Dr. Yash P. Gupta Technical Advisor, Yamuna Bridge Information Centre, COWI-DIPL Consortium, Allahabad.
Waste Management: The Waste usually relates to non usable materials produced by Industrial or human activity and waste management is generally undertaken to dispose and reduce their effect on sustainability, health and aesthetics or amenities. The waste management is also carried out to reduce its effect on environment and climate change and to recover useful material or resources from it. Thus, waste management is collection, transport, processing, recycling or disposal of waste materials. Wastes may have solid, liquid or gaseous substances.
Waste materials that the Industry has found to perform favorably as substitutes for conventional materials include: fly ash, granulated blast furnace slag, recycled concrete, demolition waste, reclaimed asphalt pavement, used tires, microsilica, glass beads, electrical and electronic industry waste, plastic waste etc. Some information given here outlines the origin, some physical properties, possible use and economic aspect. Generation and properties of recycled materials varies from place to place and from time to time depending on the location and construction activity as well as type of construction projects at a given site.
Demolition waste can be used as aggregate for making concrete or Bricks/Blocks and fines in Road pavements. Plastic waste is another waste which is the most unwanted land waste all over the World. This material is non degradable and remains as such over the time. Plastic / Polythene waste modified Bitumen (Polymerized Bitumen) can be produced and can be used for the construction of Roads / flexible Pavements. Such plastic waste or modified Bitumen can also be used for making perforated concrete blocks required for making slabs for rain harvesting.
Fly ash is a by-product produced during the operation of coal-fired power plants. In general, the coal is pulverized and combustion of pulverized coal is fired to achieve high temperature in the steam generators of thermal power plants. Fine coal particles which are fired create high temperature and turn into a gaseous form and the ash produced in molten / fused form solidifies while remaining suspended in the exhaust gases. The molten / fused ash particles also condense from high temperature in the exhaust gases in chimney. That is when coal is burned, the impurities in the coal, which do not burn are suspended and come down as bottom ash. Because of environmental concerns, ash is removed from flue gases by mechanical collectors and electrostatic precipitators before they are discharged into the atmosphere. The finely divided particles from the exhaust gases are collected in electrostatic precipitators. These particles are called Fly ash. Varying amounts of carbon in it affect the color of fly ash. Gray to black represents increasing percentages of carbon, while tan color is indicative of lime and/or calcium content.
Fly ash particles are very smooth and quite spherical in shape. These particles range from 1 to 150 µm in diameter, depending on the type of collection system. A typical shape of fly ash particles is seen in figure 1. Based on its composition, fly ash is classified into two groups: ASTM Class C or high calcium fly ash and ASTM Class F or low calcium fly ash as given below with indicative reaction.
Class F – Low Ca O with Si O2 + Al2 O3 + fe2 O3 > 70%
Class F fly ash is generally produced from the combustion of anthracite or bituminous coal. It has pozzolanic properties, but little or no cementitious properties. Due to their low calcium oxide content, this fly ash requires an external source of calcium for their reaction. Class C fly ash is normally produced from the combustion of lignite or sub-bituminous coal. Fly ash exhibits pozzolanic properties and in certain type, cementitious properties as well. In Concrete, Class F fly ash has pozzolanic properties when introduced to water, whereas Class C fly ash is naturally cememtitious due to its high amount of calcium oxide. Class C fly ash exhibits both autogenous cementitious and pozzolanic properties. It has been reported that Class C fly ash contains less than one percent of carbon and huge amount of Calcium oxide.
Most of the fly ash produced in India is equivalent to class F type with low CaO. However, some thermal power stations use different type of coal, which may be imported, can result in production of Class C fly ash. India generates more than 150 million tons of fly ash each year. Lots of it is used by cement industry in producing PPC cement or blended cement, which is almost 60% of the total cement produced. The permissible limit of un-burnt carbon should generally be low.
