Eco-friendly Concrete, as the name suggests, is a kind of concrete that is relatively environment friendly. It is not just a single type of Concrete, rather one of at least four different types of Concrete.
Concrete is a major contributor to the production of the world’s greenhouse gas through the production process of Cement. As per some research, almost 1 ton of Carbon Dioxide is produced for 1 ton of Cement production. Researchers, in order to make construction a sustainable industry, have been coming up with a number of solutions. Some of which are discussed today.
Using Waste Products in Eco-Friendly Concrete
This includes the usage of waste materials like Fly Ash, Blast Furnace Slag, Husk Ash and much more. These waste products are difficult to recycle and therefore scientists and civil engineers started to partially replace the portland cement content with these waste products.
This strategy is effective in two ways. Not only they are using these waste products but also reducing the production of portland cement. A concrete mix, for instance, uses 20 % Fly Ash by the weight of cement translates to 20 % less Portland cement used in that product. A simple logic of ‘lower demand = lower production.
Research studies show that the resulting concrete, especially when made with Fly Ash (FA) and Blast Furnace Slag (BFS), results in a stronger and more durable concrete since it has better resistance to chemical attacks,
The concrete made with Blast Furnace Slag also has a lower pH which is ideal for artificial reefs. Recent research has shown that concrete made with BFS can host higher alga on the surface as compared to conventional concrete when used as an Artificial Reef.
Self-Healing Eco-Friendly Concrete
Eco-Friendly Concrete which is also known as ‘Green Concrete’ or ‘Environment Friendly Concrete’ is much more than using waste products. Innovative materials like Self-healing Concrete can also be a part of it. Self-Healing Concrete is also known as “Live Concrete” for it fills its own cracks by itself. This healing of cracks is achieved with the help of Bacteria, Fungi and/ or chemicals promise a longer service life. A longer service life means the structures are going to stay for a longer tenure and therefore reducing the construction life time costs. Less reconstruction means less production of cement.
Cracks in concrete provide a passage to water and gases which can make their way inside the concrete. The problem with intrusion of fluids is that it can take other chemicals along with it. Sulphates and Chlorides being prime examples. They tend to attack the Concrete and Steel – Sulphates are common to trigger Sulphate attack while Chlorides together with oxygen can cause steel corrosion.
Carbon Dioxide ingression on the other actually makes Concrete stronger. Such concrete in which Carbon Dioxide has made its way deep is called Carbonated Concrete. This reacts with Calcium Hydroxide – the alkaline part of Concrete – and produces Calcium Carbonate that is actually stronger than the former. But, the latter is not as alkaline as former and therefore reduces the pH of concrete and consequently its resistance to acid attacks.
Self-Healing Concrete is currently being utilised in a number of projects is finding practical uses in many different applications.
Carbon Dioxide Absorbing Eco-Friendly Concrete
Similarly, there are other concrete types like Carbon Dioxide absorbing Concrete. This Concrete type absorbs Carbon Dioxide that comes into contact with its surface and therefore making this environment a bit better.
Carbon Dioxide Absorbing Concrete is still under research. Carbon Dioxide gets its way inside the concrete and produces Calcite (Calcium Carbonate). Although this reaction makes concrete stronger but reduces the PH. The alkaline layer around steel reinforcement protects the steel from acid attack which can cause corrosion of steel. Once corroded, the steel would expand and cause stresses inside the concrete and therefore might result in cracks.
The applications for such kind of concrete are still under discussion and the scientists are currently working to come up with a viable option.
Recycled Aggregate Concrete
On the other hand, it is also important to realize that demolished concrete is also been recycled since landfill is not a viable option anymore. The demolished concrete is crushed and then used again as aggregate in new concrete – the resulting concrete is called Recycled Aggregate Concrete.
Recycled Aggregate Concrete usually has a little lower strength, less workability and lower resistance to chemical attacks as compared to conventional concrete. But with recent research, the gap is getting smaller and soon recycled aggregate concrete would be as good as conventional concrete.
Another kind of recycled concrete is currently under research at different universities. The University of Tokyo, Japan, for instance, is currently working on using demolished concrete with zero cement. The demolished concrete is crushed and brought into powder form which later is compressed with the right amount of water for lubrication. The powder is compressed into the desired shape which later can be used for a number of purposes.
The compressive strength of such kind of concrete is not comparable to conventional concrete since most of the strength comes from mechanical compression and hardly any chemical reaction occurs between the particles. The cement particles from the demolished concrete is usually unable to hydrate – hydration is reaction of cement and water which in turn produces hydration products like Allite, Bellite and Portlandite which provide strength and alkalinity.
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