Last edited 28 Jul 2017

Carbon dioxide in construction


[edit] Introduction

Carbon dioxide is a naturally-occurring gas that is integral to life and characterised by being colourless and odorless. Its chemical formula is CO2, made up of a carbon atom which is covalently double-bonded to two oxygen atoms.

In the Earth’s atmosphere, carbon dioxide exists at a concentration of around 0.04% (400 ppm) by volume. Carbon dioxide is released into the atmosphere by dissolution from carbonate rocks, volcanoes, hot springs and geysers, as well as occurring in groundwater, glaciers, oceans, rivers and lakes. In addition all aerobic organisms produce carbon dioxide when respiring.

Plants and trees take in carbon dioxide and produce oxygen.

Carbon dioxide is a greenhouse gas and the increase in burning of carbon-based fossil fuels, as well as increasing deforestation, since the Industrial Revolution, is leading to higher rates of global warming as a result of more carbon being concentrated in the atmosphere.

Greenhouse gases are relatively transparent to short-wave infrared radiation (such as heat from the sun). This means that they allow sunlight to enter the atmosphere and heat the Earth’s surface. These surfaces then re-radiate that heat as long-wave infrared radiation, whichgreenhouse gases tend to absorb rather than transmit. The result is that the long-wave infraredradiation is ‘trapped’ and heat accumulates in the atmosphere causing a warming process. This process is known as the ‘greenhouse’ effect because it is similar to the effect that glass has, trapping heat in greenhouses.

Despite some uncertainty regarding the severity of the temperature response to a given increase in carbon dioxide in the atmosphere, there is a general consensus that:

  • That the earth’s climate has always changed over timescales ranging from thousands of years to millennia; that alongside natural forcings.
  • Greenhouse gases from human activity are warming the world.
  • Effort is needed to reduce emissions and to adapt to the changes that are likely to occur from the gases already in the atmosphere.

[edit] Climate Change Act

The Climate Change Act 2008 established a legally binding target to reduce the UK’s greenhouse gas emissions by at least 80% below 1990 year levels by 2050.

To drive progress, the Act introduced a system of carbon budgets which provide legally binding limits on the amount of emissions that may be produced in successive five-year periods:

  1. 2008-2012, 23% reduction below 1990 levels.
  2. 2013-2017, 29% reduction below 1990 levels.
  3. 2018-2022, 35% reduction below 1990 levels.
  4. 2023-2027, 50% reduction below 1990 levels.

[edit] Uses in construction

There are a number of direct uses of carbon dioxide by the construction industry:

  • Carbon dioxide is one of the most commonly used compressed gases for pneumatic systems (pressurised gas) in portable pressure tools that are ubiquitous in the construction industry.
  • MIG/MAG welding uses carbon dioxide as an atmosphere, as a means of protecting the weld puddle from the surrounding air and oxidizing. When mixed with argon, a higher welding rate can be achieved which often reduces the need for post-weld treatment. In manufacturing casting moulds, carbon dioxide helps to ensure their hardness and rigidity.
  • Carbon dioxide is also used to create dry ice pellets which can be used to replace sandblasting for removing paint from surfaces.

However, more significantly, there are considerable emissions of carbon dioxide as a result of activities to construct and then operate built assets.

According to the Technology Strategy Board, in the UK, the construction, operation and maintenance of the built environment accounts for 45% of total UK carbon emissions (27% from domestic buildings and 18% from non-domestic buildings).

According to the UK Green Building Council, around 10% of the UK’s carbon dioxide emissions are directly associated with construction. This includes the CO2 generated through the entire building process:

In order to meet emissions targets, the construction industry has been trying to adopt various strategies to reduce the level of CO2 that is produced during construction. Some of these strategies include:

[edit] Sustainable materials

Optimising the use of less polluting materials is an important way of cutting embedded carbon in new buildings. Around half of all CO2 emissions in the industry are from cement production, both in the manufacturing process and as a by-product of the chemical reactions. Low-carbon cements are available which are less energy-intensive to produce as they often include magnesia, enabling the absorption of carbon dioxide during curing.

For more information, see Research on novel cements to reduce CO2 emissions.

Other 'sustainable' materials such as timber, straw and compressed earth have lower carbon footprints than cement, as well as absorbing CO2 while growing.

For more information see: Sustainable materials.

[edit] Waste management

Cutting waste through the ‘three Rs’ – reduce, reuse and recycle – is an important hierarchy for cutting CO2 emissions in construction. Waste is often produced by ordering excess materials for a project, which emphasise the need for accurate estimating and having effective strategies for reusing materials on other projects.

Programmes such as the Waste and Resources Action Programme (WRAP) attempt to encourage efforts towards a resource-efficient economy.

See also: Site waste management plan and Waste hierarchy for construction.

[edit] Transportation

Currently, transportation accounts for around 20% of the UK’s carbon dioxide emissions. Solutions that could be adopted include switching to more efficient vehicles and plant; sourcing materials locally thereby reducing the distance they have to be transported; and trying to condense deliveries from the same suppliers wherever possible as a means of reducing the number of journeys needed to and from the site.

[edit] Other strategies

There are several other strategies that can be practiced to reduce CO2 on construction sites, such as:

  • Producing an energy plan during early planning stages to assess the energy requirements of the project.
  • Securing early, high-capacity electricity grid connection, thereby reducing the need for generators.
  • Avoid using over-sized generators.
  • Efficient energy management in site offices, such as intelligent electrical installations (i.e. daylight sensors).
  • Using site accommodation with an energy performance certificate (EPC) rating of A, B, or C to reduce heating and lighting costs.
  • Avoiding leaving plant and vehicles idling.

[edit] Energy consumption

80% of the emissions associated with the built environment are from buildings in use. Strategies to reduce this, include designing buildings that consume less energy, and ensuring that renewable energy is sourced.

In addition, energy consumption can be directly attributed to the the life cycle of building products and materials: See embodied energy for more information.

[edit] Carbon capture and storage

Carbon capture and storage (CCS) refers to a range of technologies that capture CO2 emissions and then store them permanently so that they do not enter the atmosphere and contribute to climate change.

For more information see: Carbon capture and storage.

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