RECYCLING TABLE OF CONTENTS Abstract 3 Types of Construction and Demolition Wastes 4 Type I- Roadway and Site Conversion C&D Waste 4 Type II- Construction and Interior Demolition Waste 5 C&D Waste Processing Strategies 5 Type I C&D Waste Processing Strategy 6 Type II C&D Waste Processing Strategy 7 Conclusion 9 References 10 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 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. 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. 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 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. Figure 3. Separating and sorting After removing big contamineous material, the mix is introduced into a disk screen in order to separate the soil from rocks. . Figure 4. 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). Figure 5. 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. REFERENCES 1.
Nesmith, L. (1993, December). Ready or not, Construction Recycling is on the way. Architectural Record, pp.18-23. 2.
von Stein, E. McGraw-Hill Encyclopedia for Recycling . New Haven, Connecticut : McGraw-Hill.