A Yellow River ultrafine sand-based high-performance concrete and its preparation method

Abstract

The application belongs to the technical field of building materials, and relates to a high-performance concrete based on Yellow River superfine sand and a preparation method thereof. According to weight parts, the high-performance concrete comprises the following components: cement 161-294 parts, circulating fluidized bed fly ash 30-60 parts, mineral powder 83-132 parts, Yellow River superfine sand 270-870 parts, machine-made sand 270-870 parts, stone 640-680 parts, CNTs-SAL composite shrinkage and cracking reducing agent 2-4 parts, water reducing agent 10-30 parts, and water 160-170 parts. The Yellow River superfine sand is used as a raw material to prepare the high-performance concrete, realizing resource utilization of the Yellow River superfine sand accumulated in the lower reaches of the Yellow River. The Yellow River superfine sand has a round particle shape and a small particle size, can form a good grading complement with other aggregates and powder components, reduces the overall porosity of the concrete, improves the workability of the concrete mixture, and improves the compactness and impermeability of the concrete.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and in particular relates to a high-performance concrete based on ultrafine sand from the Yellow River and its preparation method. Background Technology

[0002] The Yellow River flows through the Loess Plateau region, carrying a large amount of ultrafine sand. The treatment of this ultrafine sand occupies a significant amount of arable land and has a substantial impact on the ecological environment and residents of the Yellow River basin. However, the utilization potential of the Yellow River's ultrafine sand cannot be ignored. Employing appropriate technologies for the resource utilization of this sand is beneficial for river silt management and the regeneration of Yellow River ultrafine sand resources, yielding significant social and economic benefits.

[0003] Due to the severe scarcity of natural sand and gravel resources and their continuously rising costs, the concrete industry has begun to explore and apply Yellow River ultrafine sand. However, when using Yellow River ultrafine sand to prepare concrete, its high fineness and large specific surface area lead to the absorption of more water, resulting in a high water-cement ratio. Simultaneously, its high fineness accelerates the hydration rate of concrete, causing significant early shrinkage. Therefore, the use of Yellow River ultrafine sand to prepare a high-performance concrete with low early shrinkage is urgently needed.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The first objective of this invention is to provide a high-performance concrete based on Yellow River ultrafine sand, which uses a composite of Yellow River ultrafine sand and manufactured sand as fine aggregate. The resulting high-performance concrete has low early shrinkage and is not prone to cracking, thus realizing the resource utilization of Yellow River ultrafine sand.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0007] A high-performance concrete based on ultrafine sand from the Yellow River, the high-performance concrete comprising the following components in parts by weight:

[0008] The ingredients are: 161-294 parts cement, 30-60 parts circulating fluidized bed fly ash (CFA), 83-132 parts mineral powder, 270-870 parts Yellow River ultrafine sand, 270-870 parts manufactured sand, 640-680 parts aggregate, 2-4 parts CNTs-SAL composite shrinkage-reducing and crack-resistant agent, 10-30 parts water-reducing agent, and 160-170 parts water. This invention employs a continuous gradation of multiple components, resulting in concrete with better workability and less prone to segregation and bleeding.

[0009] Preferably, the cement is P.O42.5 ordinary Portland cement.

[0010] Preferably, the specific surface area of ​​the circulating fluidized bed fly ash is 410 m². 2 / kg, the specific surface area of ​​the mineral powder is 450m². 2 / kg.

[0011] Chemical composition of circulating fluidized bed fly ash

[0012]

[0013] The circulating fluidized bed fly ash (CFA) used in this invention is a byproduct of power plant emissions. Because the operating temperature of the circulating fluidized bed boiler (850-900℃) is lower than that of ordinary pulverized coal boiler (1200-1400℃), CFA contains more amorphous minerals. Therefore, the pozzolanic activity of CFA is better than that of fly ash from pulverized coal boiler.

