A high-strength concrete and its preparation method

Abstract

The present invention discloses a high-strength concrete and a preparation method thereof, belonging to the technical field of building materials. The concrete is made from the following raw materials in parts by weight: 50-80 parts of modified recycled coarse aggregate, 100-120 parts of fine aggregate, 160-200 parts of cement, 10-30 parts of fiber reinforcing agent, 5-8 parts of water reducing agent, and 180-200 parts of water; the fiber reinforcing agent is boron-titanium modified carbon fiber. The present invention uses the coarse aggregate obtained after the modification treatment of construction waste, and uses boron-titanium modified carbon fiber as the reinforcing agent. The two act synergistically to achieve the effect of enhancing the mechanical properties of the concrete, and at the same time improve the recycling rate of construction waste, having good economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a high-strength concrete and a preparation method thereof. Background Art

[0002] Concrete is one of the main materials in the construction industry and is also the backbone material of buildings. High-strength concrete refers to concrete with a strength grade of C60 and above. It is obtained by adding water-reducing agents to raw materials such as cement, sand, and stone, or by adding admixtures such as fly ash, slag powder, slag, and silica fume at the same time, and is produced by conventional processes to obtain high-strength concrete. As a new building material, high-strength concrete has been widely used in high-rise building structures, long-span bridge structures, and some special structures due to its advantages of high compressive strength, strong anti-deformation ability, high density, and low porosity. The biggest feature of high-strength concrete is its high compressive strength, which is generally 4-6 times that of ordinary-strength concrete. Therefore, the cross-section of components can be reduced, so it is most suitable for high-rise buildings.

[0003] In recent years, the construction industry, as one of the pillar industries of China's national economy, has always maintained rapid development, and the urbanization process has been accelerating. With the continuous increase of the urbanization process, more and more old communities and rural self-built houses have been demolished, resulting in a large amount of waste construction waste. The solid waste generated by demolishing buildings in China has exceeded two trillion tons per year, and this figure will continue to increase with the rapid development of the infrastructure construction industry. A large amount of waste concrete from building demolitions and unqualified concrete from commercial concrete plants are piled up on suburban open spaces, occupying a large amount of arable land and causing certain pollution to the environment. In terms of the resource utilization of construction waste, the resource utilization rate of construction waste in China is only 5%, far lower than 97% in South Korea. Therefore, the problem of resource utilization of construction waste needs to be solved urgently. The waste concrete after the demolition of buildings and structures is one of the difficult problems hindering the sustainable development of building materials. In the prior art, recycled aggregates are usually obtained by removing sundries such as steel bars from construction waste concrete and then mechanically crushing and screening. Compared with natural aggregates, the recycled aggregates obtained by this method have insufficient performance, such as low strength, many microcracks, low apparent density, high water absorption, etc., which makes recycled concrete inferior in performance such as compressive strength and durability, and to a certain extent limits the popularization and use of recycled concrete. Research has found that by modifying recycled aggregates, using nano-materials or high-quality mineral admixtures to pretreat recycled aggregates before use, the performance of recycled aggregates can be effectively improved, and the transition zone between cement paste and aggregates can be optimized, thereby improving the performance of recycled concrete. Although there are many methods for modifying recycled concrete aggregates at present, the mechanical properties, durability and stability of the concrete prepared by using modified recycled aggregates vary greatly. Therefore, there is an urgent need to develop a high-strength concrete with good stability and durability. Summary of the Invention

[0004] The object of the present invention is to provide a high-strength concrete, in which modified recycled coarse aggregate and boron-titanium modified carbon fiber reinforcing agent are used in combination, and the concrete prepared by mixing with other raw materials has excellent mechanical properties and good application prospects.

[0005] To achieve the above technical object, the technical solution adopted by the present invention is as follows:

[0006] A high-strength concrete is made from the following raw materials in parts by weight: 50-80 parts of modified recycled coarse aggregate, 100-120 parts of fine aggregate, 160-200 parts of cement, 10-30 parts of fiber reinforcing agent, 5-8 parts of water reducing agent, and 180-200 parts of water; the fiber reinforcing agent is boron-titanium modified carbon fiber.

[0007] Preferably, the particle size of the modified recycled coarse aggregate is 5-30 mm.

[0008] Preferably, the modified recycled coarse aggregate is prepared by the following method:

[0009] (a) After removing impurities from waste concrete blocks, they are placed in a muffle furnace, heated to 600 °C, calcined for 1 h, then naturally cooled to room temperature, and pulverized and ground to obtain pretreated recycled coarse aggregate;

[0010] (b) The pretreated recycled coarse aggregate is soaked in a modified silica sol solution, taken out after soaking for 6 h, and dried in an oven at 120 °C for 2 h to obtain the modified recycled coarse aggregate.

