Preparation process of graphene concrete

Abstract

The invention relates to a preparation technology of graphene concrete and relates to the technical field of concrete.The preparation technology comprises the steps that graphene is subjected to in-situ acrylic acid molecular brush grafting modification; the preparation method comprises the following steps: mixing coarse aggregate, performing ultrasonic-centrifugal synergistic classification to separate the coarse aggregate into an interface enhancing component rich in large-size lamellas and a pore filling component rich in small-size lamellas, spraying the interface enhancing component to the surface of the coarse aggregate, and performing micro-area flash coagulation anchoring with dry cement powder to form a semi-rigid hard shell on the surface of the aggregate; a composite corrosion inhibitor is introduced into a pore filling component and is mixed with a cementing material, and secondary crosslinking of residual monomers is initiated by utilizing hydration heat. According to the preparation method disclosed by the invention, through a graded directional distribution strategy, bridging enhancement of large-size graphene to an aggregate interface transition region and filling of small-size graphene to matrix micropores are realized; and in combination with chemical passivation and secondary crosslinking technologies, the problems of graphene agglomeration, size mismatch and poor alkali resistance are solved, and the mechanical strength, compactness and conductive stability of the concrete are remarkably improved.

Description

Technical Field

[0001] This application relates to the field of concrete technology, and in particular to the preparation process of graphene concrete. Background Technology

[0002] Graphene, due to its excellent mechanical and electrical properties, is used to modify cement-based composites. However, in the actual preparation process, graphene's high specific surface area and strong van der Waals forces between its layers, coupled with the high ionic strength of the pore solution generated during cement hydration, make it highly prone to agglomeration in the cement matrix. This agglomeration not only reduces the specific surface area utilization of graphene and hinders the construction of a continuous conductive network, but the agglomerates themselves also become defects and stress concentration sources within the matrix, leading to a decline in the mechanical properties of concrete.

[0003] Current preparation processes typically incorporate graphene directly as a single component, neglecting the compatibility between the polydispersity of graphene raw materials and the multi-level porous structure of concrete. Concrete is a heterogeneous multiphase material composed of coarse aggregate, fine aggregate, and hardened cement paste. The interfacial transition zone between coarse aggregate and paste is relatively loose, representing a weak point in mechanical properties. Introducing large-sized graphene sheets into nanoscale gel pores can easily lead to steric hindrance due to size mismatch, compromising the compactness of the matrix's microstructure. Conversely, if small-sized graphene is distributed on the surface of coarse aggregate, its insufficient span makes it difficult to effectively bridge and prevent cracking at the interface. This randomness in spatial distribution prevents graphene from specifically enhancing the interfacial transition zone, limiting the improvement of the overall performance of concrete.

[0004] Furthermore, the cement hydration environment is highly alkaline, with the pH of the pore solution typically above 13. Under these conditions, oxygen-containing functional groups and edge defect sites on the graphene surface are prone to chemical erosion, leading to damage to the crystal structure. This structural degradation can cause breakage of conductive pathways and a decrease in reinforcing effects, thereby affecting the durability and functional stability of graphene concrete during long-term service.

[0005] In response to the aforementioned technologies, a preparation process for graphene concrete is provided. Summary of the Invention

[0006] The purpose of this application is to provide a preparation process for graphene concrete, which solves the technical problems in the prior art such as poor uniformity of graphene dispersion in concrete, mismatch between size distribution and matrix structure, and insufficient long-term stability in a strongly alkaline environment.

[0007] By adopting the above technical solution:

[0008] The first aspect of this invention provides a process for preparing graphene concrete. This process achieves graded distribution and in-situ passivation of graphene in the concrete matrix by in-situ chemical modification of graphene, hydrodynamic grading, micro-region flash setting and anchoring at the aggregate interface, and biphase targeted grouting.

[0009] The preparation process specifically includes the following steps:

[0010] S1. Graphene oxide is reduced and dispersed in water, and acrylic acid monomers and an initiator are added to carry out an in-situ polymerization reaction. During this process, the acrylic acid monomers undergo graft polymerization on the surface of the reduced graphene oxide to obtain a modified graphene dispersion with polyacrylic acid molecular brushes grafted onto its surface. The thickness of this polyacrylic acid molecular brush layer is controlled between 5 nm and 10 nm. This modified layer chemically bonds with subsequent cement hydration products through carboxyl groups and also acts as a physical barrier to prevent direct contact between hydroxide ions in the alkaline porous solution and the graphene lattice.

[0011] S2. The modified graphene dispersion was placed in an ultrasonic-centrifugal co-dispersion system. First, ultrasonic cavitation was performed at a frequency of 20 kHz and a power density of 0.5 W / mL to open the van der Waals forces between the graphene sheets. Then, a stepwise centrifugation separation was performed: first, centrifugation was carried out at 3000 rpm to 5000 rpm for 10 to 20 minutes, and the sediment was collected to obtain the interface-enhancing component, which is rich in large-sized graphene sheets; then, the remaining liquid was centrifuged at 8000 rpm to 10000 rpm for 20 to 30 minutes, and the supernatant was collected to obtain the pore-filling component, which is rich in small-sized and monolayer graphene sheets. Through this step, the polydisperse graphene raw material was separated into two-phase fluids with different geometric dimensions.

