JP7019401B2 - Cross-section reduction rate estimation method and load bearing capacity estimation method - Google Patents

Description

The present invention relates to a technique for estimating the cross-sectional reduction rate of a reinforcing bar and a technique for estimating the load bearing capacity of the reinforcing bar.

In structures such as RC (Reinforced Concrete) and SRC (Steel Reinforced Concrete) structures, rebar corrosion significantly reduces the structural performance of the structure. Reinforcing bars mainly bear the tensile stress generated in the members, and in the case of healthy reinforcing bars, the entire cross-sectional area is effective, but in the case of corrosion, iron is converted into corrosion products, so the corroded part is mechanically effective. However, the cross-section is reduced by that amount.

For example, Non-Patent Document 1 shows that the cross-sectional area decreases due to corrosion of the reinforcing bar, and the load-bearing performance of the “beam” as a structure decreases as the rate of decrease in the cross-sectional area of the reinforcing bar increases. .. That is, if the cross-sectional reduction rate of the reinforcing bar is known, the load-bearing performance of the corroded and deteriorated structure at the present time can be evaluated.

As a method for measuring the cross-sectional reduction rate of the reinforcing bar, as in Non-Patent Document 2, the outer shape of the reinforcing bar from which the corroded portion before and after the corrosion of the reinforcing bar is removed is measured, and the difference in cross-sectional area is used as the cross-sectional reduction rate. However, this method cannot measure the rate of cross-sectional reduction due to corrosion of reinforcing bars in existing concrete structures. Therefore, if the cross-sectional reduction rate of the reinforcing bar in the concrete in the corrosion process can be estimated without taking out the reinforcing bar, it is possible to evaluate the load bearing performance of the actual structure. For example, in order to estimate the load bearing capacity of the beam, the relationship between the reinforcing bar cross-section reduction rate and the load bearing capacity may be used as in Non-Patent Document 1.

Further, Patent Document 1 discloses a method of detecting corrosion of a reinforcing bar by an optical fiber sensor.

Japanese Unexamined Patent Publication No. 2016-186482

Mitsuyasu Iwanami, 2 others, "Effects of Reinforcing Bar Corrosion on the Load-Resistant Performance of RC Beams", Annual Papers on Concrete Engineering, Vol.24, 2002, No.2, 1501-1506 Yusuke Uchida and 2 others "Study on the effect of corrosion on the strength properties of high-strength large-diameter reinforcing bars", Annual Proceedings of Concrete Engineering, Vol.37, 2015, No.1, 979-984

The cross-sectional reduction rate of the reinforcing bar is calculated by the following formula.
((Cross-sectional area of reinforcing bar before corrosion)-(Cross-sectional area of reinforcing bar with corroded part removed)) / (Cross-sectional area of reinforcing bar before corrosion) x 100 (%)

However, in these non-patent documents, it is necessary to take out the reinforcing bar from the concrete after corrosion, remove the corrosion product, and then measure the outer shape to calculate the cross-sectional area. It is difficult to measure in a structure and even continuously.

Further, in Patent Document 1, although non-destructive reinforcement corrosion can be detected, the cross-sectional reduction rate of the reinforcing bar cannot be quantitatively estimated.

The present invention has been made in view of such circumstances, and the reduction rate of the cross section of the reinforcing bar in concrete is non-destructively and quantitatively grasped based on the behavior of the expansion strain due to the corrosion of the reinforcing bar of the actual structure. It is an object of the present invention to provide a method for estimating a cross-sectional reduction rate and a method for estimating a load bearing capacity.

(1) In order to achieve the above object, the present invention has taken the following measures. That is, the cross-section reduction rate estimation method of the present invention is a cross-section reduction rate estimation method for estimating the cross-section reduction rate of the steel material reduced due to corrosion of the steel material, and is a step of fixing the optical fiber sensor to the surface of the steel material. The process of detecting the strain of the steel material due to the generation of corrosion products by detecting the change in the characteristics of the light wave propagating in the optical fiber sensor, and the cross-sectional reduction rate of the steel material and the strain due to the corrosion expansion of the steel material. It is characterized by including a step of estimating the cross-sectional reduction rate of the steel material corresponding to the detected strain by using a predetermined function indicating the relationship.

