JP2009257795A - Covering depth management method for reinforced concrete structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for extensively and quantitatively obtaining/controlling the covering depth of a reinforced concrete structure. <P>SOLUTION: Prior to concrete 4 being placed, detection electrodes 10 each having a prescribed area S are firmly fixed on form confronting surfaces of a row 3 of rebars 2, confronting a form 5 with the detection electrodes insulated from the row 3 while substantially maintaining concrete adhesive areas of the row 3, and counter electrodes 14, each having the prescribed area, S are stuck to detection electrode confronting parts on rebar confronting surfaces of the form 5 or on opposite side surfaces thereof. In placing the concrete 4, capacitance C between the detection electrodes 10 and the counter electrodes 14 is measured, thereby the covering depths d of the concrete 4 relevant to the row 3 is controlled. Preferably, the detection electrodes 10 are fixed firmly on the form confronting surfaces of the row 3, along the entire horizontal and/or vertical lengths thereof. With the detection electrodes 10 embedded in the concrete 4, actual concrete thicknesses d can be also inspected by measuring the capacitance C between the detection electrodes 10 in the concrete 4 and the counter electrodes 14 stuck to the surface of the concrete 4, after the completion of the structure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for managing the covering thickness of a reinforced concrete structure, and more particularly to a method for managing the covering thickness of concrete on a reinforcing bar as part of construction management.

  Reinforced concrete structures have excellent durability and are a major component of social capital such as houses, bridges and tunnels. However, reinforced concrete structures are affected by the influence of materials, design, construction, maintenance, external environment, etc., and quality will vary, so appropriate material selection, design, construction, and maintenance are necessary to ensure durability. It is a premise. In particular, the thickness of the concrete covering the reinforcing bars of a reinforced concrete structure (hereinafter sometimes referred to as the covering thickness) is an extremely important factor for preventing corrosion of the reinforcing bars and thus ensuring the durability of the structure. An appropriate cover thickness standard is defined for each structural part. For this reason, in reinforced concrete structures, it is necessary to perform construction management to check whether or not the cover thickness exceeding the standard is secured, and maintenance management to check whether or not the required cover thickness exists after completion. Become.

Conventionally, the covering thickness during construction of reinforced concrete structures is generally managed by measuring the distance between the reinforcing bar and the formwork using a measure, etc., or placing the member called the spacer between the reinforcing bar and the formwork. (For example, Non-Patent Document 1). Further, after the structure is completed, a method of inspecting and maintaining the cover thickness by a nondestructive inspection system such as a radar exploration method, an electromagnetic induction method, or an X-ray transmission method has been attempted (Non-Patent Document 2). ). The radar exploration method is a method of measuring the depth (cover thickness) from the concrete surface to the reinforcing bar by the reflected wave from the reinforcing bar of the electromagnetic wave radiated from the concrete surface to the inside of the concrete. The electromagnetic induction method is a method of investigating a distance (cover thickness) to a reinforcing bar by using an eddy current flowing in a detection coil using an excitation coil and a detection coil.
Tsuneo Shimamoto et al. “Science of Architecture”, Science and Engineering Company, March 25, 1999, 4th edition, 5th edition, 10:25 Kento Uomoto “Non-destructive inspection of concrete structures” Dam Technology No. 158, November 1999 Japanese Patent Application No. 2003-214841

  However, the conventional method for managing the cover thickness at the time of construction has a problem that it is difficult to quantitatively check the cover thickness over a wide range. For example, in the method of managing the cover thickness using a spacer, the position of the spacer may be misaligned. Have difficulty. In addition, the method of quantitatively grasping the covering thickness by applying a measure between the reinforcing bar and the formwork takes time, so it is necessary to quantitatively grasp the covering thickness over a wide range within a limited construction period. Is practically difficult.

  On the other hand, conventional non-destructive inspection systems such as radar exploration methods, electromagnetic induction methods, and X-ray transmission methods can quantitatively grasp the covering thickness after the structure is completed, but at the same time they are in a relatively narrow range. Since only the covering thickness can be grasped and the detection accuracy is not necessarily high, it is not suitable for grasping the covering thickness in a wide range at the construction stage.