Use & Economic Impact
Finer the fly ash, better is its reactivity and lesser is its water requirement. Fly ash particles finer than 10 microns get adsorbed on cement particles giving a negative charge causing dispersion of cement particle flocks, thereby releasing the water trapped within the cement particle flocks and improves workability. Fly ash particles or glassy or amorphous phase of them and diameter less than 45 microns have good pozzolanic reactivity. Particles more than 45 microns in size are less reactive and therefore likely to increase the water requirement. Particles, smaller than 10 microns, are main contributors towards the 7 to 28 days strength. Sizes between 10 to 45 microns react slowly to give the full strength in 28 days to about one year and onwards. However, particles over 45 microns do not contribute towards strength but act as filler, like fine sand particles. Residue of fly ash on 45 microns should generally not exceed more than 34%. Fly Ash is also used as a partial cement replacement in concrete. It must meet strict construction standards; however no standard environmental regulations have been established in India so far. Generally 75% of the ash must have a fineness of 45µm or less, and have carbon content, measured by the loss on ignition (LOI), of less than 4%. Some of the specific uses are given here:
- Mix fly ash with clinker to make blended or Portland Pozzolana Cement
- Mix fly ash as one component in making concrete in addition of cement, sand, aggregate etc.
- Make high volume fly ash concrete.
- Dry fly ash can be used as an inert fill material for Road / soil embankments or supplementary cementitious material to improve cohesion and stability of bituminous concrete binder etc.
Advantages of Using Flyash in Concrete:
- Cement production units emit around 0.88 Ton of co2 per Ton of clinker produced. Fly ash replacement in cement production reduces carbon dioxide emission to that extent.
- Utilization of fly ash as a part replacement of cement or as a mineral admixture in concrete solves its disposal problem to some extent.
- Use of good quality fly ash in cement and / or concrete has shown remarkable improvement in giving dense concrete and thus better durability of concrete, especially in aggressive environment. Thus it is economical and saves on Cement.
- The advantages include: higher substitution (up to 60%) of cement by fly ash reduces heat of hydration, consequently lowers the expenses on cooling infrastructure.
- Some of the technical benefits of fly ash use are:
- Higher ultimate strength
- Increased durability
- Improved workability
- Reduced bleeding
- Increased resistance to sulfate attack
- Increased resistance to alkali-silica reactivity.
- Reduced shrinkage.
Availability: Silica Fume is available in two forms: dry and wet. Dry silica can be provided as produced or densified with or without dry admixtures. Silica Fume slurry with low or high dosages of chemical admixtures are also available. They are generally not produced in India and it is imported when required.
Possible Applications & Economic Impact:
Silica Fume is used in concrete to improve its properties like compressive strength, bond strength and abrasion resistance; reduces permeability and therefore more durable and helps in protecting reinforcing steel from corrosion. Microsilica’s high silica content is also high in purity and thus better pozzolanic properties. Reacting with calcium hydroxide (product of cement’s pozzolanic reaction), microsilica will produce calcium silicates that will result in denser concrete with increased compressive strength like 100 MPa or more with is similar to mild steel. In the specific application like bridge deck overlays, water retaining structures or monumental structures; it is very useful. Therefore, it will save on the cement quantity and thus cost. Small amounts of microsilica are also used in high performance shotcrete for structural repairs. Silica Fume can generally be used in concrete from 7 to 10 percent or sometimes up to 15%. With an addition of about 10 percent silica fume, the potential exists for very strong concrete. However, high replacement rates will require the use of high range water reducers. Effects of addition of Microsilica on various parameters of concrete are given below.
- Effects on Air Entrainment and workability of Fresh Concrete: The dosage of air-entraining agent needed to maintain the required air content when using Silica Fume is slightly higher than that for conventional concrete because of high surface area and the presence of carbon. This dosage is increased with increasing amounts of Silica Fume in concrete. It has been found that Silica Fume reduces bleeding because of its effect on rheologic properties. Concrete incorporating more than 10% Silica Fume becomes sticky and in order to enhance workability, the initial slump should be adjusted or increased with HRWR.
