Sudhakar P.V.S., Sr. General Manager, Station (I/C), Power Grid Corporation of India Ltd, Maheshwaram 765 KV GIS Substation, Meerkhanpet, Kandukur Mandal Ranga Reddy District Telangana., Pandey Sangeeta, Chief Manager (Civil) Power Grid Corporation of India Limited, Regional Headquarter, Shastri Nagar, Board Colony, Eastern Region – 1, Patna & Achintya, (Corresponding Author) B.E. (Hons.), M. Tech., Ph. D. (Engg.) Professor of Civil Engineering and Principal, Darbhanga College of Engineering, Mabbi, Darbhanga
The main constituent of concrete, cement, during its production has a substantial effect on the environment by releasing carbon dioxide (CO2). Similarly, extensive mining of stone to produce coarse aggregates creates many new fault lines in the natural rocky terrain, making it prone to earthquakes and causing diversion of flow of water from its natural course. Due to excessive mining of sand, the river course is being changed, leading to floods.
Concrete is the most vital material used in construction. While demolishing buildings, a lot of building debris gets accumulated, which is generally dumped in low lying areas or wastelands, thereby closing the natural water drains or storage places for rain water. Recycling of demolished materials is carried out in many recycling plants, so that construction material, mainly coarse aggregate and sand, is produced from demolished debris or waste ready mix material and reused in construction. Similarly, there are substitutes for cement to reduce the CO2 emissions. Concrete produced with recycled / waste material or with substitutes has less impact on the environment and may be termed as Green Concrete. Green concrete is made up of environment friendly materials as well as recycled material from construction and demolition waste, and can be used for construction purposes.
About 35% of the total population in India comprises the urban population. The demand of building materials for 2021-22 is estimated to be about 380 million tonnes of cement, 50 million tonnes of steel, 600 billion number of bricks, 400 million cubic meters aggregate, and 40 million cubic meters of timber. There is a considerable amount of shortage of conventional and traditional building materials in India. Of late, fine aggregates are being imported and manufactured sand/stone dust is being used as replacement.
On the other hand, the re-development of housing and infrastructure as well as new construction to meet the increasing demand generates large volume of construction and demolition wastes. Indiscriminate dumping and non-utilization of generated debris results in fugitive air pollution and other hazards of solid waste dumping in drains, water bodies, empty plots and mixing up with municipal solid waste.
The Swachh Bharat Mission of Government of India has aimed for processing of 100% solid waste, including construction and demolition waste, in major cities and towns. The Ministry of Urban Development wants all the states to set up Construction and Demolition waste recycling facilities in all the cities and town with population over 1 million.
The proper management and processing of Construction and Demolition waste would be a win-win situation for all stakeholders. It would avoid indiscriminate dumping, land and air pollution, and would make available the building construction materials that are in short supply. It would also reduce the pressure on natural resources that are being otherwise exploited for building and road construction materials.
The Government is focusing on 100% utilization of waste material from construction and demolition industries. Construction and demolition waste in India in %age clearly shows that concrete holds majority of its parts.
As per the charts, it is unambiguous that 91% of total waste is Construction and Demolition waste and concrete hold more than half of Construction and Demolition waste alone. But India recycles only 1% of its Construction and Demolition waste.
Construction works using concrete are increasing all over the world for infrastructural development, which in turn increases the demand for construction materials. Aggregates are the main constituent of concrete. Due to continuous mining by blasting, the availability of aggregates has emerged as a major problem in recent times. In order to overcome this, there is an urgent need to find alternatives / replacement to some extent. Now a days, recycling of demolished materials is being done in many recycling plants, so that construction material (mainly coarse aggregate and sand) is produced from demolished debris or waste ready mix material and reused in construction.
Similarly, there are substitutes to cement to reduce the CO2 emissions. The concrete produced with recycled / waste material or with substitutes has less impact on environment and may be termed as Green Concrete. It is a concept of translating environment into concrete considering every aspect from raw materials manufacture over mix design to structural design, construction, and service life.
