High-strength gravel concrete and preparation method thereof

Abstract

The present invention discloses a high-strength gravel concrete and a preparation method thereof, belonging to the field of concrete technology. The concrete comprises the following components, calculated by mass: 300-420 parts of cement, 60-120 parts of mineral admixtures, 850-1050 parts of modified gravel aggregate, 580-680 parts of machine-made sand, 130-165 parts of water, 0.8-12 parts of an admixture, 0.5-3.0 parts of a graphene-carbon nanotube composite emulsion, 1.0-3.0 parts of self-healing microcapsules, 0.1-0.5 parts of dispersible nano-silicon particles, and 3-10 parts of an expansion agent. The present invention constructs a multi-scale synergistic reinforcement structure by introducing active nano-silicon particles, self-healing microcapsules, and modified gravel aggregates, solving the problems of microcrack initiation and expansion and limited strength improvement in traditional concrete: the modified gravel is treated with silane coupling and inorganic composite coating to have higher interfacial bonding strength, thereby improving the bonding performance between coarse aggregate and cement paste; the nano-silicon particles fill the pores and participate in the secondary hydration reaction, thereby improving the paste density and early strength.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and more particularly 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, with its excellent workability and economical construction, plays a key supporting role in structures such as bridges, high-rise buildings, roads, and tunnels. Traditional ordinary gravel concrete forms a skeleton structure through the hydration reaction of cement and aggregate. Its physical and mechanical properties meet general load requirements. However, under high-strength, high-durability conditions and in special environments (such as freeze-thaw cycles, chloride ion attack, and high carbonation), it still faces the following major technical bottlenecks: the interfacial transition zone (ITZ) between ordinary natural gravel and cement-based paste often contains microscopic pores and microcracks, creating a "weak link" for stress concentration and crack propagation. Under long-term loads and environmental corrosion, microcracks in the ITZ continuously initiate, expand, and connect, resulting in a decrease in the overall compressive, flexural, and impermeability properties of the concrete. While existing high-performance concrete can enhance its strength and toughness through the addition of mineral admixtures or fiber reinforcement, it lacks an internal repair mechanism for existing microcracks and defects. Once concrete cracks form, manual grouting or external maintenance is often required, which increases maintenance costs and construction difficulty, making it difficult to achieve long-term adaptive maintenance of the structure. Summary of the Invention

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

[0004] A high-strength gravel concrete comprises the following components, calculated by weight: 300-420 parts of cement, 60-120 parts of mineral admixture, 850-1050 parts of modified gravel aggregate, 580-680 parts of machine-made 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-silicon particles, and 3-10 parts of expansion agent.

[0005] The high-strength gravel concrete has the following performance parameters:

[0006] The water-binder ratio is 0.28-0.40, the sand ratio is 0.36-0.42, the 28-day compressive strength is ≥80MPa, the chloride ion permeation flux is ≤800C, and the 56-day drying shrinkage is ≤280×10 -6 ;

[0007] The specific definitions of the raw materials are as follows:

[0008] The cement is 42.5R or 52.5 ordinary Portland cement;

[0009] The mineral admixture includes nano silica fume and metakaolin in a mass ratio of 1 to 2:1;

[0010] The gravel is natural gravel with a particle size of 5 to 25 mm, the surface of which is impregnated with a nano-silicate composite liquid and then dried at 80 to 90° C. for 2 hours;

[0011] The graphene-carbon nanotube composite emulsion is prepared by mixing graphene oxide and multi-walled carbon nanotubes in a mass ratio of 2 to 3:1 and ultrasonically dispersing the mixture.

[0012] The self-healing microcapsule has a particle size of 80 to 150 μm and a coverage rate of not less than 85%;

[0013] The dispersible nano-silicon particles are surface-organically modified gas-phase SiO2 nano-particles with a particle size of 5 to 30 nm;

[0014] The expansion agent is a calcium oxide-calcium aluminate composite expansion agent;

[0015] The admixture includes one or more of a polycarboxylic acid high-performance water-reducing agent, a retarder, an early strength agent, and an air-entraining agent.

[0016] Preferably, the graphene-carbon nanotube composite emulsion is ultrasonically dispersed for 20 minutes before use and then allowed to stand for 1 hour. The emulsion has good stability, and the conductivity and density are synergistically enhanced.

