Salinity removal method and recoating method

Abstract

To provide a new salinity removal method different from a conventional method, and a recoating method which applies a coating material to a steel material surface after salinity removal.SOLUTION: A salinity removal method for removing salinity from a steel material surface includes the steps of: blasting the steel material surface; sticking a desalting sheet containing nitrite ions onto the steel material surface; curing the desalting sheet; and peeling the desalting sheet from the steel material surface. In the salinity removal method, instead of the step of sticking the desalting sheet containing the nitrite ions onto the steel material surface, a step of coating a solution containing nitrite ions onto the steel material surface, and a step of sticking a desalting sheet containing no nitrite ion onto the steel material surface may be performed. A recoating method for recoating coating of a steel material surface includes the steps of: removing salinity on a steel material surface by the salinity removal method; and coating a coating material onto the steel material surface after desalting.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a desalination method for removing salts containing chloride ions that cause corrosion of steel materials attached to the surface of steel materials, and a repainting method for applying paint to the surface of steel materials after the salt has been removed. [Background technology]

[0002] The steel used in steel bridges and other structures is produced by reducing iron ore found in nature, and so oxidizes (corrodes) when it tries to return to its original state. Because steel loses its original functionality when it corrodes, it is common to apply paint or plating to the surface of the steel to prevent corrosion and cut off the supply of oxygen and moisture.

[0003] However, even with such rust prevention treatment, the coating is prone to deterioration and corrosion in environments with high salt content (for example, airborne salt or salt contained in antifreeze).

[0004] Steel structures with deteriorated paint can be restored to a healthy state by being repainted. Generally, when repainting, the steel surface is blasted, which is expected to remove some of the salt. However, the salt can sometimes be embedded deep in the pitting corrosion, making it difficult to remove mechanically.

[0005] To reduce the effects of salt, base materials for coatings containing anion adsorbents (such as nitrite ions) or composite hydroxides containing them have been developed (Patent Document 1). In recent years, paints that are resistant to salt damage have been sold, and salt removal methods using high-pressure water (water jets) have also been tried. However, due to the construction conditions of bridges and drainage issues, it is often difficult to carry out sufficient work. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4343570 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of these circumstances, and its problem to be solved is to provide a new salt removal method that differs from the various conventional methods, and a repainting method in which paint is applied to the steel surface after salt removal. [Means for solving the problem]

[0008] [Salt removal method] The salt removal method of the present invention is a method for removing salt from the surface of steel material, and includes the steps of blasting the surface of the steel material, attaching a desalination sheet containing nitrite ions to the surface of the steel material, curing the desalination sheet, and peeling the desalination sheet from the surface of the steel material.

[0009] The desalination method may also include a step of applying a solution containing nitrite ions to the blasted steel surface. The desalination sheet may be a layered double hydroxide-containing desalination sheet. The desalination method may also include a step of re-blasting the steel surface after the desalination sheet has been removed.

[0010] [Painting repainting method] The repainting method of the present invention is a method for repainting the surface of steel material, and includes a step of removing salt from the surface of the steel material using the salt removal method of the present invention, and a step of applying paint to the surface of the steel material after desalting. [Effects of the Invention]

