A fiber-reinforced modified concrete and its preparation method

Abstract

This invention relates to fiber-reinforced modified concrete and its preparation method, belonging to the field of concrete technology. The fiber-reinforced modified concrete contains modified steel fibers. The modified steel fibers are obtained by surface treatment of steel fibers with hydrolyzed polymaleic anhydride and a silane coupling agent as surface modifiers. The silane coupling agent contains alkyl chains with 4 to 8 carbon atoms. Based on existing concrete mix design systems, this invention introduces modified steel fibers obtained by treating with a specific surface modifier composed of hydrolyzed polymaleic anhydride and a silane coupling agent with a suitable carbon chain length. This not only significantly improves the mechanical properties of concrete but also enhances its resistance to freeze-thaw cycles, thereby meeting the stringent requirements for concrete strength and freeze-thaw resistance in special environmental conditions such as high-altitude and cold regions.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and in particular to a fiber-reinforced modified concrete and its preparation method. Background Technology

[0002] Concrete, as an important material widely used in infrastructure construction such as buildings, roads, and bridges, directly affects the safety and durability of engineering structures. With the continuous development of the construction industry and the increasing demands for engineering quality, traditional concrete has gradually revealed some performance deficiencies when facing certain special environmental conditions.

[0003] For example, in terms of mechanical properties, although traditional concrete possesses a certain strength, it is prone to cracking or even failure when subjected to large loads or complex stresses, making it difficult to meet the requirements of some engineering projects with high strength requirements, such as high-rise buildings, large bridges, and heavy-duty traffic roads. These engineering structures require concrete with higher compressive, tensile, and flexural mechanical properties to ensure their stability and safety during use.

[0004] Furthermore, resistance to freeze-thaw cycles is a significant issue for concrete in cold regions or environments with frequent temperature fluctuations. Under freeze-thaw cycles, the moisture inside the concrete expands and generates stress due to freezing, leading to microcracks within the concrete. With each freeze-thaw cycle, these microcracks gradually expand and connect, ultimately causing a significant reduction in the concrete's strength and durability, severely impacting the service life of the engineering structure. For example, in roads, bridges, and water conservancy projects in cold northern regions, concrete structures often require frequent repairs and reinforcement due to freeze-thaw damage, increasing project costs and affecting normal use.

[0005] To improve the performance of concrete, researchers have conducted extensive research and practice. Adding fibers is a commonly used method. The addition of fibers can form a three-dimensionally randomly distributed reinforcing system within the concrete, playing a role in crack prevention, toughening, and reinforcement. However, in traditional fiber-reinforced concrete, the interfacial bonding and compatibility between the fibers and the concrete matrix are often poor, resulting in less than ideal reinforcement effects from the fibers. Summary of the Invention

[0006] To address the above problems, this invention provides a fiber-reinforced modified concrete and its preparation method.

[0007] In a first aspect, the present invention provides a fiber-reinforced modified concrete, wherein the fiber-reinforced modified concrete contains modified steel fibers;

[0008] The modified steel fiber is obtained by surface treatment of steel fiber with hydrolyzed polymaleic anhydride and silane coupling agent as surface modifiers, wherein the silane coupling agent contains alkyl chains with 4 to 8 carbon atoms.

[0009] Furthermore, the mass percentage of hydrolyzed polymaleic anhydride in the surface modifier is 0.8% to 1.5%, for example, it can be 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.;

[0010] And / or, the mass percentage of the silane coupling agent in the surface modifier is 0.5% to 2%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc.;

[0011] And / or, the solvent in the surface modifier is composed of ethanol and water in a volume ratio of (6-10):1, for example, the solvent may be composed of ethanol and water in a ratio of 7.5:1;

[0012] And / or, the pH of the surface modifier is 4 to 5, for example, pH 5.5; in addition, the pH of the surface modifier can be adjusted to a preset value, for example, using a 0.1 mol / L sodium hydroxide solution and a 0.1 mol / L hydrochloric acid solution.

[0013] Furthermore, the silane coupling agent includes at least one of n-butyltrimethoxysilane, n-pentyltrimethoxysilane, n-hexyltrimethoxysilane, n-heptyltrimethoxysilane, and n-octyltrimethoxysilane.

[0014] Furthermore, the physicochemical properties of the steel fibers include: a length of 25–35 mm, such as 25 mm, 26 mm, 27 mm, 28 mm, 29 mm, 30 mm, 31 mm, 32 mm, 33 mm, 34 mm, 35 mm, etc.; a diameter of 0.4–0.8 mm, such as 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, etc.; and a density of 7–8 g / cm³. 3 For example, it could be 7.85 g / cm³. 3 .