[0012] S3. Spray the interface reinforcement component onto the surface of the coarse aggregate while it is rolling, using the moisture in the interface reinforcement component to wet the aggregate. Then, spray 2% to 5% of the total cement mass of dry cement powder onto the surface of the coarse aggregate, maintaining rolling and stirring for 30 to 60 seconds and allowing it to stand for 2 to 5 minutes. During this process, the dry cement powder absorbs moisture from the interface reinforcement component, undergoing a localized high water-cement ratio hydration reaction, generating a semi-rigid shell composed of cement hydration products in situ on the surface of the coarse aggregate. This semi-rigid shell physically fixes the large-sized graphene sheets to the aggregate surface, preventing them from falling off due to slurry erosion during subsequent water addition and mixing.

[0013] S4. Sodium pyrophosphate and sodium tripolyphosphate are added to the pore-filling component, with a mass ratio of sodium pyrophosphate to sodium tripolyphosphate of 1:2, to prepare a composite modified liquid. Cement, fine aggregate, water, and the composite modified liquid are mixed and stirred to prepare a mortar matrix containing free phosphate ions and small-sized graphene. Finally, the coarse aggregate treated in step S3 is added to the mortar matrix and mixed, then poured to obtain graphene concrete.

[0014] Furthermore, after the in-situ polymerization reaction described in step S1, no washing or purification operation is performed, and the unreacted acrylic monomer residues in the dispersion are retained. During the mixing and stirring process in step S4, the slurry temperature is monitored. The heat of hydration at 40°C to 60°C generated by the cement hydration reaction is used as a thermal initiation source to initiate a secondary in-situ crosslinking reaction of the residual acrylic monomers within the slurry. The resulting polymer network further fills the micropores of the cement matrix and helps to fix small-sized graphene sheets.

[0015] Furthermore, the total amount of the sodium pyrophosphate and sodium tripolyphosphate composite corrosion inhibitor added in step S4 is 20% to 30% of the graphene mass. In the slurry liquid phase environment, phosphate ions adsorb onto the defect sites at the edges of the graphene, forming a chelate passivation film in situ with iron and aluminum ions precipitated in the slurry. This passivation film covers the structural defects caused by the redox process, inhibiting chemical corrosion under alkaline conditions.

[0016] Furthermore, in step S1, the graphene oxide used has a monolayer ratio greater than 98% and a sheet diameter ranging from 0.5 μm to 5 μm; hydrazine hydrate is used as a reducing agent in the reduction process, with a mass ratio of hydrazine hydrate to graphene oxide of 2:1. In the in-situ polymerization reaction, the mass ratio of acrylic acid monomer to reduced graphene oxide is 10:1 to 20:1, and the amount of ammonium persulfate initiator is 1.0% to 2.0% of the mass of acrylic acid monomer.

[0017] A second aspect of this invention provides a graphene concrete prepared by the above-described process. This concrete exhibits a hierarchically reinforced microstructure: large-sized graphene sheets are enriched and fixed in the interfacial transition zone between coarse aggregate and cement paste, while small-sized graphene sheets are dispersed in the gel pores of the cement mortar matrix. Simultaneously, the graphene surface is coated with a polyacrylic acid molecular brush layer, and phosphate chelate passivation films are bonded to edge defects.

[0018] In summary, this application includes at least one of the following beneficial technical effects:

[0019] 1. This application employs an ultrasonic-centrifugal synergistic process to separate modified graphene into an interface-reinforcing component rich in large-sized sheets and a pore-filling component rich in small-sized sheets. Through a dry powder flash condensation process, the large-sized graphene is physically anchored to the surface of the coarse aggregate to prevent it from falling off during mixing, thereby specifically strengthening the weak interface between the aggregate and the mortar. The small-sized graphene is dispersed in the mortar matrix to fill the micropores between hydration products. This differentiated distribution strategy solves the problem of the mismatch between the size of graphene and the pore structure of concrete, thereby improving the compressive strength and density of concrete.

[0020] 2. The process of this application retains the residual acrylic monomers in the in-situ modification process. The heat released by cement hydration is used as the initiation source to induce the monomers to undergo a secondary in-situ cross-linking reaction inside the slurry. The resulting polymer network fills the interior of the matrix, which restricts the microscopic displacement and rearrangement of graphene sheets during the slurry setting and hardening process. This prevents local delamination caused by gravity settlement or water migration, ensures the continuity of the graphene conductive pathway in three-dimensional space, and reduces the volume resistivity of concrete.