[0011] Preferably, the modified silica sol is prepared by the following method: Take 50 g of alkaline silica sol, magnetically stir at a rotation speed of 300 r / min while adding glacial acetic acid to adjust the pH value of the silica sol solution to 5.5, then add 14.5 g of dimethyldimethoxysilane thereto, adjust the rotation speed to 600 r / min, stir and react for 1 h, and then stand for 10 h to obtain the modified silica sol.

[0012] Preferably, the alkaline silica sol contains 30% of nano-silica, has a particle size of 50-80 nm, and a pH of 8-8.5.

[0013] Preferably, the boron-titanium modified carbon fiber is prepared by the following method:

[0014] (1) Put the carbon fiber into a vacuum furnace, set the vacuum degree at 0.05 Pa, then heat it to 500 °C and keep it warm for 2 h, and naturally cool it to obtain pretreated carbon fiber;

[0015] (2) Add 1 g of dopamine hydrochloride and 1.35 g of tris(hydroxymethyl)aminomethane to 1 L of deionized water to make a solution, then immerse the pretreated carbon fiber obtained in step (1) therein, take it out after 2 h, and dry it in an oven at 60 °C for 24 h to obtain carbon fiber coated with a carbon nanolayer;

[0016] (3) Mix 3 ml of absolute ethanol and 1 ml of deionized water, and adjust the pH of the solution to 3.0 with nitric acid to obtain a mixed solution A;

[0017] (4) Add 1 g of tetrabutyl titanate and 0.2 g of acetylacetone to 6 ml of absolute ethanol, and ultrasonically disperse for 5 min to obtain a mixed solution B;

[0018] (5) Slowly pour the mixed solution A into the mixed solution B under magnetic stirring, and then add 1.3 g of ammonium pentaborate thereto, and stir until completely dissolved to obtain a uniform sol solution;

[0019] (6) Immerse the carbon fiber coated with a carbon nanolayer obtained in step (2) in the sol obtained in step (5), after ultrasonic treatment for 10 - 15 min, take it out, dry it completely in an oven, and then transfer it to a vacuum furnace, heat it up to 1300 °C under 0.05 Pa, and keep it warm for 90 min to obtain boron-titanium modified carbon fiber.

[0020] Preferably, in step (1), the length of the carbon fiber is 5 - 10 mm.

[0021] Preferably, the fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:1.

[0022] Preferably, the water reducing agent is a polycarboxylate based superplasticizer.

[0023] The present invention also provides a method for preparing the above-mentioned high-strength concrete, which comprises the following steps:

[0024] (1) Prepare modified recycled coarse aggregate and fiber reinforcing agent respectively;

[0025] (2) Mix the modified recycled coarse aggregate, fine aggregate, cement, and water reducing agent evenly to obtain a mixed material;

[0026] (3) Stir water and the fiber reinforcing agent evenly with the mixed material to obtain concrete mortar; pour the mortar into a mold, demold it after molding, and cure it to obtain high-strength concrete.

[0027] The cement used in the present invention is ordinary Portland cement.

[0028] Due to its high specific surface energy, high activation, nucleation effect and other characteristics, nano-silica sol can significantly enhance the hydration activity and accelerate the hydration reaction rate after being incorporated into cement-based materials. Moreover, its extremely small nano-size enables it to physically fill the pores and cracks on the surface of recycled aggregates, thereby achieving the effect of enhancing the mechanical properties of concrete substrates. However, nano-silica sol with high specific surface energy is extremely prone to agglomeration. Excessive incorporation will still cause the strength of recycled aggregate concrete to only decrease but not increase. The key to improving the performance of recycled aggregate concrete with nano-silica sol is how to uniformly incorporate it into recycled aggregate concrete and how to select an appropriate dosage. In the present invention, dimethyldimethoxysilane is used to modify silica sol, which can enhance the stability and dispersibility of silica sol, prevent the agglomeration of silica sol. By soaking recycled coarse aggregates in the modified silica sol, nano-particles can better fill into the pores inside the aggregates, obtaining modified recycled coarse aggregates with a denser structure. At the same time, due to the enhanced hydrophobicity of the recycled coarse aggregates treated with modified silica sol, the water absorption rate of the modified recycled coarse aggregates can be significantly reduced, thus effectively preventing the occurrence of ion erosion caused by excessive water absorption and improving the durability of concrete.

[0029] The fiber reinforcing agent used in the present invention is boron-titanium modified carbon fiber. It forms a uniform carbon film on the surface of carbon fiber by coating with dopamine hydrochloride, and at the same time, a boron-titanium nano-layer prepared by the sol-gel method is uniformly coated on the surface of carbon fiber. Compared with the unmodified carbon fiber, the surface of the carbon fiber coated with the boron-titanium nano-layer is significantly smoother ( Figure 1 as shown). By utilizing the special surface energy of nano-materials, the interfacial binding energy between carbon fiber and other concrete materials is enhanced, which is conducive to forming a more stable concrete material. At the same time, the modified carbon fiber has characteristics such as high strength, high modulus, and high chemical stability, which can effectively improve the mechanical properties and durability of concrete. When the obtained boron-titanium modified carbon fiber is used in combination with the modified recycled coarse aggregates, it can effectively improve the bonding strength between old and new cement mortars and reduce the water absorption rate and porosity of recycled aggregates, thereby reducing the weak interfaces generated inside the concrete during the use of recycled aggregates. At the same time, boron-titanium modified carbon fiber can enhance the interfacial bonding force between carbon fiber and the concrete matrix, significantly improve the tensile strength, flexural strength and compressive strength of concrete, and improve the overall performance of concrete materials.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) The present invention uses waste construction waste to prepare modified recycled coarse aggregates, improving the utilization rate of construction waste and providing more channels for the resource utilization of construction waste, with good social, environmental and economic benefits.

