Freeze-thaw resistant concrete and preparation method thereof

Abstract

The invention discloses freeze-thaw resistant concrete and a preparation method thereof, and belongs to the technical field of cement-based building materials, the freeze-thaw resistant concrete comprises the following raw materials by mass: 35-40 parts of ordinary Portland cement, 100-180 parts of aggregate, 0.5-0.8 part of a water reducer, 4-6 parts of a phase change material, 2-5 parts of modified composite cellulose and 15-20 parts of water. According to the freeze-thaw resistant concrete prepared by the invention, polar groups on the surface of the modified fiber and the phase-change material form chemical bonds, so that the heat conduction efficiency is improved, the phase-change material quickly absorbs / releases heat during temperature change, the thermal response time is shortened, and the adaptability of a concrete structure to environmental temperature fluctuation is improved. The cellulose network with controllable porosity limits the volume expansion of the phase change material in the phase change process, so that the stress concentration in the concrete is avoided, and the generation of microcracks is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of cement-based building materials, and particularly relates to a freeze-thaw resistant concrete and a preparation method thereof. Background Art

[0002] As the most widely used building material, the durability of concrete directly determines the service life of engineering structures. However, in cold regions or environments with frequent freeze-thaw cycles, concrete often develops microcracks, spalling, and even structural failure due to the repeated action of internal water freezing and expansion and melting and shrinkage, a phenomenon known as freeze-thaw damage. According to statistics, approximately 30% of hydraulic concrete structures in the northern region show significant freeze-thaw damage within 20 years of service, and the service life of key infrastructure such as dams and bridges in some severely cold regions is even shortened to less than 15 years. Freeze-thaw damage not only threatens structural safety but also brings high maintenance costs. Therefore, improving the freeze-thaw resistance of concrete has always been a research focus in the field of building materials.

[0003] Traditional freeze-thaw resistance technologies include adding air-entraining agents or modifying with mineral admixtures during the preparation of concrete. Among them, air-entraining agents relieve freeze-thaw stress by introducing uniformly distributed tiny bubbles (pore diameter 20 - 200 μm), which is the most mainstream freeze-thaw resistance means currently. These bubbles can accommodate the volume expansion (about 9%) when water freezes, reducing the damage of internal pressure to concrete. However, the introduction of bubbles reduces the compactness of concrete, resulting in a 10% - 20% decrease in compressive strength and elastic modulus. In an environment of long-term load or high-frequency vibration, the bubbles are prone to coalescence or rupture, weakening the freeze-thaw resistance effect; in a coupled salt-freezing environment (such as the penetration of road deicing salts), Cl- will accelerate the corrosion of the paste around the bubbles, forming connected pores, which instead exacerbates freeze-thaw. Fly ash, silica fume, slag and other admixtures can indirectly improve freeze-thaw resistance by filling pores and refining pore structures through the pozzolanic effect. However, the hydration reaction of the above admixtures significantly slows down at low temperatures, resulting in insufficient early strength development and difficulty in meeting the requirements of winter construction. At the same time, excessive incorporation (such as fly ash > 40%) will increase the porosity due to insufficient cementitious materials, resulting in a counter-effect.

[0004] Therefore, there is an urgent need in this field for a freeze-thaw resistant concrete material with high freeze-thaw resistance performance to meet the durability requirements of concrete in severely cold regions. Summary of the Invention

[0005] The purpose of the present invention is to provide a freeze-thaw resistant concrete and a preparation method thereof to solve the problems existing in the above-mentioned prior art.

[0006] One of the technical solutions provided by the present invention:

[0007] An anti-freeze and thaw concrete, by mass, comprises the following raw materials: 35-40 parts of ordinary portland cement, 100-180 parts of aggregate, 0.5-0.8 parts of water reducer, 4-6 parts of phase change material, 2-5 parts of composite cellulose and 15-20 parts of water.

[0008] Preferably, the anti-freeze and thaw concrete, by mass, comprises the following raw materials: 35 parts of ordinary portland cement, 150 parts of aggregate, 0.5 parts of water reducer, 5 parts of phase change material, 3 parts of modified composite cellulose and 18 parts of water.

