Concrete surface impregnation material, concrete product, and method of protecting concrete surface

Abstract

To provide a concrete surface impregnation material capable of suppressing the deterioration of a concrete product.SOLUTION: The concrete surface impregnation material is mixed with a layered composite hydroxide whose chemical formula is expressed by M2+1-xM3+x(OH)2(NO3-)x / n-mH2O (M2+ represents divalent metal, M3+ represents trivalent metal, and n is a natural number).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a concrete surface impregnating material, a concrete product, and a method for protecting a concrete surface. [Background technology]

[0002] Reinforced concrete is a structure that combines reinforcing bars with high tensile strength and concrete with high compressive strength. Reinforcing bars are prone to oxidizing and rusting, but the highly alkaline cement contained in the concrete forms a passive film on the surface of the reinforcing bars. Therefore, the reinforcing bars inside the concrete do not corrode and can continue to meet the required performance.

[0003] A method of applying an impregnating material to the surface of concrete (surface impregnation method) is known in order to improve the durability of structures by modifying the structure of the surface layer of concrete or by imparting special functions to the surface layer of concrete (see, for example, Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 189915 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even if an impregnating material is applied to the surface of concrete, there is a limit to the effectiveness of the impregnating material alone, and the concrete may be neutralized by carbon dioxide (carbonate ions), reducing its durability.In addition, there is a risk of corrosion of reinforcing bars due to the effects of salt that penetrates into the concrete from the outside or that was present inside the concrete.

[0006] Therefore, an object of the present invention is to provide a concrete surface impregnation material capable of suppressing deterioration of concrete products, a concrete product in which deterioration is suppressed, and a method for protecting a concrete surface capable of suppressing deterioration of concrete. [Means for solving the problem]

[0007] The concrete surface impregnation material of the present invention has the chemical formula M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n Layered double hydroxide (M 2+ is a divalent metal, M 3+ It is a concrete surface impregnation material mixed with ammonium hydroxide (where n is a natural number).

[0008] The concrete product of the present invention has the chemical formula M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n Layered double hydroxide (M 2+ is a divalent metal, M 3+ It is a concrete product formed by impregnating a concrete surface with a concrete surface impregnation material containing a trivalent metal (where n is a natural number) and then drying it.

[0009] The method for protecting a concrete surface of the present invention is a method for protecting a concrete surface of a compound represented by the chemical formula M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n Layered double hydroxide (M 2+ is a divalent metal, M 3+ This is a method of protecting concrete surfaces by applying and impregnating a concrete surface with a concrete surface impregnating material containing a metal (where n is a natural number, and represents a trivalent metal). [Effects of the Invention]

[0010] The concrete surface impregnation material of the present invention can suppress deterioration of concrete products. The concrete product of the present invention can also suppress deterioration. The concrete surface protection method of the present invention can also suppress deterioration of concrete. [Brief explanation of the drawings]

[0011] [Figure 1] Figure 1(a) shows the state in which a concrete surface impregnating material containing nitric acid-type layered double hydroxide is applied to the surface of concrete, and Figure 1(b) shows the carbonation-inhibiting effect of the nitric acid-type layered double hydroxide. [Figure 2] FIG. 2(a) is a diagram showing the salt penetration suppression effect of the nitric acid type layered double hydroxide, and FIG. 2(b) is a diagram showing the internal salt adsorption effect of the nitric acid type layered double hydroxide. [Figure 3] FIG. 3 is a graph showing the results of an experiment on the impregnation depth of a concrete surface impregnation material. [Figure 4] FIG. 4 is a graph showing the results of an experiment on the salt penetration suppression effect of a concrete surface impregnation material. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment will be described in detail below with reference to FIGS.

[0013] The concrete surface impregnation material of this embodiment is a silane-based or silicate-based surface impregnation material having the chemical formula M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n Layered double hydroxide (M 2+ is a divalent metal, M 3+ represents a trivalent metal, and n is a natural number).

[0014] (Surface impregnated material) The surface impregnating material is either a silane-based or silicate-based surface impregnating material.

[0015] Silane-based surface impregnating materials penetrate into the surface layer by being applied to the concrete surface, form an R(Si-O) structure (R is an alkyl group), and impart water-repellent performance. In addition, silane-based surface impregnating materials suppress the intrusion of deterioration factors (such as water, carbon dioxide gas, chloride ions, etc.) into the concrete due to their water-repellent performance, and improve the durability of the concrete. Since this silane-based surface impregnating material does not form a coating film, the moisture contained in the concrete can be released as water vapor. Silane-based surface impregnating materials include alkylalkoxysilane-based and alkylsilicate-based materials.

