Concrete strength estimation method and concrete strength estimation system for existing structure using drilling machine

Abstract

To provide a concrete strength estimation method and a concrete strength estimation system for an existing structure using a drilling machine, capable of estimating concrete strength accurately even when a tip of a drill of the drilling machine is in direct contact with a coarse aggregate.SOLUTION: A concrete strength estimation method for drilling an existing concrete structure X using a drilling machine 2 having a small-diameter bit of a predetermined diameter or less, and estimating concrete strength from a drilling speed, comprises: pressing the drilling machine 2 against a concrete structure X with a constant pressure; measuring a drilling speed by performing a drilling process for drilling holes at a rotation speed within a certain range; and estimating the concrete strength of the concrete structure X by calculating an average drilling speed excluding a time during which the measured drilling speed is equal to or less than a predetermined drilling speed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and system for estimating concrete strength of an existing structure using a drilling machine, which uses the drilling machine to drill holes in an existing concrete structure such as a deck, bridge girder, or pier, and estimates the current concrete strength from the drilling speed, etc. [Background technology]

[0002] Many of the civil engineering infrastructures (bridges, tunnels, highways, etc.) constructed mainly in urban areas during the postwar era of rapid economic growth are reaching the end of their lifespan and are now in need of large-scale repairs, renewal, or reconstruction. In particular, concrete structures are in some cases suffering a significant decrease in strength due to aging, salt damage, neutralization, and other factors, and urgent action is required.

[0003] For concrete structures that require such repairs, it is considered essential to first estimate the concrete strength, which allows an objective assessment of the degree of deterioration, and various methods have been proposed for estimating the concrete strength of existing structures.

[0004] For example, conventional methods for estimating the concrete strength of existing concrete structures include percussion measurements, feature extraction using ultrasonic waves or electromagnetic waves, destructive testing of materials by core boring, etc. However, there is a problem in that it is difficult to capture features deep inside using percussion measurements, ultrasonic waves, and electromagnetic waves.

[0005] On the other hand, while core boring can directly grasp the internal condition, it requires large equipment, which takes a lot of time and money, and it is difficult to carry and set up at the actual site, making it difficult to measure easily. For this reason, there is a demand for a method to estimate concrete strength using equipment that is easy to carry, lightweight, and simple.

[0006] Therefore, the inventors proposed a method of estimating the compressive strength of concrete (hereinafter referred to as concrete strength) from the relationship between the drilling speed and the pressing force of a small-diameter grinding drill (hole-boring machine) (see Patent Documents 1 and 2).

[0007] In the method of estimating concrete strength described in Patent Document 1, a concrete structure 65 is cut with a grindstone bit 55 at a constant driving force while the grindstone bit 55 measures the cutting speed of the grindstone bit 55, and the concrete strength of the concrete structure 65 is estimated based on the measured value. In the method of estimating concrete strength described in Patent Document 1, the drilling (perforation) speed of the concrete is constant by controlling the drilling part with air pressure or a torque motor, and the drilling (perforation) speed differs depending on the concrete strength, so that the concrete strength is estimated by measuring the drilling (perforation) speed (see claim 1 in the scope of claims of Patent Document 1, paragraphs

[0024] to

[0049] of the specification, and Figures 1, 13, and 14 of the drawings, etc.).

[0008] Furthermore, the method of estimating concrete strength described in Patent Document 2 involves measuring in advance the drilling speed relative to the concrete strength of each target concrete structure, and identifying the relationship between the concrete strength and the drilling speed based on the measurement results. When drilling a hole h1 into the concrete structure, the control means 7 measures the drilling speed when the feed speed of the drilling section 41 is controlled to a constant value by the constant torque motor 32, and estimates the concrete strength of the concrete structure W from the change in the measured drilling speed (see claim 1 in the claims of Patent Document 2, paragraphs

[0062] to

[0108] of the specification, Figure 1 of the drawings, etc.).

[0009] The concrete strength estimation methods described in Patent Documents 1 and 2 can calculate the drilling speed from the gradient of time and drilling depth even when drilling a hole of about 50 to 100 mm, so they can estimate concrete strength even when drilling a relatively shallow hole. Therefore, they are considered suitable as a simple measurement method at actual sites such as bridges, harbors, and dams.

[0010] However, drilling holes in existing concrete structures damages them and reduces their strength and durability, so there is a demand for smaller drilling diameters. In recent years, with the development of robotics and information technology, attempts have been made to automatically inspect the deterioration of concrete structures using wall-climbing robots and drones. For this reason, if the reaction force of the inspection drill can be reduced, it is expected that such wall-climbing robots and drones will be equipped with small-diameter drilling machines that receive small reaction forces when drilling holes, and that can estimate the strength of concrete.

[0011] Therefore, the grinding drill used in the concrete strength estimation methods described in Patent Documents 1 and 2 was further improved, and an attempt was made to estimate concrete strength by drilling holes using a small-diameter bit (20 mm or less, preferably 3 mm to 5 mm). However, when strength estimation was performed by drilling holes, the smaller the diameter of the grinding bit, the greater the effect when the tip of the grinding bit of the drilling machine comes into direct contact with the coarse aggregate inside the concrete, and the concrete strength estimation methods described in Patent Documents 1 and 2 had a problem of being unable to estimate concrete strength well due to larger errors.

[0012] As another method of estimating the concrete strength of an existing structure using a drilling machine, Patent Document 3 discloses a method of measuring the compressive strength of a concrete member, in which a hammer drill is used to drill a hole at a constant speed to a predetermined depth in the concrete member whose compressive strength is to be measured, and the reaction force that the hammer drill receives from the concrete member during drilling and the displacement of the hammer drill in the drilling direction are measured over time, and the compressive strength is estimated by determining the drilling energy obtained from the sum of the product of the reaction force and the displacement (see claim 2 in the claims of Patent Document 3, paragraphs

[0009] to

[0027] of the specification, and Figures 1, 4, and 5 of the drawings, etc.).