[0021] 3. In the preparation process, sodium pyrophosphate and sodium tripolyphosphate composite components are introduced. The adsorption of phosphate ions on the active sites at the edge of graphene is utilized to form an insoluble chelate film with the metal ions precipitated in the slurry in situ. The modified layer seals the structural defects of graphene, blocks the direct erosion of the carbon lattice by high-concentration alkaline pore solution, and inhibits the chemical degradation of graphene, thereby ensuring the stability of the mechanical and electrical properties of graphene concrete under long-term service conditions. Detailed Implementation

[0022] Example:

[0023] Example 1

[0024] This embodiment provides a process for preparing graphene concrete, the specific steps of which are as follows:

[0025] S1. Graphene oxide was dispersed in water, and hydrazine hydrate was added as a reducing agent (hydrazine hydrate to GO mass ratio of 2:1) to obtain reduced graphene oxide (rGO). Subsequently, acrylic acid monomer was added at a mass ratio of acrylic acid monomer to rGO of 15:1, along with 1.5% by mass of ammonium persulfate initiator. The system was heated to carry out an in-situ polymerization reaction, with strict control of the reaction time, so that the thickness of the polyacrylic acid molecular brush on the surface of the modified graphene was approximately 7.5 nm. After the reaction, no washing was performed, and the unreacted acrylic acid monomer residue in the dispersion was retained.

[0026] S2. The modified graphene dispersion obtained in step S1 was placed in an ultrasonic-centrifugal synergistic dispersion system. First, it was ultrasonically treated for 22 minutes at a frequency of 20 kHz and a power density of 0.5 W / mL. Then, a stepwise centrifugation was performed: in the first step, the mixture was centrifuged at 4000 rpm for 15 minutes, and the precipitate was collected as the interface enhancement component; in the second step, the remaining liquid was centrifuged at 9000 rpm for 25 minutes, and the supernatant was collected as the pore-filling component.

[0027] S3. Place continuously graded crushed stone (coarse aggregate) with a particle size of 5-20mm in a mixer and roll it. Spray the above-mentioned interface reinforcement component to wet it. While keeping it rolling, immediately spray in 3.5% of the total cement mass of dry cement powder and continue to roll and mix for 45 seconds. Then stop mixing and let it stand for 3.5 minutes. The moisture in the interface reinforcement component will trigger the hydration of the dry cement powder, forming a semi-rigid hard shell on the surface of the coarse aggregate.

[0028] S4. Add a composite corrosion inhibitor to the above-mentioned pore-filling component. This corrosion inhibitor is composed of sodium pyrophosphate and sodium tripolyphosphate in a mass ratio of 1:2, and the total addition amount is 25% of the graphene mass. P O42.5 cement, river sand (fine aggregate), water, and the composite modified liquid are mixed and stirred to form a mortar matrix. Temperature is monitored during mixing, and the heat of hydration (approximately 50°C) generated by cement hydration initiates secondary cross-linking of the residual monomers from step S1. Finally, the coarse aggregate treated in step S3 is added to the mortar matrix and mixed thoroughly before being cast into shape. In this embodiment, the water-cement ratio is controlled at 0.40.

[0029] Example 2

[0030] This embodiment provides a process for preparing graphene concrete, the specific steps of which are as follows:

[0031] S1. Raw material specifications are the same as in Example 1. Acrylic monomer is added at a mass ratio of acrylic monomer to rGO of 10:1, along with 1.0% (by mass) of ammonium persulfate initiator. In-situ polymerization is carried out, controlling the thickness of the polyacrylic acid molecular brush on the modified graphene surface to be approximately 5 nm. No cleaning is performed after the reaction, and residual monomers are retained.

[0032] S2. The ultrasonic treatment conditions are the same as in Example 1, but the time is adjusted to 15 minutes. Then, a step-by-step centrifugation is performed: the first step is to centrifuge at 3000 rpm for 10 minutes and collect the sediment as the interface enhancement component; the second step is to centrifuge the remaining liquid at 8000 rpm for 20 minutes and collect the supernatant as the pore-filling component.

[0033] S3. Place the coarse aggregate in the mixer and roll it, then spray the interface reinforcement component. Continue rolling, spray in 2.0% (by weight of total cement) of dry cement powder, and continue rolling and mixing for 30 seconds. Then stop mixing and let it stand for 2.0 minutes to form a semi-rigid shell on the surface of the coarse aggregate.

[0034] S4. Add a composite corrosion inhibitor (with the same proportion as in Example 1) to the pore-filling component, with a total addition amount of 20% of the graphene mass. Mix cement, fine aggregate, water, and the composite modified liquid to form a mortar matrix, and use the heat of hydration to initiate secondary cross-linking. Finally, add the treated coarse aggregate, mix, and cast into shape. The water-cement ratio is controlled at 0.40.