In this way, the strain is detected because the cross-sectional reduction rate of the reinforcing bar corresponding to the detected strain is estimated based on a predetermined function showing the relationship between the cross-sectional reduction rate of the steel material and the strain due to the corrosion expansion of the steel material. This makes it possible to obtain the cross-sectional reduction rate of the reinforcing bar. This makes it possible to quantitatively grasp the cross-sectional reduction rate when the steel material is corroded in a non-destructive manner.

(2) Further, in the method for estimating the cross-section reduction rate of the present invention, the predetermined function actually measures the strain detected by the optical fiber sensor wound around the steel material corroded in the concrete and the cross-section reduction rate of the steel material. It is characterized by being a function specified from the value obtained in the above.

As described above, since the predetermined function is based on the actually measured value, it is possible to accurately grasp the cross-sectional reduction rate.

(3) Further, in the cross-section reduction rate estimation method of the present invention, the steel material is characterized by being a reinforcing bar in a real concrete structure.

In this way, since the optical fiber sensor is wound around the reinforcing bar in the actual concrete structure, it is possible to quantitatively grasp the state of the decrease in the cross-section of the reinforcing bar in the actual structure without destruction.

(4) Further, in the load bearing capacity estimation method of the present invention, the cross-section reduction rate of the steel material obtained by the cross-section reduction rate estimation method according to any one of (1) to (3) above is used to form a concrete structure. It is characterized by estimating the load bearing capacity.

With this configuration, a structure model can be created and analysis such as FEM can be performed using the cross-section reduction rate obtained here. As a result, the load bearing capacity of the concrete member deteriorated by corrosion can be estimated, and by grasping how much the load bearing capacity has deteriorated compared to the time of construction, it will be useful for proper maintenance of the structure.

According to the present invention, since the corrosion reduction rate corresponding to the detected strain is estimated based on a predetermined function, it is possible to obtain the corrosion reduction rate if the strain can be detected. This makes it possible to quantitatively grasp the corrosion reduction rate when the steel material is corroded.

It is a figure which shows the method of installing the optical fiber sensor which concerns on this embodiment on the steel material such as a reinforcing bar in concrete. It is a figure which shows the outline of the corrosion sensor which concerns on this embodiment. It is a figure which shows the outline of the electric corrosion test. It is a figure which shows the outline of the polishing steel bar 60 around which the optical fiber sensor 61 is wound. It is a graph which shows the relationship between the cross-sectional reduction rate of a steel material, and the strain due to the corrosion expansion of a steel material.

The present inventors focused on the relationship between the corrosion expansion of the steel material due to corrosion and the cross-sectional reduction rate, fixed the optical fiber sensor to the steel material, and corroded the steel material obtained from the strain of the optical fiber sensor in a corrosive environment in concrete. We have found that the cross-sectional reduction rate of reinforcing bars can be grasped by formulating the relationship between the expansion strain and the cross-sectional reduction rate of steel materials, and have reached the present invention.

That is, in the method for estimating the cross-sectional reduction rate of the reinforcing bar of the present invention, the generation of corrosion products is generated by verifying the step of fixing the optical fiber sensor on the surface of the steel material and the change in the characteristics of the optical wave propagating in the optical fiber sensor. Using a predetermined function showing the relationship between the step of detecting the corrosion expansion strain of the steel material and the strain due to the corrosion expansion of the steel material, the cross-sectional reduction of the steel material corresponding to the detected strain is performed. It is characterized by including a step of estimating the rate.

This made it possible for the present inventors to quantitatively grasp the cross-sectional reduction rate of the steel material. Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a diagram showing a method of installing an optical fiber sensor according to the present embodiment on a steel material such as a reinforcing bar in concrete. An optical fiber sensor 61 having a detection unit for detecting strain is provided on the reinforcing bar 59 of the structure. As a result, an optical signal capable of long-distance transmission can be used, and non-destructive multipoint measurement can be performed. Further, a covering portion that covers the reinforcing bar 59 and the optical fiber sensor 61 may be provided. By providing the covering portion, it is possible to prevent the reinforcing bar from rusting before being installed in the reinforced concrete structure.

