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Concrete and the environment
Concrete is one of the most versatile, durable and cost-effective building materials known to man. It is also environmentally sustainable, with green credentials that outperform both steel and timber. Concrete is the second most consumed substance on Earth after water. 90% of materials used in concrete can be from recycled sources including aggregate and the use of Ground Granulated Blastfurnace Slag (GGBS), a by-product from blast furnaces or fly ash from power stations as a replacement for cement in concrete. This significantly reduces the overall greenhouse gas emissions associated with the production of concrete. GGBS can replace up to 70% of cement in a concrete mix and reduce carbon dioxide emissions per tonne of concrete by up to 70%.
Embodied energy. The Concrete Centre has published the latest information which should be used for comparing concrete with different materials on an embodied energy basis. Its report entitled 'Sustainable Concrete: The Environmental, Social and Economic Sustainability Credentials of Concrete' confirms that structural concrete has an embodied CO2 (ECO2) rating per kilogramme per tonne (KG/T) of 153 ECO2KG/T compared with 1932 ECO2KG/T for structural steel and 449 ECO2KG/T for hardwood timber. Copies of 'Sustainable Concrete: The Environmental, Social and Economic Sustainability Credentials of Concrete' may be downloaded from the Concrete Centre Publications Library www.concretecentre.com and further information is available from www.sustainableconcrete.org.uk.
Concrete is a small net contributor to greenhouse gases responsible for 2.6% of UK CO2 emissions in 2002. This compares with 33% of total CO2 emissions from transport and 47% from buildings in use. This is before taking into account benefits provided by the use of GGBS, fly ash or other recycled material.
Concrete can be re-cycled. Construction and demolition waste is the UK’s largest single source of recycled material, representing 72% of all recycled and secondary materials used in construction in 2001. Of this approximately 10% is used directly in the manufacture of new concrete. The rest is used in low-grade applications such as sub-base and fills, with some diverted into high quality uses such as asphalt. This down-cycling preserves our reserves of primary aggregate for applications where the quality of aggregate is important for durability and performance.
Through concrete's excellent thermal mass energy consumption in commercial and residential buildings can be reduced by up to 50% - a key component in the UK's effort to reduce its greenhouse gas emissions. Thermal mass is the ability of a material to absorb heat. A lot of heat energy is required to change the temperature of a high-density material like concrete. High thermal mass materials act as thermal sponges, absorbing heat during the summer and so cooling the building, and storing heat from the sun or heaters to release it at night. Thermal mass is not a substitute for insulation as it generally stores and re-radiates heat. Insulation stops heat flowing into or out of the building. The right combination of these two elements, plus a building design that allows the capture of solar energy can improve the thermal performance of new buildings and lower energy requirements.
The thermal capacity of concrete structures can be utilised to improve the energy efficiency of buildings. Compared to air conditioning, Active Fabric Energy Storage (FES) reduces carbon dioxide emissions by up to 50%. About 90% of the environmental impact from buildings is from heating, cooling and lighting, and only about 10% is from the embodied energy used to produce the fabric of the building itself (taken over a 60 year life-cycle).
Concrete structures offer long-term construction solutions that do not need additional coverings or coatings for resistance, durability or sound insulation thereby reducing the embodied environment impact of a building still further. Furthermore, the UK is self-sufficient in concrete which is made locally whilst UK reinforcement is made from 100% UK recycled steel. This locally sourced benefit of concrete compares favourably with the fact that over 98% of the timber used in the UK is imported whilst approximately 60% of the country's requirement for steel is imported. This comes at a time when a recent research from the Institute for Physics and Atmosphere in Wessling, Germany, has found that global shipping is responsible for over 5% of the world's CO2 emissions. To put this into context, air travel is responsible for less than 2% of world emissions.
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