CHAPTER 3 Life cycle of SS frame and RC frame
3.8 End of life – Demolition and recycling
3.8.1 Demolish
Demolition of a building or structure can be considered under two headings: a) Taking down or removals: partial demolition of a structure; b) Demolition:
complete removal of a structure (McGrath & Anderson, 2007).
There are 6 types demolish methods:1) Hand demolition; 2) pusher arm demolition; 3) deliberate collapse demolition, 4) demolition ball techniques (should not be used on buildings over 30m high); 5) wired rope pulling demolition; and 6) demolition by explosives. Choice of demolition methods are determined by type of structure, type of construction, and location site (Kibert, 2008).
Concrete waste from construction and demolition is an environmental concern, but great strides have been made in the last decade to lessen the waste burden
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through reuse of concrete debris. Concrete is estimated to account for 67% by weight of construction and demolition waste – the largest single component (U.S.EPA, 1998).
3.8.2 Reuse
According to the waste hierarchy, the options for waste management in order of preference are: waste minimization; reuse; recycling, incineration with energy recovery, and composting; and lastly incineration without energy recovery, and landfill (BRE, 2007).
Reuse is high in the waste hierarchy, but structural items such as sections or I- beams may be difficult to reuse for two reasons (Conroy et al., 2007). One reason is that it is difficult to derive the strength characteristics such as shear and bending of a demolished frame element. This enable designers reuse demolish material if its strength properties is unknown or in doubt. The other reason is that most structural elements are designed with very long service lives and are not installed with reuse in mind. Once those elements are demolished, it is difficult to directly reuse them in new construction project.
3.8.3 Recycle 3.8.3.1 Recycled concrete
About 75-80% of secondary and recycled aggregates are thought to end up as sub-base and fill, including use in road building and airfield pavements (Conroy et al., 2007). However, the concrete industry actively utilizes industrial ecology in the production of modern concrete products due to concrete's inherent inert nature. The constituents of concrete can be recycled materials, and concrete itself can also be recycled. These materials are available for locally recycling. Concrete pieces from demolished structures can be reused to protect shorelines, for example in gabion walls or as rip rap.
Recycled concrete can be used as aggregates in new concrete, particularly the coarse portion. When using the recycled concrete as aggregates, the following should be taken into consideration (McGrath & Anderson, 2007):
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a) Recycled concrete as aggregates will typically have higher absorption and lower specific gravity than natural aggregates and will produce concrete with slightly higher drying shrinkage and creep. These differences become greater with increasing amounts of recycled fine aggregates.
b) The chloride content of recycled aggregates is of concern if the material will be used in reinforced concrete. The alkali content and type of aggregates in the system is probably unknown, and therefore if mixed with unsuitable materials, a risk of alkali-silica reaction is possible.
c) Recycled aggregates from crushed concrete and masonry offer a range of high-grade and low-grade applications in construction. According to BS 8500: 2002, coarse aggregates in a wide range of concrete mixes can be replaced up to 20% by crushed concrete.
d) Recycled concrete can be less expensive than natural aggregates because concrete is easily recycled on-site by bring in equipment to break, remove, and crush the old material. This practice also can save on landfill and transportation fees.
3.8.3.2 Recycled steel
Steel, easily separated magnetically from other wastes, is one of the most recycled construction materials. Appliance recycling rates remained stable at 90 percent as did structural steel at 97.5 percent, while construction reinforcement steel (i.e. rebar) increased slightly to 70 percent (SRI, 2009).
These steel recycling rates accomplish much more than simply saving landfill space. For every ton of steel recycled, 2500 pounds of iron ore, 1400 pounds of coal and 120 pounds of limestone are conserved.
Metal scrap that is collected for recycling is material that does not have to be managed as a waste. It is a valuable resource that is converted into value- added commodities. Perhaps even more importantly, recycled metal substitutes or displaces the necessity to mine new metal.
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Consequently, metal recycling offsets primary production processes—and their associated environmental impacts s and energy consumption—required to dig, crush, grind and otherwise metallurgical process virgin ore. Recycling increases the material and energy efficiency of product systems throughout the life cycle and thus is good management practice.
Steel recycling has the following characters (SRI, 2006):
a) Recycling of metals has environmental, economic and social value.
Consequently, and for many years, metals from end-of-life products are widely recycled at high rates.
b) Recycled metal is readily sold on the market. The constraint to greater levels of metal recycling is the availability of feedstock material.
c) Metals are characterized by metallic bonding that provides distinct structures and properties. As this type of bonding is not affected by melting, metals can be, and are, recycled over and over again.
d) Material grade is determined by conformity to established specifications. The origin of metal (whether primary or recycled) in a specific lot of material is driven by availability and economics.
e) Metal may be lost during product use (e.g., via corrosion or wear), and some material may not be economically recoverable at end-of-life due to material dispersion or difficulties in separating components.
3.8.3.3 The end-of-life recycling approach
The end-of-life recycling approach encourages manufacturers, policy-makers and other decision-makers to evaluate real performance and improve the design and management of products, including their disposal and recycling.
This forward-looking perspective supports sustainable development. By supporting solutions where high amounts of metal are made available for the future by recycling, it assists society in meeting the needs of the present without compromising the ability of future generations to meet their own needs (WCED, 1987).
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A designer using an end-of-life recycling approach focuses on optimizing product recovery and material recyclability (McGrath & Anderson, 2007). By facilitating greater end-of-life recycling, the decision-maker mitigates the loss of material after product use. This approach assesses the consequences at the end-of-life of the product based on established technical practices, and supports decisions for an efficient market. This concept allows design for recycling.
3.8.4 Landfill
A landfill is a site for the disposal of waste materials by burial and it is the oldest form of waste treatment. Historically, landfills have been the most common methods of organized waste disposal and remain so in many places around the world because of low disposal cost.
As landfill taxes increases to a value where recycling or incineration become viable alternative, or legislation, most of demolish waste will end up disposed of in the ground (Conroy et al., 2007). Furthermore, BRE (2007) recommends that landfill or combustion is the final option where no energy recovery systems are in place. Only a limited of construction and demolition waste can be incinerated but this is costly and has environmental implications, such as air pollution as well as GHG emission.