Concrete is being revolutionized in order to contribute to the immense transformation that needs to take place in the construction world, which is a high emitter of CO2. When we consider the global environmental impacts, this material does provide one solution to the challenges of sustainable construction. Alternative fuels are now being used to manufacture concrete and innovative products are being developed, which may in practice prove to save energy.
Whether we are States or companies, we all have a role to play in meeting the future challenges for the planet: 9 billion human beings by 2050, the increasing scarcity of fossil energies, but also of water, and climate disorder. Concrete is the second most consumed product in the world after water. 10 billion m3 of concrete are produced every year, i.e. over 1.5 m3 per person.
Just like cement, its main component, roughly 80% of concrete is produced in developing countries. It is, more than any other material, essential for economic and human progress, particularly in developing countries, and has an extremely large number of the qualities that are sought after in construction. Its resistance to fire, adverse weather conditions, pollution, shocks, humidity… guarantees great durability and can even guarantee that structures will last for over 100 years. As it is extremely compact (2 400 kg/m3), its high level of thermal inertia allows it to store thermal flows and subsequently release them. It is a source of comfort and energy saving. This material can be adapted to all forms of architecture and can be used for foundations, housing, roads, bridges, tunnels, water treatment and distribution networks alike. Finally, concrete can be manufactured locally, which reduces transport and creates local jobs. However, concrete emits high levels of CO2 and is being revolutionized with its own energy consumption being reduced, as well as that of buildings, thanks to improvements to its properties.
Measuring environmental impact throughout the product life cycle
These qualities obviously do not prevent concrete from having an impact on the environment. High levels of CO2 are emitted during the different manufacturing stages for some of its components. At the end of the manufacturing process, concrete has a carbon footprint of roughly 80 kg of CO2 per ton. Most of this comes from cement, the “hydraulic glue” made of sand and gravel, which are also its components.
It is important to emphasize here the limits of comparing the carbon footprints of different construction materials. For example, the footprint of steel use – 2 tons of CO2 per ton produced – cannot be compared to that of concrete. Similarly, wood is no longer neutral in CO2 if we include the carbon weight of its processing, chemical treatments and its transport. Research is currently being conducted on a broader and more comparable definition of the notion of global environmental footprint. This definition will make it possible to assess both the carbon footprint and the other environmental impacts throughout the life cycle of products: contribution to energy saving in buildings, impacts of recycling
and possible depositing of each product in a dump at the end of its life cycle. This is a fundamental task for identifying the most efficient materials throughout their life cycle, but also for positioning new innovative solutions in the future.
With just over 2 billion tons of cement produced every year, the cement industry causes roughly 5% of global CO2 emissions of anthropic origin. According to growth forecasts, particularly in developing countries, the volumes of concrete – and consequently of cement – consumed in the world are expected to double by 2030.
CO2 emissions falling
For a group like Lafarge, which manufactures both concrete and cement, the first step in reducing its CO2 emissions involves reducing the carbon content of its cement. The production of clinker,1 the basic component of cement, requires high-temperature transformation in furnaces – limestone decarbonation – which causes up to 60% of emissions. The remaining 40% are due to fossil fuels which are burned to bring the material up to a temperature of around 1,500°C.
Ten years ago, Lafarge, in partnership with WWF, set out to reduce its global CO2 emissions by 20% per ton of cement produced for the period 1990-2010. Part of the clinker used to produce cement has consequently been replaced by industrial coproducts with compatible properties, such as fly-ash from coal-fired thermal power plants or the so-called “slag” residue from the blast furnaces in the steel industry. As for the fossil fuels burned in the furnaces, manufacturing processes have been optimized. Lafarge has consequently launched a program to replace them with alternative fuels, mainly from industrial, household or plant waste. Today, they account for almost 13% of the Group’s energy mix with a strong variation from country to country depending on available supplies (Figure 1).
For example, in the Philippines 30% of furnace firing uses rice hull and in Uganda, coffee hull is used. Finally, in Malaysia the two plants consume oil palm nut shells: this project was registered under the Clean Development Mechanism2 (CDM) in 2006 and generates 60,000 tons of carbon credits a year. The target of reducing emissions per ton of cement between 1990 and 2010 has been reached a year in advance: – 20.7% at the end of 2009 and – 21.7% at the end of 2010 (Figure 2).
