CN110803880A

CN110803880A - Chloride ion curing agent for reinforced concrete and preparation method and application thereof

Info

Publication number: CN110803880A
Application number: CN201911182963.7A
Authority: CN
Inventors: 芦令超; 杨磊; 赵丕琪; 陈明旭; 程新
Original assignee: University of Jinan
Current assignee: University of Jinan
Priority date: 2019-11-27
Filing date: 2019-11-27
Publication date: 2020-02-18
Anticipated expiration: 2039-11-27
Also published as: CN110803880B

Abstract

The invention belongs to the technical field of chloride ion curing agents, and particularly relates to a chloride ion curing agent for reinforced concrete, and a preparation method and application thereof. The curing agent is CaFe-NO₃LDHs and CaFeAl-NO₃The LDHs nanosheets are compounded into metal double hydroxide with a layered structure, and the metal double hydroxide is micro-nano granular; the CaFe-NO is calculated by weight₃50-80 parts of LDHs (layered double hydroxides), CaFeAl-NO₃20-50 parts of LDHs. The chloride ion curing agent prepared by the invention has no damage effect on cement-based materials, can stably and efficiently adsorb chloride ions in simulated concrete pore solution, obviously weakens the corrosivity of the chloride ions in a pure slurry sample soaked by 3.5 percent of sodium chloride, obtains excellent effect, and is an efficient and stable chloride ion curing agent.

Description

Chloride ion curing agent for reinforced concrete and preparation method and application thereof

Technical Field

The invention belongs to the technical field of chloride ion curing agents, and particularly relates to a chloride ion curing agent for reinforced concrete, and a preparation method and application thereof.

Background

The information disclosed in this background of the invention is only for enhancement of understanding of the general background of the invention and is not necessarily to be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Free chloride ions (Cl) in concrete^-) The structure and performance of the reinforced concrete are easy to be deteriorated, and the safety, reliability and service life of the engineering are damaged. This is mainly manifested as: when chloride ions enter the concrete, electrochemical corrosion of the steel bar can be promoted (anode: Fe → Fe)²⁺+2e^-(ii) a Cathode: o is₂+2H₂O+4e^-→4OH^-). After the steel bar in the concrete corrodes and begins, on the one hand, the effective section of the steel bar is reduced due to the corrosion of the steel bar, so that the bearing capacity of the reinforced concrete structure is reduced and the bond stress of the steel bar is reduced; on the other hand, due to accumulation of corrosion products, the surface volume of the steel bar expands by 3-8 times, so that the concrete structure has the symptoms of rib-following expansion crack, layer crack, peeling and the like. At present, the protection measures for reinforced concrete mainly include:

(1) adding fly ash, slag and an aluminum-rich mineral admixture to generate C-S-H gel and Friedel' S salt (C)₃A·CaCl₂·10H₂O)、Kuzel’s salt(C₃A·0.5CaCl₂·0.5CaSO₄·10H₂O) to achieve para-Cl^-Adsorption of (3). However, the inventor researches and discovers that: although C in the cement clinker₃Phase A can react with chloride ions to produce Friedel' ssalt, but when the content of the aluminate-rich phase is higher, the crystalline hydration product of the phase A causes more porous structure, provides convenient channels for chloride ion erosion, and even offsets the advantage of solidifying chloride ions. In addition, due to C₃A has a high early hydration heat release, which causes the temperature inside the concrete to rise, which is particularly disadvantageous in marine concrete structures.

(2) Sacrificial anode cathodic protection: the cost of the replacement steel bar required by the cathodic protection method in the method is high.

(3) Epoxy coating steel bar: although the organic coating has good water resistance and toughness, it has poor aging resistance and abrasion resistance, resulting in a low service life. In addition, the inorganic coating has poor adhesion and toughness with the steel bar, so that the coating on the surface of the steel bar is easy to fall off, and the corrosion of the steel bar is caused.

(4) Applying a concrete corrosion inhibitor; although the inorganic corrosion inhibitor can form an oxide film on the surface of the steel bar, when the concentration of the corrosion inhibitor is lower than the concentration required by self film forming, the corrosion of chloride ions to the steel bar is accelerated. The organic rust inhibitor is not easy to disperse in concrete and has no obvious effect on reinforcing steel bars. Therefore, it is important to prepare a novel chloride ion curing agent to cure chloride ions in large amounts.

