1. INTRODUCTION
We know every structure is designed for a specific life period generally 100years. The existence of the structure after the service life period is over is very dangerous to its occupants and surrounding buildings .The building act usually based on the provisions that enable in charge authorities to control demolition works for the protection of public safety with their belongings and to ensure adjoining premises and the site are made good on completion of the demolition.
Many structures already passed their design life and need to be reconstructed for safety and operational requirements. For this purpose, the old structures need to be demolished for replacement by new structures. Small structures can be demolished by manual methods but machinery and advanced techniques are required for demolition of bigger structures. Advanced techniques are also required for faster demolition in confined areas.
Demolition of any structure is the process of destroying down or falling down or collapsing down of large buildings after its useful life period with the help of some equipment or other method with a legal procedure followed by the consent of the local authority. Buildings when demolished with the help of explosions are called as an implosion a systematic technique of bringing down the structure. Every civil engineering structure is designed for a certain life period generally 100 years. After that the existence of a structure is very dangerous and unstable which may cause a severe impact and be a cause of many deaths. So removal of such structures with proper safety measures has got great importance.
2. PRE-PLANNING OF DEMOLITION ACTIVITY
The different steps before the start of a demolition process are:
· Surveying of site
· Removal of hazardous materials from the site
· Preparation of plan along with strategy to implement
· Stability report from local authorities
· Safety measures to be used
· Surveying of site
· Removal of hazardous materials from the site
· Preparation of plan along with strategy to implement
· Stability report from local authorities
· Safety measures to be used
2.1 SURVEYING OF SITE
Study of different parameters with different views of the structure and its surroundings with structural point of view is carried in surveying. Two types of surveying which are mainly conducted. They are
· Building surveying
· Structural surveying
· Building surveying
· Structural surveying
2.1.1 Building surveying
It includes the following,
(a) Record Drawings Prior to the Building Survey, the existing record plan, including layout plan showing various adjoining properties, pedestrian walkway, roads and street, etc. shall be shown and studied.
(b) Survey of Buildings The Building Survey shall cover the following:
· The construction materials used and its quality;
· The existing use and, if possible, the past uses of the building prior to demolition with maximum utilization;
· The presence of wastewater, hazardous materials, matters arising from toxic chemicals, flammable or explosive and radioactive materials, etc. and possible presence of materials which can create air pollution and soil contamination;
· Dangerous areas, e.g., abnormal layouts,
· Surrounding properties and site conditions, such as the presence of slope and retaining wall, wall supporting ground, illegal structures, bridges, underground railway and its above ground structures, including entrances, vent shafts, distribution substations, plant rooms, overhead railway structures, overhead cables or guy wires, and other utility Service connections should be considered;
· Drainage conditions and possible problems on water pollution, flooding and erosion,
· Common facilities with adjoining building, including common staircases, walls, and possible effect on it, such as self-enclosed walls to the adjoining buildings,
· Hoarding and covered walkway requirements;
· Adjoining pedestrian walkway and vehicular traffic conditions;
(c) Hazardous Materials on and in surrounding
· Unless and until the Building Survey found that no obvious hazardous material is present in the building, the Authorized Person shall carry sampling and testing for the hazardous materials;
· When hazardous materials e.g., asbestos containing materials, or petroleum, are present, they shall be removed and cleaned/disposed of according to the statutory requirements administered by the Environmental Protection Department.
· When the site has previously been used to store chemicals, and other dangerous goods, soil contamination assessment shall be required at pre-demolition stage and/or post-demolition stage; and
· When the site has previously been used to store explosives, special procedures to ensure no explosives remain on site will be required.
2.1.2 Structural surveying
(a) Record Drawings Before Structural Survey, the existing record layout, structural plans and structural details shall be studied carefully. The Registered Structural Engineer or the concern local authority shall check the presence of unusual detailing that may cause abnormal structural behavior during demolition, e.g., upward anchor of tensile reinforcement in cantilevered structures. If existing record plans are available, these plans shall be used as reference and preferably be brought along with the Structural Survey.
(b) Survey Items The Structural Survey shall cover the following:
· The structural materials used with quantity;
· The original structural system employed in the design;
· The method of construction;
· Any disintegration and deterioration on any structural elements;
· The structural conditions of adjoining structures
· The presence of continuous structures that may be affected by the demolition;
· The presence of basements, underground tanks or underground vaults;
(c) Special Structures The Structural Survey looks at the following:
· The correctness of structural data available;
· The presence of any unconventional structural elements which may require special attention and well-defined modification procedures
· The possibilities of structural modification to enable efficient demolition traffic during demolition
· Any limitation on shoring and other temporary supports.
(d) Investigation and Testing at site When no structural details are available, the structural survey includes on site measurement and finds any structural framing as much as practicable, performing tests and exposing some key structural elements to facilitate checking on present structure. This allows the development of procedures that ensure the stability of the building at all stages during demolition.
2.2 REMOVAL OF HAZARDOUS MATERIALS FROM SITE
Hazardous materials if any, such as asbestos containing materials, petroleum contamination and radioactive contamination, etc exist in the building, further investigation and removal of such hazardous material or contamination by experts shall be done.
2.2.1 Asbestos Containing Material if any on site Experts shall be employed to take samples and such samples shall be tested for asbestos containing material. When asbestos containing materials are found, expert contractor shall be employed to remove such asbestos containing material.
2.2.2 Presence of Soil Contamination Material When possible soil contamination material is present, experts shall be employed to prepare soil contamination test proposal and submit such proposal to the Environmental Department for comment. Upon agreement by the Environmental Department, and completion of the tests, a Soil Contamination Assessment shall be submitted to the Environmental Department for acceptance. When remedial works are required, the remedial proposal has to be submitted to the Environmental Department for consent approval before implementation of such remedial works.
2.3 PREPARATION OF PLAN AND STRATEGY
A Demolition Plan and strategy shall include the following:
2.3.1 A detail plan showing:
· The building location to be demolished;
· Topography of the site with its ground level contours and sections of the slopes and ground supported by the building where appropriate in detailed;
· Details of ground removal and/or backfilling; and
· The distances from the building to be demolished to its adjacent buildings, streets, structures and significant street furniture.
2.3.2 A detail layout plan of all floors of the building to be demolished, showing:
· The resident usage of the floors;
· The structural support;
· Materials of construction with quantity;
· Building Condition e.g. the degree of deterioration; and
· The relationship of the building to be demolished with surrounding properties affected by the demolition, which include all adjoining buildings and unauthorized structures,
2.3.3 A Detail plan showing the structural arrangement
Construction of all unconventional structural elements, such as pre-stressed concrete structures, precast concrete members, stressed skin structures, steel framed structures, hangers, hanging ties, trusses or girders, deep beams, long span beams (greater than 10m), arches shall be studied.
2.3.4 A Detail plan showing the steps for the demolition
Detailed sequence of demolishing particular structural members; and the method of demolition to be adopted including the restrictions on the use of any particular type of equipment if any shall be highlighted.
