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Environmental Sciences 代写 Issues Of Construction And Demolition Waste

Construction waste is becoming a serious environmental problem in many countries in the world. Construction and demolition (C and D) debris frequently makes up 10-30% of the waste receive at many landfill sites around the world (Fishbein, 1998). The construction industry has long been regarded as one of the major contributors of negative impact to the environment, due to the high amount of waste generated from construction, demolition, renovation and activities associated with construction. The construction industry plays a significant role in Malaysia’s development both in terms of infrastructure and economic development. Waste minimization and effective waste management is a most pressing issue nowadays. Construction is a unique industry. The success or failure of a project is relying on the accuracy estimation done throughout the course of the project. In this chapter, the timber or wood and asphalt are usually used in the construction industry will be reviewed follow by the discussion to carry out by researcher in recycling technical for construction and demolish waste. Besides that, this chapter also carries out and identifies products produce from construction and demolishes waste in construction site.

2.2 Definition of Construction and Demolition Waste

Waste is defined as the-by product generated and removed from construction, renovation and demolition workplaces or sites of building (Cheung, 1993). Solid is defined as all wastes in solid form which are useless or unwanted and in general arise from human activities. Construction wastes are wastes generated from building, demolition and renovation works for individual housing, commercial buildings and others. Solid wastes also can be defined as those wastes from human activities. Solid wastes can be classified as municipal waste such as, paper, plastic, food waste and so on. Industries wastes include construction and demolition waste, hazardous waste and others (Kiely, 1997).

Construction waste are in the forms of building debris, rubble, earth, concrete, steel, timber, and mixed site clearance materials, arising from various construction activities including land excavation or formation, civil and building construction, demolition activities, roadwork and building renovation (Shen et al. 2004). Normally construction wastes are the wastage such timber from fabricated formwork, steel when steel bar cutting and so on. Even though prefabricated assemblies such as windows and doors, which are packaged in large quantities of cardboard, metal or plastic strapping and wood tend to produce a significant amount of waste (Dolan, 1999). Construction waste could be classified in the form of solid, liquid, gas or combination of all these. Due to the huge use of construction raw materials in the industry, there is certainly a need to evaluate the environmental impact of waste generated from the construction site activities.

Construction and demolition (C&D) waste is produced during new construction, renovation and demolition of structures such as residential and non- residential buildings, and public work projects such as highways, bridges and so on (United States Environmental Protection Agency, 2000). Construction and demolition waste includes bricks, concrete, soil, rock, masonry, paving materials, lumber, shingles, glass, plastic, aluminum, steel, drywall, asphalt, plumbing fixtures, wood or timber, cardboard and so on.

The construction and demolition (C&D) industry generates a significant quantity of waste (Table 1), although estimates of total amounts vary in England.

Table 1. Quantities of waste from various sources in England (Lawson et al. 2001)

2.3 Construction & Demolition Wastes in Malaysia

Our country, Malaysia is same as other country, because Malaysia also have been created construction wastes substantially during the process of renovation, new construction, demolition and refurbishment such as bricks, concretes, steels, timbers and etcetera. At each stage of new construction, renovation, demolition and refurbishment have created different type of wastes.

2.4 Relationships between Construction and Demolition (C&D) Waste

Although construction wastes are similar to demolition wastes, they are often cleaner, because the waste materials usually have not been painted or mixed with other materials. Construction wastes are also generated in distinct stages as construction progresses. For example, framing and sheathing produces large quantities of wood waste; drywalling produces waste sheet rock; pallets, metal, plastics and cardboard during plumbing and mechanical installations. The sequential nature of construction allows targeted recovery of specific recyclable materials as a construction project proceeds. In remodeling projects, manual demolition provides the potential for a high degree of source separation.

Demolition waste is more difficult to source-separate than construction waste. Reusable items and certain recyclables are sometimes recovered before mechanical demolition begins. There are two type of demolition which is manual and mechanical. Manual demolition, also known as "deconstruction," can maximize the separation and recovery of recyclable materials, but is not always feasible. Mechanical demolition is done by bulldozer or excavator, tends to crush and combine materials, limiting source-separation, unless recovery facilities that sort mixed materials are available. Mechanically crushed materials are commonly land filled, with limited attempts at recovery (Clark Country Washington, 2008)

2.5 Contamination of Construction and Demolition (C&D) Waste

Waste from new construction is composed primarily of a mixture of unused or damaged raw materials, as well as off-cuts (discarded cut material) and packaging. Demolition waste includes actual building components, such as full length studs and concrete slabs. The largest component of demolition waste is concrete followed by brick, wood and metals.