[0011] According to the present invention, a high desalination effect and anti-rust effect can be obtained by a relatively simple method, and therefore productivity and durability of the coating can be improved compared to conventional methods. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a flowchart showing an example of a salt removal method of the present invention. [Figure 2] 1(a) to 1(c) are explanatory diagrams illustrating the principle of salt removal using the salt removal method of the present invention. [Figure 3] (a) shows the gusset plate removed from the actual bridge used in the test construction, and (b) shows the test specimen cut out from the gusset plate in (a). [Figure 4] An explanatory diagram of the salinity measurement positions on the test specimen. [Figure 5] (a) shows the test specimen after the first blasting, (b) shows the test specimen with the desalination sheet attached, (c) shows the area where the first desalination sheet has been peeled off, (d) shows the area where the second desalination sheet has been peeled off, and (e) shows the test specimen after the final blasting. [Figure 6] (a) is a graph showing a comparison of surface salt content when using the electrical conductivity method, and (b) is a graph showing a comparison of surface salt content when using the chloride ion detector tube method. [Figure 7] A photo of the test specimen 10 days after the test construction date. [Figure 8] This shows a test specimen cut from a gusset plate and blasted. [Figure 9] This shows the test specimen with the desalination sheet attached. [Figure 10] Showing the area where the desalination sheet has been peeled off [Figure 11] This shows the test specimen after finish blasting. [Figure 12] Photo of the test specimen 30 days after the test construction date. [Figure 13] (a) and (b) show specimens cut out from gusset plates and blasted. [Figure 14] (a)(b) is an explanatory diagram of the salinity measurement position of the test specimen. [Figure 15] (a) is a photograph of the test specimen after the first blasting and high-pressure cleaning of area a1, and (b) shows the area a2 after a solution containing nitrite ions has been applied and a desalination sheet with nonwoven fabric has been attached. [Figure 16] (a) shows the area a1 that has been washed with water, and (b) shows the area a2 after the desalination sheet has been peeled off. [Figure 17] (a) shows area a1 after finish blasting, and (b) shows area a2 after finish blasting. [Figure 18] (a) is a graph showing a comparison of surface salt content when using the electrical conductivity method, and (b) is a graph showing a comparison of surface salt content when using the chloride ion detector tube method. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Embodiment) An example of an embodiment of the present invention will be described with reference to the drawings. As an example, the salt removal method shown in Figure 1 is a method including a blasting step S001, a solution application step S002, a desalination sheet application step S003, a curing step S004, a desalination sheet removal step S005, and a finish blasting step S006.

[0014] The blasting step S001 is a step of blasting the surface of the steel material (hereinafter referred to as "primary blasting" for the sake of convenience). In this step, paint deteriorated by the primary blasting and rust formed on the surface of the steel material are removed. There are no particular limitations on the method of primary blasting, and a method using a power tool can be used. Furthermore, the primary blasting can be performed in one go or in multiple rounds.

[0015] The solution application step S002 is a step of applying a solution containing nitrite ions to the surface of the steel material. In this step, the solution containing nitrite ions is applied to the surface of the steel material that has been subjected to the primary blasting. This step is preferably performed after the primary blasting and before turning occurs (as a guideline, within 4 hours after the primary blasting; the same applies below).

[0016] The solution containing nitrite ions can be a salt containing alkali metal ions, such as an aqueous solution of lithium nitrite (LiNO2) or sodium nitrite (NaNO2). The solution can be applied using a sponge roller, a brush, a sprayer, or the like. It is preferable to apply the solution in an amount that does not drip.

[0017] As shown in Figure 2(a), by applying a solution containing nitrite ions, the solution penetrates into the pitting corrosion on the steel surface, and the diffusion action and ion exchange action of nitrite ions can be exerted on the salt that has penetrated deep into the pitting corrosion.

[0018] The solution application step S002 is not an essential step, and can be replaced with pure water that does not contain ions, or can be omitted if not required.

[0019] The desalination sheet application step S003 is a step of applying a desalination sheet containing nitrite ions to the surface of the steel material. In this step, the desalination sheet containing nitrite ions is applied to the surface of the steel material to which the solution has been applied.

[0020] In order to adhere the desalination sheet to the steel material with as few gaps as possible, it is preferable to press (press) the desalination sheet against the steel material using a roller or the like when attaching it. As with the solution application step S002, this step is also preferably carried out after the primary blasting and before turning occurs.

[0021] The desalination sheet to be applied can be, for example, a gel sheet (chloride absorbent) based on sodium polyacrylate with nonwoven fabric on the surface (the surface facing the steel material) (see Figures 2(b) and (c)). In this embodiment, the desalination sheet used contains nitrite ions in the gel portion.

[0022] The term "gel" as used here generally refers to a state in which colloidal particles have lost their independent mobility and have aggregated together to form a solid, or a sol (colloidal solution) that has solidified into a jelly-like substance.

