US3580637A - Method of destroying ferroconcrete, rock or the like - Google Patents

Method of destroying ferroconcrete, rock or the like Download PDF

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Publication number
US3580637A
US3580637A US766262A US3580637DA US3580637A US 3580637 A US3580637 A US 3580637A US 766262 A US766262 A US 766262A US 3580637D A US3580637D A US 3580637DA US 3580637 A US3580637 A US 3580637A
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Prior art keywords
concrete
current
frequency
iron
ferroconcrete
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Expired - Lifetime
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US766262A
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English (en)
Inventor
Yoshishige Itoh
Masatada Kawamura
Yoshio Kasai
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Fujimotors Inc
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Fujimotors Inc
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21C—MINING OR QUARRYING
    • E21C37/00—Other methods or devices for dislodging with or without loading
    • E21C37/18—Other methods or devices for dislodging with or without loading by electricity

Definitions

  • This invention relates to method of destroying ferroconcrete bodies, and more particularly to electrical method of destroying these bodies.
  • ferroconcrete body when an iron bar of 9 mm. diam. buried in a ferroconcrete rectangular body of l 20 cm. sectional area and 100 cm. long at about 3 cm. from its surface is connected through conductor wires to an electric source, and an electric current of 10 V. is applied to this circuit, said ferroconcrete body will be destroyed by cracking.
  • the temperature of the buried iron bar becomes 800 to 1000" C. in a few minutes by its electric resistance and thermal expansion in said bar is produced in radial and longitudinal directions.
  • the rage of thermal expansion of iron is about 0.0000l3/l C.
  • the length of a 100 cm. long iron bar becomes approx. 101.3 cm.
  • the diameter of the iron bar having) mm. diam. becomes approx. 9.12 mm.
  • the heat conductivity of concrete is 1.2- l.3 Kcal/m.h. C. at open air drying, which is about 1/30- -l/40 of iron, even when the temperature in the iron bar rapidly increases, the temperature increase in concrete is limited to the portion around the iron bar.
  • ferroconcrete structure As a ferroconcrete structure is substantially unitary body because of the adhesion between the iron bar and its surrounding concrete, it is very difiicult to destroy the structure by applying a mechanical force such as impact or the like, but when the adhesion between the iron bar and the concrete has been decreased or eliminated with and cracking occurring at some portions in concrete, it then becomes very easy to destroy the said structure by applying mechanical energy.
  • iron and steel conductor I massive application of current is required for heating an iron bar or steel-frame structure (hereinafter referred to as iron and steel conductor) with the increase in the sectional area of said iron bar or steelframe structure to be applied with electric current. As the result, the following problems occur.
  • the present inventors have conducted experiments, and, as the result, found that with an increase in thefrequency the temperature of the iron and steel conductor rapidly increases. More particularly, the present inventors have confirmed that the current flows close to the surface of the iron and steel conductor by the skin effect, and, as the result, the equivalent electric resistance of said conductor increasesand the Joule loss thereof due to the same current increases and therefore a current having far less value than in the case of commercial frequency is sufficient to obtain the same increase in the temperature.
  • One of the prime objects and characteristics of the present invention is to apply electric current to a conductor buried in advance in a concrete body to reduce the strength of the ferroconcrete body owing to thermal expansion of the iron and steel conductor and decrease or eliminate adhesion of the concrete to the conductor. As the result, it becomes very easy to destroy said bodies by applying a form of mechanical ener- 8)"
  • Another characteristic of the present invention is to apply electric current of higher frequency than commercial frequency of 50 to 60 c/s. to the buried conductor to make a higher temperature rise with far less quantity by utilizing the skin effect of electric current. As the result, the above mentioned connecting apparatus to carry a large quantity of electric current can be eliminated, and furthermore, economical profit may arise from the decrease of electric charge.
  • FIG. 1 is a diagram showing the relation between the frequency and the current invasion depth in the case of a flowing current to an iron and steel'conductor having circular section.
  • FIG. 2 is a diagram showing one embodiment of a device used in the experiment of the present invention.
  • FIGS. 3 to 5 are diagrams respectively showing embodiments of the results of the experiments.
  • FIGS. 6 and 7 are diagrams respectively showing embodiments of results of other experiments.
  • FIG. 8 is a diagram showing the relation between temperature change at some portions in the concrete and heating time when an iron bar buried in the said concrete is heated by electric current.
