Preparation method of concrete based on composite modification of graphene oxide and metakaolin

Abstract

The invention relates to the field of novel materials for civil engineering, and discloses a preparation method of concrete based on composite modification of graphene oxide and metakaolin, micro pores and cracks in the concrete are filled through doping of GO and MK, and the pore structure is refined, so that the impermeability of the concrete is greatly improved, and meanwhile, the water absorption rate of the concrete is reduced. GO and MK have a synergistic effect, so that the limitation of a single modified material is overcome, the filling effect improves the grain composition between gelling systems and the cement particle distribution of an interface region, optimizes the pore size distribution, and improves the compactness of the cement-based material.

Description

Technical Field

[0001] The invention relates to the field of new civil engineering materials, and in particular to a method for preparing concrete based on composite modification of graphene oxide and metakaolin. Background Art

[0002] In the field of concrete materials, it is an important research direction to continuously seek innovative modification methods to improve the performance of concrete. Cement-based materials are widely used around the world due to their excellent high compressive strength and relatively low cost. However, the annual carbon dioxide emissions caused by their production process account for a high proportion, which makes the construction industry urgently need to achieve rapid transformation to reduce the adverse impact on the environment.

[0003] Among them, auxiliary cementitious materials with volcanic ash activity, such as kaolin, slag, fly ash, silica fume, etc., are generally volcanic ash materials rich in alumina and silicate. By using these materials to partially replace cement, on the one hand, the strength, toughness and durability of cement-based composite materials can be enhanced, and on the other hand, the amount of cement used and carbon dioxide emissions can be reduced, thereby reducing energy consumption.

[0004] In recent years, highly effective pozzolanic materials such as metakaolin (MK) have been used as mineral admixtures to improve the strength and durability of cementitious materials. MK is an amorphous aluminosilicate material obtained by calcining kaolinite clay at a temperature range of 550 to 850 °C. During the heating process, most of the octahedral alumina content is converted into tetra- and penta-coordinated units, which are more active than octahedral alumina. During this process, the crystal structure or bonds between the kaolinite layers are partially or completely destroyed (i.e., the clay undergoes a phase transition process), resulting in amorphous MK. At ambient temperature, MK exhibits a very high pozzolanic activity, whereby silicates and aluminates react with the toxic hydration product calcium hydroxide to form more calcium silicate hydrate and calcium aluminate hydrate products, respectively.

[0005] Metakaolin can also be used as a filler, which is beneficial to the strength improvement of cement-based materials and cement mortars in the early stage of hydration (3-7 days), while its pozzolanic reactivity begins at 1 day (late hydration stage). In addition, metakaolin significantly enhances the ability of cement-based structures to resist sulfate attack and chloride penetration.

[0006] In addition, carbon nanomaterials, especially graphene and its derivative, graphene oxide (GO), play a key role in optimizing mechanical properties. As a material with volcanic ash activity, kaolin can improve the performance of cement-based materials, while graphene oxide brings new possibilities for concrete modification with its unique physical and chemical properties. The mechanism of action of composite modified concrete by graphene oxide and kaolin includes the filling effect. Both can fill the tiny pores and cracks in concrete and refine the pore structure; the volcanic ash reaction of kaolin can generate more cementitious products; the nucleation effect of kaolin can accelerate the cement hydration process; graphene oxide can optimize the interface transition zone and enhance the interface adhesion; both also regulate the cement hydration process through chemical bonding and physical adsorption, and produce a synergistic enhancement effect, significantly improving the strength, toughness and durability of concrete.

[0007] The composite modified concrete has broad application prospects. It can improve the performance of engineering structures and be applied to projects such as pavements, bridge decks, ports, etc. with high strength requirements; enhance durability, extend the service life of the project, and reduce maintenance costs; meet special engineering needs, such as waste solidification; be environmentally friendly, reduce cement consumption and carbon dioxide emissions; promote the development of related industries, and promote the transformation and upgrading of the graphene new material industry. However, there are still some problems that need to be solved in this technology, such as cost control, long-term performance monitoring, and quality stability of large-scale production. However, with the deepening of research and technological progress, these problems are expected to be solved, and its development potential and application value in the field of construction engineering are huge. my country's concrete market is huge, and related application examples have shown its advantages in wear resistance, impermeability, etc. Compared with traditional technologies, it has economic advantages and broad application prospects in the future. For this reason, we propose a concrete preparation method based on composite modification of graphene oxide and metakaolin. Summary of the invention

[0008] 1. Technical issues to be resolved

[0009] In view of the shortcomings of the prior art, the present invention provides a method for preparing concrete based on composite modification of graphene oxide and kaolin, and further improves various concrete properties by adding different amounts of graphene oxide and kaolin modification measures.

