Concrete surface treatment method

Abstract

To provide a concrete surface treatment method that suppresses vitrification even in a case of performing high-speed processing.SOLUTION: A concrete surface is irradiated with laser light such that a beam spot scans a surface along a predetermined scan pattern and the scan pattern moves along the surface at a predetermined feed speed. When the beam spot BS repeatedly passes through a predetermined position in the scan pattern, a lap rate being a ratio of a passage route of the beam spot overlapping with a passage route of the beam spot in irradiation of immediately preceding on the surface is equal to or less than 90%.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a concrete surface treatment method in which a laser beam is irradiated onto the surface of concrete to excavate the surface, and to a laser-treated concrete surface. [Background technology]

[0002] In concrete buildings and structures, the surface layer of the concrete may be peeled off for maintenance purposes such as inspecting the internal structure or creating a base for applying repair materials (mortar, paint, etc.). Conventionally, a water jet method has been known as a technique that can be used for such stripping, in which highly pressurized water is sprayed from a nozzle to break the bonds in the concrete by water pressure. In addition, chipping work is known, in which the surface is excavated by mechanical force using picks, drills, and other equipment and tools to destroy or reshape parts of a structure for repair work, etc.

[0003] The surface treatment using the water jet method described above is carried out until relatively large coarse aggregate (gravel, etc.) of about 20 mm in size is exposed, but in recent years it has been proposed to treat such concrete surfaces by irradiating them with laser light. For example, Non-Patent Document 1 describes the use of a quasi-CW laser (QCW) to irradiate a pulsed laser onto a concrete surface. Non-Patent Document 2 describes a method of irradiating a pulsed laser onto the surface of concrete to remove minute parts by thermal shock. Furthermore, although Patent Document 1 does not relate to the surface treatment of concrete, it describes a method in which an irradiation head that irradiates an object with continuous wave (CW) laser light is provided with a wedge prism that deflects the laser light by a predetermined deflection angle, and the laser light is irradiated while rotating this wedge prism, thereby scanning the irradiation point while rotating across the surface of the object. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-89033 [Non-patent literature]

[0005] [Non-Patent Document 1] “Experimental characterization of concrete removal by high-power quasicontinuous wave fiber laser irradiation” Nguyen Phi Long, Hiroyuki Daido, Tomonori Yamada, Akihiko Nishimura, Noboru Hasegawa, and Tetsuya Kawachi, JOURNAL OF LASER APPLICATIONS VOLUME 29, NUMBER 4, NOVEMBER 2017 [Non-patent document 2] “Efficiency of concrete removal with a pulsed Nd:YAG laser” Michael Savina, Zhiyue Xu, Yong Wang, Claude Reed, Michael Pellin, Journal of Laser Applications 12, 200 (2000) p.200-204 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology described in Non-Patent Document 1 has a problem in that silicon-based components such as quartz in the concrete melt, resolidify, and vitrify due to the heat of irradiation. In the technique described in Non-Patent Document 2, vitrification is suppressed by irradiating a high-energy-density pulsed laser for a short irradiation time. However, when performing industrial surface treatment of concrete using laser light, high speed treatment is required. In view of the above-mentioned problems, an object of the present invention is to provide a concrete surface treatment method that suppresses vitrification even when high-speed treatment is performed, and a laser-treated concrete surface. [Means for solving the problem]

[0007] The present invention solves the above-mentioned problems by the following means. The first concrete surface treatment method of the present invention is characterized in that laser light is irradiated onto the surface of concrete so that a beam spot scans along a predetermined scanning pattern and the scanning pattern moves along the surface at a predetermined feed rate, and when the beam spot repeatedly passes through a predetermined location in the scanning pattern, an overlap rate, which is the rate at which the path of the beam spot on the surface overlaps with the path of the beam spot in the immediately previous irradiation, is 90% or less. The inventors of the present invention have discovered that when performing excavation processes such as surface layer peeling by irradiating a concrete surface with a laser, the overlap rate, which is the range in which the irradiation range of the beam spot overlaps with the irradiation range of the previous scanning pattern cycle, is a dominant factor in determining whether vitrification occurs and the extent to which it occurs. According to the present invention, by irradiating the surface of concrete with laser light while scanning in a predetermined pattern so that the overlap rate is 90% or less, it is possible to suppress the occurrence of vitrification even in high-speed processing and obtain a good processed surface. Here, an overlap rate of 90% or less means that the overlap rate calculated based on at least one of the multiple overlap rate definitions described in this specification is 90% or less.