Green Concrete is cheap to produce because waste products are used as partial substitute for cement, charges for the disposal are avoided, energy consumption in production is lower, and durability is greater. Waste can be used to produce new products or can be used as admixtures so that natural resources are used more efficiently and the environment is protected from waste deposits. Concrete recycling is increasing due to improved environmental awareness, governmental laws and economic benefits.
Impact on Environment Due to Concrete
The cement industry is one of largest producers of carbon dioxide (CO2), creating up to 5% of worldwide man-made emissions of this gas, of which 50% is from the chemical process and 40% from burning fuel. The CO2 produced for the manufacture of one ton of structural concrete (using ~14% cement) is estimated at 410 kg/m3 (~180 kg/ton @ density of 2.3 g/cm3) (reduced to 290 kg/m3 with 30% fly ash replacement of cement). The CO2 emission from the concrete production is directly proportional to the cement content used in the concrete mix; 900 kg of CO2 are emitted for the fabrication of every ton of cement, accounting for 88% of the emissions associated with the average concrete mix.
Cement manufacture contributes greenhouse gases both directly through the production of carbon dioxide when calcium carbonate is thermally decomposed, producing lime and carbon dioxide during formation of cement clinker at high temperatures, and also through the use of energy. Lime the major ingredient of cement which leads to blasting, excavation in mines etc. causes loss of natural resources.
By reducing the usage of cement in concrete the damage it causes to the environment can be reduced. Another approach has been the partial replacement of conventional clinker with such alternatives as fly ash, bottom ash, and slag, all of which are by-products of other industries that would otherwise end up in landfills.
Properties of Green Concrete
Properties like Absorption Capacity, Specific Gravity, LA Abrasion, Sodium Sulphate, Magnesium Sulphate, Chloride Content, Compressive Strength, Split Tensile Strength have been compared for both Conventional Concrete (Virgin) and Green concrete (Recycled Concrete Aggregate) as shown in Table 1.
|Table 1: Properties of Virgin Concrete and Green Concrete|
|Parameter||Virgin Aggregate||Green Concrete (Recycled Concrete Aggregate)|
|L.A Abrasion||15% -30%||20%-45%|
|Sodium Sulphate||7%- 21%||18%- 59%|
|Magnesium Sulphate||4% - 7%||1%- 9%|
|Chloride Content||0-1.18 Kg/m3||0.59 to 7.12 Kg/m3|
|Table 2: Compressive Strength of Virgin Concrete and Green Concrete|
|Table 3: Compressive Strength of Virgin Concrete and Green Concrete|
The lower compressive strength recorded for concrete produced with recycled aggregate was due to higher water cement ratio, which is required to facilitate mixing due to absorption of the recycled fine particles. Recycled aggregate concrete will have higher water absorption than conventional concrete; it is mainly due to adhered mortar with recycled aggregates. Recycled aggregate concrete have slightly higher drying shrinkage; this is mainly because of increase in water/cement ratio.
Recycled aggregate concrete has better resistance to carbonation. It is mainly due to porous recycled aggregates and presence of old mortar attached to crushed stone aggregate. Recycled aggregate concrete provides better resistance to freezing and thawing than concrete produced by mixing natural aggregates. Provisions of utilization green concretefrom Construction and Demolition waste, to the extent of its utilization as coarse aggregate and / or fine aggregate, as per IS 383, is shown in Table 4. Further, replacement materials of traditional ingredients for Green Concrete are shown in Table 5.
