JP2020125945A - Formwork for determining concrete demolding strength - Google Patents

Abstract

To provide a formwork for determining concrete demolding strength that improves determination accuracy of a demolding time and can be used repeatedly while leaving no mold to be buried on a concrete side at the time of demolding the concrete.SOLUTION: With a formwork for determining demolding strength, specific resistance is obtained by measuring a potential difference between electrodes 4, 4 in a state in which the plurality of electrodes 4, 4 are brought into contact with concrete placed in a framework, and strength at the time of demolding is determined from the specific resistance. The formwork for determining demolding strength includes a resin plate 2 that also serves as the framework, and a sheet 5 with an electrode in which a plurality of, at least four or more, flexible thin electrodes 4, 4. are arranged side by side at one surface side of an insulating sheet 3 at an interval in a certain direction. The other surface side of the sheet 5 with the electrode is adhered and attached relative to the resin plate 2 in an area A avoiding a section corresponding to the electrodes 4, 4.SELECTED DRAWING: Figure 5

Description

The present invention relates to a mold for demolding strength judgment for estimating the demolding strength of concrete cast in a mold.

Conventionally, lining concrete for mountain tunnel construction has been required to be repeatedly placed in a short cycle in order to shorten the construction period. In the actual work, usually, on the first day, demolding (centre down), moving the center, installing and mounting the formwork, and on the second day, concrete placing is done at a pace of three times a week. It is common to repeat. At this time, the curing time of the lining concrete was set to about 18 hours due to restrictions on work processes and conventional results.

It is said that concrete strength of ^{2 to 3} N/mm ² or more is usually required for demolding, but it is not confirmed every time demolding is performed. The time for demolding had been decided. However, if the demolding time is set uniformly from the curing time, there is a problem that it is not possible to cope with changes in the site environment.

Therefore, in recent years, as shown in, for example, Patent Documents 1 and 2 below, various methods have been proposed for estimating concrete strength during demolding and determining the demolding time. In Patent Document 1 below, in order to determine the demolding time of the lining concrete that has been cast using the formwork, the concrete temperature at any location within the formwork of the lining concrete is measured at any time intervals. , A lining concrete demolding time determination method for calculating an integrated temperature from the measured temperature, and estimating that the desired compressive strength is reached when the integrated temperature reaches an arbitrary value and determining that it is the demolding time It is disclosed.

Further, in Patent Document 2 below, it is a method of determining the quality of a cast concrete during curing, under the condition of being in a mold during curing, and four pieces are arranged in parallel at specific equal intervals. A set of multiple electrodes is placed from the outside of the formwork so that at least a part of each electrode is buried in the cast concrete, and the concrete is placed in the formwork and cured. After that, calculate the specific resistance value in the concrete placed by the four-electrode method based on the value measured by applying a voltage from outside the concrete placed into the electrode, and obtain the specific resistance value There is disclosed a method for determining the quality of a cast concrete during curing, in which the quality is determined by grasping the progress of the hydration reaction of the cast concrete.

JP 2012-26734A JP, 2014-35269, A

However, in the method described in Patent Document 1, the temperature sensor has to be buried in the concrete every time the lining concrete is placed, and the temperature sensor is buried, and the integrated temperature is measured for a long time. Therefore, wiring from temperature sensors installed at multiple locations to the data logger is required, which complicates the equipment, and the accumulated temperature does not capture changes in the physical properties of the concrete itself, and it is only indirect from temperature conditions. However, since the relationship between the integrated temperature and strength differs depending on the type of concrete, the accuracy of the demolding time determination is poor.

On the other hand, since the method described in Patent Document 2 is a method of determining the demolding time by measuring the specific resistance of concrete, the demolding time is directly determined from the change in the electrical properties associated with the hydration reaction of concrete. It is effective in that it is possible to estimate that the electrode placed at a predetermined depth must be buried in the concrete every time the lining concrete is placed, and it is buried. Was becoming a problem.

Therefore, the main problem of the present invention is to obtain the specific resistance by measuring the potential difference between the electrodes in a state where a plurality of electrodes are in contact with the concrete placed in the formwork, and when releasing from this specific resistance. A mold for determining strength during demolding of concrete for estimating strength, which enables repeated use of the mold for strength determination during demolding without burying the electrode in the concrete. is there.

