GREEN CONCRETE: EFFICIENT & ECO-FRIENDLY CONSTRUCTION MATERIALS

BY-ANKIT KUMAR

ROLL No.-1204200011

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.

Table 1 Total CO2 emissions for 1 cubic yard (yd3 ) + of concrete for different strength classes and mixture proportions5

Ready Mix Id

Strength 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 )

Cement SCM Aggregate Plant Operations Transport

1 5000(351) 564/0/0 (335/0/0)

528 (313)

96.8% 0% 0.6% 0.6% 2.0%

2 4000(281) 470/0/0 (279/0/0)

442 (262)

96.3% 0% 0.7% 0.7% 2.3%

3 3000(210) 376/0/0 (223/0/0)

355 (211)

95.7% 0% 0.9% 0.8% 2.6%

4 3000(210) 301/75/0 (179/44/0)

288 (171)

94.6% 0% 1.1% 1.0% 3.2%

5 3000(210) 282/94/0 (167/56/0)

270 (160)

94.3% 0% 1.2% 1.1% 3.4%

6 3000(210) 244/0/132 (145/0/78)

239 (142)

92.4% 1.2% 1.4% 1.2% 3.9%

7 3000(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 wastes

There 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 Moderate Average Extra average

Environmental Class

Environmental Class

Environmental Class

Environmental Class

Max content F+M from

C+F+M (%)

X 35 25 25

Max content M from

C+F+M (%)

X 10 10 10

(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 concrete‘s 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. Denmark‘s 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 ash

Combustion 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 continuous

grading was used. The content of flaky and elongated particles is <3%, the crushing

index ≤6% and the specific gravity 2.738.

Water: The qualities of water samples are uniform and potable

Super plasticizer: A superplasticizer based on refined lingo Sulphonates, ‗Roff Superplast 320‘ was used to get and preserve the designed workability.

5.1.3. Mix proportion of concrete:

For durability studies the Indian standard mix proportion (by weight) use in the mixes of conventional concrete and green concrete were fixed as (Cement: River sand/marble sludge + stone dust: coarse agg) 1:1.81:2.04, 1:1.73:2.04 after several trials. Based on properties of raw materials, two different mix proportions were taken. 0 10 20 30 40 50 60 70 80 90 100 8.616 6.112 4.351 3.106 2.218 1.597 1.184 0.845 0.604 0.176 % of finer Particle Size X10-3 mm Mix A is the controlled concrete using river sand and Mix B is the green concrete using industrial waste (50% quarry rock dust and 50% marble sludge powder) as fine aggregate. The

water/cement ratio for both two mixes was 0.55% by weight. Water reducing admixture was used to improve the workability and its dose was fixed as 250 ml/50kg of cement.

5.1.4. Results and Discussion

Workability:

Compressive and Split tensile strength:The 150 mm size concrete cubes, concrete cylinder of size 150 mm diameter and 300 mm height were used as test specimens to determine the compressive strength and split tensile strength respectively. The results of standard cubes and cylinders are compiled:

Durability and Resistance to Sulphate attack

The resistance to sulphate attack was studied by storage of standard prism specimens were immersed in standard condition for 28 and 90 days and 150 days in testing baths (containing 7.5 percent MgSO4 and 7.5 percent Na2SO4 by weight of water). From the above table it can be deduced that the durability of Green concrete under sulphate is higher to that of conventional concrete. This is due to that the active SiO2 in marble powder and quarry rock dust can react with the Ca (OH)2 in concrete to form secondary calcium silicate hydrate and make it chemically stable and structurally dense, the impermeability of concrete is enhanced as well. In addition, the marble powder can reduce the content of calcium aluminates in cementitious material, leading to increase of sulphate resistance of concrete.

5.1.5. ConclusionsAll the experimental data shows that the addition of the industrial wastes improves the physical and mechanical properties. These results are of great importance because this kind of innovative concrete requires large amounts of fine particles. Due to its high fineness of the marble sludge powder it provided to be very effective in assuring very good cohesiveness of concrete. From the above study, it is concluded that the quarry rock dust and marble sludge powder may be used as a replacement material for fine aggregate.