|Table 4: Provisions of Utilization of Green Concrete as per IS 383|
|SL. NO.||CONSTRUCTION AND DEMOLITION WASTE AS PER IS 383||PLAIN CONCRETE||REINFORCED CONCRETE||LEAN CONCRETE||EXTENT OF UTILIZATION|
|1||Recycled Concrete Aggregate (RCA)||25%||20% (Only up to M 25 grade)||100%||As coarse aggregate.|
|2||Recycled Aggregate (RA)||Nil||Nil||100%||As coarse aggregate.|
|3||Recycled Concrete Aggregate (RCA)||25%||20% (Only up to M 25 grade)||100%||As fine aggregate.|
|Table 5: Replacement Materials for Green Concrete|
|S.NO||TRADITIONAL INGREDIENTS||REPLACEMENT MATERIALS FOR GREEN CONCRETE|
|1||CEMENT||Eco-Cement, Sludge Ash, Municipal solid waste, fly ash, Blast furnace slag.|
|2||COARSE AGGREGATES||Recycled Aggregates, Waste Ready Mix Concrete, Waste Glass, and Recycled Aggregates with crushed glass, and Recycled aggregates with silica fume. Waste Porcelain and cemented portion of Insulators.|
|3||FINE AGGREGATES||Fine recycled aggregate, Demolished Brick waste, Quarry dust, waste glass powder, Marble sludge powder, Rock dust and pebbles, Artificial sand, Waste glass, Fly ash and Micro silica, Bottom ash of Municipal solid waste.|
Construction and Demolition disposal has emerged as a major problem all over the world. Widely generated wastes need to be reused wisely so that proper disposal happen, and ultimately utilizes all the wastes with proper strength. It is now widely accepted that there is a significant potential for reclaiming and recycling demolished debris for use in value added applications to maximize economic and environmental benefits. As a result, recycling industries have matured.
Now, various measures are introduced which aim at reducing the use of primary aggregates and encouraging reuse and recycling, where it is technically, economically, or environmentally acceptable. Recycling industries in many parts of the world convert low-value waste into secondary construction material such as aggregate grades, road materials and aggregate fines. Green Concrete may be used in concrete for bulk fills, bank protection, base/fill of drainage structures, pavements, sidewalks, kerbstones and gutters, etc.
Up to 30 % of natural crushed coarse aggregate can be replaced by the recycled concrete aggregate. This %age can be increased up to 50 % for pavements and other areas which are under pure compression specific to the standards and practices pertaining to construction of roads.
Gardening and Landscaping: For drainage material, layer in sport fields, improvement in soil characteristics, improvement of bearing capacity, e.g., below garden walls, retaining wall etc.
Earthwork: Filling of line ditches and working spaces, improvement of bearing capacity of soil, soil exchanges etc.
Civil Engineering: Gravel base layer, combined gravel and anti-freeze base layer, bituminous base layer, hydraulically bounded base layer, concrete base layer, as input in concrete, mix in situ concrete, ready mix concrete, as input material in mortar, stones such as burned bricks, sand lime bricks or light weight concrete etc.
Other civil engineering elements like paver block, kerb stone, tile, concrete jali, concrete block, wall cladding, bollard, fence post, pre cast compound wall, planter, pavement, drain cover, park benches, on site assembly toilets and other small structures may be opted of Green concrete material.
Manufacturing Process of Green Concrete
Considerable attention is required to the control of waste processing and subsequent sorting, crushing, separating and grading the aggregate for use of the concrete construction industry. Construction and Demolition waste material often contains foreign matter in the form of metals, wood, hardboard, plastics, papers etc. Hence, a process scheme has to be adopted as sown in Fig. 4 and Fig. 5, which removes large pieces of these materials, mechanically or manually, before crushing and thorough cleaning of the crushed product.
Common river sand is expensive due to excessive cost of transportation from natural sources. Also, large-scale depletion of these sources creates environmental problems. As environmental transportation and other constraints make the availability and use of river sand less attractive, a substitute or replacement product for concrete industry needs to be found.
River sand is the most commonly used fine aggregate in the production of concrete but poses the problem of acute shortage in many areas. Continued use has started posing serious problems with respect to its availability, cost and environmental impact. In such a situation the Quarry rock dust can be an economic alternative to the river sand. Quarry rock dust can be defined as residue, tailing or other non-valuable waste material after the extraction and processing of rocks to form fine particles less than 4.75mm.
Usually, Quarry rock dust is used on a large scale in the highways as a surface finishing material, and also for manufacturing hollow blocks and lightweight concrete prefabricated elements. Use of Quarry rock dust as a fine aggregate in concrete draws serious attention of researchers and investigators.