[0023] In addition, desalination sheets can also be made by using a gel sheet containing layered double hydroxide (LDH) and sodium polyacrylate as the main component, with nonwoven fabric on the surface (see Figures 2(b) and (c)).

[0024] A typical LDH has the formula [M 2+1-x M 3+ x (OH)2] x+ [A n- x / n ·yH2O] x- (In the formula, M 2+ represents a divalent metal cation, and M 3+ denotes a trivalent metal cation, and A n- represents an n-valent anion.) It is a layered inorganic compound with anion exchange ability.

[0025] Divalent metal cations of hydroxides (M 2+ ) in a nonstoichiometric ratio with trivalent metal cations (M 3+ ) is substituted, it has a positive charge. Therefore, it has an exchangeable anion (A n- ) can be captured and retained.

[0026] In this embodiment, a nonwoven fabric is provided on the surface of the gel sheet. The purpose of providing the nonwoven fabric is to minimize the amount of gel or the like remaining on the steel material when the desalination sheet is peeled off. The nonwoven fabric can also be attached to the gel sheet on-site rather than provided during manufacturing. In this case, manufacturing of the desalination sheet becomes easier. The nonwoven fabric can be provided as needed, and can be omitted if not required.

[0027] The desalination sheet shown in this embodiment is an example, and other desalination sheets can be used.

[0028] In this application, "deionization sheets containing nitrite ions" also include those that do not contain nitrite ions at the time of manufacture, but are later impregnated with a solution containing nitrite ions at the site or elsewhere (those that contain nitrite ions at the time of application).

[0029] The curing step S004 is a step of curing the desalination sheet attached to the steel material. In this step, aluminum tape is applied to the periphery of the desalination sheet attached to the surface of the steel material (including the joints and glued areas when multiple desalination sheets are attached side by side; the same applies below), and the sheet is cured for a predetermined time in a state where the water contained in the solution and the desalination sheet does not evaporate, thereby diffusing the nitrite ions contained in the solution and the desalination sheet. The predetermined time refers to the time required for the diffusion of nitrite ions.

[0030] The term "diffusion" used here refers to the change (phenomenon) in which particles move and the concentration distribution becomes uniform when the temperature is kept uniform in a mixture of different types of particles and there is a concentration distribution, or the process of change in the concentration distribution that occurs when a mixture of different types of particles approaches thermal equilibrium.

[0031] The desalination sheet peeling step S005 is a step of peeling the desalination sheet from the surface of the steel material. The desalination sheet can be peeled off manually. If gel or the like remains on the periphery of the nonwoven fabric of the desalination sheet, it can be removed manually or by finish blasting in a subsequent step.

[0032] The timing for peeling off the desalination sheet may be any time after the specified curing time has elapsed since the sheet was attached to the steel material. Peeling off can be done on the same day as the attachment of the desalination sheet or on a later day (for example, the next day).

[0033] The finish blasting step S006 is a step of blasting the surface of the steel material after the desalination treatment. In this step, residues remaining after the desalination sheet is removed are removed, and the steel material is prepared to a state suitable for the subsequent paint application step.

[0034] There is no particular limitation on the method of finish blasting, and it can be a method using a power tool, for example.

[0035] Next, an example of the repainting method of the present invention will be described. The repainting method of the present invention is a method for repainting a steel surface, and includes a step of removing salt from the steel surface using the salt removal method of the present invention, and a step of applying paint to the desalted steel surface.

[0036] As an example, the repainting method shown in Fig. 1 is a method including a paint application step S007 in which paint is applied to the steel surface from which salt has been removed by the salt removal method. This step is preferably performed after finish blasting and before turning occurs.

[0037] In this process, for example, an undercoat of anti-rust material (anti-corrosion base material) is applied, an intermediate coat of epoxy resin or the like is applied, and a top coat of fluorine-based resin, polyurethane-based resin, etc. The type of paint to be applied and the order in which it is applied can be determined appropriately for each site.

[0038] The processes required for removing salt (in the above embodiment, the solution application process S002, the desalting sheet application process S003, the curing process S004, and the desalting sheet peeling process S005) can be performed on the entire steel material, but basically they only need to be performed on the corroded parts and do not need to be performed on the non-corroded parts (parts where the coating film remains).

