MIT Weighs the Lifecycle Impacts of Concrete

MIT Weighs the Lifecycle Impacts of Concrete

Concrete is literally the backbone of our infrastructure, but it often takes a bad rap for the carbon intensity of its key ingredient: cement.

Research just out of MIT's Concrete Sustainability Hub finds that concrete has some good properties that can be overlooked if assessments of the building material do not truly look at the entire lifecycle.

And beyond that, the studies say, taking a look at how we put concrete to use can make a big difference: For example, using concrete to pave roads and highways can yield greater fuel efficiency for cars than asphalt.

While much work has been done to try to reduce the greenhouse gas emissions associated with manufacturing cement, an MIT research team examined the impacts of concrete across its lifecycle as a building material and took into account elements like use, operations and, in the case of roads, "rehabilitation."

"Products and services have impacts throughout their life, beginning with raw materials extraction and product manufacturing, continuing through construction, operation and maintenance, and finally ending with a waste management strategy," the study on concrete's lifecycle in buildings said. "Conventional environmental assessments often overlook one or more of these phases, leading to incomplete results and inadequate conclusions."

The approach MIT took on lifecycle assessment and benchmarking is as important as the findings that resulted from researchers' extensive modeling projects on buildings and roads, reports on the research said. MIT released its studies, "Methods, Impacts, and Opportunities in the Concrete Building Life Cycle" and "Methods, Impacts, and Opportunities in the Concrete Pavement Life Cycle" last week.

John Ochsendorf, who led the research team and is an associate professor in MIT's departments of architecture and civil and environmental engineering, described the work about midway through the project last year/"We are trying to create a new level of clarity and a new level of literacy about the emissions related to buildings (and roads) and ways to reduce them,"  Ochsendorf told me at the time.

Construction and maintenance of buildings are responsible for the majority of materials consumption in the U.S., and buildings account for about 40 percent of national energy use and about the same percentage of greenhouse gas emissions.

Here are some key findings from the studies:

• Residential concrete buildings have higher embodied global warming potential than a wood alternative, and commercial concrete buildings are roughly equivalent to a steel alternative.
• However, concrete structures have lower annual operating global warming potential than than the alternate designs in wood or steel, ranging from 2 percent to 10 percent in savings.
• Over a 60-year lifecycle,  the lower operating global warming potential outweighs the initially equal or higher embodied GWP for concrete buildings. The total life cycle GWP is equal to, or lower than, alternate designs in steel or wood.
• In roads, researchers found the stiffer the pavement, the better the fuel economy for vehicles, which gives concrete an edge. Initial results indicate that asphalt pavement must be up to 60 percent thicker than a concrete pavement to achieve the same stiffness and fuel consumption rates.

The studies are available for free download at MIT's Concrete Sustainability Hub, which is supported by the Portland Cement Association and the Ready Mixed Concrete Research and Education Foundation.

Image CC licensed by Flickr user ShuttrKing|KT.