[0008] The second concrete surface treatment method of the present invention is characterized in that, in the first method, the beam spot moves on the surface along a predetermined path having a width equivalent to its diameter, and the overlap ratio is the ratio of the width of overlap between the most recently irradiated path and the most recent path to the diameter of the beam spot. The third concrete surface treatment method of the present invention is characterized in that, in the first method, the overlap ratio is the ratio of the diameter of the beam spot to the feed amount of the scanning pattern at the feed speed in one cycle of the scanning pattern. A fourth concrete surface treatment method of the present invention is characterized in that, in the first method, the overlap ratio is ((1-(S / (V×d×t))×100(%), where V is the moving speed of the beam spot on the surface, d is the diameter of the beam spot, and S is the irradiation area during irradiation time t. According to each of these inventions, the overlap rate can be appropriately defined, and the above-mentioned effects can be reliably obtained.

[0009] A fifth concrete surface treatment method of the present invention is characterized in that, in each of the above methods, the beam spot moves on the surface at a speed of 6 m per second or more. In this way, the beam spot moves at high speed over the surface, so that when a specific point is focused on, it is cooled immediately after receiving heat, thereby suppressing an increase in the surface temperature and preventing vitrification from occurring. A sixth concrete surface treatment method of the present invention is the method described above, wherein the power density of the beam spot on the surface is 0.53 MW / cm 2 The present invention is characterized in that: This allows the amount of heat required for peeling off the concrete surface to be applied in a short time using a high power density, thereby suppressing an increase in surface temperature and preventing vitrification from occurring.

[0010] The seventh concrete surface treatment method of the present invention is to treat the concrete surface with a 0.53 MW / cm 2The laser beam has the above power density, and each irradiation time is 0.12 msec or less, and irradiation is repeated at predetermined intervals. According to this method, by periodically repeating short-term irradiation at high power density at specified intervals, it is possible to excavate the concrete surface while suppressing an increase in surface temperature and preventing vitrification. An eighth concrete surface treatment method of the present invention is characterized in that, in the seventh method, the number of repeated irradiations on the same location on the surface is 10 or less. This makes it possible to prevent vitrification from occurring due to excessively repeated irradiation.

[0011] A ninth concrete surface treatment method of the present invention is characterized in that, in each of the above methods, the output of the laser oscillator that generates the laser light is 2 kW or more. This makes it possible to appropriately form a beam spot with an energy density sufficient to peel off the concrete surface, and to reliably obtain the above-mentioned effects.

[0012] A tenth concrete surface treatment method of the present invention is characterized in that, in each of the above methods, the scanning pattern is set so that the beam spot revolves along a predetermined shape on the surface. According to this, by providing a deflecting means such as a rotating wedge prism in the optical system that emits the laser light, it is possible to form a scanning pattern with a simple configuration. An eleventh concrete surface treatment method of the present invention is characterized in that, in each of the above methods, the scanning pattern is set so that the beam spot moves back and forth on the surface within a predetermined interval. According to this, by providing a deflection means such as a galvano scanner in the optical system that emits the laser light, a scanning pattern can be formed with a simple configuration.

[0013] The first laser-treated concrete surface of the present invention is a laser-treated concrete surface that has been irradiated with laser light so that a beam spot scans the surface of the concrete along a predetermined scanning pattern and the scanning pattern moves along the surface at a predetermined feed rate, and is characterized in that, in at least a portion of the area, excavation marks formed as the beam spot repeatedly passes through a predetermined location in the scanning pattern are arranged so as to overlap with other excavation marks formed immediately before them over an area of ​​90% or less of the diameter of the beam spot in the feed rate direction of the scanning pattern. The second laser-treated concrete surface of the present invention is characterized in that the area of ​​the first concrete surface where vitrification has occurred through melting and re-solidification due to irradiation with the laser light is 50% or less. The third laser-treated concrete surface of the present invention is characterized in that, on the first or second concrete surface, the width of the excavation marks is 0.85 mm or less and the depth of the excavation marks is 1 mm or less. In each of these inventions, the same effects as those of the invention relating to the concrete surface treatment method described above can be obtained. [Effects of the Invention]

[0014] As described above, the present invention can provide a concrete surface treatment method that suppresses vitrification even when high-speed treatment is performed, and a laser-treated concrete surface. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of an irradiation head used in a first embodiment of a concrete surface treatment method to which the present invention is applied. [Figure 2] 1 is a photograph of the surface after irradiation in the first embodiment. [Figure 3] FIG. 3 is a diagram showing an example of a trajectory of a beam spot in the first embodiment. [Figure 4] FIG. 3 is a schematic diagram illustrating the concept of irradiation time in the first embodiment. [Figure 5] FIG. 10 is a diagram showing the correlation between the overlap ratio and the vitrification evaluation results. [Figure 6] FIG. 10 is a diagram schematically illustrating the difference in surface temperature history depending on the overlap ratio. [Figure 7] FIG. 10 is a diagram showing the correlation between the wrap ratio and the power density and the vitrification evaluation results. [Figure 8] FIG. 10 is a diagram showing an example of a trajectory of a beam spot in the second embodiment of the present invention. [Figure 9] FIG. 10 is a diagram showing an example of a trajectory of a beam spot in the third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment A first embodiment of a concrete surface treatment method to which the present invention is applied and a laser-treated concrete surface will be described below. The laser irradiation device for carrying out the concrete surface treatment method of the first embodiment is equipped with an irradiation head 1 that irradiates a beam of laser light R supplied from a laser oscillator via a fiber onto an irradiation object O made of concrete, and performs excavation and peeling treatment of the surface layer of the concrete by scanning the irradiation point (beam spot BS) along a scanning pattern on a circular arc over the surface of the irradiation object O.