  Recently, there is a growing need for inspections during construction (construction inspection) as well as confirmation of the required performance of reinforced concrete structures at the time of completion, and construction personnel are required to record and store the covering thickness during construction. It has been. In addition, if the covering thickness is found to be insufficient after completion, a huge cost is required for repair. Therefore, if the covering thickness can be managed quantitatively during construction, it is reasonable and economical. Since further increase in social performance required for durability of reinforced concrete structures is expected in the future, establishment of construction management technology that can easily and quantitatively grasp a wide range of covering thickness during construction is desired. .

  Accordingly, an object of the present invention is to provide a method for quantitatively grasping and managing the covering thickness of a reinforced concrete structure over a wide range.

  Referring to the embodiment of FIG. 1, the covering thickness management method for a reinforced concrete structure according to the present invention is a method for managing the covering thickness d of the concrete 4 with respect to the reinforcing bar 2 of the reinforced concrete structure 1. The detection electrode 10 having a predetermined area S is insulated from the reinforcing bar row 3 on the surface facing the mold of the row 3 of the reinforcing bars 2 facing the form 5 before, and the concrete adhesion area of the reinforcing bar row 3 is substantially maintained. The counter electrode 14 having the predetermined area S is pasted to the detection electrode facing portion on the reinforcing bar facing surface or the opposite side surface of the form 5 and the static electricity between the detecting electrode 10 and the facing electrode 14 is placed when the concrete 4 is placed. The covering thickness d of the concrete 4 with respect to the reinforcing bar row 3 is managed by measuring the electric capacity C.

  Preferably, the detection electrode 10 is fixed over the entire length in the horizontal and / or vertical direction on the mold facing surface of the reinforcing bar row 3. More preferably, the detection electrode 10 is embedded in the concrete 4, and after the structure is completed, the counter electrode 14 is pasted on the surface of the concrete 4 facing the detection electrode 10, and the detection electrode 10 and the surface of the concrete 4 in the concrete 4 are adhered. The actual concrete thickness d for the reinforcing bar row 3 is inspected by measuring the capacitance C between the counter electrode 14 and the counter electrode 14.

  The covering thickness management method and apparatus for a reinforced concrete structure according to the present invention includes a method in which a detection electrode having a predetermined area is insulated from a reinforcing bar array on a surface of the reinforcing bar array facing the mold frame before placing the concrete, and the reinforcing bar array Reinforcement by sticking while maintaining the adhesion area of concrete, sticking a counter electrode of a predetermined area to the detection electrode facing part on the mold, and measuring the capacitance between the detection electrode and the counter electrode when placing concrete Since the concrete covering thickness for the row is managed, the following advantageous effects are obtained.

(B) Cover thickness can be easily checked over a wide range and the cover thickness can be detected quantitatively, thereby contributing to labor saving at the site and improvement in the reliability of construction quality.
(B) Since the cover thickness can be checked quantitatively in rebar and formwork to deal with the danger of insufficient cover thickness, the cost of repair of insufficient cover thickness can be reduced compared to the cover thickness inspection after completion. Can be planned.
(C) It can be expected to be used as a means for quantitatively recording and storing the thickness of the cover during construction, which has conventionally been troublesome.
(D) It can be used not only for confirmation before placing concrete, but also for filling during concrete placement.
(E) Since the detection electrode is embedded in the concrete, it can be used for covering thickness inspection after the structure is completed.

  FIG. 1 shows an embodiment in which the present invention is applied to construction management of a reinforced concrete structure 1 which is a columnar frame in this case. In the reinforced concrete structure 1 shown in the figure, a reinforcing bar 2 serving as a main reinforcing bar and a reinforcing bar of a pillar frame is arranged, and a form 5 is assembled in a shape surrounding the reinforcing bar 2, and concrete 4 is driven into the form 5 and cured. It is constructed by removing the formwork 5 after the concrete is hardened. The present invention manages the covering thickness of the concrete 4 with respect to the reinforcing bar 2 by quantitatively grasping the distance d between the row 3 of the reinforcing bars 2 facing the mold 5 and the mold 5.