[0017] Preferably, the microcapsule coating core material is a precursor of ettringite or a polyurea compound, and the coating material is a urea-formaldehyde resin or polyurethane, which releases self-healing substances to seal the cracks when the concrete cracks are exposed to water or CO2 environment.

[0018] Preferably, after the gravel is surface roughened and modified with nano-silicon, the density of the interface transition zone (ITZ) between the gravel and the cement paste is improved, and the interface bonding strength is increased by more than 15%.

[0019] Preferably, the mass loss rate of the concrete after 300 freeze-thaw cycles at −20° C. does not exceed 2%, and the relative dynamic elastic modulus retention rate is not less than 90%.

[0020] Preferably, the dispersible nano-silicon particles participate in a secondary hydration reaction in an alkaline environment to generate gel-state CSH, thereby improving the density of the pore structure and the carbonization resistance.

[0021] A method for preparing high-strength gravel concrete comprises the following steps:

[0022] S1. Raw material pretreatment: Natural gravel is soaked in a 5% to 15% sodium silicate and nano-SiO2 composite solution for 2 to 6 hours. After removal, it is dried at 80 to 90°C for 2 hours to obtain modified gravel aggregate;

[0023] S2. Raw material weighing and dry mixing: Cement, mineral admixtures, machine-made sand, and dispersible nano-silicon particles are weighed in proportion and added to a mixer and dry mixed for 2 to 3 minutes;

[0024] S3. Additive preparation: The graphene - carbon nanotube composite emulsion, the admixture and water are mixed uniformly and stirred to form a uniform emulsion system;

[0025] S4 wet mix molding: the dry mix was added to the additive liquid, stirred to form a uniform slurry, followed by the addition of modified gravel, self-healing microcapsules and expansion agent, stirring at low speed for 3 minutes, high speed stirring for 2 minutes to obtain a mixture;

[0026] S5. Casting and curing: Pour the mixture into the mold, compact it with mechanical vibration, let it stand to form, and then perform standard curing for 28 days at a temperature of 20±2℃ and a relative humidity of ≥95%. Alternatively, steam curing at 80℃ for 12 hours and then switching to standard curing conditions.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] (1) The present invention constructs a multi-scale synergistic reinforcement structure by introducing active nano-silicon particles, self-healing microcapsules, and modified gravel aggregates, solving the problems of microcrack initiation and expansion and limited strength improvement in traditional concrete: the modified gravel is treated with silane coupling and inorganic composite coating to have higher interfacial bonding strength, thereby improving the bonding performance between coarse aggregate and cement paste; the nano-silicon particles fill the pores and participate in the secondary hydration reaction, thereby improving the density and early strength of the paste; the microcapsule system releases repair substances when microcracks initiate, delaying crack expansion and enhancing the later bearing capacity;

[0029] (2) The self-healing microcapsule system and highly active mineral admixtures introduced in the present invention significantly improve the overall durability of concrete: the non-polar repair agent encapsulated in the microcapsules is released during stress or aging, which can automatically fill cracks and delay the deterioration of structural performance; mineral admixtures such as kaolin and silica fume form a dense hydration structure, which significantly inhibits the penetration of chloride ions and water; after freeze-thaw and dry-wet cycle tests, the material has better strength retention and mass loss rate than conventional technologies, has better resistance to environmental erosion, and extends the service life of concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an overall flow chart of the method for preparing high-strength gravel concrete of the present invention. DETAILED DESCRIPTION

[0031] The following describes embodiments of the present disclosure in more detail with reference to the accompanying drawings. Although certain embodiments of the present disclosure are shown in the accompanying 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 described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are for illustrative purposes only and are not intended to limit the scope of protection of the present disclosure.

[0032] It should be understood that the various steps described in the method embodiments of the present disclosure may be performed 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 respect.

[0033] As used herein, the term "including" and its variations are open-ended, i.e., "including but not limited to." The term "based on" means "based, at least in part, on." The term "one embodiment" means "at least one embodiment," the term "another embodiment" means "at least one additional embodiment," and the term "some embodiments" means "at least some embodiments." Other terms are defined in the following description.

[0034] It should be noted that the concepts of "first" and "second" 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.

[0035] It should be noted that the modifications of "one" and "multiple" mentioned in the present disclosure are illustrative rather than restrictive, and those skilled in the art should understand that unless otherwise clearly indicated in the context, they should be understood as "one or more".

