Green buildings: Concrete's role

The most-used building material in the world, concrete, is used to construct many of the country’s homes and office buildings, but a new report from the world-renowned Massachusetts Institute of Technology (MIT) says a variety of measures could drastically reduce, and ultimately even eliminate, the carbon footprint of most new concrete buildings, as well as some older ones.

The new report, summarised by the MIT News Office, outlines some of  those measures, analysing buildings’ energy use and carbon emissions over their entire life cycle of construction, use and eventual demolition.  

The report is one of two issued in August by the MIT Concrete Sustainability Hub, a multidisciplinary research collaboration founded by the cement and concrete industries. The researchers say the report provides the most detailed and open accounting ever undertaken of the full life cycle of buildings.

The report reflects nearly two years of work by the MIT team, says lead author John Ochsendorf, associate professor of civil and environmental engineering and architecture.

His group’s life-cycle analysis extends all the way down to details of where the components come from, and how they were transported. In doing so, researchers were able to quantify emissions and potential savings, and also put a cost on them, he says.

Not only are there significant savings possible in the energy use of  buildings and their associated emissions, but some of these are cost-free. “There are steps to reduce carbon emissions that save money, that pay back owners,” Ochsendorf says.

Concrete’s properties

Typically today, concrete is used in construction purely for its structural properties, but by harnessing concrete’s thermal properties for passive solar storage, the material could greatly reduce a building’s energy needs.

For example, by designing windows and overhangs so that concrete is exposed to sunlight during the winter, the material can effectively store heat during the day and release it at night. 

In addition, pipes embedded in concrete floors, walls and ceilings can be used for both heating and cooling, providing greater efficiency as well as greater comfort than systems that rely on heating the air in the room, the report says.

“Life-cycle assessment of buildings is still a relatively new field,” says Ochsendorf.  
Yet governments around the world are already starting to set up requirements for significant reductions in buildings’ carbon footprints, and the Intergovernmental Panel on Climate Change has identified buildings as the most cost-effective sector for implementing policy to reduce greenhouse gas emissions.

But, says Ochsendorf, in order to show that real reductions are taking place, one first needs a reliable assessment of the emissions associated with existing buildings, and a methodology for comparing those with newer ones.  The new MIT report provides that, he says.    

As for the fuel used for kilns that make cement, the director of the Concrete Sustainability Hub, Hamlin Jennings, says, “It turns out that often a significant amount of that fuel might otherwise be waste material, and some of it even toxic waste.”  The MIT report, he says, attempts to provide a more complete approach than others have.  The team “produced a model that is transparent and can be tested by others,” he adds.

Already, the American Institute of Architects has embraced an initiative, called the 2030 Challenge, to spur dramatic reductions in buildings’ energy use and emissions.  Many cities and organisations have agreed to its goals, which call for a 60 per cent reduction in emissions (compared to the existing average) right away, and a 100 per cent reduction by 2030. In other words, by then buildings should have no net energy consumption at all – which, amazingly, is already feasible today, Ochsendorf says.

“There have been zero-energy schools built in the last five years,” he says, as well as other types of buildings, including the new zero-net-energy headquarters of the National Renewable Energy Laboratory in Colorado.  

These primarily rely on tight construction and good insulation, and compensate for their remaining energy use by installing solar arrays or other energy-producing systems.
For reducing total life-cycle energy use, “the real opportunities are in operation of  buildings rather than in their initial construction,” Ochsendorf says.  

For many consumer goods such as  computers, the energy used over their operating lifetime is about equal to that used for their manufacture, he says, but “for buildings, energy for operation is about ten times that of their construction.”