When powered mechanical plants and equipment are used, a plan showing the route of movement of powered mechanical plants and equipment including the method of lifting mechanical plant, where necessary, onto the top floors of the structure; any structural alterations required to suit the demolition.
2.3.5 A plan or descriptive notes on the proposed methods for handling and disposal of debris including
· The permissible temporary accumulation of building debris at upper floors and at ground floor;
· Method of handling demolished building debris;
· The routing and movement of debris from each floor to on grade holding area prior to leaving the site;
· Means of transportation of debris off the site;
· Time and frequency of debris disposal off site;
2.4 DETAIL STABILITY REPORT
According to Building (Administration) Regulation act (U.P. Act XXXIV of 1958), the Demolition Plan must be accompanied by a Stability Report with supporting calculations. The Stability Report shall include the following parts:
· A report on the stability of the building to be demolished during all stages of demolition;
· In the case when powered mechanical plants or equipment are used, a report on the stability of the building with supporting calculations to demonstrate that the use of the plants and equipment will not render inadequate the margin of safety of, or cause damage to any building, structure, street, land and services
· In the case when powered mechanical plants or equipment are used, structural calculations for all temporary supports and bracings;
· A report on the stability of neighbouring buildings, adjoining properties.
· In the case when temporary or permanent supports are required to these neighboring buildings, adjoining properties, and party walls, structural calculations for these temporary and permanent supports
2.5 SAFETY MEASURES TO BE USED
2.5.1 General
According to IS 4130:1991, site safety features shall emphasise protection of the public, particularly, the pedestrian and vehicular traffic and the adjacent properties. Proper safety features shall be designed to make sure that the demolition can be carried out safely and the site personal are protected. The demolition works including precautionary measures shall be carried out in accordance with the approved plans and other related documents, with continuous supervision to the works.
On every demolition job, danger sign shall be conspicuously posted all around the structure and all doors and openings giving access to the structure shall be kept barricaded or manned except during the actual passage of workmen or equipment. However, provision shall be made for at least two independent exits for escape of workmen during any emergency. During night, red lights shall be placed on or about all the barricades.
Where in any work of demolition it is imperative, because of danger existing, to ensure that no unauthorized person shall enter the site of demolition outside working hours, a watchman should be employed. In addition to watching the site, he shall also be responsible for maintaining all notices, lights and barricades.
All necessary safety applications shall be issued to the workers and their use explained. It shall be ensured that the workers are using all the safety appliances while at work. Goggles preferably made of celluloid lens shall be worn at the time of demolition of walls, floors, tearing of plaster, etc, especially when instruments like jack hammers are employed in demolition work, to protect the eyes from injuries from flying pieces, dirt, dust, etc , that may be blown up by the wind.
Leather or rubber gloves should be worn by the workers while demolition RCC work or removing steel work, etc, where the hands of the workers are likely to be injured.
Safety belts shall be used by labourers while working at higher level to prevent falling from the structure. First-aid equipment shall be got available at all demolition works of any magnitude. Also, by prior arrangement, a qualified doctor shall be available at call.
If a structure to be demolished has been partially wrecked by fire, explosion or other catastrophe, the walls and damaged roofs shall be shored or braced suitably.
2.5.2 Walkways and sidewalks
Walkways shall be provided for the use of the workmen who shall be instructed to use them and all such walkways shall be kept adequately lighted, free from debris and other materials.
Before any demolition work started, every sidewalk or adjacent to the work likely to be affected shall be closed or protected. Children and members of the public shall be kept out of the building and the adjoining yard. A typical sketch of sidewalk shed is in figure 2.1.
Fig 2.1 Typical sketch of a sidewalk shed
As per IS 4130 if the structure to be demolished is more than two storeyed or 7.5m high, measured from the sidewalk or street which cannot to be closed or safely diverted, and the horizontal distance from the inside of the sidewalk to the structure is 4.5 metre or less than a substantial sidewalk shed shall be constructed over the entire length of the sidewalk adjacent to the structure of the sufficient width with a view to accommodating the pedestrian traffic without causing congestion. The sidewalk shed shall be lighted sufficiently to ensure safety at all times.
A toe board of at least 1m high above the roof of shed shall be provided on the outside edge and ends of the sidewalk shed. Such boards may be vertical or inclined outward at not more than 45 degrees.
Except where the roof of a sidewalk shed solidly abuts the structure, the face of the sidewalk shed towards the building shall be completely closed by providing sheeting planking to prevent falling material from penetrating into the shed.
As per IS-4130, the roof of sidewalk sheds shall be capable of sustaining a load of 73 N/mm2 (very high-may be 7.3KN/m2). Only in exceptional cases, say due to lack of other space, the storing of material on a sidewalk shed may be permitted in which case the shed shall be designed for a load of 146N/mm2. Roof of sidewalk shed shall be such as to give a minimum clearance of 2.4m.
The deck flooring of the sidewalk shed shall consist of plank of not less than 20mm in thickness, closely laid and deck made watertight. All members of the shed shall be adequately braced and connected to resist displacement of members or distortion of framework.
2.5.3 Catch platforms
In demolition of exterior wall of multi-storeyed structure, catch platform of heavy planking shall be provide to prevent injuries to the worker working below and to the public, when the external walls are more than 20m in height.
Such catch platform shall be constructed and maintained not more than 3 storeys below the storey from which exterior wall is being demolished. When demolition has progressed to within 3 storeys of ground level, catch platform will not be considered necessary.
Catch platform shall not be less than 1.5m in width and shall consist of outriggers and planks laid tight together. Catch platform shall be provided with a continuous solid parapet along its outer edge of at least 1m height.
Materials shall not be dumped on catch platform nor shall such catch platform be used for the storage of materials.
2.5.4 Protective screens
Protective screen covers shall be placed, where necessary, to prevent flying pieces from injuring the fellow workmen. Bamboo scaffolds or metal scaffolds shall be used for providing protective screens to completely enclose the building structure for retaining dust and small debris. Tarpaulin and heavy duty nets shall be used to cover the exterior face of the scaffold. The protective screens shall be secured to the scaffoldings at intervals in both horizontal and vertical directions.
2.5.5 Temporary supports
Temporary supports are required to cater the loads due the machinery used in demolition, debris accumulated, impact from fallen debris and lateral loads due to the fallen debris and wind force etc. a suitable factor of safety shall be considered. They are also provide when any part of the structure or any element being demolished is not self supporting or when the temporary stability of the structure or its elements could be impaired as a result of the demolition activities.
The temporary supports used for demolition shall be built with structural steel, heavy timber, or other materials which is considered to be appropriate for the purpose. Premanufactured components such as tubular shores, telescope steel props, framed towers, etc. may be used as temporary supports provided their design capacity and their erection and maintenance requirements are followed in strict accordance with manufacturer’s recommendations.
All temporary support systems shall be supported on adequate foundations or floors. In the case when the immediate floor below the floor under demolition is not adequate to carry 5he imposed loading from the demolition activities, shoring shall be carried down to the lower floors until adequate support is achieved.