- Effects on Permeability and Strength of Hardened Concrete: Silica Fume has been successfully used to produce low-permeability, high-strength and chemically better resistant concrete. Incorporation of Silica Fume into a mixture with HRWR also enables the use of a lower water-to-cementitious material ratio, than otherwise required hence higher strength. It has been shown by several researchers that addition of Silica Fume to concrete reduces its permeability (ACI Comm. 226 1987b). This reduction is primarily the result of the increased density matrix due to the presence of Silica Fume. Addition of Silica Fume by itself, keeping other factors constant, increases the concrete strength.
Blast Furnace Slag (BFS)
In India more than 10 million tones of Blast Furnace Slag is produced every year and it is increasing with the increase in steel production. Blast furnace slag is a byproduct from the manufacture of pig iron and obtained through rapid cooling by water or quenching molten slag. Iron ore, as well as scrap iron, is reduced to a molten state by burning coke fuel with fluxing agents of limestone and/or dolomite. Blast furnace slag is a nonmetallic by-product produced in the process of steel production. BFS consists primarily of silicates, aluminates, silicates, and calcium-alumina-silicates. BFS forms, when slagging agents (e.g., iron ore, coke ash, and limestone) are added to iron ore to remove impurities. In the process of reducing iron ore to iron, a molten slag forms as a nonmetallic liquid (consisting primarily of silicates and alumino silicates of calcium and other bases) that floats on top of molten iron. The molten slag is then separated from the liquid metal and cooled. Different forms of slag product are obtained depending on the method used to cool the molten slag and subsequent processing: Air-Cooled Blast Furnace Slag (ACBFS), one of various slag products, is also available when the liquid slag is allowed to cool under atmospheric conditions.
- Air-Cooled Blast Furnace Slag (ACBFS)
Physical Properties: ACBFS has significant material properties including favorable frictional properties, high stability, and resistance to stripping and rutting. On the other hand, steel slag may contain calcium or magnesium oxides, which will hydrate - leading to rapid short-term and long-term expansion, respectively. It is mildly alkaline, so steel slag may be potentially harmful to aluminum or galvanized metals. It is a hard, angular material with textures ranging from rough, porous surfaces to smooth, shell-like fractured surfaces. Though vesicular, the slag structure’s cells are not inter-connected and little absorption is likely. Physical properties (e.g. unit weight and size) can vary considerably depending on the method of production; for example, high use of scrap iron can lead to higher unit weights.
Crushed Air-Cooled Blast Furnace Slag (Aggregate):
ACBFS may be broken down as typical aggregate with the help of processing equipment to meet gradation specifications. Thus, steel slag can be available as aggregate as construction materials and acceptable as coarse aggregate for use in Concrete and bituminous concrete mixes and seal coats. A typical shape of ACBFS (aggregate) is shown in figure 3.
Possible Use & Some Properties: Crushed ACBFS can be used in nearly all applications utilizing it as natural aggregates, such as bituminous and portland cement concrete, embankment, or sub-base, embankments, and fills. ACBFS has potentially favorable resistance to polishing, weathering, durability and abrasion. However, the material’s inherent variability in physical properties can be of concern. When included in bituminous concrete pavements, this material provides exceptional frictional properties and increased stability, but its tendency for high surface absorption may require greater amounts of asphalt binder.
Figure 3: A typical shape of ACBFS (aggregate)
Other Type of Blast Furnace Slag
- Expanded Blast Furnace Slag Crushed expanded slag is angular, roughly cubical in shape, and has texture that is rougher than that of air cooled slag. The porosity of expanded blast furnace slag aggregates is higher than ACBFS aggregates. The bulk view of blast furnace expanded slag is approximately 70% of that of air-cooled slag. Typical compacted unit weight for expanded blast furnace slag aggregates may be as low as about 800 kg/m3.
- Pelletized Blast Furnace Slag: Unlike air-cooled and expanded blast furnace slag, pelletized blast furnace slag has a smooth texture and rounded shape. Consequently, the porosity and water absorption are much lower than those of ACBFS or expanded blast furnace slag. Pelletized blast furnace slag may have unit weight of about 840 kg/m3.