[0010] (II) Technical solution

[0011] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a method for preparing concrete based on composite modification of graphene oxide and metakaolin, comprising the following contents:

[0012] S1: When GO is added alone, weigh the GO required for the test into a beaker, add appropriate amount of admixture and water, and set the GO dosage to 0%, 0.005wt%, 0.01wt%, 0.015wt%, 0.02wt%, 0.025wt%, and 0.03wt% of the cementitious material. Perform the first stirring, weigh the dry materials required for the test, mix them evenly, and pour the mixture of GO and admixture in small amounts and multiple times. At the same time, use the remaining water to wash the beaker containing the GO-admixture mixture and pour it into the mixing pot. Mix and stir, pour out the concrete and measure the slump. After confirming that it meets the requirements, perform mold curing;

[0013] S2: When only MK is added, weigh the dry materials required for the test, set the MK dosage to 0wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, and 7wt% of the cementitious material, mix, and after the dry mixing is completed, add the admixture and water in small amounts and multiple times. After the admixture is added, use the remaining water to wash the beaker containing the admixture and pour it into the mixing pot together, mix and stir for 3 minutes. After the mixing is completed, pour out the concrete and measure the slump. After confirming that it meets the requirements, perform formwork maintenance;

[0014] S3: When GO-MK is added, the GO required for the test is weighed into a beaker, and appropriate amounts of admixtures and water are added for the first stirring. The GO dosage is 0.005wt%, 0.01wt% and 0.015wt% respectively. The dry materials and MK required for the test are weighed, and the MK dosage is 2wt%, 3wt% and 4wt% respectively. Place them in a concrete mixing pot and dry stir. After the GO and admixture are stirred, continue to stir the dry materials while pouring the mixture of GO and admixture in small amounts and multiple times. At the same time, use the remaining water to clean the beaker containing the GO-admixture mixture and pour it into the mixing pot. The mixing time is 3 minutes. After the stirring is completed, pour out the concrete and measure the slump. After confirming that it meets the requirements, perform mold curing.

[0015] Preferably, the first stirring condition in S1 and S3 is to start stirring at a rotation speed of 1000 rpm for 3 minutes in a cantilever electric stirrer.

[0016] Preferably, the GO content in the S1 is 0.01 wt%.

[0017] Preferably, the mixing condition in S2 is to place MK and dry materials together in a concrete mixing pot and stir for 1 minute to ensure that the dry materials are evenly mixed.

[0018] Preferably, the content of MK in the S2 is 3wt%.

[0019] Preferably, the GO content in the S3 is 0.01wt% and the MK content is 3wt%.

[0020] Preferably, the dry materials in S1, S2 and S3 are cement, sand, pebbles and large stones.

[0021] Preferably, the condition for measuring the slump in S1, S2 and S3 is whether it meets 180 mm ± 10 mm.

[0022] (III) Beneficial effects

[0023] Compared with the prior art, the present invention provides a method for preparing concrete based on composite modification of graphene oxide and metakaolin, which has the following beneficial effects:

[0024] 1. The concrete preparation method based on composite modification of graphene oxide and kaolin, in which kaolin is added in an appropriate amount to partially replace cement, makes full use of waste resources, reduces production energy consumption and carbon emissions, reduces environmental damage and pollution, and is a green and environmentally friendly material.

[0025] 2. The concrete preparation method based on the composite modification of graphene oxide and metakaolin. The metakaolin has volcanic ash activity, which can provide crystal nuclei for cement hydration products, accelerate the hydration process of cement, and promote the development of early strength of cement. During the hydration process, metakaolin will react with the cement hydration product calcium hydroxide to generate more gelling products, thereby enhancing the strength and durability of cement-based materials. It has unique advantages in promoting cement hydration.