Waste materials from new construction are usually clean and relatively uncontaminated, whereas demolition waste materials are often dirty or contaminated and are mixed with other materials. These differences between construction and demolition (C&D) wastes create specific opportunities and challenges for waste reduction.

The contamination of construction and demolition (C&D) wastes can take various forms:

Mixed contamination

Mixed contamination is resulting from mixing of materials during excavation from site. Waste concrete removed, for example, from a floor may be mixed with contaminated soil, other materials or other wastes. It will cause the negative impact on the potential for recycling concrete.

Surface contamination

Surface contamination is materials that have been used in foundations, road construction or in ground works are likely to have been in intimate contact with soil. Surface contamination could also include coatings and sheeting that have been used to protect the materials during their service life but a barrier to reuse.

Absorbed contamination

Absorbed contamination is contaminants that are soluble and mobile can potentially be absorbed into porous building materials. These contaminants are likely to be preset in groundwater or contaminated surface water. (Lawson et al. 2001)

2.6 Sources of Construction Wastes

The construction wastes are usually generated by the construction activities take place. It consist all building materials that being used for construction purposes. Material wastes are unavoidable. One of the reasons to identify the source of construction wastes is to understand the recycling potential of construction wastes. The major construction wastes are bricks, concretes, timbers, glasses, metals, asphalt, plastic and others. Each of them have own characteristic. In this chapter will review two construction wastes which are timber and asphalt.

2.6.1 Timber/Wood

Wood is produced by trees and sometimes other fibrous plants, used for construction purposes when cut into lumber and timber such as board, plank, and similar materials. Wood can be very flexible under loads, keeping strength when bending and it is also incredibly strong when compressed it into vertically. Wood is a generic building material and used in building just about any type of structure in most climates. There are many different type and quality of woods. This means specific species are better for various uses than other. Deciding the wood used in construction activities is depends on the wood’s quality.

Historically, wood for large building structures was used in its unprocessed form as logs. The trees were just cut into the needed length, sometimes stripped of bark, and then notched in to place. In earlier times, some parts of the world, many country homes or communities had a personal wood lot from which the family or community would grow and harvest trees to build with. These lots would be tended to like a garden. With the invention of mechanizing saws came the mass production of dimensional lumber. This made buildings to put up and more uniform quickly. Thus, the modern western style home was made.

Wood is one of the most frequent used by human in the world. Wood and the by-products are found in every area of modern existence, the timber is usually used in construction, furniture and domestic uses to fibre board, chipboard, paper, newsprint and cardboard. As usage for construction material, wood is strong, light, durable, flexible and easily worked. It has excellent insulating properties. In contrast to the substitutes for wood used in structural and architectural such as brick, concrete, metals and plastics, wood can be produced and transported with little energy consumed and the products are renewable and usually biodegradable (Koch, 1991).

Wood will continue to be a major construction material in subsequent decades in Southeast Asia. A large part of the volume used for construction will be in the form of lumber and plywood but more reconstituted wood-panel products will be used in the form of fibre boards, particle board and wood-cement boards. The decreasing wood supply from natural forests will be supplemented by wood from plantations and secondary or lesser-used species will be adopted more as construction materials. In future non-traditional materials will also be used extensively. Rubber wood looms as an important source for both household furniture and construction.

The palm stem of coconut will be used in a large extent for house construction, particularly for low cost housing. Laminated products will also become important as the supply of large diameter wood declines further. A more extensive use of nontraditional materials will depend largely on advancing technologies in processing to promote productivity and economy.

Nowadays, the growing population causes the increase of housing needs. With the demands, countries of the Southeast Asia are decreasing amounts of their forest resources. In the same time, a diminishing natural forest resource is creating a need to find new sources and new processes for wood based construction materials. The present and future use of wood for construction in several ASEAN (Association of Southeast Asian Nations) countries had suggested that the future requirements must be met from some unconventional sources and with increased use of new technologies.

