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Study Of Recycling Of Construction Materials

This chapter is literature review on the study of recycling of construction materials in construction industry. This study was undertaking more specific subjects on the application, benefits and concept of recycling of construction materials. Therefore, it was study further on the application, benefits, procedures, barriers of recycling of construction materials, and the strategies to enhance recycling. The literature recourses were search from the reference books and journals article that getting from the internal research and library.

2.1 Fact

In nowadays, the biggest problem for the construction industry is the construction wastage. The construction and demolition wastes were produced in the bulk quantity in every year and the amount was increasing seriously year by year. It is because the construction industry is one of the most important industries and a lot of construction work will be carry out in every year to satisfy the demand of the market and the end user.

The construction and demolition wastes are the surplus materials produced during new construction, renovation, and demolition of buildings and structures. The wastes comprise the construction materials such as asphalt, brick, concrete, masonry, lumber, shingles, roofing materials, glass, plastics, aluminium, steel, architectural elements, drywall, insulation, wiring, plumbing and electrical fixtures, vinyl and aluminium siding, corrugated cardboard, soil, rocks, tree stumps and other landscaping.

In the practical construction industry, majority of the construction and demolition wastes are disposing off site or on site. The ways of disposal for these wastes is landfills or burn. However, some of the construction and demolition wastes which are recyclable that will be separate on site for further processing and recycling. The recycling is the most effective and efficient method to reduce the construction and demolition wastes.

“Recycle refers to the act of reprocessing discarded goods or materials into new goods materials which can be used again.”

2.2 Application of Recycled Materials

In the practical construction industry, it is only minority of the construction and demolition wastes are using to do the further processing and recycling work and the other majority wastes are disposing by landfills. Actually, most of the construction and demolition wastes produced by the construction industry are recyclable. “The recyclable materials are Asphalt, Brick, concrete, ferrous metal, glass, masonry, non-ferrous metal, paper and cardboard, plastic and timber.”

2.2.1 Brick

The brick is one of the recyclable materials in construction industry. During manufacturing, if some of the brick failed to achieve standard of production, those brick can be recycle and reproduce to avoid the materials wastage. For construction and demolition wastes, the brick waste which is normally mix with the plastering can be crush and form the hardcore that as a base support for the concrete bed of a building. In addition, the brick waste also can be the filling materials that use for backfilling to strengthen the earth. Some of the brick waste can be recycle and use as aggregate and drainage media which as same as the concrete waste.

2.2.2 Concrete

Concrete rubble from the construction and demolition wastes is also recyclable. Most of the recycled concrete rubble is use as aggregate which is to be mix with cement and sand to form the new concrete. Besides that, concrete waste also has a potential of being recycled as the road base, hardcore, sub-base, general filling, paving stone, and drainage media. Concrete waste is more suitable than the brick wastes to be form as the aggregate and supporting agent because it is stronger than the brick.

Reuse of demolished concrete (Kawano, 1995)

Demolished member

Man-made reef, paving stone

Broken into 200–400mm

Protection of levee

Crushed (−50 mm)

Sub-base, backfilling, foundation materials

Crushed and worn (−40 mm)

Concrete and asphalt concrete aggregate

sub-base material, backfilling material

Powder (product through crushing)

Filler for asphalt concrete, soil stabilization material

2.2.3 Wood and Timber

The construction and demolition works produced a large quantity of wood and timber waste for every project in the construction industry. The wood and timber waste was produced from broken and unusable timber formwork, door member and window frame. However, the wood and timber waste can be recycle and reuse in the construction industry. After the demolition works, the unbroken wood and timber can be reuse directly in other contraction project after cleaning and nail removing. The wood and timber waste can be recycle as furniture, wood bench, timber staircase, wood base panel, insulation board, and roof member. The furniture make by the wood and timber waste is recycled as chipboard first and then manufacture to be the furniture. In addition, there is an idea that the wood and timber waste maybe able to recycle as energy, such as fuel for the power generation.

“Undamaged wood can be reused as plank, beam, door, floorboard, rafter, panel, balcony parapet and pile (Hendriks and Pietersen, 2000).”

2.2.4Metal

Construction industry also produces a lot of metal waste during construction and demolition works. The metal waste produced is separate into two groups which are ferrous metal and non-ferrous metal. The ferrous metal such as steel and iron is the lower valued metal. Conversely, the non-ferrous metal such as copper, brass, solder, alloy, lead, zinc and aluminium is high valued metal. Both of them are high profitable and recyclable materials.

2.2.4.1 Ferrous metal

“Scrap steel is almost totally recycled and allowed repeated recycling

(Coventry, 1999).”