  • FIG. 9 is a diagram showing the temperature distribution in the case of FIG. 8.
  • FIG. 10 is a diagram showing the temperature distribution in the case where the iron bar is heated more rapidly than in the case of FIG. 9.
  • FIG. I1 is a diagram showing the stress distribution in the case of FIG. 9and FIG. 10.
  • FIG. 1 is a graphical representation showing the relation between the frequency f and the current invasion depth 8 in the case of flowing the current to the iron and steel conductor of circular section using permeability p. as a parameter.
  • the following formula can be established.
  • FIG. 2 shows one example of an experiment device used in the present invention.
  • Reference numeral 1 designates a DC motor, 2, an induction frequency converter, 3, an autotransformer, 4, a transformer for heating, and 5, an iron bar for heating experiment. More particularly, the frequency is converted by the induction frequency converter 2 and introduced into the autotransformer 3, thus the secondary side voltage of the transformer for heating being controlled.
  • the iron and steel conductor 5 was heated in air within the windless chamber. The heating temperature was measured by contacting copper with constantan. Also, with respect to the flowing current of the iron and steel conductor 5 the induction voltage of search coil was measured by a vacuum tube voltmeter.
  • FIGS. 3 to 5 The results are shown in FIGS. 3 to 5.
  • the vertical axis shows the temperatureof the iron and steel conducv tor (C), and the transverse axis shows the flowing current time (minute).
  • FIG. 3 shows'the case of heating a round steel bar (nominal diameter: 9 mm.)
  • FIG. 4 the case of heating a round steel bar (nominal diameter: l9 mm.). In these cases, comparing the temperature 2 minutes after the commencement of flowing current in cases of 200 c/s.
  • FIG. 5 shows the case of heating an equilateral an'gle steel (nominal dimension: 40x40 X5). About the same tendency as the foregoing can be recognized.
  • FIG. 6 indicates the relation between the current and the drawing 16 1 Rdc shown by dotted line indicates the DC re-' sistance of an iron bar having a diameter of 16 mm. and is shown for comparisons sake. Compared with this, the impedance is indicated about 4.2 times at the value of 300 A. and about 3.3 times at the value more than 700 A. even in the case of frequency 50'c/s. Further, power factor on this occasion showed a value of about 0.95.
  • FIG. 7 shows the results of an experiment carried out by using a relatively small current at the frequency 200 c/s. It can be inferred from this that with the increase in the frequency the skin effect is increased further.
  • FIG. 8 shows the relation between temperature change at some portion in the concrete and heating time when an iron bar of 16 mm. diam. buried in the concrete is heated by applying electric current of a constant electric power.
  • the temperature was measured by a copper-constantan instrument previously buriedin the concrete at a distance of d cm. from the surface of the iron bar.
  • the temperature in the concrete does not exceed 100 C. which is understandable from the fact that the moisture, which is always contained in any quality of concrete, takes evaporation heat from the concrete.
  • FIG. 9 is a diagram showing the temperature distribution in the case of FIGS. 9 and I0.
  • the stress was estimat ed from the stress caused by thermal expansion of the II'OI'I bar considerating the displacement of concrete by thermal expansion and from the thermal expansion stress of concrete itself.
  • the curve A shows the stress distribution in the case of FIG. 9 at 2 minutes after applying electric current; curve B shows the same at 5 minutes after; curve C shows the stress distribution in the case of FIG. 10 at 2 minutes after applying electric current.
  • the tensile strength of concrete is 50 Kg/cmF
  • the cracking stress exits at 4.7 mm. from the center at curve A, but the cracking stress reaches to the cylinder surface at curve C in the same heating time with curve A.
  • the frequency of current employed is increased whereby the current value for causing the temperature rise is decreased by utilizing the skin effect to make it easily adapted to the spot operation. It is preferably to select the frequency between 100 to 500 c/s. With the progress in electric equipments it is possible to use a current of approximately 10,000 c/s., whereby it may be more effective.
  • the portion to be heated as the result of skin effect is limited to a portion close to the surface, the iron and steel conductor to be buried later for destruction is not always a core body and it is also possible to use a tubular body in the present invention.
  • the method of destroying a ferroconcrete body formed of a concrete mass having metal reinforcements embedded therein comprising the application of an alternating electric current directly to the metal reinforcement, applying said current for. a sufficient time to heat said metal reinforcements to produce a thermal expansion of said reinforcements thereby cracking the surrounding concrete and substantially reducing the adhesion between the metal reinforcements and the concrete.