[0035] Example 3

[0036] This embodiment provides a process for preparing graphene concrete, the specific steps of which are as follows:

[0037] S1. Raw material specifications are the same as in Example 1. Acrylic monomer is added at a mass ratio of acrylic monomer to rGO of 20:1, along with 2.0% (by mass) of ammonium persulfate initiator. In-situ polymerization is carried out, controlling the thickness of the polyacrylic acid molecular brush on the modified graphene surface to be approximately 10 nm. No cleaning is performed after the reaction, and the residual monomer is retained.

[0038] S2. The ultrasonic treatment conditions are the same as in Example 1, but the time is adjusted to 30 minutes. Then, a step-by-step centrifugation is performed: in the first step, centrifuge at 5000 rpm for 20 minutes and collect the sediment as the interface enhancement component; in the second step, centrifuge the remaining liquid at 10000 rpm for 30 minutes and collect the supernatant as the pore-filling component.

[0039] S3. Place the coarse aggregate in the mixer and roll it, then spray the interface reinforcement component. While continuing to roll, spray in 5.0% of the total cement mass of dry cement powder, and continue to roll and mix for 60 seconds. After that, stop mixing and let it stand for 5.0 minutes to form a semi-rigid hard shell on the surface of the coarse aggregate.

[0040] S4. Add a composite corrosion inhibitor (with the same proportion as in Example 1) to the pore-filling component, with a total addition amount of 30% of the graphene mass. Mix cement, fine aggregate, water, and the composite modified liquid to form a mortar matrix, and use the heat of hydration to initiate secondary cross-linking. Finally, add the treated coarse aggregate, mix, and cast into shape. The water-cement ratio is controlled at 0.40.

[0041] Comparative example:

[0042] Comparative Example 1

[0043] Compared to Example 1, the difference lies in that no in-situ polymerization reaction is performed in step S1. Specifically, the reduced graphene oxide is directly dispersed in water without the addition of acrylic acid monomers and initiators, and only simple physical ultrasonic dispersion is performed. Then, it directly proceeds to step S2 for fractionation. The remaining raw material specifications and process steps are the same as in Example 1.

[0044] Comparative Example 2

[0045] Compared to Example 1, the difference lies in the omission of the centrifugal separation operation in step S2. Specifically, the modified graphene dispersion obtained in step S1 is ultrasonically treated, but without any centrifugal classification, the entire dispersion is directly used as a pore-filling component for slurry mixing in step S4; the coarse aggregate is only wetted with an equal amount of pure water in step S3, without being sprayed with the interface-reinforcing component containing large-sized graphene. Everything else is the same as in Example 1.

[0046] Comparative Example 3

[0047] Compared to Example 1, the difference lies in the omission of the dry powder flash setting and anchoring process in step S3. Specifically, after spraying the interface reinforcement component onto the surface of the coarse aggregate, dry cement powder is not sprayed in, nor is static curing performed. Instead, the moistened coarse aggregate is immediately added to the mortar matrix prepared in step S4 for final mixing. Everything else is the same as in Example 1.

[0048] Comparative Example 4

[0049] Compared to Example 1, the difference lies in that no composite corrosion inhibitor is added in step S4. Specifically, sodium pyrophosphate and sodium tripolyphosphate are not added to the pore-filling component; the mortar matrix is ​​prepared directly by mixing it with cement, fine aggregate, and water. Everything else is the same as in Example 1.

[0050] Comparative Example 5

[0051] Compared with Example 1, the difference is that after the reaction in step S1 is completed, the product is repeatedly centrifuged and washed to completely remove unreacted acrylic monomer residues, and then the washed modified graphene is redispersed for subsequent steps. Everything else is the same as in Example 1.

[0052] Test example:

[0053] Test Example 1: Mechanical Property Test

[0054] 1. Experiment Description

[0055] This test example is used to determine the 28-day compressive strength of the graphene concrete specimens prepared in each embodiment and comparative example. The experiment was conducted in accordance with the national standard GB / T50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0056] The specific steps are as follows:

[0057] S1. The fresh concrete slurry of Examples 1 to 3 and Comparative Examples 1 to 5 is poured into a standard cubic steel mold of 100mm×100mm×100mm, vibrated on a vibrating table to form the slurry, and the excess slurry on the surface is removed and smoothed.

[0058] S2. After the specimens have been molded for 24 hours, they are removed from the mold and immediately placed in a standard curing room for curing. Curing conditions are controlled as follows: temperature 20±2℃, relative humidity above 95%. Curing continues for up to 28 days.

[0059] S3. Remove the test block that has reached the curing age and wipe off the surface moisture. Use an electro-hydraulic servo universal pressure testing machine to test the compressive strength. Place the test block in the center of the pressure plate of the testing machine, start the testing machine, and apply a uniform and continuous load at a loading rate of 0.5 MPa / s until the test block fails. Record the maximum failure load F (unit: N).

[0060] S4. According to the formula Calculate the compressive strength (MPa), where A is the bearing area of ​​the test block (10000 mm²). 2 Each test group consists of 3 test blocks, and the results are taken as the arithmetic mean.