[0017] This process involves rotating and scanning the irradiation point (beam spot BS) on the surface of the object to be irradiated O along a relatively large arc, for example, with a diameter of about 10 mm or more, and excavating the surface of the concrete along the path P through which the beam spot BS passes. While continuously performing such irradiation with a CW laser, the scanning pattern is moved relative to the irradiation object O at a predetermined feed rate, so that the entire surface of the irradiation object O is irradiated with the laser. The surface layer can be peeled off by irradiating it with light R. The laser-treated concrete surface is inspected for defects such as cracks and other mechanical defects, chemical alterations, and deterioration of physical properties, and the surface is refinished with mortar, paint, or the like. FIG. 1 is a cross-sectional view of an irradiation head in a laser irradiation device of the first embodiment.

[0018] The irradiation head 1 irradiates an irradiation object O with a continuous wave (CW) laser beam R transmitted from a laser oscillator (not shown) via a fiber (not shown). The irradiation head 1 is, for example, a handheld type that can be held by an operator while working, but it can also be used by attaching it to a robot that can move the irradiation head 1 along a predetermined path. Alternatively, the irradiation object O may be displaced relative to the irradiation head 1 while the irradiation head 1 is fixed.

[0019] The irradiation head 1 includes a focus lens 10, a wedge prism 20, a protective glass 30, a rotary cylinder 40, a motor 50, a motor holder 60, a protective glass holder 70, a housing 80, a duct 90, and the like.

[0020] The focus lens 10 is an optical element onto which the laser beam R, which is transmitted from a laser oscillator (not shown) to the irradiation head 1 via a fiber, is incident after passing through a collimator lens (not shown). A collimating lens is an optical element that converts (collimates) the laser light emitted from the end of the fiber into a substantially parallel beam. The focus lens 10 is an optical element that condenses (focuses) the laser beam R emitted from the collimator lens at a predetermined focal position. The focus lens 10 may be, for example, a convex lens having a positive power.

[0021] The beam spot BS, which is the point of irradiation on the surface of the object O by the laser beam R, is positioned either coincident with this focal position or in a close state within the focal depth (focus state), or spaced apart from the focal position (defocus state). The depth of focus means the range in the optical axis direction in which the beam diameter is equal to or smaller than the diameter of a predetermined allowable circle of confusion.

[0022] The wedge prism 20 is an optical element that deflects the laser beam R emitted by the focus lens 10 by a predetermined deflection angle θ (see FIG. 1) to make the optical axis angles on the incident side and the exit side different. The wedge prism 20 is formed in the shape of a plate whose thickness changes continuously so that the thickness on one side in a direction perpendicular to the optical axis direction on the incident side is greater than the thickness on the other side. The protective glass 30 is an optical element made of a flat glass or the like and arranged adjacent to the wedge prism 20 on the focal position side (on the irradiation object O side, on the beam spot BS side) along the optical axis direction.

[0023] The protective glass 30 is a protective member that prevents foreign matter such as peeled matter and dust that scatters from the irradiation object O side from adhering to other optical elements such as the wedge prism 20. The protective glass 30 is an optical element that is positioned closest to the focal position along the optical axis direction among the optical systems possessed by the irradiation head 1, and is exposed to the irradiation object O side through the space A and the inside of the duct 90 described later. The focus lens 10, wedge prism 20, and protective glass 30 are configured by applying coatings for the purpose of preventing reflection, surface protection, etc. to the surfaces of members made of a transparent material such as optical glass.

[0024] The rotary cylinder 40 is a cylindrical member that holds the focus lens 10 and the wedge prism 20 on its inner diameter side. The rotary cylinder 40 is formed concentrically with the optical axis of the focus lens 10 and the optical axis of the laser beam R incident on the focus lens 10 (the optical axis of the collimator lens). The rotary cylinder 40 is supported by a bearing (not shown) relative to the housing 80 so as to be rotatable about a central axis of rotation that coincides with the optical axis of the focus lens 10 . The rotary cylinder 40 is made of metal such as an aluminum alloy, engineering plastic, or the like.

[0025] The motor 50 is an electric actuator that rotates the rotary cylinder 40 relative to the housing 80 around the central axis of rotation. The motor 50 is configured, for example, as a ring-shaped motor that is concentric with the rotary cylinder 40 and provided on the outer diameter side of the rotary cylinder 40 . A stator (not shown) of the motor 50 is fixed to the housing 80 via a motor holder 60 (described later). A rotor (not shown) of the motor 50 is fixed to the rotary barrel 40 . The motor 50 is controlled by a motor drive device (not shown) so that the rotation speed of the rotating barrel 40 substantially coincides with a desired target rotation speed.

