Waste is generated from all directions. It may be from Industry, Municipality and Agriculture or from any other process of human or animal use. The waste may be in the form of solid, liquid or in gases form. They not only require huge space to stock it but also pollute the environment. The polluted environment is harmful to human health and for the sustainability of system. Thus, generation of waste must be minimized or recycled for human use. Most of such waste can be used in industry or human cycle after its proper processing. Three major amounts of wastes are from municipality, industry and building demolition. Wastes like demolition waste, fly ash, industrial waste can be easily used in Construction Industry. A summary given here is only about few wastes which can be used in construction industry for infrastructure and thus save huge resources and protect environment. However, properties – both physical & chemical must be investigated to see the suitability and compatibility as one component of construction materials.

Dr. Yash P. Gupta Technical Advisor, Yamuna Bridge Information Centre, COWI-DIPL Consortium, Allahabad.

Introduction

Construction industry is the largest consumer of basic material of both the natural ones (like stone, sand, clay, lime) and manufactured and synthetic ones. During the last 50 years or so, there has been some unplanned, unchecked and haphazard exploitation of the mineral resources like limestone, clay, iron ore, bauxite, coal etc. Further the growth in industries is continuously throwing huge quantities of wastes and byproducts such as flyash from power generation & blast furnace slag from iron industry, red mud from aluminum industry etc. Also huge amount of Municipal waste is generated every day in each Indian city and World over. For example, Delhi alone generates about 650 tons of Garbage every day. By 2020 its amount may reach 1,800 tons. Generally, the disposal areas are outside city which are miles apart. Such amount of waste disposal is a Herculean task and needs space for dumping and fuel for transportation. As waste continues to accumulate and availability and capacity of landfill spaces diminish, so it is necessary to recycle and use it as construction material especially for sustainable Development. Infrastructure construction uses tremendous amount of material which can also be recycled materials.

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

Source and Type

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.

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Figure 1: Fly ash particles at 2,000x magnification (seen through Electron Microscope)
Class C – High Ca O with Si O2 + Al2 O3 + fe2 O3 > 50%

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:
  1. Mix fly ash with clinker to make blended or Portland Pozzolana Cement
  2. Mix fly ash as one component in making concrete in addition of cement, sand, aggregate etc.
  3. Make high volume fly ash concrete.
  4. 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:
    1. Higher ultimate strength
    2. Increased durability
    3. Improved workability
    4. Reduced bleeding
    5. Increased resistance to sulfate attack
    6. Increased resistance to alkali-silica reactivity.
    7. Reduced shrinkage.

Microsilica

Source and type: Microsilica (SiO2) also known as Silica fume, is a byproduct of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys. Silica Fume is also collected as a byproduct in the production of other silicon alloys such as ferrochromium, ferromanganese, ferromagnesium, and calcium silicon (ACI Comm. 226 1987b). Before the mid-1970s, nearly all Silica Fume was discharged into the atmosphere. Environmental concerns necessitated the collection and use of Silica Fume in various applications.

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Figure 2: A typical form of Microsilica in powder form
Silica fume particles are smooth and spherical in nature. They are very fine vitreous particles with a surface area of the order of 20,000 m2/kg or between 0.1 and 0.2 µm when measured by nitrogen absorption techniques, that is, the particles are approximately 100 times smaller than the average cement particle. A typical form of Microsilica is shown in figure 2 in powder form. Because of its extreme fineness and high silica content, Silica Fume is a highly effective pozzolanic material (ACI Comm. 226 1987b) and with its use, the concrete can achieve very dense concrete and much higher strengths. The first national standard for use of Silica Fume (microsilica) in concrete was adopted by AASHTO in 1990 (AASHTO Designation M 307-90). The AASHTO and ASTM C 1240 covers microsilica for use as a mineral admixture in Concrete and mortar to fill small voids and in case where pozzolanic action is desired.

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.
  1. 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.
  2. 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)

Source and Type

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.
  1. 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.

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    Figure 3: A typical shape of ACBFS (aggregate)
    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.

    Other Type of Blast Furnace Slag
  2. 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.
  3. 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)

Granulated Blast Furnace Slag: It is pulverized / grinded to reduce the particle size to cement fineness, fine powder and cement like material. GGBFS is a non-crystalline material varying in size depending on its chemical composition and method of production; its own production as well as that of its iron source. If slag is properly processed then it develops hydraulic property and it can be effectively used as pozzolanic material (powder form) similar to fly ash. Thus its properties and use are also similar which can act as cementitious material when used with cement. It is a glassy granular material that varies in structure and allows its use in Portland cement and in producing concrete.