In addition, patent document CN200810030796.X discloses an additive for improving the performance of curing free chloride ions of a cement-based material and a using method thereof, the additive has a good chloride ion curing effect, the mass ratio of silicon-aluminum oxide minerals to nitrite in the formula is 8-9: 1, the chloride ion curing capability of the cement-based material can be obviously improved when the silicon-aluminum oxide minerals and the nitrite are mixed and doped into the cement material, but the doping amount reaches 25-35% of the cement-based material, the cost is high, the nitrite has certain toxicity, and the large-dose doping is harmful to human bodies.

Patent document CN201410465488.5X discloses a chloride ion curing agent and a method for using the same, the additive has good chloride ion curing property, is compounded by Ca-Al-LDH and water reducing agent intercalation product (Ca-Al-SP-LDH), the doping amount is 2-5% of the mass of the cementing material, the curing of chloride ions is achieved through ion exchange, the chloride ion permeation resistance of reinforced concrete can be improved to I-II level, but the desorption rate of the Ca-Al-LDH obtained in simulated concrete pore solution is high, the Ca-Al-LDH can easily react with sulfate radicals in the solution to generate a large amount of ettringite crystals, and the curing effect and the volume stability of the reinforced concrete are reduced.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a chloride ion curing agent for reinforced concrete and a preparation method and application thereof. The chloride ion curing agent prepared by the invention has no damage effect on cement-based materials, can stably and efficiently adsorb chloride ions in simulated concrete pore solution, obviously weakens the corrosivity of the chloride ions in a pure slurry sample soaked by 3.5 percent of sodium chloride, obtains excellent effect, and is an efficient and stable chloride ion curing agent.

The invention provides a chloride ion curing agent for reinforced concrete.

The invention also provides a preparation method of the chloride ion curing agent for reinforced concrete.

The invention also provides the application of the chloride ion curing agent for the reinforced concrete.

In order to realize the purpose, the invention discloses the following technical scheme:

firstly, the invention discloses a chloride ion curing agent for reinforced concrete, which is CaFe-NO₃LDHs nano-sheet, the curing agent is a metal double hydroxide with a layered structure.

Secondly, the invention discloses another chloride ion curing agent for reinforced concrete, which is CaFeAl-NO₃LDHs nano-sheet, the curing agent is a metal double hydroxide with a layered structure.

Thirdly, the invention discloses another chloride ion curing agent for reinforced concrete, which is prepared from CaFe-NO₃LDHs and CaFeAl-NO₃The LDHs nanosheets are compounded into metal double hydroxide with a layered structure, and the metal double hydroxide is micro-nano granular; the CaFe-NO is calculated by weight₃50-80 parts of LDHs (layered double hydroxides), CaFeAl-NO₃20-50 parts of LDHs.

The chloride ion curing agent of the invention is characterized in that: which is made of CaFe-NO₃LDHs and CaFeAl-NO₃The metal double hydroxide with a layered structure compounded by LDHs2D nano sheets comprises Ca, Fe, Al and other elements, the elements are elements contained in cement, the existence of the elements cannot damage the structure of concrete, and the non-synthesized components can also participate in the hydration of the cement to generate more ettringite crystals and C-S-H gel, so that the performance of the cement base material is obviously improved; compared with CaAl LDHs, the addition of the Fe phase can stabilize the crystal form of the CaFeAl LDHs, so that the crystal structure is more complete, and the peak value is sharper. Therefore, the chloride ion curing agent of the invention not only has NO damage to a concrete matrix per se, but also has the advantages of being compared with CaAl-NO₃LDHs are not easy to desorb, the hydration heat release is lower, the stress concentration phenomenon caused by large temperature difference inside and outside the mass concrete can be reduced, and the mechanical and durability of the mass concrete can be prevented from being influenced by the cracking of the mass concrete. Meanwhile, the micro-nano particles can also effectively compact the structure of the cement-based material, thereby better achieving the solidification and transmission retardation of chloride ions. The low desorption rate of CaFe-NO₃The LDHs and the CaFeAl LDHs with large adsorption rate are mixed, so that the good curing effect on chloride ions can be achieved, the desorption rate can be reduced, and the chlorine fixing stability of the LDHs is improved.

Secondly, the present invention discloses the CaFe-NO₃The preparation method of the LDHs comprises the following steps: dissolving calcium nitrate and ferric nitrate in water to prepare solution A; dropwise adding the solution A into a sodium hydroxide solution under the protection of nitrogen, carrying out magnetic stirring after titration, then filtering, washing the obtained solid product to be neutral, and finally carrying out vacuum drying to obtain the catalyst.

