High-strength gravel concrete and preparation method thereof

Abstract

The invention discloses high-strength gravel concrete and a preparation method thereof, and belongs to the technical field of concrete. Comprising the following components in parts by mass: 300 to 420 parts of cement, 60 to 120 parts of a mineral admixture, 850 to 1050 parts of modified gravel aggregate, 580 to 680 parts of machine-made sand, 130 to 165 parts of water, 0.8 to 12 parts of an additive, 0.5 to 3.0 parts of a graphene-carbon nanotube composite emulsion, 1.0 to 3.0 parts of a self-healing microcapsule, 0.1 to 0.5 part of dispersible nano silicon particles and 3 to 10 parts of an expanding agent. According to the invention, by introducing the active nano silicon particles, the self-healing microcapsules and the modified gravel aggregate, a multi-scale synergistic enhancement structure is constructed, and the problems of microcrack initiation and propagation and limited strength improvement in traditional concrete are solved: the modified gravel is subjected to silane coupling and inorganic composite coating treatment, so that the modified gravel has higher interface bonding strength; the bonding performance of the coarse aggregate and the cement paste is improved; the nano silicon particles fill pores and participate in a secondary hydration reaction, so that the density and early strength of the slurry are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and more specifically, to a high-strength gravel concrete and a preparation method thereof. Background Art

[0002] As one of the most widely used building materials in civil engineering, concrete plays a key supporting role in structures such as bridges, high-rise buildings, roads, and tunnels due to its good workability and economy. Traditional ordinary gravel concrete forms a skeleton structure through the hydration reaction of cement and aggregates, and its physical and mechanical properties can meet the requirements of general loads. However, under high strength, high durability, and special environments (such as freeze-thaw cycles, chloride ion erosion, and high carbonation environments), there are still the following main technical bottlenecks: There are usually microscopic pores and microcracks in the interfacial transition zone (ITZ) between ordinary natural gravel and cement-based paste, which become the "weak links" of stress concentration and crack propagation. Under the action of long-term loads and environmental erosion, microcracks in the ITZ continuously initiate, expand, and connect, resulting in a decrease in the overall compressive, flexural, and impermeability properties of the concrete. Although existing high-performance concretes can improve strength and toughness through technologies such as adding mineral admixtures or fiber reinforcement, they lack an internal repair mechanism for the microcracks and defects that have already occurred. Once concrete cracks form, it is often necessary to take artificial grouting or external maintenance, which increases the maintenance cost and construction difficulty and is difficult to achieve the long-term self-adaptive maintenance of the structure. Summary of the Invention

[0003] The purpose of the present invention is to provide a high-strength gravel concrete and a preparation method thereof to solve the problems raised in the above background art.

[0004] A high-strength gravel concrete, comprising the following components by mass: 300 - 420 parts of cement, 60 - 120 parts of mineral admixture, 850 - 1050 parts of modified gravel aggregate, 580 - 680 parts of manufactured sand, 130 - 165 parts of water, 0.8 - 12 parts of admixture, 0.5 - 3.0 parts of graphene-carbon nanotube composite emulsion, 1.0 - 3.0 parts of self-healing microcapsules, 0.1 - 0.5 parts of dispersible nano-silica particles, and 3 - 10 parts of expansive agent; Among them, the high-strength gravel concrete has the following performance parameters: The water-binder ratio is 0.28 - 0.40, the sand ratio is 0.36 - 0.42, the 28-day compressive strength ≥ 80 MPa, the chloride ion penetration electric flux ≤ 800 C, and the 56-day drying shrinkage rate ≤ 280×10 -6 ; The specific limitations of each raw material are as follows: The cement is 42.5R or 52.5 ordinary Portland cement; The mineral admixture includes nano-silica fume and metakaolin, and the mass ratio is 1 - 2:1; The gravel is natural gravel with a particle size of 5 - 25 mm, and its surface is impregnated with a nano-silicate composite solution and then dried at 80 - 90 °C for 2 hours; The graphene-carbon nanotube composite emulsion is prepared by mixing graphene oxide and multi-walled carbon nanotubes in a mass ratio of 2 - 3:1 and subjecting them to ultrasonic dispersion; The self-healing microcapsules have a particle size of 80 - 150 μm and a coating rate of not less than 85%; The dispersible nano-silica particles are organically modified fumed SiO2 nanoparticles with a particle size of 5 - 30 nm; The expansive agent is a calcium oxide-calcium aluminate composite expansive agent; The admixtures include one or more of polycarboxylate superplasticizer, retarder, early strength agent, and air-entraining agent.