[0013] Furthermore, Patent Document 4 discloses a method for measuring compressive strength of concrete, including the steps of: screwing a male screw into a concrete member using an electric screwdriver having a function of maintaining a constant rotational speed; measuring data by a measuring device for determining a torque reaction force generated when the male screw is being screwed; and determining the torque reaction force based on the measurement data measured while the head of the male screw is in contact with the concrete member and over-torque is generated, and estimating the compressive strength of the concrete member by an analyzing device (see claim 1 in the claims of Patent Document 4, paragraphs

[0054] to

[0061] of the specification, Figures 5 and 6 of the drawings, etc.).

[0014] However, although the method for measuring the compressive strength of a concrete member described in Patent Document 3 and the method for measuring the compressive strength of concrete described in Patent Document 4 are capable of estimating concrete strength by drilling holes of a certain small diameter, they do not take into account the effect of directly contacting coarse aggregate when drilling the holes, and the accuracy of the estimation is questionable. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] JP 2001-336251 A [Patent Document 2] JP 2014-105527 A [Patent Document 3] JP 2003-139670 A [Patent Document 4] JP 2023-25442 A Summary of the Invention [Problem to be solved by the invention]

[0016] Therefore, the present invention has been devised in consideration of the above-mentioned problems, and an object of the present invention is to provide a method and a system for estimating concrete strength of an existing structure using a drilling machine, which can accurately estimate concrete strength even when the tip of the drill of the drilling machine directly contacts coarse aggregate. [Means for solving the problem]

[0017] The method for estimating concrete strength of an existing structure using a drilling machine according to claim 1 is a method for estimating concrete strength in which an existing concrete structure is drilled using a drilling machine having a small diameter bit of a predetermined diameter or less, and the concrete strength is estimated from the drilling speed, characterized in that the drilling machine is pressed against the concrete structure with a constant pressing pressure, a drilling process is performed to drill holes at a rotation speed within a certain range, the drilling speed is measured, and the concrete strength of the concrete structure is estimated by calculating an average drilling speed excluding the time during which the measured drilling speed is equal to or less than the predetermined drilling speed.

[0018] The method for estimating concrete strength of an existing structure using a drilling machine according to claim 2 is characterized in that, in the method for estimating concrete strength of an existing structure using a drilling machine according to claim 1, the selection of the predetermined drilling speed serving as a threshold value comprises dividing the measured drilling speed into predetermined speeds, selecting a predetermined drilling speed influenced by coarse aggregate from the distribution of the number of hours for each divided speed, and estimating the concrete strength by calculating an average drilling speed excluding the number of hours below the selected predetermined drilling speed.

[0019] The method for estimating concrete strength of an existing structure using a drilling machine according to claim 3 is characterized in that, in the method for estimating concrete strength of an existing structure using a drilling machine according to claim 2, the average drilling speed is calculated by the following formula (1). Here, L Total is the total drilling depth, T Total is the total drilling time, i is the speed range number for removing the effect of coarse aggregate, v c,i is the lower limit of the i-th speed range, t irepresents the number of hours for the i-th speed range.

[0020]

number

[0021] The method for estimating concrete strength of an existing structure using a drilling machine according to claim 4 is characterized in that, in the method for estimating concrete strength of an existing structure using a drilling machine according to claim 1 or 2, the predetermined drilling speed serving as a threshold value is 0.75 mm / s to 1.0 mm / s.

[0022] The concrete strength estimation system of claim 5 is a concrete strength estimation system that estimates the concrete strength of an existing concrete structure using a drilling machine having a small diameter bit equal to or less than a predetermined diameter and a control means, and is equipped with the drilling machine, a propulsion means that guides the drilling machine in the drilling direction and presses the drilling machine with a predetermined pressing pressure, a water supply and drainage means that supplies water to the drilled holes and sucks up the dust generated by the drilling and the supplied water, and a control means that controls the drilling machine and the propulsion means, wherein the propulsion means presses the drilling machine against the concrete structure with a constant pressing pressure, and the drilling machine drills holes at a rotation speed within a certain range, and the control means stores the drilling speed at which the drilling machine drills holes in the concrete structure, calculates an average drilling speed excluding the time during which the measured drilling speed is equal to or less than the predetermined drilling speed, and estimates the concrete strength of the concrete structure by comparing the calculated average drilling speed from the relationship between the concrete strength and the drilling speed that has been stored in advance.

[0023] The concrete strength estimation system of claim 6 is the concrete strength estimation system of claim 5, wherein the control means divides the recorded drilling speed into predetermined speeds, selects a predetermined drilling speed influenced by coarse aggregate from the distribution of the number of hours for each divided speed, and estimates the concrete strength by calculating an average drilling speed excluding the number of hours that are equal to or less than the selected predetermined drilling speed.

[0024] A concrete strength estimation system according to a seventh aspect of the present invention is the concrete strength estimation system according to the sixth aspect, characterized in that the control means calculates the average drilling speed by the following formula (1). Here, L Total is the total drilling depth, T Total is the total drilling time, i is the speed range number for removing the effect of coarse aggregate, v c,i is the lower limit of the i-th speed range, t i represents the number of hours for the i-th speed range.

[0025]

number

[0026] The concrete strength estimation system of claim 8 is characterized in that, in the concrete strength estimation system of claim 5 or 6, the specified drilling speed, which is the threshold value stored in the control means, is 0.75 mm / s to 1.0 mm / s. Effect of the Invention