Further, the proportion of the calcium nitrate, the ferric nitrate and the sodium hydroxide is 2-10mmol in sequence: 1-5 mmol: 6-28 mmol.

Further, the magnetic stirring time is 12-48h, and the vacuum drying conditions are as follows: drying for 6-24 h at 60-120 ℃.

Thirdly, the invention discloses the CaFeAl-NO₃The preparation method of the LDHs comprises the following steps: dissolving calcium nitrate, ferric nitrate and aluminum nitrate in water to prepare a solution B; dissolving sodium hydroxide and sodium nitrate in water to prepare solution C; and simultaneously dropwise adding the solution B and the solution C into a three-neck flask, stirring after dropwise adding, heating the obtained reaction solution for reaction, filtering, washing the obtained solid product to be neutral, and finally performing vacuum drying to obtain the catalyst.

Further, the proportion of the calcium nitrate, the ferric nitrate, the aluminum nitrate, the sodium hydroxide and the sodium nitrate is 6-30mmol in sequence: 1-4 mmol: 2-10 mmol: 16-60 mmol: 20-40 mmol.

Further, the heating reaction is as follows: reacting at 100-120 ℃ for 12-48 h.

Further, the stirring time is 2-6h, and the vacuum drying conditions are as follows: drying for 6-24 h at 60-120 ℃.

In the preparation method, the obtained CaFe LDHs and CaFeAl LDHs are prepared by one step by a coprecipitation method, so that the preparation process is simple, and the raw material sources are wide.

Finally, the invention discloses the application of the chloride ion curing agent for reinforced concrete in the field of constructional engineering.

Compared with the prior art, the invention has the following beneficial effects:

(1) the chloride ion curing agent of the invention has the technical advantages of large adsorption rate and small desorption rate under the condition of low doping amount (0.5-2.5%), and has obvious curing effect on chloride ions in the purified slurry.

(2) The chloride ion curing agent disclosed by the invention has good chloride ion curing performance and good stability in simulated concrete pore solution. Meanwhile, in the presence of excessive desorption agent (sodium sulfate), the chloride ion curing agent still keeps good curing effect and has low desorption rate.

(3) The raw materials adopted for synthesizing the chloride ion curing agent are solid wastes, the price is low, the acting force of interlayer anions of the synthesized LDHs is weak, and the LDHs can be easily replaced with other ions, and meanwhile, the invention is based on the special ion exchange characteristics and ion exchange sequence (CO) of the LDHs₃ ^2->SO₄ ^2->Cl^->NO₃ ^-) Adding Cl^-By insertion between layers of a layered compound to replace NO₃ ^-The layered structure of the concrete can not be damaged while the chloride ions are cured, so that the chloride ions can stably exist in the concrete without decomposition, and the adverse effect on the concrete structure is avoided.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is an XRD test pattern of the curing agent prepared in example 1 of the present invention.

FIG. 2 is an SEM image of the curing agent represented by A4 after equilibrium desorption of chloride ions in example of the present invention.

FIG. 3 is an SEM image of the curing agent represented by A5 after equilibrium desorption of chloride ions in example of the present invention.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As mentioned above, some existing measures for solving the problem that free chloride ions in concrete are liable to cause deterioration of reinforced concrete structure and performance still have the problems of poor curing effect, high desorption rate, poor stability, etc. Therefore, the invention provides a chloride ion curing agent for reinforced concrete and a preparation method thereof; the invention will now be further described with reference to specific embodiments.

In the following examples, the cement was obtained from Shandong's Organin Cement Co., Ltd, type 42.5 sulfate-resistant Portland cement.

Example 1

A preparation method of a chloride ion curing agent for reinforced concrete comprises the following steps:

1、CaFe-NO₃synthesizing and preparing LDHs: will be 10mmDissolving ol of calcium nitrate and 5mmol of ferric nitrate in 100mL of distilled water to prepare solution A; and (3) dropwise adding the solution A into 30mL of 1mol/L sodium hydroxide solution (the gas flow is 100mL/min under the protection of nitrogen), magnetically stirring for 36h after titration, filtering to be neutral, drying for 12h in a vacuum drying oven at the temperature of 80 ℃, and grinding the obtained product into powder to obtain the compound.