The chemical compositions of quarry rock dust and marble sludge powder are comparable with that of cement. The replacement of fine aggregate with 50% marble sludge powder and 50% Quarry rock dust (Green concrete) gives an excellent result in strength aspect and quality aspect. The results showed that the M4 mix induced higher compressive strength, higher splitting tensile strength. Increase the marble sludge powder content by more than 50% improves the workability but affects the compressive and split tensile strength of concrete. Green concrete induced higher workability and it satisfy the self compacting concrete performance which is the slump flow is 657mm without affecting the strength of concrete. Slump flow increases with the increase of marble sludge powder content. V-funnel time decreases with the increase of marble sludge powder content Test results show that these industrial wastes are capable of improving hardened concrete performance. Green concrete enhancing fresh concrete behaviour and can be used in architectural concrete mixtures containing white cement. The water absorption of green concrete is slightly higher than conventional concrete. The durability of green concrete under sulphate is higher to that of conventional concrete. From the results after 90-day immersion, the mortar specimens with green concrete in 7.5% sulphate solution have similar effect with those immersed

for 28 days, but for those in 7.5% magnesium sulphate, the influence of addition on anti corrosion factor is not obvious.

The combined use of quarry rock dust and marble sludge powder exhibited excellent performance due to efficient micro filling ability and pozzolanic activity. Therefore, the results of this study provide a strong recommendation for the use of quarry rock dust and marble sludge powder as fine aggregate in concrete manufacturing.

5.2. Behaviour of different mixes to different environmental classes

In another study to analyse the behaviour of different compositions in various environmental classes was conducted at The Danish Centre for Resource Saving Concrete Structures. In this test several different mixes were prepared and exposed to different environmental conditions. The control parameters for the mixes were a slump of approximately 100 mm and, for the aggressive environment, an air content of 5.5%. The different green concrete mixes and their respective environmental conditions are tabulated as below:

Tables 7 and 8 show concrete mixes tested with high-volume fly ash for the passive and aggressive environmental classes. In the passive environmental class the fly ash content was increased from 24 to 70%, resulting in a reduction of CO2 emission from 18 to 57%.

In the aggressive environmental class the fly ash content was increased from 9 to 40% resulting in a reduction of CO2 emission from 33 to 54%. AV5 is a modified version of AV4 with increased air content.Strength development is shown in Figures 4 and 5. The figures show that PV4, which has a fly ash content of 70%, has strength that is far too low: it appears that the fly ash content must not exceed approximately 60%. Even so, the strength development is still too slow. As regards the concrete in the aggressive environmental class, the strength development is similar for all concrete types. However, preliminary testing indicates that the high-volume fly ash concrete might have problems with frost resistance.

Passive: Dry atmosphere with no risk of corrosionAggressive: Moist atmosphere, with significant alkaline and/or chloride influence on the concrete surface or where there is risk of water saturation combined with frost.

5.3. Comparison between Conventional and Green ConcreteAfter enough development of Green concrete, the question arose about its relevance before conventional concrete. Lesser environmental impact was one thing but other properties like durability and resistance to fire etcetera were suspected and under heavy scrutiny. Several tests thus carried out clearly showed that green concrete was not a bad bargain indeed.

An environmental screening has been performed for a column presenting the different design principles as described in Table 7 (green concrete columns defined as A, B, C). For comparison, the same environmental screening has been performed for a reference column (traditional concrete column defined as R), which is similar to column A, except that the green concrete type being substituted by a traditional concrete suitable for aggressive environment. The objective of the screening is to identify significant resource consumption and environmental loads of traditional concrete/design compared to green concrete/design occurring during the entire service life, this includes the environmentally viewed most critical maintenance/repair stage. The performed lifecycle screenings quantify material usage (consumption of concrete) as well as CO2 emissions generated at the involved stages during the lifecycle of the columns

The environmental parameters related to the working environment have not been included. The results of the environmental screening for the 3 green concrete columns (A, B, C) and the traditional concrete column (R) is presented in Table 3 with regard to the CO2-emission and in Table 4 with regard to the consumption of concrete

This comparison demonstrates that column B (stainless steel reinforcement) and column C (stainless steel cladding) present the most environmental-friendly design solutions both with regard to the CO2 emissions and the consumption of concrete. An even more environmental-friendly solution is if the selected concrete at column C would be substituted by a more environmental-friendly (greener) concrete type provided that the steel cladding assures the long-term protection of the reinforced concrete.