[0036] The names of the messages or information exchanged between multiple devices in the embodiments of the present disclosure are only used for illustrative purposes and are not used to limit the scope of these messages or information.

[0037] Example:

[0038] Example 1: Component ratio (parts by mass): cement: 400 parts; nano-silica fume: 60 parts; metakaolin: 60 parts; modified gravel: 1000 parts; machine-made sand: 600 parts; water: 150 parts; polycarboxylate water reducer: 8 parts; graphene-carbon nanotube composite emulsion: 1.5 parts; self-healing microcapsules: 2.0 parts; dispersible nano-silicon particles: 0.3 parts; expansion agent: 6 parts;

[0039] Preparation steps:

[0040] S1. The natural gravel was immersed in a composite solution containing 10% sodium silicate and nano-SiO2 for 4 hours and then dried at 85 ° C for 2 hours to obtain modified gravel;

[0041] S2. Cement, nano-silica fume, metakaolin, machine-made sand, and nano-silicon particles were weighed in proportion and dry-mixed for 3 minutes;

[0042] S3. Graphene and carbon nanotubes were mixed in a mass ratio of 2.5:1 and ultrasonically treated with deionized water and a dispersant for 20 minutes to form a composite emulsion;

[0043] S4. The emulsion, water, and water reducer are mixed and stirred with the dry mix to form a slurry;

[0044] S5. Add modified gravel, self-healing microcapsules and expansion agent, stir at low speed for 2 minutes, then stir at high speed for 2 minutes to obtain a concrete mixture;

[0045] S6. Pour into a 100×100×100mm mold, vibrate to compact, and standard cure for 28 days.

[0046] Example 2: Component ratio (parts by mass): cement: 420 parts; nano silica fume: 70 parts; metakaolin: 50 parts; modified gravel: 960 parts; machine-made sand: 620 parts; water: 135 parts; polycarboxylic acid high-performance water-reducing agent: 10 parts; graphene-carbon nanotube composite emulsion: 2.5 parts; self-healing microcapsules: 2.5 parts; dispersible nano-silicon particles: 0.4 parts; expansion agent: 5 parts;

[0047] The preparation steps were the same as those in Example 1, except that the water-binder ratio was controlled to be 0.28.

[0048] Example 3: Component ratio (parts by mass): cement: 380 parts; nano silica fume: 60 parts; metakaolin: 60 parts; modified gravel: 890 parts; machine-made 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; expansion agent: 4 parts;

[0049] The core material of the microcapsules is ettringite precursor, with a coverage rate of 90% and a particle size of 120 μm;

[0050] Example 4: Component ratio (parts by mass): cement: 400 parts; nano-silica fume: 80 parts; metakaolin: 40 parts; modified gravel: 1000 parts; machine-made sand: 590 parts; water: 140 parts; high-efficiency water reducer: 8 parts; graphene-carbon nanotube emulsion: 1.0 parts; self-healing microcapsules: 1.5 parts; dispersible nano-silicon particles: 0.1 parts; expansion agent: 5 parts;

[0051] Steaming process: After the mold is left to stand for 1 hour, it enters the steaming room and is steamed at a constant temperature of 80℃ for 12 hours, and then transferred to standard curing.

[0052] Example 5: Component ratio (parts by mass): cement: 390 parts; nano silica fume: 50 parts; metakaolin: 70 parts; modified gravel: 930 parts; machine-made 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 parts; expansion agent: 7 parts;

[0053] Preparation points: Add 0.15% polyvinyl alcohol fiber to enhance toughness; cover with film to keep moist for 24 hours after pouring, and then transfer to standard curing.

[0054] Comparative Example 1: Component ratio (parts by mass): cement: 400 parts; fly ash: 60 parts; machine-made sand: 650 parts; ordinary natural gravel: 1050 parts (unmodified); water: 165 parts; naphthalene-based water reducer: 7 parts; no microcapsules, no nano-silicon particles, no graphene materials;

[0055] Preparation steps:

[0056] Stir the components normally for about 4 minutes, pour into the mold, let it stand naturally and perform standard curing for 28 days.

[0057] Comparative Example 2: Component proportions (parts by mass): cement: 410 parts; silica fume: 65 parts; metakaolin: 50 parts; modified gravel: 980 parts (same as in Example); machine-made sand: 600 parts; water: 160 parts; polycarboxylate superplasticizer: 8 parts; no self-healing microcapsules; no graphene / carbon nanotube emulsion; no dispersible nano-silicon particles;

[0058] Preparation steps: Except for omitting the three functional components, the remaining operations are the same as those in Example 1.