[0026] The orientation of the irradiation head 1 is maintained so that the rotational center axis of the rotating cylinder 40 is perpendicular to the surface of the irradiation object O near the irradiation point, and the motor 50 rotates the wedge prism 20 together with the rotating cylinder 40, so that the beam spot BS rotates and scans in an arc around the rotational center axis of the rotating cylinder 40 along the surface of the irradiation object O. In this state, when the irradiation head 1 is translated along the surface of the irradiation object O, the beam spot BS scans the surface of the irradiation object O while revolving in a circular shape (arc shape). As a result, when focusing on an arbitrary point on the irradiation object O, the laser beam R is intermittently incident for only a short time, and rapid heating and rapid cooling are sequentially performed within a short time. At this time, the surface layer of the irradiation object O is crushed, excavated, and scattered.

[0027] The motor holder 60 is a support member that holds the stator of the motor 50 in a predetermined position inside the housing 80. The main body of the motor holder 60 is formed in a cylindrical shape and is fixed to the housing 80 in a state where it is inserted into the inner diameter side of the housing 80 . The inner peripheral surface of the motor holder 60 is disposed opposite the outer peripheral surface of the motor 50 and is fixed to the stator of the motor 50 .

[0028] A purge gas flow path 61 through which purge gas PG flows is formed in part of the gap between the outer peripheral surface and the inner peripheral surface of the motor holder 60. The purge gas PG is a gas that is blown out toward the irradiation object O from a space A that contacts the surface of the protective glass 30 on the side of the irradiation object O inside the inner cylinder 91 of the duct 90, which will be described later, when the irradiation head 1 is in use (during irradiation). The surface of the protective glass 30 on the side of the irradiation object O is exposed and disposed inside this space A. The purge gas PG has the function of preventing dust and foreign matter, such as fragments of the excavated surface layer, scattered from the irradiation object O side from flying into the housing 80 and adhering to the protective glass 30.

[0029] The purge gas flow path 61 is an opening formed by penetrating a part of the motor holder 60 in the axial direction of the motor 50 . The purge gas PG discharged from the purge gas flow path 61 passes through a flow path provided in the housing 80 and is introduced into the inner diameter side of the inner cylinder 91 of the duct 90 .

[0030] The protection glass holder 70 is a member that is fixed to the inner diameter side of the housing 80 while holding the protection glass 30 . The protective glass holder 70 is formed, for example, in the shape of a disk with a circular opening formed in the center. The laser beam R passes through the opening from the wedge prism 20 side to the irradiation object O side. A recess into which the protective glass 30 is fitted is formed on the surface of the protective glass holder 70 facing the irradiation object O. The protective glass 30 is held inside the housing 80 in a state where it is fitted into this recess.

[0031] The protective glass 30 is detachably attached to a protective glass holder 70 so that it can be replaced if it becomes contaminated or burned. The surface of the protective glass holder 70 opposite to the irradiation object O side is disposed opposite to the end face of the motor holder 60 on the irradiation object O side with a gap therebetween. This gap constitutes part of a flow path (part of a fluid supply portion) that introduces the purge gas PG introduced from the purge gas flow path 61 of the motor holder 60 into the space A on the irradiation object O side of the protective glass 30.

[0032] The housing 80 is a cylindrical member that constitutes the enclosure of the main body of the irradiation head 1. The housing 80 contains the above-mentioned focus lens 10, wedge prism 20, protective glass 30, rotating cylinder 40, motor 50, motor holder 60, protective glass holder 70, etc., as well as the end of the fiber on the irradiation head 1 side (not shown), a collimator lens, etc.

[0033] The duct 90 is a double-tube member provided so as to protrude from the end of the housing 80 on the irradiation object O side. The duct 90 includes an inner cylinder 91, an outer cylinder 92, a dust collector connection cylinder 93, and the like. The motor holder 60, the protective glass holder 70, and the housing 80 are made of metal such as an aluminum alloy, engineering plastic, or the like.

[0034] The inner cylinder 91 is formed in a cylindrical shape. The laser light R passes through the inner diameter side of the inner cylinder 91 and is emitted to the irradiation object O side. The inner cylinder 91 has a small diameter portion 91a at its end on the housing 80 side, the small diameter portion 91a being stepped smaller than the other portions. A purge gas PG is introduced from the inside of the housing 80 into the space A inside the small diameter portion 91a.

[0035] The inner cylinder 91 has a tapered portion 91b formed at its end on the irradiation object O side, the tapered portion 91b narrowing toward the irradiation object O side. The tapered portion 91b has a function of allowing the laser light R to pass through, while throttling the flow of the purge gas PG to increase the flow rate.

