RECYCLING Essay, Research Paper

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

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, 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 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.