2、CaFeAl-NO₃Synthesizing and preparing LDHs: dissolving 100mmol of calcium nitrate, 10mmol of ferric nitrate and 40mmol of aluminum nitrate in 100mL of distilled water to prepare a solution B; dissolving 240mmol of sodium hydroxide and 120mmol of sodium nitrate in 100mL of distilled water to prepare a solution C; and simultaneously dropwise adding the solution B and the solution C into a three-neck flask, stirring for 2 hours after dropwise adding is finished, then placing the mixture into an evaporation reaction kettle for reaction for 48 hours at the temperature of 110 ℃, filtering to be neutral, drying for 12 hours in a vacuum drying oven at the temperature of 80 ℃, and grinding the obtained product into powder to obtain the compound.

Example 2

1、CaFe-NO₃synthesizing and preparing LDHs: dissolving 40mmol of calcium nitrate and 15mmol of ferric nitrate in 100mL of distilled water to prepare solution A; and dropwise adding the solution A into 100mL of 1mol/L sodium hydroxide solution (the gas flow is 100mL/min under the protection of nitrogen), magnetically stirring for 12h after titration, filtering to neutrality, drying for 24h in a vacuum drying oven at 60 ℃, and grinding the obtained product into powder to obtain the compound.

2、CaFeAl-NO₃Synthesizing and preparing LDHs: dissolving 30mmol of calcium nitrate, 5mmol of ferric nitrate and 10mmol of aluminum nitrate in 120mL of distilled water to prepare a solution B; dissolving 80mmol of sodium hydroxide and 100mmol of sodium nitrate in 120mL of distilled water to prepare a solution C; and simultaneously dropwise adding the solution B and the solution C into a three-neck flask, stirring for 2 hours after dropwise adding is finished, then placing the mixture into an evaporation reaction kettle for reaction for 48 hours at the temperature of 100 ℃, filtering to be neutral, drying for 24 hours in a vacuum drying oven at the temperature of 60 ℃, and grinding the obtained product into powder to obtain the compound.

Example 3

1、CaFeL-NO₃synthesis and preparation of DHs: dissolving 50mmol of calcium nitrate and 25mmol of ferric nitrate in 120mL of distilled water to prepare solution A; and dropwise adding the solution A into 140mL of 1mol/L sodium hydroxide solution (the gas flow is 100mL/min under the protection of nitrogen), magnetically stirring for 48 hours after titration, filtering to neutrality, drying for 6 hours in a vacuum drying oven at the temperature of 120 ℃, and grinding the obtained product into powder to obtain the compound.

2、CaFeAl-NO₃Synthesizing and preparing LDHs: dissolving 150mmol of calcium nitrate, 20mmol of ferric nitrate and 50mmol of aluminum nitrate in 150mL of distilled water to prepare a solution B; dissolving 300mmol of sodium hydroxide and 200mmol of sodium nitrate in 150mL of distilled water to prepare a solution C; and simultaneously dropwise adding the solution B and the solution C into a three-neck flask, stirring for 2 hours after dropwise adding is finished, then placing the three-neck flask into an evaporation reaction kettle for reaction at 120 ℃ for 12 hours, filtering to be neutral, drying for 24 hours in a vacuum drying oven at 120 ℃, and grinding the obtained product into powder to obtain the product.

Performance testing：

1. XRD test: when XRD test is performed on the product prepared in example 1, as shown in fig. 1, it can be seen that the peak is evident in the (002), (110) and other crystal planes at 2 θ ═ 10, which is an important sign for the synthesis of the layered compound. The successful insertion of nitrate ions into the material is seen, demonstrating the successful synthesis of CaFe-NO₃LDHs and CaFeAl-NO₃LDHs, and CaFeAl-NO₃Has a crystal structure compared with CaFe-NO₃The LDHs is more complete and the crystal form is sharper.

2. Preparation of chloride ion curing agent, according to the weight part, the CaFe-NO prepared in example 1 is weighed in different proportions₃LDHs、CaFeAl-NO₃LDHs are stirred in a VH type mixer for 20 minutes until the mixture is evenly mixed to obtain chloride ion curing agents with different compounding proportions, namely A1, A2, A3 and A4, and meanwhile, CaAl-NO adopted at present is used₃LDHs are used as a control group and are named as A5; the method specifically comprises the following steps:

a1: 0 part of CaFe-NO₃LDHs, 100 parts of CaFeAl-NO₃LDHs。

A2: 50 parts of CaFe-NO₃LDHs, 50 parts of CaFeAl-NO₃LDHs。

A3: 80 parts of CaFe-NO₃LDHs, 20 parts of CaFeAl-NO₃LDHs。

A4: 100 parts of CaFe-NO₃LDHs, 0 part of CaFeAl-NO₃LDHs。

A5: 100 parts of CaAl-NO₃LDHs。

3. Simulation test on the curing amount and stability of chloride ions:

(1) 0.015mol sodium hydroxide, 0.025mol potassium hydroxide and 0.0005mol calcium hydroxide were dissolved in 1 liter deionized water and configured to simulate a concrete pore solution having a pH of about 12.71 for use.