Moreover, research conducted by Lafarge in the field of granular stacking has opened up new avenues for producing cement that is more and more durable. The principle involves replacing part of the water used in the composition of concrete by fine and ultra-fine grains that are intercalated with the larger grains. This process makes concrete even more compact, more resistant and more durable; it uses less water and has a lower carbon footprint.
Reducing energy consumption in buildings
Buildings today consume almost 40% of global energy supplies in the form of heating, ventilation, air-conditioning, lighting, hot water production, etc. More than the emissions from manufacturing materials, the climate change challenge for the construction industry lies in reducing energy consumption in buildings during their utilization phase. Improving energy efficiency in buildings is the main challenge of what we call sustainable construction. This concept must be based on integrated policies for land-use, city and neighbourhood planning.
This approach is necessarily extremely broad and leads us to conduct reflection beyond our core business: from raw material extraction to recycling after demolition, from the thermal efficiency of structures to renewable energy production programmed right from the design stage, from occupants’ living comfort to reducing negative effects during construction works, and of course, the social and environmental responsibility of the company itself.
Today, the implementation of sustainable construction is notably demonstrated by the creation of certifications and labels (HEQ – High Environmental Quality, Habitat and Environment, Minergy, LEED – Leadership in Energy and Environmental Design, BREEAM – BRE Environmental Assessment Method…), the number of which has been constantly increasing all over the world in the last few years, giving all actors in the construction chain incentives to meet the new challenges.
Solutions for tomorrow
In order to ensure that these new products meet the challenges of sustainable construction, Lafarge uses the Life Cycle Assessment (LCA) method. It involves quantifying the environmental impact using several criteria (primary energy consumption, greenhouse gas emissions, air pollution, water consumption, transport, waste production…) and factors in the complete life cycle of a material, from raw material extraction to it being recycled or deposited in a dump.
LCA is the only method to allow a truly scientific approach to the issue. It is also the most objective method, as it relies on a standardized methodology – ISO 14040 – and factors in all the key environmental indicators. Its relevance also stems from the fact that it applies to the entire life cycle of the product or building being assessed.
The aim of this is to enhance the environmental balance of products and also to offer more efficient construction systems. When we speak about sustainable construction, there is little point in taking each material separately. One must think in terms of the extremely close links that exist between them, but also factor in the needs and trends in architecture and the parameters related to urban planning policies (density, organization of mobility…).
There are, in addition, geographical specificities and local customs. One does not build in the same manner in Europe, Asia, America or Africa: climate (more or less cold or humid), the type of construction (wood, steel, concrete, brick), the availability of natural resources and the level of development of the country also have an extremely considerable impact on the behavior of buildings or on the performance of a specific construction method. There is not one single solution applicable to all and everywhere.
The systematic approach of LCA, along with research on construction systems, challenge a large number of preconceived ideas. Concrete can improve thermal inertia, airtightness and compactness, which are three fundamental factors for energy efficiency in buildings, while guaranteeing the latter a longer life cycle and greater resistance. In two years, energy savings during the utilization phase offset any additional costs for above-standard insulation and airtightness.
One of the direct consequences of this global and integrated approach to sustainable construction is that Lafarge is developing new generation concrete solutions. The Group has notably just designed a structural ready-to-use concrete in partnership with Bouygues, which reduces thermal losses, or again a new thermal bridge breaker based on ultra-high performance fiber-reinforced concrete that reduces thermal bridges by up to 70%. The latter alone account for between 10% and 20% of energy losses in a building.
Concrete may have a considerable carbon footprint due to its production method, but it can, thanks to properties that reduce CO2 emissions related to the utilization of residential units, be part of the global process for sustainable construction.
¹ Clinker is the main component of industrial cement and is obtained by firing mixtures of limestone and clay.
² The Kyoto Protocol’s Clean Development Mechanism allows industrialized countries to finance projects that reduce greenhouse gas (GHG) emissions in developing countries. In exchange, the investor obtains emission credits.
References / Lafarge, 2011, Annual report