[0032] (2) By combining modified recycled coarse aggregate with fiber reinforcing agent, the high-strength concrete prepared by mixing various raw materials has excellent mechanical properties, good impermeability and good durability, and has broad market application prospects. Description of the Drawings

[0033] Figure 1 It is the SEM image of the surface morphology before and after modification of the fiber reinforcing agent used in the present invention, wherein a) is carbon fiber before modification, and b) is boron-titanium modified carbon fiber after modification. Specific Embodiments

[0034] The technical solution of the present invention will be further described below in conjunction with specific embodiments, but not limited thereto.

[0035] Example 1

[0036] A high-strength concrete is made from the following raw materials in parts by weight: 50 kg of modified recycled coarse aggregate, 100 kg of fine aggregate, 160 kg of cement, 10 kg of fiber reinforcing agent, 5 kg of water reducing agent, and 180 kg of water; the fiber reinforcing agent is boron-titanium modified carbon fiber. The particle size of the modified recycled coarse aggregate is 5 - 30 mm.

[0037] The modified recycled coarse aggregate is prepared by the following method:

[0038] (a) After removing impurities from waste concrete blocks, they are placed in a muffle furnace, heated to 600 °C, calcined for 1 h, and then naturally cooled to room temperature. After pulverizing and grinding, pre-treated recycled coarse aggregate is obtained;

[0039] (b) The pre-treated recycled coarse aggregate is soaked in a modified silica sol solution, taken out after soaking for 6 h, and dried in an oven at 120 °C for 2 h to obtain the modified recycled coarse aggregate.

[0040] The modified silica sol is prepared by the following method: Take 50 g of alkaline silica sol, magnetically stir at a speed of 300 r / min while adding glacial acetic acid to adjust the pH value of the silica sol solution to 5.5, then add 14.5 g of dimethyldimethoxysilane to it, adjust the speed to 600 r / min and stir for 1 h, and then stand for 10 h to obtain the modified silica sol.

[0041] The alkaline silica sol contains 30% nano-silica, has a particle size of 50 - 80 nm, and a pH of 8 - 8.5.

[0042] The boron-titanium modified carbon fiber is prepared by the following method:

[0043] (1) Put the carbon fiber into a vacuum furnace, set the vacuum degree at 0.05 Pa, then heat it to 500 °C and keep it warm for 2 h, and naturally cool it to obtain pre-treated carbon fiber; the length of the carbon fiber is 5 - 10 mm;

[0044] (2) Add 1 g of dopamine hydrochloride and 1.35 g of tris(hydroxymethyl)aminomethane to 1 L of deionized water to make a solution, then immerse the pretreated carbon fiber obtained in step (1) therein, take it out after 2 h, and put it into an oven to dry at 60 °C for 24 h to obtain carbon fiber coated with a carbon nanolayer;

[0045] (3) Mix 3 ml of absolute ethanol and 1 ml of deionized water, and adjust the pH of the solution to 3.0 with nitric acid to obtain a mixed solution A;

[0046] (4) Add 1 g of tetrabutyl titanate and 0.2 g of acetylacetone to 6 ml of absolute ethanol, and ultrasonically disperse for 5 min to obtain a mixed solution B;

[0047] (5) Slowly pour the mixed solution A into the mixed solution B under magnetic stirring, and then add 1.3 g of ammonium pentaborate thereto, and stir until completely dissolved to obtain a uniform sol solution;

[0048] (6) Immerse the carbon fiber coated with a carbon nanolayer obtained in step (2) in the sol obtained in step (5), after ultrasonic treatment for 10 - 15 min, take it out, dry it completely in an oven, and then transfer it to a vacuum furnace, heat it up to 1300 °C under 0.05 Pa, and keep it warm for 90 min to obtain boron-titanium modified carbon fiber.

[0049] The fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:1.

[0050] The water reducing agent is a polycarboxylate-based high-performance water reducing agent.

[0051] The preparation method of the above high-strength concrete is as follows:

[0052] (1) Prepare modified recycled coarse aggregate and fiber reinforcement respectively;

[0053] (2) Mix the modified recycled coarse aggregate, fine aggregate, cement, and water reducing agent evenly to obtain a mixed material;

[0054] (3) Stir the water and fiber reinforcement evenly with the mixed material to obtain concrete mortar; pour the mortar into a mold, demold it after molding, and cure it to obtain high-strength concrete.