[0014] Specifically, CFA contains a large amount of unstable components f-CaO and SO3. SO3 can directly react with active Al2O3 and f-CaO to form ettringite (AFt), and the silicating of f-CaO and secondary hydration of Ca(OH)2 can generate an additional mixture of hydrated calcium silicate (CSH) and hydrated calcium aluminosilicate (CASH) gels. The chemical reaction formula is as follows:

[0015] f-CaO + free active SiO2 + OH- + H2O → CSH gel (1)

[0016] CaSO4(SO3)+Ca3Al2O6+H2O→Ca6Al2(SO4)3(OH) 12 ·26H2O (2)

[0017] CaSO4(SO3)+active Al2O3+f-CaO+H2O→Ca6Al2(SO4)3(OH) 12 ·26H2O (3)

[0018] AlO2 - +OH - +H₂O→[Al(OH)₆] 3- (4)

[0019] 2[Al(OH)6] 3- +6Ca 2+ +3SO4 2- +26H2O→Ca6Al2(SO4)3(OH) 12 ·26H2O (5)

[0020] AlO2 -+OH - +H₂O→[H₃AlO₄] 2- (6)

[0021] SiO2+OH - +H₂O→[H₃SiO₄] - (7)

[0022] [H3AlO4] 2- +[H3SiO4]-+Ca 2+ →CASH Gel(8)

[0023] On the one hand, f-CaO in CFA can generate additional AFt, which works synergistically with the CNTs-SAL composite shrinkage-reducing and crack-resistant agent to avoid the problem of insufficient AFt generation due to low CNTs-SAL dosage, resulting in weak shrinkage compensation effect on Yellow River ultrafine sand-based concrete. Simultaneously, it also avoids the problem of excessive CNTs-SAL dosage causing CNT agglomeration due to van der Waals forces, hindering the successful bonding of CNTs-SAL with adjacent hydration products, leading to defects between CNTs-SAL and cement-based materials, weakening the material, creating voids, and reducing the structural and bond strength of the concrete. The appropriate amount of CFA incorporation plays a balancing role with the CNTs-SAL composite shrinkage-reducing and crack-resistant agent, compensating for the early shrinkage of Yellow River ultrafine sand-based concrete. On the other hand, the CSH and CASH hydration products generated by CFA improve the mechanical properties of Yellow River ultrafine sand-based concrete, enhancing its macroscopic properties.

[0024] Preferably, the residue on a 0.075mm sieve of the Yellow River ultrafine sand is 90% to 95%.

[0025] Chemical composition of Yellow River sediment

[0026]

[0027] Preferably, the 0.075mm sieve residue of the manufactured sand is 85%–90%. Yellow River ultrafine sand has a finer particle size than manufactured sand. Yellow River ultrafine sand, manufactured sand, and cementitious materials mutually fill the pore structure. Appropriate amounts of Yellow River ultrafine sand can produce high-performance concrete with a denser structure. Furthermore, due to its unique properties, Yellow River ultrafine sand contains an aluminum-calcium phase, exhibiting potential activity. In the alkaline environment of cement hydration, it may slowly generate more hydration products.

[0028] Preferably, the aggregate consists of large stones with a diameter of 1-2 cm and small stones with a diameter of 0.5-1 cm, wherein the mass ratio of large stones to small stones is 54-55:11-12. The intergranular gaps formed between the large and small stones allow for better filling of the Yellow River's fine sand and other materials, increasing the concrete strength. Furthermore, the appropriate ratio of large and small stones conforms to the theory of close packing.

[0029] Preferably, the preparation method of the CNTs-SAL composite shrinkage-reducing and crack-resistant agent includes the following steps:

[0030] S01: Add 0.5% to 2% of a certain amount of polyvinyl alcohol (PVA) to distilled water and stir for 180s to 240s until the PVA is completely dissolved. Specifically, the proportion of PVA to distilled water is 0.5% to 2%.

[0031] S02: Add CNTs to the mixed solution in step S01. Under the dispersion effect of PVA, the large clusters are dispersed by magnetic stirring. Then, an ultrasonic instrument is used to open the van der Waals forces between CNTs. During the entire stirring process, the temperature probe of the ultrasonic disperser is controlled below 20°C to control the dispersion temperature inside the solution. The mass ratio of CNTs to the mixed solution is 1:20.

[0032] S03: Add sulfur-aluminum composite expanding agent to the mixed solution and continue stirring at low speed for 180s to 300s to obtain a uniform CNTs-SAL mixture.