[0015] Furthermore, the method for preparing the modified steel fiber includes:

[0016] The hydrolyzed polymaleic anhydride and the silane coupling agent were added to an alcohol-water solvent and stirred and mixed. The pH was then adjusted to obtain the surface modifier.

[0017] The steel fibers are added to the surface modifier and stirred and mixed, then allowed to stand, filtered and dried to obtain the modified steel fibers.

[0018] Furthermore, the volumetric content of the modified steel fiber is 0.8% to 1.2% of the total volume of the fiber-reinforced modified concrete, for example, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, etc.

[0019] Furthermore, the fiber-reinforced modified concrete also includes cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, and water.

[0020] Further, the weight ratio of the cement, the fine aggregate, the coarse aggregate, the fly ash, the water-reducing agent, and the water is (490-500):(540-560):(1050-1100):(50-60):(4-6):(160-180), for example, 490:540:1050:50:4:160 or 495:545: 1060:52:5:165, 500:550:1070:55:5.5:170, 492:555:1080:58:5:173, 492:555:1080:58:6:175, 498:560:1090:60:4.5:180, etc., with 492:555:1080:58:5:173 being the preferred choice.

[0021] Furthermore, the cement comprises 42.5 grade ordinary Portland cement;

[0022] And / or, the fine aggregate includes river sand with a fineness modulus of 2.5 to 3.0, for example, river sand with a fineness modulus of 2.8;

[0023] And / or, the coarse aggregate comprises crushed stone with a continuous gradation of 5 to 20 mm;

[0024] And / or, the fly ash includes Class II fly ash;

[0025] And / or, the water-reducing agent includes naphthalene-based water-reducing agents, such as FDN-2 type high-efficiency water-reducing agent.

[0026] Secondly, based on the same inventive concept, the present invention provides a method for preparing fiber-reinforced modified concrete according to any one of the first aspects, the method comprising the following steps:

[0027] Cement, fine aggregate and coarse aggregate are mixed evenly to obtain the first mixture;

[0028] Modified steel fibers and fly ash are added to the first mixture and mixed thoroughly to obtain the second mixture;

[0029] The water-reducing agent and water are added to the second mixture simultaneously and mixed evenly to obtain the fiber-reinforced modified concrete.

[0030] The technical solutions provided in the embodiments of the present invention have at least the following advantages compared with the prior art:

[0031] This invention provides a fiber-reinforced modified concrete and its preparation method. Based on the existing concrete mix design, this invention introduces modified steel fibers obtained by treating a specific surface modifier that is compounded with hydrolyzed polymaleic anhydride and a silane coupling agent with a suitable carbon chain length. This not only significantly improves the mechanical properties of the concrete but also enhances its resistance to freeze-thaw cycles, thereby meeting the stringent requirements for concrete strength and freeze-thaw resistance in special environmental conditions such as high-altitude and cold regions. Detailed Implementation

[0032] 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 will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention, such as hydrolyzed polymaleic anhydride (also known as HPMA, CAS No. 26099-09-2), cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, silane coupling agent, steel fiber, etc., can be purchased from the market or prepared by existing methods.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0035] The main raw material information involved in the embodiments and comparative examples of this invention is as follows:

[0036] Cement: Grade 42.5 ordinary Portland cement;

[0037] Fine aggregate: River sand with a fineness modulus of 2.8;

[0038] Coarse aggregate: 5-20mm continuously graded crushed stone;

[0039] Fly ash: Grade II fly ash;

[0040] Water-reducing agent: Naphthalene-based water-reducing agent, FDN-2 type high-efficiency water-reducing agent;

[0041] Steel fiber: 30mm in length, 0.5mm in diameter, and 7.85g / cm³. 3 .

[0042] Example 1

[0043] This example provides a fiber-reinforced modified concrete, which includes cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, and water. The weight ratio of the cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, and water is 492:555:1080:58:5:173. Modified steel fibers are also added to the fiber-reinforced modified concrete, and the volumetric content of the modified steel fibers is 1% of the total volume of the fiber-reinforced modified concrete.

[0044] The method for preparing the modified steel fiber includes the following steps:

[0045] Preparation of surface modifier: Hydrolyzed polymaleic anhydride and silane coupling agent (specifically n-hexyltrimethoxysilane) were added to a solvent consisting of ethanol and water in a volume ratio of 7.5:1 and stirred and mixed. The pH of the system was then adjusted to 4.2 to obtain a surface modifier containing 1 wt% hydrolyzed polymaleic anhydride and 1 wt% silane coupling agent.