[0005] Preferably, the graphene-carbon nanotube composite emulsion is ultrasonically dispersed for 20 minutes and then left to stand for 1 hour before use. The emulsion has good stability, and the conductivity and compactness are synergistically enhanced.

[0006] Preferably, the core material of the microcapsule coating is ettringite precursor or polyurea compound, and the coating material is urea-formaldehyde resin or polyurethane. When the concrete crack is exposed to water or CO2 environment, the self-healing substance is released to seal the crack.

[0007] Preferably, after the gravel is subjected to surface roughening and nano-silica modification treatment, the compactness of the interfacial transition zone (ITZ) between it and the cement paste is improved, and the interfacial bond strength is increased by more than 15%.

[0008] Preferably, after 300 freeze-thaw cycles at -20 °C, the mass loss rate of the concrete does not exceed 2%, and the relative dynamic elastic modulus retention rate is not less than 90%.

[0009] Preferably, the dispersible nano-silica particles participate in the secondary hydration reaction in an alkaline environment to generate gel-like C-S-H, improving the compactness of the pore structure and the carbonation resistance.

[0010] A preparation method of high-strength gravel concrete includes the following steps: S1. Raw material pretreatment: Add natural gravel to a composite solution of 5% - 15% sodium silicate and nano-SiO2, soak for 2 - 6 hours, take it out and dry at 80 - 90 °C for 2 hours to obtain modified gravel aggregate; S2. Raw material weighing and dry mixing: Weigh cement, mineral admixture, manufactured sand, and dispersible nano-silica particles according to the ratio, and add them to a mixer for dry mixing for 2 - 3 minutes; S3. Preparation of additive solution: Mix the graphene-carbon nanotube composite emulsion, admixtures, and water evenly and stir to form a uniform emulsion system; S4. Wet Mixing and Molding: Add the additive liquid to the dry mixture and stir to form a uniform slurry. Subsequently, add the modified gravel, self-healing microcapsules, and expansive agent in sequence, and stir at low speed for 3 minutes and at high speed for 2 minutes to obtain a mixture; S5. Pouring and Curing: Pour the mixture into a mold, vibrate it mechanically until it is dense. After standing and forming, cure it under standard conditions at a temperature of 20 ± 2°C and a relative humidity of ≥ 95% for 28 days; alternatively, it can be cured with steam at 80°C for 12 hours and then transferred to standard curing conditions.

[0011] Compared with the prior art, the advantages of the present invention are as follows: (1) By introducing active nano-silicon particles, self-healing microcapsules, and modified gravel aggregates, the present invention constructs a multi-scale synergistic reinforcement structure, solving the problems of micro-crack initiation and propagation and limited strength improvement in traditional concrete: The modified gravel is treated with silane coupling and inorganic composite coatings, having a higher interfacial bonding strength and improving the bonding performance between coarse aggregates and cement paste; Nano-silicon particles fill the pores and participate in the secondary hydration reaction, enhancing the density and early strength of the paste; The microcapsule system releases repair substances when micro-cracks initiate, delaying crack propagation and enhancing the later bearing capacity; (2) The self-healing microcapsule system and highly active mineral admixtures introduced in the present invention significantly improve the overall durability performance of concrete: The non-polar repair agent encapsulated in the microcapsules is released during stress or aging, automatically filling the cracks and delaying the deterioration of structural performance; Mineral admixtures such as metakaolin and silica fume form a dense hydration structure, significantly inhibiting the penetration of chloride ions and moisture; After the materials are tested by freeze-thaw and wet-dry cycles, the strength retention rate and mass loss rate are better than those of conventional technologies, having better resistance to environmental erosion and extending the service life of concrete. Description of the Drawings

[0012] Figure 1 It is the overall flowchart of the preparation method of the high-strength gravel concrete of the present invention. Detailed Embodiments

[0013] Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although some embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Instead, these embodiments are provided to more thoroughly and completely understand the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are only for exemplary purposes and are not used to limit the protection scope of the present disclosure.