[0009] Preferably, the aggregate is composed of medium sand and graded gravel in a mass ratio of (15-16):(20-22).

[0010] More preferably, the particle size of the medium sand is 0.25-0.5 mm; the particle size of the graded gravel is 10-30 mm.

[0011] Preferably, the preparation method of the phase change material comprises the following steps: mixing methyl palmitate and methyl stearate and heating to melt, loading the molten mixture onto modified expanded perlite by vacuum impregnation to obtain a loaded phase change material; placing the loaded phase change material in an aqueous solution of polyvinyl alcohol and modified nano-silica, stirring, filtering, and drying to obtain primary encapsulated particles; impregnating the primary encapsulated particles in an ethanol solution of titanate coupling agent and drying to prepare the phase change material.

[0012] The present invention uses a methyl palmitate-methyl stearate blend as the phase change core, expanded perlite as the carrier, a polyvinyl alcohol (PVA)-nano-silica composite film as the encapsulation layer, and a titanate coupling agent as the interface enhancer to prepare a "core-shell-crown" structure composite phase change material. The methyl palmitate-methyl stearate blend has a high phase change latent heat and an adjustable phase change temperature, adapting to the freeze-thaw environment in cold regions.

[0013] More preferably, the mass ratio of methyl palmitate to methyl stearate is 7:3.

[0014] More preferably, the mass ratio of the molten mixture to the modified expanded perlite is 9:11.

[0015] More preferably, the preparation method of the modified expanded perlite is: immersing expanded perlite in a sulfuric acid solution, ultrasonic treatment, washing, and roasting to obtain the modified expanded perlite.

[0016] More preferably, in the aqueous solution of polyvinyl alcohol and modified nano-silica, the concentration of polyvinyl alcohol is 5-8 wt.%, and the concentration of the modified nano-silica is 2-4 wt.%.

[0017] More preferably, the preparation method of the modified nano-silica includes the following steps: adding nano-silica into a hydrolyzed solution of a silane coupling agent, heating and reacting, filtering, and drying to obtain the modified nano-silica. Among them, the silane coupling agent is selected from methyltriethoxysilane or vinyltriethoxysilane; the dosage of the silane coupling agent is 4 wt% of the nano-silica.

[0018] Preferably, the preparation method of the modified composite cellulose includes the following steps: adding a silane coupling agent into an aqueous ethanol solution, adding sulfuric acid (1 mol / L), adjusting the pH to 3 - 5, heating and reacting, then adding composite cellulose, stirring and reacting, filtering, and drying to obtain the modified composite cellulose.

[0019] More preferably, the composite cellulose is prepared by mixing basalt fiber and polypropylene fiber according to a mass ratio of 2:1 and modifying.

[0020] The basalt fiber and polypropylene fiber are compounded, and after being surface-treated with a silane coupling agent, they are chemically anchored to the cement matrix to construct a multi-level reinforcement system of "rigid support + flexible energy dissipation", which helps to improve the crack resistance performance.

[0021] More preferably, the addition amount of the silane coupling agent is 1 - 1.5% of the composite cellulose.

[0022] In the present invention, the fiber surface is treated with a silane coupling agent to form chemical bonds with the polar groups in the phase change material. The modified fiber can serve as a "thermal conduction bridge" to accelerate the thermal response speed of the phase change material. The network of cellulose restricts the volume expansion of the phase change material during the phase change process, avoiding the generation of microcracks inside the concrete.

[0023] The second technical solution provided by the present invention:

[0024] A preparation method of the above-mentioned freeze-thaw resistant concrete includes the following steps: mixing aggregates and ordinary Portland cement, adding a water reducing agent and water, stirring, adding a phase change material and modified composite cellulose, continuing to stir, injecting into a mold, and curing the obtained concrete matrix to obtain the freeze-thaw resistant concrete.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] In the freeze-thaw resistant concrete prepared by the present invention, the polar groups on the surface of the modified fiber form chemical bonds with the phase change material, improving the heat conduction efficiency, enabling the phase change material to quickly absorb / emit heat when the temperature changes, shortening the thermal response time, and enhancing the adaptability of the concrete structure to environmental temperature fluctuations. The cellulose network with controllable porosity restricts the volume expansion of the phase change material during the phase change process, avoiding stress concentration inside the concrete and reducing the generation of microcracks. Specific embodiments

[0027] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation on the present invention, but rather as a more detailed description of certain aspects, features, and implementation schemes of the present invention.

