Additive for enhancing chloride ion permeability resistance and application thereof

Abstract

The invention belongs to the technical field of civil engineering materials, and particularly relates to an additive for enhancing chloride ion permeability resistance and application thereof. The additive comprises an amino organic ligand modified aluminum-based metal organic framework material coated with polycarboxylic acid and nano calcium hydroxide. Aiming at the problems of pore structure coarsening, poor chloride ion resistance and the like caused by insufficient hydration of solid waste cement prepared from high-doping-amount iron tailing powder, an amino organic ligand is utilized to modify an aluminum-based MOF material, chloride ions are adsorbed by electrostatic attraction and hydrogen bonds synergistically, and meanwhile, agglomeration of the MOF material is prevented through polycarboxylic acid coating; the dispersity and the compatibility in a cement system are improved; the nano calcium hydroxide promotes cement hydration and improves the slurry compactness, and the nano calcium hydroxide and the slurry synergistically prevent chloride ion permeation.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering materials technology, specifically relating to an additive for enhancing resistance to chloride ion penetration and its application. Background Technology

[0002] In recent years, the use of solid waste to produce low-carbon cement has received considerable attention, as it not only reduces carbon dioxide emissions but also reduces reliance on non-renewable resources, thereby promoting the sustainable development of building materials.

[0003] Excessive iron tailings production and low recovery rates have led to the accumulation of large amounts of iron tailings powder (ITP), causing serious environmental problems. To improve the comprehensive utilization rate of tailings, especially to address the difficulty in processing fine-grained tailings, many researchers have used iron tailings powder to prepare low-carbon cementitious materials. However, since the main components of iron tailings powder are SiO2 (35%–83%) and Fe2O3 (7%–47%), with low levels of active SiO2 and Al2O3, when the admixture exceeds 30%, the cement hydration reaction is incomplete, the pore structure becomes coarser, and the concrete prepared from it has low resistance to chloride ion penetration.

[0004] Resistance to chloride ion penetration is an important indicator of concrete durability. Therefore, developing additives for cement with high iron tailings powder content that can enhance resistance to chloride ion penetration is of great significance for practical engineering applications. In view of this, this invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an additive for enhancing chloride ion permeability and its application. It uses an aluminum-based metal-organic framework material modified with amino organic ligands coated with polycarboxylic acid as the main body to adsorb and fix chloride ions. It is compounded with nano-calcium hydroxide to improve the reactivity of iron tailings powder. The nano-sized filling and dense structure enhance the chloride ion permeability resistance of high-content solid waste cement.

[0006] Specifically, the present invention provides the following technical solutions: An additive for enhancing resistance to chloride ion penetration comprises a polycarboxylic acid-coated amino-organic ligand-modified aluminum-based metal-organic framework material and nano-calcium hydroxide.

[0007] Amino-organic ligand-modified aluminum-based metal-organic frameworks contain positively charged metal ion sites and amino functional groups, enabling them to react with chloride ions (Cl-). -Synergistic adsorption is achieved through mechanisms such as electrostatic attraction and hydrogen bonding. The polycarboxylic acid coating on the MOF surface provides steric hindrance to prevent MOF aggregation, while enhancing its dispersibility and compatibility in the cement system. The introduction of nano-calcium hydroxide provides crystal nuclei to promote hydration reactions, accelerates the reaction of solid waste, and generates more CSH gel, thereby filling micropores, refining the pore structure, significantly reducing the material's permeability and diffusion coefficient, making it more difficult for chloride ions to penetrate. Simultaneously, the fixed chloride ions, under the promotion of CH, accelerate the formation of Freund's salt with the aluminum and iron phases in the solid waste. The components complement each other, giving the cement concrete material excellent resistance to chloride ion penetration.

[0008] Preferably, the mass ratio of the polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework (MOF) to nano-calcium hydroxide is 1:2-2:5. If the ratio is too high, the amount of nano-calcium hydroxide will be insufficient, and since nano-calcium hydroxide is a promoter and activator for solid waste, insufficient dosage will not be able to fully activate the solid waste. If the ratio is too low, the MOF effect will be reduced, its high adsorption capacity will not be manifested, and its role in resisting chloride ions will be weakened.

[0009] Preferably, the particle size of the polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material is 0.1-1 μm. Studies have found that if the particle size is too large, firstly, the specific surface area decreases, and its capture efficiency and fixation capacity are significantly reduced; secondly, the filling efficiency is low, and it cannot be uniformly dispersed.

[0010] And / or, the particle size of the nano-calcium hydroxide is less than 100 nm, more preferably 10-80 nm, to provide nucleation-induced hydration product generation.

