Deconstruction And Methods Of Demolition Construction Essay

There are many advantages of deconstruction over standard demolition. These advantages include (1) conservation of landfill space; (2) makes recycling easier; (3) potential building materials available for reuse; (4) preserves natural resources that would otherwise have to be used.

In order to minimise the amount of natural resources being used and the energy involved in manufacturing these materials, a cautious approach to the disposal of C&D waste needs to considered. Reusing materials prevents the use of embodied energy. This is the energy that goes into the production and manufacturing of a new product. Reducing the amount of energy required in manufacturing, producing and transporting new products leads to a reduction in damage to the environment. The figure below shows a system which could be implemented in order to limit the number of materials being disposed of on construction sites.

Waste Management Hierarchy for construction and demolition operations

Challenges facing deconstruction

There are a number of challenges which face deconstruction including (1) tools needed for deconstruction do not always exist; (2) disposal costs of C&D waste is relatively low; (3) deconstruction takes up more time than conventional demolition; (4) building and design codes do not always cover the reuse of building materials; (5) buildings are not designed to be dismantled; (6) the environmental and economic advantages of deconstruction are not recognized.

Deconstruction around the world

Australia

Volume of waste produced

The total volume of waste produced in Australia almost doubled between 1997 and 2007. In 1997, the total volume of waste produced in Australia stood at 22.7 million tonnes while in 2007, the total volume of waste shot up to 43.8 million tonnes. While 29% of the total waste produced was directly from household waste, the C&D sector accounted for almost 40%. (ABS, 2010)

Demolition Procedure

The Netherlands

Waste Tax

Waste taxes are placed on waste brought to the landfill or to the incinerator. The rate of tax can vary depending on the type of waste. In 1995, the Netherlands imposed a tax on the disposal of waste. The reason for this tax was to make other forms of waste treatment more appealing. Since the introduction of the tax the total volume of waste sent to landfills has decreased by a significant amount. The figure below shows how the huge decline in waste sent to landfills since the tax was imposed in 1995. (Oosterhuis et al, 2009)

This landfill tax is always on the increase in the Netherlands. In 2009, the landfill tax was €90 per toone. This is one of the highest landfill tax rates in the European Union. (defra.gov.uk, 2010)

Waste production and treatment in the Netherlands

Landfill Waste Ban

Along with imposing waste taxes, the Netherlands also implemented bans on sending recyclable and combustible waste to the landfill. This came into operation in 1997. This included separated C&D waste. The reason for this ban was to limit the amount of waste going to landfills which is seen as the least favoured method of disposal. The responsibility for implementing the ban lies with the landfill operators who are inspected regularly by the government’s waste management agency, SenterNovern. The introduction of the ban in the Netherlands proved to be a success in cutting down the amount of C&D waste sent to landfill. In 2009, 97% of C&D waste in the Netherlands is recovered. (defra.gov.uk)

Deconstruction Procedure

Step 1

The first step in dismantling a building is to check to see if the building contains any hazardous substances. One of the main hazardous wastes which cause concern in Ireland is asbestos. This is a natural mineral which is used in many buildings for fire proofing or thermal insulation. The danger with asbestos is that if it breaks up, the fibres which make up asbestos may then be inhaled into the lungs as dust. This increases the risk of lung cancer and causes lung tissue scarring. Under EU legislation it is no longer allowable to re-use asbestos or to even buy products containing asbestos in Ireland. This means that asbestos cannot be recycled; it must be disposed of after it has been removed from the building. (citizensinformation.ie)

Step 2

After a specialist contractor strips the building of all hazardous materials it is time to investigate the building and salvage any objects that can be reused as they are. This may include marble fireplaces, timber floors, radiators, doors, sinks and central heating boilers.

Step 3

The building is categorised under one of the following three headings:

Brickwork or block work buildings with timber floors and timber roof structure with roof tiles.

Concrete frame buildings with prestressed concrete components.

Steel frame buildings.

Step 4:

For all three categories above, the next step is to remove the flooring, tiles, plaster from the walls and ceiling. Windows are removed along with services installations (e.g. wall plugs, light switches). Metals are then removed and piping is also removed before the proper demoltion of the building starts.

Step 5:

There are a number of different types of waste that arise from stripping the building. These should be then split up into burnable and non-burnable materials. The burnable components brought to be incinerated while the non-burnables brought to the landfill.

Step 6:

Demolition:

Brickwork or block work buildings with timber floors and timber roof structure with roof tiles.

When every component of the building has been removed with the exception of the masonry works and the floors it is time to start taking the building apart floor by floor. Floor joists and timber floors are removed using a crane. These timber joists and flooring can then be reused. The advantage to using these second hand joists and flooring is that they are fully seasoned meaning they will not shrink.