  The distance d between the reinforcing bar row 3 and the mold 5 is grasped by measuring the capacitance C between the detection electrode 10 fixed on the reinforcing bar row 3 and the counter electrode 14 attached to the mold 5. The detection electrode 10 has a predetermined area S. For example, as shown in FIG. 1, the detection electrode 10 is electrically insulated and fixed from the reinforcing bar row 3 over the entire length of the reinforcing bar row 3 in the horizontal direction. The reason why the detection electrode 10 is insulated from the muscle row 3 is to limit the area S of the detection electrode 10 and the distance d to be measured. For example, as shown in FIG. 1, a strip-shaped laminated tape in which an insulating layer 11 having a predetermined width and a conductive layer (for example, galvanized, copper, conductive nonwoven fabric, etc.) 12 are overlapped is used as a detection electrode 10, and the insulating layer 11 is The detection electrode 10 and the reinforcing bar row 3 are insulated from each other by attaching the reinforcing bar row 3 on the surface facing the formwork. In this case, the area S of the detection electrode 10 can be determined by the length of the laminated tape. However, the detection electrode 10 is not limited to the laminated tape as long as it is insulated and fixed from the reinforcing bar row 3.

  In the reinforced concrete structure, it is essential to ensure the integration of the reinforcing bar 2 and the concrete 4, and the detection electrode 10 needs to be fixed so as not to hinder the integration of the reinforcing bar row 3 and the concrete 4. The integration of the reinforcing bar 2 and the concrete 4 is obtained by the adhesion between the reinforcing bar surface and the concrete. Therefore, the detection electrode 10 is fixed so that the adhesion area between the reinforcing bars 2 and the concrete 4 of the reinforcing bar row 3 is substantially maintained. For example, in the embodiment of FIG. 1 in which the detection electrode 10 is a laminated tape, the adhesive surface of the laminated tape to the reinforcing bar 2 is linear so that the laminated tape does not wrap around the reinforcing bar 2 in the circumferential direction. It is fixed to the reinforcing bar row 3.

  The counter electrode 14 is affixed to a portion on the mold 5 that faces the detection electrode 10 at the time of, for example, mold work. Affixing the counter electrode 14 to the reinforcing bar-facing surface of the mold 5 is not affected by the thickness of the mold 5 so that a slight improvement in accuracy can be expected. For example, as shown in FIG. You may affix on the opposite side. By making the area S of the counter electrode 14 the same as the area S of the detection electrode 10, a parallel electrode pair is formed between the mold frame facing surface of the reinforcing bar group 3 and the mold 5.

  Before the rebar and formwork work is completed and the concrete 4 is placed, the capacitance C between the electrodes 10 and 14 is measured between the detection electrode 10 and the counter electrode 14 to measure between the electrodes 10 and 14. The detecting means 16 for detecting the interval d is connected. The detection means 16 in FIG. 1 has a capacitance measurement means 18 and a storage means 17 for measuring the capacitance C between the electrodes 10 and 14. An example of the capacitance measuring means 18 is a capacitance meter belonging to the prior art that measures a capacitance C from a change in impedance between both electrodes 10 and 14 by applying a high frequency AC voltage of about several hundred volts.

  Referring to FIG. 4 showing the measurement principle of the detection means 16, the capacitance C between the detection electrode 10 and the counter electrode 14 can be expressed by equation (1). In equation (1), S represents the area of both electrodes 10 and 14, d represents the distance between both electrodes 10 and 14, and ε represents the dielectric constant between both electrodes 10 and 14 (the dielectric constant of air before placing concrete). . For example, if the storage unit 17 of the detection unit 16 stores the dielectric constant ε of air and the area S of the electrodes 10 and 14, the measured value of the capacitance C between the electrodes 10 and 14 and the equation (1) From this, the distance d between the electrodes 10 and 14 can be calculated. An example of the detection means 16 in FIG. 1 is a computer with a built-in program for calculating the distance d from the measured value of the capacitance C and the equation (1).