[0055] The cement used in this example is P.O 42.5 ordinary Portland cement of Shandong Linyi Yizhou Cement Co., Ltd.

[0056] Example 2

[0057] A high-strength concrete is made from the following raw materials in parts by weight: 80 kg of modified recycled coarse aggregate, 120 kg of fine aggregate, 200 kg of cement, 30 kg of fiber enhancer, 8 kg of water reducer, and 200 kg of water; the fiber enhancer is boron-titanium modified carbon fiber.

[0058] The particle size of the modified recycled coarse aggregate is 5 - 30 mm.

[0059] The modified recycled coarse aggregate is prepared by the following method:

[0060] (a) After removing impurities from waste concrete blocks, place them in a muffle furnace, heat to 600 °C, calcine for 1 h, then naturally cool to room temperature, and obtain pre-treated recycled coarse aggregate after pulverizing and grinding.

[0061] (b) Immerse the pre-treated recycled coarse aggregate in a modified silica sol solution, take it out after soaking for 6 h, and dry it in an oven at 120 °C for 2 h to obtain the modified recycled coarse aggregate.

[0062] The modified silica sol is prepared by the following method: Take 50 g of alkaline silica sol, magnetically stir at a speed of 300 r / min while adding glacial acetic acid to adjust the pH value of the silica sol solution to 5.5, then add 14.5 g of dimethyldimethoxysilane to it, adjust the speed to 600 r / min, stir and react for 1 h, and then stand for 10 h to obtain the modified silica sol.

[0063] The alkaline silica sol contains 30% nano-silica, has a particle size of 50 - 80 nm, and a pH of 8 - 8.5.

[0064] The boron-titanium modified carbon fiber is prepared by the following method:

[0065] (1) Put the carbon fiber into a vacuum furnace, set the vacuum degree at 0.05 Pa, then heat to 500 °C and keep it warm for 2 h, and obtain pre-treated carbon fiber after natural cooling; the length of the carbon fiber is 5 - 10 mm.

[0066] (2) Add 1 g of dopamine hydrochloride and 1.35 g of tris(hydroxymethyl)aminomethane to 1 L of deionized water to make a solution, then immerse the pre-treated carbon fiber obtained in step (1) into it, take it out after 2 h, and dry it in an oven at 60 °C for 24 h to obtain carbon fiber coated with a carbon nano-layer.

[0067] (3) Mix 3 ml of absolute ethanol and 1 ml of deionized water, and adjust the pH of the solution to 3.0 with nitric acid to obtain a mixed solution A.

[0068] (4) Add 1 g of tetrabutyl titanate and 0.2 g of acetylacetone to 6 ml of absolute ethanol, and ultrasonically disperse for 5 min to obtain a mixed solution B.

[0069] (5) Slowly pour the mixture A into the mixture B under magnetic stirring, and then add 1.3 g of ammonium pentaborate to it. After stirring until completely dissolved, a uniform sol solution is obtained.

[0070] (6) Immerse the carbon fiber layer-coated carbon fiber obtained in step (2) in the sol obtained in step (5). After ultrasonic treatment for 10 - 15 min, take it out, dry it completely in an oven, and then transfer it to a vacuum furnace. Heat it to 1300 °C under 0.05 Pa and keep it at this temperature for 90 min to obtain boron-titanium modified carbon fiber.

[0071] The fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:1.

[0072] The water reducing agent is a polycarboxylate-based high-performance water reducing agent.

[0073] The preparation method of the above high-strength concrete is as follows:

[0074] (1) Prepare modified recycled coarse aggregate and fiber reinforcing agent respectively;

[0075] (2) Mix the modified recycled coarse aggregate, fine aggregate, cement, and water reducing agent evenly to obtain a mixed material;

[0076] (3) Stir the water and fiber reinforcing agent evenly with the mixed material to obtain concrete mortar; pour the mortar into a mold, demold it after molding, and obtain high-strength concrete after curing.

[0077] The cement used in this example is P.O 42.5 ordinary Portland cement from Shandong Linyi Yizhou Cement Co., Ltd.

[0078] Example 3

[0079] A kind of high-strength concrete is made from the following raw materials in parts by weight: 70 kg of modified recycled coarse aggregate, 110 kg of fine aggregate, 180 kg of cement, 20 kg of fiber reinforcing agent, 7 kg of water reducing agent, and 190 kg of water; the fiber reinforcing agent is boron-titanium modified carbon fiber.

[0080] The particle size of the modified recycled coarse aggregate is 5 - 30 mm.

