Preparation method of POM fiber reinforced and toughened high-performance concrete

Abstract

The application discloses a preparation method of POM fiber reinforced and toughened high-performance concrete, and belongs to the technical field of concrete materials, which comprises the steps of raw material pretreatment, mixed dry material preparation, cement paste preparation, mortar preparation, concrete paste preparation, molding and curing and the like. In the application, a magnetic moment is applied to the fiber modified by nano-Fe3O4 by a low-frequency rotating magnetic field, micro-amplitude vibration and rotation are generated, van der Waals force can be effectively overcome, fiber groups are dispersed, uneven distribution caused by gravity or centrifugal force is avoided, three-dimensional uniform distribution is promoted, through deep coupling of three core technologies of 'honeycomb interface strengthening','magnetic field uniform dispersion' and'matrix shrinkage regulation and control', mutual multi-core synergistic effects are generated, and a new generation of fiber reinforced concrete which simultaneously meets ultrahigh strength, ultrahigh toughness, high durability and good construction performance is prepared.

Description

Technical Field

[0001] This invention relates to the field of concrete materials technology, and in particular to a method for preparing POM fiber-reinforced and toughened high-performance concrete. Background Technology

[0002] High-performance concrete (HPC) is widely used in important engineering structures due to its high strength and durability, but its inherent brittleness limits its application in earthquake-resistant and impact-resistant structures. Fiber reinforcement is an effective means to improve the toughness of concrete. Currently used steel fibers, PVA fibers, and PP fibers each have their shortcomings, such as steel fibers being prone to corrosion and having high costs, and PVA fibers having poor dispersibility.

[0003] Polyoxymethylene (POM) fiber, as a high-performance engineering plastic fiber, possesses high strength, high modulus, and resistance to chemical corrosion, theoretically making it an ideal concrete reinforcement material. However, directly using ordinary POM fiber in concrete presents the following problems:

[0004] 1. Insufficient interfacial bond strength: The smooth fiber surface has limited mechanical interlocking force with the cement matrix, making the fibers easy to pull out and failing to fully utilize their high strength advantage;

[0005] 2. Fibers are prone to agglomeration: Especially at higher dosages, fibers are prone to entanglement and clumping during mixing, affecting the homogeneity and workability of concrete and creating weak points;

[0006] 3. Poor synergistic effect between matrix and fiber: The matrix formulation was not optimized for the characteristics of POM fiber, and the synergistic performance improvement was not achieved.

[0007] Therefore, developing a type of concrete and its preparation method that can fundamentally solve the problems of bonding and dispersion at the interface between POM fibers and concrete, and achieve high-performance synergy between the matrix and fibers, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to solve the problems existing in the prior art and to propose a method for preparing POM fiber reinforced and toughened high-performance concrete.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing POM fiber-reinforced and toughened high-performance concrete, the method comprising the following steps:

[0011] S1. Raw material pretreatment: The manufactured sand is screened, washed, and dried at 75℃ until the moisture content is ≤0.5%; the POM fiber is surface modified.

[0012] S2. Preparation of mixed dry material: Put silicate cement, silica fume, metakaolin, and limestone powder into a forced mixer and dry mix at a speed of 300 r / min for 1.5-2 min to obtain mixed dry material;

[0013] S3. Preparation of gelling paste: After mixing polycarboxylate superplasticizer with water at 10-15℃, add it to the mixed dry material and stir at 400r / min for 3-4min to form gelling paste.

[0014] S4. Mortar preparation: Add manufactured sand to the cementitious mortar in three portions, with a 1-minute interval between each portion, and stir at a speed of 400 r / min for 4 minutes to form a uniform mortar.

[0015] S5. Concrete paste preparation: Preheat the mortar obtained in step S4 to 35-40℃, then slowly add the modified POM fiber while stirring at a speed of 350r / min, and apply a low-frequency rotating magnetic field with a frequency of 5Hz and a magnetic field strength of 300Gauss. Continue stirring for 5-6 minutes to obtain concrete paste.

[0016] S6. Molding and curing: Inject the concrete slurry into the mold, vibrate and compact it, cover it with a film, and let it stand for 48 hours at 20±2℃ and relative humidity ≥95% before demolding; place the specimen in a steam curing chamber at 85±3℃ for 3 days, and then transfer it to a standard curing room for curing until the specified age.