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  • Engineering & Computer Science (AREA)
  • Mining & Mineral Resources (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Geology (AREA)
  • Working Measures On Existing Buildindgs (AREA)
  • Drilling And Exploitation, And Mining Machines And Methods (AREA)
US766262A 1967-10-21 1968-10-09 Method of destroying ferroconcrete, rock or the like Expired - Lifetime US3580637A (en)

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JP6750367 1967-10-21

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US (1) US3580637A (cg-RX-API-DMAC7.html)
DE (1) DE1804310A1 (cg-RX-API-DMAC7.html)
FR (1) FR1587983A (cg-RX-API-DMAC7.html)
GB (1) GB1240185A (cg-RX-API-DMAC7.html)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3727982A (en) * 1970-03-20 1973-04-17 Fuji Motors Corp Method of electrically destroying concrete and/or mortar and device therefor
US20120018550A1 (en) * 2008-12-08 2012-01-26 Christopher Geoffrey Goodes Method and apparatus for reducing the size of materials
US9649780B1 (en) 2014-05-15 2017-05-16 United States Of America As Represented By The Administrator Of National Aeronautics And Space Administration Shape memory alloy rock splitters (SMARS)
CN112430014A (zh) * 2020-10-29 2021-03-02 昆明华城兴建材有限公司 一种增强纤维水泥防爆墙及其生产工艺

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3411412A1 (de) * 1984-03-28 1985-10-03 Johannes 5466 Neustadt Schützeichel Verfahren zum zerstoeren von bewehrten betonkoerpern u.dgl.
GB2209791A (en) * 1987-08-11 1989-05-24 Robin John Tollast Removal of forces in pre-tensioned or cost tensioned tendons in concrete prior to demolition

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1719257A (en) * 1926-05-17 1929-07-02 John C Booth Process for splitting granite, marble, and other rocks
GB933744A (en) * 1960-12-28 1963-08-14 Commissariat Energie Atomique Method for the destruction of compact masses
US3144545A (en) * 1962-03-26 1964-08-11 Heated Concrete Products Inc Heating assembly
US3208674A (en) * 1961-10-19 1965-09-28 Gen Electric Electrothermal fragmentation
US3223825A (en) * 1958-03-21 1965-12-14 Chester I Williams Electric grid floor heating system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1719257A (en) * 1926-05-17 1929-07-02 John C Booth Process for splitting granite, marble, and other rocks
US3223825A (en) * 1958-03-21 1965-12-14 Chester I Williams Electric grid floor heating system
GB933744A (en) * 1960-12-28 1963-08-14 Commissariat Energie Atomique Method for the destruction of compact masses
US3208674A (en) * 1961-10-19 1965-09-28 Gen Electric Electrothermal fragmentation
US3144545A (en) * 1962-03-26 1964-08-11 Heated Concrete Products Inc Heating assembly

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3727982A (en) * 1970-03-20 1973-04-17 Fuji Motors Corp Method of electrically destroying concrete and/or mortar and device therefor
US20120018550A1 (en) * 2008-12-08 2012-01-26 Christopher Geoffrey Goodes Method and apparatus for reducing the size of materials
US8840051B2 (en) * 2008-12-08 2014-09-23 Technological Resources Pty. Limited Method and apparatus for reducing the size of materials
US9649780B1 (en) 2014-05-15 2017-05-16 United States Of America As Represented By The Administrator Of National Aeronautics And Space Administration Shape memory alloy rock splitters (SMARS)
US10675781B1 (en) 2014-05-15 2020-06-09 United States Of America As Represented By The Administrator Of National Aeronautics And Space Administration Shape memory alloy rock splitters (SMARS)
CN112430014A (zh) * 2020-10-29 2021-03-02 昆明华城兴建材有限公司 一种增强纤维水泥防爆墙及其生产工艺

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Publication number Publication date
DE1804310A1 (de) 1969-08-07
FR1587983A (cg-RX-API-DMAC7.html) 1970-04-03
GB1240185A (en) 1971-07-21

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