[0036] The outer cylinder 92 is a cylindrical member that is arranged concentrically with the inner cylinder 91 and is provided on the outer diameter side of the inner cylinder 91 . A continuous gap is formed between the inner peripheral surface of the outer cylinder 92 and the outer peripheral surface of the outer cylinder 91 over the entire circumference. The outer cylinder 92 has a small diameter portion 92a at its end on the housing 80 side, the small diameter portion 92a being stepped smaller than the other portions. The small diameter portion 92a is fitted into and fixed to the end of the housing 80 on the irradiation target O side. The edge of the end 92b of the outer tube 92 on the side of the object to be irradiated O is formed at an angle with respect to the rotational axis of the rotating tube 40 so that during normal use when irradiating with the rotational axis of the rotating tube 40 horizontal, the upper side is closer to the housing 80 than the lower side.

[0037] The dust collector connection tube 93 is a cylindrical body that protrudes outward from the outer tube 92 and is connected in a state of communication with the inner diameter side of the outer tube 92 near the end of the outer tube 92 on the side of the irradiation target O. The dust collector connection tube 93 is provided below the outer tube 92 during normal use as described above. The dust collector connection tube 93 is disposed at an angle relative to the outer tube 92 so as to approach the housing 80 from the irradiation object O side and move away from the outer tube 92. The other end of the dust collector connection tube 93 is connected to a dust collector (not shown) and is adapted to be vacuum-suctioned so that the inside is at negative pressure.

[0038] In the first embodiment, by rotating the rotary cylinder 40 and the wedge prism 20 while emitting the laser beam R, the beam spot BS revolves along an arc of a predetermined radius along the surface of the irradiation object O. In this state, by moving the irradiation head 1 in a relative translational motion along the surface of the irradiation object O, it is possible to perform an excavation process in which the beam spot BS scans the surface of the irradiation object O while the scanning pattern (circular rotation in the first embodiment) moves over the surface at a predetermined feed rate.

[0039] Hereinafter, an experiment was carried out in which the surface of concrete was irradiated with laser light using the above-described laser irradiation device. The irradiation object O is, for example, a concrete block of 100 mm x 100 mm x 50 mm. First, the output of the CW laser oscillator must be capable of continuously generating a power density that is sufficient to excavate the surface of concrete. In this regard, preliminary experiments confirmed that surface excavation is possible with an output of 2 kW or more. On the other hand, vitrification occurs when silicon-based components such as quartz are heated by the laser, so in the following experiments, we decided to use an ytterbium fiber laser with a maximum output of 3 kW and a wavelength of 1070 nm, which is more likely to cause vitrification than a 2 kW laser and is therefore more severe.

[0040] The diameter of the gyration circle at the focal position of the laser beam R depends on the focal length, the deflection angle of the wedge prism 20, etc., and is, for example, 26 mm. However, since the defocus amount described below is adjusted by changing the distance between the irradiation head 1 and the object to be irradiated O (the position of the beam spot BS and the focal length do not necessarily coincide), the diameter of the gyration circle changes according to the change in the defocus amount. The diameter of the beam spot BS on the surface of the irradiation object O is varied in three stages: 0.43 mm, 0.85 mm, and 1.27 mm, which is adjusted by changing the distance between the irradiation head 1 and the irradiation object O, which is a concrete block.

[0041] The feed speed (the speed at which the circular scanning pattern moves on the surface) when the irradiation head 1 moves parallel to the concrete block is set to two levels: 22 mm / sec and 11 mm / sec. In this experiment, this feed speed was achieved by fixing the irradiation object O, a concrete block, to an automatic stage having, for example, an XY table, but the irradiation head 1 may also be moved while the concrete block is fixed. The number of irradiations was two in each case, and the second irradiation was carried out without delay after the first irradiation. Regarding the number of irradiations, it was previously known that vitrification occurs after multiple irradiations, so we evaluated whether vitrification occurs after the second irradiation.

[0042] The laser beam R was irradiated while changing the irradiation conditions, and the degree of vitrification was evaluated. The results are shown in Table 1. The irradiated sample surfaces were visually observed, and the degree of vitrification was evaluated on a four-point scale. ○ ((4) in Figure 5): Almost no vitrification was observed △ ((3) in Figure 5): Partial vitrification is observed, but not entirely. □ ((2) in Figure 5): Thin vitrification was observed over almost the entire surface ■ ((1) in Figure 5): Severe vitrification (the formation of bubble-like protrusions) was observed over almost the entire surface. FIG. 2 is a photograph of the surface after irradiation in the first embodiment. Figure 2 shows photographs of surfaces representative of each stage in the four-stage evaluation, specifically, from top to bottom, it shows Example 1 (◯), Comparative Example 4 (△), Comparative Example 8 (□), and Comparative Example 6 (■). [Table 1]