Furthermore, in order to measure the curing amount and stability of the chloride ion curing agents (A1, A2, A3, A4 and A5) in the five groups to the chloride ions in the simulated concrete pore solution, the simulated concrete pore solution is prepared into the simulated solution with the chloride ion concentration of 90mM, and the five groups of the simulated solution are respectively named as B1, B2, B3, B4 and B5, and each group is 50 mL. First, 0.75g of a1, a2, A3, a4 and a5 chloride ion curing agents were added to simulated solutions represented by B1, B2, B3, B4 and B5 in this order, followed by 120-hour adsorption, and after adsorption equilibrium, 1.667mmol of sodium sulfate (desorbent) was added to each of B1, B2, B3, B4 and B5, followed by 120-hour desorption.

According to the standard of SL 352-2006 'hydraulic concrete test procedure', an ion selective electrode method is adopted to rapidly determine the content of free chloride ions in the simulated solution at room temperature. A rapid chloride ion content tester with the model number of NELD-CL 420; measurement range: 1.0X 10^-5～1.0×10^-1mol/L; measuring time: and 2 min. The test results obtained are shown in table 1.

TABLE 1 curing agent after equilibrium of adsorption and desorption for chloride ion

Experimental group	Amount of adsorption (mol/mol)	Desorption rate (%)
			A1	1.977	41.33
A2	1.948	33.26
			A3	1.971	31.27
A4	1.963	30.05
			A5	1.864	49.45

(1) As can be seen from Table 1, the curing agents A1-A4 prepared by the process proposed by the present invention have an adsorption capacity for chloride ions that is substantially close to the limit of 2mol/mol in the simulated solution, whereas the A5 curing agent has a somewhat lower adsorption capacity.

(2) As can be seen from Table 1, the curing agent A1-A4 prepared by the method provided by the invention can significantly reduce the desorption rate of chloride ions. Among them, the unit mole adsorption quantity of A1 to chloride ion is the largest, the desorption rate of A4 is the lowest, the desorption rate of A4 is low, and 3 CaO. Fe with chlorine fixing effect is generated in large quantity due to crystal form transformation in desorption experiment₂O₃·0.5CaSO₄·0.5CaCl₂·10H₂O and FeCl₃·(OH)_nEtc., and the morphology of the a4 curing agent is less disrupted, as shown in fig. 2. The morphology of the layered compound of control A5 was significantly destroyed (see FIG. 3) because it generated a large amount of needle-like ettringite crystals (3 CaO. Al) upon desorption₂O₃·CaSO₄·32H₂O), resulting in a significant reduction in its stability to cure chloride ions. Therefore, the A2 and A3 formulas with the complex doping property can not only exert the advantage of maximum adsorption capacity, but also reduce the desorption rate of the layered compound to chloride ions.

(2) According to the standard of SL 352-2006 'Hydraulic concrete test procedure', an ion selective electrode method is adopted to quickly measure the content of free chloride ions in the mortar test block at room temperature. A rapid chloride ion content tester with the model number of NELD-CL 420; measurement range: 1.0X 10^-5～1.0×10^-1mol/L; measuring time: and 2 min.

Further, the cement paste sample is prepared according to the curing method specified in GB/T17671-1999 Cement mortar Strength test method. The specific test steps are as follows:

(1) mixing the sulfate-resistant portland cement and water in a ratio of 1:0.4, adding a chloride ion curing agent accounting for 0.5-2.5% of the mass of the cement, and uniformly stirring in an NJ-160A type cement paste mixer.

(2) Pouring the stirred slurry into a forming die with the size of 20 multiplied by 20mm, demoulding after 24 days, sealing the surface of five surfaces of a test block by paraffin after the slurry reaches the age of 28d, only leaving one side surface with the size of 20 multiplied by 20mm, soaking the test block in a sodium chloride solution with the mass concentration of 3.5%, taking out the test block after soaking for 3d, wiping the surface of the test block, placing the test block in a blast drying box for drying to constant weight at 45 ℃, cutting the test block from the surface into small blocks with the sizes of 0-5mm, 6-10 mm, 11-15mm and 16-20mm, crushing and grinding the small blocks into powder, measuring the content of chloride ions at different depths by using a rapid chloride ion content tester of NELD-CL420, and evaluating the content of the chloride ions at different depths of the clean slurry sample by each component in example 1, wherein the detection results are shown in Table 2.