[0039] The steps of the above embodiment are merely examples, and the steps of the salt removal method and repainting method of the present invention are not limited to the configuration of this embodiment. The salt removal method and repainting method of the present invention can be modified, such as by adding, omitting, or replacing steps as appropriate, within the scope of achieving the intended purpose. Examples of modifications include the following.

[0040] <Variation 1> In the above embodiment, an example is given in which a desalination sheet containing nitrite ions is used, but in the salt removal method and repainting method of the present invention, a desalination sheet that does not contain nitrite ions can also be used.

[0041] Specifically, a solution containing nitrite ions is applied to the surface of the steel material blasted in the blasting step S001 (solution application step S002), and a desalination sheet not containing nitrite ions is attached thereon. After attachment, a curing step S004 and a desalination sheet peeling step S005 are performed in the same manner as in the above embodiment.

[0042] <Variation 2> In the above embodiment, the finish blasting step S006 is performed after the desalination sheet peeling step S005, but if there is a concern that the finish blasting step S006 may cause salt to re-adhere, the desalination sheet may be left attached when the finish blasting is performed, and the finish blasting may not be performed on the area where the desalination sheet is attached. In this case, paint may be applied to the area where the desalination sheet is attached without performing the finish blasting.

[0043] Alternatively, if there is a concern that the finish blasting step S006 may cause redeposition of salt, the finish blasting step S006 may be performed first, followed by the desalination sheet attaching step S003, the curing step S004, and the desalination sheet peeling step S005. In this case, there is no need to perform finish blasting after the desalination sheet peeling step S005, and the paint may be applied directly.

[0044] <Test construction 1> In order to demonstrate the effectiveness of the present invention, the applicant conducted a test (hereinafter referred to as "Test 1") using removed components from an actual bridge that had been replaced due to severe corrosion. Test 1 was a test using a desalination sheet that had been impregnated with nitrite ions during the manufacturing process. The outline of Test 1 is as follows.

[0045] [Test specimen] In test construction 1, a portion of a gusset plate removed from an actual bridge was cut out and used as a test specimen. A photograph of the gusset plate is shown in Figure 3(a), and a photograph of the cut-out portion of the gusset plate (test specimen) is shown in Figure 3(b).

[0046] As shown in Figure 3(b), in test construction 1, the area with the same amount of corrosion was divided into three regions a1 to a3, and two locations in region a1 and two locations in each of regions a2 and a3 of the test specimen were set as salt measurement locations, as shown in Figure 4. The solid circle indicates the measurement location after the primary blasting, the dotted circle indicates the measurement location after the desalination sheet was removed, and the dashed circle indicates the measurement location after the final blasting.

[0047] In test construction 1, area a1 was an area without desalination treatment, area a2 was an area where desalination treatment was performed using a first desalination sheet (represented as "desalination sheet 3" in the graphs in Figures 6(a) and (b)), and area a3 was an area where desalination treatment was performed using a second desalination sheet of a different type than the first desalination sheet (represented as "desalination sheet 6" in the graphs in Figures 6(a) and (b)).

[0048] [Desalination sheet] In test construction 1, the desalination sheet applied to area a2 was a gel sheet containing nitrite ions with nonwoven fabric on the surface, and the desalination sheet applied to area a3 was a gel sheet containing nitrite ions and layered double hydroxide with nonwoven fabric on the surface.

[0049] The gel sheet used in Test Construction 1 was manufactured using the method described in JP 2021-066938 A. Its composition was 3 g of sodium polyacrylate, 10 g of glycerin, 0.15 g of aluminum hydroxide, 0.625 g of nickel-aluminum layered double hydroxide, 0.375 g of aluminum oxide, 1.855 g of lithium nitrite, and 83.845 g of water per 100 g of gel. Prior to use, the gel was heated to 50°C under vacuum to remove the water and dry it to an absolute dry state. A gel sheet with the same composition but without the layered double hydroxide was also used. Note that the gel sheet may have a different composition, such as one that does not contain lithium nitrite.