[0043] The concepts of the overlap rate and irradiation time shown in Table 1 will be explained below. FIG. 3 is a diagram showing an example of the trajectory (path) of the beam spot BS in the first embodiment. As shown in FIG. 3, the beam spot BS rotates in response to the rotation of the wedge prism 20, and moves in the feed direction of the irradiation head 1 relative to the irradiation object O. As a result, when the wedge prism 20 rotates one revolution (360°), an offset occurs between the previously irradiated path P0 (the locus of the beam spot) and the currently irradiated path P1. Therefore, in this specification, claims, etc., the overlap ratio is defined as the ratio (w / d×100(%)) of the width w of overlap between the most recently irradiated pass P0 and the latest pass P1 to the diameter d of the beam spot BS. The overlap ratio is a value that indicates the percentage of the path of the beam spot BS on the surface that overlaps with the path of the beam spot BS in the previous irradiation when the beam spot BS repeatedly passes through a specified location in the scanning pattern. Here, when the scanning pattern is a circular rotation as in this embodiment, the width w can also be defined as the scanning amount (the amount of feed of the irradiation head) during the period (during one cycle) in which the wedge prism 20 rotates 360°. In other words, the overlap ratio can be defined as the ratio of the beam spot diameter to the feed speed of the scanning pattern in one period of the scanning pattern. For example, in the regions on the left and right of the circular rotation trajectory in Figure 3, the overlap ratio according to this definition is substantially the same as the overlap ratio defined above.

[0044] FIG. 4 is a schematic diagram showing the concept of irradiation time in the embodiment. As shown in Figure 4, the time it takes for the beam spot BS to pass through any point (processing point) set on the path of the beam spot BS is the irradiation time, and if the diameter of the beam spot BS is d and the moving speed of the beam spot BS on the irradiation surface is V, it can be defined as d / V (sec).

[0045] As a result of the above experiment, it is considered that within the range of conditions in which surface excavation occurs using a laser with a wavelength of, for example, 1 μm, the overlap ratio is an important factor determining whether or not vitrification occurs. FIG. 5 is a diagram showing the correlation between the overlap ratio and the vitrification evaluation results. In FIG. 5, the horizontal axis indicates the overlap rate, and the vertical axis indicates the evaluation result (the larger the number, the better. 4, 3, 2, and 1 correspond to ○, △, □, and ■ in Table 1, respectively). As shown in Figure 5, regardless of the power density or scanning speed, the degree of vitrification increased as the overlap ratio increased, and particularly when the overlap ratio exceeded 90%, severe vitrification was observed. This shows that the overlap ratio must be 90% or less, and that a ratio of 85% or less is particularly preferable because it effectively prevents vitrification over almost the entire treated surface.

[0046] FIG. 6 is a diagram showing a schematic diagram of the difference in surface temperature history depending on the lapping ratio. In FIG. 6, the horizontal axis indicates time, and the vertical axis indicates the temperature at a certain point on the surface of the concrete. A state in which the overlap ratio is relatively low is shown by a solid line, and a state in which the overlap ratio is relatively high is shown by a dashed line. When the overlap ratio is changed while keeping the amount of energy given by the laser in one process constant, a high overlap ratio means that the laser light R is irradiated multiple times during scanning.

[0047] In order to excavate the surface of concrete, it is necessary to apply a high amount of energy to the surface layer of the concrete in a short period of time. However, when the overlap ratio is high, the energy applied in one scan (circular rotation) is low, so that energy is not used efficiently for excavation, and the excess energy that does not contribute to excavation is wasted on heating the surface. This causes the surface temperature to rise and exceed the melting point of the silicon-based components contained in the concrete, such as quartz. In contrast, when the overlap ratio is reduced, the number of times the laser light R is irradiated during scanning is reduced, which makes it possible to increase the efficiency of excavation, suppress temperature rise, and suppress vitrification.

[0048] FIG. 7 is a diagram showing the correlation between the lapping ratio and the power density and the vitrification evaluation results. The horizontal axis indicates the overlap ratio, and the vertical axis indicates the power density (irradiation energy per unit irradiation area). As shown in Figure 7, vitrification is suppressed when the power density is higher, for example, 0.53 MW / cm 2 If this is the case, it is clear that vitrification can be suppressed to a sufficient degree unless the overlap rate exceeds 90%. It was also found that vitrification could be effectively suppressed when the beam spot was moved at a speed of 6 m / s or more on the surface.