[0033] Carbon nanotubes (CNTs) can enhance concrete strength and reduce early shrinkage to some extent. However, high doses of CNTs can easily entangle and form clusters, interfering with the movement of concrete particles and reducing its fluidity. Sulfoaluminum-sulfur composite expansive agents can compensate for concrete shrinkage to some extent, but the AFt they produce has poor stability, easily decomposes at 70℃, and consumes a large amount of water, thus limiting their shrinkage compensation ability. Therefore, this invention presents a carbon nanotube-sulfoaluminum composite expansive agent composite material, named CNTs-SAL composite shrinkage-reducing and crack-resistant agent material. It is used to control the problems of high mud content, increased shrinkage, and easy cracking caused by the introduction of ultrafine sand from the Yellow River.

[0034] In this application, the mass ratio of sulfur-aluminum composite expansive agent to CNTs in the CNTs-SAL composite shrinkage-reducing and crack-resistant agent is 10:1. Large clusters are dispersed by magnetic stirring under the dispersion effect of PVA, preventing uneven distribution of CNTs within the concrete and reducing concrete viscosity, thus improving its fluidity. Based on this, the sulfur-aluminum composite expansive agent is added to the dispersed CNTs solution to ensure uniform mixing. During construction, the CNTs-SAL composite shrinkage-reducing and crack-resistant agent is added to the concrete. At this point, the CNTs fill the internal nanopores of the cement paste, causing the paste pores to develop into smaller gel pores. This process leads to a denser paste structure, improving the concrete's shrinkage resistance and effectively controlling the high mud content and increased shrinkage caused by the introduction of Yellow River ultrafine sand, which makes the concrete prone to cracking. As the curing time increases, the content of ettringite (AFt) gradually increases, and a large number of hydration products intertwine to form a denser structure. At this time, CNTs can quickly disperse heat and enhance the high-temperature resilience of concrete to alleviate the instability of AFt at high temperatures and prevent premature decomposition of AFt. On the one hand, this improves the concrete's impermeability, and on the other hand, it enhances the shrinkage compensation capacity of AFt, inhibiting early shrinkage of concrete and preventing cracking.

[0035] Preferably, the carbon nanotubes (CNTs) have a purity of ≥95%, a diameter of 20–30 nm, and a length of 5–15 μm. CNTs have a good aspect ratio and can act as a connector and bridge in the slurry, inhibiting concrete shrinkage.

[0036] Preferably, the water-reducing agent is a shrinkage-reducing polycarboxylate-based high-performance water-reducing agent with a water reduction rate of 25% and a 28-day shrinkage rate of 105%.

[0037] The second objective of this invention is to provide a method for preparing high-performance concrete based on ultrafine sand from the Yellow River, thereby reducing the early shrinkage of the concrete.

[0038] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0039] A method for preparing high-performance concrete based on ultrafine sand from the Yellow River, characterized by comprising the following steps:

[0040] T01: Mix cement, circulating fluidized bed fly ash, mineral powder, Yellow River ultrafine sand, manufactured sand, and gravel to obtain a mixture.

[0041] material;

[0042] T02: Prepare the CNTs-SAL mixture and place it in a mixing tank for later use;

[0043] T03: Put the mixture into a mixing pot and stir for 30 seconds, then add water and continue stirring for 90 seconds, then add water-reducing agent and CNTs-SAL mixture and continue stirring for 120 seconds. Pour the concrete mixture into a mold and demold it after 24 hours. Then place it in a standard curing room for curing to obtain Yellow River ultra-fine sand-based high-performance concrete.

[0044] In summary, the present invention has the following beneficial effects:

[0045] 1. This invention prepares a CNTs-SAL composite shrinkage-reducing and crack-resistant agent by combining CNTs with a sulfur-aluminum composite expansive agent. This reduces the dosage of CNTs, avoids the clustering of high-dose CNTs in the system, and leverages the high thermal conductivity of CNTs to rapidly disperse heat, enhancing the high-temperature resilience of concrete and mitigating the instability of AFt at high temperatures. The combined effect of both reduces early shrinkage of concrete; their long-diameter structure and AFt act as a connector and bridge in the concrete, optimizing the pore structure of the system and improving the crack resistance, compressive strength, and impermeability of the concrete. Compared with existing technologies, this invention can solve the early shrinkage problem faced by Yellow River ultrafine sand-based concrete to a certain extent, increases the dosage of Yellow River ultrafine sand, and facilitates the resource utilization of Yellow River ultrafine sand.

