Polyformaldehyde fiber concrete based on stud area of steel box girder

Abstract

The invention relates to polyformaldehyde fiber concrete based on a stud area of a steel box girder, and belongs to the technical field of building materials. The polyformaldehyde fiber concrete comprises the following components in parts by weight: 400-550 parts of cement; 80 to 180 parts of water; 1000 to 1100 parts of coarse aggregate; 700 to 780 parts of fine aggregate; the surface of the calcium sulfate whisker is coated with a silane coupling agent. The polyformaldehyde fibers and the calcium sulfate whiskers are added into the concrete at the same time, the calcium sulfate whiskers are doped to provide a framework support for the concrete, after the calcium sulfate whiskers are wrapped by the cement paste, the calcium sulfate whiskers and other materials jointly form a three-dimensional supporting structure, and concrete pores can be filled with part of the whiskers, so that the compactness and compressive strength of the concrete are enhanced. The polyformaldehyde fibers are added, so that stress can be effectively dispersed, when the concrete is pressed, the polyformaldehyde fibers and a cement matrix bear loads together, the stress concentration phenomenon is reduced, and the compressive strength of the concrete is further improved.

Description

Technical Field

[0001] This invention belongs to the technical field of building materials, and more specifically, relates to a polyoxymethylene fiber concrete based on the studded area of ​​a steel box girder. Background Technology

[0002] Steel box girder bridges, as an important type of bridge structure, have advantages such as large span capacity and fast construction speed, and are widely used in modern bridge engineering.

[0003] Concrete is widely used in my country's infrastructure construction due to its advantages such as low price, easy molding, and large reserves. In the connection between steel box girders and concrete bridge decks, studs are key force transmission components. Studs connect the concrete bridge decks and steel box girders together to form a steel-concrete composite beam structure, which jointly bears external loads.

[0004] However, in the studded zone of the steel box girder, due to the stiffness difference and deformation incoordination between the studs and concrete, traditional concrete materials, due to their large self-weight, have disadvantages such as poor toughness, low tensile strength, and susceptibility to cracking, making it difficult to meet the performance requirements of the studded zone of the steel box girder. If cracks appear in the bridge deck structure, it will reduce the rigidity of the structure and the shear, tensile, and flexural strength of the concrete, leading to stress redistribution and water seepage in the concrete structure. This accelerates concrete neutralization, chemical erosion, freeze-thaw cycles, carbonation, steel corrosion, and alkali-aggregate reaction, deteriorating the concrete structure and causing continuous corrosion of the internal steel reinforcement, shortening the service life of the concrete structure and affecting the normal function of traffic facilities. Especially under long-term loads, these cracks may further develop, affecting the integrity and durability of the structure. In recent years, the requirements for special-performance concrete have been continuously increasing, and fiber adsorption has gradually been used as a technical means to improve or strengthen concrete performance. To address these issues, existing technologies disclose the use of steel fiber reinforced concrete or synthetic fiber reinforced concrete to improve the crack resistance and compressive strength of concrete. However, when these technologies are applied to the studded zone of steel box girders, the material adaptability under the complex stress environment of the studded zone has not been fully considered. Furthermore, existing steel fibers have poor dispersion in concrete and pose a risk of corrosion. Polypropylene fibers (POM) tend to form clusters in concrete and have certain limitations in terms of strength improvement and durability. Therefore, developing a polyoxymethylene fiber-reinforced concrete suitable for the studded areas of steel box girders has significant engineering and economic value. Summary of the Invention

[0005] The purpose of this invention is to provide a polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder, which can improve the dispersion performance of concrete to a certain extent, enhance the cohesiveness of the concrete mixture, and improve the compressive and flexural properties of concrete.

[0006] The objective of this invention can be achieved through the following technical solutions: A polyoxymethylene fiber-reinforced concrete based on the studded zone of a steel box girder, comprising the following components by weight: 400-550 parts cement; 80-180 parts water; 1000-1100 parts coarse aggregate; 700-780 parts fine aggregate; 3-8 parts of polyoxymethylene fiber; and 3-4 parts of calcium sulfate whiskers coated with silane coupling agent; Furthermore, the method for coating the surface of the calcium sulfate whiskers with silane coupling agent is as follows: add the calcium sulfate whiskers to an aqueous solution containing 1-10% polyethylene glycol, stir to form a suspension, then filter, dry, then immerse in silane hydrolysate, stir and let stand for 8-10 hours, wash and dry to obtain the product.