Wood remains the most important construction material that is available in the region in substantial quantities. In the coming years, wood will still continue to be a major construction material, but in a variety of new forms. Number of unconventional sources will be invented due to the declining supply of traditional tropical species. These will also be supplemented through the increased use of plantation trees and lesser known natural species, supported by technological advances in wood processing.

2.6.1.1 Type of Wood in construction

Cement Bonded Board

This type of wood came in various forms and sizes such as chips, particles or narrow long strips like wood wool that has been bonded with cement to produce panel products for construction. Research on this type of panel was carried out more than 20 years ago in Europe but only now it is being seriously considered in the ASEAN countries. Malaysia, Indonesia and Thailand started into commercial production of this material. Malaysia produces wood wool cement boards and particle boards bonded with cement. Cement bonded boards can be used for external walling. It has sound and heat insulating properties and resistant to the attack of insects and fungi. It has great potential for low-cost housing because of its cost competitive with other materials (Anonymous, 1984). Wood cement board is light with a density of only 600 kg/m3. The thermal conductivity of cement-bonded boards is lower than resin-bonded particleboard’s and is comparable to fibre insulating boards.

Glued Laminated Wood

Glulam is stand for "Glued Laminated Timber." It is made from gluing many small pieces of timber planks together to form deep members. The advantages of using Glued Laminated Timber are strength of the product, the opportunities for creative architectural use especially in curved and tapered beams and excellent fire performance of the product ( Dr Tan et al. 2005).

LVL is stands for "Laminated Veneer Lumber". It is made from laminating thin sheets of wood which enables very deep and long sections with high strength possible. The other option is the use of "Plywood" which is made by gluing and pressing thin laminates together to form a sheet. The grain is laminated in alternate directions, which results in strength in two directions. These manufactured products are used in large spans, deep beams and large cross sections that incorporates large span truss. There have many advantages of Laminated Timber for trusses. In terms of material, the product is known for its efficiency and quality. Laminated Timber uses short length and small pieces of wood resources intelligently. On the other hand, the process is subject to certain quality criteria on bonding, finger jointing and wood quality ( Dr Tan et al. 2005).

The advantages are also inherent in the process required:

Drying – In Glulam, not more than 40mm of thickness is used. Drying and even preservative treatment become easier and better quality is attainable.

Shape and form – Timber could be "bent" to produce structural members of virtually any shape and size. The final geometry is normally restricted by ease of transportation and handling.

Termite, mould and rot – General solution is to either specify timber species which are naturally resistant to chemically treat the material accordingly. Proper technical detailing is also essential to minimize exposure to sunlight, collection of water and possible termite attack.

Glulam trusses are widely used for large span structures for its aesthetic appeal apart from cost effectiveness and this helps by doing away with false ceilings or other decorative items. Besides that, the other uses include pre-assembled or knock down Glulam components for transportation purposes, pre-drilled holes and also all connection hardware (primered, painted or powder-coated) as specified ( Dr Tan et al. 2005).

Palm Wood

The possibility of utilizing the coconut palm wood on a commercial scale has been recognized only in the last decade, although usage of wood from palm species has been known by people in the villages since time immemorial. Currently, coconut palm wood has been successfully utilized in a number of coconut growing countries such as the Philippines, Indonesia, Sri Lanka, Fiji, the Tonga Islands and others. Coconut timber is suitable for housing components like trusses, purlins, walls, joists, doors, window frames and jalousies. Low density coconut wood materials (from the centre of the stem) should be used only in non-load structures like walls and panels while high density coconut wood (from the perimeter of the stem) can be used for load-bearing structures like trusses and joints. High density coconut wood could also be used as posts, power and telecommunication poles, trusses, floor tiles (parquet), girts, floor joists, purlins, balustrades and railings and other load bearing structures. When coconut logs are to be used in ground contact under exposed conditions (for examples as posts or as poles for electrical wires) they must be properly treated. Medium density boards can be effectively used for walling, horizontal studs, ceiling joists and door or window frames. As a regulation, if density of coconut wood is below 400 kg/m3, it is should not be used as structural framing materials. However, they can be used in the internal parts of a building as ceiling and wall lining in the form of boards and shingles. A problem related to structural application of coco wood is the difficulty of nailing and subsequently splitting of high density wood finishes. Coconut wood can be a promising material for the manufacture of furniture and other handicrafts due to its beautiful grain and attractive natural appearance. High value coconut wood products which include furniture, decorative interior walls, parquet floors, various novelties and curio items like walking sticks, ash trays, hammer handles, egg cups, plates, bowls, vases and so on. Comparable to the traditional wood species commonly used in the furniture industry as far as appearance is concerned. Thus, with effective product promotion, quality furniture and other high value coconut wood products can have a potential share not only in the domestic but also in the world markets. Coconut wood has potential for the manufacture of high value and export quality finished products. (Asia Pacific Forestry Sector Outlook: Focus on Coconut Wood, 1997).