[0046] 2. This invention utilizes circulating fluidized bed fly ash (CFA) and a CNTs-SAL composite shrinkage-reducing and crack-resistant agent to compensate for the early shrinkage of Yellow River ultrafine sand-based concrete. This significantly reduces the early shrinkage rate of the concrete, lowering the risk of cracking. Simultaneously, using the same amount of cementitious materials, the concrete strength at 7 days and 28 days shows a significant improvement. Furthermore, the hydration products such as CSH and CASH generated by CFA enhance the mechanical properties of the Yellow River ultrafine sand-based concrete, improving its macroscopic performance. Compared to existing technologies, this invention uses Yellow River ultrafine sand as a raw material to produce high-performance concrete, realizing the resource utilization of Yellow River silt and sand, greatly reducing concrete costs. The rounded shape and small particle size of the Yellow River ultrafine sand result in better gradation of the raw material components, improving the workability of the concrete. Simultaneously, it significantly improves the density and impermeability of the concrete. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1This is a phase composition diagram of the Yellow River ultrafine sand in an embodiment of the present invention. Detailed Implementation

[0049] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific implementation methods, features and effects of the Yellow River ultrafine sand-based high-performance concrete and its preparation method proposed according to the present invention are described in detail below.

[0050] Sources of raw materials used in the examples:

[0051] Cement: P.O42.5 cement, sourced from Dezhou Zhonglian Dam Cement Co., Ltd.;

[0052] Pebbles: sourced from Tianjin Jiangchuan Building Materials Technology Co., Ltd.

[0053] Manufactured sand: sourced from the Fourth Engineering Bureau of China Railway 12th Bureau Group Co., Ltd.;

[0054] Yellow River ultrafine sand: sourced from Tianjin Jiangchuan Building Materials Technology Co., Ltd.;

[0055] River sand: sourced from Tianjin Jiangchuan Building Materials Technology Co., Ltd.;

[0056] Circulating fluidized bed fly ash (CFA): sourced from Shanxi Yaoguang Coal and Power Co., Ltd.;

[0057] Mineral powder: sourced from Xinji Gangxin New Building Materials Co., Ltd.;

[0058] Polycarboxylate superplasticizer: Tianjin Yueming Superplasticizer Factory;

[0059] Sulfur-aluminum composite expanding agent: Produced by Xi'an Qinbote Building Materials Co., Ltd.

[0060] Carbon nanotubes (CNTs): Produced by Shenzhen Nanoport Co., Ltd.

[0061] Example 1

[0062] A high-performance concrete based on ultrafine sand from the Yellow River, comprising the following components by weight:

[0063] 294 parts of P.O42.5 ordinary silicate cement, 50 parts of circulating fluidized bed fly ash, 104 parts of mineral powder, 289 parts of Yellow River ultrafine sand, 867 parts of manufactured sand, 659 parts of gravel, 3 parts of CNTs-SAL composite shrinkage-reducing and crack-resistant agent, 25 parts of polycarboxylate high-performance water-reducing agent, and 165 parts of water.

[0064] The stones consist of large stones with a diameter of 1 to 2 cm and small stones with a diameter of 0.5 to 1 cm, with a mass ratio of large stones to small stones of 55:12.

[0065] A method for preparing high-performance concrete based on ultrafine sand from the Yellow River includes the following steps:

[0066] T01: Mix cement, circulating fluidized bed fly ash, mineral powder, Yellow River ultrafine sand, manufactured sand, and gravel to obtain a mixture.

[0067] T02: Prepare the CNTs-SAL mixture and place it in a mixing tank for later use;

[0068] A certain amount of 1% polyvinyl alcohol (PVA) was added to distilled water and stirred until the PVA was completely dissolved. Then, CNTs were added to the mixture from the above steps, and large clusters were dispersed by magnetic stirring. Then, an ultrasonic instrument was used to open the van der Waals forces between CNTs, and the temperature probe of the ultrasonic disperser was controlled below 20°C. After that, a sulfur-aluminum composite expansion agent was added to the mixture, and stirring was continued at low speed for 240 seconds to obtain a uniform CNTs-SAL mixture.