[0027] According to the invention as set forth in claims 1 to 8, even when the tip of the drill of the drilling machine directly contacts the coarse aggregate, the concrete strength of the existing concrete structure can be estimated with high accuracy. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a configuration explanatory diagram showing the configuration of a concrete strength estimation system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing a configuration of a control means of the above concrete strength estimation system. [Diagram 3] FIG. 3 is a photograph showing the state of each test specimen after the drilling test. [Figure 4] FIG. 4 is a diagram showing the relationship between drilling time and coarse aggregate. [Diagram 5] FIG. 5 is a graph showing the distribution of time for each range of drilling speeds. [Figure 6] Figure 6 is a graph showing the change in drilling speed and drilling depth over time for a test specimen with a compressive strength of 24.6 N / mm2. [Figure 7] Figure 7 is a graph showing the change in drilling speed and drilling depth over time for a test specimen with a compressive strength of 30.6 N / mm2. [Figure 8] Figure 8 is a graph showing the change in drilling speed and drilling depth over time for a test specimen with a compressive strength of 37.9 N / mm2. [Figure 9] Figure 9 is a graph showing the change in drilling speed and drilling depth over time for a test specimen with a compressive strength of 49.5 N / mm2. [Figure 10] Figure 10 is a graph showing the change in drilling speed and drilling depth over time for a test specimen with a compressive strength of 83.8 N / mm2. [Figure 11] FIG. 11 is a graph showing the relationship between average drilling speed and compressive strength, taking into account a range of drilling speeds. [Figure 12] FIG. 12 is a graph showing the change in drilling speed and drilling depth over time for the mortar test specimen. [Figure 13] FIG. 13 is a graph showing the change in drilling speed and drilling depth over time for the grout test specimen. [Figure 14] FIG. 14(a) is a graph showing the relationship between the compressive strength of the mortar specimens and the average drilling speed, and FIG. 14(b) is a graph showing the relationship between the compressive strength of the grout specimens and the average drilling speed. [Figure 15] FIG. 15 shows a diagram illustrating a drilling test of an actual bridge specimen using a small-diameter grinding drill, and is a graph showing the time change in the drilling speed and drilling depth of the actual bridge. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, an embodiment of a method and system for estimating concrete strength of an existing structure using a drilling machine according to the present invention will be described in detail with reference to the drawings.

[0030] First, a concrete strength estimation system 1 according to an embodiment of the present invention (hereinafter, simply referred to as concrete strength estimation system 1) will be described with reference to Fig. 1 and Fig. 2. A case will be described in which a concrete floor slab X1, which is an existing concrete structure (existing structure), is drilled by a drilling machine 2 of the concrete strength estimation system 1 according to this embodiment, and the compressive strength of the concrete of the concrete floor slab is estimated from the drilling speed. Fig. 1 is a configuration explanatory diagram showing the configuration of the concrete strength estimation system 1.

[0031] The concrete strength estimation system 1 is composed of a drilling machine 2, a propulsion means 3 that guides and presses the drilling machine 2 in the drilling direction with a predetermined pressure, a water supply and drainage means 4 that supplies water to the drilled hole and sucks up the dust generated by drilling and the supplied water, and a control means 5 that controls the drilling machine 2 and the propulsion means 3.

[0032] (Drilling machine) 1, the drilling machine 2 is a device that has an electric motor 20 as a drive motor whose rotation speed can be measured by an encoder and which can drill holes at a predetermined rated torque, and rotates a shank 21 with the electric motor 20, and grinds and drills a concrete structure X such as a concrete floor slab X1 with a drill bit 22 attached to the tip of the shank 21. For the electric motor 20 in this embodiment, a lightweight, high-output, compact motor with a maximum rotation speed of 8000 rpm, a current of 10 A, an output of 1 kW, and a weight of 0.8 kg is adopted.

[0033] The shank 21 is composed of a water supply shank 23 that connects to the water supply hose 41 of the water supply and drainage means 4, and a shank shaft 24 that connects to the water supply shank. The shank shafts 24 are available in various lengths depending on the depth of the hole h1 to be drilled, and are structured so that multiple shafts can be added as needed by screwing them in. The shank shaft 24 in this embodiment is made of cemented carbide and is 200 mm long and has a shaft diameter of 5 mm.

[0034] For the drill bit 22 according to this embodiment, a small-diameter bit of a predetermined diameter (diameter 20 mm) or less is adopted in order to minimize damage to the concrete structure X caused by drilling. Specifically, a round-rod-shaped non-core bit having a diameter of 5 mm and a length of 15 mm and a flat contact surface is adopted. The drill bit 22 is a diamond bit made of an alloy containing a large number of artificial diamonds as an abrasive. Therefore, the drill bit 22 is capable of drilling a small-diameter hole of about 5 mm in diameter even in the high-strength concrete structure X. The drill bit 22 may be a small-diameter bit of a diameter of 20 mm or less, and a diameter of 3 mm to 5 mm is preferable because it does not damage the structure. At the present stage, a bit with a diameter of less than 3 mm has not been put to practical use.

[0035] (propulsion means) The propulsion means 3 is composed of a base 30 that is placed on or attached to a concrete structure X such as a concrete floor slab X1, a support 31 erected on the base 30, a slide block 32 that is configured to be able to slide along the support 31, and a positioning plate 33 that is attached to the side of the base 30 and positions the shank 21 and drill bit 22 of the drilling machine 2. The propulsion means 3 has the function of guiding the rotation of the drilling machine 2 to prevent it from shaking, and of pressing the drilling machine 2 against the concrete structure with a predetermined pressure (e.g., 0.3 MPa) to propel it.

[0036] The base 30 is connected to a vacuum pump 6, and is fixed to the concrete structure X by creating a pressure (vacuum) lower than atmospheric pressure inside the base 30. Therefore, the propulsion means 3 can be fixed to either a horizontal surface such as a concrete deck X1 or a vertical surface such as a bridge substructure. Of course, the drilling machine 2 may be bolted to the horizontal or vertical surface of the concrete structure X using anchor bolts (not shown). The vacuum pump 6 according to this embodiment has a vacuum pressure of 750 mmAq, a flow rate of 1.5 m 3 / min and uses a pump with an output of 1.5kW.

[0037] The propulsion means 3 is connected to a compressor 7, which is an air compressor, via a pressure reducing valve 7a, and the support 31 is a linear air cylinder that can move the slide block 32 up and down with a predetermined pressure. In addition, the support 31 in the illustrated embodiment is erected approximately perpendicular to the base 30, but it may be configured so that the angle is freely adjustable with respect to the base 30 by a configuration of a bolt and an arc-shaped long hole. By making the angle of the support 31 freely adjustable with respect to the base 30, it becomes possible to guide the drilling machine 2 at an angle with respect to the working surface of the concrete structure X.

[0038] In this embodiment, the support 31 is a support with a length of 450 mm and a square cross section of 50 mm x 50 mm, and the compressor 7 is an air compressor of type EWS-30, with a power supply of 100 W, a rated current of 7.5 A, a power consumption of 700 W, a maximum pressure of 0.78 MPa, a rotation speed of 1400 rpm, a discharge volume of 75 L / min, and a tank capacity of 30 L.