[0061] Experimental data

[0062] Table 1. Test results of 28-day compressive strength of graphene concrete in each group.

[0063] Group Average compressive strength after 28 days (MPa) Example 1 64.2 Example 2 57.8 Example 3 61.5 Comparative Example 1 41.3 Comparative Example 2 49.7 Comparative Example 3 46.2 Comparative Example 4 60.1 Comparative Example 5 59.4

[0064] Results Analysis

[0065] The compressive strength data of Examples 1 to 3 show that the mechanical properties of the concrete specimens obtained using the preparation process of this invention are in the range of 57.8 MPa to 64.2 MPa, significantly higher than the 41.3 MPa of Comparative Example 1. Comparative Example 1 did not undergo in-situ molecular brush grafting modification, resulting in graphene agglomeration in the cement matrix, leading to stress concentration points and reduced material strength. In contrast, the Example group grafted polyacrylic acid molecular brushes onto the graphene surface through in-situ polymerization. This molecular brush layer improved the dispersion stability of graphene in strongly alkaline pore liquids and enhanced the interfacial bonding force through chemical bonding with cement hydration products via carboxyl groups.

[0066] Comparing the data from Example 1 with Comparative Examples 2 and 3, it was found that the lack of fluid classification (Comparative Example 2) or the lack of interfacial flash anchoring (Comparative Example 3) both resulted in a significant decrease in compressive strength, to 49.7 MPa and 46.2 MPa, respectively. In Comparative Example 2, large-sized graphene was randomly distributed within the slurry, failing to concentrate on reinforcing the aggregate interface transition zone, and some large-sized sheets formed defects in the nanoscale gel pores. Although Comparative Example 3 underwent classification, it lacked a dry powder flash anchoring process, causing the large-sized graphene sprayed on the aggregate surface to be washed away by the slurry during subsequent stirring, failing to achieve the preset interfacial reinforcement distribution. Example 1, through classification, directionally transported large-sized graphene to the aggregate surface and physically fixed it through a semi-rigid hard shell formed by local hydration, effectively suppressing the propagation of microcracks in the interfacial transition zone.

[0067] Comparing the data from Example 1 and Comparative Example 5, the strength of Example 1 (64.2 MPa) is higher than that of Comparative Example 5 (59.4 MPa). Comparative Example 5, by cleaning away unreacted acrylic monomers, lacks the secondary crosslinking enhancement mechanism. Example 1 utilizes the heat of cement hydration to induce secondary in-situ crosslinking of residual monomers within the slurry. The resulting polymer network fills the micropores of the cement matrix and further helps to fix small-sized graphene sheets, improving the density and overall load-bearing capacity of the matrix.

[0068] Test Example 2: Conductivity Test

[0069] 1. Experiment Description

[0070] This test example is used to determine the 28-day volume resistivity of the graphene concrete specimens prepared in each embodiment and comparative example to evaluate the construction effect of the graphene conductive network.

[0071] The specific steps are as follows:

[0072] S1. Take concrete cube specimens (100mm×100mm×100mm) from the same batch as in Test Example 1, cured to 28 days. Place the specimens in a forced-air drying oven and dry them at 60℃ for 48 hours until constant weight to eliminate the interference of pore water on electrical conductivity;

[0073] S2. Remove the test block after it has cooled to room temperature and select two opposite molded sides as test surfaces. Apply a layer of conductive silver paste evenly to the test surfaces, and attach copper foil as a current collector while the silver paste is still wet, ensuring that the electrode is in close contact with the concrete surface and covers the entire side (100mm×100mm).

[0074] S3. The two-electrode method is used for testing. The positive and negative terminals of the high-precision digital insulation resistance tester are connected to the copper foil electrodes on both sides of the test block through wires.

[0075] S4. Apply a 20V DC voltage and wait for the reading to stabilize for 30 seconds before reading the resistance value. ;

[0076] S5. According to the formula Calculate volume resistivity ( ), where S is the electrode contact area (0.01m²). 2 L is the distance between the two electrodes (0.1m). Three test blocks were tested in each group, and the results were taken as the arithmetic mean.

[0077] 2. Experimental Data

[0078] Table 2. Volume resistivity test results of graphene concrete in each group after 28 days.

[0079] Group 28-day average volume resistivity ( ) Example 1 38.5 Example 2 45.2 Example 3 41.7 Comparative Example 1 286.4 Comparative Example 2 87.9 Comparative Example 3 102.3 Comparative Example 4 42.1 Comparative Example 5 58.6

[0080] 3. Results Analysis

[0081] Test data from Examples 1 to 3 show that its volume resistivity is 38.5%. Up to 45.2 The low value range indicates that an effective conductive pathway has been constructed within the material. In contrast, the volume resistivity of Comparative Example 1 is as high as 286.4. Comparative Example 1 lacked in-situ molecular brush grafting modification, resulting in strong van der Waals forces between graphene sheets. This led to severe agglomeration in the cement matrix, preventing the formation of continuous, interconnected electron transport pathways. The in-situ polymerization process used in this example introduced hydrophilic polyacrylic acid molecular brushes onto the graphene surface. Utilizing steric hindrance, uniform dispersion of graphene was achieved in the complex cement paste environment, thereby constructing a connected, conductive permeation network.