Ground Granulated Blast Furnace Slag (GGBFS)
Use and Economic Impact: The primary use of GGBFS is as fine aggregate substitute, in concrete or as a mineral admixture or as component of blended cement or as partial substitute for Portland cement. It may be used as part replacement of Cement as per IS 456: 2000 to make concrete or add to clinker to produce Pozzolana Cement conforming to IS 12089. In blended cement, GGBFS has a low heat of hydration, which slows the chemical reaction responsible for strength gain, resulting in a gradual strengthening of the concrete. Generally its use is not more than 25% to be included in concrete as partial replacement of Cement.
Use of GGBFS concrete has a positive effect in disposing blast furnace slag in environmentally friendly way and preserving resources and above all producing concrete of better quality. Experimental studies were conducted to develop and examine the performance of concrete mixes using GGBFS as cement replacing pozzolana and mixing it in the batching plant. The study showed that concrete can be easily made by using GGBS. The gain in strength with age was also higher with time with the use of GGBFS.
Demolition Waste (MALWA)
- Collection and Disposal for landfill area and/or incineration.
- Recycling – physical and biological processing
- Energy recovery
Recycling the Waste:
Step 1: Collection: Recyclables differ from time to time and region to region, however there are different steps / methods to recycle it like:
1. Deposit it at encash Centers
2. Municipal Collectors and deposit at recycle centres.
Step 2: Processing: Waste is sent to a recovery Industry / facility to be sorted and prepared into marketable or manufacturable commodities for manufacturing or processing for useful products.
Step 3: Manufacturing: Once waste is separated in different lots, the recyclables are ready to undergo the third phase of recycling loop. Many of new-generation products are being manufactured with total or partial recycled content. Some household items that contain recycled materials include paper for newspapers, paper towels, soft drink containers, steel cans and plastic laundry detergent bottles, packing cartons, polythene begs, furniture apart from composting for manure and producing energy etc.
- Low grade fresh concrete
- Use such Concrete in casting conventional type of bricks and using them in place of Burnt clay bricks.
- Highway Construction for casting curve, chute drain, median drain & side drain components of Highways
- Demolition waste or recycled materials used in embankment filling.
- Making benches for park and pedestrian paths etc.
Use of Demolition Waste Aggregate in Chute Drain Elements of Elevated Highways:
Recycled Concrete Material (RCM)
Possible use & Economy: Crushed concrete’s physical characteristics make it a viable substitute for aggregate and can be used in highways at granular bases level, as well as fill material. This can also be used in making concrete, concrete blocks/Bricks. RCM obtained on construction site may be used immediately for project use in making concrete by proper mix design. Such concrete can be used in DLC, curbs or Block making etc. It can also be stockpiled for future use.
Advantages of Using both Demolition Waste (MALWA & RCM):
- By making use of locally available demolition waste and concrete material aggregates, there would be sufficient reduction in aggregate requirement at construction site.
- Processing of waste will make the system Sustainable. It will also save energy & resource of materials which can be usefully utilized at a later time.
Possible Use and Economy: When glass is properly crushed, this material exhibits physical properties similar to coarse sand. It has very low water absorption. High angularity of this material, compared to rounded sand, may enhance the stability of Bituminous / asphalt mixes. In general, glass is known for its heat retention properties, which can help decrease the depth of frost penetration. Such material can be used in concrete construction as fine or course aggregate.
Reclaimed Bitumen/Asphalt Pavement (RAP)
Possible Use: RAP is produced by crushing and screening the material to a 6 – 12 mm in size. It is tested to ensure that the proper applicable gradation and quality is satisfied, and if so, the RAP is mixed with virgin aggregate and asphalt, as needed for use in bituminous roads. The amount of RAP allowed for low volume roads is from 25% to 30%. For some non-critical mixes, such as the shoulder, base and sub-base up to 50% RAP can be used. For surface courses, the amount used ranges from 10 to 15% for all but for the highest volume highways. RAP may not be allowed in the highest grade bituminous concrete surface or polymer-modified mixes to maintain acceptable friction requirements.