In the recent past, attempts have been made for the successful utilization of various industrial byproducts (such as fly ash, silica fume, rice husk ash, foundry waste) to save environmental pollution. In addition to this, an alternative source for the potential replacement of natural aggregates in concrete has gained good attention. The utilization of Quarry rock dust which can be called as manufactured sand has been accepted as a building material. The durability of quarry dust concrete under sulphate attack and acid attack is higher compared to conventional concrete. The effects of quarry dust on the elastic modulus property are good with conventional concrete containing natural sand.
The fine quarry dust tends to increase the amount of super plasticizers needed for the quarry mixes in order to achieve the rheological properties. Replacement of natural sand with Quarry rock dust, as full replacement in concrete is possible. However, trial casting with Quarry rock dust may be done, in order to arrive at the water content and mix proportion to suit the required workability levels and strength requirement.
Fly ash is very fine powder and can travel far in air. It pollutes air and water when not properly disposed. Use of fly ash concrete in place of Plain Cement Concrete (PCC) can bring substantial savings in consumption of cement and energy and also provide economy. Optimum replacement level is around 30% of Portland cement. Fly ash can increase durability of concrete.
Use of fly ash in place of PCC enables substantial savings in consumption of cement, energy and economy. It is possible to replace 100% of Portland cement by fly ash, but replacement level above 80% require chemical activator. However, optimum replacement level is 30% only. Due to less heat of hydration generation, it can be used for mass concrete application.
Waste Marble Dust
Marble disposal may contain very fine powder. Marble powder is produced from the marble processing plants during the cutting, shaping and polishing and while construction. During these processes, about 20-25% of the process marble is turn into the powder form. India is topmost exporter of marble.
Every year a million tons of marble waste form processing plants are released. The disposal of this waste marble on soils reduces permeability and contaminates the overall ground water when deposited along catchment area. Hence, marble wastes powder utilization in construction industry may protect the environment from dumpsites of marble and also limit the excessive mining of natural resources of sand.
Advantages of Green Concrete
Not much change is required for the preparation of Green Concrete as compared to conventional concrete. The advantages of Green Concrete are as follows:
- It reduces environmental pollution
- Has good thermal and acid resistance
- Compressive and split tensile strength is better with some materials
- Reduces overall consumption of cement
- More economical that conventional concrete as shown in Table 6
- Uses local recycled materials
- The heat of hydration of green concrete is significantly lower than traditional concrete which results in lower temperature rise.
- Green concrete reduces dead weight of structure, allows handling, lifting flexibility with lighter weight; this leads to reduction of the overall consumption of cement
|Table 6: Savings in Cement Consumption of Building Product|
|Sl. No.||Building Product||% Saving|
|3||Paving Block 50mm thick||25|
|4||Paving Block 80mm thick||20|
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 degree Celsius using natural gas or coal as a fuel. This process is responsible for 5 to 8 % of all CO2 emissions worldwide. The manufacturing of Green Concrete releases heat up to 80 % less CO2 emissions.
Disadvantages of Green Concrete
As every coin has two sides, there are certain disadvantages in the use of Green Concrete, which must not be ignored.
- Water absorption is high
- Shrinkage and creep are high compared to conventional concrete
- Flexural strength is less
- Structure constructed with green concrete has shorter lifespan\
- By using stainless steel, cost of construction will increase.
- Tensile strength is less.
There is significant potential in waste materials to produce Green Concrete. The replacement of traditional ingredients of concrete by waste materials and byproducts gives an opportunity to manufacture economical and environment-friendly concrete. Partial replacement of ingredients by using waste materials and admixtures shows better compressive and tensile strength, improved sulphate resistance, decreased permeability and improved workability. The cost per unit volume of concrete with waste materials like quarry dust is lower than the corresponding control concrete mixes. A detailed life cycle analysis of Green Concrete by considering various parameters is necessary to understand the resultant concrete properties.