In order to solve the above-mentioned problems, the present invention according to claim 1 obtains a specific resistance by measuring a potential difference between the electrodes in a state where a plurality of electrodes are in contact with concrete placed in a mold, A mold for determining strength during demolding of concrete for estimating the strength at demolding from this specific resistance,
The mold for strength determination during demolding is an insulating plate material that also serves as a mold, and a plurality of thin electrodes having flexibility and juxtaposed on one surface side of the insulating sheet in a certain direction with a gap therebetween. At the time of demolding of concrete, characterized in that the other side of the sheet with electrodes is adhered and attached to the plate material in a region avoiding the portion corresponding to the electrodes. A strength determination formwork is provided.

In the invention according to claim 1, the strength of the concrete cast in the mold at the time of demolding is not estimated indirectly from the curing time or the integrated temperature, but is associated with the hydration reaction. By measuring the electrical properties (potential difference) of the concrete itself, we are using a method that makes it possible to directly estimate the strength development of the concrete. Therefore, the strength at the time of demolding can be directly estimated, and the accuracy can be improved.

A mold for strength determination during demolding according to the present invention includes an insulating plate material that also serves as a mold, and a plurality of flexible electrodes that are spaced in a certain direction on one surface side of the insulating sheet material. The electrode-equipped sheet is provided, and the other surface side of the electrode-attached sheet is adhered and attached to the plate material in a region avoiding a portion corresponding to the electrode. Therefore, instead of installing the electrodes in the concrete in a buried state, the sheet with electrodes in which multiple electrodes are arranged side by side on one side of the insulating sheet material is used. When the sheet is removed, the electrodes can also be peeled off from the concrete together, and the mold for strength determination during demolding can be used repeatedly.

Further, in the case of the electrode attached to the surface of the sheet as in the present invention, the adhesion (contact property) with the concrete becomes a problem as the concrete shrinks after being filled with the concrete. Therefore, in the present invention, the other surface side of the electrode-attached sheet is attached to the plate member by adhesion in a region other than the portion corresponding to the electrode. That is, the electrode portion of the sheet with electrodes is separated from the resin plate and floated. As a result, the electrode can follow the contraction accompanying the hardening of the concrete and ensure the adhesion (adhesiveness), so that the contact state between the electrode and the concrete can be maintained, and the energized state can be maintained. ..

The electrodes are thinly formed on the surface of the sheet material, and the bite into the concrete is very small, and the demolded concrete surface is almost flat.

As a second aspect of the present invention, there is provided the concrete-demolding strength determination formwork according to claim 1, wherein the electrode has a rectangular planar shape having a predetermined width and long in one direction.

According to the second aspect of the invention, regarding the shape of the electrode, the planar shape of the electrode is a rectangular shape having a predetermined width and long in one direction. With such a shape, the contact surface with the concrete is elongated and formed in a planar shape, so that a good contact state between the concrete and the electrode can be realized and the measurement accuracy can be improved.

As a third aspect of the present invention, there is provided a mold for determining strength during demolding of concrete according to any one of the first and second aspects, wherein the electrode is a print type electrode or a tape type electrode.

The invention according to claim 3 exemplifies a specific example of the electrode, and a print type electrode or a tape type electrode can be preferably used as the electrode. Since these electrodes have flexibility and can be formed to have a thin wall, they can easily follow shrinkage deformation due to hardening of concrete, and the thickness thereof is generally 500 μm or less, so that the amount of bite into concrete is small.

As a fourth aspect of the present invention, there is provided a concrete-demolding strength determination formwork according to any one of claims 1 to 3, wherein at least four electrodes are arranged in parallel at equal intervals. ..

According to the invention described in claim 4, with respect to the number of electrodes, at least four or more electrodes are arranged in parallel at equal intervals. This is because the four-electrode method in which four adjacent electrodes are set as one set is used when measuring the specific resistance. Further, when the number of electrodes is 5 or more, a set of 4 electrodes is set, and the electrodes are shifted one by one and measured a plurality of times, and the average thereof is used as the specific resistance to enable highly accurate data acquisition. There is. For example, when 5 electrodes are arranged side by side, the electrodes to be set can be shifted one by one and the measurement can be performed twice, and when 6 electrodes are arranged side by side, one electrode to be set can be set. It becomes possible to shift and measure three times. By adopting these average values, the measurement accuracy can be improved.