[0026] 3. In the concrete preparation method based on composite modification of graphene oxide and kaolin, the addition of GO and MK can increase the mechanical properties of concrete, among which the early strength improvement is particularly significant, and the GO and MK composite group has the best improvement. Its compressive strength reaches 33.10MPa at 3d, which is 33.04% higher than that of the control group. At 28d, the compressive strength and flexural strength are 49.90MPa and 5.68MPa respectively, which are 21.13% and 19.33% higher than that of the control group.

[0027] 4. The preparation method of concrete based on composite modification of graphene oxide and metakaolin, the addition of GO and MK fills the tiny pores and cracks in the concrete, refines the pore structure, thereby greatly improving the anti-permeability of the concrete and reducing the water absorption of the concrete. GO and MK synergize to overcome the limitations of a single modified material. The filling effect improves the particle grading between the cementitious system and the distribution of cement particles in the interface area, optimizes the pore size distribution, and improves the density of cement-based materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of graphene oxide (GO);

[0029] Figure 2It is a schematic diagram of metakaolin (MK);

[0030] Figure 3 This is a schematic diagram of river sand particle size distribution;

[0031] Figure 4 This is a schematic diagram of the distribution of large stone particle size;

[0032] Figure 5 This is a schematic diagram of the distribution of small stone particle size;

[0033] Figure 6 Schematic diagram of compressive strength of GO modified concrete;

[0034] Figure 7 Schematic diagram of the improvement rate of compressive strength of GO modified concrete;

[0035] Figure 8 It is a schematic diagram of the compressive strength of MK modified concrete;

[0036] Fig. 9 This is a schematic diagram of the improvement rate of compressive strength of MK modified concrete;

[0037] Fig.10 Schematic diagram of compressive strength of GO-MK modified concrete;

[0038] Fig.11 Schematic diagram of the improvement rate of compressive strength of GO-MK modified concrete;

[0039] Fig.12 Schematic diagram of flexural strength of GO-MK modified concrete;

[0040] Fig.13 Schematic diagram of the improvement rate of flexural strength of GO-MK modified concrete;

[0041] Fig.14 Schematic diagram of the impermeability strength of GO-MK modified concrete;

[0042] Fig.15 Schematic diagram of the improvement rate of the anti-permeability strength of GO-MK modified concrete;

[0043] Fig.16 Schematic diagram of water absorption rate Wx of GO-MK modified concrete;

[0044] Fig.17 Schematic diagram of the water absorption reduction rate of GO-MK modified concrete. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] See also Figure 1-17 , a method for preparing concrete based on composite modification of graphene oxide and metakaolin, comprising the following contents:

[0047] When GO is added alone, weigh the GO required for the test into a beaker, add appropriate amount of admixture and water, place the beaker in a cantilever electric mixer and start stirring at 1000rpm for 3min. Weigh the dry materials (cement, sand, pebbles, and large stones) required for the test, place them in a concrete mixing pot and stir for 1min to ensure that the dry materials are evenly mixed. After the GO and admixture are mixed, continue to stir the dry materials, pour the mixture of GO and admixture in small amounts and multiple times, and at the same time, wash the beaker containing the GO-admixture mixture with the remaining water and pour it into the mixing pot. The mixing time is 3min. After the mixing is completed, pour out the concrete and measure whether the slump meets 180mm±10mm. After confirming that it meets the requirements, perform mold curing.

[0048] When adding MK alone, weigh the dry materials required for the test (cement, sand, small stones, large stones, MK), put them together in the concrete mixing pot and stir for 1 minute to ensure that the dry materials are evenly mixed. Use a beaker to weigh the required admixtures and water. After the dry stirring is completed, add the admixtures and water separately in small amounts and multiple times. After the admixtures are added, use the remaining water to wash the beaker containing the admixtures and pour them into the mixing pot together. Mix and stir for 3 minutes. After the stirring is completed, pour out the concrete and measure whether the slump meets 180mm±10mm. After confirming that it meets the requirements, perform mold curing.