Concrete debris is to be kept separately and be processed/ supplied to processing plant without mixing with masonry, soil and other debris. Construction and Demolition waste is to be segregated in different streams such as concrete, soil, bricks and mortar and other streams stated above for supply to second raw materials market/ re-meltors/ re-users/ processors. The Construction and Demolition waste generated at the site is to be evacuated at the required frequency to avoid mix up and spilling over to neighboring areas. Safety of equipment and manpower is to be ensured. As a part of a global effort to reduce emissions of CO2, switching over completely to using Green Concrete for construction is the best way.
The overall financial management is such including the tipping fee payable by Construction and Demolition waste generator, that the selling prices of end building construction products manufactured by recycling Construction and Demolition (C&D) waste are at least 20 per cent lesser than corresponding conventional materialsused. All government and redevelopment constructions may be mandated to use recycled Construction and Demolition waste products like Green Concrete at least to the extent of 20 per cent of the total corresponding materials use.
New private constructions may be mandated to use recycled C&D waste products to the extent of at least 10 per cent of the total corresponding materials’ use. Large projects of re-development, like the ones being implemented by CPWD and NBCC at New Delhi, may be mandated to the following:
- Undertake deconstruction of old structures and not demolition.
- Minimize debris, maximize re-usable.
- Concrete debris be collected, stored, transported and processed separately to get RCAs.
- Process the C&D debris in situ and utilize all the produce directly or by converting into downstream products
- Environment norms are strictly followed, especially for air, water and noise.
- Rajput B.L. and Singh Indrasen, “Green Concrete- An Overview”, Indian Highways Journal, The Indian Roads Congress Association, New Delhi. February 2012.
- Hammed Shahul M. and Sekar A.S.S. “Properties of Green Concrete Containing Quarry Dust and Marble Sludge Powder as Fine Aggregate”, APRN Journal of Engineering and Applied Sciences, Volume 4, No.4, June 2009.
- Anantha Lekshmi M L, “Green Concrete-for the Future-A Review” 2016, International Journal of Engineering Research & Technology (IJERT). (Vol. No.4, Issue 08, Special Issue).
- Limbachiya M.C., Koulouris A, Roberts J.J. and Fried A.N., “Performance of Recycled Aggregate Concrete”, RILEM Publications SARL
- Abhijeet Baikerkar “A Review on Green concrete”. November 2014(Volume I, issue VI), JETIR (Journal of Emerging Technology and Innovative Research).
- Construction and Demolition Waste Management Rules, 2016. Ministry of Environment, Forest and Climate Change.
- Guidelines for Utilization of Construction and Demolition Waste in Construction of Dwelling Units and Related Infrastructure in Housing Schemes of the Government, 2016, Building Material and Technology Promotion Council, Ministry of Housing and Urban Affairs.
- Guidelines on Environmental Management of Construction & Demolition (C&D) Wastes, March, 2017, Central Pollution Control Board, Ministry of Environment, Forests and Climate Change.
- Swachh Bharat Mission Document, October 2017, Ministry of Drinking Water and Sanitation.
- Guidelines for Sustainable Habitat, March, 2014, Central Public Works Department.
- Circular dated 28 June, 2012 of the Ministry of Urban Development.
- National Ambient Air Quality Standards notified by Central Pollution Control Board, 18 November, 2009, Ministry of Environment, Forests and Climate Change.
- The Noise Pollution (Regulation and Control) Rules, 2000 (As amended till 10/08/2017 vide S.O. 2555(E)), Central Pollution Control Board, Ministry of Environment, Forests and Climate Change.
- Website of Environmental Protection Agency (EPA), USA www.epa.gov
- Website of European Demolition Association. www.europeandemolition.org
- IS-383:2016 Specification for Coarse and Fine Aggregates from natural sources for Concrete, Third Revision, The Bureau of Indian Standards, New Delhi.
- KPMG-NAREDCO Urban Housing Shortage in India.2012. Report of the Technical Urban Group (TG-12) on Urban Housing Shortage 2012-17, Ministry of Housing and Urban Poverty Alleviation, September 2012 2012 KPMG.
- IRC-121: 2017 Guidelines for use of C&D Waste Roads Sector. The Indian Roads Congress Association, New Delhi.