[0028] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0030] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0031] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0032] The room temperature in the present invention refers to 25 ± 2 °C.

[0033] In the embodiments of the present invention, "parts" shall refer to "parts by mass" unless otherwise specified.

[0034] As a typical but non-limiting example, the silane coupling agent in the embodiments of the present invention is methyltriethoxysilane.

[0035] As a typical but non-limiting example, the water reducing agent in the embodiments of the present invention is a polycarboxylate-based high-performance water reducing agent maleic anhydride copolymer.

[0036] As a typical but non-limiting example, the composite cellulose in the embodiments of the present invention is modified by mixing basalt fiber and polypropylene fiber in a mass ratio of 2:1.

[0037] The raw materials required in the embodiments of the present invention were all purchased.

[0038] Example 1 Preparation method of modified composite cellulose

[0039] Slowly add 10 parts of silane coupling agent into a water / alcohol (the volume ratio of water to alcohol is 9:1) solution. The adding speed should not be too fast to prevent the silane coupling agent molecules from causing condensation reaction due to contact. Add sulfuric acid solution (1 mol / L) to adjust the pH to 4, and heat the reaction (30°C, 30 min); then add 100 parts of composite cellulose, continue stirring the reaction (30°C, 10 min), filter, and dry (40°C, 20 min) to obtain modified composite cellulose.

[0040] Example 2 Preparation method of phase change material

[0041] 1) 120 parts of expanded perlite were immersed in a sulfuric acid solution with a concentration of 1 mol / L, subjected to ultrasonic treatment for 30 min, washed with deionized water until neutral, dried at 80° C., and calcined at 500° C. for 2 h to obtain modified expanded perlite;

[0042] 2) Methyl palmitate and methyl stearate were mixed in a mass ratio of 7:3, and the mixture was heated to 65° C. to melt. 90 parts of the molten mixture and 110 parts of the modified expanded perlite prepared in step 1) were mixed, and the mixture was stirred sufficiently to ensure that the molten mixture and the modified expanded perlite were mixed evenly, and vacuum impregnation was performed (maintaining a vacuum degree of -0.08 MPa for 2 hours) to obtain a loaded phase change material;

[0043] 3) 3.2 parts of silane coupling agent were slowly added to a water / alcohol (the volume ratio of water to alcohol was 9:1) solution, sulfuric acid solution (1 mol / L) was added to adjust the pH to 4, and stirred for reaction (30°C, 30 min); then 80 parts of nano-silicon dioxide were added, and the reaction was continued with stirring (30°C, 10 min), filtered, and dried (40°C, 20 min) to obtain modified nano-silicon dioxide;

[0044] 4) placing the loaded phase change material prepared in step 2) in an aqueous solution of polyvinyl alcohol and modified nano-silica (the concentration of polyvinyl alcohol is 8wt.%, the concentration of modified nano-silica is 4wt.%), stirring the reaction (room temperature, 20min), filtering, and drying (40°C, 20min) to obtain primary encapsulated particles; immersing the primary encapsulated particles in an ethanol solution of 5wt.% titanate coupling agent, stirring the reaction (40°C, 30min), and drying (60°C, 10min) to prepare a phase change material.

[0045] Example 3-5 A method for preparing freeze-thaw resistant concrete

[0046] Table 1

[0047]

[0048]

[0049] Note: In Example 3, the aggregate is composed of medium sand and graded crushed stone in a mass ratio of 15:20; in Examples 4 and 5, the aggregate is composed of medium sand and graded crushed stone in a mass ratio of 16:26; the particle size of the medium sand is 0.25 - 0.5 mm, and the particle size of the graded crushed stone is 10 - 30 mm.

