Method and structure for protecting sprayed metal film

Abstract

To provide a method and structure for protecting a sprayed metal film capable of protecting a sprayed metal film on a joint part between a steel material and concrete when metal spraying is executed on the steel material.SOLUTION: A predetermined width W from the joint surface with a concrete deck 11 is left as a non-sprayed portion 10B on a steel girder 10, and a sprayed metal film 12 is formed by spraying metal while avoiding the non-sprayed portion 10B. The surface of the sprayed metal film 12 is subjected to a sealing treatment to form a sealed surface 13A. A fluorine-based paint is applied from the non-sprayed portion 10B to the side end portion 12A of the sprayed metal film 12 and the sealed surface 13A to form a protective film 14.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and structure for protecting a metal spray coating applied to a steel material at a joint between the steel material and concrete. [Background technology]

[0002] Metal spraying has high corrosion protection properties and is therefore used as a corrosion protection method for steel bridges in locations where repainting is difficult or in severely corrosive environments. In particular, plasma arc spraying using aluminum-magnesium alloys has been shown to have excellent durability in combined cycle tests (see Non-Patent Document 1), and is being systematically adopted as a corrosion protection method for steel bridge girder ends.

[0003] When metal spraying is applied to the girder ends of an existing steel bridge, a boundary for the metal spraying occurs at the joint between the steel girder and the concrete deck. Non-Patent Document 2 states that caution is required when applying metal spraying in environments where water leaking from concrete decks is often alkaline, and that sufficient care must be taken as this can accelerate the wear of the metal spray coating. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] East Nippon Expressway Co., Ltd., Central Nippon Expressway Co., Ltd., West Nippon Expressway Co., Ltd., Design Guidelines Volume 2: Bridge Maintenance, "3-2-6 Metal Thermal Spraying", August 2016 [Non-patent document 2] Japan Road Association, Steel Highway Bridge Corrosion Prevention Handbook, "Part V Metallic Spraying 2.2.1 Application Environment", March 2014 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, an object of the present invention is to provide a method and structure for protecting a metal sprayed coating that can protect the metal sprayed coating at the joint between steel and concrete when metal spraying is performed on steel. [Means for solving the problem]

[0006] The method for protecting a metal sprayed coating of the present invention is a method for protecting a metal sprayed coating applied to steel at a joint between the steel and concrete, and is characterized by comprising the steps of: when forming the metal sprayed coating on the steel, leaving a predetermined width from the edge of the joint surface with the concrete as a non-sprayed area, spraying metal while avoiding this non-sprayed area; sealing the surface of the metal sprayed coating to form a sealed surface; and forming a protective film made of a fluorine-based paint from the non-sprayed area to the side edge and sealed surface of the metal sprayed coating.

[0007] According to the method for protecting a metal sprayed coating of the present invention, a protective structure for the metal sprayed coating can be obtained, which includes a metal sprayed coating formed on a steel material, with a non-sprayed portion extending for a predetermined width from the edge of the joint surface with the concrete, the metal sprayed coating being formed so as to avoid this non-sprayed portion, a sealed surface formed by sealing the surface of the metal sprayed coating, and a protective film formed from a fluorine-based paint from the non-sprayed portion to the side edge and sealed surface of the metal sprayed coating.

[0008] In this protective structure for a metal sprayed coating, a metal sprayed coating is formed on the steel at the joint between the steel and concrete, from the edge of the joint surface with the concrete, avoiding a predetermined width of the non-sprayed area, and the protective film covers the area from the non-sprayed area, including the side edges of this metal sprayed coating, to the sealed surface of the metal sprayed coating. Therefore, the protective film prevents water that has become alkaline upon contact with the concrete from penetrating into the metal sprayed coating from the side edges, making it possible to protect the metal sprayed coating.

