Green Concrete.. Advantages & Limitations

Concrete is generally considered as a composite material consists of coarse aggregate "gravel" and fine aggregate "sand" bonded and mixed together with cement paste, which gradually harden over time. As known, concrete is very strong in compression, that because aggregate-especially coarse aggregate- efficiently carries the compression load.

Nowadays the word "Green" isn't limited for just color, it's referred to the whole environment, which is the most important part globally.

Such a kind of concrete which considered as eco-friendly and made from normal concrete waste is called "Green Concrete". These wastes include lots of materials like slag, power plant wastes, recycled concrete, mining and quarrying wastes, waste glass, incinerator residue, red mud, burnt clay, sawdust, combustor ash and foundry sand.

Green Concrete has different properties in the mix design and placement to ensure more durable structure with reduced environmental impacts for wastewater, CO2 emissions and energy saving.

The goal of the Centre for Green Concrete is to reduce the environmental impact of concrete. To enable this, new technology is developed. The technology considers all phases of a concrete construction’s life cycle, i.e. structural design, specification, manufacturing and maintenance, and it includes all aspects of performance, i.e.

1) Mechanical properties (strength, shrinkage, creep, static behaviour etc.)

2) Fire resistance (spalling, heat transfer etc.)

3) Workmanship (workability, strength development, curing etc.)

4) Durability (corrosion protection, frost, new deterioration mechanisms etc.)

5) Thermodynamic properties (input to the other properties)

6) Environmental aspects (CO2-emission, energy, recycling etc.)

There are a number of alternative environmental requirements with which green concrete structures must comply:

• CO2 emissions shall be reduced by at least 30 %.
• At least 20 % of the concrete shall be residual products used as aggregate.
• Use of concrete industries own residual products.
• Use of new types of residual products, previously land filled or disposed of in other ways.
• CO2-neutral, waste-derived fuels shall substitute fossil fuels in the cement production by at least 10 %.

In addition to the environmental goals there are a number of environmental intentions. Most important are:

To avoid the use of materials which contain substances on the Environmental Protection Agency’s list of unwanted materials, not to reduce the recycling ability of green concrete compared with conventional concrete and not to increase the content of hazardous substances in the wastewater from concrete production compared with wastewater from production of existing concrete types.

Different concrete types are tested for workability, changes in workability after 30 min., air-content, compressive strength development, E-modulus, heat development, homogeneity, water separation, setting time, density and pumpability. Furthermore, frost testing, chloride penetration and an air void analysis are carried out for the concretes in the aggressive environmental class.

The water/cement ratio, water/binder ratio and the chloride content are calculated from the mixing report of the precise mixture proportions and from the chloride content in the different raw materials.

- Environmental Benefits to using Green Concrete:

• Geo- polymer concrete, or green concrete, is part of a movement to create construction materials that having a reduction impact on the environment. It is made from a combination of an inorganic polymer and 25 to 100 percent industrial waste.

        Here is a list of 4 benefits to using green concrete.

   1. Lasts Longer

• Green concrete gains strength faster and has a lower rate of shrinkage than concrete made up of Portland Cement.
• Structures build using green concrete have a better chance of surve a fire ( it can withstand temperatures of up to 2400 degrees on the Fahrenheit scale ). It also has a greater resistance to corrosion which is important with the effect of pollution has on the environment ( acid rain greatly reduces the longevity of traditional building materials ).

• All of those factors add up to a building that will last much longer than one made with ordinary concrete. Similar concrete mixtures have been found in ancient Roman structures and this material was also used in the Ukraine in the 1950 and 1960.

• Over 40 years later those Ukrainian buildings are still standing. If buildings don’t have to be rebuilt, fewer construction materials have needed and the impact to the environment is reduced.

  2. Uses Industrial Waste

• Instead of a 100 percent Portland cement mixture, green concrete uses 25 to 100 percent fly ash. Fly ash is a byproduct of coal combustion and is gathered from the chimneys of industrial plants ( such as power plants ) that use coal as a power source.

• Hundreds of thousands of acres of land are used to dispose of fly ash. A large increase in the use of green concrete in construction will provide a way to use up fly ash and hopefully free many acres of land. 

   3. Reduces Energy Consumption

• If you use less Portland cement and more fly ash when mixing concrete, then you will use less energy. The materials use in Portland cement require huge amounts of coal or natural gas to heat it up to the appropriate temperature to turn them into Portland cement.

• Fly ash already exists as a byproduct of another industrial process so you are not expending much more energy to use it to create green concrete. Another way that green concrete reduces energy consumption is that a building construct from it is more resistant to temperature changes.
• An architect can use this and design a green concrete building to use energy for heating and cooling more efficiently. 

  4. Reduces CO2 Emissions

• In order to make Portland cement – one of the main ingredients in ordinary cement – pulverized limestone, clay, and sand are heated to 1450 degrees C using natural gas or coal as a fuel. This process is responsible for 5 to 8 percent of all carbon dioxide ( CO2 ) emissions worldwide.
• The manufacturing of green concrete releases has up to 80 percent fewer CO2 emissions. As a part of a global effort to reduce emissions, switching over completely to using green concrete for construction will help considerably.

- Advantages:

• It will give increase same particle attraction so user friendly – easier to place, compact & finish concrete. It can be seen in concrete slump.
• Optimize mix designs mean easier handling, better consistency and easier finishing.
• Reduction in shrinkage & creep.
• They use local and recycled materials in concrete.
• The heat of hydration of green concrete is significantly lower than traditional concrete.
• This result in a lower temperature rise in large concrete pours which is a distinct advantage for green concrete.
• It decreases wastage of materials and opens way of use of waste materials in this generation.

- Limitations:

• By using stainless steel, cost of reinforcement increases.
• Structures constructed with green concrete have less life than structures with conventional concrete.
• Split tension of green concrete is less than that of conventional concrete.
• Corrosion in the steel bars can also occur if the aggregates used are not free from corrosion leading agents.

- Conclusion:

• Green concrete have reduced environmental impact with reduction of the concrete industries CO2 omissions by 30%. They have good thermal and fire resistant. In this concrete recycling, use of waste material such as ceramic wastes and aggregates increase concrete industry waste products by 20%.

• Hence, they consume less energy and becomes economical. So, the use of concrete product like green concrete in future will not only reduce the emission of CO2 in environment and environmental impact but it is also economical to produce.