From: David A Gabel, ENN
Published September 2, 2011 09:25 AM

Sustainable Concrete

Concrete is the most widely used building material for residential and commercial buildings. From its humble origins in Roman times, this mixture of Portland cement, aggregate, water, and chemical additives is now a $35 billion industry in the US alone, employing over two million workers. However, when it comes to greenhouse gases, concrete is believed to be a major culprit. The construction and operation of buildings in the United States accounts for about 40 percent of all greenhouse gas emissions. According to a new study from the Massachusetts Institute of Technology (MIT), certain measures can be taken to drastically reduce and possibly eliminate the carbon footprint of new concrete buildings, and even some older ones.

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The study looks at the carbon emissions produced over the entire life-cycle of a concrete building, including construction, use, and demolition. It was published by the MIT Concrete Sustainability Hub, funded by the cement and concrete industries, and led by associate professor, John Ochsendorf. The two year study is believed to be the most detailed accounting ever taken of the life-cycle of buildings, focusing on all the details like the source of raw materials and how they were transported.

The researchers found many areas of potential savings that would also cut emissions. For example, concrete is typically used for its structural properties, but could be more greatly used for its thermal properties, which could reduce a building's energy needs. For example pipes could be embedded in concrete floors, walls, and ceilings to better insulate them. Also buildings can be designed so that exterior concrete has direct exposure to sunlight in the winter so it can store heat, even at night.

The UN Intergovernmental Panel on Climate Change has identified green building as the most cost-effective way policy to reduce greenhouse gas emissions. But before real reductions take place, a reliable method for quantifying emissions need to be established. According to lead author, John Ochsendorf, the MIT study provides that.

The MIT report attempts to provide a more complete approach, examining cradle-to-grave analysis for all materials that go into concrete. For example, the impact of adding fly ash (a waste product from coal combustion) was studied. They looked at the question of whether to include its transportation into the overall life-cycle analysis, because the fly ash would have had to be transported anyway. This was a common question for all beneficial secondary use materials.

The goal of reducing life-cycle emissions from concrete buildings have been embraced by many. The American Institute of Engineers have entered into the 2030 challenge, an initiative to spur dramatic reductions in building energy use. Cities and other organizations have also agreed to the initiative which calls for a 60 percent reduction in emissions immediately and 100 percent reductions by 2030. At that point, concrete buildings will have no net energy consumption at all.

Link to MIT Report: http://web.mit.edu/cshub/news/pdf/MIT%20Buildings%20LCA%20Report.pdf

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