Reviewing The Recycling Of The Concrete Business Construction Essay

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Recycling of concrete is a relatively simple process similar to crushing natural aggregate. It involves breaking, removing and crushing existing concrete into a material with a specified size and quality. For a good quality product it is essential to separate out different types of material before it enters the crusher. A high level of cleanliness of the material is essential to creating a quality end product that can be reused. An aggregate recycling is most likely to be successful where transportation dynamics, disposal and tipping fee structures, resource supply/product markets, and municipal support are favourable. Recycling operations often must overcome risks associated with feed and product availability, pricing, and quality.

Figure 3.: Recycling Plant

3.1.1. SOURCES OF RECYCLED AGGREGATE

Traditionally, Portland concrete aggregate from the demolition construction is used for landfill. But nowadays, Portland concrete aggregate can be used as a new material for construction usage. Recycled aggregate are mainly produced from the crushing of Portland concrete pavement and structures building. The main reason that choosing the structural building as the source for recycled aggregate is because there is a huge amount of crushed demolition Portland cement concrete can be produced.

3.1.2. RECYCLING PLANT

Recycling plant normally located in the suburbs of cities due to the noise pollution that make by the equipments that used during recycling process. All the machinery used in recycling has to fit with the effective mufflers to reduce the noise from the processing activity.

3.1.3. TRANSPORTATION

After the structural buildings and Portland cement pavements are demolished, the concrete debris has to send to the recycling plants for processing. In many countries they use the roll - off containers or large dump body trailers to transport the mixed load of construction and demolition debris. This is the most effective and cost effective means of the transportation. It also mentioned that the construction and demolition debris can be transport by the closed box trailers and covered containers.

3.1.4. CRUSHING PLANT

Crushing is the initial process of producing the construction and demolition debris into recycled aggregate. The concrete debris is crushed into pieces in this process. The equipments used for crushing process are either jaw or impacted mill crushers. All the recycling crushers have a special protection for conveyor belts to prevent damage by the reinforcement steel that in the concrete debris. They are fitted with the magnetic conveyors to remove all the scrap metal.

During the crushing process, all the reinforcing steels have to remove away. There are mainly three methods of sorting and cleaning the recycled aggregate, which are electromagnetic separation, dry separation and wet separation. Electromagnetic separation process is removal of reinforcing steel by the magnet that fitted across the conveyor belt in the primary and secondary crushers. Dry separation process is removing the lighter particles from the heavier stony materials by bowing air. This method always causes lot of dust. Wet separation process is the aquamator, which the low density contaminants are removed by the water jets and float - sink tank, and this will produces very clean aggregate.

3.1.5. LOCATING AND AGGREGATE RECYCLING FACILITY

Minimization of the distances between a recycler and its suppliers and markets is critical to the economic success of an aggregates recycling facility. The primary source of recyclable concrete is obsolete infrastructure. Areas of urban renewal or suburban growth offer the greatest opportunity as markets for recycled concrete aggregates.

3.2. METHOD OF RECYCLING

Concrete aggregate collected from demolition sites is put through a crushing machine. Crushing facilities accept only uncontaminated concrete, which must be free of trash, wood, paper and other such materials. Metals such as rebar are accepted, since they can be removed with magnets and other sorting devices and melted down for recycling elsewhere. The remaining aggregate pieces are sorted by size. Larger pieces may go through the crusher again. Crushing at the actual construction site using portable crushers reduces construction costs and the pollution generated when compared with transporting material to and from a quarry. Large road-portable plants can crush concrete and asphalt rubble at up to 600 tons per hour or more. These systems normally consist of a rubble crusher, side discharge conveyor, screening plant, and a return conveyor from the screen to the crusher inlet for reprocessing oversize materials. Compact, self-contained mini-crushers are also available that can handle up to 150 tons per hour and fit into tighter areas. With the advent of crusher attachments - those connected to various construction equipment, such as excavators - the trend towards recycling on-site with smaller volumes of material is growing rapidly. These attachments encompass volumes of 100 tons/hour and less.

There are no specific methods of recycling. It may vary from country to country. But quality of recycled concrete strongly depends on method of recycling. Concrete aggregate collected from demolition sites is put through a crushing machine, often along with asphalt, bricks, dirt, and rocks. Crushing facilities accept only uncontaminated concrete, which must be free of trash, wood, paper and other such materials. Metals such as rebar are accepted, since they can be removed with magnets and other sorting devices and melted down for recycling elsewhere. The remaining aggregate chunks are sorted by size. Larger chunks may go through the crusher again. After that, standard sieve is used to separate coarse recycled aggregate from fine aggregate.