[0081] The modified recycled coarse aggregate is prepared by the following method:

[0082] (a) Remove impurities from the waste concrete blocks, place them in a muffle furnace, heat them to 600 °C, calcine for 1 h, then naturally cool to room temperature, and obtain pre-treated recycled coarse aggregate after crushing and grinding;

[0083] (b) Immerse the pre-treated recycled coarse aggregate in the modified silica sol solution, take it out after soaking for 6 h, and dry it at 120 °C in an oven for 2 h to obtain the modified recycled coarse aggregate.

[0084] The modified silica sol is prepared by the following method: Take 50 g of alkaline silica sol, magnetically stir at a rotation speed of 300 r / min while adding glacial acetic acid to adjust the pH value of the silica sol solution to 5.5, then add 14.5 g of dimethyldimethoxysilane thereto, adjust the rotation speed to 600 r / min, stir and react for 1 h, and then stand for 10 h to obtain the modified silica sol.

[0085] The alkaline silica sol contains 30% of nano-silica, has a particle size of 50 - 80 nm, and a pH of 8 - 8.5.

[0086] The boron-titanium modified carbon fiber is prepared by the following method:

[0087] (1) Put the carbon fiber into a vacuum furnace, set the vacuum degree at 0.05 Pa, then heat it to 500 °C and keep it warm for 2 h, and naturally cool it to obtain the pretreated carbon fiber; the length of the carbon fiber is 5 - 10 mm;

[0088] (2) Add 1 g of hydrochloric acid dopamine and 1.35 g of tris(hydroxymethyl)aminomethane to 1 L of deionized water to make a solution, then immerse the pretreated carbon fiber obtained in step (1) therein, take it out after 2 h, and put it into an oven to dry at 60 °C for 24 h to obtain the carbon fiber coated with a carbon nano-layer;

[0089] (3) Mix 3 ml of absolute ethanol and 1 ml of deionized water, and adjust the pH of the solution to 3.0 with nitric acid to obtain a mixed solution A;

[0090] (4) Add 1 g of tetrabutyl titanate and 0.2 g of acetylacetone to 6 ml of absolute ethanol, and ultrasonically disperse for 5 min to obtain a mixed solution B;

[0091] (5) Slowly pour the mixed solution A into the mixed solution B under magnetic stirring, and then add 1.3 g of ammonium pentaborate thereto, and stir until completely dissolved to obtain a uniform sol solution;

[0092] (6) Immerse the carbon fiber coated with a carbon nano-layer obtained in step (2) in the sol obtained in step (5), ultrasonically treat for 10 - 15 min, take it out, dry it completely in an oven, then transfer it to a vacuum furnace, heat it to 1300 °C under 0.05 Pa, and keep it warm for 90 min to obtain the boron-titanium modified carbon fiber.

[0093] The fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:1.

[0094] The water reducer is a polycarboxylate-based high-performance water reducer.

[0095] The preparation method of the above high-strength concrete is as follows:

[0096] (1) Prepare modified recycled coarse aggregate and fiber reinforcing agent respectively;

[0097] (2) Mix the modified recycled coarse aggregate, fine aggregate, cement and water reducing agent evenly to obtain a mixed material;

[0098] (3) Stir water and fiber reinforcing agent evenly with the mixed material to obtain concrete mortar; Pour the mortar into a mold, demold after molding, and obtain high-strength concrete after curing.

[0099] The cement used in this example is P.O 42.5 ordinary Portland cement of Shandong Linyi Yizhou Cement Co., Ltd.

[0100] Comparative Example 1

[0101] A kind of high-strength concrete is made from the following raw materials in parts by weight: 70 kg of modified recycled coarse aggregate, 110 kg of fine aggregate, 180 kg of cement, 20 kg of fiber reinforcing agent, 7 kg of water reducing agent, 190 kg of water; The fiber reinforcing agent is boron-titanium modified carbon fiber.

[0102] The particle size of the modified recycled coarse aggregate is 5 - 30 mm.

[0103] The modified recycled coarse aggregate is prepared by the following method:

[0104] (a) Remove impurities from waste concrete blocks, place them in a muffle furnace, heat to 600 °C, calcine for 1 h, then cool naturally to room temperature, and obtain pretreated recycled coarse aggregate after crushing and grinding;

[0105] (b) Immerse the pretreated recycled coarse aggregate in an alkaline silica sol solution, take it out after soaking for 6 h, and dry it in an oven at 120 °C for 2 h to obtain the modified recycled coarse aggregate.

[0106] The alkaline silica sol contains 30% nano-silica, has a particle size of 50 - 80 nm, and a pH of 8 - 8.5.