[0039] The positioning plate 33 has a function of positioning the drilling position by inserting the shank shaft 24 of the drilling machine 2 near the center and preventing lateral shaking during rotation. This positioning plate 33 is attached so as to be freely swingable, so that even when drilling holes with the support 31 tilted relative to the base 30, the shank shaft 24 can be positioned at a predetermined position and lateral shaking during rotation can be prevented.

[0040] In addition, a cavity is formed on the underside of the positioning plate 33, and a drainage hose 42 of the water supply and drainage means 4 is connected to the side of this cavity, so that the hollow part abutting the concrete structure X is made low pressure (vacuum) and the water supplied through the drilled hole h1 is sucked up.

[0041] In addition, a laser displacement meter 34 manufactured by Hokuyo Denki Co., Ltd. is installed near the top of the support 31, which automatically measures the displacement of the slide block 32 and transmits it to the control means 5, and measures the displacement and advancement speed of the drilling machine 2 fixedly attached to the slide block 32 and records it in the control means 5.

[0042] (Water supply and drainage means) The water supply and drainage means 4 is composed of an apparatus main body 40 having a pump (not shown) that pumps cooling water inside and sucks up wastewater and a 15 L tank, a water supply hose 41 that connects this apparatus main body 40 to the shank 21 of the drilling machine 2 and sends cooling water from the apparatus main body 40 to the water supply chamber, and a drainage hose 42 that connects the apparatus main body 40 to the positioning plate 33 and collects wastewater from the positioning plate 33 to the apparatus main body 40.

[0043] This water supply and drainage means 4 has the function of supplying cooling water to the hole h1 drilled by the drilling machine 2 via a water supply hose 41 using a pump in the device body 40 to cool the drill bit 22, and also of sucking up the supplied water together with dust generated by drilling as drainage water via a drainage hose 42 using a pump in the device body 40. Note that the drainage water returning to the device body 40 via the drainage hose 42 has foreign matter such as dust removed by a filter, and is reused as cooling water from the water supply hose 41.

[0044] (Control Means) Next, the control means 5 of the concrete strength estimation system 1 will be described with reference to Figures 2 and 1. Figure 2 is a block diagram showing the configuration of the control means 5 of the concrete strength estimation system 1. As shown in Figure 1, the control means 5 is connected to the electric motor 20 of the drilling machine 2 via a motor driver 5a, and is also connected to the above-mentioned water supply and drainage means 4, vacuum pump 6, and compressor 7, and has the function of controlling the drilling machine 2 and the propulsion means 3 to record and control the drilling speed v and rotation speed of the drilling machine 2 and the pressing force (pressing force) with which the propulsion means 3 presses the drilling machine 2 against the concrete structure X, and measuring the drilling time.

[0045] The control means 5 is an electronic computer such as a personal computer, a smartphone, or a tablet terminal, and as shown in FIG. 2, it has a memory unit 51 for storing various data, a measurement unit 52 for measuring the drilling time, and a measuring unit 53 for measuring the drilling speed v and the concrete strength (compressive stress of concrete σ: N / mm 2), an estimation unit 54 that estimates the concrete strength σ of the existing concrete structure X, and a display control unit 55 that controls the display means 8.

[0046] The storage unit 51 is a non-volatile memory such as a flash memory that stores various data of the drilling machine 2, etc., or a volatile memory such as a hard disk or an optical disk. The storage unit 51 stores data of a feed speed at which the slide block 32 is moved toward the concrete structure X, which is measured in advance, within a range in which the torque of the electric motor 20 of the drilling machine 2 is constant for the concrete strength σ of each existing concrete structure X serving as a reference. The storage unit 51 also stores data specifying the speed relationship between the concrete strength σ of the reference concrete structure X and the drilling speed v of the drilling machine 2, based on the results of measurements performed while changing a constant value of the torque T.

[0047] The measuring unit 52 is a part that measures the drilling time required to open the hole h1 in the concrete structure X from the time required for the drilling distance (depth), which is the displacement successively measured and sent by the laser displacement meter 34. The data on the drilling time measured by the measuring unit 52 is sent to the calculation unit 53.

[0048] The calculation unit 53 is a part that calculates the hole drilling speed v from the displacement of the slide block 32 (the drilling machine 2) measured by the laser displacement meter 34 and the hole drilling time measured by the measurement unit 52. In addition, as described later, the calculation unit 53 excludes the region of the time period with a low hole drilling speed, and divides the total time period by the remaining total time period to calculate the average hole drilling speed v excluding the influence of the coarse aggregate. mean,i Specifically, the average drilling speed v is calculated from the formula (1) described below. mean,i The value calculated by the calculation unit 53 is sent to the estimation unit 54.

[0049] The estimation unit 54 is a part that estimates the concrete strength σ of the concrete structure X based on the known data of the relationship between the reference concrete strength σ and the drilling speed v stored in the memory unit 51 from the change value of the drilling speed v calculated by the calculation unit 53. That is, the estimation unit 54 compares the drilling speed v for the concrete strength σ of the reference concrete structure X measured in advance and stored in the memory unit 51 with the drilling speed v during drilling of the concrete structure X calculated by the calculation unit 53, and estimates the concrete strength σ of the reference concrete structure X with the matching drilling speed v as the concrete strength σ of the existing concrete structure X. The value of the concrete strength σ estimated by the estimation unit 54 is output to the display means 8 as concrete strength information.

[0050] The display control unit 55 is a unit that controls the display of the display means 8 such as a CRT monitor or a liquid crystal monitor, and causes the display means 8 to display the concrete strength σ estimated by the estimation unit 54, etc.

[0051] Moreover, the estimation unit 54 estimates the concrete strength σ of the concrete structure X from the drilling speed v using equation (2) as described later.

[0052] <Experiment for estimating concrete strength> Next, we will explain the experiment conducted to estimate the concrete strength of an existing structure from the drilling speed of a drilling machine.

[0053] (Experimental Equipment) The experimental device used was the concrete strength estimation system 1 according to the embodiment of the present invention described above and shown in Fig. 1. Specifically, the drilling machine 2 used was an electric motor 20, which was a lightweight, high-output, small motor with a maximum rotation speed of 8000 rpm, a current of 10 A, an output of 1 kW, and a weight of 0.8 kg. The shank shaft 24 was a shank shaft made of cemented carbide with a length of 200 mm and a shaft diameter of 5 mm, and the drill bit 22 was a diamond bit with a diameter of 5 mm and a length of 15 mm.