[0007] Calcium sulfate whiskers (CSW) are fibrous inorganic materials grown in single-crystal form. CSW forms a uniformly distributed fiber network in cement paste, effectively filling micropores and optimizing pore size distribution. Its surface properties facilitate the uniform dispersion of POM fibers in the concrete matrix, reducing agglomeration.

[0008] Furthermore, the concrete also includes 40-175 parts of mineral admixtures.

[0009] In a preferred embodiment of the present invention, the mineral admixture comprises fly ash. The fly ash is Class F, Grade II fly ash.

[0010] Preferably, the mineral admixture further includes mineral powder. The mineral powder is S95 grade mineral powder.

[0011] Preferably, the fly ash comprises 40-130 parts by weight, and the mineral powder comprises 0-45 parts by weight.

[0012] Furthermore, the concrete also includes 8.5-9.5 parts of a water-reducing agent.

[0013] In another preferred embodiment of the present invention, the water-reducing agent is a polycarboxylate-based water-reducing agent with a water reduction rate ≥25%, a solid content of 0.90-1.10%, an air content ≤6.0%, and a pH value ≤6.

[0014] Furthermore, the concrete also includes 30-35 parts of an expansion agent.

[0015] Furthermore, the concrete also includes 3-6 parts of other fiber materials, wherein the other fiber materials are at least one of steel fibers, basalt fibers or polypropylene fibers.

[0016] Basalt fiber is a new type of synthetic fiber material, which is prepared from basalt ore at a high temperature of 1500℃.

[0017] Furthermore, the water-cement ratio of the concrete components is 0.25-0.35; the cement-cement ratio is 280-350 m². 2 / kg.

[0018] In a preferred embodiment of the present invention, the coarse aggregate is crushed stone; the fine aggregate is river sand.

[0019] In a preferred embodiment of the present invention, the cement has a particle size of 5-10 mm.

[0020] Preferably, the particle size of the crushed stone is 5-20 mm, and the mass ratio of 5-10 mm crushed stone to 10-20 mm crushed stone is 1:2-3.

[0021] Furthermore, the particle size of the microencapsulated healing agent is 50-200 micrometers.

[0022] Furthermore, the polyoxymethylene fiber has a length of 10-65 mm, a diameter of 0.1-0.3 mm, and a tensile strength ≥700 MPa.

[0023] The concrete of this invention incorporates polyoxymethylene (POM) fibers. POM fibers possess high strength and high modulus, effectively improving the tensile and flexural strength of the concrete. Simultaneously, the POM fibers form a three-dimensional network structure within the concrete, effectively inhibiting the generation and development of microcracks and enhancing the concrete's toughness and crack resistance.

[0024] Furthermore, the polyoxymethylene fiber is pre-treated with a surface treatment method as follows: A. The surface of the polyoxymethylene fiber is activated by dielectric barrier discharge plasma; B. The plasma-treated polyoxymethylene fiber is immersed in a solution containing nano-SiO2 and reacted at 50-70℃ for 2-5 hours, followed by washing, drying, and collecting the product.

[0025] Furthermore, in step A above, the surface activation treatment power is 250-1000W, and the treatment time is 5-1200s.

[0026] A method for preparing polyoxymethylene fiber-reinforced concrete based on the studded zone of a steel box girder, as described above, includes the following steps: S1. Add all dry materials except polyoxymethylene fiber and calcium sulfate whiskers to a mixer and mix to form a dry material premix. S2. Then add polyoxymethylene fiber and calcium sulfate whiskers to the dry material premix and stir to disperse to form a dry material mixture; S3. Dissolve the water-reducing agent in water to obtain an aqueous solution. Then, add the aqueous solution to a mixer and stir to form a concrete mixture.

[0027] Furthermore, it also includes step S4, pouring the concrete mixture into the studded area of ​​the steel box girder, vibrating and shaping it to obtain polyoxymethylene fiber concrete.

[0028] As a preferred embodiment of the present invention, in steps S1 and S2, the stirring speed is 60-100 rpm and the time is 1-2 minutes; in step S3, the aqueous solution is added to the mixer, and first stirred at a speed of 60-100 rpm for 1-2 minutes, and then stirred at a speed of 150-200 rpm for 2-3 minutes.