2.6.2 Asphalt

Asphalt or bitumen can sometimes be confused with tar, which is a similar black thermo-plastic material produced by the destructive distillation of coal. During the early century, when town gas was produced, tar was a readily available product and extensively used as the binder for road aggregates. The addition of tar to macadam roads led to the word tarmac, which is now used to refer to road making materials. However, since the 1970s, when natural gas succeeded town gas, asphalt (bitumen) has completely overtaken the use of tar in these applications. Asphalt is used for the oil refinery product used to pave roads and manufacture roof shingles.

2.7 Waste Management Planning

Good planning is the most important part of construction waste management. Like anything else in construction, recycling is straight forward if you have a good blueprint, but becomes much more difficult and expensive if it’s an add-on. Good planning allows to identify all recyclable materials and know how going to manage the site before the job starts. Good planning addresses how each waste material will be handled, what containers will be used and when they’ll be on site, and where each material will be marketed. Good planning allows to assess the costs and benefits of recycling and decide which materials to source separate, which to recycle as mixed debris, and which to discard as trash. Good planning covers communications, training, and troubleshooting, and lays out tracking and reporting procedures. The Waste Management Plan is the document that lays out the start-to-finish strategy for job site recycling. It is prepared directly from the drawings and specifications for the job, and a good plan will closely follow these documents. The Waste Management Plan should includes estimating types and quantities of wastes generated during each phase of the job, identify how each waste will be managed and marketed, provide an estimate of the overall job recycling rate, lay out plans for training, meetings, and other communications related to job-site waste management and provide troubleshooting instructions and contact information. The Waste Management Plan is the cornerstone for successful construction waste recycling and reduction. It is a comprehensive document that provides all of the information needed by any individual on site to understand and achieve the waste management goals for the project. All of this can and should be done before you break ground or during the planning stage so that recycling is incorporated seamlessly into overall performance of the job. It’s best if the Waste Management Plan is written and signed off on by all parties (owner, architect, and contractor) a month or more before site possession or the first day of site work. This allows time for all parties to participate in developing the plan, allows contractors and subcontractors to integrate recycling into their setup and work plans, and assures that training can be provided to supervisors and workers. The Waste Management Plan is also a living document, used as a day-to-day reference just like blueprints and specifications. This fact cannot be overemphasized. Handling procedures or markets may change during the course of a job, these changes should be noted in modifications to the plan. As waste materials move from the site, information on waste and recycling tonnages and costs will be gathered. These should be matched against initial projections, variances should be analyzed, and a running recycling rate should be calculated. Besides that, also should be publicized the recycling rate to laborers and trades. It’s a good way to help boost morale, and keep workers striving to achieve recycling goals (Construction Materials Management Guidelines, Feb1994).

2.8 Construction Waste Management

Construction waste management may be defined as the discipline associated with

the control of generation, recovering, processing and disposal of construction wastes in a

manner that is in accord with the best principles of human health, economic, engineering, aesthetics, and other environmental considerations (Tchobanoglous, 1993). Construction waste management is becoming more pressing problem in worldwide. The management of construction waste is not only of government’s responsibility but also responsibility of the developer of the particular land area. There are two ways to manage the waste will be discussed later.

2.8.1 Reuse

The reuse of waste material is one of the important form of pollution prevention. It is because these changes reduce the amount of waste generated year to year. Source reduction and reuse are regularly undertaken in developing countries, while these are only beginning to be practiced widely in industrialized countries. Several obstacles have stop waste prevention efforts including manufacturing decision and consumer buying patterns. For an example, manufacturers have little incentive to consider the cost of waste collection and disposal when designing a product because the consumers do not take these factors into consideration when making purchase decisions.