[0069] T03: Put the mixture into a mixing pot and stir for 30 seconds, then add water and continue stirring for 90 seconds, then add water-reducing agent and CNTs-SAL mixture and continue stirring for 120 seconds. Pour the concrete mixture into a mold and demold it after 24 hours. Then place it in a standard curing room for curing to obtain Yellow River ultrafine sand-based high-performance concrete.

[0070] Example 2

[0071] A high-performance concrete based on ultrafine sand from the Yellow River, comprising the following components by weight:

[0072] 294 parts of P.O42.5 ordinary silicate cement, 50 parts of circulating fluidized bed fly ash, 104 parts of mineral powder, 578 parts of Yellow River ultrafine sand, 578 parts of manufactured sand, 659 parts of gravel, 3 parts of CNTs-SAL composite shrinkage-reducing and crack-resistant agent, 15 parts of polycarboxylate high-performance water-reducing agent, and 165 parts of water.

[0073] The stones consist of large stones with a diameter of 1 to 2 cm and small stones with a diameter of 0.5 to 1 cm, with a mass ratio of large stones to small stones of 54:11.

[0074] A method for preparing high-performance concrete based on ultrafine sand from the Yellow River includes the following steps:

[0075] T01: Mix cement, circulating fluidized bed fly ash, mineral powder, Yellow River ultrafine sand, manufactured sand, and gravel to obtain a mixture.

[0076] T02: Prepare the CNTs-SAL mixture and place it in a mixing tank for later use;

[0077] A certain amount of 1% polyvinyl alcohol (PVA) was added to distilled water and stirred until the PVA was completely dissolved. Then, CNTs were added to the mixture from the above steps, and large clusters were dispersed by magnetic stirring. Then, an ultrasonic instrument was used to open the van der Waals forces between CNTs, and the temperature probe of the ultrasonic disperser was controlled below 20°C. After that, a sulfur-aluminum composite expansion agent was added to the mixture, and stirring was continued at low speed for 240 seconds to obtain a uniform CNTs-SAL mixture.

[0078] T03: Put the mixture into a mixing pot and stir for 30 seconds, then add water and continue stirring for 90 seconds, then add water-reducing agent and CNTs-SAL mixture and continue stirring for 120 seconds. Pour the concrete mixture into a mold and demold it after 24 hours. Then place it in a standard curing room for curing to obtain Yellow River ultrafine sand-based high-performance concrete.

[0079] Example 3

[0080] A high-performance concrete based on ultrafine sand from the Yellow River, comprising the following components by weight:

[0081] 294 parts of P.O42.5 ordinary silicate cement, 50 parts of circulating fluidized bed fly ash, 104 parts of mineral powder, 867 parts of Yellow River ultrafine sand, 289 parts of manufactured sand, 659 parts of gravel, 3 parts of CNTs-SAL composite shrinkage-reducing and crack-resistant agent, 10 parts of polycarboxylate high-performance water-reducing agent, and 165 parts of water.

[0082] The stones consist of large stones with a diameter of 1 to 2 cm and small stones with a diameter of 0.5 to 1 cm, with a mass ratio of large stones to small stones of 54:11.

[0083] A method for preparing high-performance concrete based on ultrafine sand from the Yellow River includes the following steps:

[0084] T01: Mix cement, circulating fluidized bed fly ash, mineral powder, Yellow River ultrafine sand, manufactured sand, and gravel to obtain a mixture.

[0085] T02: Prepare the CNTs-SAL mixture and place it in a mixing tank for later use;

[0086] A certain amount of 1% polyvinyl alcohol (PVA) was added to distilled water and stirred until the PVA was completely dissolved. Then, CNTs were added to the mixture from the above steps, and large clusters were dispersed by magnetic stirring. Then, an ultrasonic instrument was used to open the van der Waals forces between CNTs, and the temperature probe of the ultrasonic disperser was controlled below 20°C. After that, a sulfur-aluminum composite expansion agent was added to the mixture, and stirring was continued at low speed for 240 seconds to obtain a uniform CNTs-SAL mixture.