For ferrous metal, it is usually almost 100 percent of the steel wastes produced in the construction industry are used to recycling to avoid material wastage. In addition, the steel is able to be recycled and reuse for more than one time. Normally, the scrap steel produced from the construction work can be reuse directly in other construction works. If it is unsuitable to reuse directly, it will be recycle the scrap steel by melting it to reproduce the steel. Recycled scrap can be use as new steel reinforcement, steel section, framing connectors, nails, structural framing, and steel formwork.

2.2.4.2 Non-ferrous metal

For non-ferrous metal, since the wastes are high valued metal, thus most of them are use to recycling in the construction industry. Among the non-ferrous metal, aluminium is one of the most efficient material which is recycled extensively. It is because the aluminium is able to repeated recycle and reuse by the ways of re-melt and reform it. The recycled aluminium can mostly perform the same function as primary aluminium, since it also can use as window components, flashing materials, roofing, siding, and ironmongeries.

Ten material recycling practices:

1. Asphalt- bonded with cements and used in place of sand or cement sub-bases.

2. Brick- crushed to form filling materials and hardcore.

3. Concrete- categorized as bound (aggregate) and unbound (road base, trench.)

4. Ferrous metal- 100% steel can be recycled to avoid wastage at construction site.

5. Glass- reused as glass fibre, filling material, tile, asphalt, aggregate, and etc.

6. Masonry- crushed to recycled aggregate as thermal insulation and as a replacement for clay in brick.

7. Non-ferrous metal- recycled zinc sheet is used for roofing cladding and flashing, and production of brass

8. Paper and cardboard- reprocess as new paper product by purification.

9. Plastic- recycled as roofing panel, aggregate, man-made soil, and etc.

10. Timber- recycled as roof member, furniture, wood bench and timber stair.

2.3 Benefits of Recycled Materials

Reduction on Environmental Impact

“Using scrap steel and iron rather than virgin products results in an 86 percent reduction in air pollution and a 76 percent reduction in water pollution.”

The quantity of steel and iron wastes was produced in a bulk amount in the construction industry. The continuously production and application of the new steel and iron in the construction industry make the people lazy and omit to do the recycling on steel and iron wastes. Actually, the new steel and iron production will bring a lot of negative impact not only to the construction industry but also to the general public. It will cause the high percentage of pollution to the air and water condition. Consequently, the environment will be influenced seriously by the bulk quantity of new steel and iron production and will affect the health of the people.

However, this problem can be solving easily by the way of doing the recycling on steel and iron wastes. Recycling of steel and iron is a need for the construction industry. It is the best method to reduce the quantity of steel and iron wastes and also reduce the requirement of the new steel and iron production. Therefore, recycling is important for the construction industry to have a non-polluted air and water condition in order to have a healthy and green environment. Furthermore, recycling minimise the environmental impact by reduce the extraction and manufacturing processes for production of new materials.

“Recycling can prevent emissions of many greenhouse gases and water pollutants.” Besides that, recycling also can avoid the additional discharge of greenhouse gases and water pollutants in construction industry. The recycling of construction wastes can reduce the need to extract raw materials and produce new material in order to reduce the production of greenhouse gas emissions and water pollutants.

Cost Saving

The recycling of construction waste can save the overall construction project cost. The materials cost can be decrease substantially through the recycling by the substitution from the new materials to recycled materials in the construction industry. In addition, recycling also decrease the disposal and transportation cost for the construction wastes. Since most of the construction wastes is going to be recycle, thus the amount of waste is reduce so as to save the additional disposal and transportation cost. Furthermore, recycling save the construction cost by using the construction wastes which will otherwise be lost to landfill sites.

Materials Saving

Recycling can save the construction materials by reduce the needs of new resources that use to produce the new materials. The quantity of supply for new construction materials can be reduce since most of the construction wastes are recyclable and reusable in construction industry. Therefore, the recycling of construction wastes can reduce the needs of new resources in order to achieve the materials saving.

Energy Saving

“Recycling aluminium saves 95 percent of the energy used to produce it from virgin products.”

The construction industry also facing the problem on the aluminium wastes. In the construction industry, the aluminium wastes are from the broken roller shutter, window components and door frame. Since the aluminium was difficult to be dissolve by the land, it will produce the problem of disposal on it. In addition, it would consume a lot of energy to product the new aluminium product. It is because the aluminium is a soft metal that need to be forming by the high temperature thus will consume a lot of energy on new production.

However, there is a ways to solve these problems which is recycling of aluminium wastes. During recycling, re-melting aluminium requires only 5 per cent of the energy that is use to produce primary aluminium. Recycling aluminium is the most efficient method to reduce the demand of new production and thus achieve the energy saving. Generally, the production cost for recycled aluminium will be cheaper than the primary aluminium because it is less energy used during production.

