Demolition techniques

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1 Demolition techniques Autor(en): Objekttyp: Molin, Chister Article Zeitschrift: IABSE congress report = Rapport du congrès AIPC = IVBH Kongressbericht Band (Jahr): 15 (1996) PDF erstellt am: Persistenter Link: Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. Das Veröffentlichen von Bildern in Print- und Online-Publikationen ist nur mit vorheriger Genehmigung der Rechteinhaber erlaubt. Die systematische Speicherung von Teilen des elektronischen Angebots auf anderen Servern bedarf ebenfalls des schriftlichen Einverständnisses der Rechteinhaber. Haftungsausschluss Alle Angaben erfolgen ohne Gewähr für Vollständigkeit oder Richtigkeit. Es wird keine Haftung übernommen für Schäden durch die Verwendung von Informationen aus diesem Online-Angebot oder durch das Fehlen von Informationen. Dies gilt auch für Inhalte Dritter, die über dieses Angebot zugänglich sind. Ein Dienst der ETH-Bibliothek ETH Zürich, Rämistrasse 101, 8092 Zürich, Schweiz,

2 473 DemoUtion thechniques Chister MOLIN D.Sc. Civil Engineer Eur Ing Stockholm Sweden Christer Molin, bom 1944, earned his B.Sc and D. Sc. degree at the Royal Institute oftechnology, Stockholm. He has worked as a structural engineer, project leader at the Cement and Concrete Research Institute, head ofa department of National Testing Instituteand K&D manager of a manufacturing Company. He is now a Consultant in concrete technology. Summary The main target in this paper is concrete demolition techniques. Economy and impact on environment are considered. Common techniques for total demolition like the use of rock-bucket, steel ball, demolition hammer, crushing jaw and blasting are presented. there are even more techniques used for partial demolition e g diamond drilling and sawing, bursting, waterjet and miniblasting. Demolition cause many environmental problems, which must be considered when choosing demolition techniques. The future demolition need more planning, selectivity, precrushing and quality assessment. 1. Introduction Li many countries in developed world new construction is not done on virgin land. Demolition of an old building or structure has to be carried out first or the owner choose to refurbish the building, which often means partial demolition of structural elements. What we realize is that building activity Starts with demolition. This of course gives us a good opportunity to recycle or reuse at least crusched material. The owner, the designer and contractor have to consider the old building, the demolishing process giving maximized reuse and minimized waste. In this context demolition techniques become more important as an integrated part ofthe construction procedure. 2. Classification of demolition methods According to Kasai et al/1988/ are demolition methods classified into principles and mechanisms of breaking. In this presentation common or interesting methods are shortly described and classified according to type of impact on the concrete.

3 474 DEMOLITION TECHNIQUES 2.1 Simple demolition methods The demolition tools are different types of buckets, demolition boom and elephant tusk. They are mainly used to demolish masonry buildings but can also be used for concrete. These types of equipments are mounted on a hydraulic excavator. 2.2 Hammering Repeated hammering is often used to fracture and break concrete mainly due to acurring tensile and shear stress. There are three levels of hammering: - Stone chisel. It is operated by manpower and is not in use any more for concrete demolition. - Hand-held breaker. There are three types of breakers - pneumatic, hydraulic or electric driven. The first type is relatively light and small but noisy compared with the second type. Both need extra equipment but this is not needed for the third alternative. Electrical breakers are less efficient and heavy. - Impact hammer on a carrier. This machine is manufactured in different sizes and strength from huge ones to small light ones, which can be operated on floor and travel through doors. The hydraulic type is most common, they can be remote controlled. 2.3 Hitting This is a common method for total demolition. To demolish concrete elements a steel ball with a weight of 0,5-2,0 ton is either dropped on the element or swung into it. This method demands however a great deal of skill from the crane Operator. The concrete element can after several hits be demolished in small pieces, although the reinforcement has to be eut afterwards. The method can of course be dangerous, especially when tall cranes have to be used. The process also causes considerable dust and Vibration, which is not acceptable in heavily built up areas. 2.4 Crushing A C-shaped frame or a strong jaw is either suspended or mounted on top ofthe arm ofan excavator. This type of demolition equipment was developed i Japan. There are many different variations of demolition equipment, which can eut, break or pulverize reinforced concrete elements of most sizes and degree of reinforcements. The jaws are quite efficient, silent, cause little dust and no Vibration. Accordingly the jaws are well suited for concrete demolition in residential areas. 2.5 Abrasion There are different demolition machines based on abrasion e.g. diamond drilling, sawing, wire sawing and water jet. - Diamond drilling. The drilling device is always mounted on a stand. The holes, mm in diameter, is produced with considerable accuracy. The drills are driven by pneumatic, hydraulic or electrical power. Medium and heavy drilling Operations are carried out only with vehicle mounted drills. When the holes are drilled side by side, the method can be used for demolition, however, not very effeciently but the method is veiy useful when refurbishing buildings. It is a necessity to cool with water. The noise level is very high and and ofa high frequency.

