green concrete ankit final
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GREEN CONCRETE: EFFICIENT & ECO-FRIENDLY CONSTRUCTION MATERIALSBY-ANKIT KUMARROLL No.-12042000111. INTRODUCTIONGreen 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 worlds 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 worlds 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 GoalsGreen 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. GENESISConsidering 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 Denmarks 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 Denmarks 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 PollutantsThese, 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 worlds 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 Denmarks 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 indicatorsincluding 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.
Table 1 Total CO2 emissions for 1 cubic yard (yd3 ) + of concrete for different strength classes and mixture proportions5Ready Mix IdStrength Class psi(kgf/cm2 )Mixture Proportions* lb/yd3(kg/m3 )Total CO2 emission lb/yd3(kg/m3 )Breakdown of CO2 emissions for 1 yd3 ,% (0.76455 m3 )
15000(351)564/0/0 (335/0/0)528 (313)96.8%0%0.6%0.6%2.0%
24000(281)470/0/0 (279/0/0)442 (262)96.3%0%0.7%0.7%2.3%
33000(210)376/0/0 (223/0/0)355 (211)95.7%0%0.9%0.8%2.6%
43000(210)301/75/0 (179/44/0)288 (171)94.6%0%1.1%1.0%3.2%
53000(210)282/94/0 (167/56/0)270 (160)94.3%0%1.2%1.1%3.4%
63000(210)244/0/132 (145/0/78)239 (142)92.4%1.2%1.4%1.2%3.9%
73000(210)188/0/188 (111/0/111)189 (112)89.8%2.1%1.7%1.6%4.9%
*564/0/0 signifies that the mixture contains 564 lb/yd3 cement, 0 lb/yd3 fly ash, 0 lb/yd3 slag cement #Transport costs is for material shipped to ready mix plant +1 yd3 = 0.76455 m3 The following observations can be made: Since a cubic yard of concrete weighs about 2 tons, CO2 emissions from 1 ton of concrete varies between 0.05 to 0.13 tons. Approximately 95% of all CO2 emissions from a cubic yard of concrete are from cement manufacturing and so it is no wonder that much attention is paid to using greater amounts of SCM hence use green concrete.
3. ADVANTAGES OF GREEN CONCRETEGreen concrete has manifold advantages over the conventional concrete. Since it uses the recycled aggregates and materials, it reduces the extra load in landfills and mitigates the wastage of aggregates. Thus, the net CO2 emissions are reduced. The reuse of materials also contributes intensively to economy. Since the waste materials like aggregates from a nearby area and fly ash from a nearby power plant are not much expensive and also transport costs are minimal.Green concrete can be considered elemental to sustainable development since it is eco-friendly itself. Green concrete is being widely used in green building practices. It also helps the green buildings achieve LEED and Golden Globe certifications. Use of fly ash in the concrete also increases its workability and many other properties like durability to an appreciable extent. One of the practices to manufacture green concrete involves reduction of amount cement in the mix, this practice helps in reducing the consumption of cement overall. The use waste materials also solve the problem of disposing the excessive amount industrial wastesThere are several other advantages related to green concrete and can be summarized as below:a) Reduced CO2 emissions. b) Low production costs as wastes directly substitute the cement. c) Saves energy, emissions and waste water. d) Helps in recycling industry wastes. e) Reduces the consumption of cement overall. f) Better workability. g) Sustainable development. h) Greater strength and durability than normal concrete. i) Compressive strength and Flexural behaviour is fairly equal to that of the conventional concrete. j) Green concrete might solve some of the societies problems with the use of inorganic, residual products which should otherwise be deposited.
4. METHODS TO PRODUCE GREEN CONCRETE4.1. Desirable properties in green concreteToday, it is already possible to produce and cast very green concrete. Even a super green type of concrete without cement but with, for example, 300 kg of fly ash instead can be produced and cast without any changes in the production equipment. But this concrete will not develop strength, and it will of course not be durable. Therefore, the concrete must include aspects of performance like:a) Mechanical properties (strength, shrinkage, creep, static behaviour etc.) b) Fire resistance (heat transfer, etc.) c) Workmanship (workability, strength development, curing, etc.) d) Durability (corrosion protection, frost, new deterioration mechanisms, etc.) e) Environmental impact (how green is the new concrete?).Meeting these requirements is not an easy task, and all must be reached at the same time if constructors are to be tempted to prescribe green concrete. A constructor would not normally prescribe green concrete if the performance is lower than normal, for example, a reduced service life. The new technology will therefore need to develop concretes with all properties as near normal as possible.
4.2. Energy consumption during the production4.2.1. Energy consumption in concrete mix designThe type and amount of cement has a major influence on the environmental properties of a concrete. An example of this is shown in Figure 2, where the energy consumption in mega joules per kilogram of a concrete edge beam through all its life cycle phases is illustrated. The energy consumption of cement production make up more than 90% of the total energy consumption of all constituent materials and approximately one-third of the total life cycle energy consumption. By selecting a cement type with reduced environmental impact, and by minimizing the amount of cement, the environmental properties of the concrete are drastically changed. This must, however, be done while still taking account of the technical requirements of the concrete for the type and amount of cement. One method of minimizing the cement content in a concrete mix is by using packing calculations to determine the optimum composition of the aggregate. A high level of aggregate packing reduces the cavities between the aggregates, and thereby the need for cement paste. This results in better concrete properties.