[0049] When adding GO-MK, weigh the GO required for the test into a beaker, add appropriate amount of admixture and water, place the beaker in a cantilever electric mixer and start stirring at 1000rpm for 3min. Weigh the dry materials required for the test (cement, sand, pebbles, pebbles, MK), place them in a concrete mixing pot and stir for 1min to ensure that the dry materials are evenly mixed. After the GO and admixture are stirred, continue to stir the dry materials, pour the mixture of GO and admixture in small amounts and multiple times, and at the same time, wash the beaker containing the GO-admixture mixture with the remaining water and pour it into the mixing pot. The mixing time is 3min. After the stirring is completed, pour out the concrete and measure whether the slump meets 180mm±10mm. After confirming that it meets the requirements, perform mold curing.

[0050] Verification content:

[0051] Ordinary Portland cement is used. The specific chemical composition and performance parameters are shown in Table 3-1 and Table 3-2.

[0052] Table 1 Chemical composition of cement

[0053] <![CDATA[CL - ]]> MgO <![CDATA[SO3]]> <![CDATA[R2O]]> 0.01％ 2.50％ 2.37％ 0.53％

[0054] Table 2 Cement performance parameters

[0055]

[0056] The water reducer adopts slow-setting high-performance water reducer, and its technical parameters are shown in Table 3.

[0057] Table 3 Technical parameters of slow-setting high-performance water-reducing agent

[0058]

[0059]

[0060] Graphene oxide dispersion liquid is used. The technical parameters are shown in Table 4. The appearance is shown in Figure 1 .

[0061] Table 4 Technical parameters of graphene oxide dispersion

[0062]

[0063] The metakaolin uses high-activity metakaolin, and its technical parameters are shown in Table 5, and its appearance is shown in Figure 2 .

[0064] Table 5 Technical parameters of metakaolin

[0065]

[0066]

[0067] The detailed technical parameters of river sand are shown in Table 6, and the particle size distribution diagram is shown in Figure 3 shown.

[0068] Table 6 Technical parameters of river sand

[0069]

[0070] The coarse aggregate is continuously graded crushed stone with a grading range of 5-31.5 mm. The detailed technical parameters are shown in Table 7. The particle size distribution diagram is shown in Figure 4-Figure 5 shown.

[0071] Table 7 Technical parameters of continuously graded crushed stone

[0072]

[0073]

[0074] GO modified concrete test design scheme

[0075] By reading a lot of literature and conducting a lot of tests on GO with different proportions, it is found that the optimal GO content is mostly between 0wt% and 3wt% of the cementitious material. Too high a GO content will lead to a decrease in the performance of the specimen. Therefore, the GO content is set to 0%, 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, and 0.03% of the cementitious material. The specific test ratios are shown in Table 8.

[0076] Table 8 Effect of GO content on test mix ratio

[0077]

[0078] Table 9 shows the compressive strength of GO modified concrete. The strength development law is as follows: Figure 6-Figure 7 shown.

[0079] Table 9 Compressive strength of GO modified concrete

[0080]

[0081] In summary, when GO is added alone, the compressive strength is higher than that of the reference group (Ref) when the GO content ranges from 0.005wt% to 0.03wt%. It can be seen that GO uses its nano-scale size, high strength and large specific surface area to effectively fill the gaps in the cementitious material, enhance the density of the cementitious material, and significantly improve the compressive strength. When the GO content is 0.01wt%, the strength reaches the maximum value, and its 3d, 7d, and 28d compressive strengths are 29.03MPa, 36.50MPa, and 44.85MPa, respectively. Compared with Ref, the compressive strength is increased by 16.62%, 11%, and 8.87%. It can also be seen that the addition of GO can effectively improve the early compressive strength of concrete.

[0082] MK modified concrete test design scheme

[0083] By reading a lot of literature and conducting a lot of tests on GO with different proportions, it is found that the optimal GO content is mostly between 0wt% and 3wt% of the cementitious material. Too high a GO content will lead to a decrease in the performance of the specimen. Therefore, the MK content is set to 0wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, and 7wt% of the cementitious material. The specific test proportions are shown in Table 10.