[0087] T03: Put the mixture into a mixing pot and stir for 30 seconds, then add water and continue stirring for 90 seconds, then add water-reducing agent and CNTs-SAL mixture and continue stirring for 120 seconds. Pour the concrete mixture into a mold and demold it after 24 hours. Then place it in a standard curing room for curing to obtain Yellow River ultrafine sand-based high-performance concrete.

[0088] Example 4

[0089] A high-performance concrete based on ultrafine sand from the Yellow River, comprising the following components by weight:

[0090] 294 parts of P.O42.5 ordinary silicate cement, 30 parts of circulating fluidized bed fly ash, 104 parts of mineral powder, 578 parts of Yellow River ultrafine sand, 578 parts of manufactured sand, 659 parts of gravel, 3 parts of CNTs-SAL composite shrinkage-reducing and crack-resistant agent, 15 parts of polycarboxylate high-performance water-reducing agent, and 165 parts of water.

[0091] The stones consist of large stones with a diameter of 1 to 2 cm and small stones with a diameter of 0.5 to 1 cm, with a mass ratio of large stones to small stones of 54:11.

[0092] A method for preparing high-performance concrete based on ultrafine sand from the Yellow River includes the following steps:

[0093] T01: Mix cement, circulating fluidized bed fly ash, mineral powder, Yellow River ultrafine sand, manufactured sand, and gravel to obtain a mixture.

[0094] T02: Prepare the CNTs-SAL mixture and place it in a mixing tank for later use;

[0095] A certain amount of 1% polyvinyl alcohol (PVA) was added to distilled water and stirred until the PVA was completely dissolved. Then, CNTs were added to the mixture from the above steps, and large clusters were dispersed by magnetic stirring. Then, an ultrasonic instrument was used to open the van der Waals forces between CNTs, and the temperature probe of the ultrasonic disperser was controlled below 20°C. After that, a sulfur-aluminum composite expansion agent was added to the mixture, and stirring was continued at low speed for 240 seconds to obtain a uniform CNTs-SAL mixture.

[0096] T03: Put the mixture into a mixing pot and stir for 30 seconds, then add water and continue stirring for 90 seconds, then add water-reducing agent and CNTs-SAL mixture and continue stirring for 120 seconds. Pour the concrete mixture into a mold and demold it after 24 hours. Then place it in a standard curing room for curing to obtain Yellow River ultrafine sand-based high-performance concrete.

[0097] Comparative Example 1

[0098] A high-performance concrete, by weight, comprises the following components:

[0099] 294 parts of P.O42.5 ordinary silicate cement, 50 parts of circulating fluidized bed fly ash, 104 parts of mineral powder, 578 parts of river sand, 578 parts of manufactured sand, 659 parts of gravel, 3 parts of CNTs-SAL composite shrinkage-reducing and crack-resistant agent, 20 parts of polycarboxylate high-performance water-reducing agent, and 165 parts of water.

[0100] The stones consist of large stones with a diameter of 1 to 2 cm and small stones with a diameter of 0.5 to 1 cm, with a mass ratio of large stones to small stones of 54:11.

[0101] A method for preparing high-performance concrete based on ultrafine sand from the Yellow River includes the following steps:

[0102] T01: Mix cement, circulating fluidized bed fly ash, mineral powder, Yellow River ultrafine sand, manufactured sand, and gravel to obtain a mixture.

[0103] T02: Prepare the CNTs-SAL mixture and place it in a mixing tank for later use;

[0104] A certain amount of 1% polyvinyl alcohol (PVA) was added to distilled water and stirred until the PVA was completely dissolved. Then, CNTs were added to the mixture from the above steps, and large clusters were dispersed by magnetic stirring. Then, an ultrasonic instrument was used to open the van der Waals forces between CNTs, and the temperature probe of the ultrasonic disperser was controlled below 20°C. After that, a sulfur-aluminum composite expansion agent was added to the mixture, and stirring was continued at low speed for 240 seconds to obtain a uniform CNTs-SAL mixture.

[0105] T03: Put the mixture into a mixing pot and stir for 30 seconds, then add water and continue stirring for 90 seconds, then add water-reducing agent and CNTs-SAL mixture and continue stirring for 120 seconds. Pour the concrete mixture into a mold and demold it after 24 hours. Then place it in a standard curing room for curing to obtain Yellow River ultrafine sand-based high-performance concrete.