[0082] Comparing the data from Example 1 with Comparative Examples 2 and 3, the absence of fluid classification and interface anchoring processes resulted in a resistivity increase to 87.9%. And 102.3 In Comparative Example 2, the ungraded graphene was randomly distributed, and the large-sized sheets failed to specifically connect the aggregate spacing, while the filling efficiency of the small-sized sheets in the pores was also limited, resulting in a reduced overall conductivity probability. Although Comparative Example 3 was graded, the lack of a dry powder anchoring step caused the large-sized graphene to detach from the aggregate interface and re-incorporate into the matrix, disrupting the pre-designed aggregate-interface-matrix graded conductive structure. Example 1, through process control, achieved the directional overlapping of large-sized graphene on the aggregate surface and the filling of small-sized graphene in the slurry pores, forming a multi-scale synergistic conductive network.

[0083] Comparing the data from Example 1 and Comparative Example 5, the volume resistivity of Example 1 (38.5%) is lower. (58.6%) is lower than the comparative example 5. Comparative Example 5 removed unreacted acrylic monomers, while Example 1 utilized the heat of hydration to initiate secondary in-situ crosslinking of residual monomers around the graphene sheets and in the pores of the cement matrix. The resulting polymer network acts as a bridge at the microscale, improving the interfacial contact between graphene and the matrix, and the arrangement of polymer segments helps fix the spatial position of graphene, preventing microsegregation due to sedimentation or bleeding during hardening, thereby maintaining the stability and integrity of the conductive network.

[0084] Test Example 3: Durability and Stability Test

[0085] 1. Experiment Description

[0086] This test example uses a high-temperature strong alkali solution immersion method for accelerated aging experiments, aiming to determine the conductivity retention rate and compressive strength retention rate of each embodiment and comparative example specimen under simulated harsh chemical environment, in order to evaluate the long-term durability performance of graphene concrete.

[0087] The specific steps are as follows:

[0088] S1. Take 3 concrete cube specimens (100mm×100mm×100mm) from each group that have been cured to 28 days of age. Determine their initial compressive strength according to the methods in Test Example 1 and Test Example 2. And the initial volume resistivity, and calculate the initial conductivity ( / volume resistivity);

[0089] S2. Prepare a saturated calcium hydroxide solution and add 1% sodium hydroxide by mass to adjust the pH value to above 13.0 to simulate the highly alkaline environment of concrete pore fluid.

[0090] S3. Completely immerse the above test block in a stainless steel container filled with alkaline solution. Place the container in a constant temperature water bath, controlling the solution temperature to be maintained at 60±1℃. Set the continuous immersion period to 60 days. During this period, check the liquid level every 7 days and add deionized water in time to compensate for evaporation loss and maintain a stable solution concentration;

[0091] S4. After soaking, remove the test blocks, rinse off any residual alkali solution with running water, and dry the surface. Then, measure the compressive strength after aging again according to the same standard. And the volume resistivity after aging, and calculate the conductivity after aging. ;

[0092] S5, Strength retention rate (%) = ×100%;

[0093] Conductivity retention rate (%) = ×100% The arithmetic mean of the results for each group is taken.

[0094] 2. Experimental Data

[0095] Table 3 Performance retention rate of graphene concrete in each group after 60 days of accelerated aging

[0096] Group Conductivity retention rate (%) Strength retention rate (%) Example 1 94.2 96.5 Example 2 89.8 93.1 Example 3 92.5 95.4 Comparative Example 1 42.6 78.3 Comparative Example 2 81.4 88.7 Comparative Example 3 79.5 87.2 Comparative Example 4 53.8 85.6 Comparative Example 5 85.1 91.4

[0097] 3. Results Analysis

[0098] Examples 1 to 3 exhibited excellent performance stability after 60 days of accelerated aging with high temperature and strong alkali, maintaining conductivity between 89.8% and 94.2% and strength between 93.1% and 96.5%. This result demonstrates that the protective technology employed in this invention effectively resists the erosion of the graphene structure and matrix by the strong alkaline environment. In contrast, Comparative Example 1 showed a conductivity retention of only 42.6% and a strength retention of only 78.3%. Comparative Example 1 did not undergo in-situ polymerization modification; the exposed graphene was directly exposed to a high-concentration hydroxide ion environment, gradually destroying its sp2 hybrid carbon framework structure and causing the breakage of conductive pathways. Simultaneously, interface defects caused by poor dispersion further expanded during aging, leading to a significant decline in mechanical properties. The examples, through the in-situ polymerization of a polyacrylic acid molecular brush layer formed on the graphene surface, acted as the first physical barrier, effectively preventing direct contact between alkaline ions and the graphene lattice.