[0046] Steel fiber surface treatment: steel fibers are added to the obtained surface modifier and stirred for 15 minutes. Then, the steel fibers are completely immersed in the surface modifier and left to stand for 1 hour. The steel fibers are filtered out and vacuum dried at 100°C for 20 minutes to obtain the modified steel fibers.

[0047] The preparation method of the above-mentioned fiber-reinforced modified concrete includes the following steps:

[0048] Cement, fine aggregate and coarse aggregate are mixed evenly to obtain the first mixture;

[0049] Modified steel fibers and fly ash are added to the first mixture and mixed thoroughly to obtain the second mixture;

[0050] The water-reducing agent and water are added to the second mixture simultaneously and mixed evenly to obtain the fiber-reinforced modified concrete.

[0051] Example 2

[0052] This example provides a fiber-reinforced modified concrete, which includes cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, and water. The weight ratio of the cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, and water is 490:540:1050:50:4:160. Modified steel fibers are also added to the fiber-reinforced modified concrete, and the volume fraction of the modified steel fibers is 0.8% of the total volume of the fiber-reinforced modified concrete.

[0053] The method for preparing the modified steel fiber includes the following steps:

[0054] Preparation of surface modifier: Hydrolyzed polymaleic anhydride and silane coupling agent (specifically n-butyltrimethoxysilane) are added to a solvent consisting of ethanol and water in a volume ratio of 6:1 and stirred and mixed. The pH of the system is then adjusted to 5 to obtain a surface modifier containing 0.8 wt% hydrolyzed polymaleic anhydride and 0.5 wt% silane coupling agent.

[0055] Steel fiber surface treatment: steel fibers are added to the obtained surface modifier and stirred for 15 minutes. Then, the steel fibers are completely immersed in the surface modifier and left to stand for 1 hour. The steel fibers are filtered out and vacuum dried at 100°C for 20 minutes to obtain the modified steel fibers.

[0056] The preparation method of the fiber-reinforced modified concrete is the same as that in Example 1.

[0057] Example 3

[0058] This example provides a fiber-reinforced modified concrete, which includes cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, and water. The weight ratio of the cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, and water is 500:560:1100:60:6:180. Modified steel fibers are also added to the fiber-reinforced modified concrete, and the volume fraction of the modified steel fibers is 1.2% of the total volume of the fiber-reinforced modified concrete.

[0059] The method for preparing the modified steel fiber includes the following steps:

[0060] Preparation of surface modifier: Hydrolyzed polymaleic anhydride and silane coupling agent (specifically n-octyltrimethoxysilane) are added to a solvent consisting of ethanol and water in a volume ratio of 10:1 and stirred and mixed. The pH of the system is then adjusted to 4 to obtain a surface modifier containing 1.5 wt% hydrolyzed polymaleic anhydride and 2 wt% silane coupling agent.

[0061] Steel fiber surface treatment: steel fibers are added to the obtained surface modifier and stirred for 15 minutes. Then, the steel fibers are completely immersed in the surface modifier and left to stand for 1 hour. The steel fibers are filtered out and vacuum dried at 100°C for 20 minutes to obtain the modified steel fibers.

[0062] The preparation method of the fiber-reinforced modified concrete is the same as that in Example 1.

[0063] Comparative Example 1

[0064] This example provides a concrete and its preparation method, which differs from Example 1 only in that: the surface modifier does not contain hydrolyzed polymaleic anhydride (i.e., the surface modifier contains only 1 wt% silane coupling agent); the remaining steps and parameters are the same.

[0065] Comparative Example 2

[0066] This example provides a concrete and its preparation method, which differs from Example 1 only in that: no silane coupling agent is added to the surface modifier (i.e., the surface modifier contains only 1 wt% hydrolyzed polymaleic anhydride); the remaining steps and parameters are the same.

[0067] Comparative Example 3

[0068] This example provides a fiber-reinforced modified concrete and its preparation method, which differs from Example 1 only in that the silane coupling agent is changed to n-decyltrimethoxysilane; the remaining steps and parameters are the same.

[0069] Test Example 1

[0070] In this example, mechanical property tests were conducted on the concrete obtained in Examples 1-3 and Comparative Examples 1-3 according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". Concrete without modified steel fibers (i.e., concrete prepared using the same proportions of cement, fine aggregate, coarse aggregate, fly ash, water-reducing agent, and water as in Example 1, prepared according to the same method) was used as a baseline control. After 28 days of standard curing, the 28-day compressive strength (MPa) test results are shown in Table 1. Simultaneously, using the concrete without modified steel fibers as a benchmark, the 28-day compressive strength growth rate (%) of the concrete obtained in Examples 1-3 and Comparative Examples 1-3 was calculated according to Formula 1: Compressive strength growth rate (%) = (F1-F2) / F2×100%, where F1 represents the 28-day compressive strength of any concrete in Examples 1-3 and Comparative Examples 1-3, and F2 represents the 28-day compressive strength of the concrete without modified steel fibers. The specific results are shown in Table 1.

