Free Research Paper on Recycling
Environmental concerns about the huge landfill space that is being taken by construction and demolition debris has brought up a new technique in salvaging construction material and recycling demolition debris. Although one process exists for two types of waste, many have tried different strategies in dealing with this problem. These strategies vary between "separating and sorting" then "crushing and reducing" and "crushing and reducing" then "separating and sorting".
PROCESS OF C&D DEBRIS RECYCLING
C&D debris refers to materials generated as a result of construction and demolition projects. Metals, wood, rocks, concrete, rubble, soil, paper, plastics and glass are among the many materials that are considered C&D debris. Realizing that the disposal of C&D debris in landfills consumes large amount of space and is economically and environmentally costly, the need to get acquainted with suitable recycling processes is becoming more and more essential (1, p.18). Although, only one recycling process has been developed, there are different strategies for implementation.
__________________________________________________________PROCESS OF C&D DEBRIS RECYCLING
C&D debris refers to materials generated as a result of construction and demolition projects. Metals, wood, rocks, concrete, rubble, soil, paper, plastics and glass are among the many materials that are considered C&D debris. Realizing that the disposal of C&D debris in landfills consumes large amount of space and is economically and environmentally costly, the need to get acquainted with suitable recycling processes is becoming more and more essential (1, p.18). Although, only one recycling process has been developed, there are different strategies for implementation.
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TYPES OF CONSTRUCTION AND DEMOLITION WASTES
Type I - Roadway and Site Conversion C&D Waste
C&D waste is classified as Type I if it consists mainly of rubble with a little ratio of "clean" materials such as wood, metals, and plastics. Type I waste should be easily separable in order to be considered as "clean". The composition by weight of a Type I C&D debris is (2, p.6.31):
Rubble
concrete, asphalt 40%
soil, rock 20%
Wood 30%
Metals, plastic 10%
Type II - Construction and Interior Demolition Waste
This type is mainly generated from urban structure such as office buildings, stores, etc.. Type II contains mixed fractions of concrete, drywall, framing, ductwork, roofing, windows, corrugated, packaging, etc.(2,p.6.32) . Due to its high heterogeneous composition this type is difficult to separate, it is mainly made of:
Rubble 25%
Wood 33%
Metals 20%
Corrugated 12%
other (carpet, residue, etc.) 10%
C & D WASTE PROCESSING STRATEGIES
Primary separating equipment used with type I are very efficient while with type II this procedure along with hand sorting will take lots of time. Processing procedure is determined by the type of waste and the possible use of the output materials
(2, p.6.32). Table 1 shows the different contents of C & D waste .
Table 1 Contents of C&D Waste (2, p.6.31)
Waste type Contents
Rubble Soil, rock, concrete, asphalt, bricks
Tar-based material Shingles, tar paper
Ferrous metal Steel rebar, pipes, roofing, flashing, structural members, ductwork
Nonferrous metal Aluminum, copper, brass
Harvested wood Stumps, brush, treetops and limbs
Untreated wood Framing, scrap lumber, pallets
Treated wood Plywood, pressure-treated, laminates
Plaster Drywall, sheetrock
Glass Windows, doors
Plastic Vinyl siding, doors, windows, blinds, material packaging
White goods/bulky items Appliances, furniture, carpeting
Corrugated Material packaging, cartons, paper
Contaminants Lead paint, lead piping, asbestos, fiberglass, fuel tanks
Type I C & D Waste Processing Strategy
Clean rubble can directly be placed into a grizzly feeder where a jawcrusher and hammermiller could act on it for reduction.
- Debris placed into grizzly feeder
Sorting and reducing first is more practical than crushing if the debris contains material such as plastics, paper, rags, or contaminants such as paint, lead pipes, etc.. After crushing the mix is then screened to remove fine soil and small rocks. Any contaminants, ferrous, and non ferrous material is removed by either manual picking or magnetic field belt. If wood is present in the rubble then the mix is guided towards a flotation tank where the wood will float and thus the separation from rocks is achieved. Another system instead of a flotation tank could be used and that is an air classifier. The air system is more expensive to use, but if the recycling plant is located in a region where there is strict rules about water pollution, thus requiring that the water from the flotation tank to be treated, then an air system might be a better option.
Crushing, reducing and then sorting and separating is much more recommended with systems made from 80% to 90% rubble, wood, and few contaminants. A general processing layout is shown in figure 2 and is available as both fixed and
portable designs(2, p.6.34).
- Recycling plant
Type II C&D Waste Processing Strategy
It is essential that type II C&D waste be sorted and separated before being crushed and reduced since this type of waste could have asbestos, paint, lead pipe, etc.. These contaminants could render the mixture hazardous if they where to be crushed into small pieces, consequently making hand-picking extremely difficult or even impossible to do.
- Separating and sorting
After removing big contamineous material, the mix is introduced into a disk screen in order to separate the soil from rocks.
- Hand-picking
This has proven to be essential in order to increase the efficiency of handpicking in a later stage.
Eventually, material recovered will be free from contaminants and rubble will further be processed according to the need of the local market(2, p.6.36).