[0014] It should be understood that the steps recited in the method embodiments of the present disclosure can be executed in different orders and / or in parallel. In addition, the method embodiments may include additional steps and / or omit the steps shown. The scope of the present disclosure is not limited in this regard.

[0015] As used herein, the term "including" and its variations are open-ended, i.e., "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The relevant definitions of other terms will be given in the following description.

[0016] It should be noted that the concepts such as "first", "second", etc. mentioned in this disclosure are only used to distinguish different devices, modules or units, and are not used to limit the order or interdependence of the functions performed by these devices, modules or units.

[0017] It should be noted that the modification of "one" and "plural" mentioned in this disclosure is illustrative rather than restrictive. Those skilled in the art should understand that unless otherwise clearly specified in the context, it should be understood as "one or more".

[0018] The names of the messages or information exchanged between multiple devices in the embodiments of this disclosure are only for illustrative purposes, and are not used to limit the scope of these messages or information.

[0019] Embodiment: Embodiment 1: Group allocation ratio (parts by mass): Cement: 400 parts; Nano-silica fume: 60 parts; Metakaolin: 60 parts; Modified gravel: 1000 parts; Manufactured sand: 600 parts; Water: 150 parts; Polycarboxylate superplasticizer: 8 parts; Graphene-carbon nanotube composite emulsion: 1.5 parts; Self-healing microcapsules: 2.0 parts; Dispersible nano-silicon particles: 0.3 parts; Expansive agent: 6 parts; Preparation steps: S1. Soak natural gravel in a composite solution containing 10% sodium silicate and nano-SiO2 for 4 hours, and then dry it at 85 °C for 2 hours to obtain modified gravel; S2. Weigh cement, nano-silica fume, metakaolin, manufactured sand, and nano-silicon particles in proportion and dry-mix them for 3 minutes; S3. Graphene and carbon nanotubes are compounded at a mass ratio of 2.5:1, and ultrasonic treatment is carried out with deionized water and a dispersant for 20 minutes to form a composite emulsion; S4. Mix the above emulsion, water, and superplasticizer, and then stir with the dry-mixed material to form a slurry; S5. Add modified gravel, self-healing microcapsules, and expansive agent, first stir at low speed for 2 minutes, and then stir at high speed for 2 minutes to obtain concrete mixture; S6. Pour it into a 100×100×100 mm mold, vibrate it densely, and cure it under standard conditions for 28 days.

[0020] Example 2: Composition ratio (parts by mass): Cement: 420 parts; Nano-silica fume: 70 parts; Metakaolin: 50 parts; Modified gravel: 960 parts; Manufactured sand: 620 parts; Water: 135 parts; Polycarboxylate superplasticizer: 10 parts; Graphene-carbon nanotube composite emulsion: 2.5 parts; Self-healing microcapsules: 2.5 parts; Dispersible nano-silicon particles: 0.4 parts; Expansive agent: 5 parts; The preparation steps are the same as those in Example 1, only the water-binder ratio is controlled to be 0.28.