[0071] Table 1

[0072]

[0073] Test Example 2

[0074] In this example, the concrete obtained in Examples 1-3 and Comparative Examples 1-3 were tested for freeze-thaw cycle performance using the rapid freezing method in GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". After 100 freeze-thaw cycle tests, the compressive strength retention rate (%) was calculated according to Formula 2: M1 / M2×100%, where M1 represents the compressive strength of the concrete after the freeze-thaw cycle test and M2 represents the compressive strength of the concrete before the freeze-thaw cycle test. The specific results are shown in Table 2.

[0075] Table 2

[0076] Test sample Compressive strength retention rate (%) Example 1 94.1 Example 2 90.9 Example 3 92.7 Comparative Example 1 80.6 Comparative Example 2 78.5 Comparative Example 3 83.2

[0077] As can be seen from the above examples and comparative test results, the present invention, by introducing modified steel fibers obtained by a specific surface modifier compounded with hydrolyzed polymaleic anhydride and a silane coupling agent with a suitable carbon chain length, not only significantly improves the mechanical properties of concrete, but also enhances the concrete's resistance to freeze-thaw cycles, thereby meeting the stringent requirements of special environmental conditions such as high-altitude and cold regions for concrete strength and freeze-thaw resistance.

[0078] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0079] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A fiber reinforced modified concrete, characterized in that, The fiber-reinforced modified concrete contains modified steel fibers; The modified steel fibers are obtained by surface treatment of steel fibers with a surface modifier containing hydrolyzed polymaleic anhydride and a silane coupling agent containing an alkyl chain with 4-8 carbon atoms; The preparation method of the modified steel fibers comprises: The hydrolyzed polymaleic anhydride and the silane coupling agent are added into an alcohol-water solvent for stirring and mixing, and then the pH is adjusted to obtain the surface modifier; The steel fibers are added into the surface modifier for stirring and mixing, and then standing, filtering and drying to obtain the modified steel fibers; The mass percentage of the hydrolyzed polymaleic anhydride in the surface modifier is 0.8-1.5%; The mass percentage of the silane coupling agent in the surface modifier is 0.5-2%; The volume fraction of the modified steel fibers is 0.8-1.2% of the total volume of the fiber-reinforced modified concrete.

2. The fiber reinforced modified concrete according to claim 1, characterized in that, The solvent in the surface modifier is composed of ethanol and water in a volume ratio of (6-10):1; And / or, the pH of the surface modifier is 4-5.

3. The fiber reinforced modified concrete according to claim 1, characterized in that, The silane coupling agent includes at least one of n-butyltrimethoxysilane, n-pentyltrimethoxysilane, n-hexyltrimethoxysilane, n-heptyltrimethoxysilane and n-octyltrimethoxysilane.

4. The fiber reinforced modified concrete according to claim 1, characterized in that, The physical and chemical property parameters of the steel fiber include: length of 25-35mm, diameter of 0.4-0.8mm, density of 7-8g / cm 3 .

5. The fiber reinforced modified concrete according to claim 1, characterized in that, The fiber-reinforced modified concrete further comprises cement, fine aggregate, coarse aggregate, fly ash, water reducing agent and water.

6. The fiber reinforced modified concrete according to claim 5, characterized in that, The weight ratio of the cement, the fine aggregate, the coarse aggregate, the fly ash, the water reducing agent and the water is (490-500):(540-560):(1050-1100):(50-60):(4-6):(160-180).

7. The fiber reinforced modified concrete according to claim 6, characterized in that, The cement includes 42.5-grade ordinary portland cement; And / or, the fine aggregate includes river sand with a fineness modulus of 2.5-3.0; And / or, the coarse aggregate includes continuous gradation gravel with a size of 5-20 mm; And / or, the fly ash includes II-grade fly ash; And / or, the water reducing agent includes a naphthalene-based water reducing agent.

8. A method of producing the fiber reinforced modified concrete according to any one of claims 5 to 7, characterized by, The preparation method of the fiber-reinforced modified concrete comprises the following steps: Mixing cement, fine aggregate and coarse aggregate to obtain a first mixture; Adding modified steel fibers and fly ash to the first mixture for mixing to obtain a second mixture; Adding water reducing agent and water to the second mixture simultaneously for mixing to obtain the fiber-reinforced modified concrete.

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