2.5.6 Protection of properties
i. Party walls and external walls
Party walls that separate the adjoining building and the demolition project shall remain and be protected during and after the demolition project. Redundant party wall shall be removed as far as possible. The exposed party wall or unprotected external wall maybe temporarily supported and shall be maintained until the application of permanent treatment which may be incorporated in the construction of the new building. Demolition of structural elements adjacent to the party wall or the external wall of the adjoining building shall be performed by manual method with extreme care to prevent any damage to the party wall or external wall.
The party wall or external wall shall be protected against infiltration and water seepage, by cement mortar treatments, when it is exposed to the weather. All loose bricks or fill materials shall be removed. All openings and voids shall be filled up.
ii. Foundation support
A thorough evaluation shall be conducted for demolition involving any structure that may affect the foundation of the adjoining properties. Appropriate shoring, underpinning or other protective measures shall be installed if necessary.
iii. Protection of traffic
Any closure of roads and walkways may seriously impact the traffic/pedestrian circulation and, as far as practicable, shall be avoided. If unavoidable, prior permission/ arrangement of the Transportation Department and the Police shall be obtained. Temporary closure of a traffic lane may be considered for night work.
Proper headroom, segregation, loading/unloading location, illumination etc. shall be provided for the protection of vehicular and pedestrian traffic from the ingress and egress of construction vehicles.
2.5.7 Special safety considerations
i. Training and communication
Demolition workers, including plant or equipment operators, shall go through proper job safety training and be informed of the potential hazards by attending training sessions as well as on-the-job training. They shall be trained regarding working at heights, working in confined spaces, working with lifting appliances, use of personal protective equipment, handling of chemicals, health hazards in demolition works and safe operating zones.
Site safety and project understanding shall be promoted through an induction meeting at the beginning of the project, where information related to the project such as the proposed method and procedures, potential danger during the operation, safety measures and project specifications can be disseminated to all on site personnel. The safety concept can be maintained by regular safety meeting throughout the project period.
ii. Equipment maintenance
All equipment shall be tested and examined before use. They shall be properly stored and maintained. The equipment shall be inspected daily and results of the inspection shall be trecorded accordingly. A detailed safety instruction shall be provide to cater for specific situations of the project, if necessary.
iii. Electrical safety
A properly connected power source from a local electric utility supplier or a mobile electricity generator shall be utilized in demolition sites. The safety requirements given in the Electricity Regulation shall be adhered to.
iv. Fire
All flammable goods shall be removed from site unless they are necessary for the works involved. Any remaining flammable goods shall be stored in proper storage facilities. All furniture, timber, doors, etc. shall be removed before any welding work is performed. Firefighting appliances shall be provided and maintained in working conditions. Emergency access to site shall be provided.
v. Occupational health
The health of workers on site shall be properly protected in accordance with the relevant subsidiary regulations of the Factories Act with particular attention to Exposure to Dust, Chemical Exposure, Ventilation, Noise Exposure, Medical and First Aid Facilities, Sanitation and Occupational Diseases.
vi. Vibration
Demolition work will cause vibration to neighbouring buildings or structures to various extent, depending on the method of demolition, which should be controlled by suitable monitoring. The most serious vibration is caused by implosion.
vii. Environmental Precautions
The general requirements to minimize environmental impacts from construction sites can also be applied to demolition processes. The following sections contain some of the procedure to be adopted:
viii. Air pollution
Concrete breaking, handling of debris and hauling process are main sources of dust from building demolition. Dust mitigation measures, such as water spray, shall be adopted to minimize dust emissions. Burning of waste shall not be allowed. Diesel fumes generated by mechanical plant or equipment shall be controlled.
ix. Noise
Noise pollution arising from the demolition works due the use of powered mechanical equipment such as pneumatic breakers, excavators and generators, loading and transportation of debris, etc. affects the workers, and the sensitive receivers in the vicinity of the demolition site. Silent type equipment shall be used to reduce noise impact as much as practicable. Demolition activity shall not be performed within the restricted hours established.
x. Water
The discharge of wastewater from demolition sites shall be controlled by a licence. Effluent shall be treated to the standards as stipulated in the licence before discharge. The demolition contractor shall maintain proper control of temporary water supply and an effective temporary drainage system.
xi. Hazardous Materials
A suitable plan shall be made for removal of any asbestos containing material. Other materials such as LPG cylinders in domestic flats, toxic and corrosive chemicals for industrial undertakings, and any other hazardous materials have to be identified and properly handled and removed, as per Regulations, prior to the commencement of the demolition of the building.
3. METHODS OF DEMOLITION
There are two types of demolition
· Non explosive demolition method
· Explosive demolition method
· Non explosive demolition method
· Explosive demolition method
3.1 NON EXPLOSIVE DEMOLITION METHODS
Demolition of a structure done with some or other equipment without use of any explosive.
Different equipments used for the demolition activity are
3.1.1 Sledge Hammers and rammers
A sledge hammer and rammers, equipment used for removing a stone wall or a single column. It consists of a long stem with a metallic head. It is used to give impacts on the surfaces and that cause the demolition of structure. It cannot be used for removal of large buildings. Commonly using sledge hammer and rammers are seen in figure 3.1.
Fig 3.1 Sledge hammer and rammer
3.1.2 Excavators and Bulldozers
Hydraulic excavators may be used to topple one-or two-story buildings by an undermining process. The undermining process means erode the base or foundation, i.e., dig or excavate beneath the foundation so as to make it collapse. The strategy of excavation is to undermine the building while controlling the manner and direction in which it falls. The demolition project manager will determine where under mining is necessary so that the building is pulled into the desired manner and direction. Safety and clean up considerations are also taken into account in determining how the building is undermined and ultimately demolished. Fig 3.2 shows a hydraulic excavator and figure 3.3 shows a bulldozer.
Fig 3.2 Excavator
Fig 3.3 Bulldozer
3.1.3 Wrecking Balls or Spilling Balls
In case of buildings have greater heights 5 onwards story machineries like normal excavators and bulldozers are not sufficient. In such cases crane with wrecking balls or spilling balls are used to perform the demolition activity. The wrecking balls are steel balls hanging from a steel rope which is attached to the crane, as shown in figure 3.4. This method is more effective only for high rise masonry structures because of the uncontrolled backward movement of steel ball after the impact on the wall surface. Nowadays this method is not commonly used because of this uncontrolled behavior of wrecking balls which may cause some other accident.
Fig 3.4 Wrecking Balls
3.1.4 High reach excavators
High reach demolition excavators are more often used for tall buildings where explosive demolition is not appropriate or not possible. These excavators are used to demolish up to a height of 300 feet. These excavators with some attachments are also provided for some specific purposes. For example excavators with shear attachments are typically used to dismantle steel structural elements. A high reach excavator doing demolition work shows in figure 3.5. Hydraulic hammers are often used for concrete structures and concrete processing attachments are used to crush concrete to a manageable size, and to removing reinforcing steel.