[0021] Example 3: Composition ratio (parts by mass): Cement: 380 parts; Nano-silica fume: 60 parts; Metakaolin: 60 parts; Modified gravel: 890 parts; Manufactured sand: 650 parts; Water: 155 parts; Polycarboxylate water reducer: 9 parts; Graphene-carbon nanotube composite emulsion: 1.2 parts; Self-healing microcapsules: 3.0 parts; Dispersible nano-silicon particles: 0.2 parts; Expansive agent: 4 parts; The core material of the microcapsules is ettringite precursor, the coating rate is 90%, and the particle size is 120 μm; Example 4: Composition ratio (parts by mass): Cement: 400 parts; Nano-silica fume: 80 parts; Metakaolin: 40 parts; Modified gravel: 1000 parts; Manufactured sand: 590 parts; Water: 140 parts; High-range water reducer: 8 parts; Graphene-carbon nanotube emulsion: 1.0 part; Self-healing microcapsules: 1.5 parts; Dispersible nano-silicon particles: 0.1 part; Expansive agent: 5 parts; Steam curing process: After the mold stands still for 1 hour, it enters the steam curing chamber and is cured at a constant temperature of 80 °C for 12 hours, and then transferred to standard curing.

[0022] Example 5: Composition ratio (parts by mass): Cement: 390 parts; Nano-silica fume: 50 parts; Metakaolin: 70 parts; Modified gravel: 930 parts; Manufactured sand: 610 parts; Water: 145 parts; High-performance water reducer: 9.5 parts; Graphene-carbon nanotube emulsion: 2.0 parts; Self-healing microcapsules: 2.0 parts; Dispersible nano-silicon particles: 0.5 part; Expansive agent: 7 parts; Key points of preparation: Add 0.15% polyvinyl alcohol fiber to enhance toughness; After pouring, cover with film to keep moist for 24 h, and then transfer to standard curing.

[0023] Comparative Example 1: Composition ratio (parts by mass): Cement: 400 parts; Fly ash: 60 parts; Manufactured sand: 650 parts; Ordinary natural gravel: 1050 parts (without modification treatment); Water: 165 parts; Naphthalene-based water reducer: 7 parts; Without microcapsules, without nano-silicon particles, without graphene materials; Preparation steps: Stir the components conventionally, the mixing time is about 4 minutes, pour into the mold and let it stand still naturally and cure under standard conditions for 28 days.

[0024] Comparative Example 2: Composition ratio (parts by mass): Cement: 410 parts; Silica fume: 65 parts; Metakaolin: 50 parts; Modified gravel: 980 parts (the same as in the example); Manufactured sand: 600 parts; Water: 160 parts; Polycarboxylate superplasticizer: 8 parts; No self-healing microcapsules; No graphene / carbon nanotube emulsion; No dispersible nano-silica particles; Preparation steps: Except for omitting three functional components, the remaining operations are the same as in Example 1.

[0025] Comparative Example 3: Composition ratio (parts by mass): Cement: 390 parts; Fly ash: 80 parts; Manufactured sand: 640 parts; Ordinary natural gravel: 1000 parts; Water: 170 parts; Naphthalene-based superplasticizer: 6.5 parts; No nano-silica fume, no metakaolin; No graphene / carbon nanotubes; No microcapsules, no nano-silica particles; Preparation method: Conventional stirring process, using 3 minutes of low-speed stirring + 1 minute of high-speed stirring, followed by standard curing for 28 days.

[0026] Experimental tests I. To verify the significant superiority of the high-strength gravel concrete formula proposed in Examples 1-5 in terms of compressive strength performance, and evaluate the difference in cube compressive strength at 28 days of age between them and Comparative Examples 1-3.

[0027] 1. Specimen preparation Weigh the raw materials according to the respective ratios of Examples 1-5 and Comparative Examples 1-3.

[0028] After each group of concrete mixtures is stirred, pour them into a 150 mm cube mold and vibrate them to form.

[0029] Prepare no less than 3 specimens for each group, and mark them clearly.

[0030] 2. Curing After molding, place them in a standard curing box at a curing temperature of 20 °C and a relative humidity of 95% for 28 days.

[0031] 3. Compressive strength test Use a compressive testing machine to conduct a compressive strength test at 28 days of age, with a loading rate of 0.5 MPa / s.

[0032] Record the failure load of each specimen and calculate the compressive strength (unit: MPa):

[0033] Among them, : Cube compressive strength, F: Failure load (N), A: Compressed surface area (mm 2 ).

