RECYCLING Essays - Waste, Building Materials, Water Conservation

RECYCLING Essays - Waste, Building Materials, Water Conservation RECYCLING TABLE OF CONTENTS Abstract3 Types of Construction and Demolition Wastes4 Type I- Roadway and Site Conversion C&D Waste4 Type II- Construction and Interior Demolition Waste5 C&D Waste Processing Strategies5 Type I C&D Waste Processing Strategy6 Type II C&D Waste Processing Strategy7 Conclusion9 References10 ABSTRACT 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 CMetals, wood, rocks, concrete, rubble, soil, paper, plastics and glass are among the many materials that are considered CRealizing that the disposal of Clarge 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. TYPES OF CONSTRUCTION AND DEMOLITION WASTES Type I - Roadway and Site Conversion C&D Waste C"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, plastic10% 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: Rubble25% Wood33% Metals20% Corrugated12% 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 typeContents RubbleSoil, rock, concrete, asphalt, bricks Tar-based materialShingles, tar paper Ferrous metalSteel rebar, pipes, roofing, flashing, structural members, ductwork Nonferrous metalAluminum, copper, brass Harvested woodStumps, brush, treetops and limbs Untreated woodFraming, scrap lumber, pallets Treated woodPlywood, pressure-treated, laminates PlasterDrywall, sheetrock GlassWindows, doors PlasticVinyl siding, doors, windows, blinds, material packaging White goods/bulky itemsAppliances, furniture, carpeting CorrugatedMaterial packaging, cartons, paper ContaminantsLead 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. Figure 1 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, a! nd few contaminants. A general processing layout is shown in figure 2 and is available as both fixed and portable designs(2, p.6.34). Figure 2. 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