2.8.2 Recycling

Recycling construction and demolition (C&D) waste is defined as using or reuse a material or residual component of a material (Holt, 2001). Besides that, recycling also reprocessing of a reclaimed material and converting it into a new material or use. Recycle construction and demolition (C&D) waste can be accomplished in various ways. Deconstruction is one method of recycle construction and demolition (C&D) waste.

Deconstruction is the disassembly of structures and reuse of their parts. It is believe that there is value in salvaged materials. However for traditional recycle construction and demolition (C&D) waste methods are modifying materials remanufacture. There are many constructions and demolition (C&D) waste can be recycled. The expanding the market recycle construction and demolition (C&D) waste are depend on the recycled and salvaged goods in the market place, labour costs for removal, sorting and processing and relative disposal cost (Patterson, 2005).

2.8.3 The Important of Recycling

There are some benefits of recycling, including saving energy saving land space, saving money, creating new jobs, reducing air and water pollution and preserving habitat for wildlife. It takes less energy to process recycled materials than it does to use virgin materials. For an example, it takes less energy to recycle paper from waste material than it does to create paper from new woodland, because there is no longer a need to cut down a new tree, process the wood from the tree and make it into paper.

Energy from non-renewable resources is protected and saved for future generations, money is saved when less energy is used. This is also can mean that more competitively priced goods and often pollution and emissions are reduced when less energy is used. Recycling reduces trash in landfill sites, which cuts down on the cost of waste disposal and the clearing of more land for new landfills when the current landfills become too full to store any more waste. Recycling is an easy and less expensive alternative to clearing more land for new landfills. For an example, composting, recycling kitchen waste and yard waste into compost provides a means of free nutritious soil for gardening. Recycling would allow human to reuse the materials over and over again. Decomposing waste often release noxious gases and chemicals as it decomposes at landfill sites. These gas and chemicals create air pollution. When the chemicals leach into the groundwater, this will creates water pollution and water is contaminated. In 2000, recycling of solid waste prevented the release of 32.9 million metric tons of carbon equivalent (MMTCE, the unit of measure for greenhouse gases) into the air. Imagine how much pollution could prevent if instead of landfills had recycling centers. Human could breathe cleaner air and drink cleaner water. If the human created more recycling opportunities, this would create more jobs and no one would have to lose their jobs either. Recycling also preserves wildlife. When fewer trees are cut down to make virgin material or to make space landfills, habitat for wildlife remains. More habitats for animals mean less animal extinction. Despite what some may say, recycling is important and it can make a difference. The people may not be able to solve their landfill and pollution problems anytime soon, but at least they can help keep them from getting worse. Recycling is a easy way to do. Start with paper or plastic or both and take them to a recycling bin near your home. For an example, if any people have to go grocery shopping fill up a car with a box of recyclable paper and dump it at the recycling bin near the store. Many grocery stores now have these bins available. If not ask them to start or participate in your neighborhoods curbside recycling program. If there isn’t one available get one started in the neighborhood. In 2001 United States residents, businesses and institutions generated more than 229 million tons of municipal solid waste (MSW) (EPA, Municipal Solid Waste in the United States: 2001 Final Report). This waste adversely affects the economy and the environment. Conventional methods of disposal involve land filling. These landfills have limited capacity. As waste generation increases, new landfills must be built. Landfills are expensive to build and operate. The landfills are also highly subsidized by local governments and require significant land that then is no longer viable for wildlife habitat or residential, commercial, or recreational development. Waste negatively impacts the environment. Degradation of the natural landscape occurs through leaching from improperly lined landfills and from the extraction of resources for new materials. To reduce the amount of waste generation, communities have instituted recycling programs across the country. Recycling has economic and environmental benefits for communities. First, recycling reduces the need for new landfills and associated costs. Second, recycling can support industrial development as the recycled materials serve as raw materials for manufacturing and other uses. For an example, recycled soda bottles are used in carpet manufacturing; steel contains 85 percent recycled content and recycled paper is milled for new paper products. By supplying raw materials to industry through the reuse of materials, recycling conserves resources by reducing the need to extract virgin resources or introduce new chemicals into the environment. By not disturbing existing natural resources and by reducing noxious manufacturing processes, recycling prevents emissions of many greenhouse gases and water pollutants. From a community and environmental preservation perspective, recycling conserves green space, protects habitat, and improves quality of life for residents in natural resource locations.