[0050] [Procedure for test construction 1] Test construction 1 was carried out according to the following steps (1) to (6). (1) The prepared specimens were subjected to primary blasting (see Figure 5(a)). The primary blasting was performed using a sandblaster. White fused alumina (grain size #24) was used as the abrasive. (2) After the primary blasting, a solution containing nitrite ions was applied to the specimen. A 1 mol / L (69 g / L) aqueous solution of lithium nitrite (LiNO2) was used as the solution containing nitrite ions. (3) After applying the solution, the first desalination sheet was attached to the area a2 of the test specimen, and the second desalination sheet was attached to the area a3 (see FIG. 5(b)). (4) After the desalination sheets were attached, aluminum tape was attached to the edges of each sheet to prevent the water contained in the solution and the desalination sheets from evaporating. (5) After a predetermined time had passed, the attached desalination sheet was peeled off (see Figures 5(c) and (d)). (6) After the desalination sheet was removed, the specimen was subjected to finish blasting (see Figure 5(e)). The finish blasting was carried out in the same manner as in (1) above.

[0051] [Measurement and evaluation methods] The desalination effect of test construction 1 was confirmed by measuring the surface salinity at the salinity measurement positions in each of areas a1 to a3. Surface salinity measurements were taken after the primary blasting, after the removal of the desalination sheet (except for area a1, which was not treated with desalination), and after the final blasting.

[0052] In addition, where the desalination sheet was installed, nitrite ions remained on the base material side due to ion exchange, and it was predicted that this would affect the electrical conductivity. Therefore, measurements using the surface salinity meter were used as a reference value, and after the measurement, salinity measurements were carried out separately using the solution remaining in the measurement cell and a chloride ion detector tube. The value measured with the detector tube [ppm] was calculated as the surface salinity [mg / m ] using the following formula 1. 2 ] and evaluated. [Formula 1] TIFF2025146924000002.tif46157

[0053] [Measurement results] Figure 6(a) shows a graph comparing the amount of surface salt measured using the electrical conductivity method, and Figure 6(b) shows a graph comparing the amount of surface salt measured using the chloride ion detector tube method.

[0054] After test construction 1, the test specimen was exposed indoors and observed over time. Figure 7 shows a photograph of the test specimen 10 days after test construction.

[0055] [Consideration] The following was confirmed through test construction 1. (1) There was no significant difference in the measurement results depending on the type of desalination sheet. (2) The salt content after the primary blasting varied little from site to site, and was measured at 80 to 100 mg / m by the electrical conductivity method. 2 20 mg / m3 by the chloride ion detector tube method 2 That was about it. (3) When measuring the electrical conductivity of the desalination sheet after removing it from the installation site, values ​​exceeding the upper limit of the measuring equipment were measured. This was due to the influence of nitrite ions contained in the desalination sheet. (4) Measurements using a chloride ion detector tube at the same location showed that the amount of salt was very small. (5) Measurements after finishing blasting at the desalination sheet installation site showed 230 to 290 mg / m by the electrical conductivity method. 2 The chloride ion detector tube method did not detect any salt. (6) In the area where the desalination sheet was not installed, the electrical conductivity was 85 mg / m after the finish blasting. 2 , 11 mg / m by chloride ion detector tube method 2 It was. (7) In measurements taken after the finishing blasting of the desalination sheet application area, although no salt was detected using the chloride ion detector tube method, a relatively large value was measured using the electrical conductivity method. This indicates that nitrite ions remain even after the finishing blasting, which is thought to indicate good rust prevention effects. (8) As shown in Figure 7, in area a1, where no desalination treatment was performed, rust due to turning (numerous tiny black dots in area a1 in Figure 7) occurred 10 days after the test application date, whereas in areas a2 and a3, where the desalination sheet was applied, almost no rust due to turning was observed 10 days after the test application date. Note that the yellow rust in the photograph was formed during the process of measuring the surface salt content after the finish blasting, and was not caused by turning.