[0009] Metal spray coatings can be formed by melting zinc, aluminum, zinc-aluminum alloys, aluminum-magnesium alloys, etc. and spraying them onto the surface of steel. In particular, the metal spray coating according to the present invention is preferably a plasma arc spray coating using an aluminum-magnesium alloy. Plasma arc spray coatings using aluminum-magnesium alloys have been confirmed to have excellent durability in combined cycle tests. Furthermore, the cross section of the metal spray coating formed by spraying with this aluminum-magnesium alloy is porous. The protective structure for the metal spray coating according to the present invention prevents alkaline water leaking from the concrete deck from penetrating the gaps in the porous metal spray coating, thereby protecting the metal spray coating. [Effects of the Invention]

[0010] According to the present invention, the protective film prevents water that has become alkaline upon contact with concrete from penetrating into the metal sprayed coating applied to the steel material at the joint between the steel material and the concrete from the side edges of the metal sprayed coating, thereby protecting the metal sprayed coating and making it possible to maintain the corrosion prevention performance of the joint between the steel material and the concrete. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of a joint between a steel girder and a concrete deck of a steel bridge in a first embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram showing how rust occurs. [Figure 3] FIG. 10 is a schematic cross-sectional view of a joint between a steel girder and a concrete deck of a steel bridge in a second embodiment of the present invention. [Figure 4] FIG. 10 is a schematic cross-sectional view of a joint between a base plate of a bearing of a steel bridge and a supporting member such as an abutment or pier in a third embodiment of the present invention. [Figure 5] FIG. 1 is an explanatory diagram showing test contents. [Figure 6] FIG. 1 is a schematic diagram showing the test. [Figure 7] 1 is a photograph showing a cross-sectional view of a specimen of Example 1 of the present invention and test results. [Figure 8] 1 is a cross-sectional view of a specimen of Comparative Example 1 and photographs showing test results. [Figure 9] 1 is a cross-sectional view of a specimen of Comparative Example 2 and photographs showing test results. [Figure 10] 10 is a cross-sectional view of a specimen of Comparative Example 3 and photographs showing test results. [Figure 11] FIG. 1 is an explanatory diagram showing test contents. [Figure 12] 1 is a photograph showing a cross-sectional view of a specimen of Example 2 of the present invention and test results. [Figure 13] 10 is a photograph showing a cross-sectional view of a specimen of Comparative Example 4 and test results. DETAILED DESCRIPTION OF THE INVENTION

[0012] <First Embodiment> Fig. 1 is a schematic cross-sectional view of a joint between a steel girder and a concrete deck of a steel bridge in a first embodiment of the present invention. As shown in Fig. 1, in steel bridge 1, a concrete deck 11 made of concrete is joined onto a steel girder 10 made of steel. In the first embodiment of the present invention, a metal spray coating 12 is applied to the side of steel girder 10 at the joint between steel girder 10 and concrete deck slab 11. A predetermined width W on steel girder 10 from end 10A of the joint surface between steel girder 10 and concrete deck slab 11 is defined as a non-sprayed portion 10B. The predetermined width W of metal spray coating 12 formed by metal spraying, avoiding this non-sprayed portion W, is preferably 10 mm or more.

[0013] The metal spraying is performed by plasma arc spraying using an aluminum-magnesium alloy. In the plasma arc spraying method, the spray material (aluminum-magnesium alloy) is melted by a plasma arc to become liquid, and this liquid is then blown toward the steel girder 10 as fine particles of several μm to several tens of μm using compressed air. This forms an aluminum-magnesium alloy coating as the metal spray coating 12 on the base steel girder 10. The thickness of the metal spray coating 12 is preferably 100 μm or more, and more preferably an average thickness of 150 μm or more.

[0014] Next, the surface of metal spray coating 12 is sealed. The sealing treatment is preferably performed by spraying a mist of modified epoxy resin paint diluted 50% with thinner as the primary sealing, and then applying a fluororesin paint, which is an alkali-resistant paint, as sealing material 13 as the secondary sealing. As a result, sealed surface 13A is formed on the surface of metal spray coating 12 by sealing material 13.