Fig 3.5 High reach excavators
3.2 EXPLOSIVE DEMOLITION METHOD
The basic idea of explosive demolition is quite simple, easy and fast. If we remove the support of the structure of a building at a certain point, the section of the building above the point will come down on the part of the building below that point from where it is exploded. If this upper section is heavy enough, it will collide with the lower part with sufficient force to cause significant damage. The explosives are just trigger for the demolition. It’s gravity that brings the building down.
Demolition blasters or blasting expert (“Blasting expert” means a person who is the holder of a valid mine blasting certificate.) load explosives on several different levels of the building so that the building structure falls down on itself at multiple points. When everything is planned and executed correctly, the total damage of the explosives and falling building material is sufficient to collapse the structure entirely, so clean up crews are left with only a pile of rubble. In figure 3.6 shows blasting of Reading Grain facility, Philadelphia in 1999.
Fig 3.6 Explosive demolition
The main challenge and risk in bringing a building down is controlling which way it falls. There are mainly two ways to bring down a building,
· Falling like a tree
· Falling from crest to foot
· Falling like a tree
· Falling from crest to foot
3.2.1 Falling like a Tree
In this method the blasting crew to collapses the building over on one side, into a parking lot or other open area with the help of blast. This sort of blast is the easiest to execute, and it is generally the safest way to perform demolition which is something like felling a tree. For example to topple the building to the north, the blasters detonate explosives on the south side of the building first , in the same way you would chop into a tree from the south side if you wanted it to fall in that direction . Blasters may also secure steel cables to support columns in the building, so that they are pulled a certain way as they crumble.
3.2.2 Falling from crest to foot
Many times, a building is surrounded by numbers of structures that must be preserved. In this case, the blasters are used for true implosion, demolishing the building so that it collapses straight down into its own foot (that means the total area of building is removed into the base of the building). This requires great skill that only some handful of demolition companies in the world attempt it. Figure 3.7 is an example for falling from crest to foot, that is demolition of a chimney in Germany.
Fig 3.7 Demolition of a chimney in Germany (falling into footprint)
Blasters will explode the major support columns on the lower floors first and then a few upper stories. For example, In a 20-story building, the blasters might blow the columns on the first and second floor, as well as the 12th and 15th floors. In most cases blowing the support structures on the lower floors is sufficient for collapsing the building, but loading columns on upper floors helps break the building material into smaller pieces as it falls. This makes for a perfect demolition and easier cleanup following the blast.
4. IMPLOSION
4.1 EXPLOSIVES USED FOR IMPLOSION
Once the blasters have figured out how to set up an implosion, it's time to prepare the building and selection of the explosives used for the demolition. The most common explosives used in demolition are dynamites (straight, ammonia and gelatin), water gels, emulsions, PETN (penta-erythritol tetra-nitrate) and RDX (Cyclotrimethylene Trinitramine).
4.1.1 Dynamite
Dynamite is a combination of nitroglycerin with inert filler, making the end product stable for handling which was invented by Alfred Nobel in 1866. Dynamite is just absorbent stuffing soaked in a highly combustible chemical or mixture of chemicals. When the chemical is ignited, it burns quickly, producing a large volume of hot gas in a short amount of time. This gas expands rapidly, applying immense outward pressure (up to 600 tons per square inch) on whatever is around it. Blasters cram this explosive material into narrow bore holes drilled in the concrete columns. When the explosives are ignited, the sudden outward pressure sends a powerful shock wave busting through the column at supersonic speed, shattering the concrete into tiny chunks. For concrete columns, blasters use traditional dynamite. This has the advantages of being good to excellent for water resistance as well as being predictable and reliable. Dynamite comes in a wide range of small and medium-diameter cartridges of different lengths. A most common seen dynamite available in the market is shown in Figure 4.1
Fig 4.1 Dynamite
4.1.2 Cyclotrimethylenetrinitramine (RDX)
RDX-based explosive compounds expand at a very high rate of speed, up to 27,000 feet per second (8,230 meters per second). Available in powder form as shown in Figure 4.2. It is a high-velocity explosive. Instead of disintegrating the entire column, the concentrated, high-velocity pressure slices right through the steel, splitting it in half. Additionally, blasters may ignite dynamite on one side of the column to push it over in a particular direction. Demolishing steel columns is a bit more difficult, as the dense material is much stronger. To bring down the buildings with a steel support structure, blasters typically use this specialized explosive material cyclotrimethylenetrinitramine (RDX).
Fig 4.2. RDX
4.1.3 Water Gel and Emulsions
This consists of water-containing chemical mixtures that are either water gels or emulsions. Water gels contain oxidizing salts and fuels that are dissolved in water. Emulsions are fine droplets of oxidizing salts and water surrounded by a fuel mixture of wax and oil. These explosives are even more stable. These products are available in several forms and sizes. The standard size used to demolish concrete and brick structures is 31mm diameter by 200mm long cartridge configuration or in bulks.
4.2 QUANTITY OF EXPLOSIVES
4.2 QUANTITY OF EXPLOSIVES
Blasters determine how much explosive material to use based largely on their own experience and the information provided by the architects and engineers who originally built the building. But most of the time, they won't depend on this data alone. To make sure they don't overload or under-load the support structure, the blasters perform a test blast on a few of the columns, which they wrap in a shield for safety. The blasters try out varying degrees of explosive material, and based on the effectiveness of each explosion, they determine the minimum explosive charge needed to demolish the columns. The crosssectional dimensions of the column, its concrete compressive strength, its condition, and details of its reinforcement are all variables which affect the column charge quantity and type of explosive required. By using only the necessary amount of explosive material, the blasters minimize flying debris, reducing the likelihood of damaging nearby structures.
4.3 PLACEMENT OF EXPLOSIVES
Almost all the explosives used in implosions are placed in or on columns and load bearing walls. Columns at the lowest floor levels are the most important as that is where the stored potential energy in the structure is most effectively released. Usually, explosives will be placed on the lowest floor level and then are spaced out in blast floors along the height of the building, closer together at lower floors and more spread out at upper floors. The type of explosives placed on steel columns is very different than the ones used on reinforced concrete columns. Steel is very ductile and tough. Further, when the steel sections (flanges and webs) are thin, making internal confinement of explosives impossible, as compared to concrete columns, it can have explosives loaded into drilled holes. For steel columns shaped charges are used. Commercial shaped charges are typically Chevron shaped copper clad linear elements filled with RDX explosive.
For reinforced concrete columns, holes are first drilled in the column, the cartridge explosive is placed in the hole and stemming (typically tubular bags of sand or high density foam) are placed in the balance of the hole to confine the charge. When the explosive detonates, the concrete in the column is fragmented, leaving the reinforcing bars bent, but intact. When tightly pitched spirals or stirrups are encountered, they must often be exposed and cut first, depending on structural analysis allowances, site conditions and possible live loading. If they are uncut, unfractured concrete might remain and the column may retain some of its load carrying capacity. Hence, tight spirals and other robust reinforcing in concrete columns help resist progressive collapse. This is one of the reasons that reinforced concrete structures designed to resist intense earthquakes have some innate resistance to explosives, because their columns contain tight spirals.