[0107] The boron-titanium modified carbon fiber is prepared by the following method:

[0108] (1) Put the carbon fiber into a vacuum furnace, set the vacuum degree at 0.05 Pa, then heat up to 500 °C and keep it warm for 2 h, and obtain pretreated carbon fiber after natural cooling; The length of the carbon fiber is 5 - 10 mm;

[0109] (2) Add 1 g of hydrochloric acid dopamine and 1.35 g of tris(hydroxymethyl)aminomethane to 1 L of deionized water to make a solution, then immerse the pretreated carbon fiber obtained in step (1) into it, take it out after 2 h, and dry it in an oven at 60 °C for 24 h to obtain carbon nanofiber-coated carbon fiber;

[0110] (3) Mix 3 ml of absolute ethanol with 1 ml of deionized water, and adjust the pH of the solution to 3.0 with nitric acid to obtain a mixed solution A;

[0111] (4) Add 1 g of tetrabutyl titanate and 0.2 g of acetylacetone to 6 ml of absolute ethanol, and ultrasonically disperse for 5 min to obtain a mixed solution B;

[0112] (5) Slowly pour the mixed solution A into the mixed solution B under magnetic stirring, and then add 1.3 g of ammonium pentaborate to it. After stirring until completely dissolved, a uniform sol solution is obtained;

[0113] (6) Immerse the carbon nanofiber-coated carbon fiber obtained in step (2) in the sol obtained in step (5). After ultrasonic treatment for 10 - 15 min, take it out, dry it completely in an oven, and then transfer it to a vacuum furnace. Heat it to 1300 °C under 0.05 Pa, and keep it warm for 90 min to obtain boron-titanium modified carbon fiber.

[0114] The fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:1.

[0115] The water reducer is a polycarboxylate-based superplasticizer.

[0116] The preparation method of the above high-strength concrete is as follows:

[0117] (1) Prepare modified recycled coarse aggregate and fiber reinforcement respectively;

[0118] (2) Mix the modified recycled coarse aggregate, fine aggregate, cement, and water reducer evenly to obtain a mixed material;

[0119] (3) Stir the water and fiber reinforcement evenly with the mixed material to obtain concrete mortar; pour the mortar into a mold, demold it after molding, and obtain high-strength concrete after curing.

[0120] The cement used in this comparative example is P.O 42.5 ordinary Portland cement from Shandong Linyi Yizhou Cement Co., Ltd.

[0121] This comparative example is the same as Example 3 except that unmodified silica sol is used in the preparation process of the modified recycled coarse aggregate.

[0122] Comparative Example 2

[0123] A kind of high-strength concrete is made from the following raw materials in parts by weight: 70 kg of modified recycled coarse aggregate, 110 kg of fine aggregate, 180 kg of cement, 20 kg of fiber reinforcement, 7 kg of water reducer, and 190 kg of water; the fiber reinforcement is carbon fiber; the length of the carbon fiber is 5 - 10 mm.

[0124] The particle size of the modified recycled coarse aggregate is 5 - 30 mm.

[0125] The modified recycled coarse aggregate is prepared by the following method:

[0126] (a) After removing impurities from waste concrete blocks, they are placed in a muffle furnace, heated to 600 °C, calcined for 1 h, then naturally cooled to room temperature, and pulverized and ground to obtain pretreated recycled coarse aggregate;

[0127] (b) The pretreated recycled coarse aggregate is soaked in a modified silica sol solution, taken out after soaking for 6 h, and dried in an oven at 120 °C for 2 h to obtain the modified recycled coarse aggregate.

[0128] The modified silica sol is prepared by the following method: Take 50 g of alkaline silica sol, magnetically stir at a speed of 300 r / min while adding glacial acetic acid to adjust the pH value of the silica sol solution to 5.5, then add 14.5 g of dimethyldimethoxysilane to it, adjust the speed to 600 r / min, stir and react for 1 h, and then stand for 10 h to obtain the modified silica sol.

[0129] The alkaline silica sol contains 30% nano-silica, has a particle size of 50 - 80 nm, and a pH of 8 - 8.5.

[0130] The fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:1.

[0131] The water reducer is a polycarboxylate-based superplasticizer.

[0132] The preparation method of the above high-strength concrete is as follows:

[0133] (1) Prepare the modified recycled coarse aggregate and the fiber reinforcing agent respectively;

[0134] (2) Mix the modified recycled coarse aggregate, fine aggregate, cement, and water reducer evenly to obtain a mixed material;

[0135] (3) Stir water and the fiber reinforcing agent evenly with the mixed material to obtain concrete mortar; Pour the mortar into a mold, demold after forming, and cure to obtain high-strength concrete.

[0136] The cement used in this example is P.O 42.5 ordinary Portland cement from Shandong Linyi Yizhou Cement Co., Ltd.

[0137] This comparative example is the same as Example 3 except that the fiber reinforcing agent is carbon fiber.

[0138] Comparative Example 3

[0139] A kind of high-strength concrete is made from the following raw materials in parts by weight: 70 kg of recycled coarse aggregate, 110 kg of fine aggregate, 180 kg of cement, 20 kg of fiber reinforcing agent, 7 kg of water reducer, and 190 kg of water; The fiber reinforcing agent is boron-titanium modified carbon fiber.

[0140] The particle size of the recycled coarse aggregate is 5 - 30 mm.

[0141] The recycled coarse aggregate is prepared by the following method: After removing impurities from waste concrete blocks, they are placed in a muffle furnace, heated to 600 °C, calcined for 1 h, then naturally cooled to room temperature, and obtained after pulverizing and grinding.