Waste Vehicle Tyres/ Crumb Rubber (CR)
Crumb Rubber (CR): Shredding waste tyres and removing steel debris found in steel-belted tyres generate crumb rubber (CR). There are various mechanical methods used to shred apart these tyres to Crumb Rubber i.e. the crackermill, granulator, and micromill methods and others. CR can also be manufactured through the cryogenation method. This method involves fracturing the rubber after reducing the temperature with liquid nitrogen. CR is fine rubber particles ranging in size from 0.075mm to 0.475mm.
Application of Crumb Rubber: CR can be blended into fresh Bitumen / Asphalt of about 80-100 grade. It can also be blended in bituminous concrete by either a wet or dry process. For the dry process, the material is added into bituminous concrete at two rates: variable and fixed. The fixed rate consisted of adding at least 10 Kg CR per ton of bituminous concrete. Overall findings indicated that the fixed rate wet process method had shown fewer distresses than the control sections of conventional bituminous concrete. On the other hand, the dry process compared poorly to conventional bituminous concrete. In addition to this, the fixed rate CR areas are currently displaying, slightly higher tyre friction than the other category of road surface.
Such Crum Rubber Modified Bitumen (CRMB) shows better penetration value and softening point. So it is quite effective to use in top layers of road surface i.e. SDBC or Carpeting/BC. It also gives better resistance to water exposure and flash and fire point. Thus CRMB is effectively used in bearing coat of Flexible pavements ie in SDBC layer. This is also good for use in hot climate roads.
Plastic Waste Scenario
Plastic bags are non degradable material, so it cannot be decomposed and used as organic manure. Some plastic bags can be reused or it can be reprocessed by converting it to granular form and then re-rolling it in the form of sheets. Rest of plastic bags is either land filled or incinerated. Both methods are not eco-friendly processes and they pollute the land and water bodies.
Possible Use: Though, used Plastic is considered a pollution menace, but it can find its use in construction Industry/processes and thus can help solving the problem of pollution. Plastic waste or polythene begs is a form of a Polymer and its properties are similar to polymer to some extent.
Utilization of Plastic Waste was tried by author in two applications in the road construction Industry. These are given in brief here. The studies on the thermal behavior and binding property of the molten plastic promoted a study on the preparation and use of plastic waste-bitumen blend.
- Use of Plastic Blend Bitumen in Bearing Coat of Road Pavement:
The plastic blend bitumen was prepared by heating the normal Bitumen of grade 80-100 upto 150-1600C. Simultaneously waste plastic was shredded in smaller pieces. It was then added in hot bitumen and stirred well till it melted fully in bitumen. First the properties of such Plastic waste –Bitumen blend were found. These properties were similar or even better than original bitumen. Then this blend was tried for the top layer of road surface as is common for SDBC or Bituminous Concrete. Plastic blended bitumen was used with 10 mm size aggregate and stone dust mixture similar to normal design of SDBC Mix. Several trials were made to develop right Job mix formula. Finally Bitumen blended with 1.5 % waste polythene was chosen for such mix because this percentage gave better Mix.
- Use of Plastic-Waste as Perforated Polymer Concrete:
The plastic waste was also used for producing Perforated Polymer Concrete. Such experiment was done in the laboratory. The aggregate was heated to a temperature of around 1200 C. The shredded plastic-waste was added over hot aggregate while carrying on constant stirring to give a uniform coating of plastic waste over aggregate as seen in figure 10. The plastic waste got softened and got coated over the aggregate. The hot plastic waste coated aggregate was cast in the form of block and compacted, as seen in figure 11.
Figure 10: Mixing Plastic waste in Hot Aggregate
- Preliminary studies on the use of plastic-waste as a blending material with bitumen, suggest that the blends behave similar to PMB, thus having improved properties compared to plain bitumen.