To further reduce flying debris, each column may be wrapped with chain-link fencing and geotextile fabric. The fence keeps the large chunks of concrete from flying out, and the fabric catches most of the smaller bits. Blasters also wrap fabric around the outside of each floor that is rigged with explosives. This acts as an extra net to contain any exploding concrete that tears through the material around each individual column. Structures surrounding the building may also be covered to protect them from flying debris and the pressure of the explosions. The loading of the column and wrapping with a proper cover is shown in figure 4.3
Fig 4.3.Columns fully loaded with explosives and hooked up to blasting caps and
fuses.
4.4 ELECTRICAL DETONATOR
To ignite both RDX and dynamite, you must apply a severe shock. In building demolition, blasters accomplish this with a blasting cap, a small amount of explosive material (primer charge) connected to some sort of fuse. The traditional fuse is a long cord with explosive material inside. When we ignite one end of the cord, the explosive material inside it burns at a steady pace, and the flame travels down the cord to the detonator on the other end. When it reaches this point, it sets off the primary charge. Now-a-days blasters use an electrical detonator instead of a traditional fuse. An electrical detonator fuse (lead line) is just a long length of electrical wire. At the detonator end, the wire is surrounded by a layer of explosive material. This detonator is attached directly to the primer charge affixed to the main explosives. When current is passed through the wire (by hooking it up to a battery), electrical resistance causes the wire to heat up. This heat ignites the flammable substance on the detonator end, which in turn sets off the primer charge, which triggers the main explosives.
4.5 SEQUENCE OF DETONATIONS
The concept of implosion is to create an almost fluid motion in the collapse of the building. This methodology reduces the ground impact and resultant vibration. Carefully designed building implosions create ground vibrations less than 25 mm/s peak particle velocity. Columns at the bottom of the building are detonated first to make maximum amount of potential energy available immediately to get the progressive collapse. Columns at other floors are detonated anywhere from a few milliseconds to several seconds later to help fragment the building debris or control its fall direction and velocity. Timing of detonations between columns is part art, part science and all experience. There is chance of building to get pancake if the detonations are too close together and portions of the building may expand outward in random directions.
Too far apart and the fluid motion is disrupted. More explosives would be needed to overcome the inertia of the building between each spill. More importantly, an interruption of the fluid motion can cause elements to disengage, causing complete loss of control over the trajectory of the structure. When a column is detonated, the structure above begins to accelerate towards the ground at less than 9.8 m/ s2 freefall. The actual acceleration is less than the acceleration of gravity because still standing portions of the structure act to arrest its fall, resisting moment or consuming kinetic energy as elements are crushed. The forward momentum can be slowed or stopped by because of naturally occurring alternate load paths in the structure.
During a building implosion, the detonations are timed so that just before the alternate load path is created, the adjacent column line is detonated to allow continuity of the progressive failure. Therefore, assuming freefall, if there was a one second delay between adjacent column lines, the column line just detonated would have dropped almost 5.2 m thereby impacting the ground before the next column line is detonated. This eventuality is to be avoided as a premature ground impact by a portion of the structure may redirect the still standing portions into unexpected directions.
5. OTHER METHODS
5.1 NON EXPLOSIVE DEMOLITION AGENT
Non Explosive Demolition Agent (NEDA) is a static demolition agent. When the reaction takes place in a confined drill hole, the NEDA generates an expansive pressure to crack and break concrete and stone. The NEDA is a suitable application in a restrictive environment where noise, flying debris and vibration are less tolerated. A drilling pattern shall first be designed. For large projects, test breaking shall be performed. The NEDA shall be mixed with water to form a slurry and immediately placed into the pre-drilled holes. The loading intensity and water content shall be controlled to optimise the expansive pressure and prevent blow-out of the NEDA. The breaking effect of NEDA is relatively small comparing to explosives. Secondary efforts are required to further break down and remove the debris by mechanical means. NEDA may be used on foundation works, pile caps or structures that are fully supported. When used in rock, NEDA should be contained within strong, flexible, impermeable bags to prevent uncontrolled entry into rock joints. Demolition using NEDA is shown in figure 5.1.
Fig 5.1 Non explosive demolition agent
5.2 SAW CUTTING
Saw cutting is suitable for alternation and addition works where accuracy in the cutting is important and the tolerance to noise and vibration is very limited. It can be used to cut concrete slabs and wall elements into segments. An entire building may be dismantled by saw cutting. Saw cutting generally includes conventional disc saw and chain saw, diamond core stitch drilling and wire saw. Figure 5.2 shows a conventional disc saw.
Fig 5.2 Conventional disc saw
5.2.1 Wire Saw Cutting
Wire saw cutting comprises a special steel wire often impregnated with diamond beads to increase its cutting ability. The wire saw method is a suitable application for projects that require precision and total control of demolition work. A hole shall first be pre-drilled for the passage of the diamond wire, the wire cutting operation follows. Because of its flexibility, it may be used for “hard to reach” areas. A diamond wire saw may also be applied in cutting off piling of marine structures and bridges.
5.2.2 Diamond Core Stitch Drilling
Diamond core stitch drilling may be adopted to cut concrete elements by continuously coring a set of holes to carve up the concrete structure. The thickness of the concrete to be cut depends on the depth of the drilling or coring equipment. Diamond core stitch drilling is particularly suitable in the removal of existing pile cap for construction of large diameter bored pile foundation. Pictorial view of a diamond core stitch drilling is in figure 5.3.
5.2.3 Management of Process Water
The sawing and drilling operations require large amounts of water to cool down the blade which cuts through the concrete at high speed. Provision shall be made to provide a water source for the operation and for the disposal of the cooling water.
Fig 5.3 Diamond Core Stitch Drilling
5.3 THERMAL LANCE
Cutting of reinforced concrete by thermal lance involves very high temperature up to 2,000 - 4,000°C. The extremely high heat requires special precautionary measures and care. The use of a thermal lance in cutting reinforced concrete shall not be used unless: (A) The project demonstrated that there is no other viable alternative; (B) adequate protective measures are provided to isolate the operation and to prevent any potential fire spreading out; and (C) adequate protective measures are provided to prevent the injury of the workers, and any third party by flame and the molten concrete. A cutting operation of concrete is shown in figure 5.4.
Fig 5.4 Cutting of concrete by thermal lance
5.4 WATER JET
Water jetting involves the use of a water jet stream pumped at high pressure to erode the cement matrix and wash out the aggregates. Abrasive compounds may be added for cutting reinforcing steel. A water jet operation is shown in figure 5.5. The application of the water jetting shall be subject to the following criteria:
· City water supply shall be used in water jet cutting. Provision shall be included to dispose the water used in the operation, and to recycle the water for continuous operation through local filtration and sedimentation.
· The area behind the structural member to be cut shall be shielded to avoid damage to persons and properties during the cutting.
· In the case when abrasive water jets are used, further precautionary measures shall be provided in accordance with manufacturer recommendations to confine the rebound of the abrasive compounds. All site personnel shall wear adequate safety cover and clothing.