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After the timber has been removed, the masonry blockwork is cut into sections and transported to be crushed. It may also be the case that the blockwork may be needed by the owner of the building in a new construction project. In this case the blocks are pulled down one by one and the mortar removed.

Concrete frame buildings with prestressed concrete components.

Prestressed concrete components in a building cause problems when it comes to disassembly because most of the time it is not known that the elements are actually prestressed. If prestessed concrete is cut up it may cause a structural element in the buiding to collapse.

Steel frame buildings.

The beams are dismantled one by one working from the top down. If the steel beams cannot be reused then they are cut and to be melted and remouilded. From time to time, steel structures like bridges are only partially taken apart and shipped overseas where the exact bridge is reused in another location.

Step 7:

The foundations of the building are th final step in the deconstruction of a building. Like the other elements of the structure the foundation is separated, broken up and transported to the crusher. In the case of concrete piles, they are removed by vibrating and pulling. If it is the case that wooden piles have been used as the foundation then it may be more difficult to remove as it will tend to break into pieves when being pulled from the ground.

Demolition Techniques

Balling

This is the demolition technique where a heavy cast iron or steel ball is used to knock a building. The ball usually weighs between 500 to 5000kg. The balling technique can be used to demolish concrete, reinforced conrete and masonry. It has become less popular due to the level of disturbance which arises on site including vibrations, noise and dust.The ball can come into contact with the building in two ways (1) free fall (2) swinging. In the free fall process the demolition ball is lifted up into the air by a large magnet and then it is dropped onto the building which is to be demolished. In the swinging process the demolition ball is attached to a steel line which is attached to a machine with a rotating frame.

Demolition Ball at work

Demolition Breakers

There are two types of breakers used in demolition (1) pneumatic (2) hydraulic. The difference between the two is pneumatic breakers are run using compressed air while hydraulic breakers use compressed oil. These type of breakers are used on concrete, brickwork and stone. Both types of breakers are mainly associated with minor demolition works, however they can also be attached to excavators for major demolition works.

Pneumatic Breaker

Hydraulic Shears

Hydraulic shears are attached to excavators. They can be used in the demolition of any size structures and a wide range of materials like steel, concrete and timber. The two shears have toothed shears which slide past eachother to break up the selected material.

Hydraulic Shears cutting steel

Thermal Cutting

Thermal cutting is used to cut steel and iron. Cutting torches are used for this process. There are three types of cutting torches (1) fuel/oxygen (2) powder (3) plasma. The fuel/oxygen cutting torches are run on a combination of oxegen and fuels such as natural gas, propane and acetylene which cuts at a maximum temperature of 3200 degrees Celsius. The choice of the fuel depends on the thickness of the metal.

If the metal is too thick for a regular cutting torch then a powder cutting torch can be used. These can reach a maximum temperature of 4500 degrees Celsius. The powder cutting torch is more expensive than the regular cutting torches because there is an extra fed in the torch which allows aluminium and iron powder to be supplied. This is what increases the temperature of the flame.

The plasma cutting is run by supplying electrical energy to gases such as helium and argon. These are used to cut alloyed steel which can be a slow process using the other two methods. Plasma cutting torches can cut up to four time faster than powder cuttinf torches.

Explosives

Explosives can be used in the demolition of buildings. Explosives can be set of using a wide variety of detonators which allows different detonation speeds. Explosions can be set off immediately or can be delayed by milliseconds if required. By blasting certain components of the building before others, it will allow the collapse of the structure to be carried out in a controlled manner. Even though this may help in accurately collapsing the building, there are still numerous examples of demolitions that have gone wrong when explosives have been used. This is why a large area must be cordoned off around the demolition site before blasting takes place.

Crushing & Separating C&D Waste

Immediately after a structure has been demolished it is transported a treatment plant where crushing and separating takes place. This enables new materials to be produced. The C&D waste must go through a number of processes before it is recycled. It must get sieved, pre crushed to prevent the lager materials from damaging the main crusher and all material such as steel, glass, plastics and timber must be removed manually, by air separation or by washing. The materials must then be sieved at the end of the process in order to get the requied sizing for the new material.

Jaw Crusher

The jaw crusher is the machine use to pre-crush the C&D waste. Large components such as reinforced concrete can be fed directly into the toggle crusher and are broken down into smaller piece by the moving jaw plate.

Jaw Crusher

Cone Breaker

This type of machine cannot deal with large C&D waste. After the waste has been pre-crushed the cone breaker is used as the main crusher. Inside this crushing machine is a cone that moves at high speed crushing waste material against fixed plates.

Cone Breaker