The benefits of switching over to green concrete are manifold and this material is catching the attention of just about everybody in the business, from construction companies to architects to top remodelers. What’s also helping is that the general population is becoming increasingly aware, so the industry has no choice but to stop and take notice.
The use of concrete-like material dates back to around 6500 BC, as discovered in the regions of modern-day southern Syria and northern Jordan. By 700 BC, Nabataea traders or Bedouins of the region learnt about the self-cementing properties of hydraulic lime. This led to their building kilns that supplied mortar for constructing of rubble-wall houses, concrete floors and underground waterproof cisterns. While some of these structures still stand, concrete has come a long way since.
Now, concrete is the most commonly used material the world over. By 2016, our planet produced around 4.2 billion metric tons of cement annually. Of this United States accounted for 85.9 million metric tons. The U.S. produces around 500 million tons of concrete each year, which puts it around two tons for every man, woman and child. Cost-effectiveness, strength and longevity have made concrete the choice for small and large construction and infrastructure projects alike.
Unfortunately, the widespread use of concrete comes with a carbon footprint to match. When limestone and clays are crushed and heated at high temperatures, CO2 emissions are notable, to say the least. Cement manufacturing is responsible for around 8% to 10% of the world’s total CO2 emission. Luckily, the situation is far from bleak because of the increasing use of green concrete. The change has come about primarily by understanding that Portland cement is not environmentally friendly and that it’s best to use concrete with as little of this material as possible.
What is Green Concrete?
Green concrete or geopolymer concrete, a term coined by French materials scientist Joseph Davidovits, refers to concrete made using a combination of inorganic polymers and industrial waste. It also refers to concrete that does not result in environmental damage during production or concrete that comes with high life cycle sustainability.
When green concrete is produced to high technical and environmental standards, it’s good not just for the planet, but for the end-user as well. This is because it ends up being more cost-effective in the long term owing to better durability and performance.
The primary goal of producing green concrete is to minimize the use of Portland cement. This is easy to accomplish by replacing it with different supplementary cementitious materials (SCMs). Manufacturers of green concrete ten to give preference to byproducts of industrial processes. While cost is a factor, the process also leads to the effective use of some industrial waste.
Fly ash, the residue of coal combustion, is an excellent SCM, and its use in producing green concrete is common. Another good choice is ground granulated blast furnace slag (GGBFS). This is a byproduct that comes from the steelmaking industry.
In recent times, there has been an attempt to reduce the use of cementitious material in concrete altogether. Research on this is underway at BASF Corporation in the U.S. and at the University of Dundee in the UK. Ravindra Dhir, director of the concrete technology group at the University of Dundee, opines that “you can take out at least 20 percent of the cement content while retaining durability.” Findings have already shown that reducing the level of cement can improve the resultant concrete’s durability.
How is Green Concrete Produced?
Responsible producers of green concrete follow different approaches in coming up with products that drive toward environmental sustainability. Factor at play include:
· Innovation. They successfully replace Portland cement with suitable alternatives such as fly ash, GGBFS and microsilica.
· Recycling. By recycling materials such as aggregates and water, they manage to achieve sustainable full life cycle results.
· Localization. They source the best materials found locally and use scientific know-how to adjust formulations so that they meet regional regulations. For example, to build a LEED certified project, the harvesting and assembly of the materials should happen within 500 miles of the project site.
· Rehabilitation. They try and give back to the land from where they extract. This is done by rehabilitating quarries as well as working with local communities to find positive and sustainable use for land.
Where is Green Concrete Used?
The use of green concrete is increasing the world over, and its applications are varied.
· Infrastructure. You can find the use of green concrete at airports, train stations, stadiums, bridges, highways and city streets
· Large buildings. Its use is gaining popularity in construction of residential complexes, industrial and commercial buildings, as well as multi-storey office blocks. A great example in case is the multi-award winning University of Queensland’s four-storey Global Change Institute (GCI).
· Small buildings. While the use of green concrete in making homes in common, several concrete construction and maintenance contractors use it in projects that involves driveways, footings, paving and slabs.
Benefits of Green Concrete
Green concrete offers more than one benefit.
· Longer life. Green concrete comes with a lower shrinkage rate when compared with concrete made using only Portland cement. In addition, it gains strength faster. Since green concrete can typically withstand temperatures of up to 2,400° F, structures made using this material have good chances of surviving fires. The material offers good resistance against corrosion, which works in its favor when subjected to pollutants as well as harsh elements of nature.
· Effective use of industrial waste. Green concrete replaces Portland cement with 25% to up to 100% of an SCM. While fly ash is what’s left over after the combustion of coal, GGBFS is the waste that comes about from making steel. Astoundingly large areas are usually required to dispose these waste materials, but producers of green concrete end up using these materials rather effectively.
· Minimize consumption of energy. Using more fly ash and lesser cement in a concrete mix means you’ll use lesser energy. The making of Portland cement requires a large amount of natural gas or coal to provide the required heat. Fly ash and GGBFS, on the other hand, are byproducts of industrial processes, so they do not require additional energy in their production. Besides, buildings that are made using green concrete are generally more resistant to change in temperatures when compared to buildings made using regular concrete. This results in reduced air-conditioning costs.
· Reduces CO2 emissions. The main ingredients in regular cement include clay, pulverized limestone and sand, all of which are heated at an extremely high temperature. A rule of thumb is that every ton of cement made releases one ton of CO2. Production of green concrete results in reduction of CO2 emissions by up to 80%.