According to a fifth aspect of the present invention, there is provided a concrete-demolding strength determination formwork according to any one of the first to fourth aspects, wherein the plate material is a resin plate.

In the invention according to claim 5, a resin plate is used as the plate material. The resin plate has high strength and rigidity, and is easily provided with electric insulation.

As a sixth aspect of the present invention, a region for avoiding a portion corresponding to the electrode is a peripheral edge portion of an insulating sheet, and the mold for demolding strength determination of concrete according to any one of claims 1 to 5 is provided. To be done.

In the invention according to claim 6, in order to secure the contact state while the electrode portion is deformed due to shrinkage accompanying the hardening of concrete, the adhesive portion of the sheet with electrodes to the plate material (resin plate) corresponds to the electrode. Although the area is formed by avoiding the portion, it is desirable that the specific adhesion area is the peripheral edge portion of the insulating sheet. As a result, it becomes possible for the electrode portion to easily follow the shrinkage that accompanies the hardening of the concrete.

As the present invention according to claim 7, the formwork for strength determination during demolding is used as a part of a seed formwork for lining concrete in mountain tunnel construction. A formwork for determining the strength of concrete during demolding is provided.

The invention according to claim 7 is a specific application example of the mold for strength determination during demolding. This demolding strength determination formwork is intended to be used as a part of a burying formwork for lining concrete in mountain tunnel construction.

As described above in detail, according to the present invention, the specific resistance is obtained by measuring the potential difference between the electrodes in a state where the plurality of electrodes are in contact with the concrete cast in the formwork, and the demolding is performed from this specific resistance. A mold for determining the strength at the time of demolding of concrete for estimating the strength at time, so that the mold for strength determination at the time of demolding can be repeatedly used without burying the electrode in concrete. Become.

It is a perspective view which shows the pouring point of the lining concrete 13 in mountain tunnel construction. It is a front view of the lining center 10 which shows the installation location of the mold-removing strength determination mold 1 according to the present invention in the case mold. It is a principal part longitudinal cross-sectional view which shows the installation state of the form 1 for strength determination at the time of demolding which concerns on this invention. 1A is a front view, FIG. 1B is a left side view, and FIG. 1C is a plan view showing a mold 1 for strength determination during demolding according to the present invention. FIG. 1A is an enlarged front view of a main part, and FIG. 1B is a left side view of a mold 1 for strength determination during demolding according to the present invention. FIG. 4 is a current/potential wiring diagram for explaining a procedure for measuring specific resistance. It is a principal part front view which shows the mold 1 for strength determination at the time of mold release for calibration. The plastic mold 20 for specific resistance measurement for calibration is shown, (A) is a horizontal cross-sectional view and (B) is a vertical cross-sectional view. It is a correlation graph which shows a calibration result. 5 is a graph showing the correlation between specific resistance (plastic mold) and strength. It is a graph which shows the correlation of the estimated strength by specific resistance, and compression strength.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Application example for lining concrete placement]
As shown in Fig. 1, in the construction of a mountain tunnel, after the excavation due to blasting, etc., spray concrete T is constructed by spraying on the inner wall surface of the excavated tunnel, and after driving the rock bolt, excavation of hydraulic excavator etc. Invert excavation at the bottom of the tunnel by a machine, and a state in which a waterproof sheet is stretched on the inner peripheral surface of the sprayed concrete T using a sheet cart (this surface becomes the side wall surface of the natural ground), the lining centr 10 While sequentially moving the (movable steel form) in the axial direction of the tunnel, every one span in the axial direction of the tunnel, with a distance from the side wall surface of the natural ground, along the circumferential direction of the lining center 10 After positioning the formwork 11 and installing the bedding formwork 12 at the end, concrete is poured into the space between the side wall surface of the natural ground and the formwork 11 through the concrete placing hole 14 provided in the ceiling part, After demolding after waiting for hardening, the lining centr 10 is moved to the next pouring location and the next lining concrete 13 is repeatedly placed.

