JP7810343B2 - Reinforced concrete structure demolition system and demolition method - Google Patents

Description

The present invention relates to a system and method for demolition of reinforced concrete structures, for example, by electrical heating.

In recent years, an increasing number of new construction projects in urban areas involve the demolition of existing reinforced concrete structures. Large-section components such as pressure slabs are difficult to crush, so they are demolished using large breakers. When using large breakers for demolition, the impact on the surrounding environment, such as the noise, vibrations, and dust they generate, becomes an issue. There are also demolition methods that combine wire saws and continuous core boring, but these have the drawback of being less efficient and more costly than large breakers.

Against this background, the inventors have proposed a demolition method that involves electrically heating rebar (hereinafter referred to as the "electrical heating and crushing method"), with the aim of improving the efficiency of demolition of reinforced concrete structures and reducing the impact on the surrounding environment (Patent Document 1). This method is a demolition auxiliary method that uses a direct current to pass through the rebar, causing cracks in the concrete and facilitating subsequent demolition work.

Japanese Patent Application Laid-Open No. 2020-159080

As mentioned above, the demolition method using electric heating and crushing is effective in making demolition more efficient and reducing the impact on the surrounding environment. Therefore, it would be desirable to improve the demolition method using electric heating and crushing so that it can further reduce its impact on the environment.

The objective of the present invention is to provide a system and method for demolition of reinforced concrete structures that can further reduce the impact on the environment.

In order to solve the above problems, the present invention provides a method for supplying a direct current to a reinforcing bar exposed from a reinforced concrete structure, and the reinforcing bar thermally expands due to the supply of the current, thereby reducing the adhesive force between the reinforcing bar and the concrete,
The system and method for demolishing reinforced concrete structures are characterized in that a ground wire that electrically grounds the concrete is connected and a ground wire ammeter is placed on the ground wire.
In order to solve the above problem, the present invention provides a method for supplying a direct current to a reinforcing bar exposed from a reinforced concrete structure, and the reinforcing bar thermally expands due to the current supply, thereby reducing the adhesive force between the reinforcing bar and the concrete,
Connecting a current supply line to the reinforcing bar via a connection terminal;
This system for demolition of reinforced concrete structures is characterized in that multiple pairs of the connection terminal and the current supply line are provided on both the positive and negative sides of the DC current, and the DC current is supplied while detecting the current in each pair.
In order to solve the above problem, the present invention provides a method for supplying a direct current to a reinforcing bar exposed from a reinforced concrete structure, and the reinforcing bar thermally expands due to the current supply, thereby reducing the adhesive force between the reinforcing bar and the concrete,
This system for demolishing reinforced concrete structures is characterized in that a plate-shaped conductive member is interposed between the reinforcing bar exposed in a recess in the concrete and the end face of a connection terminal facing the reinforcing bar, and the plate-shaped conductive member has both sides in contact with the reinforcing bar and the end face of the connection terminal, thereby establishing electrical continuity between the reinforcing bar and the connection terminal within the recess, and the connection terminal is pressed against the reinforcing bar from the end face opposite the end face of the connection terminal using a pressure generating mechanism, thereby connecting a current supply line to the reinforcing bar via the connection terminal.

The present invention provides a system and method for demolition of reinforced concrete structures that can further reduce the impact on the environment.

1A and 1B are diagrams for explaining a dismantling system and a dismantling method according to an embodiment of the present invention. 10A and 10B are diagrams showing an example of a contact state between a connection terminal and a reinforcing bar. FIG. 10 is a diagram showing an example in which a plurality of connection terminals are provided.

The following describes a demolition system 10 and demolition method according to one embodiment of the present invention. Figure 1 shows a schematic diagram of a demolition system 10 according to one embodiment of the present invention. In this demolition system 10, a DC power source 17 (connected to a generator, not shown) supplies DC current to the rebars 13 of a reinforced concrete structure (hereinafter referred to as the "structure") 12, which is placed directly on the ground (earth) 11, via a control device 18 or a rectifier (not shown).

Connection terminals 19 and 20 are electrically connected to two locations along the axial direction of the rebar 13 exposed from the structure 12. The positive output cable (+) and negative output cable (-) of the DC power supply 17 are connected to these connection terminals 19 and 20. The positive output cable (+) and negative output cable (-) function as current supply lines (or power supply lines).