FIG. 2 is a diagram showing an outline of the strain sensor according to the present embodiment. As shown in FIG. 2, instead of directly installing the optical fiber sensor on a steel material such as a reinforcing bar, the optical fiber sensor 14 may be separately installed as a corrosion sensor 11 wound on the steel material. The corrosion sensor 11 includes a polishing bar steel 12 as an iron steel material, and an optical fiber sensor 14 having a detection unit 13 wound around the surface of the polishing bar steel 12 to detect strain. The embedding depth of the corrosion sensor 11 is preferably set to the same depth as the reinforcing bar of the structure so that the environment of the corrosive component is equal to that of the reinforcing bar. Instead of the polished steel bar 12, the same reinforcing bar as the structure to be buried may be used. Further, the corrosion sensor 11 may include a covering portion 15 that covers the polished steel bar 12 and the optical fiber sensor 14. Since the covering portion 15 is provided, it is possible to prevent the polished steel bar 12 from rusting before being installed in the reinforced concrete structure.

Corrosion of steel produces corrosion products and volume expansion. When the steel material is corroded, the optical fiber sensor is also stretched, so that the corrosion expansion of the steel material can be detected by measuring the strain of the optical fiber sensor. Since the behavior differs depending on the environmental conditions and concrete, when the optical fiber sensor is wound around the steel material, it is wound so as to be in close contact with each other, preferably to apply a tensile force. This makes it possible to measure strain on both the expansion side and the contraction side.

Further, when the optical fiber sensor is wound around the steel material, the optical fiber sensor may be attached in a straight line or bent in a wavy shape, but preferably in a spiral shape or a loop so as to go around. Wrap it in a shape. When wrapping around a deformed reinforcing bar, it is easier to wrap it along ribs or knots. The larger the number of laps, the more the corroded part and the optical fiber overlap, so it is detected early. However, if the number of laps is too large, it will prevent the corrosion factor from reaching the steel material. As a guide, the fiber length (mm) / steel surface area (mm ² ) is 0.01 to 2 for the number of laps when spirally wound. In any case, it suffices if the optical fiber sensor can detect the change in corrosion that occurs in the steel material. Further, an FBG (Fiber Bragg Gratings) sensor or the like can be used as the detection unit, and the longer or more the detection unit is, the more preferable.

It is preferable that the covering portion has the same composition or the same cement water ratio so that the environment of the reinforcing bar of the structure and the corrosive component are the same. The water-cement ratio should be equal to or higher than that of the structural concrete so that the invasion of the corrosive factor is not hindered at least prophylactically and the corrosive factor reaches the steel material at an early stage. The covering portion is preferably a mortar having a thickness of 3 to 15 mm so that the steel material can be protected without cracking. Further, it is preferable to use an admixture so that separation and bleeding do not occur.

When detecting corrosion, it is desirable to use a dummy sensor together. As the dummy sensor, a dummy sensor in which the entire surface of the corrosion sensor 11 is subjected to anticorrosion treatment may be used, or a second dummy sensor having substantially the same linear expansion coefficient as the polished steel bar 12 and less likely to corrode than the reinforcing bar. A dummy sensor provided on the surface of the bar material and the second bar material and provided with an optical fiber sensor for detecting strain may be used.

Then, the dummy sensor may be installed in the same environment, the strain generated by a factor other than corrosion may be detected by the dummy sensor, and the detected strain may be corrected by using the strain detected by the dummy sensor. This makes it possible to remove the influence of strain caused by factors other than corrosion, such as temperature strain.

That is, various strains occur in concrete due to temperature / humidity, shrinkage of concrete, and external force. Therefore, at least a dummy sensor that is less likely to corrode than the steel material or the corrosion sensor 11 is used, and corrosion is determined by comparing with the strain behavior thereof. As a dummy sensor, there is a method in which a coated mortar is coated with an epoxy resin or the like to prevent neutralization and invasion of deterioration factors and prevent corrosion of carbon steel inside. Alternatively, use stainless steel (for example, SUS410) having the same linear expansion coefficient as carbon steel.

Here, if the corrosion expansion strain of the steel material obtained by the optical fiber sensor and the cross-sectional reduction rate of the steel material corresponding to the strain are obtained in advance, the cross-sectional reduction rate of the steel material can be quantitatively grasped. In this specification, the detection value of the optical fiber sensor is converted into corrosion expansion strain, but if the installation method and the object are the same, the relationship between the detection value of the optical fiber sensor itself and the cross-sectional reduction rate of the steel material is obtained. Is also good.

The cross-sectional reduction rate may be measured by peeling off the corroded portion of the corroded reinforcing bar or dissolving the corroded portion with an aqueous solution of diammonium hydrogen citrate. Further, the cross-sectional reduction rate may be obtained by observing the cut surface with a microscope. Steel materials with different amounts of corrosion expansion strain are sampled, the cross-sectional reduction rate is measured, and the correlation is obtained in advance.