[0011] Preferably, the preparation method of the polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material includes the following steps: (1) Add aluminum source precursor (such as aluminum nitrate nonahydrate or aluminum chloride hexahydrate), amino organic ligand, and surfactant to solvent and sonicate for a period of time (e.g., 5-30 min); then add to a closed reaction vessel and hydrothermally react at 100-150 ℃ for 6-24 h to obtain amino organic ligand modified aluminum-based metal-organic framework material. (2) Add the amino-organic ligand-modified aluminum-based metal-organic framework material prepared in step (1) to a polycarboxylic acid solution, stir or ultrasonically disperse for a period of time (e.g., 20-60 min), then let it stand for a period of time (e.g., 1-2 h) to complete physical adsorption, then centrifuge to separate the solid product, dry and grind to obtain the final product. Letting it stand to complete adsorption and precipitation concentration facilitates subsequent separation.

[0012] More preferably, the amino organic ligand is 2-aminoterephthalic acid (NH2–BDC). Under alkaline conditions, the amino group undergoes protonation to form a cation center, thereby providing a more stable chemically bound chloride ion.

[0013] More preferably, the molar ratio of the aluminum source precursor to the amino organic ligand is 1:(1.0-1.5).

[0014] More preferably, the solvent is an aqueous solution of ethanol or pure water.

[0015] More preferably, the solid content of the polycarboxylic acid solution is 10-30 wt%; The polycarboxylic acid solution contains a polycarboxylic acid-based water-reducing agent, which includes a carboxyl group (–COOH) and a polyether side chain (–(CH2CH2O)n–) structure, and has dispersing and adsorption functions; More preferably, the polycarboxylate superplasticizer is an acrylic, methacrylic, or maleic anhydride polycarboxylate superplasticizer.

[0016] More preferably, the mass ratio of the amino-organic ligand-modified aluminum-based metal-organic framework material to the polycarboxylic acid in the polycarboxylic acid solution is 1:1.0-2.5.

[0017] The present invention also provides a concrete, the raw materials of which include cementitious materials and the above-mentioned additives; the cementitious materials include cement clinker and solid waste admixtures, and the mass fraction of the solid waste admixtures in the cementitious materials is more than 30%.

[0018] Preferably, the solid waste admixture includes iron tailings powder; And / or, based on the mass of the cementitious material, the amount of the additive is 1-3 wt%.

[0019] In practical application, the present invention is first mixed with polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material and nano-calcium hydroxide in an inert atmosphere (e.g., argon or nitrogen) to obtain an additive, which is then sealed and stored. Before use, the additive is weighed as needed and added to the cementitious material and pre-stirred thoroughly. Then, it is mixed with other raw materials to prepare concrete.

[0020] Polycarboxylic acid-coated amino-organic ligand-modified aluminum-based metal-organic framework materials The beneficial effects of this invention are at least as follows: (1) The present invention provides an additive for enhancing resistance to chloride ion penetration, which introduces amino organic ligands to modify aluminum-based metal-organic framework materials. The positively charged metal ion sites and amino functional groups contained therein can react with chloride ions (Cl... - It achieves synergistic adsorption through mechanisms such as electrostatic attraction and hydrogen bonding, thereby enhancing its adsorption capacity for chloride ions; (2) The present invention provides an additive for enhancing resistance to chloride ion penetration by using polycarboxylic acid for coating. On the one hand, it provides steric hindrance to prevent MOF material from agglomerating; on the other hand, polycarboxylic acid has hydrophilicity and dispersibility, which improves the dispersibility and compatibility of MOF material in cement system. (3) The present invention provides an additive for enhancing the resistance to chloride ion penetration by introducing nano calcium hydroxide, which promotes cement hydration through excitation and crystal nucleation effect, and can significantly improve cement strength and paste density, thereby improving the resistance to chloride ion penetration. (4) The present invention provides an additive for enhancing chloride ion penetration resistance. The polycarboxylic acid-coated amino organic ligand modified aluminum-based metal-organic framework material and nano calcium hydroxide work synergistically to give cement concrete material excellent chloride ion penetration resistance. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art, or in accordance with the product manual.

[0022] In the following embodiment: The aluminum source precursor used was aluminum nitrate nonahydrate; The amino organic ligand used is 2-aminoterephthalic acid; The surfactant used is polyethylene glycol; The solid content of the polycarboxylic acid solution used is 30wt%, and the polycarboxylic acid is sourced from China Construction Western Construction Building Materials Science Research Institute Co., Ltd., with product model ZJZQ.

[0023] Example 1 An additive for enhancing resistance to chloride ion penetration is composed of an aluminum-based metal-organic framework material modified with amino organic ligands and polycarboxylic acid in a mass ratio of 2:4.5 (particle size 0.1-1 μm) and nano-calcium hydroxide (particle size 10-80 nm). The preparation method of the polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material includes the following steps: (1) Synthesis of aluminum-based metal-organic framework material modified by amino organic ligand: An aluminum source precursor with a molar ratio of 1:1.5, an amino organic ligand, and a surfactant (the amount of surfactant is 0.5 wt% of the amount of aluminum source precursor) are added to water and sonicated for 30 min. After sonication, the mixture is transferred to a closed reactor and hydrothermally synthesized at 150 °C for 12 hours. The upper solvent is removed by standing, and the mixture is dried under vacuum at 100 °C to obtain the final product.