[0050] The preparation method of the freeze-thaw resistant concrete in Examples 3 - 5 is as follows: Weigh each raw material according to Table 1. After mixing the aggregate and ordinary Portland cement evenly, add a water reducing agent and water, stir for 10 min, add a phase change material and composite cellulose, continue to stir for 15 min, pour into a mold, and cure the obtained concrete matrix for 20 d to obtain the freeze-thaw resistant concrete.

[0051] Comparative Example 1

[0052] Same as Example 3, except that the modified composite cellulose is replaced with composite cellulose in equal mass.

[0053] Performance test of rapid freeze-thaw test

[0054] According to GB / T50082 - 2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", the performance of the rapid freeze-thaw test was carried out on the concrete prepared in Examples 3 - 5 and Comparative Example 1, and the test results are shown in Table 2.

[0055] Table 2

[0056]

[0057]

[0058] It can be seen from Table 2 that the freeze-thaw resistant concrete prepared by using the phase change material provided by the present invention in combination with the modified composite cellulose can significantly improve the frost resistance of the concrete and the durability of the concrete after 300 freeze-thaw cycles indoors, can greatly improve the durability of the concrete in a high-frequency freeze-thaw environment, and realizes the freeze-thaw resistant use requirements of concrete in cold regions. In Comparative Example 1, replacing the modified composite fiber with composite fiber in equal mass reduces the bonding effect between the composite fiber and the compared material as well as the concrete matrix, thereby affecting the durability of the concrete in a freeze-thaw environment.

[0059] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An anti-freeze-thaw concrete, characterized in that, By mass parts, it includes the following raw materials: 35 - 40 parts of ordinary portland cement, 100 - 180 parts of aggregate, 0.5 - 0.8 part of water reducer, 4 - 6 parts of phase change material, 2 - 5 parts of modified composite cellulose, and 15 - 20 parts of water.

2. An anti-freeze-thaw concrete, characterized in that, By mass parts, it includes the following raw materials: 35 parts of ordinary portland cement, 150 parts of aggregate, 0.5 part of water reducer, 5 parts of phase change material, 3 parts of modified composite cellulose, and 18 parts of water.

3. The freeze-thaw resistant concrete according to claim 1, characterized in that, The aggregate is composed of medium sand and graded gravel according to the mass ratio of (15 - 16)∶(20 - 22).

4. The freeze-thaw resistant concrete according to claim 3, wherein The particle size of the medium sand is 0.25 - 0.5 mm; the particle size of the graded gravel is 10 - 30 mm.

5. The frost-resistant and thaw-resistant concrete according to claim 1, wherein The preparation method of the phase change material includes the following steps: Mix methyl palmitate and methyl stearate and heat to melt, and load the molten mixture onto modified expanded perlite by vacuum impregnation to obtain the loaded phase change material; Place the loaded phase change material in an aqueous solution of polyvinyl alcohol and modified nano - silica, stir, filter, and dry to obtain primary encapsulated particles; Immerse the primary encapsulated particles in an ethanol solution of titanate coupling agent and dry to prepare the phase change material.

6. The freeze-thaw resistant concrete according to claim 5, wherein, The mass ratio of methyl palmitate to methyl stearate is 7∶3.

7. The freeze-thaw resistant concrete according to claim 5, characterized in that, The mass ratio of the molten mixture to modified expanded perlite is 9∶11.

8. The freeze-thaw resistant concrete according to claim 5, characterized in that, In the aqueous solution of polyvinyl alcohol and modified nano - silica, the concentration of polyvinyl alcohol is 5 - 8 wt.%, and the concentration of modified nano - silica is 2 - 4 wt.%.

9. The freeze-thaw resistant concrete according to claim 1, characterized in that, The preparation method of the modified composite cellulose includes the following steps: Add a silane coupling agent to an aqueous ethanol solution, add sulfuric acid, adjust the pH to 3 - 5, heat and react, then add composite cellulose, stir and react, filter, and dry to obtain the modified composite cellulose.

10. A method for preparing the freeze-thaw resistant concrete according to any one of claims 1-9, characterized in that, It includes the following steps: Mix the aggregate and ordinary portland cement evenly, add the water reducer and water, stir, add the phase change material and composite cellulose, continue to stir, inject into a mold, and cure the obtained concrete matrix to obtain the freeze - thaw resistant concrete.

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