[0029] The beneficial effects of this invention are: (1) The concrete of this invention incorporates both polyoxymethylene fibers and calcium sulfate whiskers. The incorporation of calcium sulfate whiskers provides a skeletal support for the concrete. After being encapsulated by cement paste, it forms a three-dimensional support structure together with other materials. Some whiskers can also fill the pores in the concrete, thereby enhancing the density and compressive strength of the concrete. The addition of polyoxymethylene fibers can effectively disperse stress. When the concrete is under pressure, it shares the load with the cement matrix, reducing stress concentration and further improving the compressive strength of the concrete. In terms of flexural strength, polyoxymethylene fibers, through their network structure and good adhesion to the cement matrix, can withstand a certain amount of tensile stress when the concrete is flexed, preventing the rapid propagation and penetration of cracks, thereby improving the flexural strength of the concrete. Calcium sulfate whiskers form a tiny reinforcing phase inside the concrete. When the concrete is subjected to bending stress, the whiskers can effectively transfer and disperse the stress, enhancing the concrete's resistance to deformation and thus improving its flexural strength. The synergistic effect of the two significantly improves the flexural performance of the concrete.

[0030] (2) The polyoxymethylene fiber reinforced concrete of the present invention is particularly suitable for the studded areas of steel box girders. Polyoxymethylene fibers can form a randomly distributed network reinforcement effect inside the concrete. When microcracks appear in the concrete, the fibers will cross the cracks and tightly bind them, preventing the further propagation of the cracks. Calcium sulfate whiskers, due to their high strength and high elastic modulus, can produce whisker pull-out, whisker fracture, crack bridging, and crack deflection at the microstructural level, thereby improving the crack resistance of the concrete. The synergistic effect of the two significantly enhances the crack resistance of the concrete. Attached Figure Description

[0031] Figure 1 This is a diagram showing the arrangement of shear studs and reinforcing bars in the shear stud zone of the steel box girder of this invention. Detailed Implementation

[0032] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific implementation methods, structures, features and effects of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0033] The performance parameters detected for the polyoxymethylene fiber, steel fiber, and basalt fiber used in the examples are as follows: Example 1 A polyoxymethylene fiber-reinforced concrete based on the studded zone of a steel box girder, comprising the following components by weight: The method for coating the surface of calcium sulfate whiskers with a silane coupling agent is as follows: The method for coating the surface of calcium sulfate whiskers with silane coupling agent is as follows: calcium sulfate whiskers are added to an aqueous solution containing 5% polyethylene glycol, stirred to form a suspension, then filtered, dried at 95°C, then immersed in silane hydrolysate, stirred for 2 hours and allowed to stand for 9 hours, then washed 3 times with ethanol, and then dried at 95°C to obtain the product.

[0034] The method for preparing concrete specimens is as follows: S1. Add cement, mineral powder, fly ash, crushed stone, natural river sand and expansion agent to the mixer and mix at 80 rpm for 1 minute; S2. Add polyoxymethylene fiber and calcium sulfate whiskers, and continue stirring at 80 rpm for 1 minute; S3. Dissolve the water-reducing agent and cement-based penetrating crystallizing waterproofing agent in water to obtain an aqueous solution. Then slowly add the aqueous solution to the mixer, with the total addition time not exceeding 2 minutes. Then stir at 80 rpm for 1 minute and then at 180 rpm for 3 minutes to obtain the concrete mixture.

[0035] Example 2 A polyoxymethylene fiber-reinforced concrete based on the studded zone of a steel box girder, comprising the following components by weight: The method for surface treatment of polyoxymethylene fibers is as follows: A. The surface activation treatment of polyoxymethylene fiber was carried out by dielectric barrier discharge plasma with a treatment power of 500W and a treatment time of 300s. B. The plasma-treated polyoxymethylene fiber is immersed in a solution containing nano-SiO2 and reacted at 60°C for 3 hours to graft nano-SiO2 particles onto the fiber surface; then it is washed and dried to obtain surface-treated polyoxymethylene fiber.

[0036] The method for preparing the concrete specimens is the same as in Example 1.

[0037] Example 3 A polyoxymethylene fiber-reinforced concrete based on the studded zone of a steel box girder, comprising the following components by weight: The method for surface-treating polyoxymethylene fibers is the same as in Example 2.

[0038] The concrete preparation method is the same as in Example 1, and the steel fibers in Example 3 are added in step S2.

[0039] Example 4 A polyoxymethylene fiber-reinforced concrete based on the studded zone of a steel box girder, comprising the following components by weight: The method for surface-treating polyoxymethylene fibers is the same as in Example 2.

[0040] The concrete preparation method is the same as in Example 1, and the basalt fiber in Example 4 is added in step S2.