Fig 5.5 Water jet cutting
5.5 MICRO-BLASTING
In micro-blasting the same concept as in dynamite is used, but in a smaller, more controlled manner. Small diameter holes are drilled on the surface to be blasted and cleaned out with air to remove all dust that interferes with the firing operation. Cartridges of a smokeless powder are placed in the holes and the blast is intiated with a firing mechanism. The blast is large enough to break thick concrete, but results in little flying debris, which can be controlled by placing carpet over the blast area. Micro blasting in a small rock is shown in figure 5.6.
Fig 5.6 Micro-blasting
6. SPECIAL STRUCTURES
6.1 PRECAST CONCRETE STRUCTURES
Precast concrete structures are constructed of precast concrete elements joined together. The continuity of the structure depends on the treatment of joints. The joint details shall be studied. In case of doubt, open up inspection at critical positions may be required.
Simple Precast Construction
The joints in this type of structure do not normally provide continuity. The stability of this type of structure relies on other elements such as stairs, lift shafts, shear walls or other framed structures.
6.1.1 Dismantling
Each precast element shall be removed in the reverse order of construction and broken on the ground or an adequately supported floor. Elements providing lateral stability shall not be demolished prior to the removal of the precast elements or prior to the installation of the temporary bracing. Temporary supports shall be adequately braced or tied to laterally stable elements.
6.1.2 Existing Lifting Points
The re-use of the existing lifting points or accessories to lift the precast elements shall not be allowed unless the record erection plans showing the function of the existing lifting points are checked and verified to be adequate for current use.
6.1.3 Lateral Support
During Lifting Special consideration shall be given to long span precast elements with narrow compression flanges during lifting. Spreader beams shall be used to reduce the spacing of the lifting points.
Fig 6.1 Spreader beam to reduce span
6.2 CONTINUOUS PRECAST CONSTRUCTION
In this type of structure, the precast elements have continuity at their joints and the lateral stability is provided by the precast elements themselves. The continuous precast elements may be in the form of shear walls or moment resisting frames. It is possible that a combination of the simple construction and continuous construction exist in a single structure.
6.2.1 Dismantling
The demolition of this type of structure may be performed in a way similar to that of a cast-in-place concrete construction provided that the continuous joints are cut in such a way that the lateral stability is maintained. If the precast elements are intended to be removed in a piece by piece manner in their reverse order of construction, the continuous joint shall be cut by appropriate pre-approved method such as saw cutting. The precast elements shall then be lifted off their support and lowered to the ground or to an adequately supported floor for demolition. Temporary bracing during lifting may be required.the position of reinforcement needs to be considered in fixing the points of lift.
6.3 STEEL STRUCTURES
Steel structures are, in most cases, designed as “simple design” or “semi-rigid design” according to earlier structural steel design codes. Under such design assumptions, the detailing of the beam column joints is, in most cases, not rigid joints and the structure may become statically determinate during demolition or substantial alteration. Failure of any member in a statically determinate structure leads to a sudden collapse and hence should be properly supported.
Similar to conventional buildings, composite structures may be demolished by top down method, cut and lift or other methods that are adequate for the site condition.
Structural steel members in steel structures and reinforced concrete composite structures are generally designed as slender members subject to bending and/or compression. Except for concrete encased steel members the Registered Structural Engineer shall check the load resisting capacity of the slender structural members when lateral restraints are removed during demolition. Proper shoring shall be installed if required. All structural steel members shall be lowered from the structure and shall not be allowed to drop.
6.4 TRUSSES
Trusses shall preferably be removed by lifting and lowering to ground level prior to demolition. In case when the truss has to be dismantled on the spot, the stability of every partially dismantled configuration shall be checked. When dismantling roof trusses,enough purlins and bracings should be retained to ensure stability of the remaining roof trusses while each individual truss is removed progressively. Temporary bracing should be added where necessary to maintain stability. The end frame opposite to the end, where dismantling is commenced should be independently and securely guyed in both directions before works starts. On no account should the bottom tie of roof trusses be cut until the principal rafters are prevented from making outward movement.
6.5 CLADDING WALLS
6.5.1 Demolition Method
Demolition of cladding walls shall be proceeded with extreme caution since cladding walls are mostly external features. Each cladding wall shall be demolished individually in the reverse order of its construction. Saw cut and lift is suitable for dismantling cladding walls.
6.5.2 Guidelines
(A) Support
The cladding wall shall be fully supported before disconnection from its supporting structural member. Crane or other lifting appliances may be used to support the total weight of the cladding. The lifting appliances and wire must have sufficient strength to support the weight of the cladding wall.
(B) Disconnecting from Building
The connections or joints to the building structure shall be disconnected only after the cladding wall is fully supported.
(C) Handling
Once the cladding wall is separated from the building frame, it may be lifted away and lowered onto the ground or adequately supported floor for further processing. Depending on the type of cladding, it may be reused as building materials or further broken down and transported away as construction debris.
6.6 HANGING STRUCTURES
6.6.1 General
The hanging structure is primarily composed of a structural system in which the floor loading is suspended by tension members hung from other elements at the upper portion of the structure. Unlike conventional structures, hanging structures shall be demolished from their bottom level and progressively upward to the support.
6.6.2 Demolition Method
Selection of methods shall depend on the actual site conditions and the construction materials. Cutting and lifting, in general, are suitable for dismantling the structural components of the hanging structure. Temporary supports may be needed to maintain the stability of the hanging structural elements during the demolition process.
6.6.3 Guidelines
The following items shall be considered in demolishing hanging structures:
· The sequence of demolition shall be planned such that the hanging loads are gradually reduced, without overstressing at any particular structural element or ties.
· Hanging ties shall be destressed before cutting
· Main gravity structures supporting the hanging ties and other elements that provide lateral stability of the hanging structure shall not be demolished prior to complete release of all hanging ties.
· The main gravity structure shall be checked so that it is stable at all stages of demolition, bracing may be required if deemed necessary.
· The sequence of demolition shall be planned such that the hanging loads are gradually reduced, without overstressing at any particular structural element or ties.
· Hanging ties shall be destressed before cutting
· Main gravity structures supporting the hanging ties and other elements that provide lateral stability of the hanging structure shall not be demolished prior to complete release of all hanging ties.
· The main gravity structure shall be checked so that it is stable at all stages of demolition, bracing may be required if deemed necessary.
6.7 OIL STORAGE FACILITIES
6.7.1 General
Oil storage facilities generally consist of structures that contain petroleum products which may be classified as hazardous materials or dangerous goods. The key issues for demolishing the oil storage facilities are the clean-up and disposal of the hazardous materials and dangerous goods. Once the contamination assessment and initial clean-up are completed, the method of demolition may be selected based on the structural and site conditions. Additional clean up may be required if the contamination has extended to the adjacent area and the subsurface soil. Precautionary measures and work systems to be adopted for working in such an environment shall comply with the factories and industrial undertakings (Confined spaces) Regulation.