[0084] Table 10 Effect of MK dosage on test mix ratio

[0085]

[0086] Table 11 shows the compressive strength of MK modified concrete. The strength development law is as follows: Figure 8-9 Shown

[0087] Table 11 Compressive strength of MK modified concrete

[0088]

[0089] In summary, when only MK is added, the compressive strength of concrete increases first and then decreases with the increase of MK content, and reaches the maximum value when the MK content is 1%. The compressive strengths at 3d, 7d and 28d are 30.64MPa, 39.07MPa and 47.36MPa, respectively. Compared with Ref, the compressive strengths are increased by 23.13%, 18.83% and 14.96%, respectively. When the MK content is too high, we find that its compressive strength is similar to that of the Ref group. The reason is that too high a content makes it difficult to effectively disperse MK particles, resulting in local MK agglomeration and affecting the internal integrity of concrete. Only a part of MK particles play a filling role, so the compressive strength is not significantly improved.

[0090] GO-MK modified concrete test design scheme

[0091] According to the experimental results of GO-modified concrete, adding graphene oxide can fill the pore space of concrete and strengthen its structure. However, due to its insufficient dispersibility, the potential of GO cannot be fully utilized. MK, as a material with a large specific surface area, is easy to adsorb with GO and improve the dispersibility of GO.

[0092] Based on the relevant research results, a series of preliminary experiments were conducted, and finally different GO dosages were determined to be 0.005wt%, 0.01wt% and 0.015wt%. According to the mix design (as shown in Table 12), GO-MK modified foam concrete with fluidity maintained between 180mm±10mm at different ages was prepared in the laboratory, put into the standard curing room for curing to the corresponding age and carried out the corresponding compressive strength test, as shown in Table 13.

[0093] Table 12 GO-MK modified concrete mix ratio

[0094]

[0095]

[0096] Table 13 Compressive strength of GO-MK modified concrete

[0097]

[0098]

[0099] When GO and MK were mixed, the 9 mixing ratios of GO-MK were divided into three groups according to the amount of MK added. Fig.11 We can see that the M2, M3 and M4 groups of G0.5 to G1.5 all show a trend of increasing first and then decreasing, indicating that the addition of MK and the adsorption of MK on GO successfully dispersed some of the agglomerated GO, causing its compressive strength to change periodically. The addition of too much GO broke the possible equilibrium ratio between GO and MK, making it impossible for the two to be completely dispersed, resulting in a downward trend in compressive strength. The curve with the largest compressive strength improvement rate appears at 3d, indicating that in the early stage of concrete curing, GO-MK began to react with the cement matrix to form new cementitious products, which improved the early compressive strength of concrete. The compressive strength at 28d increased compared with 3d and 7d, and there was an overall downward trend. This is because the addition of GO and MK has basically completed the hydration reaction of concrete at an early stage.

[0100] In the M2 group of G0.5-G1.5, when the GO content was 0.01wt%, the compressive strength of the 3d, 7d and 28d reached the maximum value, which were 31.74MPa, 39.3MPa and 48.28MPa, respectively, compared with the Ref group, the compressive strength increased by 27.56%, 19.75% and 17.18%. In the M3 group of G0.5-G1.5, when the GO content was 0.01wt%, the compressive strength of the 3d, 7d and 28d reached the maximum value, which were 33.10MPa, 41.5MPa and 49.90MPa, respectively, compared with the Ref group, the compressive strength increased by 33.04%, 26.41% and 21.13%. In the M4 group of G0.5-G1.5, when the GO content is 0.01wt%, its compressive strength at 3d, 7d, and 28d reaches the maximum value, which is 32.22MPa, 39.83MPa, and 48.48MPa, respectively. Compared with the Ref group, its compressive strength is increased by 29.49%, 21.14%, and 17.66%. Among them, the compressive strength of the M3 group of G0.5-G1.5 at three ages is the maximum among all groups, which echoes the G1 and M3 groups in the single GO and single MK groups.

[0101] Based on the above research and analysis of GO-MK modified concrete, the optimal compounding ratio of GO-MK modified concrete was determined to be 0.01wt% GO and 3wt% MK. Therefore, the Ref, G1, M3, and G1M3 groups were subjected to flexural strength tests and durability performance comparisons.

