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April 29, 2011

New MIT model paves way for greener use of concrete

  • Life-cycle research could help engineers develop less costly, more sustainable designs for roads and buildings.
  • By HAMLIN JENNINGS
    Massachusetts Institute of Technology

    mug
    Jennings

    What if our local, state and federal governments could accurately estimate the full economic and environmental costs of their infrastructure investments?

    Over the past 18 months, a team of researchers at the Massachusetts Institute of Technology has developed a life-cycle model for select building and paving materials. This effort will soon provide the scientific community, industry leaders and policymakers with an innovative cradle-to-grave analysis of both the environmental and economic costs of typical buildings and pavements in the United States.

    Life-cycle assessment (LCA) is a technique to quantify the environmental impacts, such as the global warming potential, of a product or service. The strength of LCA is that it accounts for all events, processes and activities that occur over the entire life cycle, from raw materials extraction and product manufacturing to operation and maintenance, and finally, demolition and waste management.

    From an infrastructure perspective, adopting such a cradle-to-grave approach is a necessity as we work towards understanding and reducing our environmental footprint.

    Infrastructure applications such as buildings and pavements require massive resource inputs during their construction and operate for decades into the future. LCA provides the optimal platform to break down the infrastructure life cycle, identify where environmental impacts are occurring, and propose strategies for improving the footprint.

    Infrastructure road map

    Our research focuses on concrete, asphalt, steel and wood — the foundation of our infrastructure all over the world. These materials are in widespread use every day and are inextricably linked to virtually every facet of modern life.

    The ubiquity of these core paving and building materials has given rise to several attempts to quantify our respective environmental and economic impacts, so that a data-driven understanding of these costs can allow engineers and policymakers to develop the best design techniques for sustainability and cost-effectiveness.

    Life-cycle studies have produced three primary results:

    • Focus on the operational phase: The operational phase of buildings and pavements often account for as much as 90 percent of their carbon dioxide emissions throughout their life cycles.

    • Consideration for economic and environmental impacts: Life-cycle assessments that measure environmental impacts are accompanied by equally comprehensive life-cycle cost analyses (LCCA) that include the economic costs of building and paving materials.

    • Benchmarking: Life-cycle work establishes benchmarks that will be used to create a road map for better infrastructure in the future.

    A unique aspect of the research is the coupling of LCA and LCCA with a program to develop new strategies for reducing the environmental impact of our infrastructure by using concrete.

    Concrete has a broad range of properties such as strength, density, fire resistance, thermal capacity, creep under load, shrinkage on drying, stability when exposed to water, and the ability to be cast into almost any shape.

    These properties have made concrete the most used man-made material on earth. While they have typically been optimized for use as a structural component of our infrastructure, they also influence the cost and carbon dioxide equivalents (a measure of greenhouse gas emissions) that are being analyzed by LCA and LCCA. Initial results highlight the competitive nature of concrete, but they also provide guidance for further improvement by taking into account properties that are not typically considered.

    Over the last year, the research team has quantified the environmental costs of construction and demolition, but our work with pavements, commercial buildings and residential buildings has shown that it is the period in between — the “use phase” during which buildings and pavements are operational — that comprises the bulk of the impact over the life of the structure.

    This means that heating, cooling, lighting, rolling resistance of vehicles, maintenance scheduling and materials costs often have the greatest impact, and this motivates an entirely new set of important properties, which, if taken advantage of, will help us move towards achieving goals aimed at reducing our environmental impact at an affordable cost.

    More to learn

    Surprisingly, our understanding of the science of concrete is incomplete. It has proven very difficult to decipher the structure of concrete at the atomic scale, so most modern investigative laboratory tools have provided only fragments of information.

    Many research groups around the globe, private and public, are constantly adding to our understanding, but only recently have detailed atomic scale models been possible. The team at MIT is pushing the boundaries of these sophisticated atomic-scale models to provide new insight, which then can be used as a design tool.

    The team is tackling two major issues, evaluation and design. During our first year we have published a number of summary statements on our website, web.mit.edu/cshub, and hundreds of visitors have interacted with faculty and students. These pieces of the puzzle will be provided to industry, academia and government to help make our national and international research and development programs more effective.

    Life-cycle assessments strive to combine the best data on the full range of costs — construction, maintenance, reconstruction, user, direct and indirect — with a time frame that reflects the real-world life of pavements and building materials.

    In offering up the best available science on the full costs of these materials, the research provides a model for policymakers to consider as they make decisions pertaining to the maintenance, design and construction of roads and buildings throughout the country. It will help policymakers understand the true costs, to ensure good value for infrastructure investment.

    At the same time, new strategies for developing more sustainable infrastructure through the use of concrete are emerging. Thus, data-driven models will allow a new era of budgetary and environmental forecasting that is anchored in real-world conditions and marketplace realities, providing a basis for motivating new strategies for the science and engineering of materials used in our infrastructure.

    Perhaps after a half-century of intense research, the design of concrete will use the same sophisticated principles applied to other modern materials. The fiscal and environmental challenges of the coming decades call for nothing less.


    Hamlin Jennings is executive director of the Concrete Sustainability Hub at the Massachusetts Institute of Technology, where he is also an adjunct professor in the Department of Civil and Environmental Engineering.


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