[0017] The raw materials in S1 include the following preparation ingredients by mass fraction:

[0018] The ingredients are: 530-550 parts silicate cement, 160-165 parts silica fume, 50-55 parts metakaolin, 320-330 parts limestone powder, 1075-1085 parts manufactured sand, 16-17 parts polycarboxylate superplasticizer, 170-175 parts water, and POM fiber, with a volume fraction of 2.5%-3%.

[0019] As a preferred embodiment, the surface of the POM fiber has a honeycomb porous structure, and the POM fiber is composed of short fibers with a length of 8 mm and long fibers with a length of 12 mm mixed in a mass ratio of 1:1.

[0020] As a preferred embodiment, the pore size of the honeycomb porous structure ranges from 5 to 50 micrometers.

[0021] As a preferred embodiment, the surface of the POM fiber undergoes a surface modification treatment, which includes the following steps:

[0022] D1. Pretreatment of POM fibers using air plasma;

[0023] D2. The pretreated fibers are impregnated and grafted using a solution of KH-550 and KH-560 silane coupling agents in a mass ratio of 1:1 to 1:3.

[0024] As a preferred embodiment, the silane coupling agent solution in step D2 is further provided with dispersed nano-silica particles, the nano-silica particles having a particle size of 10-30 nm and a mass of 5%-15% of the total mass of the silane coupling agent.

[0025] As a preferred embodiment, the preparation ingredients further include an internal curing component and a swelling agent;

[0026] The internal curing component is pre-saturated superabsorbent resin microspheres, and its dosage is 0.3% of the total mass of the cementitious material;

[0027] The expanding agent is a calcium sulfoaluminate expanding agent, and its dosage is 2% of the total mass of the cementitious material.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. This invention achieves a multi-core synergistic effect through the deep coupling of three core technologies: "cellular interface strengthening", "uniform magnetic field dispersion" and "matrix shrinkage regulation". Ultimately, it successfully prepares a new generation of fiber-reinforced concrete that simultaneously meets the requirements of ultra-high strength, ultra-high toughness, high durability and good workability. It is suitable for major infrastructure fields such as super high-rise buildings, long-span bridges and nuclear power projects with stringent performance requirements.

[0030] 2. This invention provides macroscopic mechanical locking through the "honeycomb porous structure" of POM fibers, which, together with the microscopic chemical bonding and roughness improvement formed by the surface modification of "plasma, silane coupling agent and nanoparticles", jointly construct a "physical-chemical" dual-reinforcement interface. Subsequent observation showed that the cement hydration products were deeply embedded in the honeycomb pores on the fiber surface, the interface transition zone was dense and crack-free, and the fiber pull-out test showed that the interface bonding strength was improved by more than 100%.

[0031] 3. This invention applies a magnetic torque to fibers modified with nano-Fe3O4 using a low-frequency rotating magnetic field, generating micro-amplitude vibration and rotation. This effectively overcomes van der Waals forces, breaks up fiber clumps, and the magnetic field force drives the fibers to move in three-dimensional space within the mortar. This avoids uneven distribution caused by gravity or centrifugal force, promoting uniform three-dimensional distribution. Compared to simply increasing mechanical shear force, the magnetization dispersion method is gentler, reducing scratches on the fiber surface and breakage caused by entanglement, thus maintaining the integrity of the fibers. Attached Figure Description

[0032] Figure 1 This is a flowchart of a method for preparing POM fiber-reinforced and toughened high-performance concrete according to the present invention;

[0033] Figure 2 The contact angle of the polyoxymethylene (POM) fiber in this invention;

[0034] Figure 3 This is a flow comparison diagram of different specimens in this invention;

[0035] Figure 4 This is a comparison chart of the compressive strength of different specimens in this invention;

[0036] Figure 5 This is a comparison diagram of the flexural strength of different specimens in this invention;

[0037] Figure 6 This is a particle size distribution diagram of the cementitious material in different specimens of this invention. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] Example, refer to Figures 1 to 6 A method for preparing POM fiber-reinforced and toughened high-performance concrete, wherein the raw materials include the following preparation ingredients in the indicated mass fractions:

[0040] The ingredients are: 530-550 parts silicate cement, 160-165 parts silica fume, 50-55 parts metakaolin, 320-330 parts limestone powder, 1075-1085 parts manufactured sand, 16-17 parts polycarboxylate superplasticizer, 170-175 parts water, and POM fiber, with a volume fraction of 2.5%-3%.

[0041] The surface of POM fiber has a honeycomb porous structure, and POM fiber is composed of short fibers with a length of 8 mm and long fibers with a length of 12 mm mixed in a mass ratio of 1:1.