[0102] Study on flexural strength of GO-MK modified concrete

[0103] Table 14 Flexural strength of GO-MK modified concrete

[0104]

[0105] See also Figure 12-13 , the single addition of GO and MK can significantly improve the flexural strength of concrete, and its 28d flexural strength reaches 5.13MPa and 5.41MPa, respectively, which is 7.77% and 13.66% higher than that of Ref. This is because GO has a unique two-dimensional sheet structure and excellent physical and chemical properties. The functional groups rich in graphene oxide surface, such as hydroxyl, carboxyl and epoxy groups, can react chemically with calcium ions in cement hydration products to form strong chemical bonds. This chemical bonding enhances the interfacial adhesion between graphene oxide and cement matrix, allowing stress to be transmitted more effectively, and can better resist the expansion of cracks when subjected to bending loads, thereby improving the flexural properties of concrete; while MK has a highly active amorphous structure, and its volcanic ash activity can react rapidly with calcium hydroxide produced during cement hydration to generate more cementitious products, such as calcium sulfonate and CSH gel. These additionally generated cementitious substances fill the pores in concrete, refine the pore structure, make the concrete denser, and thus improve the flexural strength.

[0106] When GO-MK is co-doped, the flexural strength of concrete reaches a maximum value of 5.68MPa, which is 19.33% higher than that of Ref. This is because when GO-MK is co-doped, the two have a synergistic effect, promoting and complementing each other. When graphene oxide is added alone, it is easy to agglomerate and difficult to disperse due to its nanoscale and surface characteristics; when kaolin is added alone, the dispersibility is relatively good, but there may still be local unevenness. Through effective admixture assistance and appropriate mixing technology, kaolin particles can block the agglomeration of graphene oxide to a certain extent, promote its more uniform distribution in concrete, and further improve the flexural performance of concrete.

[0107] Study on the impermeability strength of GO-MK modified concrete

[0108] Table 15 GO-MK modified concrete impermeability

[0109]

[0110] Combined with Table 15 and Figure 14-15It can be seen that the addition of GO and MK can significantly improve the water penetration resistance of concrete. The water penetration resistance of the Ref group is 0.8MPa, and the water penetration resistance of the single GO group and the single MK group is 0.9MPa, which is 12.50% higher than that of the Ref group. The water penetration resistance of the GO-MK group is 1MPa, which is 25% higher than that of the Ref group. It can be seen that the effect of the compound group is much better than that of the single group. The reasons for this phenomenon are:

[0111] (1) Optimizing pore structure. The lamellar structure of graphene oxide can fill the tiny pores in concrete, and kaolin can also refine the pores. The combined effect of the two makes the pores inside the concrete smaller and more uniform, reducing the infiltration channels and thus improving the impermeability.

[0112] (2) Improve the interface transition zone. They can significantly improve the interface transition zone between cement paste and aggregate, enhance the interface adhesion, make the interface more compact, and hinder the penetration of water.

[0113] (3) Enhance cement hydration. The volcanic ash activity of kaolin can consume calcium hydroxide and generate more hydration products. Graphene oxide may affect the hydration process of cement, promote the formation of a denser hydration product structure, and reduce permeability.

[0114] (4) Micro-nano composite effect. The nanoscale of graphene oxide and the micron scale of kaolin combined to form a multi-level filling and barrier to further prevent water penetration.

[0115] (5) Improve the integrity of concrete. Compounding can enhance the integrity of the concrete's microstructure, reduce internal weak links, and make concrete less susceptible to penetration when subjected to water pressure.

[0116] Study on water absorption of GO-MK modified concrete

[0117] Table 16 Water absorption of GO-MK modified concrete

[0118]

[0119] As shown in Table 16 and Figure 16-Figure 17 As shown in the figure, when GO is added alone, the water absorption rate of concrete is 4.65%. Compared with the Ref group, the water absorption rate of the GO group dropped by 7.37%, which is because GO has excellent barrier properties and filling effects. When added to concrete alone, its nanosheet structure can fill the tiny pores and cracks inside the concrete, thereby blocking the channels for water penetration. This will significantly reduce the water absorption rate of concrete, making it more resistant to water penetration.

[0120] When MK was added alone, the water absorption of concrete was 4.70%. Compared with the Ref group, the water absorption of the MK group decreased by 6.37%. This is because MK has a high volcanic ash activity and can react secondary with calcium hydroxide in cement hydration products to generate more cementitious substances and refine the pore structure inside the concrete. However, compared with the GO group, the water absorption of the MK group was higher. This is because GO is a nano-scale material, and its lamellar structure can directly fill the tiny pores and cracks in the concrete. At the same time, GO can also form a physical barrier to prevent water penetration, while MK mainly generates new cementitious substances through chemical reactions to fill the pores of concrete. The reaction process may be unstable or unevenly dispersed, resulting in a slightly higher water absorption rate in the MK group than in the GO group. Therefore, the addition of metakaolin alone can also reduce the water absorption of concrete to a certain extent, but its effect is not as significant as that of GO alone.