6. LIMITATIONS OF GREEN CONCRETE

Although green concrete seems very promising when it comes to an environment friendly sustainable development, the cardinal concern is its durability. Refutations are being

constantly raised regarding the service life of structures made with green concrete. Further the split tension of green concrete has been found much less than that of conventional concrete. Another challenge before green concrete is that of a market. Until the properties of green concrete are at par with the conventional concrete, green concrete is unlikely to find many customers.

Several researchers have argued that green concrete can be made durable by using stainless steel reinforcements, but the predicament is that by using stainless steel concrete the cost of the construction increases considerably. Even after this, green concrete is not as durable as the conventional concrete.

The limitations of using green concrete can be summarised as below:a) By using stainless steel, cost of reinforcement increases. b) Structures constructed with green concrete have comparatively less life than structures with conventional concrete. c) Split tension of green concrete is less than that of conventional concrete. d) Not as durable as conventional concrete.

Given these limitations coupled with the urgent need of reduction in green house gas emissions, has sparked off a number of researches across the globe to make green concrete more durable and bring it up to the mark with conventional concrete.

7. SCOPE IN INDIA

Green concrete is a revolutionary topic in the history of concrete industry. Concrete is an indispensible entity for a developing country like India which desperately needs a continuously expanding infrastructure. India is the second largest producer of cement in the world. Further India would be facing an exponential growth in the concrete demand by 2011 (Schumacher, 1999).

Table 13 Projected Cement Demand

Cement Demand (Mt/annum)

Year GDPtotal GDPindustry GDPconstruction GDPaverage

2001 103.0 107.6 106.2 105.6

2006 139.5 148.7 150.8 146.3

2011 186.9 204.2 210.4 200.5

Being produced in voluminous quantities in India, the concrete industry has a considerable part in the net CO2 emissions from the country. The net CO2 emissions from the construction agency are greater than any other industry.

In order to act in a responsible manner towards a sustainable development of the nation, Green concrete is the need of the hour. India being a developing country produces concrete in gargantuan quantities which result in huge volumes of CO2 being emitted into the atmosphere each year. The total energy consumption (a rough estimate of the net CO2 emissions) during the manufacture of cement in India is tabulated as below:

Table 14 Fuel Consumption in the Indian Cement Industry 1991-1993

Fuel Units 1991-92 1992-93 1993-94Electricity GWh 4800.52 6420.97 6754.60Coal Mt 10.8 11.7 11.1Petroleum Products

Mt 0.293 0.296 0.291

Total Cement Production

Mt 53.6 54.1 58.0

Source: TERI (1996)

The above statistics, though old, can be used as a guideline since the technological advancements have been scarce. As not much has been done and not much can be done to reduce these consumptions, the only alternative left is that of a green concrete, which will reduce the net CO2 emissions in the whole life cycle of concrete.

Thus we can deduce that, for a greener future, India needs to adopt Green concrete into practise as soon as possible. The other advantageous factor is its economy. As green concrete is made with concrete wastes and recycled aggregates, which are cheaper than conventional substitutes, and also with most of the industries facing problems with their waste disposal, put it out of the question to discard it.

Another type of green concrete, pervious concrete, is also a precious entity when it comes to storm water management and rain water harvesting. Using pervious concrete we can easily tame the run-off and harness it for future uses in relatively dry areas, which would have otherwise drained away. With the alarmingly increasing cases of droughts each year pervious concrete would prove to be a utilitarian tool. (Wikipedia)

The above facts clearly state a wide and promising scope of Green Concrete in the near future.

8. CONCLUSIONS

The overview of the present state of affairs regarding concrete types with reduced environmental impact has shown that there is considerable knowledge and experience on the subject. The Danish and European environmental policies have motivated the concrete industry to react, and will probably also motivate further development of the production and use of concrete with reduced environmental impact. The somewhat vague environmental requirements that exist have resulted in a need for more specific technical requirements, and the most important goal is to develop the technology necessary to produce and use resource saving concrete structures, i.e. green concrete. This applies to structure design, specification, manufacturing, performance, operation, and maintenance

In 1994 cement industry consumed 6.6 EJ of primary energy, corresponding with 2% of world energy consumption. Worldwide 1126 Mt CO2 or 5% of the CO2 production originates from cement production. The carbon intensity of cement making amounts to 0.81 kg CO2/kg cement. In India, North America, and China the carbon intensity is about 10% higher than on average. Specific carbon emissions range from 0.36 kg to 1.09 kg CO2/kg cement mainly depending on type of process, clinker/cement ratio and fuel used.

