For thousands of years, concrete has been a foundation of the built environment: the most widely used man-made material on the planet. However, as architects, and the public alike, sharpen their focus on the causes and effects of climate change, the environmental damage caused by cement has become a subject of unease.
As exhibited in a recent in-depth article by Lucy Rodgers for BBC News, cement is the source of about 8% of global CO2 emissions. The piece was written off the back of the UN’s COP24 climate change conference in Poland and found that in order to meet the requirements of the 2015 Paris Climate Agreement, annual cement emissions must fall by 16% by 2030.
If the cement industry were a country, it would be the third largest emitter in the world – behind China and the US. It contributes more CO2 than aviation fuel (2.5%) and is not far behind the global agriculture business. (12%).
-Lucy Rodgers, BBC News
Although the origins of concrete and cement can be traced back to Syria and Jordan in 6000BC, and more articulately by the Ancient Romans in magnificent structures such as the Pantheon, the 19th and 20th century saw an explosion in cement use. Production of cement has increased thirtyfold since 1950, and a further fourfold since 1990, driven by postwar building in Europe, and building booms across China and Asia from the 1990s onwards.
Today, over 4 billion tonnes of cement are produced each year, releasing over 1.5 billion tonnes of CO2. China is the top producer of cement and cement-related emissions, followed by India, the EU, and the US. However, the leveling off of Chinese consumption of cement has, in turn, caused global cement production to level off from 2014 onwards at the 4-billion tonne mark. As the future markets in construction move towards South East Asia and sub-Saharan Africa, it is predicted that cement production may have to increase by 25% by 2030 to keep pace.
So why is cement such a heavy polluter? The blame is frequently laid at the foot of quarrying and transport process, however this only accounts for less than 10% of cement-attributed emissions. As stressed by the BBC report, over 90% of the sector’s emissions can in fact be attributed to the process of making “clinker” – a key element of concrete.
This process sees a rotating kiln heated to over 1,400C (2,600F), fed with a quarried mix of ground limestone, clay, iron ore, and ash. The mixture is split into calcium oxide and C02, at which point the CO2 is released to leave behind marble-sized grey balls, called clinker. The clinker is then cooled, ground, and mixed with limestone and gypsum to form cement ready for transport.
As well as calls to move towards more sustainable primary building materials such as timber, the heightened awareness of the environmental damage caused by cement has led to the growth of new alternatives to the clinker process. Recently, researchers at Lancaster University in the UK unveiled a novel approach of using nanoplatelets extracted from carrots and root vegetables to enhance concrete mixes. Another trend of “bioreceptive concrete”, developed by Dr. Sandra Manso-Blanco, sees structural concrete layered with materials to encourage the growth of CO2-absorbing moss and lichen.
The approach of Taktl, meanwhile, is centered around the idea of "less is more." While this ultra-high-performance concrete is still concrete, it produces far less CO2 than traditional concrete by using less water and by being stronger, meaning you need less of it to achieve the same strength.
To further-curb runaway carbon emissions, a California-based company called Watershed Materials is developing alternatives to the traditional concrete block which uses less cement, dramatically reducing the amount of carbon dioxide produced; they even have a product in the works which they hope will offer a widely applicable concrete block alternative which uses no cement at all.
You can read Lucy Rodgers' full report for the BBC here.
News via: BBC News