[0106] Comparative Example 2

[0107] A high-performance concrete based on ultrafine sand from the Yellow River, comprising the following components by weight:

[0108] 294 parts of P.O42.5 ordinary silicate cement, 50 parts of circulating fluidized bed fly ash, 104 parts of mineral powder, 578 parts of Yellow River ultrafine sand, 578 parts of manufactured sand, 659 parts of gravel, 3 parts of sulfur-aluminum composite expansion agent, 0.3 parts of CNTs, 15 parts of polycarboxylate high-performance water-reducing agent, and 165 parts of water.

[0109] The stones consist of large stones with a diameter of 1 to 2 cm and small stones with a diameter of 0.5 to 1 cm, with a mass ratio of large stones to small stones of 54:11.

[0110] A method for preparing high-performance concrete based on ultrafine sand from the Yellow River includes the following steps:

[0111] T01: Mix cement, circulating fluidized bed fly ash, mineral powder, Yellow River ultrafine sand, manufactured sand, and gravel to obtain a mixture.

[0112] T02: Put the mixture into a mixing pot and stir for 30 seconds, then add water and continue stirring for 90 seconds. Then add water-reducing agent, sulfur-aluminum composite expansion agent and CNTs and continue stirring for 120 seconds. Pour the concrete mixture into a mold and demold it after 24 hours. Then place it in a standard curing room for curing to obtain Yellow River ultrafine sand-based high-performance concrete.

[0113] Comparative Example 3

[0114] A high-performance concrete based on ultrafine sand from the Yellow River, comprising the following components by weight:

[0115] 294 parts of P.O42.5 ordinary silicate cement, 50 parts of pulverized coal boiler fly ash, 104 parts of mineral powder, 578 parts of Yellow River ultrafine sand, 578 parts of manufactured sand, 659 parts of gravel, 3 parts of CNTs-SAL composite shrinkage-reducing and crack-resistant agent, 15 parts of polycarboxylate high-performance water-reducing agent, and 165 parts of water.

[0116] The stones consist of large stones with a diameter of 1 to 2 cm and small stones with a diameter of 0.5 to 1 cm, with a mass ratio of large stones to small stones of 54:11.

[0117] A method for preparing high-performance concrete based on ultrafine sand from the Yellow River includes the following steps:

[0118] T01: Mix cement, pulverized coal ash, mineral powder, Yellow River ultrafine sand, manufactured sand, and gravel to obtain a mixture.

[0119] T02: Prepare the CNTs-SAL mixture and place it in a mixing tank for later use;

[0120] A certain amount of 1% polyvinyl alcohol (PVA) was added to distilled water and stirred until the PVA was completely dissolved. Then, CNTs were added to the mixture from the above steps, and large clusters were dispersed by magnetic stirring. Then, an ultrasonic instrument was used to open the van der Waals forces between CNTs, and the temperature probe of the ultrasonic disperser was controlled below 20°C. After that, a sulfur-aluminum composite expansion agent was added to the mixture, and stirring was continued at low speed for 240 seconds to obtain a uniform CNTs-SAL mixture.

[0121] T03: Put the mixture into a mixing pot and stir for 30 seconds, then add water and continue stirring for 90 seconds, then add water-reducing agent and CNTs-SAL mixture and continue stirring for 120 seconds. Pour the concrete mixture into a mold and demold it after 24 hours. Then place it in a standard curing room for curing to obtain Yellow River ultrafine sand-based high-performance concrete.

[0122] Performance testing

[0123]

[0124] Compared with Example 4, Comparative Example 1 uses river sand instead of Yellow River ultrafine sand, yet achieves the same technical effect as this application. This demonstrates that the use of Yellow River ultrafine sand in this application can result in good gradation and improve the workability of concrete.

[0125] Compared with Example 4, Comparative Example 2 did not combine sulfur-aluminum composite expansion agent and CNTs. As can be seen from the data, the compressive strength was reduced to varying degrees, and the 3d shrinkage rate and early cracking were greater. This indicates that the CNTs-SAL composite shrinkage-reducing and crack-resistant agent prepared in this application improves the impermeability of concrete on the one hand, and enhances the shrinkage compensation capacity of AFt on the other hand, inhibiting the early shrinkage of concrete. It can effectively control the problem of high mud content and increased shrinkage caused by the introduction of Yellow River ultrafine sand, which makes concrete prone to cracking.

