PRESENTED BY:
Abhinav Srivastava

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1. INTRODUCTION
Green concrete is a revolutionary topic in the history of concrete industry. This was first invented in Denmark in the year 1998. Green concrete has nothing to do with colour. It is a concept of thinking environment into concrete considering every aspect from raw materials manufacture over mixture design to structural design, construction, and service life. Green concrete is very often also cheap to produce, because, for example, waste products are used as a partial substitute for cement, charges for the disposal of waste are avoided, energy consumption in production is lower, and durability is greater. Green concrete is a type of concrete which resembles the conventional concrete but the production or usage of such concrete requires minimum amount of energy and causes least harm to the environment.
The CO2 emission related to concrete production, inclusive of cement production, is between 0.1 and 0.2 t per tonne of produced concrete. However, since the total amount of concrete produced is so vast the absolute figures for the environmental impact are quite significant, due to the large amounts of cement and concrete produced. Since concrete is the second most consumed entity after water it accounts for around 5% of the world’s total CO2 emission (Ernst Worrell, 2001). The solution to this environmental problem is not to substitute concrete for other materials but to reduce the environmental impact of concrete and cement. Pravin Kumar et al, 2003, used quarry rock dust along with fly ash and micro silica and reported satisfactory properties.
The potential environmental benefit to society of being able to build with green concrete is huge. It is realistic to assume that technology can be developed, which can halve the CO2 emission related to concrete production. With the large consumption of concrete this will potentially reduce the world’s total CO2 emission by 1.5-2%. Concrete can also be the solution to environmental problems other than those related to CO2 emission. It may be possible to use residual products from other industries in the concrete production while still maintaining a high concrete quality. During the last few decades society has become aware of the deposit problems connected with residual products, and demands, restrictions and taxes have been imposed. And as it is known that several residual products have properties suited for concrete production, there is a large potential in investigating the possible use of these for concrete production. Well-known residual products such as silica fume and fly ash may be mentioned.
The concrete industry realised at an early stage that it is a good idea to be in front with regard to documenting the actual environmental aspects and working on improving the environment, rather than being forced to deal with environmental aspects due to demands from authorities, customers and economic effects such as imposed taxes. Furthermore, some companies in concrete industry have recognised that reductions in production costs often go hand in hand with reductions in environmental impacts. Thus, environmental aspects are not only interesting from an ideological point of view, but also from an economic aspect.
1.1. Environmental Goals
Green Concrete is expected to fulfil the following environmental obligations:
• Reduction of CO2 emissions by 21 %. This is in accordance with the Kyoto Protocol of 1997.
• Increase the use of inorganic residual products from industries other than the concrete industry by approx. 20%.
• Reduce the use of fossil fuels by increasing the use of waste derived fuels in the cement industry.
• The recycling capacity of the green concrete must not be less compared to existing concrete types.
• The production and the use of green concrete must not deteriorate the working environment.
• The structures do not impose much harm to the environment during their service life.
2. GENESIS
Considering the time elapsed since the commencement of the use of concrete, green concrete is very young a material. It was invented in 1998 in Denmark.
The increasing awareness and activity to conserve the environment and the realisation that concrete production too releases a considerable amount of CO2 in the atmosphere were strong initiatives to catalyse the genesis of Green Concrete.
In 1997, the Kyoto Conference took place, in which several countries, after deliberating over the then environmental conditions laid down several guidelines which would be the directive principles to the participating countries on their environment related practices. The guidelines – Kyoto Protocol, as they are called, needed the countries to cut down their CO2 emissions to a certain degree as assigned. The given goal has to be achieved by the year 2012. Since then several countries started to focus on several available options but Denmark focused on cement and concrete production because approximately 2% of Denmark’s total CO2 emission stems from cement and concrete production.
Realising the necessity of such a technology and the prospects associated the Danish government soon released a proposal. The proposal is in accordance with the International and European Conventions and Protocol, with the nationally agreed goals that comply with these. An important aspect is Denmark’s obligation to reduce the CO2-emission as previously mentioned. The proposal covers the following environmental aspects: Greenhouse effect, depletion of the ozone layer, photochemical oxidation, eutrophication, acidification, materials harmful to the environment and health, water and resources. The above mentioned priorities were included in a large Danish projects about cleaner technologies in the life cycle of concrete products. Furthermore, priorities have been made for the other participating countries, i.e. Greece, Italy, and The Netherlands, and for Europe and the International World. Although there are differences in the political environmental priorities, all agree that five environmental impacts given highest priority are:
• CO2
• Energy
• Water
• Waste
• Pollutants
These, coupled with the cost reduction benefits allured the concrete producers to incorporate green concrete into their paradigm.
Cement and concrete may have an important role to play in enabling the developed countries to fulfil their obligation to reduce the total CO2 emission by 21 % compared to the 1990-level before 2012, as agreed at the Kyoto conference. This is because the volume of concrete consumption is large. Approx. 1 m3 of concrete per capita are produced annually globally. The CO2 emission related to concrete production, inclusive of cement production, is between 0.1-0.2 tons per ton produced concrete. This corresponds to a total quantity of CO2 emission of 0.6 - 1.2 m tons per year. Approximately 5% of world’s total CO2 emission stems from cement and concrete production.
The potential environmental benefit to society of being able to build with green concrete is huge. It is realistic to assume that technology can be developed which can halve the CO2 emission related to concrete production. With the large consumption of concrete this will potentially reduce Denmark’s total CO2 emission by 0.5 % (Glavind, 2000). The somewhat soft demands in the form of environmental obligations result in rather specific technical requirements for the industry - including the concrete industry. These technical requirements include among others new concrete mix designs, new raw materials, and new knowledge (practical experience and technical models) about the properties of the new raw materials and concrete mix designs.
Due to growing interest in sustainable development engineers and architects were motivated more than ever before to choose concrete that is more sustainable. However this is not as straight forward as selecting an energy star rated appliance or a vehicle providing high gas mileage. On what “measurement” basis can engineers and architects compare materials and choose one that is more sustainable or specify a material in such a way as to minimize environmental impact?
Life Cycle Assessment (LCA) seems to offer a solution. LCA considers materials over the course of their entire life cycle including material extraction, manufacturing, construction, operations, and finally reuse/recycling. LCA takes into account a full range of environmental impact indicators—including embodied energy, air and water pollution (including greenhouse gases), potable water consumption, solid waste and recycled content just to name a few. Building rating systems such as LEED and Green Globes are in various stages of incorporating LCA so that they can help engineers and architects select materials based on their environmental performance or specify materials in such a way as to minimize environmental impact.
Every 1 ton of cement produced leads to about 0.9 tons of CO2 emissions and a typical cubic yard (0.7643 m3) of concrete contains about 10% by weight of cement. There have been a number of articles written about reducing the CO2 emissions from concrete primarily through the use of lower amounts of cement and higher amounts of supplementary cementitious material (SCM) such as fly ash and slag. Table 1 has been developed based on data presented by Marceau et al, 2002.