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)

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Figure 4: A typical Waste Dump on the Road sides
Waste Generation: Construction industry during rehabilitation, repairs and modernizing the buildings produces huge waste called demolition waste or MALWA. A typical waste dump is shown in figure 4. Further huge amount of Municipal solid waste is generated every day in each Indian city or town. It is estimated that per capita waste generation in major Indian cities generally range from 0.4 to 0.8 Kg per day per person. The central pollution Control Board estimates the current quantum of municipal solid waste generation in India to the tune of 50 million tons per annum. Out of total waste generation, construction industry accounts for over 15 million tons or about 50% of total solid waste depending upon location and duration. The waste contributes to greenhouse gas emissions which should be reduced by its recycling. Thus the greenhouse gases and methane gas emissions etc can be controlled.

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Figure 5: Typical Analysis of Waste Dump lying on Road Side
Waste Management: When analyzed, a typical waste product distribution in any solid waste dump is shown in figure 5. Waste management is on the principle of 3 R’s; i.e. Reduce, Recycle and Recover/Reuse or otherwise dispose it. The waste management involves different methods for its processing as given below:
  • Collection and Disposal for landfill area and/or incineration.
  • Recycling – physical and biological processing
  • Energy recovery
Creative ways have been found to reduce and better manage Municipal Solid Waste (MSW). This includes reduction at source, recycling (including composting), and disposal. The most environmentally sound management of Municipal Solid Waste (MSW) is achieved when these approaches are put into practice. In future everyone has to accord importance to waste management in order to have sustainability. Out of these three R’s, recycling is most relevant as it will also conserve the resources. A typical method or steps for recycling the waste is given below.

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.

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Figure 6: Distribution of Ingredients in a typical Concrete Mix
In construction Industry, concrete is widely used. Generally the requirement of course aggregate in a concrete is more than 50% as shown in figure 6. The demolition waste can be converted to Course aggregate i.e. Recover course aggregate from Demolition waste after light crushing and sieving. After sieving, fines left out can be used as filler in plinth of building or highway embankment or can go back to river bed from where river sand is coming. Then make Concrete with such aggregate after mixing with required amount of cement and other ingredients as per design. Since the waste is being generated all over the country so it should be managed locally or recycled nearby (recycling unit should be tailor made to that area) and used in construction industry there itself. This type of processing the waste will make the system Sustainable. Thus, demolition waste after processing can be used in many applications as given below.
    1. Low grade fresh concrete
    2. Use such Concrete in casting conventional type of bricks and using them in place of Burnt clay bricks.
    3. Highway Construction for casting curve, chute drain, median drain & side drain components of Highways
    4. Demolition waste or recycled materials used in embankment filling.
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Figure 7: A typical Chute drain element made with demolition waste aggregate
  1. Making benches for park and pedestrian paths etc.
A typical application of the use of such concrete in highways is investigated by the author along with casting of conventional bricks of size 230x115x70 mm size and their use. Details of one such investigation is given here.

Use of Demolition Waste Aggregate in Chute Drain Elements of Elevated Highways:

With the concept of its use in making Bricks and Highway Pavement, the recycled aggregate concrete was used for casting curve, chute drain, median drain & side drain components of Highways. A concrete mix with recycled aggregate was designed in the grade of M 25 with cement content of 300 Kg/cum. Chute drain Components were pre-cast with this concrete mix. A typical chute drain element is shown in figure 8. This has been used at elevated road side embankment and is performing very well.

Recycled Concrete Material (RCM)

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Figure 8: Typical Garbage dump on road side with used polythene begs
Source and Type: Recycled Concrete Material (RCM), also known as crushed concrete is similar to demolition waste. Primary sources of RCM are demolition of existing concrete pavement, building slabs & foundations, bridge structures, curb and gutter and from commercial/private facilities etc. It is a reclaimed material. This material is crushed by mechanical means into manageable fragments and stockpiled. RCM may include small percentages of finer particles / sub-base soil or debris. Such materials have to be screened out and used as sand or fill material. The resulting material is normally in the form of Coarse Aggregate. Comprised of highly angular conglomerates of crushed quality aggregate and hardened cement, RCM is rougher and more absorbent than its virgin constituents. The difference amongst the various grades of concrete mixes of demolition concrete, results in varying qualities of aggregate and sizes.

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.

Glass Aggregate

Source and Type: Glass is formed by super cooling a molten mixture of sand (silicon dioxide), soda ash (sodium carbonate), and/or limestone to form a rigid physical state. Glass aggregate is a bi product of recycled mixed glass from manufacturing and post consumer use as waste. Glass aggregate, also known as glass cullet, is 100% crushed material that is generally angular, flat and elongated in shape. This fragmented material comes in variety of colors or colorless. The size varies depending on the chemical composition and method of production & crushing.