[0049] Next, the laser-treated concrete surface in this embodiment will be described. By carrying out the concrete surface treatment method of the first embodiment, excavation marks having a width equivalent to the beam spot diameter d are formed at the locations where the beam spot BS has passed. This excavation mark will be superimposed on the excavation mark formed one cycle earlier, for example, at the same angular position of the wedge prism relative to the irradiation head 1, over a range of 90% or less of the diameter of the beam spot BS in the feed direction of the circular scanning pattern (left and right direction in Figure 3). On the surface of such laser-treated concrete, the area where silicon has melted and then resolidified due to irradiation with the laser light is 50% or less. In this embodiment, the width of the excavation mark corresponds to the diameter d of the beam spot BS. If the laser oscillator output is P (W) and the spot diameter is d (cm), then d (cm) ≦ 1.55 × 10 -3 ×√P. For example, if the output is about 3 kW, which allows an operator to hold and handle the irradiation head 1, the width of the excavation mark will be 0.85 mm or less. Furthermore, the depth of the excavation marks (the difference in height between the tip of the convex part and the bottom of the groove part on the surface shape) is, for example, 1 mm or less, which is characterized by being smaller than the surface irregularities produced by existing water jet methods.

[0050] According to the first embodiment described above, the following effects can be obtained. (1) By irradiating the surface of the concrete block with laser light R while moving the beam spot BS in a circular scanning pattern so that the overlap rate is 90% or less, it is possible to suppress the occurrence of vitrification and obtain a good processed surface even when high-speed processing is performed using a continuous wave (CW) laser. (2) The beam spot moves at a speed of 6 m / s or more on the surface of the concrete block, so that after a certain point receives heat, it is immediately cooled, thereby suppressing the increase in surface temperature and preventing vitrification. (3) The power density of the beam spot BS is 0.53 MW / cm 2 As a result of the above, the amount of heat required for peeling off the concrete surface can be applied in a short time using a high power density, the rise in surface temperature can be suppressed, and vitrification can be prevented. (4) The surface of the concrete is subjected to 0.53MW / cm 2 By repeatedly irradiating the laser beam with the above power density for a single irradiation time of 0.12 msec or less at specified intervals, it is possible to fracture the concrete surface while suppressing the rise in surface temperature and preventing vitrification. (5) By limiting the number of repeated irradiations to 10 or less at the same location on the surface, it is possible to prevent vitrification caused by repeated irradiations too many times. (6) By using a high-output laser oscillator with a power of 3 kW, a beam spot with sufficient energy density to peel off the concrete surface can be properly formed, and the above-mentioned effects can be reliably obtained. (7) By providing the rotating wedge prism 20 as deflection means in the optical system that emits the laser light, a scanning pattern in which the beam spot BS rotates in a circular direction can be formed with a simple configuration.

[0051] Second Embodiment Next, a second embodiment of the concrete surface treatment method to which the present invention is applied and the laser-treated concrete surface will be described. In the following embodiments, the description of the commonalities with the previous embodiments will be omitted, and differences will be mainly described. In the second embodiment, instead of the circular scanning pattern using a turning wedge prism in the first embodiment, a scanning pattern that moves back and forth linearly is formed by, for example, a galvanometer scanner having a galvanometer mirror that oscillates around a predetermined axis. FIG. 8 is a diagram showing an example of the trajectory of the beam spot in the second embodiment. In the second embodiment, the path along which the beam spot BS passes progresses in a zigzag pattern. For example, the beam spot BS travels at a speed V along paths P11, P12, and P13 in sequence. In the second embodiment described above, the same effects as those of the first embodiment can be obtained.

[0052] Third Embodiment Next, a third embodiment of the concrete surface treatment method to which the present invention is applied and the laser-treated concrete surface will be described. In the third embodiment, the scanning pattern is set to a spiral shape in which the diameter of the path P20 changes as the path P20 turns in an arc shape. FIG. 9 is a diagram showing an example of the trajectory of the beam spot in the third embodiment. Such a scanning pattern can be realized, for example, by configuring a beam to pass through a plurality of wedge prisms in sequence, and rotating each wedge prism relative to another around a central axis of rotation.

[0053] In the case of such a spiral scanning pattern, it is difficult to apply the definition of the overlap ratio in the first embodiment. However, if the average moving speed of the beam spot BS on the surface of the irradiation object is V (mm / sec), the diameter of the beam spot BS is d (mm), and the irradiation area S (mm) for an arbitrarily set predetermined irradiation time (for example, 1 second) t is 2 ) (hatched area in FIG. 9), the overlap rate can be defined as (1-(S / (V×d×t)))×100(%). Such a definition is useful when it is difficult to apply the definition of the overlap ratio described in the first embodiment due to the shape of the scanning pattern, for example. This is a calculation in which the overlap ratio is the reduction in the actual irradiation area S relative to the theoretical maximum irradiation area V×d where the beam spot BS does not overlap. However, in this case, if the same spot is repeatedly irradiated, the overlap rate will be higher than other definitions, so care should be taken to ensure that the above-mentioned unit time is not set too long. The third embodiment described above also provides the same effects as those of the above-described embodiments.