The connection terminals 19, 20 can be, for example, of a type (pressure type) that applies pressure to the reinforcing bar 13 to bring them into close contact. An example of a mechanism for generating such pressure (pressure generating mechanism), not shown, is one that presses the connection terminals 19, 20 against the reinforcing bar 13 by tightening a bolt. Another example is one in which the elastic restoring force of an elastic body such as a leaf spring, coil spring, or air spring (balloon) is applied to the connection terminals 19, 20 to press them against the reinforcing bar 13. Another example is one in which the connection terminals 19, 20 are configured as clips with leaf springs or coil springs.

By using connection terminals 19, 20 that generate a pressure force, it is possible to prevent the connection terminals 19, 20 from loosening while current is flowing. Furthermore, if a pressure force generating mechanism that applies the elastic restoring force of an air spring (balloon) to the connection terminals 19, 20 is used, the pressure force is determined by the air pressure and the contact area between the reinforcing bar 13 and the connection terminals 19, 20.

With regard to the reinforcing bars 13, if the reinforcing bars 13 are already protruding from the concrete 14 of the structure 12, the connection terminals 19, 20 are connected to the protruding reinforcing bars 13. If the reinforcing bars 13 are not exposed from the concrete 14, it is possible to expose the reinforcing bars 13 by drilling holes in the concrete 14 or by scraping and removing the area around the reinforcing bars 13 exposed at the edge of the concrete 14. Various common techniques can be used to drill holes in the structure 12 or scrape the concrete 14.

Furthermore, as shown schematically in Figure 2, in the structure 12, concrete 14 may bulge around the reinforcing bars 13. In such cases, a conductive plate (conductive member) 28 may be interposed between the reinforcing bars 13 and the connection terminal (connection terminal 19 in Figure 2) to allow electricity to flow. In this case, it is possible to ensure electrical continuity between the reinforcing bars 13 exposed in the recesses in the concrete 14 and the connection terminals 19 and 20.

In the example shown in Figure 2, a circular plate-shaped body (also called a "filler" or "spacer") 28 is in surface contact with the end face of the reinforcing bar 13, and the connection terminal 19 is in surface contact with the plate-shaped body 28. The outer dimension of the plate-shaped body 28 (here, diameter d1) is smaller than the outer dimension of the end face of the reinforcing bar 13 (here, diameter d2). Furthermore, various mechanisms such as those described above can be used to generate a pressure force that presses the connection terminal 19 (and connection terminal 20) against the reinforcing bar 13.

Note that Figure 2 only shows the reinforcing bar 13, concrete 14, connection terminal 19, and plate-like body 28 in a schematic manner; for example, the shape of concrete 14 often has complex irregularities. Furthermore, as long as a sufficient contact area between the plate-like body 28 and the reinforcing bar 13 can be ensured, the contact position between the reinforcing bar 13 and the plate-like body 28 may be a portion other than the end face (such as a portion midway along the length).

The DC power supply 17 is connected to the control device 18, and the supply of electricity from the DC power supply 17 is controlled by the control device 18. In this embodiment, the current value (rated) supplied to the reinforcing bar 13 is DC 2500A, and the voltage value (rated) is 50V. These current and voltage values take into account the maximum capacity of the power supply being used, and it is possible to increase the current and voltage values according to the capacity of the power supply being used. In addition, although not shown, the system is equipped with temperature measurement means for the reinforcing bar 13 and leakage current detection means, and the status of the electrical heating of the reinforcing bar 13 is monitored in real time.

The value of the current supplied to the rebars 13 is set taking into account the condition of the structure 12 to be demolished, the thickness and placement of the rebars 13, and other factors. For example, the power (rated) can be varied between DC 2000A-20V and DC 2500A-50V (the rated capacity can be expanded by using a single power source or combining multiple power sources), allowing the current value to be adjusted depending on the condition of the structure 12 and rebars 13 to be demolished. Furthermore, the rebars 13 thermally expand when current is applied. Due to the difference in the thermal expansion coefficients between the rebars 13 and the concrete 14, cracks occur in the concrete 14, and the concrete 14 is weakened by heat, reducing the adhesion between the rebars 13 and the concrete 14.