C = ε · S / d ……………………………………………………………………… (1)
C = 2πε / log (b / a) ……………………………………………… (2)

  Equation (1) is established when the area S is sufficiently large with respect to the distance d. In general, the covering thickness d of the concrete 4 with respect to the reinforcing bar 2 is about 30 to 70 mm. Since the counter electrode 14 can be set to 5 to 10 m or more over the entire length in the horizontal direction of the mold frame facing surface of the reinforcing bar row 3, the distance d can be calculated effectively based on the equation (1). From the calculated distance d, it is possible to quantitatively grasp the covering thickness d before placing concrete, for example, by comparing with the specified value of the covering thickness d stored in the storage means 17 of the detecting means 16 Detect d shortage or the like. When the counter electrode 14 is affixed to the side opposite to the reinforcing bar facing surface, the distance between the detection electrode 10 and the counter electrode 14 is calculated in consideration of the dielectric constant of the mold 5, and the mold is calculated from the distance d. The cover thickness d is calculated by subtracting the thickness of 5.

  In the present invention, since the detection electrode 10 and the counter electrode 14 can be provided over the entire length in the horizontal direction on the form-frame facing surface of the reinforcing bar row 3, it is possible to confirm the covering thickness d in a wide range at a time. . For example, even when a distortion or the like is generated in a part of the reinforcing bar row 3 in the horizontal direction, since the covering thickness d is changed by the detecting means 16, the distortion can be detected. Further, as shown in FIG. 1, if a plurality of electrode pairs 10 and 14 are provided at different height portions of the reinforcing bar row 3, it is possible to detect distortion of the reinforcing bar row 3 at different height portions.

  The detection electrode 10 and the counter electrode 14 are not limited to the horizontal direction, and may be provided over the entire length in the vertical direction of the mold frame facing surface of the reinforcing bar row 3 as shown in FIG. FIG. 2 shows an example in which electrode pairs 10 and 14 extending in the vertical direction are provided at the four corners of the reinforcing bar group of the columnar frame. For example, by sequentially connecting the detection means 16 to the electrode pairs 10 and 14 at the four corners, the cover at the four corners is provided. The lack of thickness d can be confirmed. By detecting the horizontal arrangement of the electrode pairs 10, 14 shown in FIG. 1 and the arrangement of the vertical electrode pairs 10, 14 shown in FIG. It is also possible to do. However, the arrangement of the detection electrode 10 and the counter electrode 14 can be arbitrarily selected within the range in which the expression (1) is satisfied, and is not limited to the embodiment of FIGS.

  FIG. 3 shows another embodiment of the present invention for measuring the covering thickness d around the group of reinforcing bars 2 (rebar bar). In this case, the detection electrode 10 is fixed in a ring shape along the periphery on the mold facing surface of the periphery of the reinforcing bar group (rebar bar), and the counter electrode 14 is attached in a ring shape on the facing portion on the mold 5 in a ring shape. The covering thickness d around the reinforcing bar group can be detected by the equation (1). Further, as shown in FIG. 3, the distance a is from the center point O of the reinforcing bar rod having a rectangular cross section to the detection electrode 10 (rebar 2), and the distance b is from the center point O to the opposing surface of the counter electrode 14 (form 5). In this case, the capacitance C between the detection electrode 10 and the counter electrode 14 can be approximated by the equation (2), and the measured value of the capacitance C between the electrodes 10 and 14 and (2) The distance d (= b−a) between the electrodes 10 and 14 may be calculated from the equation.

  Thus, provision of “a method for quantitatively grasping and managing the covering thickness of a reinforced concrete structure over a wide range”, which is an object of the present invention, can be achieved.

  The present invention can be used not only for the management of the covering thickness d before placing the concrete 4 but also for the concrete filling confirmation when placing the concrete 4. For example, if the dielectric constant ε of the concrete 4 to be placed is stored in the storage device 17 of the detecting means 16, the measured value of the capacitance C and the formula (1) (or (2) formula when the concrete 4 is placed. ), The filling thickness d of the concrete 4 between the detection electrode 10 and the counter electrode 14 can be calculated. For example, based on the difference between the calculated filling thickness d and the covering thickness d confirmed before placing the concrete, the detecting means 16 detects whether the concrete 4 is not filled between the electrodes 10 and 14. When the concrete unfilling is detected, the concrete unfilling is prevented by applying vibration until the unfilling disappears.