[0054] In addition, a linear air cylinder equipped with a support 31 having a length of 450 mm and a square cross-section of 50 mm x 50 mm was used as the propulsion means 3, and a laser displacement meter manufactured by Hokuyo Denki Co., Ltd. with a measurement distance of 250 mm ± 150 mm was used as the laser displacement meter 34.

[0055] The water supply and drainage means 4 has a pump capacity of 2000 mmAq vacuum pressure and a flow rate of 2.5 m 3 / min, a 1.1kW pump and a 15L tank were used.

[0056] Furthermore, the vacuum pump 6 is a pump with a vacuum pressure of 750mmAq, a flow rate of 1.5m3 / min, and an output of 1.5kW, and the compressor 7 is an air compressor with a model EWS-30, power supply of 100W, rated current of 7.5A, power consumption of 700W, maximum pressure of 0.78MPa, rotation speed of 1400rpm, discharge volume of 75L / min, and tank capacity of 30L.

[0057] (Test specimen) In order to understand the performance of the drilling machine 2, five types of concrete test specimens (length 300 mm × width 300 mm × height 200 mm) with different strengths, three types of mortar test specimens (length 300 mm × width 300 mm × height 200 mm) that do not contain coarse aggregate, and three types of grout test specimens (diameter 150 mm × height 200 mm) that do not contain coarse aggregate or fine aggregate were produced. Three of each test specimen were produced for the drilling experiment and the compression test. The test surface was finished flat so that the drilling machine 2 could be sufficiently sucked by the vacuum pump 6. Figure 3 shows the appearance of the test specimens. Figure 3 is a photograph showing the state of each test specimen after drilling. As shown in Figure 3, the numerous small holes on the surface of each test specimen are the result of drilling with a drill bit 22 with a diameter of 5 mm.

[0058] Tables 1, 2, and 3 show the basic mix proportions of each test specimen and the compressive strength values ​​measured in conjunction with the implementation of the experiments. Table 1 shows the basic mix proportions and compressive strengths of the concrete test specimens, Table 2 shows the basic mix proportions and compressive strengths of the mortar test specimens, and Table 3 shows the basic mix proportions and compressive strengths of the mortar test specimens. The compressive strength of the test specimens was estimated from the measurements of test pieces prepared separately in conjunction with the drilling experiments, which were destroyed using a compression testing machine.

[0059] [Table 1]

[0060] [Table 2]

[0061] [Table 3]

[0062] The specifications of the test pieces are shown in Table 4. The experiment was carried out by varying the drill speed, pressing force (pressing force), etc., and the results were evaluated under the standard conditions (rotation speed: 3000 rpm, drill pressing force: 0.3 MPa) that allowed drilling to the standard hole depth for all test pieces.

[0063] [Table 4]

[0064] When drilling holes using a small diameter (5 mm) drill, there are cases where the coarse aggregate scattered inside the concrete is directly drilled, and the drilling speed is not necessarily constant. Figure 4 shows the relationship between drilling time and drilling depth when drilling a concrete test specimen. To clearly explain the drilling time and the situation, a typical example of drilling a hole in an area containing a relatively large amount of coarse aggregate is shown, along with a columnar diagram continuously photographed with an endoscope and a frontal image when the drilling depth curve changes significantly. Figure 4 shows the relationship between drilling time and coarse aggregate.

[0065] Observing the state of the drilling depth, as shown in Figure 4, the area near the start of drilling (Photo (1)) is white due to the concrete finishing layer. From the start of drilling to around 60 seconds, the change is relatively linear, and the layer is a mixture of white (concrete) and black (coarse aggregate) (Photo (2)). Around Photo (3), the proportion of mortar increases, and it can be seen that the drilling slope is slightly higher. In the drilling time range of 130 to 190 seconds, the drilling depth is almost constant, and it can be seen that the black coarse aggregate is being drilled as seen in Photo (4). It takes a considerable amount of time to drill the hole. After passing through the coarse aggregate, the layer becomes a mixture of coarse aggregate and mortar again, and the drilling slope increases (Photo (5)), and then reaches the longest part of the drilling hole (Photo (6)). In this way, when drilling a 5 mm hole, it is drilling an area where coarse aggregate and mortar are mixed, and the drilling slope (drilling speed) constantly changes.

[0066] As is clear from Figure 4, the drilling gradient changes depending on the internal state of the concrete, so the drilling speed (mm / s) was calculated every second. Figure 4 (bottom) shows the relationship between the drilling speed and each drilling time. It can be clearly seen that the drilling speed changes in response to the gradient of the drilling depth. It can also be seen that in areas affected by coarse aggregate, the drilling speed is less than 1.0 mm / s. Figure 5 shows the distribution of the number of hours for each range of drilling speeds, with the corresponding number of hours in Table 5. Figure 5 is a graph showing the distribution of the number of hours for each range of drilling speeds.

[0067] [Table 5]

[0068] Here, drilling (1) represents the drilling position of the test specimen. The drilling speed is divided into 0.25 mm / s increments, and each value indicates the cumulative time belonging to the upper and lower speed ranges. From the distribution of the number of hours, it can be seen that the number of hours is concentrated in the range where the drilling speed is smaller than 1.0 mm / s, and it can be seen that this region is the range affected by the coarse aggregate. From this result, by excluding the region of the number of hours with a small drilling speed, and dividing the remaining total number of hours by the total drilling depth (even if the drilling speed is small, drilling progresses according to the number of hours, so this drilling depth is subtracted), the average drilling speed excluding the influence of the coarse aggregate, v mean,i can be calculated from the following equation (1).