[0142] The boron-titanium modified carbon fiber is prepared by the following method:

[0143] (1) Put the carbon fiber into a vacuum furnace, set the vacuum degree at 0.05 Pa, then heat it to 500 °C and keep it warm for 2 h, and obtain the pretreated carbon fiber after natural cooling; the length of the carbon fiber is 5 - 10 mm.

[0144] (2) Add 1 g of dopamine hydrochloride and 1.35 g of tris(hydroxymethyl)aminomethane to 1 L of deionized water to make a solution, then immerse the pretreated carbon fiber obtained in step (1) in it, take it out after 2 h, and put it into an oven to dry at 60 °C for 24 h to obtain the carbon fiber coated with a carbon nanolayer;

[0145] (3) Mix 3 ml of absolute ethanol and 1 ml of deionized water, and adjust the pH of the solution to 3.0 with nitric acid to obtain a mixed solution A;

[0146] (4) Add 1 g of tetrabutyl titanate and 0.2 g of acetylacetone to 6 ml of absolute ethanol, and ultrasonically disperse for 5 min to obtain a mixed solution B;

[0147] (5) Slowly pour the mixed solution A into the mixed solution B under magnetic stirring, then add 1.3 g of ammonium pentaborate to it, and stir until completely dissolved to obtain a uniform sol solution;

[0148] (6) Immerse the carbon fiber coated with a carbon nanolayer obtained in step (2) in the sol obtained in step (5), after ultrasonic treatment for 10 - 15 min, take it out, dry it completely in an oven, then transfer it to a vacuum furnace, heat it to 1300 °C at 0.05 Pa, and keep it warm for 90 min to obtain the boron-titanium modified carbon fiber.

[0149] The fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:1.

[0150] The water reducing agent is a polycarboxylate-based superplasticizer.

[0151] The preparation method of the above high-strength concrete is as follows:

[0152] (1) Prepare the recycled coarse aggregate and the fiber reinforcing agent respectively;

[0153] (2) Mix the recycled coarse aggregate, fine aggregate, cement, and water reducing agent evenly to obtain a mixed material;

[0154] (3) Stir water and fiber reinforcement evenly with the mixed materials to obtain concrete mortar; pour the mortar into a mold, demold after molding, and obtain high-strength concrete after curing.

[0155] The cement used in this example is P.O 42.5 ordinary Portland cement from Shandong Linyi Yizhou Cement Co., Ltd.

[0156] Except that the modified recycled coarse aggregate and the preparation method are replaced with recycled coarse aggregate and the preparation method, other aspects are the same as in Example 3 in this comparative example.

[0157] Comparative Example 4

[0158] A kind of high-strength concrete is made from the following raw materials in parts by weight: 70 kg of recycled coarse aggregate, 110 kg of fine aggregate, 180 kg of cement, 20 kg of fiber reinforcement, 7 kg of water reducer, and 190 kg of water; the fiber reinforcement is carbon fiber; the length of the carbon fiber is 5 - 10 mm. The particle size of the recycled coarse aggregate is 5 - 30 mm.

[0159] The recycled coarse aggregate is prepared by the following method: Remove impurities from waste concrete blocks, place them in a muffle furnace, heat to 600 °C, calcine for 1 h, then cool naturally to room temperature, and obtain it after crushing and grinding.

[0160] The fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:1.

[0161] The water reducer is a polycarboxylate-based superplasticizer.

[0162] The preparation method of the above high-strength concrete is as follows:

[0163] (1) Prepare recycled coarse aggregate and fiber reinforcement respectively;

[0164] (2) Mix the recycled coarse aggregate, fine aggregate, cement, and water reducer evenly to obtain a mixed material;

[0165] (3) Stir water and fiber reinforcement evenly with the mixed material to obtain concrete mortar; pour the mortar into a mold, demold after molding, and obtain high-strength concrete after curing.

[0166] The cement used in this example is P.O 42.5 ordinary Portland cement from Shandong Linyi Yizhou Cement Co., Ltd.

[0167] Except that unmodified silica sol is used in the preparation process of the modified recycled coarse aggregate in this comparative example, other aspects are the same as in Example 3.

[0168] Performance test

[0169] The high-strength concrete prepared in Examples 1-3 and Comparative Examples 1-4 was cured for 28 days under the same temperature and humidity conditions, and then the mechanical properties were tested. The specific test method refers to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019); the freeze-thaw test of concrete was carried out according to the rapid freeze-thaw method in the "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082-2009), and the mass loss rate and compressive strength of the concrete specimens after 400 cycles of freeze-thaw were tested respectively. The results are shown in Table 1 below.