Another way of minimising the cement content in a concrete is to substitute parts of the cement with other pozzolanic materials. It is common to produce concrete with fly ash and/or micro silica. Both of these materials are residual products (from production of electricity and production of silicon, respectively) and both have a pozzolanic effect. Thus, a material with large environmental impact, i.e. the cement, is substituted with materials with reduced environmental impacts. Although there is no guideline given by the BIS on the addition of above components, the Danish Standards have laid down certain restrictions as given in Table 2.
Table 2 Requirements for the contents of fly ash and microsilica according to the Danish concrete materials standard (%)Mild Environmental ClassModerate Environmental Class
Average Environmental Class
Extra average Environmental Class
Max content F+M from C+F+M (%)X352525
Max content M from C+F+M (%)X101010
(C: cement; F: fly ash; M: micro silica)Sources: ConcreteMaterials, DS 481 1998 [in Danish]4.2.2. Energy consumption during cement and concrete productionIt is also possible to reduce the environmental impact of concrete by reducing the environmental impact of cement and concrete production. As regards concrete production, experience with the reduction of primarily water consumption, energy consumption and waste production is available. Even though the contribution of concrete production to the environmental profile of concrete is minor, it does contribute, and is important environmentally and economically to the single concrete producer. By selecting a cement type with reduced environmental impacts and by minimising the amount of cement the concretes environmental properties are drastically changed. This must, however, be done whilst still taking account of the technical requirements of the concrete for the type and amount of cement. Denmarks cement manufacturer, Aalborg Portland, prioritises development of cements with reduced environmental impacts.
4.3. Evaluation of inorganic wastesThe materials, which have been judged as useable for concrete production and selected for further development, are shown in Figure 1. The judgement was based on an evaluation concerning both concrete technology and environmental aspects. Inorganic residual products from the concrete industry (e.g. stone dust and concrete slurry) and products which pose a huge waste problem to society and which are in political focus (e.g. combustion ash from water-purifying plants, smoke waste from waste combustion and fly ash from sugar production) have been given highest priority.
Stone dust. Stone dust is a residual product from the crushing of aggregates. It is an inert material with a particle size between that of cement and sand particles. Stone dust is expected to substitute part of the sand.Concrete slurry. Concrete slurry is a residual product from concrete production, i.e. washing mixers and other equipment. The concrete slurry is can be either a dry or wet substance, and can be recycled either as a dry powder or with water. In the case of recycling of the dry material, it is necessary to process it to powder. The concrete slurry can have some pozzolanic effect, and might therefore be used as a substitute for part of the cement or for other types of pozzolanic materials such as fly ashCombustion ash from water-purifying plants. This type of combustion ash has the same particle size and shape as fly ash particles. The content of heavy metals in the slurry is expected to be approximately at the same level as for fly ash. The slurry can also have some pozzolanic effect.Smoke waste from waste combustion. This smoke waste can have some pozzolanic effect. The content of heavy metals is significantly higher than that of ordinary fly ash. Furthermore, the content of chlorides, fluorides and sulphates can result in negative effects in connection with reinforcement corrosion, retardation and possible thaumasite reactions. Further processing will be necessary before its use in concrete.
4.4. Different ways to produce Green concrete1. To increase the use of conventional residual products: To minimise the clinker content, i.e. by replacing cement with fly ash, micro silica in larger amounts than are allowed today 2. By developing new green cements and binding materials, i.e. by increasing the use of alternative raw materials and alternative fuels, and by developing/improving cement with low energy consumption 3. Concrete with inorganic residual products :(stone dust, crushed concrete as aggregate in quantities and for areas that are not allowed today) and cement stabilised foundation with waste incinerator slag, low quality fly ash or other inorganic residual products. Firstly, an information-screening of potential inorganic residual products is carried out. The products are described by origin, amounts, particle size and geometry, chemical composition and possible environmental impacts. A pictorial representation of the methods is shown as below,
5. RESULTS OF STUDIES BASED ON REPORTED LITERATURE5.1. Green Concrete containing Marble sludge powder and Quarry rock dust(Hameed, 2009)In 2009, M. Shahul Hameed and A. S. S. Sekar, conducted a study on green concrete replacing the conventional materials, except cement, with marble sludge powder and quarry rock dust
5.1.1. Characterisation of wasteThe physical characteristics of the waste are furnished in Table-3. The fineness modulus of marble sludge powder and quarry rock dust is comparable to that of fine sand of 2.2 to 2.6. The coefficient of uniformity for fine sand is generally should be less than 6. Similarly the coefficient of gradation should be between 1 and 3 for fine sand.
5.1.2. Raw materialsCement: Ordinary Portland Cement (43 Grade) with 28 percent normal consistency with specific surface 3300 cm 2 /g conforming to IS: 8112-1989 was used.Marble Sludge Powder: Marble sludge powder was obtained in wet form directly taken from deposits of marble factories. It was observed that the marble sludge powder had a high specific surface area; this could mean that is addition should confer more cohesiveness to mortars and concrete. Specific gravity of the marble sludge powder is 2.212.
Quarry rock dust: The specific gravity of the quarry rock dust is 2.677. Moisture content and bulk density of waste are less than the sand properties.Fine aggregate: Medium size sand with a modulus of fineness = 2.20; Specific gravity 2.677, normal grading with the silt content 0.8%.Coarse aggregate: Crushed stone with a size of 5-20 mm and normal continuousgrading was used. The content of flaky and elongated particles is