[0034] The average compressive strength (MPa) is shown in Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 94.2 91.7 92.5 93.4 90.6 72.6 83.1 69.8 Table 1 The multi-scale enhancement system (modified gravel + nanomaterials + self-healing microcapsules) introduced in Examples 1-5 can significantly improve the strength of concrete; in the schemes of Comparative Examples 1-3, there is a significant decrease in strength when there are no functional components or only partial technologies are used.

[0035] II. To verify the durability performance and microcrack self-healing ability of the high-strength gravel concrete in the present invention, concrete preparation specimens of Examples 1-5 and Comparative Examples 1-3 were respectively selected, and the following systematic comparative tests were carried out. Standard cubes (100 mm × 100 mm × 100 mm) were prepared for each group of specimens, and the tests were carried out after 28 days of curing.

[0036] 1. Chloride ion penetration resistance test (RCM method) Test procedure: According to the NTBuild492 standard, the rapid chloride ion migration (RCM) method was used for testing. After the specimens were saturated with water, they were placed in the test device and a DC electric field of 60 V was applied for 6 hours, and the chloride ion diffusion depth was recorded and the migration coefficient (D, unit: ×10- 12 m 2 / s) was calculated.

[0037] 2. Carbonation resistance test (accelerated carbonation) Test procedure: The specimens at 28 days of age were placed in an environment with a CO2 concentration of 20%, a relative humidity of 70%, and a temperature of 20 °C for 28 days of curing. The carbonation depth was measured every 7 days after disconnection, and phenolphthalein reagent was used for color development judgment.

[0038] 3. Freeze-thaw resistance test (mass loss and dynamic elastic modulus) Test procedure: The rapid freeze-thaw cycle test (-20 °C to +20 °C) was carried out for a total of 100 cycle periods. The mass loss rate and relative dynamic elastic modulus (with the initial value as 100%) were measured respectively, and the average value was taken for 5 specimens in each group.

[0039] 4. Microcrack self-healing ability test Test procedure: Cracks with a width of about 0.2-0.3 mm were artificially prefabricated on the surface of the specimens, and they were wet-cured for 28 days under the conditions of humidity > 95% and temperature 25 °C. The closure rate was measured using crack microscopy imaging, and the compressive strength was tested again to calculate the recovery rate.

[0040] The experimental results are shown in Table 2

[0041] Table 2 The following conclusions can be drawn from the above experiments: The concrete in the embodiments is significantly superior to the conventional mix in terms of chloride ion penetration resistance, carbonation resistance, freeze-thaw resistance, etc., and is suitable for long-term service structures such as tunnels, bridges, seaports and other projects with high durability requirements. After introducing the composite self-healing functional additive, the cracks in the concrete can be significantly closed in a humid environment, and the strength is basically restored, with the characteristics of intelligent maintenance, effectively extending the service life.

[0042] The above description is only a preferred embodiment of the present disclosure and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of disclosure involved in the present disclosure is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above disclosure concept. For example, the technical solutions formed by mutually replacing the above features with the technical features (but not limited to) having similar functions disclosed in the present disclosure.

[0043] In addition, although the operations are depicted in a particular order, this should not be construed as requiring that the operations be performed in the particular order shown or in sequential order. In certain circumstances, multitasking and parallel processing may be advantageous. Similarly, although a number of specific implementation details are included in the above discussion, these should not be construed as limiting the scope of the present disclosure. Certain features described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment may also be implemented separately or in any suitable sub-combination in multiple embodiments.

[0044] Although the subject matter has been described in language specific to structural features and / or methodological act logic, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. On the contrary, the specific features and acts described above are merely example forms for implementing the claims.

