Concrete & The Environment
Concrete is Green
- Low CO2 intensity - the production of concrete, which consists of 10% - 15% cement, results in emissions of about 0.13 tonne of CO2 per tonne of concrete, equal to 1/9 the emissions of cement. Concrete manufacturing results in less CO2 per unit than almost all other construction materials, making it the sustainable construction material of choice.
- Resource efficient - the ingredients for concrete - sand, gravel and limestone - are abundant worldwide. Quarries are readily reclaimed for recreation, residential or commercial development. They can also be restored to their natural state.
- Local resource - because the ingredients of concrete exist almost everywhere, concrete can be manufactured near a job site, requiring minimal energy for transportation. At least 60% of all concrete is made within 160 km of the job site. Wood and steel products, on the other hand, typically travel hundreds or even thousands of kilometres.
- Less construction waste - as concrete is manufactured to specifications, only the product that is required is delivered to the site. This means that less material is sent to landfill upon project completion.
- Reusable - many concrete products can be reused, such as concrete pavers and precast wall panels. Concrete sidewalk slabs are reused to build "dry stone" retaining walls. A well designed concrete building with long floor spans and column-free space is adaptable to a succession of different occupants.
- Recycling medium - Concrete makes waste products useful. Concrete is ideal as a medium for the inclusion of recycling waste or industrial byproducts such as blast-furnace slag (from steel making) and fly ash (from coal-burning electric plants). About a third of the fly ash produced annually in the U.S. is used in concrete. Use of such industrial by-products as Supplementary Cementing Materials (SCMs) to replace some of the cement in concrete mixtures also improves product performance for specific applications.
- New life for old concrete - Used concrete can be 100% recycled as aggregate for use in roadbeds or as a granular material. Concrete yields 45% to 80% coarse aggregate usable for new concrete mixtures. The rest can be crushed and re-used as base material for roadbeds, parking lots or other applications.
- Replenishes aquifers - Pervious concrete pavement and permeable interlocking concrete pavers can be used to reduce stormwater runoff and allow water to return to the water table.
- Cost-effective and eco-efficient - Concrete is a budget-friendly and competitive building material, especially when full life-cycle costs are taken into account.
- Longer-lasting structures - Concrete is resistant to wear and tear, severe weather, rot, insects and fire. Building with concrete reduces energy, labour and materials costs for maintenance and reconstruction.
- Reduced transportation costs - Concrete is a locally available product across Canada.
- Lower operating costs - Concrete's thermal mass characteristics help to moderate heating and cooling peaks and reduce heating ventillating and air conditioning equipment requirements for buildings.
- Lower lighting costs - Because concrete has high reflectance, less night-lighting is necessary for concrete roadways, parking lots and other structures.
- No need for additional interior or exterior finishes - Polished concrete floors do not require carpeting. Exposed concrete walls need no paints or sealants.
Social and Quality of Life Benefits
- Safety and Quiet Comfort - Concrete structures are resistant to fire, wind, vibration, sound transmission and seismic tremors. Concrete does not burn and therefore provides comprehensive fire protection including life safety, protection of properties and of the environment in case of fire.
- Better indoor air quality - Concrete produces no off-gassing, toxicity or volatile organic compounds (VOCs), thus reducing sick building syndrome problems.
- Cleanliness - Concrete does not sustain mould growth and can be easily cleaned.
- Aesthetically and architectually pleasing - Concrete combines function and practicality with a contemporary appearance and the ability to express complex and dynamic forms. Concrete is the essence of permanence and performance - a material with limitless possibilities.
On the right is a sample concrete mix. Different proportions of materials are used depending upon how the concrete will be used.
Concrete and the Use of SCMs
Although the embodied energy associated with concrete is already low, it can be further reduced through the use of Supplementary Cementing Materials (SCMs). When used judiciously, SCMs can enhance long-term concrete properties as well. To ensure desired performance, the substitution of fly ash for more than 30% or slag for more than 35% of the portland cement in concrete should be considered a high volume SCM application and its suitability for the intended use should be pre-qualified.
Concrete and the Use of Blended Cements
Although it is most common to use SCMs for replacing some of the cement in a concrete mixture, an alternative is blended cement. Fly ash, blast furnace slag or silica fume are added to the raw cement itself during the grinding stage of production. The advantages of using blended cement include expanded production capacity, reduced CO2 emissions, reduced fuel consumption and close monitoring of the quality of SCMs.
Overall, the increased use of SCMs in cement and concrete leads to an equivalent reduction of GHG emissions.