When it comes to building structures, two of the most commonly used materials are concrete and steel. But which one is more environmentally friendly? To answer this question, it is important to understand the whole life cycle environmental impacts of each material. Life cycle analysis (LCA) is the best method to assess the impacts of all phases of the life cycle, from “cradle to grave”. When it comes to energy use and environmental emissions during the construction phase, structural concrete frame construction leads to higher energy use, CO2, CO, NO2, particulate matter, SO2 and hydrocarbon emissions due to the higher number of formworks used, higher transport impact due to a higher mass of materials and higher equipment use due to a longer installation process.
On the other hand, steel structures have higher emissions of volatile organic compounds (VOCs) and heavy metals (Cr, Ni, Mn) due to painting, torch cutting and welding of steel elements. However, when taking into account the total impacts of material manufacture, construction, transport, use, maintenance and demolition, the energy use and environmental emissions of the two buildings are comparable. The energy use and environmental emissions of office buildings can be reduced by careful selection of materials and built-in and temporary construction equipment. Of all the metals used in construction, steel is one of the most environmentally friendly.
It has a lower embodied carbon impact than concrete and generates less waste. Steel can be infinitely recycled and reused without degrading. Trees grow back and wood used in construction stores carbon dioxide. And new admixtures have the potential to drastically reduce concrete's staggering carbon footprint.
In terms of energy efficiency, engineers claim that 12-metre-high concrete walls will stop or at least slow future tsunamis. But locals have heard such promises before. It was a time of extraordinarily expensive bridges to sparsely inhabited regions, of multi-lane roads between tiny rural communities, of cementing the few remaining natural riverbanks and pouring ever-larger volumes of concrete into the dikes that were to protect Japan's coastline. Environmental scientist Vaclav Smil estimates that replacing mud floors with concrete in the world's poorest housing could reduce parasitic diseases by almost 80 per cent.
Brazilian operators boast that the 12.3 million cubic metres of concrete would be enough to fill 210 Maracana stadiums. There has also been a drive to design concrete to be as efficient as possible, for example, the use of post-tensioning to reduce the volume of concrete and steel required for slab construction. Concrete points out that it is non-flammable and the industry is making progress in reducing its emissions and input footprint. Due to their different manufacturing processes, the use of wood products produces far fewer carbon emissions than steel or concrete.
Carl Obst, director of the Institute for the Development of Environmental Accounting and former head of the National Accounting Branch of the Australian Bureau of Statistics is recognised as a world expert in the development of accounting methods that integrate natural capital and environmental services. In conclusion, when considering all aspects from material manufacture to demolition, both steel and concrete have their own environmental merits. Steel has a lower embodied carbon impact than concrete and generates less waste while concrete has non-flammable properties and is making progress in reducing its emissions and input footprint.