Recycling also saves energy through avoided extraction and manufacture processes. This can be a particularly powerful strategy when one realizes that only 10 percent of all materials extracted are used in final products. This means that 90 percent of natural resources extracted for consumer use are disposed of as waste. From an economic perspective, such high values of unused material represent inefficiencies in the market. Missed opportunities exist where inefficiencies are present. Recycling contributes to the economic base of communities. There is significant job creation and business development potential associated with recycling. Jobs in this field involve more than simple collection and separation. The remanufacture of recycled materials supports more than one million manufacturing jobs. As companies seek to find new uses for recycled materials, research and development of ‘greener’ technologies require skilled individuals and significant capital investment. A wide variety of job skills are needed to develop this industry. Hence, the more robust are the recycling activities which include collection, separation, research, manufacture and resale and the more recycling can advance economic development.

The popular phrase, reduce, reuse, recycle has become a household mantra with millions of households separating their plastics, paper, cans and glass and using curbside pick-up, drop-off centers, buy-back centers, and deposit refund programs. Certainly within these material streams, a larger percentage of recycling is possible. Further, these materials are only part of the waste stream. There are other materials that may have more impact when recycled. Construction and demolition (C&D) debris materials are easily recyclable using existing infrastructure and make up larger concentrations of waste volume than cans, bottles, paper and so on. (William McDonough and Michael Braungart. 2002. Cradle to Cradle. New York: Northpoint Press). Construction and demolition waste is currently recycled at a rate of 20-30 percent. Project-based studies indicate that the potential for recycling is much higher more than 70 percent. While many construction and demolition materials are suitable for recycling, there are external factors that influence the spread of construction and demolition recycling. The value of recycled and salvaged goods in the marketplace, labor costs for removal, sorting and processing, and relative disposal costs all play a role in expanding or contracting the market for reuse and recycled goods. Recycled and salvaged goods must be price competitive and perceived to be as desirable as or even more desirable than products produced from virgin materials. Competitive pricing is impacted by subsidies, incentives on virgin materials, and market demand. Recycled goods or secondary materials do not benefit from similar policies that could facilitate their widespread use and resultant competitive pricing. Desirability for recycled materials is a reflection of the value placed upon these goods. This desirability can be affected by industry and consumer market knowledge and acceptance. However, hesitancy to use recycled goods on the part of building code officials, contractors, and architects is often reflected in building codes. Most codes have not been designed to accommodate the use of salvaged and recycled materials. In a demolition field dominated by heavy machinery and constrained demolition timeframes, the process required for construction and demolition (C&D) waste recycling is affected by labor costs. Building deconstruction, the manual disassembly of structures and subsequent. Deconstruction is used throughout this guidebook as an example of C&D recycling because it is the most basic form of recycling and reuse. (US Green Building Council. Multiple case studies. www.usgbc.org).

Deconstruction activities are also combined with traditional recycling and some demolition for unsalvageable material reuse or recycling of their components is one method for preparing goods for secondary use. This labor intensive process affords maximum salvage and sorting opportunities as materials can be closely monitored and directed to their highest and best use. In some cases, deconstruction workers separate materials onsite. The sorted materials are then transported to recycling and reuse centers. Where space is limited, materials may be hauled to an off-site sorting facility where salvageable, recyclable, and unsalvageable materials are sorted and forwarded to their respective destinations. Given the increased labor needs in removing and determining mode of secondary use, labor costs are traditionally higher for deconstruction and recycling. Costs for disposal of construction and demolition debris have the most impact on construction and demolition recycling. Tipping fees can make or break efforts to recycle. Regional and local variation in tipping fees affects the market for recycled materials. In an industry where construction profits are tight and demolition margins even tighter, when tipping fees for construction and demolition debris are low, there is no incentive to pursue alternatives to disposal of the waste. When it is initially cheaper to send construction and demolition debris to the landfill, rather than to a recycling facility, most contractors will choose the cost saving option. An important concept is the first cost perspective. The primarily good way is valued by the initial investment. This perspective does not take into account lifecycle costs, environmental impacts, and social and human capital investments. Life cycle costs involve extraction costs, transportation costs, operating costs, and disposal costs of construction materials. These costs should play into decision-making. However, the current economic framework does not encourage decision-makers to consider these long term and comprehensive costs. Environmental costs associated with disposal of potentially recyclable materials including loss of habitat when pristine land is used for new landfills or there are expansions of existing landfills; increased extraction of raw materials for new construction products; leaching from landfill items into soil and groundwater and poor air quality from demolition activities that increase dust and noise levels. Social costs include missed opportunities for job training and employment, community involvement in reshaping local built environments, and neighborhood stability. In calculating current tipping fees, these costs are not incorporated. Thus, tipping fees are not reflective of the true costs for disposal of construction and demolition debris. As discussed in the previous section, costs have an impact on the feasibility of construction and demolition recycling. Contractors to understand that using new materials and discarding scrap from them means developers pay for materials twice which means that first for the purchase and then again for disposal. Communities requiring construction and demolition waste management plans that utilize recycling can help to reduce development costs of new and rehabilitated projects. These savings can stimulate additional development and improve the bottom line for construction firms. Current economic and political climates value virgin materials more highly than secondary materials. This is based on the use of first costs for analysis, rather than including life cycle and social and environmental costs. Construction and demolition (C&D) waste recycling is a strategy to combine with other revitalization efforts.