[0099] Comparing the data from Example 1 and Comparative Example 4, the conductivity retention rate of Comparative Example 4 significantly decreased to 53.8%, far lower than the 94.2% of Example 1. Comparative Example 4 did not add the sodium pyrophosphate and sodium tripolyphosphate composite corrosion inhibitor, lacking a chemical passivation mechanism. Under high-temperature alkaline conditions, high-energy defect sites at the edges of graphene are highly susceptible to oxidation. The free phosphate ions introduced in Example 1 can preferentially adsorb onto these active sites and react in situ with trace amounts of iron and aluminum ions precipitated in the slurry to form a stable phosphate chelate passivation film. This passivation film covers and repairs the structural defects of graphene, inhibiting the chemical corrosion reaction and thus ensuring the long-term stability of its conductivity.

[0100] Comparing the data of Example 1 and Comparative Example 5, the strength retention rate and conductivity retention rate of Comparative Example 5 were 91.4% and 85.1%, respectively, both slightly lower than those of Example 1. Comparative Example 5 removed residual monomers and failed to form a secondary cross-linked network. In Example 1, the polymer network generated using residual monomers further filled the micropores, reduced the permeability of the matrix, and decreased the channels for external corrosive media to enter the matrix, thereby macroscopically delaying the aging process of the material and improving overall durability.

[0101] Test Example 4: Density Test

[0102] 1. Experiment Description

[0103] This test case aims to determine the apparent porosity of the test blocks in each embodiment and comparative example, and to evaluate the optimization effect of the preparation process on the microstructure of the concrete matrix by quantifying the density of the micropore structure.

[0104] The specific steps are as follows:

[0105] S1. Take concrete cube specimens from each group that have been cured to 28 days of age, cut them into small specimens of 50mm×50mm×50mm, and take 3 specimens from each group. Place the specimens in an oven at 105±5℃ and dry them to constant weight. After removing them and cooling them to room temperature, weigh them and record the dried mass as follows. ;

[0106] S2. Place the dried sample in the container of the vacuum saturation apparatus, start the vacuum pump to evacuate to a residual pressure of less than 133 Pa, and maintain this negative pressure for 2 hours. Then, while maintaining the vacuum, inject deionized water until the sample is completely submerged. Return to normal pressure and allow the sample to soak in water for 24 hours to ensure that the pores are completely saturated with water.

[0107] S3. Remove the saturated sample, gently wipe the surface with a damp cloth to remove any adhering free water, and immediately weigh its saturated surface dry mass, recording it as follows. The sample was then placed in a mesh basket, and its suspended mass in water was measured and recorded as follows. ;

[0108] S4. Based on Archimedes' principle and formula Calculate the apparent porosity (%) by multiplying by 100%. Take the arithmetic mean of the results.

[0109] 2. Experimental Data

[0110] Table 4. Results of apparent porosity test of graphene concrete in each group after 28 days.

[0111] Group Average apparent porosity (%) Example 1 8.4 Example 2 9.6 Example 3 9.1 Comparative Example 1 14.7 Comparative Example 2 12.3 Comparative Example 3 11.9 Comparative Example 4 9.2 Comparative Example 5 10.5

[0112] 3. Results Analysis

[0113] The test results of Examples 1 to 3 show that their apparent porosity is controlled within a low range of 8.4% to 9.6%, significantly better than that of Comparative Example 1 (14.7%). In Comparative Example 1, uneven graphene dispersion led to agglomeration, which formed a loose, stacked structure in the matrix, hindering the normal hydration of cement and resulting in a large number of harmful pores around it. In contrast, the Example group utilized the small-sized and single-layer graphene sheets in the pore-filling components, fully leveraging their nanofiller effect. These fine graphene sheets can deeply fill the nanoscale pores between cement hydration products, not only refining the pore size distribution but also blocking the connectivity of capillary channels, thereby significantly reducing the overall porosity of the material.

[0114] Comparing the data from Example 1 with Comparative Examples 2 and 3, the lack of fluid fractionation (Comparative Example 2) resulted in a porosity increase of 12.3%, and the lack of interfacial anchoring (Comparative Example 3) resulted in a porosity increase of 11.9%. In Comparative Example 2, due to the elimination of centrifugal fractionation, larger graphene sheets were introduced into the mortar matrix. These large sheets could not effectively fill the fine gel pores and might even introduce new interfacial defects due to size mismatch. In Comparative Example 3, large graphene sheets that should have been fixed on the aggregate surface detached and entered the matrix, similarly causing inhomogeneity in the internal microstructure of the matrix and weakening the densification effect. Example 1, through a precise fractionation process, ensured that small-sized graphene was specifically used for filling matrix pores, achieving optimized microstructure gradation.