If an excessive temperature rise or leakage current is detected through monitoring using temperature measurement means, leakage current detection means, etc., the output of DC power supply 17 is adjusted or the output of DC power supply 17 is stopped. Such control of DC power supply 17 based on the detection results of the current flow status may be performed by an operator while visually checking the meters. Alternatively, various monitoring signals may be input into control device 18, which may then perform the control automatically.

A first ammeter (concrete leakage current detection line ammeter) 22 is connected to the concrete 14 of the structure 12 via a concrete leakage current detection line 21. The first ammeter 22 detects the current flowing through the concrete 14 (current between concrete surfaces) and is capable of displaying the current value. The current value display may be analog or digital. Both ends of the concrete leakage current detection line 21 are electrically connected to the concrete 14.

Furthermore, the concrete 14 is electrically grounded (earthed) via a grounding wire 23 and an earth terminal 24, and a second ammeter (grounding wire ammeter) 25 is disposed between the concrete 14 and the earth terminal 24. The second ammeter 25 detects the current flowing through the earth wire (the current between the concrete surface and the earth) and displays the current value. The current value display may be analog or digital, as with the first ammeter 22. One end of the grounding wire 23 is electrically connected to the concrete 14, and the other end is connected to the earth terminal 24.

Here, the output of the DC power supply 17 can be adjusted by monitoring the current values indicated by the first ammeter 22 and the second ammeter 25. Such adjustment of the output of the DC power supply 17 can be performed by an operator while visually checking the first ammeter 22 and the second ammeter 25 (mainly the first ammeter 22). Alternatively, the detection results of the first ammeter 22 and the second ammeter 25 can be input into the control device 18, which can then automatically adjust the output of the DC power supply 17.

A field experiment was conducted using the demolition system 10 described above, in which the structure 12 (particularly the concrete 14) was left in a dry state and electricity was passed through the reinforcing bars 13. As a result, the value of the first ammeter 22 (concrete surface - concrete surface value) was 0.001 mA. Furthermore, with regard to the value of the first ammeter 22, the structure 12 (particularly the concrete 14) was left in a wet state by spraying water, and electricity was passed through the reinforcing bars 13. As a result, the value of the first ammeter 22 was 0.025 mA, and the measured current value was higher than when it was dry.

Here, the structure 12 was a beam-shaped reinforced concrete structure, with dimensions of W (width) 600 x H (height) 600 x L (length) 1200 (units: mm). The types and sizes of the rebars 13 were main rebars (D) 25 and stirrup rebars (D10), with electricity passing through one main rebar. The current value was controlled to 2500 A using a rectifier (not shown), and the current value was read when the current and voltage stabilized. While the number of rebars to be energized is not limited to one, electricity was passed through one rebar in this field experiment. The required power (here, a current value of 2500 A) is the value used in this field experiment and will vary depending on conditions such as the size (length and diameter) of the rebar.

In contrast, the value of the second ammeter 25 (concrete surface - earth value) was 0.006 mA when the structure 12 (particularly the concrete 14) was dry. Furthermore, when the structure 12 was wetted with water, the value of the second ammeter 25 was 0.010 mA, and the measured current value of the second ammeter 25 also increased compared to when it was dry. For reference, the measured earth resistance value was 12 Ω. This value is equal to or less than the value generally measured, and it can be said that the current was likely to flow to the ground at the time of measurement.

As such, the measured values of the first ammeter 22 and the second ammeter 25 increased when the structure 12 was wet compared to when it was dry, but in both cases they were below 1 mA. The reason why the measured values of the first ammeter 22 and the second ammeter 25 were both low, below 1 mA, can be inferred as follows.

Because the structure 12 is placed on the ground 11 and is in contact with the ground 11, even if current leaks from the concrete 14 of the structure 12, most of the current returns to the structure 12 via a portion near the surface of the ground 11. In other words, a closed current loop (current-carrying circuit) is formed between the structure 12 and the ground 11, and current circulates between the structure 12 and the ground 11. For this reason, current exceeding 1 mA does not leak from the portion of the ground 11 where the structure 12 is placed to an outer portion, and it is believed that excessive leakage current is prevented.

In addition to the field experiments described above, current measurements were also conducted at actual construction sites. The target structures (corresponding to structure 12) were the foundation underground beams and the foundation footing, and the reinforcing bars to which current was applied were all main reinforcement bars D25. For the foundation underground beams, both ends of the structure (structure 12) were cut, and the structure was then lifted with a crane (not shown) and electrically heated in an above-ground demolition yard. For the foundation footing, electrically heated work was performed in situ.