  In the present invention, since the detection electrode 10 is embedded in the concrete 4, if the cable connected to the detection electrode 10 is led to the concrete surface, it can be used for the inspection of the covering thickness of the concrete 4 after the structure is completed. Is possible. That is, the counter electrode 14 is affixed to a portion facing the detection electrode 10 on the finished concrete surface, the dielectric constant ε of the concrete 4 is stored in the storage device 17 of the detection means 16, and the cable connected to the detection electrode 10 And the counter electrode 14 are connected to the detection means 16, and the capacitance C between the electrodes 10 and 14 is measured. From the measured value of the capacitance C and the formula (1) (or (2)), the actual covering thickness d of the concrete 4 with respect to the reinforcing bar row 3 can be inspected. According to this inspection method, it is possible to easily grasp the covering thickness d in a wide range, which has been difficult for the conventional nondestructive inspection system.

  In the above, the management method of the covering thickness d based on the capacitance C between the detection electrode 10 and the counter electrode 14 has been described. However, in the actual construction site of the reinforced concrete structure 1, the disturbance from the surrounding rebar 2 or heavy machinery is There is an influence, and an error may occur in the measurement value of the covering thickness d according to the equation (1) (or (2)). FIG. 5 shows an embodiment of the present invention in which the reference electrode pair 20 is fixed adjacent to the detection electrode 10 on the surface facing the form of the reinforcing bar row 3 in order to avoid the influence of disturbance. In FIG. 5B, the detection electrode 10 is a laminated tape in which the above-described insulating layer 11 and conductive layer 12 are overlaid.

  As shown in FIG. 2C, the target electrode pair 20 in the illustrated example includes a pair of electrodes 20a and 20b having a predetermined area S2 sandwiching an insulating layer 21 having a predetermined thickness d2 and a dielectric constant ε2, and the electrode pair 20a. , 20b is provided on the surface facing the form of the reinforcing bar row 3 and has an insulating fixing layer 23 that is insulated and fixed from the reinforcing bar row 3. The thickness of the insulating layer 21 of the reference electrode pair 20 can be set to about 1 to 10 mm, for example. For example, a laminated tape having an insulating layer 11 and a conductive layer 12 shown in FIG. 5B may be overlapped to form the reference electrode pair 20 shown in FIG.

  An example of the covering thickness d detecting means 16 applied to the embodiment of FIG. 5 provided with the reference electrode pair 20 is shown in FIG. The detection means 16 in the figure includes a capacitance measurement means 18 that measures the capacitance C1 between the detection electrode 10 and the counter electrode 14, and a capacitance measurement that measures the capacitance C2 between the electrode pairs 20a and 20b. Means 25 and comparison means 26 for calculating the ratio of the measured value of capacitance C1 and the measured value of capacitance C2. An example of the capacitance measuring means 18, 25 is the capacitance meter described above.

  When the influence of disturbance is taken into account, when the dielectric constant between the detection electrode 10 and the counter electrode 14 with the area S1 and the distance d1 is ε1, the capacitance C1 between the electrodes 10 and 14 is expressed by the equation (11). be able to. Α in equation (11) is a parameter indicating the influence of disturbance. On the other hand, when the control electrode 20a, 20b has an area S2, the insulating layer 21 sandwiched between the control electrodes 20a, 20b has a thickness d2, and a dielectric constant ε2, the capacitance C2 between the target electrode pair 20a, 20b is (12) It can be expressed by an expression. Since the equations (11) and (12) include the parameter α, an error may occur in the measured values C1 and C2 due to the influence of disturbance. On the other hand, since the ratio of the capacitances C1 and C2 (= C1 / C2) shown in the equation (13) does not include the parameter α, the influence of disturbance can be excluded.