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)

Source and Type: Reclaimed Bituminous/Asphalt Pavement (RAP) is bituminous concrete material removed and/or reprocessed from pavements undergoing reconstruction or resurfacing. Reclaiming the bituminous concrete may involve either cold milling a portion of the existing bituminous concrete pavement or full depth removal or crushing. RAP properties largely depend on its existing in-place components. There can be significant variability among existing in-place mixes depending on the type of mix, and in turn, aggregate quality and size, mix consistency, and asphalt content. Due to traffic loading and method of processing, RAP is finer than its original aggregate constituents. Such type of RAP can be used for extraction of costly Bitumen and / or aggregate with the help of appropriate process. The properties of reclaimed aggregate will be similar to original aggregate used. However, bitumen extracted (if possible) will have different properties.

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)

Introduction: All vehicles on road uses tyres made of rubber. During their use, the tread of tyres gets consumed and then they are not fit for further use as they have lived their life. So they are replaced with new ones and old tyres are thrown. They are dumped here and there as waste material or burnt. Some old good tyres can be reused by rethreading with fresh rubber. Now with the extensive research in road pavement material, these old tyres can be used for modifying the properties of general purpose bitumen. They are cut into pieces and then grinded in powder form. This powder is mixed in hot Bitumen. Such product is called Crum Rubber Modified Bitumen (CRMB) and used in Bituminous Mix for road construction.

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

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Figure 9: Typical used polythene begs
Introduction: The use of plastic materials such as carry bags, packing material etc. is increasing day by day as it is very convenient carrier to carry small things anywhere. However, after use it is thrown out as garbage. This is a non-degradable material. Therefore, plastic waste has become a nuisance all over the World and in each city, village and even on roads and any where & everywhere. As plastic waste is a big nuisance, so many cities and Municipal Cooperation’s have banned the use of plastic bags in day to day use in the market. In general, the consumption of plastic has increased from 4000 tons/annum in 1990 to 4 million tons/annum in 2001 and it is expected to rise to 10 million tons/annum during the current year 2011 in India. Typical garbage dump on road side with plastic begs is shown in figure 8. The ingredients distribution analysis of any general garbage dump is shown in figure 5. It shows that there is about 1% Plastic waste in such garbage dump. Typical plastic bags are shown in figure 9.

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.
  1. 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.
  2. Use of Plastic-Waste as Perforated Polymer Concrete:
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    Figure 10: Mixing Plastic waste in Hot Aggregate
    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.
Binding property
  1. 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.
  2. The molten plastic waste inhibits good binding property.
  3. 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.
Such blend is not only easy to prepare but also helps to use plastic-waste for road pavement without much difficulty

Steel Scrape and Metals waste

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Figure 11: Polythene waste coated concrete Block
Source: Steel Scrape waste and other similar metal wastes are also available in plenty. Some of these wastes are reprocessed. However, many of them are not used because the steel rerolling mills are far off from the cities. Similarly cuttings/scrape is also available from Lath and Milling Machine etc.

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

Introduction: As the technology is getting advanced in all fields including Electrical and Electronic Industry, so more and more waste is generated every day. All these can be tried to be used in Construction Industry for infrastructure construction.

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.

Waste Water

Huge amount of fresh water is used in washing aggregate, silica sand, concrete batching plants, Transit Mixtures etc. This all goes to drains as waste water. This is construction Industry waste water.

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

It is important to have sustainability of any system on earth. At present times when there is crunch of resources and at the same time global warming taking place because of green house gases, then it is all the more necessary that we have better management of resources and waste utilization. Waste may be in any form i.e. solid, liquid or some form of energy. The technologies and the materials used for development should complement the use of local resources and waste management. Possible use of several solid wastes along with waste water is described in this article. Out of the processing of waste like demolition waste one can make Concrete bricks, use in highways and roads. They can also be used in making simple things like benches, pots etc.

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.

References

  • IRC, "Guidelines for the Design of flexible pavements", IRC: 37 -1970, Indian Roads Congress.
  • Battiato, G., and Verga, C., "The AGIP Visco elastic Method For Asphalt Pavement Design," Proceedings of the Fifth International Conference on The Structural Design of Asphalt Pavements, Ba Arnhem; Netherlands, August 23-26 1982, pp. 59-66.
  • 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.
  • Heckel, Greg. Alternative Materials for the Modification and Stabilization of Unstable Subgrade Soils. Physical Research Report No. 125, Springfield: Illinois Dept. of Transportation, Bureau of Materials and Physical Research, May 1997.
  • 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.
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