[0059] Comparative Example 3: Component ratio (parts by mass): cement: 390 parts; fly ash: 80 parts; machine-made sand: 640 parts; ordinary natural gravel: 1000 parts; water: 170 parts; naphthalene-based water reducer: 6.5 parts; no nano-silica fume, no metakaolin; no graphene / carbon nanotubes; no microcapsules, no nano-silicon particles;

[0060] Preparation method:

[0061] The conventional mixing process adopts 3 minutes of low-speed mixing + 1 minute of high-speed mixing, followed by standard curing for 28 days.

[0062] Experimental testing

[0063] 1. Verify the significant superiority of the high-strength gravel concrete formulas proposed in Examples 1-5 in terms of compressive strength performance, and evaluate the difference in cube compressive strength between them and Comparative Examples 1-3 at 28 days of age.

[0064] 1. Specimen Preparation

[0065] The raw materials were weighed according to the respective proportions of Examples 1-5 and Comparative Examples 1-3.

[0066] After each batch of concrete mixture is stirred, it is poured into a 150mm cubic test mold and vibrated to form a solid.

[0067] Each group shall prepare no less than 3 specimens, with clear numbering and marking.

[0068] 2. Maintenance

[0069] After forming, place it in a standard curing box at a curing temperature of 20°C and a relative humidity of 95% for a total of 28 days.

[0070] 3. Compressive strength test

[0071] The compressive strength test at 28 days was carried out using a compression testing machine with a loading rate of 0.5 MPa / s.

[0072] Record the failure load of each specimen and calculate the compressive strength (unit: MPa):

[0073]

[0074] in, : Cube compressive strength, F: Failure load (N), A: Compressive surface area (mm 2 ).

[0075] Average compressive strength (MPa) is shown in Table 1

[0076] 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

[0077] Table 1

[0078] The multi-scale reinforcement system (modified gravel + nanomaterials + self-healing microcapsules) introduced in Examples 1-5 can significantly improve the strength of concrete; the strength of the comparative examples 1-3 is significantly reduced when there is no functional component or only part of the technology is used.

[0079] To verify the durability and microcrack self-healing capabilities of the medium- and high-strength gravel concrete of the present invention, concrete samples prepared according to Examples 1-5 and Comparative Examples 1-3 were selected and subjected to the following systematic comparative tests. Each set of specimens consisted of standard cubes (100 mm × 100 mm × 100 mm) and were tested after 28 days of curing.

[0080] 1. Chloride ion penetration resistance test (RCM method)

[0081] Test steps: According to the NTBuild492 standard, the rapid chloride migration (RCM) method was used for testing. After the specimen was saturated with water, it was placed in the test device and a DC electric field of 60V was applied for 6 hours. The diffusion depth of chloride ions was recorded and the migration coefficient (D, unit: ×10- 12 m 2 / s).

[0082] 2. Anti-carbonization performance test (accelerated carbonization)

[0083] Test steps: Place the 28-day-old specimens in an environment with a CO2 concentration of 20%, a relative humidity of 70%, and a temperature of 20°C for 28 days. Disconnect the specimens every 7 days to measure the carbonization depth, and use phenolphthalein reagent for color development to determine the color.

[0084] 3. Freeze-thaw resistance test (mass loss and dynamic elastic modulus)

[0085] Test Procedure: Perform a rapid freeze-thaw cycle test (-20°C to +20°C) for a total of 100 cycles. Measure the mass loss rate and relative dynamic elastic modulus (with the initial value as 100%). Take five specimens per group and measure the average value.

[0086] 4. Microcrack self-repair ability test

[0087] Test procedures: Artificial cracks approximately 0.2-0.3 mm wide were created on the specimen surface and then cured for 28 days at a humidity of >95% and a temperature of 25°C. Crack closure was determined using microscopic imaging, and the compressive strength was retested to calculate the recovery rate.