Claims

1. A high-strength gravel concrete, characterized in that, Raw materials comprising the following components, by mass parts: 300 - 420 parts of cement, 60 - 120 parts of mineral admixture, 850 - 1050 parts of modified gravel aggregate, 580 - 680 parts of manufactured sand, 130 - 165 parts of water, 0.8 - 12 parts of admixture, 0.5 - 3.0 parts of graphene-carbon nanotube composite emulsion, 1.0 - 3.0 parts of self-healing microcapsules, 0.1 - 0.5 parts of dispersible nano-silica particles, 3 - 10 parts of expansive agent; Among them, the high-strength gravel concrete has the following performance parameters: The water-cement ratio is 0.28 to 0.40, the sand ratio is 0.36 to 0.42, the 28-day compressive strength is ≥80 MPa, the chloride ion penetration electric flux is ≤800 C, and the 56-day drying shrinkage rate is ≤280×10 -6 ; The specific limitations of each raw material are as follows: The cement is 42.5R or 52.5 ordinary Portland cement; The mineral admixture includes nano-silica fume and metakaolin, with a mass ratio of 1 - 2:1; The gravel is natural gravel with a particle size of 5 - 25 mm, and after being impregnated with a nano-silicate composite solution on the surface, it is dried at 80 - 90 °C for 2 hours; The graphene-carbon nanotube composite emulsion is prepared by mixing graphene oxide and multi-walled carbon nanotubes in a mass ratio of 2 - 3:1 and ultrasonic dispersion; The self-healing microcapsules have a particle size of 80 - 150 μm and a coating rate of not less than 85%; The dispersible nano-silica particles are surface organically modified fumed SiO2 nanoparticles with a particle size of 5 - 30 nm; The expansive agent is a calcium oxide-calcium aluminate composite expansive agent; The admixture includes one or more of polycarboxylate superplasticizer, retarder, early strength agent, and air-entraining agent.

2. The high-strength gravel concrete according to claim 1, wherein The graphene-carbon nanotube composite emulsion is ultrasonically dispersed for 20 minutes and then left standing for 1 hour before use. The emulsion has good stability, and the conductivity and compactness are synergistically enhanced.

3. The high-strength gravel concrete according to claim 1, characterized in that, The core material of the microcapsule coating is ettringite precursor or polyurea compound, and the coating material is urea-formaldehyde resin or polyurethane, which releases self-healing substances to seal cracks when the concrete cracks are exposed to water or CO2 environment.

4. The high-strength gravel concrete according to claim 1, characterized in that, After the gravel is subjected to surface roughening and nano-silicon modification treatment, the compactness of the interfacial transition zone (ITZ) between it and the cement paste is improved, and the interfacial bond strength is increased by more than 15%.

5. The high-strength gravel concrete according to claim 1, wherein, After 300 freeze-thaw cycles at -20 °C, the mass loss rate of the concrete does not exceed 2%, and the relative dynamic elastic modulus retention rate is not less than 90%.

6. The high-strength gravel concrete according to claim 1, wherein, The dispersible nano-silica particles participate in the secondary hydration reaction in an alkaline environment to generate gel-like C-S-H, improving the pore structure compactness and carbonation resistance.

7. A method for preparing the high-strength gravel concrete according to any one of claims 1 to 6, characterized in that, Including the following steps: S1. Raw material pretreatment: Add natural gravel to a 5% - 15% sodium silicate and nano-SiO2 composite solution and soak for 2 - 6 hours. After taking it out, dry it at 80 - 90 °C for 2 hours to obtain modified gravel aggregate; S2. Raw material weighing and dry mixing: Weigh cement, mineral admixture, manufactured sand, and dispersible nano-silica particles in proportion and add them to a mixer for dry mixing for 2 - 3 minutes; S3. Preparation of additive liquid: Mix the graphene-carbon nanotube composite emulsion, admixture, and water evenly and stir to form a uniform emulsion system; S4. Wet mixing and molding: Add the additive liquid to the dry mixture, stir to form a uniform slurry, and then sequentially add modified gravel, self-healing microcapsules, and expansive agent, stir at low speed for 3 minutes and at high speed for 2 minutes to obtain a mixture; S5. Pouring and curing: Pour the mixture into the mold, vibrate it mechanically until it is dense, and after standing and forming, cure it under standard conditions at a temperature of 20 ± 2 °C and a relative humidity of ≥ 95% for 28 days; alternatively, it can be cured with steam at 80 °C for 12 hours and then transferred to the standard curing conditions.

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