2.9 Recycling Barriers

A significant barrier to increased recycling of construction and demolition (C&D) waste is the variability of supply for recyclers and re-processors. The financial success of any recycling enterprise is the dependent on the amount and quality of the supply of feedstock. Most processors will not make a large commitment of capital unless a consistent quantity and composition of waste can be guaranteed.

2.9.1 Contamination

As mentioned earlier, contamination can also be a significant problem. In most cases, a single container is used for waste collection on a construction site. Commingled waste is difficult to segregate unless the separation is done by hand or by specialized machinery. A few classes of materials, such as chemically treated wood, can alter the characteristics of the waste enough to make it unusable as feedstock for recycled materials. Hazardous materials such as asbestos or lead based paint can contaminate the waste and make it unusable as feedstock for other materials. If hazardous waste streams are mixed with nonhazardous waste streams, the entire mixture must be treated as hazardous waste. Location of the project also factors into the feasibility of construction and demolition (C&D) recycling since there is not always a highly concentrated level of construction and demolition (C&D) activity. As a result, the materials must be transported to accumulate enough material for a centralized recycling operation or to get to a recycling infrastructure. If the economics of recycling depend on the low cost of feedstock, the increased cost of transportation may preclude recycling.

2.9.2 Lack of Technical Information

Technical information about recycled-content materials is lacking also is one of the barriers to recycling. Many developers, clients and designers are unwilling to use recycled-content materials because of limited testing or code approval.

2.9.3 Economic and Time Resource Constraints

There are also several project-related barriers to recycling, such as economic and time resource constraints. For an example, in most public and private-sector construction and renovation projects, disposal of waste is considered by most contractors as overhead. In most cases, it is not directly calculated in the bid for a project. This means that the contractor will opt for the lowest, first-cost means of disposal. This explains the prevalence of on-site or illegal dumping disposal of the waste. The cost of disposal may not always be directly passed on to the client or agency funding the project.

2.9.4 The Separation of Each Material Prior to Recycling Required Increased Handling of Waste and More Work for the Contractor

Generally, in preparation for recycling, the waste has to be separated on-site, stored, and transported to a processor. It is because the contractor will choose for the lowest cost solution such as landfill disposal unless the client has specified certain disposal options.

2.9.5 Lack of Recovery Facilities

Besides that, the lack of recovery facilities is another barrier to recycling. As described in this section, the amount of capital investment necessary, lack of markets, and the variability of the waste stream has resulted in few large scale, multi-waste processors. The lack of recovery facilities means that, in many cases, contractors have no outlets for construction and demolition (C&D) waste even if they want to separate debris for recycling. This is particularly true for small scale construction and demolition (C&D) projects such as office remodels or small building construction. Individually, the amount of waste produced by these relatively small projects may not be significant, but in the aggregate of the C&D activity, it can be significant.

2.9.6 Lack of Communication

Lastly, an important barrier is the lack of communication between the design team (architects and engineers), contractors, subcontractors, and waste haulers. There are many issues that must be addressed and each party may not understand the roles, responsibilities, and expectations of the other parties. In addition, if these roles are not explicitly defined before the contract begins, important issues may not be addressed which mean the waste may not be properly characterization, or the end markets may not be identified (Dolan, 1999).