[0056] From the above, in areas where desalting sheets were not installed, a certain amount of salt remained even after finish blasting, but in areas where desalting sheets were installed, higher values ​​were measured using the electrical conductivity method than before the desalting sheets were installed, while no salt was measured using the chloride ion detection tube method, and it is thought that chloride ions have been removed and nitrite ions remain, indicating good rust prevention effects.

[0057] <Test construction 2> In order to demonstrate the effectiveness of the present invention, the applicant conducted a test (hereinafter referred to as "Test 2") using removed components from an actual bridge that had been replaced due to severe corrosion. Test 2 was a test using a desalination sheet that did not contain nitrite ions at the manufacturing stage but was later impregnated with a solution containing nitrite ions. The outline of Test 2 is as follows.

[0058] [Test specimen] In test construction 2, a portion of a gusset plate removed from an actual bridge was cut out to serve as a test specimen. Figure 8 shows a photograph of the cut-out portion of the gusset plate (test specimen) after blasting.

[0059] As shown in Figure 9, in test construction 2, area a1 was an area where no desalination treatment was performed, and area a2 was an area where desalination treatment was performed using a desalination sheet.

[0060] [Desalination sheet] In test construction 2, the desalination sheet applied to area a2 was a gel sheet that did not contain nitrite ions, but had a nonwoven fabric on the surface and was impregnated with a solution containing nitrite ions before application.

[0061] The composition of the gel sheet used in test construction 2 was 63.25 g of gel, 6 g of sodium polyacrylate, 20 g of glycerin, 0.3 g of aluminum hydroxide, 2 g of magnesium-aluminum layered double hydroxide, 0.3 g of tartaric acid, and 34.65 g of water.

[0062] [Procedure for test construction 2] Test construction 2 was carried out according to the following steps (1) to (4). (1) The prepared specimens were subjected to primary blasting using a sandblaster. The abrasive used was white fused alumina (grain size #24). (2) After the primary blasting, a desalination sheet made of nonwoven fabric and impregnated with a solution containing nitrite ions was attached to the specimen (see Figure 9). A 1 mol / L aqueous solution of sodium nitrite (NaNO2) was used as the solution containing nitrite ions. (3) After a predetermined time had passed, the attached desalination sheet was peeled off (see Figure 10). (4) After removing the desalination sheet, the specimen was subjected to finish blasting (see Figure 11). The finish blasting was carried out in the same manner as in (1) above.

[0063] After test construction 2, the specimen was exposed indoors and observed over time. Figure 12 shows a photograph of the specimen 30 days after test construction.

[0064] [Consideration] Test construction 2 confirmed the following: (1) The composition and construction method of the desalination sheet were partially changed, but there were no problems with construction. (2) As shown in Figure 12, in the area a1 where no desalination treatment was performed, rust due to turning (the black area in area a1 in Figure 12) occurred 30 days after the test application date, whereas in the area a2 where the desalination sheet was applied, almost no rust due to turning was observed 30 days after the test application date.

[0065] <Test construction 3> In order to demonstrate the effectiveness of the present invention, the applicant conducted a test (hereinafter referred to as "Test 3") using removed components from an actual bridge that had been replaced due to severe corrosion. Test 3 was a test using a desalination sheet that does not contain nitrite ions. The outline of Test 3 is as follows.

[0066] [Test specimen] In test construction 3, a portion of a gusset plate removed from an actual bridge was cut out to serve as a test specimen. Photographs of the cut-out portion of the gusset plate (test specimen) after blasting are shown in Figure 13(a)(b).

[0067] As shown in Figures 13(a) and (b), in test construction 3, area a1 was the area where desalination treatment was performed by washing with water, and area a2 was the area where desalination treatment was performed using a desalination sheet.

[0068] As shown in Figure 14(a) and (b), two locations in each of the test specimen's areas a1 and a2 were set as salinity measurement locations. The solid circle indicates the measurement location after the primary blasting, and the dashed circle indicates the measurement location after the final blasting.

[0069] [Desalination sheet] In test construction 3, the desalination sheet applied to area a2 was a gel sheet that did not contain nitrite ions, with nonwoven fabric applied to the surface before application.