[0069]

number

[0070] Here, L Total is the total drilling depth (155 mm in this experiment), T Total is the total drilling time, i is the speed range number to remove the effect of the stone layer (coarse aggregate), v c,i is the lower limit of the i-th speed range, t i represents the number of hours for the i-th speed range. Table 5 shows the average drilling speed v calculated by Eq. (1). mean,i The larger i is, the greater the average drilling speed v mean,i It can be seen that the effect of the stone material (coarse aggregate) becomes smaller, and the effect of the stone material (coarse aggregate) becomes larger. However, since it is difficult to determine the drilling speed at which to eliminate the effect, the value of the drilling speed including the effect of the coarse aggregate was experimentally verified using test specimens with different compressive strengths.

[0071] <Verification of speed range to eliminate the effects of coarse aggregate> (Drilling of concrete specimen) Drilling tests were conducted on concrete specimens containing a large amount of coarse aggregate. Figures 6 to 10 (1) to (5) show the drilling depth and drilling speed versus drilling time for each specimen with different concrete strength. Also, drilling holes (1) to (3) show the drilling positions of the specimens. Figure 6 shows the results for a concrete specimen with a compressive strength of 24.6 N / mm 27 is a graph showing the time change of the drilling speed and drilling depth of the test specimen. 2 8 is a graph showing the change in drilling speed and drilling depth over time for the test specimens. 2 9 is a graph showing the time change of the drilling speed and the drilling depth of the test specimen. 2 Fig. 10 is a graph showing the change in drilling speed and drilling depth over time for the test specimens. 2 13 is a graph showing the change in drilling speed and drilling depth over time for the test specimens.

[0072] As shown in Figures 6 to 10, regardless of the strength of the test specimen, the drilling depth is approximately proportional to the time. However, due to the influence of factors such as the distribution of coarse aggregate, the local drilling speed varies greatly. Also, when the change in drilling depth has a low gradient, the drilling speed is often 1 mm / s or less, and it takes a long time to drill through the coarse aggregate. This effect is more pronounced for test specimens with lower compressive strength, and the variation in drilling speed becomes smaller as the compressive strength increases. The range of drilling speeds and the time required for each test specimen are shown in Table 6.

[0073] [Table 6]

[0074] Although the range and duration of each drilling speed are irregular, the relationship was clarified by applying the average drilling speed mentioned above. Note that the drilling was performed on a flat finishing surface, so the effect of the finishing method on the calculation of the drilling speed is unknown.

[0075] (Strength estimation considering the effect of coarse aggregate) The values ​​in Table 6 were substituted into the above equation (1) to calculate the average drilling speed, which is shown in Table 7.

[0076] [Table 7]

[0077] Here, the upper limit of the drilling speed at which the influence of coarse aggregate is suspected is set to a value lower than 1.25 mm / s, and the drilling speed range v c,i The relationship between the strength of the test specimen and the average drilling speed was obtained by separating the test specimens into two groups. The relationship between the average drilling speed and the compressive strength is shown in Figure 11. Figure 11 is a graph showing the relationship between the average drilling speed and the compressive strength, taking into account the range of drilling speeds.

[0078] The plots for drilling holes (1) to (3) show the positions of the holes drilled in each specimen. c,i = 0~0.5), the plots are scattered and it is difficult to see the relationship between the average drilling speed and the strength of the test specimen. c,i When v = 0.75 to 1.0, the individual blots converge and the average drilling speed and the strength of the test specimen are linearly aligned (see the thick dashed line in the figure). Using this relationship, it may be possible to estimate the concrete strength from the average drilling speed. On the other hand, when v c,i At =1.25, the plot values ​​are scattered again and the relationship becomes weaker. This is thought to be because the drilling speeds related to normal drilling (when there is no effect of coarse aggregate) were also excluded.

[0079] In this way, when drilling a hole with a 5 mm diameter drill bit, V c = 0.75, the concrete strength σ can be estimated using equation (2) from the gradient of the straight line obtained in Figure 11.

[0080]

number

[0081] (Strength estimation using test specimens with little effect of coarse aggregate) Using mortar and grout specimens, drilling experiments were carried out similar to those for the concrete specimens. Examples of drilling tests are shown in Figures 12 and 13. Figure 12 is a graph showing the time-dependent changes in drilling speed and drilling depth for the mortar specimen, and Figure 13 is a graph showing the time-dependent changes in drilling speed and drilling depth for the grout specimen. As shown in Figure 12, the drilling depth for the mortar specimen shows a slightly wavy change, but is almost linear with respect to the drilling time. Photographs A, B, and C in the figure are cross-sections near the change in drilling speed, and it can be seen that all are almost uniform due to the absence of coarse aggregate.

[0082] The drilling speeds for the mortar and grout specimens are around 2-4m / s and 1.5-2mm / s, which correspond to speeds where there is no effect of coarse aggregate, as with the concrete specimens mentioned above. In this case, the drilling speed Vc = 0, and the average drilling speed can be calculated by dividing the drilling depth by the drilling time. The grout and mortar specimens show similar trends, and it can be seen that there is no effect of coarse aggregate.

[0083] Table 8 shows the relationship between the drilling speed and the compressive strength in the mortar test specimens, and Table 9 shows the relationship between the drilling speed and the compressive strength in the grout test specimens.

[0084] [Table 8]

[0085] [Table 9]

[0086] Furthermore, Figure 14 shows the relationship between the compressive strength and the average drilling speed of the mortar and grout test specimens. Figure 14(a) is a graph showing the relationship between the compressive strength and the average drilling speed of the mortar test specimens, and Figure 14(b) is a graph showing the relationship between the compressive strength and the average drilling speed of the grout test specimens. As is clear from Figure 14, in both the drilling tests of the mortar and grout test specimens, the average drilling speed has an almost linear relationship with the compressive strength. The compressive strength can be expressed by a simple linear equation with respect to the average drilling speed, and it is believed that the strength of each test specimen can be estimated.

[0087] (Strength estimation based on actual bridge concrete) The aforementioned drilling machine 2 (concrete strength estimation system 1), which is a small-diameter grinding drill used in the test specimen, was applied to an actual bridge structure, and the results were compared with those of the concrete test specimen. The bridge was the Ota Overpass, which was constructed approximately 50 years ago, and some of the components (strength: 60.7 N / mm 2 ) A drilling test was carried out. The results of the drilling test are shown in Figure 15. Figure 15 shows the results of the drilling test on an actual bridge specimen using a small-diameter grinding drill, and is a graph showing the time-dependent change in the drilling speed and drilling depth of the actual bridge.