But Japan has developed a technology to produce high-quality aggregate from demolished concrete using a 'heating and rubbing method'. Using this technology, aggregate can be recycled as raw material for ready-mixed concrete, while fine powder (HRM powder) from cement paste can be recycled as raw material for cement, cement admixture, or soil stabilizer. A detail has shown in figure.

Figure 3.: Schematic flow of concrete recycling systemhttp://docs.google.com/File?id=df5jh38j_716n7x5tgd7_b

3.2.1. EQUIPMENTS REQUIRED FOR PREPARATION OF RCA

Crushing: It is the initial process of producing the construction and demolition debris into recycled aggregate. The concrete debris is crushed into pieces in this process. Generally the equipments used for crushing process are either jaw or impacted mill crushers. All the recycling crushers have a special protection for conveyor belts to prevent damage by the reinforcement steel that in the concrete debris. They are fitted with the magnetic conveyors to remove all the scrap metal.

At first the concrete debris will break down to around 75mm by the primary jaw crusher. Second stage the secondary cone crushers will breaks the materials to the maximum size required which vary between 19mm and 75mm.

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Figure .3: Mobile crusher (for concrete demolition debris, one mobile crusher can process between 1,800 to 2,400 tons per day).

Screening: Screening is the process that separates the various sizes of recycled aggregate. The screening plant is made of a series of large sieves separates the materials into the size required. Portland cement association [1] stated that, the size of screen that used to separate the coarse recycled concrete aggregate and fine recycled aggregate is normally 10mm. The size of screen used to separate the coarse recycled aggregate can be under or over 19mm. Finally one more screen should be used to separate those particles that more than the specified size.

http://rockproducts.com/screens/snapdeck%202000.jpg

Figure 3.: Dur-X-LiveWire screens for sieving RCA (Dur-X-LiveWire have four different screen patterns to suit the producer's requirements.

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3.3. ECONOMIC COMPARISON OF CONCRETE RECYCLING

The structural applications in the modern days are judged against the cost, functionality, aesthetics or a combination of these. This makes it clear that the costs associated with the construction of the structure as well as the running costs associated with maintenance, space and repair are the critical elements that attribute to the choice of a given concrete mix over another.

The promotion of environmental management and the mission of sustainable development worldwide have exerted the pressure for the adoption of proper methods to protect the environment across all industries including building and construction.

3.3.1. HOW MUCH DOES IT COST TO PRODUCE RECYCLED AGGREGATES?

David R. and Thomas G. [2] stated that, entry into the aggregates recycling business requires a capital investment of $4 to $8 per metric ton of annual capacity, a cost that is most significant for a small producer because of economies of scale. Processing costs for the aggregates recycler range from about $2.50 to $6 per metric ton. Operating rate and revenues generated from tipping charges and product prices are the most important factors affecting profitability, but can vary considerably by operation and region. Transportation costs associated with feedstock acquisition, while significant to regional dynamics of the industry were assumed to indirectly affect profitability of a recycler, because such costs are typically incurred by a construction contractor that supplies material rather than the recycler, which processes that material. Cash flow analyses indicate that all operations except the small recycler could achieve at least a 12 percent rate of return on total investment. Larger recyclers are more profitable under study conditions because of economies of scale. Recycling operations benefit from tipping fee revenues and relatively low net production costs. Where market forces permit, smaller recyclers can, for example, increase their economic viability by increasing tipping fees or charging higher product prices, or by positioning themselves to gain transportation cost advantages over competitors, acting as subcontractors, operating ad-hoc supplementary businesses, or receiving government subsidies or recycling mandates. Economic benefits for a natural aggregates producer to begin recycling are substantial.

3.4. BUSINESS PLAN

3.4.1. SUITABLE LOCAL APPLICATION OF RCA

Before starting any business, it is necessary to know the local demand of those products. So, local structural type influences demand of aggregate. According to Environmental Council of Concrete Organization (ECCO), recycled concrete aggregate can be used for sidewalk, curbs, bridge substructures and superstructures, concrete shoulders, residential driveways, general and structural fills. It also mentioned that recycled concrete aggregate can be used in subbases and support layers such as unstabilized base and permeable bases.

3.4.2. LABOUR REQUIREMENT

Check into what the salary or hourly wage level is in the area and whether or not the type of staff you required is available in the area. For instance, in some areas it is hard to find minimum wage employees to staff centres because of a lack of public transit. How you staff your recycling business is important because staff not only will perform the day-to-day tasks, but they are also an expense for which you must plan. Therefore, it is important to look into your staffing needs very carefully.