As shown in FIG. 2, the concrete demolding strength determination mold 1 according to the present invention is installed at the end of the lining sentle 10 with the mold 11 positioned at a predetermined position. It is used as a part of the case frame 12. As shown in FIG. 2, it is desirable that the mold-for-demolding strength determination mold 1 is installed at the top end portion of the chest mold 12. In the case of tunnel lining, concrete is poured from the side wall work window and the concrete pouring hole 14 provided in the ceiling portion and gradually filled from the lower side, so that the top end on the seed side is the portion where concrete is finally filled. Becomes By attaching the mold 1 for strength determination during demolding to this portion, the strength during demolding can be estimated at the site of the youngest age, and the safest side can be determined. In addition, since the electric current that flows is perpendicular to the surface of the formwork 11 of the lining center 10, the formwork 11 (steel material) of the lining center 10 is less likely to be affected.

The mold 1 for strength judgment during demolding obtains a specific resistance by measuring a potential difference between the electrodes in a state where a plurality of electrodes are in contact with concrete cast in the mold, and from this specific resistance It is a formwork capable of estimating the strength at the time of demolding, and as shown in FIGS. 3 to 5, an insulating resin plate 2 also serving as the formwork, and a certain direction on one side of the insulating sheet 3. ... and a sheet 5 with electrodes in which a plurality of flexible and thin electrodes 4, 4... Are arranged side by side with a space between them, and the other surface side of the sheet 5 with electrodes is opposite to the resin plate 2. , Are attached and attached in a region A avoiding the portions corresponding to the electrodes 4, 4.

The resin plate 2 is a plate member having a vertically long rectangular shape and a flat plate shape in a plan view, and is installed as a part of the case frame 12 for placing lining concrete. The material may be either a thermoplastic resin or a thermosetting resin, but it is preferable to use a material having high strength and rigidity and electrical insulation. Specifically, known resins such as acrylic, polyethylene, polystyrene, polycarbonate, polybutylene terephthalate, acetal resin, phenol resin, epoxy resin, urea resin can be widely used, but strength and rigidity are high, and cost is low. It is preferable to use acrylic which has electrical insulation properties. Instead of the resin plate 2, it is possible to use a plate material other than a resin having an insulating property.

The width B of the resin plate 2 is preferably about 100 to 300 mm, and the thickness t is about 20 to 40 mm, preferably about 25 to 35 mm.

The insulating sheet 3 is made of a resin sheet material formed in a rectangular shape in a plan view, and a substantially square shape in the illustrated example. As a material, a sheet material manufactured from materials such as polystyrene, polypropylene, polyethylene terephthalate, and vinyl chloride can be preferably used. The thickness is generally 0.3 to 2.0 mm, preferably 0.5 to 1.0 mm, and it is desirable to have sufficient flexibility (deformability).

As the electrode 4, a flexible and thin electrically conductive material is used, and its planar shape is a rectangular shape having a predetermined width and long in one direction. Specifically, it is desirable that the width w is 1.5 to 10 mm, preferably 2 to 7 mm, and the length L is 50 to 150 mm, preferably 70 to 120 mm.

Specifically, the electrode 4 is formed by applying a conductive material such as copper, titanium, or aluminum to the insulating sheet 3 by a printing method such as inkjet, flexographic printing, screen printing, or gravure printing. A printed electrode or a tape-type electrode such as a copper foil, a titanium foil, or an aluminum foil may be attached. With these electrodes, it is possible to easily form a thin electrode having sufficient flexibility and having a thickness of about 0.1 to 0.5 mm.

A plurality of the electrodes 4 are arranged in parallel on one surface side at regular intervals. The electrodes 4, 4,... Are preferably arranged at equal intervals such that the center-to-center distance between adjacent electrodes 4, 4 is a constant interval a. It is desirable that the distance a between the adjacent electrodes 4 and 4 is 10 to 30 mm, preferably about 15 to 25 mm. This interval a can be set appropriately according to the quality of concrete.