[0041] Comparative Example 1 The difference between this comparative example and Example 1 is that 5 parts of polyoxymethylene fiber were replaced with 50 parts of steel fiber in this comparative example, while the remaining components, preparation steps, and parameters remained the same. The amount of steel fiber used was the optimal amount provided by the fiber manufacturer.

[0042] Comparative Example 2 The difference between this comparative example and Example 1 is that, in this comparative example, polyoxymethylene fiber is replaced with basalt fiber, while the other components, preparation steps, and parameters are the same. The basalt fiber content is the optimal content provided by the fiber manufacturer.

[0043] Comparative Example 3 The difference between this comparative example and Example 1 is that the amount of polyoxymethylene fiber added in this comparative example is 0, while the other components, preparation steps and parameters are the same.

[0044] Comparative Example 4 The difference between this comparative example and Example 1 is that the amount of calcium sulfate whiskers added in this comparative example is 0, while the other components, preparation steps and parameters are the same.

[0045] According to the test methods specified in the "Test Procedures for Cement and Cement Concrete in Highway Engineering" (JTG3420—2020), the specimens prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to the following performance tests: (1) First, the slump and spread of the concrete mixture specimens prepared above were tested to analyze their cohesiveness, water retention and fluidity. Then, the concrete mixture specimens were poured into molds, vibrated and shaped, and cured for 28 days at a temperature of 20±2℃ and a relative humidity of ≥95%. After curing, the compressive and flexural strength of the concrete specimens were tested.

[0046] The compressive strength specimen has dimensions of 150mm×150mm×150mm, and the flexural strength specimen has dimensions of 150mm×150mm×550mm.

[0047] The workability of fiber-reinforced concrete mixes refers to their ability to maintain uniform composition, resist segregation, and facilitate on-site construction. This primarily includes properties such as flowability, cohesiveness, and water retention. Cohesiveness ensures the concrete mix flows forward as a whole during pumping without stratification or segregation, resulting in uniform and consistent performance and smooth pumping without blockages. Water retention refers to the concrete mix's ability to retain water during construction, preventing significant bleeding. Flowability refers to the concrete mix's ability to overcome internal resistance and achieve plastic flow under its own weight or mechanical vibration, uniformly and densely filling the formwork.

[0048] The test results are shown in Tables 1 and 2.

[0049] Table 1 Table 2 As shown in Table 1 above, the slump results of the fiber-reinforced concrete in the examples and comparative examples are not significantly different, indicating that the limited-size concrete in both examples and comparative examples has good plasticizing and pumpability properties. However, the spread results of different fiber-reinforced concretes differ significantly. The concrete with added basalt fibers has relatively small spread, indicating that the concrete with basalt fibers has good cohesion, but requires a longer compaction time on-site and has less tolerance for on-site construction with dense reinforcement. In Comparative Example 1, because the steel fibers have hooked anchor tails at both ends and a triangular cross-section, they are prone to bending and breaking during mixing and vibration. Furthermore, the high density of the steel fibers during construction often causes them to sink to the bottom of the concrete during vibration and pouring, resulting in uneven distribution. Therefore, its fluidity, cohesion, and water retention are generally average. In contrast, the concrete with polyoxymethylene fibers has better spread, fluidity, and pumpability due to the lower specific gravity and water absorption of polyoxymethylene fibers.

[0050] As shown in Table 2 above, after 28 days of curing, the concrete obtained by combining polyoxymethylene fibers and calcium sulfate whiskers in Example 1 exhibits better compressive and flexural strength compared to other fibers or single polyoxymethylene fiber / calcium sulfate whiskers in Comparative Examples 1-4. Furthermore, both the composite fibers and the surface-modified polyoxymethylene fibers demonstrate superior compressive and flexural strength.

[0051] (2) Verification of the solid quality of polyoxymethylene fiber concrete in Example 1.

[0052] This test applied the polyoxymethylene fiber concrete from Example 1 to the studded area of ​​the steel box girder to verify its physical quality.

[0053] The arrangement of shear studs and reinforcing bars in the shear stud zone of the steel box girder is as follows: Figure 1 As shown, the spacing between the studs is 100mm, and the spacing between the reinforcing mesh is 100mm.