[0016] Silicate-based surface impregnating materials are liquid materials mainly composed of alkali metal silicate salts. By being applied to the concrete surface, they penetrate into the concrete, react with calcium hydroxide in the concrete to generate C-S-H gel, and have the function of densifying and modifying the surface layer. Silicate-based surface impregnating materials suppress the intrusion of external deterioration factors (such as water, carbon dioxide gas, chloride ions, etc.) due to densification, and improve the durability of the concrete. Silicate-based surface impregnating materials are classified into lithium silicate-based, silicate mixed type, sodium silicate-based, and potassium silicate-based according to the main component.

[0017] (Layered double hydroxide) The layered double hydroxide of this embodiment has a chemical formula of M 2+ 1-x M 3+ x (OH)2(NO3 - ) x / n ·mH2O. Here, M 2+ represents a divalent metal, M 3+ represents a trivalent metal, n is a natural number. Also, x is a number in the range of 0 < x < 1, and generally a number in the range of 1 / 6 < x < 1 / 3. m is a number greater than 0. This layered double hydroxide is sometimes called a hydrotalcite-like compound. Examples of divalent metal ions (M 2+ ) include, for example, Mg 2+ , Fe 2+ , Zn2+ , Li 2+ , Ni 2+ , Co 2+ , Cu 2+ In addition, trivalent metal ions (M 3+ ) is, for example, Al 3+ , Fe 3+ , Cr 3+ , Mn 3+ The divalent metal ions (M 2+ ) and trivalent metal ions (M 3+ ) does not have to be one type, but may include multiple types.

[0018] Nitrate ions NO3 between the layers of layered double hydroxide - is exchanged for other anions that have a higher affinity with LDHs. That is, nitrate-type LDHs exchange carbonate ions (CO 2- ) and chloride ions (Cl - ) and adsorbs nitrate ions (NO3 - ) The layered double hydroxide containing nitrate ions as in this embodiment is referred to as a nitric acid type layered double hydroxide.

[0019] The layered double hydroxide according to this embodiment may contain, for example, a divalent metal ion (M 2+ ) is Mg 2+ and trivalent metal ions (M 3+ ) is Al 3+ Mg 2+ 1-x Al 3+ x (OH)2(NO3 - ) x / n mH2O (Mg-Al type) and divalent metal ions (M 2+ ) is Mg 2+ and trivalent metal ions (M 3+ ) is Fe 3+ Mg 2+ 1-x Fe 3+ x (OH)2(NO3 - ) x / n mH2O (Mg-Fe type) and divalent metal ions (M 2+) is Fe 2+ and trivalent metal ions (M 3+ ) is Fe 3+ Fe 2+ 1-x Fe 3+ x (OH)2(NO3 - ) x / n The Mg-Fe type is superior to the Mg-Al type in that it has a high specific gravity, which makes it easy to separate by sedimentation, and it can reduce raw material costs.

[0020] The crystallite size of the layered double hydroxide according to this embodiment is 20 nm or less, and more preferably 10 nm or less. For example, if the crystallite size of the layered double hydroxide is 20 nm or less, the specific surface area can be increased to 20 m 2 / g or more, thereby improving the adsorption performance. The particle size (median size (D50)) of the layered double hydroxide according to this embodiment is 5 to 25 μm, and more preferably 10 to 12 μm.

[0021] Layered double hydroxides are synthesized by mixing an acidic solution containing divalent metal ions and trivalent metal ions with an alkaline solution. The smaller the crystallite size of the layered double hydroxide synthesized here, the larger its specific surface area can be. Therefore, the shorter the aging time after synthesis, the better. After mixing the acidic solution and the alkaline solution, neutralization is preferably performed within at least 120 minutes, preferably within 60 minutes, and more preferably simultaneously with mixing. Details of the method for synthesizing layered double hydroxides are described in JP 2021-195276 A.

[0022] In this embodiment, a concrete product is formed by applying a silane- or silicate-based concrete surface impregnating material containing the above-described nitric acid-type layered double hydroxide to the surface of concrete and drying it. The surface of the concrete product is protected by the concrete surface impregnating material. The concrete surface impregnating material can be applied to the surface of the concrete product by hand using a roller, trowel, or brush, or by spraying.

[0023] When a concrete surface impregnating material containing nitric acid-type layered double hydroxide is applied to the concrete surface as shown in Figure 1(a), the following effects are achieved in addition to the effects of the surface impregnating material alone.

[0024] For example, the concrete surface impregnation material applied to the concrete surface as shown in Figure 1(a) transfers carbonate ions (CO ) from the outside into the concrete as shown in Figure 1(b). 2- ) tries to penetrate the concrete, the nitrate-type layered double hydroxide adsorbs it. This prevents the phenomenon of strong alkaline concrete approaching neutrality (neutralization) (neutralization suppression effect). Preventing the neutralization of concrete prevents the destruction of the passive film on the reinforcing steel, thereby preventing the progression of corrosion of the reinforcing steel.