C1 = α ・ ε1 ・ S1 / d1 ……………………………………………………… (11)
C2 = α ・ ε2 ・ S2 / d2 ………………………………………………… (12)
C1 / C2 = (ε1 / ε2) · (S1 / S2) · (d2 / d1) (13)
δ = 20log (C1 / C2) …………………………………………………… (14)

  The present inventor provided the detection electrode 10 and the counter electrode 14 at intervals of covering thickness d = 25, 30, 35, and 40 cm at the actual construction site of the reinforced concrete structure, and the object adjacent to the detection electrode 10. An electrode pair 20 was provided, and an experiment was conducted to confirm the ratio between the capacitance C1 between the electrodes 10 and 14 and the capacitance C2 between the control electrode pair 20a and 20b. In this experiment, a galvanized laminated tape having a width of 100 mm and a length of 5 m was used as the detection electrode 10, and the laminated tape was doubled and used as the target electrode pair 20. Further, the ratio of the capacitances C1 and C2 was calculated as δ by the equation (14). The experimental results are shown in Table 1 and the graph of FIG. As can be seen from the graph of FIG. 7, it was confirmed that the ratio δ of the capacitances C1 and C2 was very well proportional to the covering thickness d.

  For example, if the storage means 17 of the detection means 16 in FIG. 6 stores the relationship between the covering thickness d and the ratio δ of the capacitances C1 and C2 shown in the graph of FIG. From the ratio of the measured values of the capacitances C1 and C2 calculated by the comparison means 26 and the above relationship, the covering thickness d can be obtained with high accuracy by the detection means 16 without being affected by disturbance.

It is explanatory drawing of one Example of this invention. It is explanatory drawing of other one Example of this invention. It is explanatory drawing of another one Example of this invention. It is explanatory drawing which shows the principle of this invention. It is explanatory drawing of other Example of this invention. It is explanatory drawing which shows the principle of the Example of FIG. It is a graph which shows an example of the experimental result of the Example of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Reinforced concrete structure 2 ... Reinforcing bar 3 ... Reinforcement row 4 ... Concrete 5 ... Formwork 7 ... Gap between rebar and formwork
10 ... Detection electrode 11 ... Insulating layer
12… Conductive layer 14… Counter electrode
16 ... Detection means 17 ... Storage means
18 ... Capacitance measurement means
20… Control electrode pair 21a, 21b… Target electrode
22… Insulating layer 23… Insulation fixing means
25 ... Capacitance measurement means 26 ... Comparison means

Claims (5)

In the method for managing the concrete covering thickness of the reinforced concrete structure with respect to the reinforcing bars, a detection electrode having a predetermined area is insulated from the reinforcing bar row on the surface of the reinforcing bar row facing the mold frame before placing the concrete, and It adheres while maintaining the concrete adhesion area of the reinforcing bar row, sticks the counter electrode of the predetermined area to the detection electrode facing part on the reinforcing bar facing surface or the opposite side surface of the formwork, and the detection and facing when placing concrete A method for managing the covering thickness of a reinforced concrete structure in which the covering thickness of the concrete with respect to the reinforcing bar row is managed by measuring the capacitance between the electrodes. 2. The method of managing a covering thickness of a reinforced concrete structure according to claim 1, wherein the detection electrode is fixed over the entire length in the horizontal and / or vertical direction on the form facing surface of the reinforcing bar row. In the management method of Claim 1 or 2, the said detection electrode is embedded in concrete, a counter electrode is affixed on the site | part on the concrete surface facing a detection electrode after completion of a structure, and the detection electrode in the said concrete and a concrete surface are attached. A covering thickness management method for a reinforced concrete structure in which an actual concrete thickness with respect to the reinforcing bar row is inspected by measuring a capacitance between the counter electrode and the counter electrode. 4. The method of managing a covering thickness of a reinforced concrete structure according to claim 1, wherein the detection electrode is a laminated tape having a predetermined width in which an insulating layer and a conductive layer are overlapped. 5. The control method according to claim 1, wherein a reference electrode pair having a predetermined area, which is adjacent to a detection electrode and sandwiches a predetermined insulating layer, is fixedly insulated from the reinforcing bar row on the form-facing surface of the reinforcing bar row. And a concrete reinforced concrete structure in which the concrete covering thickness is managed based on a ratio between the measured value of the capacitance between the detection and counter electrodes and the measured value of the capacitance between the reference electrode pair during concrete placement. How to control the thickness of objects.

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