For the underground foundation beams, measurements were taken after the concrete was thoroughly sprinkled with water and in a wet state. For the foundation footings, the concrete surface was wet due to the influence of groundwater and rainfall. The current value for electrical heating was DC 2500A, the same as in the field experiment.

The current measurement results (concrete surface - earth value) were 0.106mA at the underground foundation beam, 0.518mA at the top reinforcement of the foundation footing, and 0.017mA at the bottom reinforcement of the foundation footing. At all measurement points, the current was below 1mA regardless of whether water was supplied (in wet or dry conditions).

According to the demolition system 10 and demolition method described above, the cut structure 12 is placed directly on the ground, the first ammeter 22 and the second ammeter 25 are connected to the concrete 14, and the rebar 13 is heated by passing electricity through it while displaying the current value during the work. This makes it possible to reduce leakage current even while using a high current value (e.g., DC 2500A). Furthermore, it is possible to clearly indicate to workers, supervisors, etc. (workers, etc.) that the work is being carried out with low leakage current even while using a high current value.

This electrical heating causes the rebars 13 to expand, cracking the concrete 14 and reducing the concrete strength (weakening the concrete 14), as well as weakening the adhesion between the rebars 13 and the concrete 14. This allows the concrete 14 to be crushed efficiently with relatively little force. Furthermore, demolition is possible with low noise, low vibration, short time, and low dust, minimizing the impact on the surrounding environment. In addition to crushing, this method can also contribute to improved workability (labor savings, time reduction, etc.) for demolition methods using heavy machinery such as giant breakers. In experiments conducted by the inventors, the ease with which the rebars 13 separate from the concrete 14 roughly doubled the demolition efficiency (demolition efficiency) of the structure 12, and roughly halved the time required for demolition.

Here, for example, the DC power supply 17 (and generator) and control device 18 can be mounted on a work vehicle, and the DC power supply 17 and control device 18 can be moved to perform demolition work.

The structure 12 may be cut using a wire saw or other method and subjected to the method of this embodiment. The structure 12 may also be cut using a gas cutting method, which produces less vibration and noise and is quieter. Examples of gas cutting methods in this case include those in which fuel gas or powder (metal powder) is sprayed from a cutting torch and the structure 12 is cut using the flame generated by burning the fuel gas or powder (see, for example, JP 2020-138303 A).

In this type of gas cutting, fuel gas and powder (metal powder) are sprayed from the cutting torch as a mixed gas along with combustion oxygen. The mixed gas is ignited, and a high-temperature flame (2000-2500°C or higher) is sprayed onto the reinforced concrete structure. The high-temperature flame melts both the reinforcing bars 13 and the concrete 14 in the reinforced concrete structure.

As the reinforcing bars 13 and concrete 14 melt, a crack is formed in the reinforced concrete structure. By inserting a cutting torch into the crack, the internal melting progresses, and by moving the cutting torch horizontally or vertically, the structure 12 is cut out, for example, into a rectangular parallelepiped shape.

The inventors have also proposed a cutting device and method that allows a worker to manually grip a cutting torch and flexibly move it to cut reinforced concrete structures (Patent Application No. 2020-157195). In this method, cooling water is supplied to the cutting torch, and the cooling water circulates between the inside and outside of the cutting torch. This prevents the cutting torch from becoming too hot, making it possible to grip the cutting torch.

By using the demolition system 10 and cutting method of this embodiment on structures 12 cut out by gas cutting, a highly quiet construction method can be used continuously, allowing for the entire process from cutting to demolition of the structure 12. This makes it possible to demolition the structure 12 with even less impact on the environment.

In addition, at least one of the positive output cable (+) and the negative output cable (-) may be divided into multiple cables, and a connection terminal 19 (or connection terminal 20) may be provided on each cable to pass current through the rebar. Figure 3 schematically shows an example in which both the positive output cable (+) and the negative output cable (-) are multiple. In the example of Figure 3, six cables are used on both the positive and negative sides, but the number of cables is not limited to this. In this way, by connecting multiple cables to a single connection area, the connection terminals 19, 20 can be made smaller and lighter, and the work involved in connecting each of the connection terminals 19, 20 can be improved.