[0115] Comparing the data from Example 1 and Comparative Example 5, the porosity of Example 1 (8.4%) was significantly lower than that of Comparative Example 5 (10.5%). Comparative Example 5 removed unreacted acrylic monomer residues. Example 1 retained these monomers and utilized the heat of cement hydration to initiate in-situ secondary crosslinking polymerization within the slurry. The resulting polyacrylic acid polymer network interspersed between the cement hydration products, acting like glue to fill and heal the tiny voids that graphene could not completely cover, further enhancing the density of the matrix. This triple densification mechanism of inorganic gel + organic polymer + nanofiller collectively contributed to the excellent low porosity performance of Example 1.

Claims

1. A preparation process for graphene concrete, characterized in that, Includes the following steps: S1. After reducing graphene oxide, disperse it in water, add acrylic monomer and initiator, and carry out in-situ polymerization reaction to obtain a modified graphene dispersion with polyacrylic acid molecular brushes grafted on the surface. S2. The modified graphene dispersion obtained in step S1 is placed in an ultrasonic-centrifugal synergistic dispersion system and ultrasonically treated at a frequency of 20kHz and a power density of 0.5W / mL. Then, centrifugation is performed. The precipitate after centrifugation is collected as the interface enhancement component, and the supernatant after centrifugation is collected as the pore filling component. S3. Spray the interface reinforcement component onto the surface of the coarse aggregate in a rolling state, then spray 2% to 5% of dry cement powder into the surface of the coarse aggregate, tumble and stir and let stand to form a semi-rigid hard shell composed of cement hydration products on the surface of the coarse aggregate. S4. Sodium pyrophosphate and sodium tripolyphosphate are added to the pore-filling component, and the mass ratio of sodium pyrophosphate to sodium tripolyphosphate is 1:2 to prepare a composite modified liquid. Cement, fine aggregate, water and composite modified liquid are mixed and stirred to form a mortar matrix. Finally, the coarse aggregate treated in step S3 is added to the mortar matrix and mixed, and then poured to form graphene concrete.

2. The preparation process of graphene concrete according to claim 1, characterized in that, In the in-situ polymerization reaction described in step S1, the polymerization reaction time is controlled so that the thickness of the polyacrylic acid molecular brush on the surface of the modified graphene is 5 nm to 10 nm, and no cleaning or purification is performed after the reaction is completed, so that the unreacted acrylic acid monomer residues in the dispersion are retained.

3. The preparation process of graphene concrete according to claim 2, characterized in that, In the in-situ polymerization reaction described in step S1, the mass ratio of acrylic monomer to reduced graphene oxide is 10:1 to 20:1, the initiator is ammonium persulfate, and the amount of ammonium persulfate is 1.0% to 2.0% of the mass of acrylic monomer.

4. The preparation process of graphene concrete according to claim 1, characterized in that, The centrifugation in step S2 is a stepped centrifugation, and the specific process is as follows: First, the interface-enhancing component is separated by centrifugation at 3000 rpm to 5000 rpm for 10 to 20 minutes; then, the remaining liquid is separated by centrifugation at 8000 rpm to 10000 rpm for 20 to 30 minutes.

5. The preparation process of graphene concrete according to claim 1, characterized in that, The interface enhancement component described in step S3 is rich in large-size graphene sheets; The pore-filling component described in step S3 is rich in small-sized and monolayer graphene sheets.

6. The preparation process of graphene concrete according to claim 1, characterized in that, The tumbling and stirring time in step S3 is 30 to 60 seconds, and the settling time is 2 to 5 minutes. The water in the interface reinforcement component is used to initiate the hydration reaction of the dry cement powder to form the semi-rigid hard shell.

7. The preparation process of graphene concrete according to claim 1, characterized in that, In step S4, sodium pyrophosphate and sodium tripolyphosphate form a composite corrosion inhibitor, and the total amount of the composite corrosion inhibitor added is 20% to 30% of the mass of graphene.

8. The preparation process of graphene concrete according to claim 2, characterized in that, During the mixing and blending process described in step S4, the temperature of the slurry is monitored. The heat of hydration at 40°C to 60°C generated by cement hydration is used as a heat source to initiate a secondary crosslinking reaction between the acrylic monomer residue retained in step S1 and the cement matrix.

9. The preparation process of graphene concrete according to claim 1, characterized in that, Step S1 The graphene oxide has a monolayer ratio greater than 98% and a sheet diameter ranging from 0.5 micrometers to 5 micrometers; the reduction in step S1 uses hydrazine hydrate as a reducing agent, and the mass ratio of hydrazine hydrate to graphene oxide is 2:

1.

10. The preparation process of graphene concrete according to claim 1, characterized in that, The water-cement ratio of the graphene concrete described in step S4 is controlled to be 0.40; The coarse aggregate is continuously graded crushed stone with a particle size of 5 mm to 20 mm; the fine aggregate is natural river sand with a fineness modulus of 2.6 to 2.9.