[0015] A fluororesin paint is then applied from the non-sprayed portion 10B of a predetermined width W to the side edge 12A of the metal spray coating 12 and the sealed surface 13A to form a protective film 14. The protective film 14 is formed by applying two coats of a thick-film modified epoxy resin primer, followed by an alkali-resistant fluororesin paint intermediate coat and a fluororesin paint top coat. The fluororesin paint constituting the protective film 14 is composed of a modified epoxy resin paint and a fluororesin paint. The protective film 14 is formed to cover the entire non-sprayed portion 10B and a portion of the sealed surface 13A, preferably 10 mm or more, more preferably 40 mm or more. In this embodiment, the protective film 14 is formed 50 mm wide from the edge 10A of the joint surface between the steel girder 10 and the concrete deck slab 11. The thickness of the protective film 14 is equal to or greater than the thickness of the metal spray coating 12, preferably 175 μm or more, and more preferably 235 μm or more.

[0016] In a steel bridge 1 in which cracks 15 have developed in the concrete deck 11 due to deterioration over time, rainwater passes through the cracks 15, resulting in alkaline water (pH 12 or higher) leaking through. In particular, in areas where antifreeze is sprayed in winter, rainwater becomes saltwater, causing alkaline water containing saltwater to leak through. Because the cross section of the metal spray coating 12 is porous, even if the metal spray coating 12 is formed without gaps all the way to the top of the steel girder 10, as shown in Figure 2, leaking water will penetrate through the side end 12A of the metal spray coating 12, dissolving the side end 12A of the metal spray coating 12, and the leaking water will reach the base of the steel girder 10, causing rust 100.

[0017] However, in the protective structure of the metal sprayed coating described above, the metal sprayed coating 12 is formed to avoid the non-sprayed portion 10B at the top of the steel girder 10, and the entire area from the non-sprayed portions 10B above and below the side end 12A of the metal sprayed coating 12 to the sealing material 13 formed on the surface of the metal sprayed coating 12 is covered with a protective film 14 made of a fluorine-based paint. Therefore, the protective film 14 prevents water leakage from the concrete deck 11 from penetrating into the metal sprayed coating 12 from the side end 12A of the metal sprayed coating 12, protecting the metal sprayed coating 12 and maintaining the corrosion resistance of the joint between the steel girder 10 and the concrete deck 11.

[0018] <Embodiment 2> Figure 3 is a schematic cross-sectional view of a joint between a steel girder and a concrete deck slab of a steel bridge in a second embodiment of the present invention. As shown in Figure 3, in the second embodiment of the present invention, a metal spray coating 12 is applied to the underside of the steel girder 10 at the joint between the steel girder 10 and the concrete deck slab 11. Predetermined widths W1 and W2 from the end 10A of the joint surface between the steel girder 10 and the concrete deck slab 11 are defined as non-sprayed portions 10B and 10C. The metal spray coating 12 is formed by spraying metal while avoiding these non-sprayed portions W1 and W2.

[0019] Next, the surface of metal spray coating 12 is subjected to a sealing treatment in the same manner as described above. As a result, a sealed surface 13A is formed on the surface of metal spray coating 12 by sealing material 13. Then, protective film 14 is formed in the same manner as described above from non-sprayed portions 10B, 10C of predetermined widths W1, W2 to side end portions 12A of metal spray coating 12 and sealed surface 13A.

[0020] In the protective structure of the metal sprayed coating obtained in this manner, the metal sprayed coating 12 is formed on the steel girder 10, avoiding the non-sprayed portions 10B, 10C, and is covered with a protective film 14 made of a fluorine-based paint from the non-sprayed portions 10B, 10C to the side end 12A and sealed surface 13A of the metal sprayed coating 12. This prevents rainwater and the like from penetrating into the metal sprayed coating 12 from the side end 12A of the metal sprayed coating 12, protecting the metal sprayed coating 12.

[0021] <Third Embodiment> Fig. 4 is a schematic cross-sectional view of a joint between a base plate of a steel bridge bearing and a supporting member such as an abutment or pier in a third embodiment of the present invention. As shown in Fig. 4, in the third embodiment of the present invention, at the joint between a base plate 30 of the bearing made of steel and a supporting member 31 such as an abutment or pier made of concrete, a metal sprayed coating 12 is applied to the upper surface of the base plate 30. Predetermined widths W1 and W2 from an end 30A of the joint surface between the base plate 30 and the supporting member 31 are defined as non-sprayed portions 30B and 30C. The metal sprayed coating 12 is formed by metal spraying, avoiding these non-sprayed portions W1 and W2.