[0088] As shown in Figure 15, the change in drilling depth was characterized by the influence of almost flat aggregate, but there were many areas where the drilling speed was 1 mm / s or less. Based on this data, the same operation (v c The average drilling speed was calculated from the total time excluding the time less than v = 1.0. mean,i = 1.96. The plots marked with black circles in Figure 11 indicate the corresponding relationship, and it was confirmed that this is close to the relationship between the drilling speed and compressive strength of the concrete specimen.

[0089] From the above results, the effect of coarse aggregate v c By calculating the average drilling speed excluding the time period below =1.0, it is possible to estimate the relationship with concrete strength.

[0090] (summary) When drilling holes with a small 5mm drill, the drilling speed changes significantly due to the influence of coarse aggregates mixed in the concrete. Therefore, the range of drilling speeds caused by coarse aggregates was found from the analysis of drilling speeds, and the average drilling speed v excluding the influence of coarse aggregates was calculated. c,i As a result, v c,i For v = 0.75 to 1.0, the strength σ of the test specimens is almost linear, c,i It was confirmed that σ and σ have a simple linear relationship. Since mortar and grout do not contain coarse aggregate, v mean,i It was confirmed that the relationship between and σ was almost linear. From the results of this experiment, it seems possible to estimate the strength of concrete members by considering the effect of coarse aggregate even with a small-diameter grinding drill.

[0091] <Method of estimating concrete strength of existing structures using a drilling machine> Next, based on the above, a concrete strength estimation method for an existing structure using a drilling machine according to an embodiment of the present invention (hereinafter, simply referred to as a concrete strength estimation method) will be described. A case will be described in which a concrete floor slab X1, which is an existing concrete structure X, is drilled using the drilling machine 2 of the concrete strength estimation system 1 described above, and the concrete strength is estimated from the average drilling speed.

[0092] (Advance preparation) As a preliminary step, the drilling machine 2 is pressed against the concrete with a constant pressure (pressing force) (e.g., 0.3 MPa) of the propelling means 3 of the concrete strength estimation system 1 to drill holes, and the relationship between the drilling speed and the concrete strength σ is obtained and stored in the memory unit 51 of the control means 5 to be constructed as a database. At this time, in order to eliminate the influence of coarse aggregate, data in which the drilling speed falls below a predetermined speed described below is excluded, and the database is constructed from data in a range in which the drilling speed does not fall below the predetermined speed.

[0093] (Concrete strength estimation system installation process) Next, in the concrete strength estimation method according to this embodiment, a concrete strength estimation system installation process is performed in which a concrete strength estimation system 1 including a drilling machine 2 is installed at a predetermined position on the concrete deck X1 (concrete structure X) (see Figure 1).

[0094] Specifically, in this process, the vacuum pump 6 is operated, and the base 30 of the propulsion means 3 is adsorbed to a predetermined position on the concrete floor slab X1 (concrete structure X), and the drilling machine 2 attached to the slide block 32 is set in the drilling position using the positioning plate 33.

[0095] (Drilling process) Next, in the concrete strength estimating method according to this embodiment, the electric motor 20 of the drilling machine 2 is driven to perform a drilling step of drilling holes in the concrete floor slab X1 (concrete structure X).

[0096] In this process, the compressor 7 is driven to lower the slide block 32 over the support 31 of the propulsion means 3, and the drilling machine 2 attached to the slide block 32 is pressed against the concrete deck X1 (concrete structure X) with a constant pressing pressure (for example, 0.3 MPa, as in the experiment).

[0097] In addition, in this process, the water supply and drainage means 4 is operated, and cooling water is supplied to the hole h1 drilled by the drilling machine 2 via a water supply hose 41 using the pump of the device main body 40 to cool the drill bit 22, and the water supplied together with the dust generated by drilling is sucked up as drainage via a drainage hose 42 using the pump of the device main body 40, thereby removing the dust.

[0098] In this process, the control means 5 controls the electric motor 20 via the motor driver 5a so as to maintain a predetermined rotation speed of the electric motor 20 (for example, within a certain range such as 3000 rpm ±15%) as much as possible. This is to minimize changes in the drilling speed due to factors other than the concrete strength, such as the pressing pressure and the rotation speed of the electric motor 20.

[0099] (Drilling speed measurement process) Moreover, in the concrete strength estimating method according to this embodiment, a drilling speed measuring step of measuring the drilling speed of the drilling machine 2 by the control means 5 is also carried out in parallel with the hole drilling step.

[0100] Specifically, in this process, the displacement of the slide block 32 is measured by the measuring unit 52 of the control means 5 using a laser displacement meter 34, thereby measuring the displacement of the drilling machine 2 attached and fixed to the slide block 32, and storing the displacement in the memory unit 51.

[0101] Furthermore, the calculation unit 53 of the control means 5 updates the information on the drilling depth obtained from the laser displacement meter 34 every second, and sequentially calculates and calculates the drilling speed v (mm / s) per second. Of course, the calculated drilling speed v can be per minute instead of per second, but as described later, the drilling speed is divided into predetermined speeds, and a predetermined drilling speed influenced by the coarse aggregate is selected from the distribution of the number of hours for each divided speed, so that it is necessary to grasp the drilling speed per short period of time, and therefore it is desirable to measure and calculate the drilling speed in per second.

[0102] (Average drilling speed calculation process) Next, in the concrete strength estimation method according to the present embodiment, in order to eliminate the effect of the tip of the drill bit 22 coming into contact with the coarse aggregate and extremely decreasing the drilling speed, the average drilling speed v mean,i An average drilling speed calculation process is performed to calculate the average drilling speed.

[0103] Specifically, an average drilling speed is calculated excluding the time during which the measured drilling speed v is equal to or lower than a predetermined drilling speed. Here, the predetermined threshold drilling speed is selected by dividing the measured drilling speed v into predetermined speeds (for example, every 0.25 mm / s as in the above experiment), and a threshold drilling speed that is considered to be influenced by coarse aggregate is selected from the distribution of the time for each divided speed.