[0170] Table 1 Performance test results

[0171]

[0172] It can be seen from the data in Table 1 above that the compressive strength, flexural strength, splitting tensile strength, impermeability grade and freeze-thaw resistance of the high-strength concrete prepared by the present invention are significantly better than those of Comparative Examples 1-4. This shows that the raw material components in the high-strength concrete of the present invention interact with each other, and the nanoparticles in the modified recycled aggregate can better fill the pores inside the aggregate, obtaining a modified recycled coarse aggregate with a denser structure; and the hydrophobicity of the modified recycled coarse aggregate is enhanced, which can significantly reduce the water absorption rate of the modified recycled coarse aggregate, thus effectively preventing the occurrence of ion erosion caused by excessive water absorption, and improving the durability of the concrete. Combining the modified recycled coarse aggregate with boron-titanium modified carbon fiber and then mixing with other raw materials can prepare high-strength concrete with good performance. Changing any one of the raw material compositions or dosages in the raw material formula cannot achieve the same technical effect.

[0173] It should be noted that the above-mentioned embodiments are only some of the preferred embodiments for implementing the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A high-strength concrete, characterized in that: It is made of the following raw materials in parts by weight: 50-80 parts of modified recycled coarse aggregate, 100-120 parts of fine aggregate, 160-200 parts of cement, 10-30 parts of fiber reinforcing agent, 5-8 parts of water reducing agent, and 180-200 parts of water; the fiber reinforcing agent is boron-titanium modified carbon fiber; The boron-titanium modified carbon fiber is prepared by the following method: (1) placing carbon fibers with a length of 5 to 10 mm in a vacuum furnace, setting the vacuum degree at 0.05 Pa, then heating to 500 ° C and keeping the temperature for 2 h, and naturally cooling to obtain pretreated carbon fibers; (2) adding 1 g of dopamine hydrochloride and 1.35 g of tris(hydroxymethyl)aminomethane to 1 L of deionized water to prepare a solution, and then immersing the pretreated carbon fiber obtained in step (1) therein, taking it out after 2 hours, and placing it in an oven at 60° C. and drying it for 24 hours to obtain a carbon nanolayer-coated carbon fiber; (3) Mix 3 ml of anhydrous ethanol and 1 ml of deionized water, and adjust the pH of the solution to 3.0 with nitric acid to obtain a mixed solution A; (4) 1 g of tetrabutyl titanate and 0.2 g of acetylacetone were added to 6 ml of anhydrous ethanol and ultrasonically dispersed for 5 min to obtain a mixed solution B; (5) Slowly pouring the mixed solution A into the mixed solution B under magnetic stirring, then adding 1.3 g of ammonium pentaborate thereto, stirring until completely dissolved to obtain a uniform sol solution; (6) soaking the carbon fiber coated with the carbon nanolayer obtained in step (2) in the sol obtained in step (5), ultrasonically treating for 10-15 minutes, taking out, drying completely in an oven, and then transferring to a vacuum furnace, heating to 1300° C. at 0.05 Pa, and keeping the temperature for 90 minutes to obtain boron-titanium modified carbon fiber; The modified recycled coarse aggregate is prepared by the following method: (a) removing debris from the waste concrete blocks, heating them to 600° C. in a muffle furnace, calcining them for 1 hour, then naturally cooling them to room temperature, and crushing and grinding them to obtain pretreated recycled coarse aggregate; (b) The pretreated recycled coarse aggregate is soaked in the modified silica sol solution for 6 hours, taken out, and dried in an oven at 120° C. for 2 hours to obtain the modified recycled coarse aggregate.

2. The high-strength concrete according to claim 1, characterized in that: The modified recycled coarse aggregate has a particle size of 5-30 mm.

3. The high-strength concrete according to claim 1, characterized in that: The modified silica sol is prepared by the following method: 50 g of alkaline silica sol is taken, and glacial acetic acid is added while magnetically stirring at a speed of 300 r / min to adjust the pH value of the silica sol solution to 5.5, and then 14.5 g of dimethyldimethoxysilane is added thereto, and the speed is adjusted to 600 r / min, and the stirring reaction is carried out for 1 hour, and then the modified silica sol is allowed to stand for 10 hours to obtain the modified silica sol.

4. The high-strength concrete according to claim 3, characterized in that: The alkaline silica sol has a nano-silicon dioxide content of 30%, a particle size of 50-80 nm, and a pH of 8-8.

5.

5. The high-strength concrete according to claim 1, characterized in that: The fine aggregate is composed of machine-made river sand and slag in a mass ratio of 1:

1.

6. The high-strength concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid-based high-efficiency water reducing agent.

7. A method for preparing high-strength concrete according to any one of claims 1 to 6, characterized in that: It includes the following steps: (1) preparing modified recycled coarse aggregate and fiber reinforcement respectively; (2) uniformly mixing the modified recycled coarse aggregate, fine aggregate, cement, and water reducing agent to obtain a mixed material; (3) Mixing water and a fiber reinforcement agent with the mixed material to obtain concrete mortar; pouring the mortar into a mold, demolding after molding, and obtaining high-strength concrete after curing.

Images