[0121] When GO-MK is co-added, the water absorption rate of concrete is 3.84%. Compared with the Ref group, the water absorption rate of the co-added group decreased by 23.51%. When co-added, GO-MK can produce a synergistic effect. MK further optimizes the pore structure of concrete, while the nanosheet layer of GO more effectively fills and blocks tiny pores and channels. The two work together to make the internal structure of concrete denser, greatly reducing the space and channels for water to enter, thereby significantly reducing the water absorption rate of concrete, and its effect is usually better than adding GO or MK alone.

[0122] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing concrete based on composite modification of graphene oxide and metakaolin. It is characterized in that Includes the following: S1: When GO is added alone, weigh the GO required for the test into a beaker, add appropriate amount of admixture and water, and set the GO dosage to 0%, 0.005wt%, 0.01wt%, 0.015wt%, 0.02wt%, 0.025wt%, and 0.03wt% of the cementitious material. Perform the first stirring, weigh the dry materials required for the test, mix them evenly, and pour the mixture of GO and admixture in small amounts and multiple times. At the same time, use the remaining water to wash the beaker containing the GO-admixture mixture and pour it into the mixing pot. Mix and stir, pour out the concrete and measure the slump. After confirming that it meets the requirements, perform mold curing; S2: When only MK is added, weigh the dry materials required for the test, set the MK dosage to 0wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, and 7wt% of the cementitious material, mix, and after the dry mixing is completed, add the admixture and water in small amounts and multiple times. After the admixture is added, use the remaining water to wash the beaker containing the admixture and pour it into the mixing pot together, mix and stir for 3 minutes. After the mixing is completed, pour out the concrete and measure the slump. After confirming that it meets the requirements, perform formwork maintenance; S3: When GO-MK is added, the GO required for the test is weighed into a beaker, and appropriate amounts of admixtures and water are added for the first stirring. The GO dosage is 0.005wt%, 0.01wt% and 0.015wt% respectively. The dry materials and MK required for the test are weighed, and the MK dosage is 2wt%, 3wt% and 4wt% respectively. Place them in a concrete mixing pot and dry stir. After the GO and admixture are stirred, continue to stir the dry materials while pouring the mixture of GO and admixture in small amounts and multiple times. At the same time, use the remaining water to clean the beaker containing the GO-admixture mixture and pour it into the mixing pot. The mixing time is 3 minutes. After the stirring is completed, pour out the concrete and measure the slump. After confirming that it meets the requirements, perform mold curing.

2. The method for preparing concrete based on composite modification of graphene oxide and metakaolin according to claim 1, Features: The first stirring condition in S1 and S3 is to start stirring at a rotation speed of 1000 rpm for 3 minutes in a cantilever electric stirrer.

3. The method for preparing concrete based on composite modification of graphene oxide and metakaolin according to claim 1, Features: The GO content in the S1 is 0.01 wt%.

4. The method for preparing concrete based on composite modification of graphene oxide and metakaolin according to claim 1, Features: The mixing condition in S2 is to place MK and dry materials together in a concrete mixing pot and stir for 1 minute to ensure that the dry materials are evenly mixed.

5. The method for preparing concrete based on composite modification of graphene oxide and metakaolin according to claim 1, Features: The content of MK in the S2 is 3wt%.

6. The method for preparing concrete based on composite modification of graphene oxide and metakaolin according to claim 1, Features: The GO content of the S3 is 0.01 wt% and the MK content is 3 wt%.

7. The method for preparing concrete based on composite modification of graphene oxide and metakaolin according to claim 1, Features: The dry materials in S1, S2 and S3 are cement, sand, small stones and large stones.

8. The method for preparing concrete based on composite modification of graphene oxide and metakaolin according to claim 1, Features: The condition for measuring the slump in S1, S2 and S3 is whether it meets 180 mm ± 10 mm.

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