[0104] In the case shown in FIG. 5, the predetermined drilling speed serving as the threshold value is 1.0 mm / s. From the verification results in FIG. 11, it can be said that the predetermined drilling speed serving as the threshold value may be 0.75 mm / s. In other words, in the case of a general concrete mix in which the concrete strength, the coarse aggregate mix ratio, and the aggregate diameter are within normal ranges, the predetermined drilling speed serving as the threshold value is preferably 0.75 mm / s to 1.0 mm / s. Here, in the concrete strength estimation method according to this embodiment, as described above, the average drilling speed v mean,i is calculated using the above formula (1).

[0105] (Concrete strength estimation process) Next, in the concrete strength estimation method according to the present embodiment, the drilling speed v corresponding to the concrete strength σ of the reference concrete structure X, which has been measured in advance and stored in the storage unit 51, and the average drilling speed v mean,i and the concrete strength σ corresponding to the matching drilling speed v is estimated as the concrete strength σ of the concrete floor slab X1 (concrete structure X) from the data in the memory unit 51.

[0106] As mentioned above, the concrete strength σ may be calculated using the above formula (2). However, formula (2) is a relational expression obtained from the above-mentioned drilling experiment, and it is thought that it may not necessarily be applicable to test specimens with different mixes of coarse aggregate, etc. However, by introducing the concept (relationship) of the average drilling speed that removes the influence of coarse aggregate, it is possible to estimate the concrete strength with sufficient accuracy, even from the drilling speed using a small diameter drill, by removing the influence of coarse aggregate.

[0107] According to the method for estimating concrete strength of an existing structure using a drilling machine according to the embodiment of the present invention described above, the concept (relationship) of the average drilling speed that removes the influence of coarse aggregate is introduced, and the average drilling speed v is calculated using the above formula (1). mean,i Since the concrete strength of the existing concrete structure can be estimated with high accuracy even when the tip of the drill bit 22 of the drilling machine 2 directly contacts the coarse aggregate in the concrete.

[0108] Although the method and system for estimating concrete strength of an existing structure using a drilling machine according to the embodiment of the present invention have been described in detail above, the above-mentioned and illustrated embodiments are merely specific embodiments for carrying out the present invention, and therefore the technical scope of the present invention should not be interpreted as being limited by them. [Explanation of symbols]

[0109] 1: Concrete strength estimation system 2: Drilling machine 20: Electric motor 21;Shank 22: Drill bit 23: Water supply shank 24: Shank axis 3: Propulsion means 30: Foundation 31: Strut 32: Slide block 33: Positioning plate 34: Laser displacement meter 4: Water supply and drainage means 40: Device body 41: Water supply hose 42:Drain hose 5: Control means 5a: Motor driver 51: Storage part 52: Measurement section 53: Arithmetic section 54:Estimation part 55: Display control unit 6: Vacuum pump 7: Compressor 7a: Pressure reducing valve 8:Display means X: Concrete structure X1: Concrete deck

Claims

1. A method for estimating concrete strength, comprising the steps of: drilling an existing concrete structure using a drilling machine having a small-diameter bit of a predetermined diameter or less; and estimating concrete strength from the drilling speed; The drilling speed is measured by performing a drilling process in which the drilling machine is pressed against the concrete structure with a constant pressing pressure and drills holes at a rotation speed within a constant range, and the concrete strength of the concrete structure is estimated by calculating an average drilling speed excluding the time during which the measured drilling speed is equal to or lower than a predetermined drilling speed. A method for estimating concrete strength of an existing structure using a drilling machine, characterized by the above.

2. The selection of the predetermined drilling speed as the threshold value is performed by dividing the measured drilling speed into predetermined speeds, selecting a predetermined drilling speed that is influenced by coarse aggregate from the distribution of the number of hours for each divided speed, and calculating an average drilling speed excluding the number of hours that are equal to or less than the selected predetermined drilling speed, thereby estimating the concrete strength. A method for estimating concrete strength of an existing structure using the drilling machine according to claim 1.

3. The average drilling speed is calculated by the following formula (1): A method for estimating concrete strength of an existing structure using the drilling machine according to claim 2. Here, L Total is the total drilling depth, T Total is the total drilling time, i is the speed range number for removing the effect of coarse aggregate, v c,i is the lower limit of the i-th speed range, t i represents the number of hours for the i-th speed range. [0010]

4. The predetermined drilling speed serving as a threshold value is 0.75 mm / s to 1.0 mm / s. A method for estimating concrete strength of an existing structure using the drilling machine according to claim 1 or 2.

5. A concrete strength estimation system for estimating the concrete strength of an existing concrete structure using a drilling machine having a small diameter bit of a predetermined diameter or less and a control means, The drilling machine includes a propulsion means for guiding the drilling machine in the drilling direction and pressing the drilling machine with a predetermined pressing pressure, a water supply and drainage means for supplying water to the drilled hole and sucking up the dust generated by drilling and the supplied water, and a control means for controlling the drilling machine and the propulsion means, The propelling means presses the drilling machine against the concrete structure with a constant pressing pressure, and the drilling machine drills holes at a rotation speed within a constant range. The control means stores the drilling speed at which the drilling machine drills holes in the concrete structure, calculates an average drilling speed excluding the time during which the measured drilling speed is equal to or lower than a predetermined drilling speed, and estimates the concrete strength of the concrete structure by comparing the calculated average drilling speed with the previously stored relationship between the concrete strength and the drilling speed. A concrete strength estimation system characterized by the above.

6. The control means divides the recorded drilling speed into predetermined speeds, selects a predetermined drilling speed that is influenced by coarse aggregate from the distribution of the number of hours for each divided speed, and calculates an average drilling speed excluding the number of hours that are equal to or lower than the selected predetermined drilling speed, thereby estimating concrete strength. The concrete strength estimation system according to claim 5 ,

7. The control means calculates the average drilling speed by the following formula (1): The concrete strength estimation system according to claim 6 . Here, L Total is the total drilling depth, T Total is the total drilling time, i is the speed range number for removing the effect of coarse aggregate, v c,i is the lower limit of the i-th speed range, t i represents the number of hours for the i-th speed range. [0010]

8. The predetermined drilling speed serving as a threshold stored in the control means is 0.75 mm / s to 1.0 mm / s.

7. The concrete strength estimation system according to claim 5 or 6,

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