[0025] In addition, the concrete surface impregnation material applied to the concrete surface absorbs chloride ions (Cl) from the outside into the concrete, as shown in Figure 2(a). - ) tries to penetrate, the nitrate-type layered double hydroxide adsorbs it (salt penetration suppression effect). This makes it possible to prevent rust from forming on the reinforcing bars.

[0026] Furthermore, the concrete surface impregnation material applied to the concrete surface has the effect of dissolving chloride ions (Cl) inside the concrete, as shown in Figure 2(b). - ), even if chloride ions (Cl) are present, the nitrate-type layered double hydroxide adsorbs them (internal salt adsorption effect). This prevents rust from forming on the reinforcing bars.- ) and instead nitrate ions NO3 - This releases nitrate ions NO3 - is the iron ion (Fe 2+ ) to produce magnetite (Fe3O4), i.e., black rust, according to the following reaction formula (1), thereby inhibiting corrosion of reinforcing bars. 3Fe+8HNO3→8NO2+Fe3O4+4H2O…(1)

[0027] In the concrete surface impregnation material of this embodiment, the action of the nitric acid type layered double hydroxide exerts the above-mentioned effects of inhibiting carbonation, inhibiting salt penetration, and adsorbing inherent salt, but the incorporation of the nitric acid type layered double hydroxide hardly reduces the impregnation depth of the surface impregnation material.

[0028] (Example) Here, an example will be described.

[0029] In this example, an experiment was conducted to confirm the effect on impregnation depth when a nitric acid-type layered double hydroxide was mixed into a surface impregnation material. An experiment was also conducted to confirm the salt penetration suppression effect of the nitric acid-type layered double hydroxide. This experiment conformed to the test method for surface impregnation materials (JSCE-K571-2013) of the Japan Society of Civil Engineers.

[0030] (preparation) A silane-based surface impregnation material was prepared as the surface impregnation material. Concrete surface impregnation material 1 was prepared with 0% (no mixing) nitric acid-type layered double hydroxide mixed into this surface impregnation material; concrete surface impregnation material 2 was prepared with 5% (no mixing) nitric acid-type layered double hydroxide mixed into the surface impregnation material; concrete surface impregnation material 3 was prepared with 10% (no mixing) nitric acid-type layered double hydroxide mixed into the surface impregnation material; and concrete surface impregnation material 4 was prepared with 20% (no mixing) nitric acid-type layered double hydroxide mixed into the surface impregnation material.

[0031] (Creating concrete specimens) Concrete specimens were prepared in the following manner. The base material is mortar with a water-cement ratio (W / C) of 50%. The ratio of water:cement:fine aggregate was 0.5:1:3, and the air content was 6±1.5%. The specimens were rectangular columns measuring 40mm x 40mm x 160mm, and were cut appropriately to suit the various tests described below. The specimens were demolded at 1 day of age, cured in water until 7 days of age, and then cut to the dimensions described below for each test at 7 days of age. They were then cured in air until 28 days of age.

[0032] (Exam contents) (1) Impregnation depth measurement The evaluation was carried out according to "Test Method for Surface Penetrants 6.1 Impregnation Depth Test" specified in JSCE-K571-2013. After cutting the specimen into 40mm x 40mm x 40mm at 28 days of age, concrete surface impregnation materials 1 to 4 were applied to one of the cut surfaces in the specified amount (0.0625kg / m 2 , 0.125 kg / m 2 , 0.25 kg / m 2 ) was applied with a brush. Each concrete surface impregnation material was applied to two test specimens in the specified amount. Concrete surface impregnation materials 1 to 4 were mixed for 5 minutes using a mixer before application. After application, the concrete surface impregnation materials were allowed to cure for at least 7 days.

[0033] After curing, the impregnated surface of the test specimen was split in two, and the two halves were immersed in water for one minute before being removed. The depth of the water-repellent, non-wet colored part of the split surface from the impregnated surface was measured to the nearest 0.1 mm using a vernier caliper. Measurements were taken at the center of the split surface of the test specimen and at three points equidistant to the left and right of the center. The average value of the three points was rounded off to one decimal place and calculated.

[0034] The results of the above experiments were as shown in Figure 3. Figure 3 shows that even when nitric acid-type layered double hydroxide is mixed into the concrete surface impregnation agent, the impregnation depth does not change significantly, and the original performance of the concrete surface impregnation agent is maintained. Note that although a silane-based surface impregnation agent was used in this experiment, it is believed that similar experimental results would be obtained with a silicate-based surface impregnation agent.