It is desirable that the number of the electrodes is at least 4, preferably 5 or more, and more preferably 6 or more and 8 or less. The reason why at least four sets of electrodes are arranged at equal intervals is to enable the Wenner method to be adopted in the measurement of the specific resistance using the four-electrode method. As will be described later, the Wenner method includes four adjacent electrodes as a set, two outer electrodes are connected to a current-carrying device, and two inner electrodes are connected to an electrometer. This is a method of measuring the potential difference between the two inner electrodes when a predetermined current is applied by an electrometer. Other four-electrode methods include the dipole-dipole method and the Schramberger method, but the Wenner method is generally used.

When five electrodes 4 are arranged side by side, it becomes possible to measure two times by shifting electrodes one by one, and when six electrodes are arranged side by side, one electrode as a group is formed. It becomes possible to measure three times by shifting each. The measurement accuracy can be improved by adopting the average value of the measured values of the specific resistance. In the illustrated example, six electrodes are arranged in parallel to enable measurement three times.

The other side of the electrode-equipped sheet 5 is attached to the resin plate 2 by adhesion in a region A that is away from the portion corresponding to the electrode 4. Specifically, it is preferable that the electrode-attached sheet 3 is attached to the resin plate 2 at the peripheral edge portion 5 surrounding the electrodes 4, 4,... With a double-sided tape or an adhesive. That is, by keeping the electrode portions 4, 4... Of the electrode-equipped sheet 3 in a floating state (deformable state) separated from the resin plate 2, the electrodes 4, 4,... Since the adhesion (adhesiveness) is ensured by following the deformation, the contact state between the electrode 4 and the concrete can be maintained, and the energized state can be maintained. When the double-sided tape is used, it is desirable to use a double-sided tape made of a butyl rubber adhesive having a relatively large thickness.

Lead wires 6a, 6a... Are connected to the electrodes 4, 4..., and these lead wires 6a, 6a.. Has been done. As shown in FIG. 3, this connection terminal is extended to the outside when installed as a case frame and is connected to a dedicated resistivity measuring device 7.

ここで、ｃ：キャリブレーションにより得られる定数
ａ：電極の間隔
前記定数ｃは、次の手順で行った脱型時期判定用型枠１のキャリブレーションにより得られる定数である。通常の強度試験用供試体(円柱体)の比抵抗を測定する場合は、両端に電極をあてて電流を流すため平行電流になっているのに対して、本発明に係る脱型時強度判定用型枠１はコンクリート面に接触した電極での計測となるため、キャリブレーションを行い換算定数ｃを設定する必要がある。 [Measurement of specific resistance and estimation of strength]
A detailed description will be given of a method of measuring the specific resistance of the cast concrete using the strength-determining frame 1 during demolding and estimating the strength during demolding from this specific resistance.
<Measurement principle and calibration>
It is conventionally known that the resistivity changes in the process of strength development associated with the hydration reaction of cement, and there is a correlation between the resistivity and strength of concrete. In order to obtain this specific resistance ρ, when a known current I is input to the object, the potential difference V between the electrodes caused thereby is measured and calculated from the following formula (1).

Where c: constant obtained by calibration
a: Electrode spacing The constant c is a constant obtained by the calibration of the demolding timing determination mold 1 performed in the following procedure. When measuring the specific resistance of a normal strength test specimen (cylindrical body), while parallel current is applied to the electrodes by applying current to both ends, the strength determination during demolding according to the present invention is performed. Since the work frame 1 is measured by the electrode in contact with the concrete surface, it is necessary to calibrate and set the conversion constant c.

Hereinafter, an example of the calibration will be described in detail.

As shown in FIG. 7, a demolding strength determination mold 1 according to the present invention is manufactured. In the illustrated example, an acrylic plate 2 having a width of 170 mm and a thickness of 30 mm, which also serves as a mold, a resin sheet 3 of 150 mm (horizontal)×160 mm (vertical)×0.5 mm (thickness), and a 20 mm interval on one side of the resin sheet 3. ., and six electrodes 4, 4... As the electrode 4, a copper foil tape (100 mm(L)×2 mm(w)×0.1 mm(t)) is used. The other side of the electrode-equipped sheet 5 is attached to the acrylic plate 2 by a double-sided tape at a peripheral edge portion having a width of 15 mm, avoiding the regions where the electrodes 4, 4... Are arranged.