2.10 Waste Reuse and Recycling Opportunities

Although a relatively small percentage of construction and demolition wastes is now recovered, significantly greater amounts will probably be recycled in the future as a result of higher tipping fees, mandatory landfill diversion legislation and the success of entrepreneurs in processing both source-separated and mixed wastes (Tchobanoglous et al. 1993). Reuse and recycling opportunities for construction and demolition wastes depend on the markets for the individual materials comprising the wastes and the ability to process the commingled wastes or separate the individual materials. Some of the materials recovered from construction and demolition wastes include concrete, wood, metal, asphalt, asphalt shingles, drywall and others. In this chapter will discuss the recycling method for timber/wood and asphalt.

2.9.1 Timber/Wood

Timber waste from construction and demolition (C&D) works is produced in large quantity all over the world. Timber waste has a potential of being recycled as:

Whole timber arising from construction and demolition (C&D) activities can be utilized easily and directly for reused in other construction projects after cleaning, de-nailing and sizing. Undamaged wood can be reused as plank, beam, door, floorboard, rafter, panel, balcony parapet and pile (Hendriks and Pietersen, 2000). In 2004, Japan developed a new technology in turning timber waste into furniture, shoring wooden pile for relocated pine trees, wood bench and timber stair.

A special lightweight concrete can be produced from aggregate made from recycled small wood chunk.

Timber waste can be recycled as energy, such as fuel, charcoal for power generation in Japan. In the Netherlands, 400,000 tonnes of wood from C&D activities are generated (Hendriks and Pietersen, 2000); most of this wood is landfill or incinerated as a by-product in either coal-fired power plant or cement kiln; prior to incineration the wood will have be reduced in size drastically. Blast furnace deoxidization is also adopted in recycling timber.

After hydrolysis by gasification or pyrolysis in incinerating or decomposing the wasted wood, timber can be recycled as chemical product (Hendriks and Pietersen, 2000).

Timber fragment arising from C&D work can be recycled and utilized in new construction products in the production of wood-based panel for roof, ceiling and floor, cladding in agricultural building, hoarding, a packaging substitute, wall and sound barrier.

Paper, recycled board and mulching material are adopted by recycling timber in Japan. Besides that, wasted timber in the form of woodchip can also be mixed with topsoil to improve soil texture and coated with plastic to form a product called plastic lumber.

Clipped timber is recycled by spraying them onto sloped soil surface in Japan, which is called "geofibre".

Timber waste can be recycled to produce insulation board, kitchen utensil and furniture from the chipped timber by pressurization at around 180 â-¦C for 40 min with steam, water and addition of binder. In 2004, Japan practices adopted this technology in turning timber chip into paving material.

(Tam et al. 2006)

2.9.2 Asphalt

Old asphalt materials are crushed for recycling as asphalt aggregate, mixed with sand and binder. The binder can be either cement or a liquid in the form of a bituminous emulsion; a combination of cement and a liquid binder are used as well. In addition to these binders, asphalt aggregate can also be stabilized with blast furnace slag or fine slag. Only a limited proportion of asphalt can be reused in highly pervious road surface, as the composition of these mixtures is highly critical.

Several recycling technologies had been implementing in recycling asphalt materials (Hendriks and Pietersen, 2000):

Recycling Method

Explanation

Cold Recycling

Water and stabilizing agent, such as cement, foamed bitumen and emulsified bitumen are added

Heat Generation

Results in a rearrangement of the original physical properties and chemical compositions of the bitumen.

Minnesota Process

Old asphalt is heated above normal temperature (180 â-¦C) for heat transfer to restructure the old materials.

Parallel Drum

Process is undertaking preheating in a separate dryer and heater drum

Elongated Drum

Aggregate is heated and dried and followed by adding asphalt aggregate. Then, filler and bitumen are added and finally mixing of all components

Microwave Asphalt Recycling System

Includes de-ironing and crushing the asphalt rubble.

Finfalt Process

Finfalt Process can produce the recycled asphalt immediately prior to dosage by a mobile plant treating the materials.

Surface Regeneration

Surface Regeneration refers to all techniques where asphalt in the road is heated to a depth of several centimetresbelow the surface and is subsequently processed again in situ.

Table 2 Table of the recycling method for the asphalt (Tam et al. 2006)

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