[0022] Next, the surface of the metal sprayed coating 12 is subjected to a sealing treatment in the same manner as described above. As a result, a sealed surface 13A is formed on the surface of the metal sprayed coating 12 by the sealing material 13. Then, a fluorine-based paint is applied from the non-sprayed portions 30B, 30C of the specified widths W1, W2 to the side end portions 12A of the metal sprayed coating 12 and the sealed surface 13A, thereby forming a protective film 14.

[0023] In the protective structure of the metal sprayed coating obtained in this manner, metal sprayed coating 12 is formed on base plate 30, avoiding non-sprayed portions 30B, 30C, and is covered with protective film 14 made of fluorine-based paint from non-sprayed portions 30B, 30C to side end portion 12A and sealed surface 13A of metal sprayed coating 12. Therefore, rainwater, water leaking from expansion devices (salt water), etc. are prevented from penetrating into metal sprayed coating 12 from side end portion 12A of metal sprayed coating 12, and metal sprayed coating 12 is protected. [Example]

[0024] A test was conducted on the protective structure of the metal spray coating according to the embodiment of the present invention. Fig. 5 is an explanatory diagram showing the test content, and Fig. 6 is a schematic diagram showing the test. As shown in Fig. 5, the test involved immersing a test specimen in a calcium hydroxide aqueous solution with a pH of 12.5 to 13.0 for 48 hours, and then conducting a combined cycle test for 450 hours using a combined cycle tester. The test was conducted three times, and the blister width of the metal spray coating was measured and the average value was calculated for each.

[0025] Figure 7 shows a cross-sectional view of a specimen for Example 1 of the present invention and a photograph showing the test results. The specimen was prepared by spraying an aluminum-magnesium alloy onto a substrate (steel plate) using a plasma arc spraying method. After sealing, a fluororesin coating was applied from the non-sprayed areas of the substrate to the edges of the sprayed coating and the sealed surface to form a protective film. The primary sealing was performed by spraying a mist of an acrylic silicone resin coating (product name: Lilicatite Enamel (SK Chemical Co., Ltd.)) diluted 50% with thinner. The secondary sealing was performed by applying the same acrylic silicone resin coating. The protective film made of fluororesin coating was formed by applying a thick-film modified epoxy resin primer coat (90 μm thick) twice, followed by a fluororesin coating intermediate coat (30 μm thick) and a fluororesin coating top coat (25 μm thick). The total thickness of the protective film was 235 μm. As a result of the test, the average blister width was 0 mm, and it was confirmed that the penetration of calcium hydroxide aqueous solution from the edge of the thermal spray coating was prevented.

[0026] Figure 8 shows a cross-sectional view of the specimen for Comparative Example 1 and a photograph showing the test results. The difference from Example 1 is that the fluorine-based paint was applied only to the sealed surface, not to the non-sprayed portions of the substrate. In other words, no protective film made of fluorine-based paint was formed on the edges of the thermal spray coating. The test results confirmed that the average blister width was 7.4 mm, and that the calcium hydroxide aqueous solution had penetrated from the edges of the thermal spray coating, causing rust on the substrate.

[0027] FIG. 9 shows a cross-sectional view of the specimen for Comparative Example 2 and a photograph showing the test results. In Comparative Example 2, an aluminum-magnesium alloy was sprayed onto a substrate (steel plate) using a plasma arc spraying method, followed by a sealing treatment. The sealing treatment consisted of spraying a mist of an acrylic silicone resin paint (product name: Lyrica Tite Enamel (SK Chemical Co., Ltd.)) diluted 50% with thinner as a sealing material for the primary sealing, and then applying the same acrylic silicone resin paint for the secondary sealing. During the secondary sealing, the acrylic silicone resin paint was applied so as to cover the edges of the sprayed coating. The test results showed an average blister width of 3.4 mm.