3.4.3. FINANCIAL REQUIREMENT

This is the most critical part of a business plan. It needs to establish vital schedules that will guide the financial health of the business. The plan should included projected start-up costs, expected profit or return on investment for the first years, a projected income statement and balance sheet for two years and monthly cash flow statement for 12 months.

3.4.4. CARBON FOOTPRINT

Despite aggregate and sand accounting for approximately 30 percent of all emissions during the production of concrete, recycling concrete or aggregate creates few opportunities to reduce carbon emissions (Cement Sustainability Initiative, 2008). Green House Gas (GHG) emission reductions can be obtained when a high carbon footprint material or process is substituted for a lower one. Recycling concrete into aggregate, or different aggregate sources into aggregate for concrete, tends not to produce any such savings compared to using natural aggregate except in so far as transportation requirements can be reduced.

3.5. TECHNICAL FACTORS AFFECTING AGGREGATES RECYCLING

Based upon data from reference documents, the following technical factors were determined to affect the profitability of an aggregates recycling operation. All factors don't always apply, but they have been found to apply in many cases.

3.5.1. PRODUCT SIZES

Screen product-size distributions determine the amount of each product available for sale. Regional supply and demand considerations often dictate local prices for various size products. Because different products have different values in any given market, the operation that is able to market high-value size distributions is likely to improve its cash flow position. Screen configuration can be adjustable to reflect changing market conditions for different size products. Experienced operators have the ability to maximize production of high-value products and to respond to changes in product requirements.

3.5.2. OPERATIONAL DESIGN

In order to maximize efficiency and profitability, careful consideration must be given to operational layout and design, production capacity, and equipment sizing. Although economy-of-scale efficiencies benefit larger operations, the higher capital cost of equipment and the limited availability of feed material may limit the size of an operation. Equipment configuration also affects product mix (what products are produced; mixes of products) and plant efficiency. Equipment selection is influenced by the decision on whether to be a fixed or mobile recycler. Mobile plants must meet roadway restrictions to be allowed to move from site to site. Fixed site equipment can be somewhat larger and perhaps more durable, thereby trading off lower unit production costs with reduced transportation costs for the mobile unit

3.5.3. LABOUR

Labour requirements are low for recycling operations. A typical operation would require fewer than 10 personnel, whether it is a small size operation or the largest operation. For a stationary concrete recycling facility, labour accounts for about 20-30 percent of the total operating cost. For a mobile operation, labour costs can be higher due to takedown and setup requirements from frequent relocation of equipment.

3.5.4. ENERGY

Energy, primarily electricity and diesel fuel, is required for powering the processing and transportation equipment of both natural and recycled aggregates. The Portland Cement Association reported 1993 energy requirements for natural aggregate materials of 5.8 million joules per ton for sand and gravel material and approximately 54 million joules per ton for crushed stone (Portland Cement Association, 1993); however, update and corroboration of this information were not possible. These values do not include the energy required to demolish construction debris or transport this material for processing. Transportation energy requirements are estimated to be 2,700 joules/kilogram-kilometre for sand and gravel, 3,800 joules/kilogram-kilometre for crushed stone, and 3,800 joules/kilogram-kilometre for recycled aggregates.

3.5.5. INFRASTRUCTURE LIFE

The useful life of infrastructure affects both supply and demand for recycled aggregate products. Road and building design determines how long such structures will last, and the amount of maintenance required. Aggregate characteristics, economic utility choices, weather conditions, and intensity of use also impact infrastructure life.

3.6. SOUTH AFRICAN CONSTRUCTION MATERIAL WASTE PATTERNS

Demolition waste materials such as old concrete, bricks and masonry, are extensively recycled in North America and Europe. Sources of demolition waste recycled as aggregates included land-fill sites, demolition rubble arising on site and recycling centers. In the United Kingdom and other European countries, implementation of environmental legislation such as the landfill tax has resulted in haulage contractors changing their "modus operandi" by using fixed or mobile demolition waste recycling plant to convert demolition waste to aggregates.

South Africa hosted the World Summit on Sustainable Development in 2002 the driving forces for recycled construction materials seem weak or non-existent. A literature survey was conducted regarding demolition and recycling practices around South Africa but published or on-line sources were scarce due to fact that recycling of these commodities is a relatively new concept compared to the recycling and re-use of say, steel scrap, paper, plastic or glass.

South African recyclers are optimistic about the future of their business endeavours. While Quarry SA is unable to see into the future, conversations with representatives from the market provide a glimpse of things to come. South Africa has a small market in Cape Town for recycled aggregates. South African C&D waste practice indicates a high occurrence of on-site C&D waste material reuse. Disposal by land is still the main method of waste disposal in South Africa. Applications included site levelling, landscaping and backfill engineering and informal housing.