4 C. MOLIN Diamond sawing. In principle see drilling. Sawing with a disc (maximum 1000 mm diameter) can also be interesting for total demolition when demounting elements of a concrete building or a structure. There are also special carriers for sawing, especially in Japan. The elements can be used for a new building, hopefuuy for the same purpose as they were used for. The need for making good is very small. - Diamond wire. A loop wire saw with diamond bits can eut around the circumference ofa concrete section. It is mostly used for cutting in rocks but can also be used for massive concrete structures. - jet. This method is usually applicable for demolishing damaged surfaces. A high-pressure jet of water passes across the surface, penetrating into the weak concrete. When the water washes away, it takes the damaged concrete with it. Instead of digging to the same depth throughout, it only removes concrete down to a preset quality depth. The method is very suitable for high quality repairs i.e. for bridges, airport runways etc. Mostly, the equipment is mounted on a carrier, but it can be hand-held for small surfaces. The noise level is very high, also the water jet has to be handled with great care, especially if hand-held. 2.6 Bursting Concrete and rock can be split by a bursting force in a predrilled hole. - Hydraulic bursters. Two forms of such equipment are commonly used. The plunger burster consists ofa central cylinder down the side of which a series of pistons are forced out. The wedge burster consists ofa steel wedge, which is retracted under hydraulic pressure. In either case the bursters are often used in multiple arrangements fed from a common hydraulic power supply. - Chemical expansive agent. Unslaked lime composite is mixed or absorbed with water and injeeted or poured into a predrilled small hole. The bursting effect takes from some hours up to a day. There are no problems with dust, noise or Vibration when bursting except for the predrilling procedure. 2.7 Blasting The use of explosives on demolition sites should be looked upon as the application ofa controlled high energy force. The Operation has to be carried out by fully experienced personnel, who are licensed. In most countries blasting on sites is covered by regulations. For the demolition of concrete structures it is usual to drill holes obliquely into concrete to be removed at predetermined positions. The holes are then charged with explosives which are electrically detonated in intervals. Compared with other methods, the use of explosive on large and tall structures may show considerable financial savings. The disadvantages are excessive ground Vibration which may damage adjacent structures and air blast may cause superficial damage elsewhere. Precautions should taken to stop flying debris. Blasting can also be feasible for retrofitting reinforced concrete structures i.e. cutting piles, beams and making openings in slabs and thick walls. 2.8 Melting Concrete and rebars are melted by the heat of combustion of metal or organic fuel, plasma and laser beam. Only the first mentioned type, the theraiic lance method, is commerciauy availably.

5 476 DEMOLITION TECHNIQUES Aluminium or iron auoy wires are enclosed in a metal pipe of rather small diameter. The combustion of oxygen and metall melts concrete and rebars. The method is noisy and special precautions have to be taken agains fire and smoke. Laser beam could be a method for the future. Today complex and huge equipment are needed. A carbon dioxide laser beam of very high energy melt and eut concrete including the rebars. 2.9 Spalling Concrete cover is spalled by heating rebars electrically with very high current, which means that the rebars expand and cause tensile stress in the concrete. The method has been studied for nuclear reactors in Japan. 3. Evaluation of main demolition methods The evaluation of demolition method is described in Fig. 1. Table-1. There are also other factors influencing the evaluation, like the need of prework, size of demolished materials and second demolition. Other factors are type of structure, structural member, demolition ränge etc. 4. Demolition of complex structures This category may include continuous forms of construction, multi-storey structures and prestressed concrete members. Post-tensioned structures may contain many cäbles which have been stressed progressively during the additional spans or further storeys and superimposed dead load. Other special structures that have been stressed in two or three directions would all be considered in this group. It is essential that the design and construction in formation is known, in order that the temporary works and cable cutting procedures can be properly designed. An accidental collapse in part ofa semi-demolished structure could lead to a progressive failure, if the inter-dependence between spans and component parts is not fully understood. In post-tensioned concrete structures, the final order of load removal and cable cutting may only be determined, after checks have been made on the stability and local stresses at intermediate stages in the demolition. It is essential that more effort will be devoted to educate structural engineers as well as demolition contractors in the specialized precautions and techniques required for the safe removal of modern complex structures. 5. Selective demolition Today it is common to mix concrete and other materials on the demolishing site. This rubble Ls not easy to handle, transport or separate. The cost of getting rid of this unsorted rubble is increasing. The demolished concrete can, however, be used for many purposes e.g. as aggregate in fresh concrete, road struetureand filling material. It can also be eut in elements and recycled.

