Overview
The Massachusetts Institute of Technology’s (MIT) ongoing research through the MIT Concrete Sustainability Hub is positioned to set a new standard in life-cycle assessment (LCA) modeling. The two interim reports discuss initial findings on the life-cycle environmental costs of paving and building materials. The results will provide a rigorous means of testing the relative environmental impact of paving and building materials and design alternatives. In 2011, MIT plans to combine the environmental LCAs with MIT’s life-cycle cost analyses (LCCA) providing policymakers, DOTs, and designers the tools to accurately measure the environmental and economic costs of building and paving materials.
Life-Cycle Assessment (LCA) of Highway Pavements
MIT’s ongoing LCA of highway pavements will significantly improve the understanding of paving materials’ life-cycle performance. To date, the research team at the Hub has made considerable progress towards creating a new life-cycle model to capture the cradle-to-grave carbon emissions of paving materials. A comparative analysis of the carbon emissions of asphalt and concrete pavements over a 50-year lifetime has been conducted, with a focus on the operating, or "use phase," of the life-cycle. Research in this study has shown that the use phase of the pavement life-cycle can account for up to 85% of carbon emissions. The use phase emphasis sets the current MIT study apart from the majority of previous LCAs on paving materials.
The research team’s initial findings indicate that concrete pavements can lead to potentially significant vehicle fuel efficiency savings over asphalt pavements. These fuel efficiency savings could result in substantially lower life-cycle carbon emissions for concrete pavements compared to asphalt pavements. MIT researchers are poised to further analyze fuel consumption in 2011 to provide additional data on findings of fuel savings associated with pavement design.
In 2011, the LCA environmental findings will be combined with a comprehensive economic analysis conducted by MIT. In addition to providing similarly illuminating data on the economic side of pavements, the LCCA will identify practices which both save money and mitigate environmental impact.
Life-Cycle Assessment (LCA) of Buildings
The LCA of Buildings analyzes the environmental impact of commercial and residential building materials. Both the residential and commercial building LCAs utilize a comprehensive 75-year analysis period that highlights the operational energy demands of buildings in addition to construction, maintenance, and disposal costs associated with materials. For commercial buildings, MIT’s research team has conducted a comparative analysis of concrete and steel. For residential buildings, homes constructed with insulated concrete forms (ICF) are compared to those constructed with wood frames.
For residential buildings, MIT researchers have found that more than 90% of the life-cycle carbon emissions are due to the operation phase, with construction and end-of-life disposal accounting for less than 10% of the total emissions. The study also showed that in residential structures, the use of ICFs instead of code compliant wood-framed construction can produce operational energy savings of 20% or more, with the highest energy savings occurring in colder climates.
For commercial buildings, based on initial research, which compared 12-story structures in both warm and cold climates, the added thermal mass afforded by the use of concrete when compared to steel yields annual heating, ventilation, and air conditioning (HVAC) energy savings of between 5% and 6% depending on the climate.
Since HVAC energy savings directly translate to cost savings, much of the economic studies to come will build upon existing findings and highlight additional economic life-cycle attributes of commercial and residential building materials.