Cape brick one of the major recycle industries in Cape Town produces eco-friendly bricks using RCA. It is one of the first masonry manufacturers to use RCA obtained from construction and demolition waste materials. Cape brick states, their recycled bricks are engineering grade, load bearing, and structural concrete masonry units that have been approved by the Concrete Manufacturers Association (CMA). They also state that, they hold the lowest embodied energy content of all the bricks manufactured in South Africa. Bradis Crushing & Recycling (Pty) Ltd is also very famous recycling company in Western Cape. Who has vast experience in recycling. Their mission is to recycle of mountains of stone, reinforced concrete, brick and scrap steel to create a variety of useful building materials, and the levelling of the land for future business park.

3.6.1. QUANTITIES OF C&D WASTE [3]

The construction industry generates an estimated 5-8million tone of C&D waste per annum.

Over 1 million ton of building rubble reaches landfill sites every year throughout the country rest amount recycled.

Rubble recycling is limited to single operations in the Western Cape, KZN and Gauteng.

C&D waste reuse is extensive throughout the country on site and off site. There is a network of secondary material shops around the country.

3.6.2. LIMITATIONS

Estimates of C&D waste quantities are limited by poor record keeping, no site waste analyses, non-uniform waste classification in different regions, no structured plans for waste management and recovery on construction and demolition sites, ad-hoc reuse on and off site and illegal dumps. Construction practice is not moving quickly enough towards innovative techniques that will eventually result in environmental construction and yield returns from waste recovery. This is why recycling is currently perceived to be an expensive exercise.

3.6.3. RECYCLING

Recycling industries exits in South Africa, but differ tremendously by material type. Metal recycling is most successful. Due to the increasing demand for stone aggregate and the long and slow process of locating and registering new stone quarries, stone crushing companies started investigating other sources. It was only during the last decade that builder's rubble was recognised as a viable alternative and now a day, with the use of mobile crushing plants, it is quite common to see a demolished building being turned into a pile of aggregate, suitable for concrete aggregate and/or road subbase material.

3.7. BARRIERS IN PROMOTING USE OF RCA AND RAC

Acceptability of recycled material is hampered due to a poor image associated with recycling activity, and lack of confidence in a finished product made from recycled material. Cost of disposal of waste from construction industry to landfill has a direct bearing on recycling operations. Low dumping costs in developing countries also acts as a barrier to recycling activities. Imposition of charge on sanitary landfill can induce builders and owners to divert the waste for recycling. Some of these issues act as barriers in promoting more widespread use of recycled aggregate and concrete made with recycled aggregate.

3.7.1. LACK OF APPROPRIATELY LOCATED RECYCLING FACILITIES

Construction and demolition waste is generated in small quantities at locations which could be widely separated. Therefore, portable equipment is needed, which can be used and set up close to a demolition site. Transporting waste over large distances makes the proposition of using C&D waste uneconomical. Lack of such plants is a major barrier for 'Newcomers' in the field of C&D waste management. Commissioning of appropriately located recycling crusher units in a pilot plant can help in lowering barriers against recycling of construction & demolition waste.

3.7.2. ABSENCE OF APPROPRIATE TECHNOLOGY

There are very few commercially viable technologies for recycling construction and demolition wastes, and methods that can be used to crush C&D waste on a commercial scale are urgently required. In fact, when the technology is established, other issues such as quality control of raw material and finished product, etc. can be taken up.

3.7.3. LACK OF AWARENESS

Lack of awareness towards recycling possibilities and environmental implications of using only fresh mined aggregates are the main barriers due to which C&D waste is disposed only in landfills. Creating awareness and dissemination of information relating to the above barriers and the properties of concrete made with recycled aggregate are essential to mobilize public opinion and instil confidence in favour of the recycling option. There is a need to create a market for recycled products by involving the construction industry and encouraging them to use recycled materials in projects.

3.7.4. LACK OF GOVERNMENT SUPPORT

A lack of government support and commitment towards development of recycling industry is often seen. Developing appropriate policy supported by proper regulatory framework can provide necessary impetus. It will also help in data compilation, documentation and control over disposal of waste material.

3.7.5. LACK OF PROPER STANDARDS

Apart from the specifications of RILEM (1994), JIS and those used in Hong Kong, only very limited code specifications/standards regarding use of recycled aggregates are available. In fact, use of concrete with 100% recycled coarse aggregate for lower grade applications is allowed in Hong Kong, though for higher grade applications (above M35 concrete), only 20% replacement is allowed, and the concrete can be used for general applications, except in water retaining structures. In Japan, JIS has drafted a Technical Report, TRA 0006 "Recycled Concrete Using Recycled Aggregate" to promote the use of concrete made with recycled aggregate. Development of relevant standards for recycled materials would provide producers with targets and users an assurance of quality of material. Standards formulated in the above mentioned countries can be a guideline for development of specifications.