On the other hand, for calibration, the resistivity measuring plastic mold 20 shown in FIG. 8 is manufactured. In this resistivity measuring plastic mold 20, a copper plate is provided on a lid plate 21 and a bottom plate 22, and three conductors 23, 23... The specific resistance is measured by using the lid plate 21 and the bottom plate 22 as current electrodes and the selected two conducting wires as potential electrodes.

Then, in the actual concrete construction place (lining concrete laying), the specific resistance is measured by the mold 1 for strength judgment during demolding at a predetermined time after the concrete laying. The measurement procedure is according to the procedure described in [Measurement of resistivity of lining concrete] described later.

On the other hand, the same concrete as the cast lining concrete is used to fill the specific resistance measuring plastic mold 20 with concrete to prepare a sample for measuring specific resistance.

Then, at a plurality of timings with different curing times, almost simultaneously with measuring the specific resistance of the lining concrete by the mold 1 for strength determination during demolding, the specific resistance is measured by the plastic mold 20 for measuring specific resistance. .. By plotting the measurement results of both of these on a graph, a correlation diagram (y=0.723x) between the specific resistance by the mold of the present invention and the specific resistance by plastic molding as shown in FIG. 9 is obtained. According to this measurement result, it was found that c=0.723 was set to convert the specific resistance measured by the mold 1 for strength determination during demolding of the present invention into the specific resistance by plastic molding.

[Measurement of resistivity of lining concrete]
In the construction of a mountain tunnel, if the lining center 10 is positioned at a predetermined position and the formwork 11 is positioned at a position separated from the ground side wall surface by a predetermined distance as shown in FIGS. 2 and 3. When installing the case form 12, the mold-removing strength determination form 1 according to the present invention is attached to the top end portion in place of a part of the case form 12. The electric wire cable 6 extending from the demolding strength determination frame 1 is connected to the resistivity measuring device 7.

When the preparations up to this point are completed, concrete is poured and cured.

For the measurement of the specific resistance, as shown in FIG. 6, the specific resistance is obtained by the four-electrode method using four adjacent electrodes 4 ₁ , 4 ₂ , 4 ₃ , 4 ₄ as one set in order from one end side. At this time, the function as the outer two electrodes ₄ 1, _{4 4} the energization device 8 connected these electrodes ₄ 1, _{4 4} a current electrode, the inner side of the two electrodes ₄ 2, _{4 3} connect the electrometer 9 to function 4 _2, 4 ₃ these electrodes as potential electrode.

In order to obtain the specific resistance, when the current I is applied from the energizing device 8 to the current electrodes 4 ₁ , 4 ₄ , the potential difference V generated between the potential electrodes 4 ₂ , 4 ₃ is measured by the electrometer 9. Then, the specific resistance ρ is obtained from the above equation (1).

Then, the combination of the set of four electrodes 4, 4,... Is shifted one by one as follows to change the combination of the current electrode connecting the energization device 8 and the potential electrode connecting the electrometer 9. The specific resistance ρ is measured for each combination, and the average of the specific resistances obtained in each set is defined as the average specific resistance ρ _m . In the illustrated example, since the six electrodes 4 ₁ to 4 ₆ are attached to the mold 1 for strength determination during demolding, the average specific resistance ρ _m during the next three measurements is obtained.
(1) First time: current electrodes 4 ₁ , 4 ₄ , potential electrodes 4 ₂ , 4 ₃
(2) Second time: current electrodes 4 ₂ , 4 ₅ , potential electrodes 4 ₃ , 4 ₄
(3) Third time: current electrodes 4 ₃ , 4 ₆ , potential electrodes 4 ₄ , 4 ₅

<Estimation of strength during demolding>
Next, before demolding, the strength at the time of demolding is predicted and the demolding time is determined by the following procedure.