Conserves Landfill Space

Recycling of construction and demolition waste can also reduce the need for new landfills. Recycling can conserve the landfill space since most of the construction waste is going to be recycling and landfills is only for small amount of waste in construction industry. In addition, recycling reduce the need for landfills in order reduce the associated cost for landfills.

Creates job

Recycling also creates the employment opportunities and economic activities in construction industry. Since the construction industry have a lot of recycling works which is require to be carry out by manpower, therefore it create more opportunity for people to acquire the job.

Motivation for green technology development

- Helps communities, contractors, and/or building owners comply with state and

local policies, such as disposal bans and recycling goals.

-Enhances the public image of companies and organizations that reduce disposal.

2.3 Procedures of Recycled Materials

Collection

The three main categories of collection are drop-off centres, buy-back centres and curbside collection. Drop-off centres require the construction staffs to carry the construction wastes to a central location, either an installed or mobile collection station or the reprocessing plant themselves. Buy-back centres differ in that the construction wastes are purchased by the manufacturers to recycling, thus providing a clear incentive for use and creating a stable supply. The post-processed material can then be sold on, hopefully creating a profit.

The curbside collection encompasses many subtly different systems. The main categories are mixed waste collection, commingled recyclables and source separation. The mixed waste collection is all wastes are collected mixed in with the rest of the waste, and the desired material is then sorted out and cleaned at a central sorting facility. In a Commingled system, all wastes for collection are mixed but kept separate from other waste. Source separation is where each material is cleaned and sorted prior to collection.

Sorting

Once mixed construction wastes are collected and delivered to a central collection facility, the different types of materials must be sorted. This is done in a series of stages, many of which involve automated processes such that a truck-load of material can be fully sorted by using lesser time. Furthermore, some plants can now sort the materials automatically without using any manpower.

Proceeding recycling

The recycling process can be proceed after the sorting process for the wastes. Most of the construction wastes are recyclable but each type requires a different technique.

2.3.1 Concrete Recycling

Crushing and screening

Crushing and screening systems start with primary jaws, cones and large impactors taking rubble from 30 inches to 4 feet. A scalping screen will remove dirt and foreign particles. A fine harp deck screen will remove fine material from coarse aggregate.

Cleaning

Further cleaning is necessary to ensure the recycled concrete product is free of dirt, clay, wood, plastic and organic materials. This is done by water floatation, hand picking, air separators, and electromagnetic separators. Occasionally asphalt overlay or patch is found. A mixture of asphalt and concrete is not recommended but small patches are not detrimental.

2.3.2 Aluminium Recycling

Shredding and De-lacquering

To recycle aluminium efficiently, the aluminium must first be shredded and cut into small, consistently sized pieces, about 3 inches square. If the pieces are in a consistent size, the melting process can proceed more effective and allows more loads of aluminium to be processed at the same time.

De-lacquering process is then to be carry out by the ways of all additional elements must then be stripped from the aluminium. Any additional element such as paint, stickers and any other non-aluminium components must be removed from the aluminium.

Melting

Because aluminium has such a high melting point which is reach until 660 degrees C, effectively melting large quantities of aluminium requires a highly concentrated furnace that can reach such temperatures. After that, insert the stripped, de-lacquered aluminium into the furnace. When the aluminium has reached a molten liquid stage, pour the aluminium into ingot moulds. The ingots have to in the regular shapes for easier to repurpose the aluminium.

Repurposing

After the ingots have cooled, flatten each with a high-pressure roller to create thin sheets of aluminium. These thin, flat sheets will then become rolls of recycled aluminium, which can be used to create new aluminium products.

2.4 Barriers of Recycled Materials

In this 21st century, even the building and construction technology is getting advance and advance, but most of the local construction projects are still not using the recycling method to the construction wastes.

“The barrier of recycling is convenience: the easier the recycling process, the more people will take park on it.”

Recycling will slow down the job

Waste time: construction workers need take extra time to sort the wastes.

Difficult to ensure cooperative work

Reliability of services provided

Complication of recycling work

There is no room on site to recycle

Recycling costs too high

No contract language for recycling

2.5 Strategies of Recycled Materials

Determine Project Waste

Choose a Diversion Method

Calculate Costs and Savings

Buying recycled product

According to Name (year)…….“Buying recycled-content building products helps to ensure that materials collected in recycling programs will be used again in the manufacture of new products.”

Purchasing the construction recycling product is an important part of the recycling work. It is to avoid the surplus of supply of the recycling product and cause the wastage to it. Before recycling product been manufactured, the surveying of the demand on those recycling product is important to ensure that the product is required and useful to the contractor. In this case, the construction industry is playing an important role to promote and use the recycling product to enhance the recycling.

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