Introduction
Concrete is used worldwide as the most popular building material presently known to mankind. Many contractors and even countries make it their choice of primary building material due to its sustainability.
Today’s development decisions are heavily influenced by the issue of sustainability and this trend will only continue to grow in the years ahead. Modern concrete, due to its manufacturing process, is not presently a green construction material.
Changes are occurring daily as research is ongoing to produce a source of green concrete for future construction projects. Some are already produced and used in small amounts.
Making and transporting concrete is extremely energy and emission-intensive. The production of concrete today, according to a 2010 Cement Sustainability Initiative Report from the concrete manufacturing industry itself, produces approximately five percent of all global emissions of CO2 generated by the actions of humans.
This high percentage is a result of the sheer volume of concrete the world produces annually. Second, only to the use of water, is the most often used material on earth.
Its environmental impact unfortunately begins with the process of quarrying the limestone needed to make cement and continues through the superheating and grinding processes that produce cement and binds more particulates like gravel and sand to make finished concrete.
The manufacturing plants use a great deal of fuel which produces CO2 emissions. The process itself produces more emissions. Together, the entire process adds up to three percent of all manmade greenhouse gases. The current process does not produce green concrete.
Why then is concrete such a popular building material for today’s environmentally conscious society? It is used because it lasts like no other construction material.
Insects, weather, and vermin cannot harm it. It creates walls that are themselves energy-efficient, creating green concrete use. Concrete walls, due to their thermal mass, can store coolness and warmth and thus reduce the fluctuations of indoor temperatures within those walls.
This leads to reduced energy use for heating and cooling. Concrete lasts for many decades, sparing trees and stone from being used.
The material known as white concrete reflects heat, thus mitigating the environmental effect known as urban heat islands. All of these results come from intelligent green concrete usage.
When concrete is the building material of choice, CO2 emissions from materials transportation are greatly lowered because it is a locally-sourced building material. There are very few regions in the world that do not have the necessary resources at hand for creating concrete.
Its service life is extensive and once it ends, concrete can be crushed then recycled as an excellent aggregate for many other construction applications. This green concrete quality is different from that of materials like asphalt which produces toxic runoff.
Concrete does not. It is also used as fill for road beds and as shoreline erosion protection in the form of rip rap.
New technologies and manufacturing alteration efforts to decrease energy use in the processing is currently underway. These efforts will produce enormous carbon-emissions savings.
An innovative and green concrete material known as geopolymer concrete is already being developed using an industrial by-product of “fly ash” as a cement substitute. It has greater fire and erosion resistance than current concrete.
Leadership in Energy and Environmental Design (LEED) is a newly developed set of green building specifications that many nations and developers are willingly adopting. The future of concrete is becoming increasingly more green annually.
CO2 absorbing cement
Part of the growing trend toward more environmentally sustainable homes and buildings is an increasing demand for building materials that have less of an impact on the environment. This lesser environmental impact might be from reusing building materials or using materials that have been recycled.
It could also be from using building materials that require less energy in their production. Less energy generally means lower CO2 emissions. Some companies now have come up with a product that not only generates fewer carbon emissions in its production process but can actually absorb CO2.
The overall impact the cement industry has on the environment is substantial. According to some news articles, cement production accounts for about 8% of total CO2 emissions, which is more than the entire aviation industry.
And the demand for cement will continue to rise along with economic growth and development around the world. That’s because it’s the most popular building material of them all.
To produce standard, or Portland cement, limestone or clay is heated to around 1,500 degrees Celsius. The process releases about 0.8 tons of CO2 per ton of cement.
Then, when the cement is mixed with water, each ton of cement can absorb up to 0.4 tons of CO2, but the net overall effect is still 0.4 tons of CO2 emissions.
There are some ways to reduce the emissions from the cement-making process by changing the basic ingredient, using alternative heat like waste heat, CO2 capturing methods, and storing them like mixing the ratios in cement and using some alternative fuels.
One way is also to change the base ingredients from limestone and clay to those that need less heat to produce cement. The magnesium-based ingredients require lower temperatures in the cement production process (up to around 650 degrees C) and therefore less CO2 emissions (0.5 tons) are produced in generating the heat.
And cement based on magnesium ingredients also absorbs CO2 as it hardens, up to 1.1 tons per ton of cement. So the overall process results in net absorption of about 0.6 tons of CO2 per ton of cement, making it a carbon-negative product.
Conclusion
It’s good to see that some steps are being made to make concrete greener building material. It’s also recycled a lot, but more needs to be done presently as many landfills are already full of it.
