspection and maintenance strategies is critical to ensure adequate safety, serviceability and extended service life that minimizes the risk of failure for structures and infrastructure. Design, construction, maintenance, climate adaptation and resiliency are all considerations to secure long-term sustainability of new bridge assets. Hence, enhancing the resilience of bridge infrastructure through designed robustness, durability, longevity, disaster resistance, and safety should also be a priority for the bridge engineer.

Ms. Buffenbarger is the current Chairman of ACI’s Sustainable Concrete Committee. For more information, she can be contacted at [email protected].

References

  1. Collings, D., “An environmental comparison of bridge forms”, Proceedings of the Institution of Civil Engineers, Bridge Engineering, Vol 159, Issue BE4, December 2006, pp. 163-168.
  2. Long, A.E., Basheer, P.A. M., Taylor, S.E., Rankin, B. and Kirkpatrick, J. “Sustainable bridges through innovative advances”, Proceedings of the Institution of Civil Engineers, Bridge Engineering, Vol 161, Issue 4, December 2008, pp. 183-188.
  3. Hammervold, J., M. Reenaas, and H. Brattebø, Environmental Life Cycle Assessment of Bridges. Journal of Bridge Engineering, 2013. 18(2): p. 153-161.
  4. Hammervold, J. and C. Grossrieder, E6: Vinstra-Sjoa; Life cycle assessment (LCA) of 3 bridge alternatives, in Misa reports. 2011, MiSA AS.
  5. Dequidt, T.C.E., “Life Cycle Assessment of a Norwegian Bridge”, Master’s Thesis, Department of Civil and Transport Engineering, Norwegian University of Science and Technology, Trondheim, Norway, 2012.
  6. Buffenbarger, J.K., Kazanis, K.G., and Miltenberger, M.A., “Sustainable Concrete Pavements with Blended Cements, ” 10th International Conference on Concrete Pavements: Sustainable Solutions to Global Transportation Needs Organized by International Society of Concrete Pavements, Québec City, Québec, Canada, July 8-12, 2012.
  7. Mirza, S., “Design of Durable and Sustainable Concrete Bridges”, Proceedings International Workshop on Cement Based Materials and Civil Infrastructure, Karachi, Pakistan, December 2007, pp. 333-343.
  8. Connal, J and Berndt, M. Sustainable Bridges – 300 Year Design Life for Second Gateway Bridge. Proceedings, Austroads Bridges Conference, Auckland, 2009, pp. 1-16.
  9. Macía, J.M. “Design of Concrete Bridges for Sustainability and Durability”, Master’s Thesis, Department of Civil Engineering and Applied Mechanics, McGill University, Montréal, Canada. 2011.
  10. Lepech, M.D., and Li, V.C., 2006 “Sustainable Infrastructure Engineering: Integrating Material and Structural Design with Life Cycle Analysis”, Advances in Cement and Concrete X: Sustainability, edited by Schrivener, K., Monteiro, P., Hanehara, S.ECI., pp. 55-60.
  11. Sarja, A. Durability design of concrete Structures – Committee Report 130-CSL. Technical Research Centre of Finland, VTT Building Technology. RILEM Technical Committees, Materials and Structures/Matériaux et Constructions, Vol. 33, January-February 2000, pp. 14-20.
  12. Lounis, Z. et al. (2006). Life Cycle Analysis and Sustainability of High Performance Concrete Structures. Report for Government of Canada’s Action Plan 2000 on Climate Change, p. 106.
  13. Lounis, Z., and Daigle, L. (2010). Towards sustainable design of highway bridges., Bridge Maintenance, Safety, Management and Life Cycle Optimization, Frangopol, Sause & Kusko (eds), Taylor & Francis Group, pp. 1233-1239.
  14. University of Michigan. (2006) “Sustainable Concrete and Infrastructure Systems”, Ann Arbor, Michigan. Web. 16 February 2010.
  15. CEEQUAL. “The Civil Engineering Environmental Quality and Assessment Scheme”, Web. 6 September 2014.
  16. Envision™ Sustainable Infrastructure Rating System. Institute for Sustainable Infrastructure. Web. 8 September 2014.
  17. INVEST. Federal Highway Administration. 2012. Web. 8 September 2014.
  18. National Cooperative Highway Research Program, Report No. 708 “Guidebook for Sustainability Performance Measurement for Transportation Agencies”, Transportation Research Board, Washington D.C., 2011.
  19. Research, Development, and Technology Turner-Fairbank Highway Research Center, “Highways of the Future—A Strategic Plan for Highway Infrastructure Research and Development”, Report No. FHWA-HRT-08-068, US Department of Transportation Federal Highway Administration, McLean, Virginia, July 2008.
  20. Sakai, K. and Noguchi, T., The Sustainable Use of Concrete, CRC Press, Boca Raton, Florida, 2013, pp. 142-151.
  21. Sustainability Guidelines for the Structural Engineer, Editors Kestner, D.M., Goupil, J., and Lorenz, E., ASCE Publications, Reston, Virginia, 2010, pp. 243-256.
  22. George V. Voinovich Bridge Project. Ohio Department of Transportation. Web. 8 September 2014.  

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