TABLE 2 chloride ion content (%) -at various depths from the surface in neat pastes

As can be seen from Table 2, the chloride ion content of the neat paste gradually decreased with increasing depth from the surface of the sample; when the doping amount is 1%, the A3-1.5% samples show the minimum chloride ion content at different net slurry depths, which shows that the effect of the chloride ion curing agent and the permeability resistance of the chloride ion are better; with the continuous increase of the mixing amount, the chlorine fixing effect and the chloride ion impermeability of the curing agent are not obviously increased, because excessive curing agent can block the hydration of cement, so that the compactness of a net slurry sample is reduced, the porosity is increased, and the transmission and the diffusion of chloride ions are facilitated. The mortar sample doped with the chloride ion curing agent has the chloride ion content far lower than that of a blank sample at different depths, which shows that the curing agent has good effect of curing chloride ions; compared with the curing agents, the compound A3 curing agent has the best effect of curing chloride ions.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. CaFe-NO₃The preparation method of LDHs is characterized by comprising the following steps: dissolving calcium nitrate and ferric nitrate in water to prepare solution A; and (3) dropwise adding the solution A into a sodium hydroxide solution under the protection of nitrogen, magnetically stirring after titration, filtering for multiple times until the solution is neutral, and finally performing vacuum drying to obtain the sodium hydroxide.

2. CaFe-NO according to claim 1₃The preparation method of LDHs is characterized in that the proportion of calcium nitrate, ferric nitrate and sodium hydroxide is 2-10 mmol: 1-5 mmol: 6-28 mmol.

3. As claimed in claim 1 or 2CaFe-NO of₃The preparation method of LDHs is characterized in that the magnetic stirring time is 12-48h, and the vacuum drying condition is as follows: drying for 6-24 h at 60-120 ℃.

4. CaFeAl-NO₃The preparation method of LDHs is characterized by comprising the following steps: dissolving calcium nitrate, ferric nitrate and aluminum nitrate in water to prepare a solution B; dissolving sodium hydroxide and sodium nitrate in water to prepare solution C; and simultaneously dropwise adding the solution B and the solution C into a three-neck flask, stirring after dropwise adding, heating the obtained reaction solution for reaction, filtering to be neutral, and finally performing vacuum drying to obtain the compound.

5. CaFeAl-NO according to claim 4₃The preparation method of LDHs is characterized in that the proportions of calcium nitrate, ferric nitrate, aluminum nitrate, sodium hydroxide and sodium nitrate are as follows in order of 6-30 mmol: 1-4 mmol: 2-10 mmol: 16-60 mmol: 20-40 mmol.

6. CaFeAl-NO according to claim 4 or 5₃The preparation method of LDHs is characterized in that the heating reaction is as follows: reacting at 100-120 ℃ for 12-48 h;

preferably, the stirring time is 2-6h, and the vacuum drying condition is as follows: drying for 6-24 h at 60-120 ℃.

7. The chloride ion curing agent for reinforced concrete is characterized by being CaFe-NO₃LDHs nano-sheets, wherein the curing agent is a metal double hydroxide with a layered structure;

preferably, said CaFe-NO₃The LDHs are obtained by the preparation method of any one of claims 1 to 3.

8. The chloride ion curing agent for reinforced concrete is characterized by being CaFeAl-NO₃LDHs nano-sheets, wherein the curing agent is a metal double hydroxide with a layered structure;

preferably, the CaFeAl-NO₃LDHs rights of ownershipThe method according to any one of claims 4 to 6.

9. The chloride ion curing agent for reinforced concrete is characterized by being prepared from CaFe-NO₃LDHs and CaFeAl-NO₃The LDHs nanosheets are compounded into metal double hydroxide with a layered structure, and the metal double hydroxide is micro-nano granular; the CaFe-NO is calculated by weight₃50-80 parts of LDHs (layered double hydroxides), CaFeAl-NO₃20-50 parts of LDHs;

preferably, said CaFe-NO₃The LDHs are obtained by the preparation method of any one of claims 1 to 3;

preferably, the CaFeAl-NO₃The LDHs are obtained by the preparation method of any one of claims 4 to 6.

10. Use of a chloride ion curing agent for reinforced concrete according to any one of claims 7 to 9 in the field of construction engineering.