The potential environmental benefit to society of being able to build with green concrete is huge. It is realistic to assume that the technology can be developed, which can halve the CO2 emission related to concrete production, and with the large energy consumption of concrete and the

following large emission of CO2 this will mean a potential reduction of total CO2 emission by 2% (Obla 2009).

Seventeen different energy efficiency improvement options are identified. The improvement ranges from a small percentage to more than 25% per option, depending on the reference case (i.e type of process, fuel used) and local situation. The use of waste instead of fossil fuel may reduce CO2 emissions by 0.1 to 0.5 kg/kg cement (varying from 20 to 40%). An end-of-pipe technology to reduce carbon emissions may be CO2 removal. Probably the main technique is combustion under oxygen while recycling CO2 (Hendriks, 2004). However, considerably research is required to all unknown aspects of this technique.

It is important to keep a holistic cradle to cradle perspective when it comes to the use of a material. Based on a research Gajda et al. concluded that occupant energy use accounts for 99% of life cycle energy use of a single family home. Less than 1% of the life cycle energy used in that home was due to manufacturing cement and producing concrete. The global cement industry accounts for approximately 5% of global CO2 emissions. So whatever way one looks at it focusing on just the production of concrete accounts for a very small percent of overall CO2 emissions. This is not to say that progress should not be made in reducing the CO2 emissions from concrete as produced. However one should keep in mind that whatever CO2 emission reductions that are possible will still account for at best a 2% global CO2 reduction (assuming a challenging 21% reduction in global CO2 emissions from cement manufacture from now on).

REFERENCES:

1. Au Youn Thean Seng http://www.madisonvelocity.blogspot.com/

2. Carbon di oxide Information Analysis Centre, http://cdiac.ornl.gov/

3. Concrete Materials, DS 481:1998 [in Danish].

4. Gajda, J., VanGeem, Martha G., Marceau, Medgar L., ―Environmental Life Cycle Inventory of Single Family Housing‖, SN2582a, Portland Cement Association, Skokie, IL, PCA, 2002, www.cement.org

5. Glavind M. and Munch-Petersen C., ―‗Green‘ Concrete in Denmark‖, Structural Concrete, 1(1), March 2000.

6. Green Globes, The Green Building Initiative, Portland, Oregon, http://www.thegbi.org/

7. Hendriks, C. A., Worrell, E., de Jager, D., Blok, K. and Riemer P., ―Emission Reduction of Greenhouse Gases from the Cement Industry‖, Conference Paper- Cement, 2004, http://www.ieagreen.org.uk/

8. http://en.wikipedia.org/Pervious_Concrete

9. http://www.enercon.com/

10. http://www.epa.gov/nrmrl/news/news102008.html

11. http://www.greenconcretedenmark.dk/

12. http://www.perviousblog.com/

13. Leadership in Energy and Environmental Design (LEED), U.S. Green Building Council, Washington, DC, http://www.usgbc.org/

14. Medgar L. Marceau, Michael A. Nisbet, and Martha G. VanGeem, ―Life Cycle Inventory of Portland Cement Concrete‖, SN3011, Portland Cement Association, Skokie, IL, PCA, 2002, www.cement.org

15. Obla, K. H., ―What is Green Concrete?‖, Point of view, The Indian Concrete Journal, 24(4):26-28, April 2009.

16. Pravin K., Kaushik S.K. ―SCC with crusher sludge, fly ash and micro silica.‖ The Indian Concrete Journal. 79(8): 32-37, August 2005.

17. Shahul Hameed, M. and Sekar, A. S. S., ―Properties of Green Concrete containing quarry rock dust and marble sludge powder as fine aggregate‖ ARPN journal of engineering and applied sciences, 4(4), June 2009.

18. Shumacher, K. and Sathaye J., ―India‘s Cement Industry: Productivity, Energy Efficiency and Carbon Emissions‖, Energy Analysis Program, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, July 1999.

19. TERI, 1996: Teri Energy Data Directory and Yearbook 1996/97, Tata Energy Research Institute, New Delhi, India: Pauls Press.