[0126] Compared with Example 4, Comparative Example 3 used pulverized coal furnace fly ash instead of circulating fluidized bed fly ash. The data shows that the compressive strength was reduced to varying degrees, and the 3d shrinkage rate and early cracking were greater. This indicates that the hydration products such as CSH and CASH generated by CFA improved the mechanical properties of Yellow River ultrafine sand-based concrete and enhanced the macroscopic properties of the concrete.

[0127] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A kind of Yellow River superfine sand-based high-performance concrete, it is characterized by, The cement 161~294 parts, the circulating fluidized bed fly ash 30~60 parts, the mineral powder 83~132 parts, the Yellow River superfine sand 270~870 parts, the machine-made sand 270~870 parts, the stone 640~680 parts, the CNTs-SAL composite shrinkage and cracking inhibitor 2~4 parts, the water reducing agent 10~30 parts, and water 160~170 parts are included. The preparation method of the CNTs-SAL composite shrinkage and cracking inhibitor comprises the following steps: S01: a certain amount of polyvinyl alcohol (PVA) 0.5%~2% is put into distilled water, and stirred for 180 s~240 s until the PVA is completely dissolved, S02: CNTs are added into the mixed solution of step S01, and the large clusters are dispersed by magnetic stirring, and then the van der Waals force between the CNTs is opened by using an ultrasonic instrument, and the temperature probe of the ultrasonic dispersion instrument is controlled below 20 ℃; S03: the sulfur-aluminum type composite expansion agent is added into the mixed solution, and the low-speed stirring is continued for 180 s~300 s to obtain a uniform CNTs-SAL mixed solution; In the CNTs-SAL composite shrinkage and cracking inhibitor, the mass ratio of the sulfur-aluminum type composite expansion agent to the CNTs is 10:

1. The stone is composed of large stones with a particle size of 1~2 cm and small stones with a particle size of 0.5~1 cm, and the mass ratio of the large stones to the small stones is 54~55:11~12. The cement is P.O42.5 ordinary portland cement.

2. The high performance concrete according to claim 1, wherein, The sieve residue of the Yellow River superfine sand at 0.075 mm is 90%~95%.

3. The high performance concrete according to claim 1, wherein the high performance concrete is a Yellow River ultra-fine sand-based high performance concrete. The specific surface area of the circulating fluidized bed fly ash is 412 m 2 / kg, and the bulk density of the mineral powder is 950-1000 kg / m 3 .

4. The high performance concrete according to claim 1, wherein the high performance concrete is a Yellow River ultra-fine sand-based high performance concrete. The sieve residue of the machine-made sand at 0.075 mm is 85%~90%.

5. The high performance concrete according to claim 1, wherein the high performance concrete is a Yellow River ultra-fine sand-based high performance concrete. The purity of the CNTs is ≥95%, the diameter is 20~30 nm, and the length is 5~15 μm.

6. The high performance concrete according to claim 1, wherein the high performance concrete is a Yellow River ultra-fine sand-based high performance concrete. The water reducing agent is a shrinkage type polycarboxylic acid high-performance water reducing agent, the water reducing rate is 25%, and the 28 d shrinkage rate is 105%.

7. The high performance concrete according to claim 1, wherein the high performance concrete is a Yellow River ultra-fine sand-based high performance concrete. The operation steps comprise:

8. The preparation method of the Yellow River ultra-fine sand-based high-performance concrete according to claim 1, characterized in that, T01: the cement, the circulating fluidized bed fly ash, the mineral powder, the Yellow River superfine sand, the machine-made sand, and the stone are mixed to obtain a mixed material; T02: the CNTs-SAL mixed solution is prepared and placed in a stirring pot for standby; T03: the mixed material is put into the stirring pot and stirred for 30 s, then the water is added and stirred for 90 s, and then the water reducing agent and the CNTs-SAL mixed solution are added and stirred for 120 s, the concrete mixture is poured into a mold, and after 24 h demolding, it is placed in a standard curing room for curing, and the Yellow River superfine sand-based high-performance concrete is obtained. ​

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