[0035] (2) Measurement of salt penetration suppression effect After cutting the specimen into 40mm x 40mm x 80mm, concrete surface impregnation materials 1, 2, and 4 were applied in the specified amount (0.25kg / m) to one side (40mm x 80mm) excluding the driving surface. 2 ) was applied with a brush. Each concrete surface impregnation material was applied to one test specimen. The five surfaces that would not receive the concrete surface impregnation material were previously coated with epoxy resin. After applying the concrete surface impregnation material, the specimens were left to cure for at least 28 days, and then immersed in 3% salt water.

[0036] After immersion in salt water for approximately 100 days, Cl was detected at 5mm and 15mm from the surface. - The concentration was measured, and the results shown in Figure 4 were obtained. Figure 4 shows that when nitric acid type layered double hydroxide was not mixed into the concrete surface impregnation material (0%), the Cl concentration increased the further the distance from the surface (the deeper the material was). - However, the Cl concentration increases as the distance from the surface increases due to the addition of nitric acid-type layered double hydroxide to the concrete surface impregnation material. - In other words, it was found that the nitrate-type layered double hydroxide adsorbs chloride ions and prevents them from penetrating deep into the concrete.

[0037] The above experiments demonstrated that nitric acid-type layered double hydroxides, when mixed into concrete surface impregnation materials, still exert their inherent effects (carbonation inhibition, salt penetration inhibition, and inherent salt adsorption), namely, the salt penetration inhibition effect. As such, since nitric acid-type layered double hydroxides can exert their inherent effects even when mixed into concrete surface impregnation materials, it is believed that they will also exert their other effects (carbonation inhibition and inherent salt adsorption).

[0038] As described above in detail, the concrete surface impregnation material of this embodiment contains a nitric acid-type layered double hydroxide, and exhibits the inherent functions of the nitric acid-type layered double hydroxide (carbonation suppression effect, salt penetration suppression effect, and inherent salt adsorption effect) without deteriorating the performance (impregnation depth) of the surface impregnation material. Therefore, the carbonation suppression effect suppresses the carbonation of concrete and the destruction of the passive film on the reinforcing bar, thereby suppressing the progression of corrosion of the reinforcing bar. Furthermore, the salt penetration suppression effect and inherent salt adsorption effect suppress the formation of rust on the reinforcing bar. Furthermore, because the inherent performance of the surface impregnation material can be maintained even when a nitric acid-type layered double hydroxide is incorporated, the densification and water-repellent properties can suppress the penetration of external deterioration factors, thereby improving the durability of the concrete.

[0039] In this embodiment, the mass ratio of the layered double hydroxide in the concrete surface penetrant is 5 to 20%. The above experimental results show that, at least in this range, the viscosity of the concrete surface penetrant does not increase significantly, so the impregnation depth is not reduced and the effects of the layered double hydroxide can be exerted.

[0040] The concrete surface impregnation material of the above embodiment may be applied to the surface of a concrete product immediately after the concrete product is manufactured, or may be applied to the surface of a concrete product including a deteriorated area when the concrete product has deteriorated.

[0041] The above-described embodiment is a preferred example of the present invention, but the present invention is not limited to this and can be modified in various ways without departing from the spirit of the present invention.

Claims

1. Chemical formula is M 2+ 1-x M 3+ x (OH) 2 (NO 3 - ) x / n ・mH 2 Layered double hydroxide (M 2+ is a divalent metal, M 3+ A concrete surface impregnation material containing a trivalent metal (where n is a natural number).

2. 2. The concrete surface penetrant according to claim 1, wherein the mass ratio of the layered double hydroxide in the concrete surface penetrant is 5 to 20%.

3. The layered double hydroxide M 2+ and M 3+ The combination of Mg 2+ and Al 3+ , Mg 2+ and Fe 3+ , Fe 2+ and Fe 3+ 3. The concrete surface impregnating material according to claim 1, wherein the concrete surface impregnating material is either one of the following:

4. 3. The concrete surface penetrant according to claim 1, wherein the layered double hydroxide has a median diameter (D50) of 5 to 25 μm.

5. Chemical formula is M 2+ 1-x M 3+ x (OH) 2 (NO 3 - ) x / n ・mH 2 Layered double hydroxide (M 2+ is a divalent metal, M 3+ A concrete product formed by impregnating a concrete surface with a concrete surface impregnation material containing a trivalent metal (wherein n is a natural number) and then drying the material.

6. Chemical formula is M 2+ 1-x M 3+ x (OH) 2 (NO 3 - ) x / n ・mH 2 Layered double hydroxide (M 2+ is a divalent metal, M 3+ A method for protecting a concrete surface, comprising applying a concrete surface impregnating material containing a trivalent metal, and n is a natural number, to the concrete surface and allowing the material to penetrate the surface.

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