[0028] Figure 10 shows a cross-sectional view of the specimen for Comparative Example 3 and a photograph showing the test results. The difference from Comparative Example 2 is that during secondary sealing, the acrylic silicone resin paint was not applied to the non-sprayed portion of the substrate, i.e., the edges of the sprayed coating were not covered with the acrylic silicone resin paint. The test results showed an average blister width of 9.4 mm, confirming that calcium hydroxide solution had penetrated through the edges of the sprayed coating, causing rust on the substrate. The average blister width for Comparative Example 2 was smaller than for Comparative Examples 1 and 3. Although the acrylic silicone resin paint covering the edges of the sprayed coating initially prevented calcium hydroxide solution from penetrating through the edges of the sprayed coating, it is believed that the acrylic silicone resin itself dissolved over time.

[0029] Next, corrosion prevention tests were conducted under different test conditions. Figure 11 is an explanatory diagram showing the test details. As shown in Figure 11, the test involved conducting a combined cycle test for 21 days (504 hours) using a combined cycle testing machine, and then immersing the test specimen in a calcium hydroxide aqueous solution with a pH of 12.5 to 13.0 for 7 days (168 hours). The test was conducted nine times, and the blister width of the metal spray coating was measured and the average value was calculated for each.

[0030] Figure 12 shows a cross-sectional view of a specimen for Example 2 of the present invention and a photograph showing the test results. The specimen was prepared by spraying an aluminum-magnesium alloy onto a substrate (steel plate) using a plasma arc spraying method, sealing the pores using a modified epoxy resin paint as a sealant, and then applying a fluororesin paint from the non-sprayed area of ​​the substrate to the edge of the sprayed coating and the sealed surface to form a protective film. The primary sealing was performed by spraying a mist of modified epoxy resin paint diluted 50% with thinner, followed by a secondary sealing with a fluororesin paint top coat. The protective film was formed by applying two coats of modified epoxy resin paint primer (60 μm thick), followed by a fluororesin paint intermediate coat (30 μm thick), and a fluororesin paint top coat (25 μm thick). The total thickness of the protective film was 175 μm. The test results showed that the average blister width was 1.6 mm, confirming that the penetration of calcium hydroxide solution from the edge of the thermal spray coating was prevented for a long period of time.

[0031] Figure 13 shows a cross-sectional view of the specimen of Comparative Example 4 and a photograph showing the test results. The specimen was the same as that of Comparative Example 2. As a result of the test, it was confirmed that the metal spray coating was in tatters and the average blister width was impossible to measure, and that the calcium hydroxide aqueous solution had penetrated from the edge of the spray coating, causing rust on the substrate. [Industrial Applicability]

[0032] The present invention is useful as a method and structure for protecting a metal spray coating applied to a steel material at a joint between the steel material and concrete. [Explanation of symbols]

[0033] 1 steel bridge 10 steel girder 11 Concrete deck 12 Metal spray coating 13 Sealing material 13A Sealed surface 14 Protective film 30 base plate 31 Support member

Claims

1. A method for protecting a metal spray coating applied to a steel material at a joint between the steel material and concrete, comprising: When forming a metal spray coating on the steel material, a predetermined width from the edge of the joint surface with the concrete is left as a non-sprayed portion, and metal spraying is performed while avoiding this non-sprayed portion; sealing the surface of the metal spray coating to form a sealed surface; forming a protective film of fluorine-based paint from the non-sprayed portion to the side edge of the metal spray coating and the sealing treatment surface; A method for protecting a metal sprayed coating, comprising:

2. 2. The method for protecting a metal sprayed coating according to claim 1, wherein the metal spraying is performed by plasma arc spraying using an aluminum-magnesium alloy.

3. 3. The method for protecting a metal spray coating according to claim 1, wherein the sealing treatment is performed with a fluorine-based paint.

4. A protective structure for a metal spray coating applied to a steel material at a joint between the steel material and concrete, comprising: a metal sprayed coating formed on the steel material, the metal sprayed coating being formed so as to avoid a predetermined width from an edge of the joint surface with the concrete as a non-sprayed portion; a sealed surface formed by sealing the surface of the metal spray coating; a protective film formed of a fluorine-based paint from the non-sprayed portion to the side end of the metal spray coating and the sealed surface; A protective structure of a metal spray coating including:

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