Furthermore, although not shown in the figures, an ammeter may be installed on each cable to monitor the balance of the current flowing through each cable. In this case, it is possible to prevent, for example, current from concentrating in one cable, causing the cable to overheat or melt.

For example, if there are six cables on the positive and negative sides, when power is first applied, the ammeter values on each cable are monitored to check the balance of the current supply. If there are no problems with the balance of the current supply, the current supply continues. In this way, by checking the ammeters at the beginning of power application, it is possible to omit monitoring the ammeters thereafter. However, if power is stopped and then restarted, it is also possible to check the balance of the current supply again using the ammeters at the beginning of power application.

Furthermore, by simultaneously passing electricity through multiple reinforcing bars 13, it is possible to perform electrical heating on the area including the reinforcing bars 13 that have been passed through. In this case, it is possible to connect one or more cables (connection terminals) to each reinforcing bar 13.

Although one embodiment of the present invention has been described above, the present invention is not limited to this, and many modifications are possible within the scope of the technical concept of the present invention. Furthermore, the described embodiment is merely one example of a concrete implementation of the present invention, and the technical scope of the present invention should not be interpreted as being limited thereby.

10 Demolition system 11 Ground 12 Reinforced concrete structure 13 Reinforcement bar 14 Concrete 17 DC power supply 18 Control device 19, 20 Connection terminal 21 Concrete leakage current detection line 22 First ammeter (ammeter for concrete leakage current detection line)
23 Ground wire 24 Ground terminal 25 Second ammeter (ammeter for ground wire)
28 Plate-shaped body

Claims (8)

A direct current is supplied to the reinforcing bars exposed from the reinforced concrete structure, and the supply of current causes the reinforcing bars to thermally expand, thereby reducing the adhesive force between the reinforcing bars and the concrete;
A system for demolition of reinforced concrete structures, characterized in that a ground wire that electrically grounds the concrete is connected and a ground wire ammeter is placed on the ground wire. A reinforced concrete structure demolition system as described in claim 1, characterized in that both ends of a concrete leakage current detection line are connected to the concrete, and an ammeter for the concrete leakage current detection line is arranged on the concrete leakage current detection line. A system for dismantling reinforced concrete structures as described in claim 1 or 2, characterized in that the reinforced concrete structure is cut out by gas cutting. A direct current is supplied to the reinforcing bars exposed from the reinforced concrete structure, and the supply of current causes the reinforcing bars to thermally expand, thereby reducing the adhesive force between the reinforcing bars and the concrete;
A method for demolishing a reinforced concrete structure, characterized in that a ground wire that electrically grounds the concrete is connected and a ground wire ammeter is placed on the ground wire. A method for demolishing a reinforced concrete structure as described in claim 4, characterized in that both ends of a concrete leakage current detection wire are connected to the concrete, and an ammeter for the concrete leakage current detection wire is placed on the concrete leakage current detection wire. A method for demolishing a reinforced concrete structure according to claim 4 or 5, characterized in that the reinforced concrete structure is cut out by gas cutting. A direct current is supplied to the reinforcing bars exposed from the reinforced concrete structure, and the supply of current causes the reinforcing bars to thermally expand, thereby reducing the adhesive force between the reinforcing bars and the concrete;
Connecting a current supply line to the reinforcing bar via a connection terminal;
A system for dismantling reinforced concrete structures, characterized in that multiple pairs of the connection terminal and the current supply line are provided on both the positive and negative sides of the DC current, and the DC current is supplied while detecting the current in each pair. A direct current is supplied to the reinforcing bars exposed from the reinforced concrete structure, and the supply of current causes the reinforcing bars to thermally expand, thereby reducing the adhesive force between the reinforcing bars and the concrete;
A system for demolishing reinforced concrete structures, characterized in that a plate-shaped conductive member is interposed between the reinforcing bar exposed in a recess in the concrete and the end face of a connection terminal facing the reinforcing bar, the plate-shaped conductive member having both sides in contact with the reinforcing bar and the end face of the connection terminal to establish electrical continuity between the reinforcing bar and the connection terminal within the recess, and a current supply line is connected to the reinforcing bar via the connection terminal by pressing the connection terminal against the reinforcing bar from the end face opposite the end face of the connection terminal using a pressure generating mechanism.