The relationship between the specific resistance and strength of concrete is obtained in advance by preliminary experiments.
Specifically, at the time of the above-described calibration, when the resistivity measuring plastic mold 20 is filled with concrete to produce the resistivity measuring specimens, some strength measuring specimens are prepared in advance. A compressive strength test is carried out at different stages to obtain a correlation equation between specific resistance (plastic mold) (Ω·m) and strength (N/mm 2) as shown in FIG. 10. The relationship between the average specific resistance (Ω·m) and the strength (N/mm2) can be linearly approximated by a linear equation as shown in FIG. 10, and the strength can be estimated from the measured specific resistance. Then, the strength is obtained by substituting the measured value of the specific resistance into this linear expression (y=0.717x-4.4109).

The strength is obtained from the average value ρ _m of the specific resistance obtained at the site, and if it is confirmed that the strength is equal to or higher than the target strength (usually ^{2 to 3} N/mm ² ), it is judged as the demolding time and demolded.

In addition, FIG. 11 shows some actual tunnel construction sites, where some concrete samples were made using concrete whose strength was estimated from the specific resistance, the strength test was performed, and comparison with the estimated strength based on the specific resistance was performed. It is the result. As shown in FIG. 11, the estimated strength based on the specific resistance and the compressive strength test value form a slope line of approximately 45°, and it was verified that the estimated strength based on the specific resistance can be estimated with high accuracy.

In the mold 1 for strength determination during demolding having the above configuration, in order to judge the demolding time of the concrete placed in the mold, the electrical properties (potential difference) of the concrete itself due to the hydration reaction are determined. Since a specific resistance method is used, which can measure and directly estimate the strength development of concrete, the method of demolding after a uniform curing time as in the past or the method of indirect calculation from the integrated temperature using heat of hydration It is possible to improve the accuracy of determination of the demolding time by the method of estimating in advance.

Moreover, since the sheet 5 with electrodes is provided on the surface of the resin plate 2 in the frame 1 for strength determination during demolding, the surface of the concrete becomes a flat finish, and at the time of demolding the concrete, the electrode 5 You will not have to leave anything to be buried on the concrete side.

Further, with the present mold 1 for strength determination during demolding, the work is simplified by simply incorporating it as a part of the mold, and since the surface that becomes the contact surface with concrete is formed flat, it is possible to use it when pouring concrete. The risk of equipment failure or damage can be reduced.

[Another form example]
(1) In the above-described example of the form, the form 1 for strength determination during demolding was used for the tunnel lining of mountain tunnels. However, as a part of the form used when constructing a concrete structure such as a building, It is also possible to use the mold 1 for strength determination during demolding.

DESCRIPTION OF SYMBOLS 1... Formwork for strength determination during demolding, 2... Resin plate, 3... Insulating sheet, 4... Electrode, 5... Sheet with electrode, 6... Electric wire cable, 7... Resistivity measuring device, 8... Current carrying device, 9 ... Electrometer, 10... Lining center, 11... Formwork, 12... Seedling form, 13... Lining concrete, 14... Concrete pouring hole, 20... Plastic mold for measuring resistivity

Claims (7)

The specific resistance is obtained by measuring the potential difference between the electrodes in the state where multiple electrodes are in contact with the concrete placed in the formwork, and the concrete for estimating the strength during demolding from this specific resistance. A mold for strength determination during demolding,
The mold for strength determination during demolding is an insulating plate material that also serves as a mold, and a plurality of thin electrodes having flexibility and juxtaposed on one surface side of the insulating sheet in a certain direction with a gap therebetween. At the time of demolding of concrete, characterized in that the other side of the sheet with electrodes is adhered and attached to the plate material in a region avoiding the portion corresponding to the electrodes. Formwork for strength judgment. The mold for concrete strength judgment at demolding according to claim 1, wherein the electrode has a rectangular planar shape having a predetermined width and long in one direction. The mold for strength determination during demolding of concrete according to claim 1, wherein the electrode is a print-type electrode or a tape-type electrode. 4. The mold for demolding strength of concrete according to claim 1, wherein at least four or more electrodes are arranged in parallel at equal intervals. The said board|plate material is a resin board, The mold for strength determination at the time of concrete demolding in any one of Claims 1-4. The mold for demolding strength judgment of concrete according to any one of claims 1 to 5, wherein the region avoiding the part corresponding to the electrode is a peripheral part of the insulating sheet. The mold for strength judgment during demolding is used as a part of a case form for lining concrete in mountain tunnel construction. frame.

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