Here, since the relationship between the strain of the optical fiber sensor and the cross-sectional reduction rate of the steel material differs slightly depending on the type and diameter of the reinforcing bar, it is preferable to obtain the relationship between the two for each condition. When the corrosion sensor 11 is used, the relationship between the two may be obtained for each specification. The relationship between the two may be obtained in the laboratory, or data may be accumulated or obtained in the actual structure.

With the obtained cross-section reduction rate, it is possible to evaluate the load-bearing performance of the actual structure based on the already known relationship between the cross-section reduction rate of the reinforcing bar and the load-bearing capacity without taking out the reinforcing bar.

[Verification example]
Next, a verification example will be described. FIG. 3 is a diagram showing an outline of the galvanic corrosion test. A polished steel bar 60 (JIS G3108) with a diameter of 30 mm and a length of 350 mm is used. The volume of this polished steel bar 60 is V. The optical fiber sensor 61 (φ150 μm) shown in Table 1 is wound, the cable 62 is connected, and the optical fiber sensor 61 (φ150 μm) is embedded in the concrete 64. At that time, the cover in the horizontal direction is set to 135 mm evenly on the left and right, and the cover in the depth direction is set to 50 mm from the upper end and 220 mm from the lower end. This is referred to as a specimen 66, and the specimen 66 is submerged in a container 69 having a diameter of 310 mm, and a copper plate electrode 68 as a cathode material is provided at a position 10 mm away from the specimen in water. The copper plate electrode 68 has a width of 100 mm and a length of 300 mm, and a cable 70 is connected to the copper plate electrode 68. Further, a waterproof gauge 72 is installed on the specimen 66 at a position facing the copper plate electrode 68.

図４は、光ファイバセンサ６１を巻き付けたみがき棒鋼６０の概要を示す図である。みがき棒鋼６０のうち、両端の２０ｍｍの部分はコンクリートの外部にあり、それ以外がコンクリート中にあるものとする。コンクリート中の部分を区間１から区間８に分割し、各区間で光ファイバセンサ６１によるひずみの測定を行なう。すなわち、みがき棒鋼６０において、コンクリート中にある部分は、（３５０ｍｍ－４０ｍｍ）より、３１０ｍｍである。

FIG. 4 is a diagram showing an outline of the polished steel bar 60 around which the optical fiber sensor 61 is wound. It is assumed that the 20 mm portions at both ends of the polished steel bar 60 are outside the concrete, and the rest are inside the concrete. The portion in the concrete is divided into sections 1 to 8, and the strain is measured by the optical fiber sensor 61 in each section. That is, in the polished steel bar 60, the portion in the concrete is 310 mm rather than (350 mm-40 mm).

The method of winding the optical fiber sensor 61 is as follows. That is, it is started to be wound from a portion 20 mm from the end portion in the concrete, and is wound so as to advance 25 mm in the longitudinal direction of the polished steel bar 60 for each round. Each section has an interval of 10 mm. To wind the optical fiber cable around the polished steel bar, perform the winding work under a certain tension, for example, after confirming that some tensile strain is generated during winding, and fix both ends of the measuring part with adhesive. .. As a result, in the concrete steel bar 60, there are two 20 mm parts from both ends, eight 25 mm parts around which the optical fiber sensor is wound around, and seven 10 mm parts as the interval between each section, for a total of 310 mm. It has become. This polished steel bar was embedded in concrete (water-cement ratio 60%, 28-day compressive strength 41 N / mm ² ). After demolding, the steel bars exposed from the concrete were coated so as not to corrode, and were wet-cured until the age of 22 days.

As shown in FIGS. 3 and 4, the concrete test piece is immersed in water at a constant temperature of 20 ° C., a copper plate as a cathode material is arranged, and an electrolytic corrosion test with a constant current of 200 mA is performed using the polished steel bar 60 as an anode material. I did. During the test, the corrosion expansion strain of the polished steel bar 60 was continuously measured by an optical fiber sensor in 8 sections.

In the optical fiber sensor, the wavelength was converted to strain by the following equation, and the change in strain due to corrosion was confirmed.

ここで、ε：ひずみ（μ）、λ：測定時の波長（ｎｍ）、λ^*：初期波長（ｎｍ）である。

Here, ε: strain (μ), λ: wavelength at the time of measurement (nm), λ ^* : initial wavelength (nm).