[0042] The pore size of the honeycomb porous structure ranges from 5 to 50 micrometers.

[0043] like Figure 1 As shown, the preparation method of the present invention mainly includes the following steps:

[0044] Before preparation, a co-precipitation method or impregnation method is used to prepare the nanoparticles. Particles are loaded onto the surface of POM fibers;

[0045] Raw material pretreatment: The manufactured sand is screened, washed, and dried at 75℃ until the moisture content is ≤0.5%; the POM fiber is surface modified.

[0046] Preparation of mixed dry material: Put silicate cement, silica fume, metakaolin and limestone powder into a forced mixer and dry mix at 300 r / min for 1.5-2 min to obtain mixed dry material;

[0047] Preparation of gelling paste: After mixing polycarboxylate superplasticizer with water at 10-15℃, add it to the mixed dry materials and stir at 400r / min for 3-4min to form gelling paste;

[0048] Mortar preparation: Add manufactured sand to the cementitious cement paste in 3 portions, with an interval of 1 minute between each addition, and stir at a speed of 400 r / min for 4 minutes to form a uniform mortar;

[0049] Concrete paste preparation: Preheat the mortar obtained in step S4 to 35-40℃, then slowly add the modified POM fiber while stirring at a speed of 350r / min, and apply a low-frequency rotating magnetic field with a frequency of 5Hz and a magnetic field strength of 300Gauss. Continue stirring for 5-6 minutes to obtain concrete paste.

[0050] Molding and curing: The concrete slurry was injected into the mold, vibrated to compact it, covered with a film, and left to stand for 48 hours at 20±2℃ and relative humidity ≥95% before demolding; the specimens were placed in a steam curing chamber at 85±3℃ for 3 days, and then transferred to a standard curing room for curing until the specified age.

[0051] Applying a low-frequency rotating magnetic field during the fiber incorporation stage, its core mechanism is based on the superparamagnetic nano-iron oxide (Fe3O4) POM fibers are magnetized and dispersed using the effect of magnetization.

[0052] Its advantages include breaking up agglomerations: fibers tend to agglomerate due to van der Waals forces during stirring. The rotating magnetic field applies a continuously changing magnetic torque to the magnetic fibers, causing them to vibrate and rotate slightly, thus effectively overcoming van der Waals forces and breaking up the formed fiber clumps.

[0053] Promotes uniform spatial distribution: The rotating magnetic field drives the fibers to move in three-dimensional space, avoiding the concentration of fibers in a certain area due to gravity or centrifugal force, and ensuring their uniform three-dimensional distribution in the mortar matrix.

[0054] Reduce fiber damage: Compared to simply increasing mechanical shear force to disperse fibers, magnetization dispersion is a gentler "soft dispersion" method that can significantly reduce the scratches on the fiber surface caused by high-speed stirring and the fiber breakage caused by entanglement, thus maintaining the integrity and mechanical properties of the fibers.

[0055] Implementation method:

[0056] A low-frequency rotating magnetic field can be achieved by symmetrically arranging one or more pairs of permanent magnets or electromagnets outside a non-magnetic stirring drum (such as a stainless steel drum). This magnet assembly is driven by an independent servo motor and can rotate at a low speed around the axis of the stirring drum. The control system can adjust the rotation frequency and intensity of the magnetic field, preferably 100-500 Gauss. During stirring, the rotation of the external magnetic field is coupled with the shearing action of the internal stirring blades, jointly achieving efficient and gentle dispersion of the magnetic fibers.

[0057] The surface of the POM fiber was modified, which significantly reduced the contact angle of the POM fiber (see [reference]). Figure 2 This indicates that the hydrophilicity of the fiber surface has been effectively improved; the surface modification treatment includes the following steps:

[0058] D1. Plasma pretreatment: POM fibers are treated for 60-180 seconds in a radio frequency plasma device with a power of 200-500W and a frequency of 13.56MHz, using air or oxygen as the treatment gas and a pressure of 10-50Pa.

[0059] D2. Silane Coupling Agent Grafting: POM fibers pretreated by plasma are immersed in an aqueous solution of 1-3 wt% silane coupling agent in ethanol, where the ratio of ethanol to water is 9:1, and the silane coupling agent is a mixture of KH-550 and KH-560 in a mass ratio of 1:1 to 1:3. The pH of the solution is adjusted to 4-5 with acetic acid, and the immersion time is 20-40 minutes. The fibers are then removed and dried at 80°C for 2 hours.