3.8. STEP REQUIRED INTRODUCING RCA IN SOUTH AFRICA

The implementation of waste management requires a large amount of investment such as facilities and equipment, which is the main burden to the industry. To coordinate various construction stakeholders in implementing waste management it is necessary that long-term polices and strategies should be developed and implement. Beyond these, some steps given below must be required introducing RCA in South Africa.

3.8.1. EDUCATION AND INFORMATION

Use of recycled concrete from building and demolition waste is tied to an understanding of the problems, challenges and opportunities. Therefore, education and information within all parts of the industry, including architects, design engineers, specifiers, building inspectors, contractors, building owners, regulators and the general public, is urgently needed.

3.8.2. RESEARCH AND DEVELOPMENT

No barriers exist due to lack of technical and engineering knowledge of recycling and reuse of clean, unpolluted building and demolition concrete waste is technically proven. However, research and development is still needed into the treatment of contaminated building wastes.

3.8.3. MARKETING IN CONSTRUCTION INDUSTRY

Industry studies in Europe have shown a variation in the comparable profit margin as is illustrated in the following example. In Paris, a lack of natural aggregates makes recycled aggregate an attractive alternative, and the recycling market there is driven mainly by civil works companies with vertical integration of recycling outfits. Similarly, in Rotterdam the profit margin for recycled aggregate is high but in this case it is due more to the selling price and despite higher production costs for recycled materials compared to virgin materials. In Brussels the lack of dumping possibilities means that construction and demolition companies drop the market price to find solutions for the waste, while in Lille the abundance of quarries make the higher production costs a limiting factor.

Industry studies have shown that in Europe recycled concrete aggregate can sell for 3 to 12 € per tonne with a production cost of 2.5 to 10 € per tonne. The higher selling price is obtained on sites where all C&DW is reclaimed and maximum sorting is achieved, there is strong consumer demand, lack of natural alternatives and supportive regulatory regimes [9].

3.9. ECONOMY OF SCALE OF RECYCLING

Materials make up 40% to 50% of the cost of a construction job. Current ordering practices and materials tend to allow for materials wastage, but reuse and recycling can turn excess materials into usable materials.

An inflated economy, along with the fact that natural resources are limited, has caused a substantial increase in the cost of construction materials. This is well as the rising cost of fuel and equipment required to haul the concrete has encouraged recycling.

Proximity to market is critical due to high transportation costs. Transporting concrete to the landfill can cost as much as $0.25 per ton/mile (www.concretenetwork.com). For large reconstruction projects, on-site processing and recycling of RCA is likely to result in economic benefits through reduced aggregate hauling costs. Since the need for processing will remain common to conventional aggregates and to recycled concrete, the energy reduction will come largely through the elimination or reduction of transportation costs. This can also reduce the overall cost for recycled aggregates. In some regions, RCA may cost 20 to 30% less than natural aggregate.

Below is an economic analysis of the cost of recycling C&D concrete waste compared to landfill disposal. Landfill costs for concrete, asphalt and brick will vary greatly depending on the location, but the best all around estimate is $1/ton [4].

Other assumptions are that:

Recycle crushed concrete on base at 240 ton/yr.

Crushing cost: $4/ton (includes labour and crusher rental)

Landfill costs (inert waste): $1/ton

Hauling costs: $5/ton

Avoided new fill material costs: $12/ton

Table 3.1: Annual operating cost comparison for Diversion and Disposal of (240 tons/yr) C&D wastes. [4]

Diversion

Disposal

Operational costs

Crusher costs (labour & rental)

$1000

$0

Waste disposal

$0

$240

Hauling

$0

$1200

Total operational costs

$0

$1440

Total recovered income

$2900

$0

Net annual cost/benefit

+$1900

-$1440

Source: METRO Solid Waste Management Division of Portland Oregon (P2 opportunity handbook, Naval facilities engineering service centre [NFESC]).

The cost of recycling can be up to $4.00 per ton to crush, and may included other expenses. But, by eliminating the cost of removing the old concrete and factoring in savings on disposal costs, potential use of recycled aggregates, and potential income generated from the sale of scrap rebar, annual savings are approximately $3340 (Table 3.1). Recycling concrete makes sense for the cost benefits, the conservation of resources, and for the redirection of material that would otherwise be waste.

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