[0070] The composition of the gel sheet used in test construction 3 was 63.25 g of gel, 6 g of sodium polyacrylate, 20 g of glycerin, 0.3 g of aluminum hydroxide, 2 g of magnesium-aluminum layered double hydroxide, 0.3 g of tartaric acid, and 34.65 g of water.

[0071] [Procedure for test construction 3] Test construction 3 was carried out according to the following steps (1) to (4). (1) The prepared specimens were subjected to primary blasting using a sandblaster. The abrasive used was white fused alumina (grain size #24). (2) After the primary blasting, area a1 of the specimen was cleaned with high-pressure water (see Figure 15(a)). Area a2 was coated with a solution containing nitrite ions, and a desalination sheet with nonwoven fabric was attached (see Figure 15(b)). A 0.1 mol / L aqueous solution of sodium nitrite (NaNO2) was used as the solution containing nitrite ions. (3) For the region a2, the attached desalination sheet was peeled off after a predetermined time had elapsed. (4) After washing the area a1 with water (see Fig. 16(a)), and after removing the desalination sheet from the area a2 (see Fig. 16(b)), the specimens were subjected to finish blasting (see Figs. 17(a) and 17(b)). The finish blasting was carried out in the same manner as in (1) above.

[0072] [Measurement and evaluation methods] The desalination effect of test construction 3 was confirmed by measuring the surface salinity at the salinity measurement positions in each of areas a1 to a2. Measurements of the surface salinity were carried out at each stage, after the primary blasting and after the finish blasting.

[0073] [Measurement results] Figure 18(a) shows a graph comparing the amount of surface salt measured using the electrical conductivity method, and Figure 18(b) shows a graph comparing the amount of surface salt measured using the chloride ion detector tube method.

[0074] [Consideration] Test construction 3 confirmed the following: (1) The composition and construction method of the desalination sheet were partially changed, but there were no problems with construction. (2) In the area a2 where desalination treatment was performed using a desalination sheet, the electrical conductivity method showed a value of 346 mg / m 2 The chloride ion detector tube method did not detect any salt. As with Test Construction 1, chloride ions were removed and nitrite ions remained, which is thought to provide good rust prevention effects. (3) In the area a1 that was desalted by washing with water, the electrical conductivity method showed that after the first blasting, the 2 After finish blasting, it was 84mg / m 2 and no change was observed. (4) In the area a1 where desalination was performed by washing with water, the chloride ion detection tube method showed that after the first blasting, the concentration was 11 mg / m 2 After finish blasting, it was 3mg / m 2 Although a certain degree of desalination effect was observed, the desalination effect was not as great as that observed when desalination treatment was performed using a desalination sheet. [Industrial Applicability]

[0075] The salt removal method and repainting method of the present invention can be used for desalination and repainting of various steel structures, and can be particularly suitably used for desalination and repainting of steel structures used as components of existing bridges.

Claims

1. A desalination method for removing salt from the surface of steel materials, A step of blasting the surface of the steel material; a step of attaching a desalination sheet containing nitrite ions to the surface of the steel material; A step of curing the desalination sheet; A step of peeling the desalination sheet from the steel surface is included. A salt removal method characterized by:

2. The salt removal method according to claim 1, Applying a solution containing nitrite ions to the blasted steel surface, A salt removal method characterized by:

3. The salt removal method according to claim 1, A desalination sheet containing a layered double hydroxide is used as the desalination sheet. A salt removal method characterized by:

4. The salt removal method according to claim 1, and a step of re-blasting the steel surface after removing the desalting sheet. A salt removal method characterized by:

5. A desalination method for removing salt from the surface of steel materials, A step of blasting the surface of the steel material; applying a solution containing nitrite ions to the surface of the steel material; a step of attaching a desalination sheet not containing nitrite ions to the surface of the steel material; A step of curing the desalination sheet; A step of peeling the desalination sheet from the steel surface is included. A salt removal method characterized by:

6. In the repainting method for repainting the surface of steel materials, A step of removing salt from a steel material surface by the salt removal method according to any one of claims 1 to 5; This includes a process of applying paint to the surface of the steel after desalting. A painting repainting method characterized by the following.

Images