Concrete / Cement - Can it be a "Green" material?

Regardless of the size and type of building, it is fairly hard to build conventionally without the use of CONCRETE or CEMENT. Unless of course you are building straw bale, adobe or similar. But even then, foundations may still be cast in concrete, or the walls plastered using a cement based product. So, it is useful to look at concrete or cement and ask – can it be a “green” material?

Its durable nature and versatile applications have made its usage ever-present throughout the world. However it is extremely energy intensive to make and transport, and produces a significant amount of the world’s greenhouse gas emissions. According to the World Business Council for Sustainable Development, concrete is the most widely used substance on Earth apart from water.

“Buildings and their construction account for nearly half of all the greenhouse gas emissions and energy consumed in this country (USA) each year. Globally, the percentage is even greater.”

It is estimated that cement manufacturing produces about 5% of global CO2 emissions, and 3% of global emissions of all greenhouse gases. However, concrete manufactures say that as the cement ages, it reabsorbs all the CO2 released during the manufacturing process – but this takes hundreds of years.

So what is “the green advantage” of concrete, and is it enough to negate the CO2 emissions?

• For one, it is extremely durable. Buildings constructed of concrete last lifetimes, with just the less durable finishes and fittings having to be replaced.
• It can almost always be locally sourced. So no green house gas omissions from shipping the material around the world.
• It can be recycled. Either as fill or road base, or reused as the aggregates in new concrete. However, because its chemical properties change over time and with each processing, this is limited.
• Exterior concrete walls can be energy-efficient in climates that have daily temperature fluctuations. It creates thermal mass that can store warmth or cold, reducing indoor temperature fluctuation.
• Potential new manufacturing techniques have improved the CO2 emissions. However the cost of these techniques remain to be seen and are unlikely to be available in developing countries for some time to come.
  

Despite some advantages, at the end of the day, cement & concrete are too big a contributor to green house gas emissions to be able to argue that this material may be “green”. Maybe in the future the technology will become widely available to manufacture this incredible material in a manner that will have a negative carbon footprint. It is possible, just ask Vinod Khosla…