[0054] The polyoxymethylene fiber concrete was paved across the entire cross-section using an ultrasonic paver. The elevation and thickness were controlled using a line-marking method, with 10cm paving lines marked on the curb stones on both sides. Simultaneously, a pin-insertion method was used for process control to ensure a basic 10cm thickness of the fiber concrete. The paving speed was controlled at 1m / min, with three passes forward and backward. Vibratory compaction was used in localized areas to ensure the density of the fiber concrete. After 28 days of on-site curing, core samples were taken from the finished fiber concrete for compressive strength verification. Before core sampling, a rebar cover thickness gauge was used to locate and avoid the rebar, ensuring smooth core sampling.

[0055] The solid core sample has a size of 100mm×200mm and the concrete strength grade is less than C60. The compressive strength should be corrected according to the corresponding size conversion factor.

[0056] The experimental results are shown in Table 3.

[0057] Table 3 As shown in Table 3, the average 28-day compressive strength of the polyoxymethylene fiber concrete specimen was 58.68 MPa, which is higher than that of the indoor molded specimens, indicating better actual performance. This suggests that the polyoxymethylene fiber concrete mixed at the cement concrete mixing plant has good uniformity, with no uneven fiber distribution, and no obvious segregation occurred during on-site vibration. This demonstrates that the polyoxymethylene fiber concrete of this invention has more significant advantages.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder, characterized in that, The following components are included by weight: 400-550 parts cement; 80-180 parts water; 1000-1100 parts coarse aggregate; 700-780 parts fine aggregate; 3-8 parts of polyoxymethylene fiber; and 3-4 parts of calcium sulfate whiskers coated with silane coupling agent.

2. The polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder according to claim 1, characterized in that, The concrete also includes 40-175 parts of mineral admixtures; And / or may also include 8.5-9.5 parts of water-reducing agent; And / or may also include 30-35 parts of a swelling agent; And / or may also include 3-6 parts of other fibrous materials.

3. The polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder according to claim 2, characterized in that, The mineral admixture includes fly ash; The water-reducing agent is a polycarboxylate-based water-reducing agent with a water reduction rate ≥25%, a solid content of 0.90-1.10%, an air content ≤6.0%, and a pH value ≤6. The other fiber material is at least one of steel fiber, basalt fiber or polypropylene fiber.

4. The polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder according to claim 1, characterized in that, The water-cement ratio of the concrete components is 0.25-0.35; the cement-cement ratio is 280-350 m². 2 / kg.

5. The polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder according to claim 1, characterized in that, The coarse aggregate is crushed stone; the fine aggregate is river sand.

6. The polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder according to claim 5, characterized in that, The particle size of the crushed stone is 5-20mm, and the mass ratio of 5-10mm crushed stone to 10-20mm crushed stone is 1:2-3.

7. The polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder according to claim 1, characterized in that, The calcium sulfate whiskers have a diameter of 0.1–4 μm, an aspect ratio > 20, and an elastic modulus > 70 GPa; the polyoxymethylene fibers have a length of 10–65 mm, a diameter of 0.1–0.3 mm, and a tensile strength ≥ 700 MPa.

8. The polyoxymethylene fiber reinforced concrete based on the studded zone of a steel box girder according to claim 1, characterized in that, The polyoxymethylene fiber was pre-treated with the following methods: A) using dielectric barrier discharge plasma to activate the surface of the polyoxymethylene fiber; B) immersing the plasma-treated polyoxymethylene fiber in a solution containing nano-SiO2 and reacting it at 50-70℃ for 2-5 hours, followed by washing, drying, and collecting the product. The method for coating the surface of calcium sulfate whiskers with silane coupling agent is as follows: add calcium sulfate whiskers to an aqueous solution containing 1-10% polyethylene glycol, stir to form a suspension, then filter, dry, then immerse in silane hydrolysate, stir and let stand for 8-10 hours, wash and dry to obtain the product.

9. A method for preparing polyoxymethylene fiber-reinforced concrete based on the studded zone of a steel box girder as described in any one of claims 1-8, characterized in that, The preparation method includes the following steps: S1. Add all dry materials except polyoxymethylene fiber and calcium sulfate whiskers to a mixer and mix to form a dry material premix. S2. Then add polyoxymethylene fiber and calcium sulfate whiskers to the dry material premix and stir to disperse to form a dry material mixture; S3. Dissolve the water-reducing agent in water to obtain an aqueous solution. Then, add the aqueous solution to a mixer and stir to form a concrete mixture.

10. The preparation method according to claim 9, characterized in that, It also includes step S4, pouring the concrete mixture into the stud area of ​​the steel box girder, vibrating and shaping it to obtain polyoxymethylene fiber concrete.

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