After the concrete was cracked, the concrete portion of the test piece was removed, and the polished steel bar 60 was taken out and immersed in a 10% diammonium hydrogen citrate aqueous solution at 60 ° C. to remove corrosion products. Before the test and after removing the corrosion product, the diameter of the polished steel bar 60 was measured at 10 points in each section using a caliper, the cross-sectional area was calculated from the average diameter, and the cross-sectional area reduction rate after corrosion was calculated.

As a result, as shown in Table 2, the corrosion conditions were different in each of the eight sections at the end of the test, and the results of the corrosion expansion strain and the cross-sectional reduction rate were different in each section. Since the optical fiber sensor is installed in a spiral shape, it is converted into the corrosive expansion strain of the reinforcing bar in the circumferential direction.

図５は、鋼材の断面減少率と鋼材の腐食膨張によるひずみとの関係を示すグラフである。図５に示すように、８区間における鉄筋の断面減少率と腐食膨張ひずみの関係は、「ｙ＝２９．８ｅ^{９．９９９}Ｘ」という関数が得られた。この結果から明らかなように、光ファイバセンサで計測したコンクリート中の腐食膨張ひずみが分かれば、鉄筋の断面減少率が推定でき、構造物モデルを作成してＦＥＭ（Finite Element Method）等の解析を行なう方法などで内部鉄筋が腐食した構造物としての構造耐力の評価もできる。

FIG. 5 is a graph showing the relationship between the cross-sectional reduction rate of the steel material and the strain due to the corrosion expansion of the steel material. As shown in FIG. 5, a function of "y = 29.8e ^9.999 X" was obtained for the relationship between the cross-sectional reduction rate of the reinforcing bar and the corrosion expansion strain in the eight sections. As is clear from this result, if the corrosion expansion strain in the concrete measured by the optical fiber sensor is known, the cross-sectional reduction rate of the reinforcing bar can be estimated, a structure model is created, and analysis such as FEM (Finite Element Method) is performed. It is also possible to evaluate the structural strength of a structure in which the internal reinforcing bars are corroded by the method used.

As described above, according to the present invention, the cross-sectional reduction rate of the reinforcing bar corresponding to the strain detected by the optical fiber is estimated based on a predetermined function. Therefore, the cross-sectional reduction rate is determined by detecting the strain. It becomes possible to ask. This makes it possible to quantitatively grasp the cross-sectional reduction rate of the steel material.

11 Corrosion sensor 12, 60 Polished steel bar 13 Detection part 14, 61 Optical fiber sensor 15 Coating part 59 Reinforcing bar 62 Cable 64 Concrete 66 Specimen 68 Copper plate electrode 69 Container 70 Cable 72 Waterproof gauge

Claims (4)

It is a cross-section reduction rate estimation method that estimates the reduction rate of the cross section of the steel material that has decreased due to the corrosion of the steel material in the actual concrete structure .
The process of fixing the optical fiber sensor to the surface of the steel material and
A step of detecting the strain of the steel material due to the generation of a corrosion product by detecting a change in the characteristics of the light wave propagating in the optical fiber sensor, and a step of detecting the strain of the steel material.
The strain detected by the optical fiber sensor wound around the corroded test steel in the concrete structure and the cross-sectional reduction rate of the test steel are identified from the measured values, and the cross-sectional reduction rate of the steel and the corrosion of the steel are specified. A method for estimating a cross-section reduction rate, which comprises a step of estimating a cross-section reduction rate of a steel material corresponding to the detected strain by using a predetermined function showing a relationship with a strain due to expansion. The cross-section reduction rate estimation method according to claim 1, wherein the predetermined function is obtained according to a change in the type and diameter of the steel material. A dummy sensor, which is an optical fiber sensor provided on the surface of a steel material of the same type as the steel material and having a rust-preventive treatment on the entire surface, or a dummy sensor having a linear expansion coefficient substantially the same as that of the steel material and less likely to corrode than the steel material. The process of installing one of the dummy sensors with an optical fiber sensor on the surface of the steel material in the same environment as the steel material, and
The cross-sectional reduction rate estimation method according to claim 1 or 2, further comprising a step of correcting the strain of the steel material by using the strain detected by the optical fiber sensor constituting the dummy sensor. A load bearing capacity estimation method, characterized in that the load bearing capacity of a concrete structure is estimated using the cross-section reduction rate of a steel material obtained by the cross-section reduction rate estimation method according to any one of claims 1 to 3.

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