- Aggregate of size 0-60mm
CONCLUSION
In recycling C&D debris, many considerations should be accounted for; such as the nature and the type of the material. Knowing these properties, it is possible to choose and apply the suitable process strategy: with type II materials, sorting and separating at an early stage before crushing reduces the risk of coming out with a contaminated recycled material. In contrast to type II material, type I material can be ,in most cases, more easily and safely crushed before being sorted since the percentage of contaminants is negligible.
TYPES OF CONSTRUCTION AND DEMOLITION WASTES
Type I - Roadway and Site Conversion C&D Waste
C&D waste is classified as Type I if it consists mainly of rubble with a little ratio of "clean" materials such as wood, metals, and plastics. Type I waste should be easily separable in order to be considered as "clean". The composition by weight of a Type I C&D debris is (2, p.6.31):
Rubble
concrete, asphalt 40%
soil, rock 20%
Wood 30%
Metals, plastic 10%
Type II - Construction and Interior Demolition Waste
This type is mainly generated from urban structure such as office buildings, stores, etc.. Type II contains mixed fractions of concrete, drywall, framing, ductwork, roofing, windows, corrugated, packaging, etc.(2,p.6.32) . Due to its high heterogeneous composition this type is difficult to separate, it is mainly made of:
Rubble 25%
Wood 33%
Metals 20%
Corrugated 12%
other (carpet, residue, etc.) 10%
C & D WASTE PROCESSING STRATEGIES
Primary separating equipment used with type I are very efficient while with type II this procedure along with hand sorting will take lots of time. Processing procedure is determined by the type of waste and the possible use of the output materials
(2, p.6.32). Table 1 shows the different contents of C & D waste .
Table 1 Contents of C&D Waste (2, p.6.31)
Waste type Contents
Rubble Soil, rock, concrete, asphalt, bricks
Tar-based material Shingles, tar paper
Ferrous metal Steel rebar, pipes, roofing, flashing, structural members, ductwork
Nonferrous metal Aluminum, copper, brass
Harvested wood Stumps, brush, treetops and limbs
Untreated wood Framing, scrap lumber, pallets
Treated wood Plywood, pressure-treated, laminates
Plaster Drywall, sheetrock
Glass Windows, doors
Plastic Vinyl siding, doors, windows, blinds, material packaging
White goods/bulky items Appliances, furniture, carpeting
Corrugated Material packaging, cartons, paper
Contaminants Lead paint, lead piping, asbestos, fiberglass, fuel tanks
Type I C & D Waste Processing Strategy
Clean rubble can directly be placed into a grizzly feeder where a jawcrusher and hammermiller could act on it for reduction.
- Debris placed into grizzly feeder
Sorting and reducing first is more practical than crushing if the debris contains material such as plastics, paper, rags, or contaminants such as paint, lead pipes, etc.. After crushing the mix is then screened to remove fine soil and small rocks. Any contaminants, ferrous, and non ferrous material is removed by either manual picking or magnetic field belt. If wood is present in the rubble then the mix is guided towards a flotation tank where the wood will float and thus the separation from rocks is achieved. Another system instead of a flotation tank could be used and that is an air classifier. The air system is more expensive to use, but if the recycling plant is located in a region where there is strict rules about water pollution, thus requiring that the water from the flotation tank to be treated, then an air system might be a better option.
Crushing, reducing and then sorting and separating is much more recommended with systems made from 80% to 90% rubble, wood, and few contaminants. A general processing layout is shown in figure 2 and is available as both fixed and
portable designs(2, p.6.34).
- Recycling plant
Type II C&D Waste Processing Strategy
It is essential that type II C&D waste be sorted and separated before being crushed and reduced since this type of waste could have asbestos, paint, lead pipe, etc.. These contaminants could render the mixture hazardous if they where to be crushed into small pieces, consequently making hand-picking extremely difficult or even impossible to do.
- Separating and sorting
After removing big contamineous material, the mix is introduced into a disk screen in order to separate the soil from rocks.
- Hand-picking
This has proven to be essential in order to increase the efficiency of handpicking in a later stage.
Eventually, material recovered will be free from contaminants and rubble will further be processed according to the need of the local market(2, p.6.36).
- Aggregate of size 0-60mm
CONCLUSION
In recycling C&D debris, many considerations should be accounted for; such as the nature and the type of the material. Knowing these properties, it is possible to choose and apply the suitable process strategy: with type II materials, sorting and separating at an early stage before crushing reduces the risk of coming out with a contaminated recycled material. In contrast to type II material, type I material can be ,in most cases, more easily and safely crushed before being sorted since the percentage of contaminants is negligible.
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___________________________________________________________Warning!!! All free online research papers, research paper samples and example research papers on Recycling topics are plagiarized and cannot be fully used in your high school, college or university education.
If you need a custom research paper, research proposal, essay, dissertation, thesis paper or term paper on your topic, EffectivePapers.com will write your research papers from scratch. Starting at $12/page you can order custom written papers online. We work with experienced PhD. and Master's freelance writers to help you with writing any academic papers in any subject! High quality and 100% non-plagiarized papers guaranteed!