[0088] The experimental results are shown in Table 2

[0089]

[0090] Table 2

[0091] The above experiments lead to the following conclusions: The concrete in this example significantly outperforms conventional mixes in terms of resistance to chloride ion penetration, carbonation, and freeze-thaw resistance, making it suitable for long-term structures such as tunnels, bridges, and seaports, requiring high durability. The introduction of a composite self-healing additive significantly closes concrete cracks in humid environments, substantially restoring strength and demonstrating intelligent maintenance properties, effectively extending its service life.

[0092] The above description is merely a preferred embodiment of the present disclosure and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of the present disclosure is not limited to technical solutions formed by specific combinations of the aforementioned technical features. It also encompasses other technical solutions formed by any combination of the aforementioned technical features or their equivalents, without departing from the aforementioned concepts. For example, a technical solution formed by replacing the aforementioned features with (but not limited to) technical features with similar functions disclosed in this disclosure.

[0093] In addition, although each operation is described in a specific order, this should not be understood as requiring these operations to be performed in the specific order shown or in a sequential order. Under certain circumstances, multitasking and parallel processing may be advantageous. Similarly, although some specific implementation details have been included in the above discussion, these should not be interpreted as limiting the scope of the present disclosure. Some features described in the context of a separate embodiment can also be implemented in a single embodiment in combination. On the contrary, the various features described in the context of a single embodiment can also be implemented in multiple embodiments individually or in any suitable sub-combination mode.

[0094] Although the subject matter has been described in language specific to structural features and / or methodological logical acts, 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. Rather, the specific features and acts described above are merely example forms of implementing the claims.

Claims

1. A high-strength gravel concrete, characterized in that: The raw materials include the following components, calculated by mass: 300-420 parts of cement, 60-120 parts of mineral admixture, 850-1050 parts of modified gravel aggregate, 580-680 parts of machine-made 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-silicon particles, and 3-10 parts of expansion agent; 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 compressive strength after 28 days is ≥80MPa, the chloride ion permeation flux is ≤800C, and the drying shrinkage after 56 days is ≤280×10 -6 ; The specific definitions of the raw materials are as follows: The cement is 42.5R or 52.5 ordinary Portland cement; The mineral admixture includes nano silica fume and metakaolin in a mass ratio of 1 to 2:1; The gravel is natural gravel with a particle size of 5 to 25 mm, the surface of which is impregnated with a nano-silicate composite liquid and then dried at 80 to 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 to 3:1 and ultrasonically dispersing the mixture. The self-healing microcapsule has a particle size of 80 to 150 μm and a coverage rate of not less than 85%; The dispersible nano-silicon particles are surface-organically modified gas-phase SiO2 nano-particles with a particle size of 5 to 30 nm; The expansion agent is a calcium oxide-calcium aluminate composite expansion agent; The admixture includes one or more of polycarboxylic acid high performance water reducer, retarder, early strength agent and air entraining agent; The microcapsule coating core material is a precursor of ettringite or a polyurea compound, and the coating material is a urea-formaldehyde resin or polyurethane. When the concrete cracks are exposed to water or a CO2 environment, self-healing substances are released to seal the cracks.

2. The high-strength gravel concrete according to claim 1, characterized in that: The graphene-carbon nanotube composite emulsion was ultrasonically dispersed for 20 minutes before use and then allowed to stand for 1 hour.

3. A method for preparing high-strength gravel concrete according to claim 2, characterized in that: The steps include: S1. Raw material pretreatment: Natural gravel is soaked in a 5% to 15% sodium silicate and nano-SiO2 composite solution for 2 to 6 hours. After removal, it is dried at 80 to 90°C for 2 hours to obtain modified gravel aggregate; S2. Raw material weighing and dry mixing: Cement, mineral admixtures, machine-made sand, and dispersible nano-silicon particles are weighed in proportion and added to a mixer and dry mixed for 2 to 3 minutes; S3. Additive preparation: The graphene - carbon nanotube composite emulsion, the admixture and water are mixed uniformly and stirred to form a uniform emulsion system; S4 wet mix molding: the dry mix was added to the additive liquid, stirred to form a uniform slurry, followed by the addition of modified gravel aggregate, self-healing microcapsules and expansion agent, stirring at low speed for 3 minutes, high speed stirring for 2 minutes to obtain a mixture; S5. Casting and curing: Pour the mixture into the mold, compact it with mechanical vibration, let it stand to form, and then carry out standard curing for 28 days at a temperature of 20±2℃ and a relative humidity of ≥95%, or use 80℃ steam curing for 12 hours and then transfer to standard curing conditions.

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