[0024] (2) Coating of MIL material: The prepared amino-organic ligand modified aluminum-based metal-organic framework material is added to a polycarboxylic acid solution (the mass ratio of amino-organic ligand modified aluminum-based metal-organic framework material to polycarboxylic acid is 1:1.0), magnetically stirred for 30 minutes, allowed to stand for 2 hours to complete physical adsorption, centrifuged to separate the solid product, dried and ground to obtain the final product.

[0025] Example 2 The only difference from Example 1 is that the mass ratio of polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material to nano-calcium hydroxide is 1:2.

[0026] Example 3 The only difference from Example 1 is that the mass ratio of polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material to nano-calcium hydroxide is 2:5.

[0027] Example 4 The only difference from Example 1 is that the mass ratio of polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material to nano-calcium hydroxide is 1:1.

[0028] Example 5 The only difference from Example 1 is that the mass ratio of polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material to nano-calcium hydroxide is 1:3.

[0029] Example 6 The only difference from Example 1 is that the particle size of the polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material is 10 μm-100 μm.

[0030] Comparative Example 2 Compared with Example 1, the only difference is that the additive contains only polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material, and does not contain nano-calcium hydroxide.

[0031] Comparative Example 3 Compared with Example 1, the only difference is that the additive contains only nano-calcium hydroxide and does not contain polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework materials.

[0032] Test case Concrete was prepared using the additives in Examples 1 and Comparative Examples 2-3, with the following formulation: 220 kg of cementitious material, 800 kg of fine aggregate, 1090 kg of coarse aggregate, 160 kg of water, and the aforementioned additive. The cementitious material consisted of 60% PO 42.5 cement and 40 wt% iron tailings powder; the additive was added at a rate of 2 wt% by weight of the cementitious material. Performance test results are shown in Table 1, where Comparative Example 1 is the baseline group without the additive. According to relevant research, concrete with high solid waste content exhibits a secondary hydration effect; therefore, its durability performance testing age is often chosen to be 56 days or 90 days. This project selected curing to 90 days and conducted the test according to Chapter 7 of GB50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete"—the chloride ion penetration test.

[0033] Table 1. Concrete performance test results

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An additive for enhancing resistance to chloride ion penetration, characterized in that, These include aluminum-based metal-organic framework materials modified with amino-organic ligands coated with polycarboxylic acid, and nano-calcium hydroxide.

2. The additive for enhancing resistance to chloride ion penetration according to claim 1, characterized in that, The mass ratio of the polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material to nano-calcium hydroxide is 1:2-2:

5.

3. An additive for enhancing resistance to chloride ion penetration according to claim 1 or 2, characterized in that, The particle size of the polycarboxylic acid-coated amino organic ligand-modified aluminum-based metal-organic framework material is 0.1-1 μm; And / or, the particle size of the nano-calcium hydroxide is less than 100 nm, preferably 10-80 nm.

4. An additive for enhancing resistance to chloride ion penetration according to claim 1 or 2, characterized in that, The preparation method of the polycarboxylic acid-coated amino-organic ligand-modified aluminum-based metal-organic framework material includes the following steps: (1) Add aluminum source precursor, amino organic ligand and surfactant to solvent and sonicate for a period of time; then add to a closed reaction vessel and hydrothermally react at 100-150 ℃ for 6-24 h to obtain amino organic ligand modified aluminum-based metal-organic framework material. (2) Add the amino organic ligand modified aluminum-based metal-organic framework material prepared in step (1) into a polycarboxylic acid solution, stir or ultrasonically disperse for a period of time, then let it stand for a period of time to complete physical adsorption, then centrifuge to separate the solid product, dry and grind it to obtain the product.

5. An additive for enhancing resistance to chloride ion penetration according to claim 4, characterized in that, The amino organic ligand is 2-aminoterephthalic acid.

6. An additive for enhancing resistance to chloride ion penetration according to claim 4, characterized in that, The molar ratio of the aluminum source precursor to the amino organic ligand is 1:(1.0-1.5).

7. An additive for enhancing resistance to chloride ion penetration according to claim 4, characterized in that, The solid content of the polycarboxylic acid solution is 10-30 wt%; the polycarboxylic acid in the polycarboxylic acid solution is a polycarboxylic acid-based water-reducing agent. Preferably, the polycarboxylate superplasticizer is an acrylic, methacrylic, or maleic anhydride polycarboxylate superplasticizer.

8. An additive for enhancing resistance to chloride ion penetration according to claim 4, characterized in that, The mass ratio of the amino-organic ligand-modified aluminum-based metal-organic framework material to the polycarboxylic acid solution is 1:1.0-2.

5.

9. A type of concrete, characterized in that, The raw materials include cementitious materials and additives as described in any one of claims 1-8; the cementitious materials include cement clinker and solid waste admixtures, and the mass fraction of the solid waste admixtures in the cementitious materials is more than 30%.

10. The concrete according to claim 9, characterized in that, The solid waste admixture includes iron tailings sand; And / or, based on the mass of the cementitious material, the amount of the additive is 1-3 wt%.

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