[0060] In the silane coupling agent solution in step D2, dispersed nano-silica particles are also provided. The particle size of the nano-silica particles is 10-30 nm, and their mass is 5%-15% of the total mass of the silane coupling agent.

[0061] The preparation ingredients also include an internal curing component and an expanding agent; the internal curing component is pre-saturated superabsorbent resin microspheres, and its dosage is 0.3% of the total mass of the cementitious material; the expanding agent is a calcium sulfoaluminate expanding agent, and its dosage is 2% of the total mass of the cementitious material.

[0062] It should be noted that in this invention, the total mass of cementitious materials refers to the sum of the masses of silicate cement, silica fume, and metakaolin.

[0063] The specific operation of the preparation method of the present invention is as follows:

[0064] Raw material pretreatment: The manufactured sand is screened, washed, and the mud and sand content is reduced. It is then dried in a 75℃ oven until the moisture content is ≤0.5%. Particles with a diameter >0.15mm and <4.75mm are removed by screening to ensure continuous gradation.

[0065] Preparation of mixed dry material: Put silicate cement, silica fume, metakaolin, and limestone powder into a forced concrete mixer and dry mix at a speed of 300 r / min for 1.5-2 minutes until the material is uniform in color to obtain mixed dry material.

[0066] Preparation of gelling paste: Mix polycarboxylate superplasticizer with water and stir for 30 seconds to prepare a superplasticizer aqueous solution; slowly add the superplasticizer aqueous solution to the mixed dry materials, adjust the mixer speed to 400 r / min, stir for 3-4 minutes to form a uniform gelling paste.

[0067] Mortar preparation: Add manufactured sand to the cementitious mortar in three batches (1 minute apart each time), and stir at 400 r / min for 4 minutes until the mixture changes from the mortar state to a uniform mortar with no obvious particle agglomeration.

[0068] Concrete slurry preparation: Modified 8mm and 12mm POM fibers (mass ratio 1:1) are slowly added to the mortar. One or more pairs of permanent magnets or electromagnets are symmetrically arranged outside a non-magnetic mixing drum (such as a stainless steel drum). The mixer speed is adjusted to 350r / min. The fibers are added while stirring, and the stirring is continued for 5-6 minutes. During stirring, the rotation of the external magnetic field and the shearing action of the internal mixing blades are coupled to achieve efficient and gentle dispersion of the magnetic fibers, thus obtaining concrete slurry.

[0069] Molding and curing: Pour the concrete slurry into a 40mm×40mm×160mm mold and vibrate it for 20-30 seconds using a high-frequency vibrator (50Hz) until no air bubbles overflow from the surface. After vibration, cover the mold with plastic film and let it stand in a standard environment (temperature 20±2℃, relative humidity ≥95%) for 48 hours before demolding. Place the demolded specimens in an 85±3℃ steam curing chamber for 3 days, and then transfer them to a standard curing room for curing to the specified age to obtain high-toughness POM fiber-reinforced high-performance concrete.

[0070] The specific experimental data are as follows:

[0071] 1. Experimental Group 1: Raw material ratio (parts by mass):

[0072] 540 parts silicate cement, 162 parts silica fume, 54 parts metakaolin, 324 parts limestone powder, 1079 parts manufactured sand, 17.26 parts polycarboxylate superplasticizer, 1.5% volume fraction of 8mm POM fiber, 1.5% volume fraction of 12mm POM fiber, and 172.6 parts water.

[0073] Preparation steps:

[0074] Dry mix: Cement, silica fume, metakaolin, and limestone powder are dry mixed at 300 rpm for 2 minutes;

[0075] Cemented cement paste: After mixing the water-reducing agent with water, add the dry material and stir at 400 r / min for 4 min;

[0076] Mortar: Add manufactured sand in 3 batches, mixing for 1 minute each time, for a total mixing time of 4 minutes;

[0077] Concrete grout: POM fibers are added slowly, and the mixture is stirred at 350 rpm for 6 minutes;

[0078] Curing: After vibration molding, allow to stand for 48 hours before demolding, steam at 85℃ for 3 days, and then cure according to standard for 28 days.

[0079] Performance test results:

[0080] Compressive strength: 107.05 MPa; flexural strength: 16.76 MPa; fiber dispersion: 88.16%.

[0081] 2. Experimental Group Two: High-Toughness POM Fiber Reinforced Concrete with MC Matrix

[0082] Raw material ratio (parts by mass):

[0083] 539.5 parts silicate cement, 53.9 parts silica fume, 269.7 parts metakaolin, 431.6 parts limestone powder, 1079 parts manufactured sand, 15.1 parts polycarboxylate superplasticizer, 1.5% volume fraction of 8mm POM fiber, 1.5% volume fraction of 12mm POM fiber, and 220 parts water.

