CONCRETE is the most prevalent building material on the planet and the world would be pretty flat, with no tall buildings and structures, without it. But no construction material is more ecologically destructive than concrete – chiefly because of cement, the binding agent in concrete.
Cement production is a big driver of climate change, responsible for 5% of man-made carbon dioxide (2008 data from the Cement Sustainability Initiative, a coalition of major cement companies worldwide). Production of cement exceeds 2.6 billion tonnes a year and is growing at 5% annually – this gives for a lot of carbon load.
For every tonne of cement produced, about 0.8 tonne of carbon dioxide (CO2) is released, the bulk of it when limestone is heated at high temperatures. The combustion fuel, mostly coal, emits CO2 as does limestone itself, which is calcium carbonate (CaCO3). The mining of limestone also depletes our natural resources, disfigures the landscape, and causes noise and dust pollution.
“Cement manufacturing is fundamentally an unsustainable and non-renewable process,” says Matthias Gelber, co-founder of Maleki, a German building materials development company. “When we burn limestone, we release the carbon captured in limestone by Mother Nature over millions of years. Limestones are carbon sinks that we’re destroying to make cement. It’s crazy from an environmental viewpoint.”
To green cement production, some producers replace portions of the limestone with fly ash (byproduct of coal power plant), slag (byproduct of steel industry) and volcanic ash. Recycling these waste further curbs air and land contamination as well as help conserve land currently needed for their disposal. Some producers have also switched to alternative fuels such as palm kernel shells and tyres during the manufacturing process to reduce carbon emissions.
Last year, Lafarge Malayan Cement introduced two cement products which use fly ash. These have received the Green Label certification by the Singapore Environment Council.
In Germany, Maleki processes ground granulated blast furnace slag and fly ash with its proprietary technology to make low-level cement products.
“By replacing cement with the industrial byproducts, we won’t have to burn limestone,” says Gelber. He is based in Malaysia but his company does not manufacture here as fly ash and slag are available only in limited quantities and at inflated prices.
“You can reduce the carbon footprint of concrete to a low level by using a minimal amount of cement and accelerate the hardening process with alkaline activation. There are already cement-free concrete in the market. The idea of green cement is using waste materials that have properties similar to cement. The Pantheon in Rome was built from volcanic ash. In countries such as Indonesia and China, there is a huge volume of volcanic ash available that can be used to build buildings. Some companies here are importing volcanic ash to make cement. With these technology, you don’t need cement to make concrete.
“But the construction industry here is conservative and not keen to change too much as it is already making money with existing materials and methods.”
Many governments have mandated cement producers to use byproducts in their formulations but this is not yet a requirement in Malaysia. – TanChengLi