6 C. MOLIN 477 The main idea should be to demount and demolish step by step. The concrete structure is demolished when all installations and other materials have been removed. If possible, whole concrete elements can be demounted or sawn out. However, usuauy the concrete has to be fragmented when choosing a feasible method. Fraction size and quality should be considered. A clean dense, well-distributed fraction with the right size can in many cases replace virgin gravel. 6. Conclusions and comments The real improvement of demolition techniques took place, when building market changed from almost only new constructions to more refurbishing ones. Specialized equipment were developed for the alteration of concrete structures. Diamond drilling and sawing replaced hand-held breaking. The first tau buildings were taken by controlled blasting and miniblasting was introduced for partial demolition. Somewhat later water jet was found feasible for prcparing surfaces to be repaired. The introduction some years ago of crushing and cutting attachments speeifieally designed for today's demolition have made the Standard hydraulic excavater one ofthe most useful pieces of equipment which a contractor can have. The development can be characterised by mechanization, increased mobility and many meassure taken for the working environement. But the next very important step is the consideration ofthe total environement. Therefore, the future demolition need more planning, less transports, selectivity, precrushing, sorting and crushing plants and quality assessment. All these requirements for the future will very much change the way the contractor works and also change the demolition techniques he will use. 7. References - EDA. Demolition Techniques European Demolition Association. Rilem Committee DRC 37, Task Force 1. Den Haag FIP. Guide to good practice. Demolition of reinforced and prestressed concrete structures, Wexham Springs, Slough Ingvarsson H and Eriksson B. Hydrodemolition for bridge repairs. Vägverket Publ 1988:16, Borlänge Kasai Y et al. Outline of varous demolition methods and theil- evaluation. Proceedings ofthe Second International Rilem Symposium, volym one, Tokyo. Chapman and Hall Lauritzen E.K., Jakobsen J B. Nedrivning af byggninger og anlaegskonstruktioner. SBI-anvisning 171. Statens Byggcforskningsinstitut, Hoersholm Lindseil P. Demolition procedures. Seminar Modem Demolition and Explosives, O.xford. The Institute of Demolition Engineers Molin C. Ombyggnadsrivning i betong. Cement- och Betonginstitutet, CBI Informcrar 3.86, Stockholm 1986.

7 Fig 1. Table-1. Evaluation of main demolition methods - Nuisance, security measures and performance Demolition methods Noise Nuisance Vibla tion (X) Heat - Fire Security Measures (X) Environ- Fume mental Projection protection Perfor mances (X) Hazards tothe worker Execu tion rapidity Cost Remarks Hand-held breaker proof mask, glasses, ear defenders, vibrationproof, gloves and safely band are needed. - Need a working stage. Impact hammer on a camer Noise and dust insulation fence are required according to demand. - Rigid working floor is required. Steel ball Pro Prohibited to entry into the working area. - Taking care of hitting wrongly. - Not to over-turn the crane. Crashing jaw on an excavater Pro Taking care of failing materials. - Rigid working floor slab is required. - Widely used in urban centre. Diamond drilling Drill holes along a cutting line. Diamond sawing Crane is needed to suspend eut materials. Diamond wire saw Same as mentioned in "Diamond sawing". - Protection is needed in case the wire saw snaps. (X) In increasing order of number, it shows from favourable to very unfavourable for this item.

8 Continue Fig. 1. Table-1 Demolition methods Nuisance (1) Security Performeasures (1) mances (1) Heat Environ- Hazards Execumental tothe tion Noise Vibla- Fire Fume Cost Remarks tion Projection protection worker rapidity jet Burster with wedges Chemical expensive agent 2 Drilling 2 Drilling Blasting Pro Pro. 5 - Protection is needed for water jet. - Wear ear defenders. - No crossing a water jel 4 - Noise and dust are generated while drilling, otherwise noiseless and vibratiorüess. 4 - Same as mentioned in "Burster with wedges". - Wear protective glasses, never watch a charged hole from uprigh position. 1 - A blast fence is needed at blasting time. - Rigid safety precautions and licensed personal needed. Thermic lance Fume 4 Fire 5 - Effect of fumes and fire prevention are needed. Electrical heatins of rebar Heat - Noise and dust or spray are generated during exposure of rebar and removal work, otherwise no noise and no Vibration. - Developing for use in demolition of atomic power plants. (1) In increasing order of number, it shows from favourable to very unfavourable for this item.

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