[0084] Preparation steps:

[0085] Same as experimental group 1;

[0086] Performance test results:

[0087] Compressive strength: 90.19 MPa; flexural strength: 25.52 MPa; fiber dispersion: 82.45%.

[0088] 3. Experimental Group 3: High-toughness POM fiber reinforced concrete with LC matrix;

[0089] Raw material ratio (parts by mass):

[0090] 377 parts silicate cement, 54 parts silica fume, 269 parts metakaolin, 432 parts limestone powder, 1079 parts manufactured sand, 15.08 parts polycarboxylate superplasticizer, 1.5% volume fraction of 8mm POM fiber, 1.5% volume fraction of 12mm POM fiber, and 220 parts water.

[0091] Preparation steps:

[0092] Same as experimental group 1;

[0093] Performance test results:

[0094] Compressive strength: 72.15 MPa; 28-day flexural strength: 24.18 MPa; fiber dispersion: 79.82%.

[0095] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing POM fiber-reinforced and toughened high-performance concrete, characterized in that, The preparation method includes the following steps: S1. Raw material pretreatment: The manufactured sand is screened, washed, and dried at 75℃ until the moisture content is ≤0.5%; the POM fiber is surface modified. S2. Preparation of mixed dry material: Put silicate cement, silica fume, metakaolin, and limestone powder into a forced mixer and dry mix at a speed of 300 r / min for 1.5-2 min to obtain mixed dry material; S3. Preparation of gelling paste: After mixing polycarboxylate superplasticizer with water at 10-15℃, add it to the mixed dry material and stir at 400r / min for 3-4min to form gelling paste. S4. Mortar preparation: Add manufactured sand to the cementitious mortar in three portions, with a 1-minute interval between each portion, and stir at a speed of 400 r / min for 4 minutes to form a uniform mortar. S5. Concrete paste preparation: Preheat the mortar obtained in step S4 to 35-40℃, then slowly add the modified POM fiber while stirring at a speed of 350r / min, and apply a low-frequency rotating magnetic field with a frequency of 5Hz and a magnetic field strength of 300Gauss. Continue stirring for 5-6 minutes to obtain concrete paste. S6. Molding and curing: Inject the concrete slurry into the mold, vibrate and compact it, cover it with a film, and let it stand for 48 hours at 20±2℃ and relative humidity ≥95% before demolding; place the specimen in a steam curing chamber at 85±3℃ for 3 days, and then transfer it to a standard curing room for curing until the specified age. The raw materials in S1 include the following preparation ingredients by mass fraction: The ingredients are: 530-550 parts silicate cement, 160-165 parts silica fume, 50-55 parts metakaolin, 320-330 parts limestone powder, 1075-1085 parts manufactured sand, 16-17 parts polycarboxylate superplasticizer, 170-175 parts water, and POM fiber, with a volume fraction of 2.5-3%.

2. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 1, characterized in that, The surface of the POM fiber has a honeycomb porous structure.

3. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 1, characterized in that, The POM fiber is composed of short fibers with a length of 8 mm and long fibers with a length of 12 mm mixed in a mass ratio of 1:

1.

4. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 2, characterized in that, The pore size of the honeycomb porous structure ranges from 5 to 50 micrometers.

5. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 1, characterized in that, The surface of the POM fiber undergoes a surface modification treatment, which includes the following steps: D1. Pretreatment of POM fibers using air plasma; D2. The pretreated fibers are impregnated and grafted using a solution of KH-550 and KH-560 silane coupling agents in a mass ratio of 1:1 to 1:

3.

6. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 5, characterized in that, In the silane coupling agent solution of step D2, dispersed nano-silica particles are also provided.

7. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 6, characterized in that, The particle size of the nano-silica particles is 10-30 nm.

8. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 6, characterized in that, The mass of the nano-silica particles is 5%-15% of the total mass of the silane coupling agent.

9. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 1, characterized in that, The preparation ingredients also include internal curing components and expanding agents.

10. The method for preparing POM fiber-reinforced and toughened high-performance concrete according to claim 9, characterized in that, The internal curing component is pre-saturated superabsorbent resin microspheres, and its dosage is 0.3% of the total mass of the cementitious material; The expanding agent is a calcium sulfoaluminate expanding agent, and its dosage is 2% of the total mass of the cementitious material.

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