6.7.2 Demolition Method
The selection of methods and actual demolition of oil storage structures shall be carried out in accordance with the structural aspects. Storage buildings may be demolished by top down method or other methods for building demolition. Circular steel tanks may be dismantled by the use of hydraulic shear or other appropriate methods. Reinforced concrete tanks may be dismantled by any method that is suitable for reinforced concrete construction. If flammable fuel is likely to be present, use of flame cutting shall be avoided.
6.7.3 Guidelines
The following items shall be considered in demolishing oil storage facilities:
(A) Chemical Waste
Clean up Prior to demolition, all oil storage facilities shall be thoroughly cleaned. Any accumulated gas shall be removed. The management of waste and wastewater generated from the process must conform with the Waste Disposal Ordinance and the Water Pollution Control Ordinance. Additionally, the management of any waste which is classifiable as a chemical waste, such as oil sludge from tank cleaning must also comply with the Waste Disposal (Chemical Waste) (General) Regulation. In the case when a dangerous goods storage licence has been issued, the relevant licensing authority, i.e. Fire Services Department, or Gas Standard Office, shall be informed prior to any demolition operation. Any risk of fire explosion and exposure to toxicity shall be minimised.
(B) Soil Contamination Assessment
After completion of demolition, Soil Contamination Assessment (SCA) shall be carried out according to the SCA and Clean-up proposal agreed by the EPD (Environmental Protection Department). In the case when soil contamination is discovered, the contaminated soil shall be removed in its entirety and replaced with clean fills. The placement of the fill shall be under the supervision of the Authorized Person or Registered Structural Engineer or an equivalent professional. The disposal of contaminated soil shall be carried out in strict accordance with the EPD requirements. In-situ treatment of the contaminant may be applied subject to the approval of the EPD.
(C) Handling of Contaminated Soil
Precautions must be taken during excavation and removal of the storage tank. The excavation and disposal of contaminated soil shall be handled with care and be in compliance with the EPD requirements. Special care shall be taken to confine the contamination. Protection of the surrounding properties to provide a safe support for any below ground works shall be considered.
6.8 MARINE STRUCTURES
6.8.1 General
Marine structures include ocean structures and all kinds of water front structures. Besides the basic considerations for normal land operation, marine demolition shall also attend to the debris handling and the dismantling of the marine piles.
6.8.2 Demolition Method
The methods used for demolishing marine structures are similar to those for buildings founded on land. Top down methods may be applied to demolish the superstructure. Non-explosive demolition agent may be used to demolish the piers. For sensitive water, saw cut and lift can be used to demolish the platform and the piers to minimise debris falling into water.
6.8.3 Guidelines
(A) Soundings
Soundings shall be performed before the demolition so that the seabed condition is defined and any unanticipated underwater structure can be reviewed. The pre-demolition sounding record shall be used as a basis for the scope of restoration.
(B) Pier Structure
If mechanical plants and/or trucks will travel on the platform supported by piers, the structure of the platform slab shall be checked to ensure that it can support the machine operation and the anticipated debris loading.
(C) Protection of Marine Environment
The effect of the demolition on the marine environment shall be considered. If the demolition site is scheduled to be reclaimed, concrete debris may be left on the seabed. Otherwise, all the debris dropped on the seabed during demolition must be removed. The seabed shall be restored to the comparable depth of the pre-demolition stage. A silt screen or underwater fence shall encompass the site to contain debris and turbulence generated by the demolition. The silt screen shall be taken out after the area is completely restored.
(D) Piling
As far as practicable, piling shall be pulled out entirely, or, as a minimum, it shall be cut off at 3m below the seabed or a desirable depth below the original seabed level, depending on the future use of the area.
6.9 UNDERGROUND STRUCTURES
6.9.1 General
From the operational and economic standpoints, demolition of underground structure shall be incorporated into the new foundation construction. Such arrangement 37 may eliminate the redundancy of the temporary works for soil retention and dewatering systems.
6.9.2 Demolition Method
With appropriate shoring and protection, underground structures above the basement floor may be demolished by top down methods or other methods that are suitable for the specific site conditions. The use of non-explosive demolition agents may minimise vibration impact on the adjacent foundation. Diamond core stitch drilling is suitable for cutting localised underground obstructions such as an old pile cap without completely demolishing the whole pile cap.
6.9.3 Guidelines
(A) Overall Stability
During the course of demolition, the stability of the building under demolition and any remaining parts of it shall be maintained at all times. In high water table areas, assessment shall be made to ensure that the remaining structure will have adequate factor of safety against uplift upon demolition at all stages. If necessary, the uplift pressure acting on the basement structure shall be relieved before demolishing the structure.
(B) Shoring
A geotechnical evaluation shall be conducted to determine the soil stabilisation and retaining schemes for protection of the adjacent properties as well as the operation of the below ground demolition. The shoring plan shall be taken into account of the construction method to the original underground structure. If the floors or part of the building structure acts as propping to the basement wall, this propping system shall be maintained or a shoring system shall be provided to safely support the basement wall when demolishing the building structure.
(C) Dewatering
If a dewatering system is required, the effect of the dewatering on adjacent buildings, structures, land, street and services must be considered in the design. It is also important that the disposal of the ground water shall not affect the quality of the surrounding water resource and/or cause localised flooding.
(D) Existing Foundation
The existing piles shall be evaluated and, if possible, incorporated into the new foundation system. The bearing capacity of the old foundation can be determined by reviewing the previous design and by performing actual load tests and/or test borings.
(E) Site Security and Safety
The site shall be secured to prevent any unauthorized person from entry, particularly into the basement area. If work is to be performed in deep excavated area, an escape route must be provided.
6.10 STRUCTURES SUPPORTING GROUND OR SITTING ON SLOPES
6.10.1 General
Demolition of buildings or structures supporting land or slopes; or buildings or structures sitting on slopes or retaining walls may affect the stability of adjacent buildings, structures and land and may even create regional slope instability due to removal of toe weight. Maintaining adequate ground support by backfilling or structural support during demolition work is important. The demolition plan should be properly engineered by a competent and experienced geotechnical engineer.
6.10.2 Demolition method
Top down method is suitable for demolition of hillside slope structures. Other methods may be applicable depending on the actual site conditions.
6.10.3 Guidelines
(A) Buttress/Shoring for Building Supporting Ground
If part of the building structure serves as a retaining wall system, the height of the building that is required to be left in order to safely support the retaining structure shall be determined. Adequate shoring and/or buttress shall be provided prior to the demolition of the remaining structure. A demolition plan shall be provided to the foundation contractor so that the shoring work installed during demolition are considered and protected during the foundation work.
(B) Retaining Wall System
Prior to demolition of the retaining wall, the slope or land supported by the retaining wall system must first be stabilised. Stabilisation may be achieved by excavation of the soil behind the retaining wall to a free standing stable slope or by installing temporary or permanent support such as sheet piling, soldier pile, soil nails or other appropriate methods. The scheme for stabilisation of the slope or land behind the retaining wall shall be properly engineered.