- The molten plastic waste inhibits good binding property.
- The polymer coated aggregate was soaked in water for 48 hours. There was no stripping which shows that the coated plastic waste material sticks well with the surface of the aggregate and looks to have enough voids in its body. This proves that such concrete can be used where perforations are required for permeable media.
Steel Scrape and Metals waste
Physical Properties: Steel waste and other metal waste have good material properties including favorable frictional properties, high stability, and resistance to rutting etc. Chemical composition of such production has good physical characteristics, such as density, porosity, and odd shape and size. In general, they are more angular, more dense and harder than many other materials.
Application: Such Steel Scrape and Metals waste can be shredded in small elongated pieces and used in making small Fiber Reinforced Concrete or SIFCON (Slurry infiltrated concrete) which is similar to Fiber Reinforced Concrete for small jobs.
Electrical and Electronic Waste
Possible Use: These wastes can be shredded in the form of small strips or wire pieces. These pieces can be used as fibers in the construction industry similar to Steel scrape or in abrasion layer of rigid pavements.
Further nearly 90% of the waste water i.e. about 40,000 million liters –generated daily by cities that flow into drains, streams, rivers and sea doesn’t met environment norms. Generally waste water should be of bathing quality to meet the standard of waste water disposal system. In cities, where about 40% of the country’s population live, is polluting over 70% of the water sources, says a report released by the Central Pollution control Board. The report states that existing services of treating waste water should be improved drastically, otherwise the per capita water supply to an average citizen could drop from an average of 105 litres to only 65 litres or less a day in the coming years. This is municipal waste water scenario.
Such waste water could be treated and used back in construction Industry. For secondary construction purposes like washing (except in making concrete) use simple processed waste water. The treatment of construction and bathroom waste water, which contains suspended solids, oil and soapy material, involves removal of these materials and stabilisation of pollutants present in such waste water. This can be done in a sedimentation tank in which sludge gets settled and stabilised. Once the waste water passes through it and suspended particles are removed, the water then can pass through a pebble bed for purification and could be stored for construction use or for further use. Thus the reuse of construction cycle waste water and domestic waste water can meet the crises of water shortage to a great extend in coming times.
Conclusion and Advantages of Using Waste in Construction
Since the waste is being generated all over the country i.e. in each of 5,161 cities and towns of the Country. So as far as possible, its management efforts should be focused at decentralized locations through small scale units for recycling and used in construction industry there itself. Further poverty alleviation in the developing countries can also be effectively achieved by conservation of resources and energy and thus creation of further employment opportunities. Public as well as well as government should encourage using waste at priority. Some advantages of using Demolition Waste and Plastic waste In Construction are:
- Disposal of Demolition and Plastic Waste becomes easier.
- By making use of locally available demolition waste aggregates, there would be sufficient reduction in aggregate requirement at construction site.
- Top soil of earth will be saved which is used in making burnt clay bricks and thus environmentally viable.
- It is possible to produce a plastic waste modified Bitumen using this Bitumen for highways.
- It will save the resources like Aggregates (hill stones) Bitumen / Polymer etc.
- It can generate work for unemployed people like collecting all plastic waste by Rag pickers etc, and deposit it at Bitumen or Hot mix plants or Concrete batching plants.
- Generally demolition and plastic bags are lying on road sides and Street cows eat the kitchen waste. Along with that they also consume plastics giving rise to various diseases in these animals.
- The processing waste will also make the system Sustainable and can also conserve energy.
- CO2 emission is almost nil in this process.
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- Al-Qadi, I. L., Brandon, T. L., Smith, T., and Lacina, B. A., "How Do Geosynthetics Improve Pavement’s Performance," Proceedings of Material Engineering Conference, San Diego, CA. 1996, pp. 606-616.
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- Meyer, C., S. Baxter, and W. Jin, W. Proceedings of the Fourth Materials Engineering Conference: Alkali-Silica Reaction in Concrete with Waste Glass as Aggregate, Materials for the New Millennium Vol. 2. New York.