[0054] (Variation) The present invention is not limited to the above-described embodiments, and various modifications and variations are possible, and these are also within the technical scope of the present invention. (1) The concrete surface treatment method and the configuration of the laser-treated concrete surface are not limited to the above-described embodiments and can be modified as appropriate. For example, the shape, structure, material, manufacturing method, arrangement, number, etc. of each member constituting the laser irradiation device can be changed as appropriate. In addition, the type of laser can be appropriately selected from fiber lasers, YAG lasers, and the like. (2) In each embodiment, the scanning pattern is set to a circular pattern, a linear reciprocating pattern, or a spiral pattern as an example, but the scanning pattern is not limited to this and can be changed as appropriate. Furthermore, the method for forming the scanning pattern is not limited to the rotating wedge prism or the galvanometer scanner. For example, a polygon mirror may be used so that the beam spot repeatedly travels straight in one direction. In addition, for example, a two-axis galvanometer scanner can be used to create a polygonal or other shape scan pattern. It may also be in the form of The scanning pattern may also be a variety of curves such as a hypocycloid, epicycloid, hypotrochoid, or epitrochoid. [Explanation of symbols]

[0055] 1 Irradiation head 10 Focus lens 20 Wedge prism 30 Protective glass 40 Rotating cylinder 50 Motor 60 motor holder 61 purge gas flow path 70 Protective glass holder 80 Housing 90 Duct 91 Inner cylinder 91a Small diameter section 91b Tapered section 92 Outer cylinder 92a Small diameter section 92b End 93 Dust collector connection tube BS Beam Spot P Beam Spot Path A space part

Claims

1. irradiating the concrete surface with laser light so that the beam spot scans along a predetermined scanning pattern and the scanning pattern moves along the surface at a predetermined feed rate, thereby forming excavation marks in the surface layer and peeling off the surface layer; The beam spot is caused to repeatedly pass through a predetermined portion of the scanning pattern, and a passing path of the beam spot on the surface is made to overlap with a passing path of the beam spot in the immediately preceding irradiation. A concrete surface treatment method characterized by:

2. The beam spot is moved on the surface at a speed of 6 m per second or more.

2. The method for treating the surface of concrete according to claim 1,

3. The power density of the beam spot on the surface is 0.53 MW / cm 2 or more.

3. The method for treating the surface of concrete according to claim 1 or 2, characterized by:

4. Repeated irradiation of the surface of concrete with laser light having a power density of 0.53 MW / cm 2 or more for a single irradiation time of 0.12 msec or less at predetermined intervals. The method for treating the surface of concrete according to any one of claims 1 to 3, characterized by:

5. A method for treating concrete surfaces as described in Claim 4, characterized in that the specified interval is based on a period for repeatedly passing through a specified location in the scanning pattern.

6. The number of times of the repeated irradiation at the same location on the surface is 10 or less.

6. The method for treating the surface of concrete according to claim 4 or 5,

7. The output of the laser oscillator that generates the laser light is 2 kW or more, and the laser oscillator oscillates a continuous wave (CW) laser.

7. The method for treating the surface of concrete according to claim 1, wherein the surface of the concrete is treated with a solvent.

8. The beam spot is caused to repeatedly pass through a predetermined location in the scanning pattern, and the path of the beam spot on the surface is made to overlap with the path of the beam spot in the immediately preceding irradiation, and the feed rate of the scanning pattern is adjusted so that the overlap rate is equal to or less than the level at which the degree of vitrification on the surface is acceptable.

8. The method for treating the surface of concrete according to claim 1, wherein the surface of the concrete is treated with a solvent.

9. The beam spot is caused to repeatedly pass through a predetermined location in the scanning pattern, and the path of the beam spot on the surface is made to overlap with the path of the beam spot in the immediately preceding irradiation, and the overlap rate, which is the rate of overlap, is adjusted so as not to exceed the temperature at which components containing Si among the components on the surface of the concrete in the excavated state vitrify.

9. The method for treating the surface of concrete according to claim 1, wherein the surface of the concrete is treated with a solvent.

10. The beam spot is caused to repeatedly pass through a predetermined portion of the scanning pattern; Excavation is performed while maintaining the temperature of the components containing Si at or below the vitrification temperature of the excavated concrete surface.

10. The method for treating the surface of concrete according to claim 1, wherein the surface of the concrete is treated with a solvent.

11. A laser-treated concrete surface having an array of excavation marks along the surface of the concrete, the excavation marks being formed by scanning a beam spot along a predetermined scanning pattern on the surface of the concrete, comprising: In at least a part of the range, the excavation marks are arranged so as to overlap with other adjacent excavation marks in the arrangement direction of the scanning pattern. Laser treated concrete surfaces characterized by:

12. The laser-treated concrete surface of claim 11, wherein the area of ​​the surface that has undergone vitrification is 50% or less.

13. A laser-treated concrete surface as described in claim 11 or claim 12, characterized in that the width of the excavation marks is 0.85 mm or less and the depth of the excavation marks is 1 mm or less.

Images