(C) On-grade Floor Slab
Unless site conditions allow and with the support of an engineering report, the ongrade floor slabs shall remain to protect against erosion. The floor slabs can also serve as impermeable cover against infiltration.
(D) Surcharge on Slope and Retaining Wall
No storage of debris or surcharge shall be imposed on the area behind or on the top of the retaining wall and/or slope. Surcharge on the top of the retaining wall and/or slope may affect its stability.
(E) Drainage
The water table may affect the stability of the slope. Drainage from surface runoff, off site drainage and infiltration shall be considered and managed throughout the project. Existing subsoil slope drainage system should also be maintained.
7. DEMOLITION WASTE
According to the survey based on the Swachh Bharat program, with rapid urbanization the quantum of construction & demolition waste (C&D Waste) is constantly increasing. While it is estimated that the construction industry in India generates about 10- 12 million tons of Construction and Demolition (C&D) waste annually, efforts to manage and utilize this waste is very little. This has led to Private contractors utilising unscientific dumping methods there-by putting severe pressure on scarce urban land as well as reducing life spans of landfills.
The 245,000+ strong “Swachh Bharat” online community has come together to collectively identify the key issues, root causes and solutions for Construction and 40 Demolition Waste in India and the community expects that the Government will work with urban local bodies towards implementing the identified solutions.
7.1 ISSUES IDENTIFIED
1. In most cities, there is no permanent site for C&D waste collection
2. Many times, C&D waste is dumped on open roads and outside sites
3. The wastes generates huge air pollution and also makes the areas dirty
4. This turns into a garbage dump in a few days
5. Open canals are choked with C&D waste material dumped in
6. C&D waste blocks roads and pathways making commuting difficult
7. Waste material is not cleared for days causing problems for neighbours
8. These materials are carried in open vehicles which drops debris on the way
9. This waste leads to collection of water during rains 10. Municipality does not pay much attention to this issue even after complaints.
7.2 ROOT CAUSES IDENTIFIED
1. This has never been an area of priority for the Government
2. Lack of vigilance by municipal departments
3. Lack of a concrete law for disposing construction and demolition waste
4. No strict mandate for vehicles carrying the c & d waste
5. People are unaware of what to do with this waste
6. No fines for offenders
7. People caught discarding construction waste on the roads are let off easily
8. No helpline to complaint about this problem
9. Too much corruption in the regulating authorities
10. No way of recycling the construction waste
11. Clear C&D waste disposal guidelines not issued to builders by municipalities
7.3 WASTE GENERATION IN CONSTRUCTION INDUSTRY
All over the world, the growth of construction industry is enormous in the past decade. The pace of generation of C&D waste is also significant. In general, there are two sources for generation of waste materials, namely, bulk generators and retail or small generators. The classification of sources is given in Fig 7.1. The infrastructure development sector and real estate sector are the bulk generators of waste. Construction and repair of roads, bridges, flyovers etc. are classified under infrastructure development sector. Real estate sector consists of housing, industrial, and commercial building construction, demolition of unauthorized structures etc. Small commercial enterprises and individual house building teams are considered as retail or small generators. The contributors of C&D waste in a project are given in Fig 7.2. The project activities are to be planned at every stage by every personnel, who are involved, to minimize the overall waste generation.
Fig. 7.2 Contributors of C& D waste in a project
7.4 SOLUTIONS IDENTIFIED
1. Municipal Corporations, Municipalities/Panchayats should frame Rules & Regulations for C&D Waste
2. Civic Bodies should provide a facility for collection and disposal of C&D waste and charge a reasonable amount for the same
3. Civic Bodies can also charge builders/contractors who are willing to buy C&D waste for construction purposes
4. A collection center should be established and managed by the municipality for construction and demolition waste in each town/ village
5. A separate department in the municipal bodies should be created for addressing the issue of collecting and disposal of this waste
6. C & D recycling units should be set up in every town and state
7. Civic Bodies can recycle/reuse C&D Waste for filling of low lying areas and construction of Roads etc.
8. A law pronouncing the disposal of C & D waste should be made
9. C&D permit grants must have terms for removal of waste
10. Severe penalties must be imposed if waste removal guidelines are violated
11. Awareness among the builders and contractors should be increased
12. Private entities setting up C & D recycling units should be given tax breaks
13. Demolition permit itself can have a clause for waste recycling
7.5 PRESENT PRACTICES OF WASTE DISPOSAL
The common treatment methods of C&D waste are given in Fig 7.3. Among the various approaches, the manual separation is highly labour oriented and the mechanical separation requires costly installations. The present waste handling practices adopted by the construction industry in India at different levels are:-
· Items recovered during construction /demolition is sold in the market at a discount rates
· The feasibility of recycling is not even considered seriously in most cases. Items that cannot be re-used are used for filling the land.
· Landfill tax is not imposed by the municipality.
· The waste is disposed without segregation.
· No penal action is taken against violators.
Fig. 7.3 C&D waste treatment methods
7.6 THE ‘3R’ CONCEPT
Until last two decades, landfill was considered as the cheapest and convenient method of C&D waste disposal. But land filling is considered to be undesirable due to environmental and ecosystem hazards. Now most of the landfills are at the verge of arriving at its full capacity. Hence, more valuable lands may have to be employed in the future, which increase cost for C&D waste disposal.
7.6.1 Reduce
Potential wastes can be identified early in the design process itself and measures should be taken during design stage to minimize the waste that may generate. Waste reduction can be achieved by design with standard sizes for all building materials, design spaces to be flexible and adaptable to changing uses and design for deconstruction.
7.6.2 Reuse
This involves identification of waste that can be salvaged for reuse on the current project or another project or that can be donated. A comparison of the value of the materials “as it is” for salvage and to their value as materials for recycling may be considered prior to reuse in many cases. Some of these materials may be valuable to reuse on-site; others may be sold to be used building material in another site or donated to a charitable organization
7.6.3 Recycle
After adopting all the options to prevent waste, salvage and reuse materials, the next step is to recycle as much of the remaining debris as possible. Recycling saves money by minimizing disposal costs.
8. CONCLUSION
Any type of building to be demolished, its method depends upon various factors such as site condition, type of structures, age of building, height of building and economy and most important its location with presence of its surrounding with its structural stability. Controlled demolition of building is necessary to ensure safety of both the workers and the surroundings so as to cause least amount of injuries and accidents. Explosive demolition is the most preferred method for safely and efficiently demolishing the larger structures which requires a very high precision. The exploitation of potential resources from construction and demolition (C&D) wastes is yet another opportunity and future profession in the construction industry in India. Waste minimization and waste management programs are in its infancy in India. It is possible to minimize the volume of C&D waste generated by identifying the potential waste early in the design. But even with proper resource-efficient design and by adopting proper construction and deconstruction procedure, some waste may essentially be generated in every project. The plan should also target for waste diversion and recycling through implementation of new policies, information technologies, awareness and waste management facilities. Reduce, Reuse and Recycle [3R’s] should be adopted to minimize C & D waste.
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