A high-performance concrete made from recycled sand and its preparation method

Abstract

This application relates to the field of building materials, specifically disclosing a high-performance recycled sand concrete and its preparation method. The high-performance recycled sand concrete, by weight, comprises 800-900 parts modified recycled sand, 600-650 parts cement, 400-500 parts modified fly ash, 50-80 parts recycled fiber, 30-40 parts MgO expansion agent, 20-30 parts water-reducing agent, and 100-200 parts cenospheres. The modified recycled sand is obtained by modifying recycled sand from waste construction debris after demolition. The modified fly ash is obtained by modifying fly ash from coal combustion waste. The high-performance recycled sand concrete of this application exhibits good comprehensive performance, characterized by high strength, low water absorption, and excellent durability, thus alleviating the shortage of natural sand resources. Furthermore, the preparation method of this application can produce high-performance recycled sand concrete with excellent comprehensive performance.

Description

Technical Field

[0001] This application relates to the field of building materials, and more specifically, to a high-performance concrete made from recycled sand and a method for its preparation. Background Technology

[0002] With the rapid development of my country's construction industry and the continuous advancement of urbanization and urban renewal, a large amount of demolition and renovation construction waste has been generated. This construction waste includes waste concrete, waste mortar, clay bricks and other materials. If a large amount of construction waste can be used to make aggregates and powders to replace the natural sand used in the traditional concrete preparation process, it will greatly alleviate the problem of natural sand resource shortage and effectively solve the problem of difficult disposal and recycling of large amounts of construction waste.

[0003] Regarding the aforementioned technologies, the inventors discovered that the current recycling of large amounts of construction waste generated from building demolition and renovation mainly involves crushing, washing, screening, and removing impurities to produce recycled sand to replace natural sand and gravel. However, these recycled sands often have many defects in their properties. Recycled sand has many microcracks, high water absorption, and poor stability, resulting in more pores and weak interfaces in the prepared concrete matrix. The overall performance of the concrete is poor, especially in terms of strength and durability, which are significantly insufficient and cannot meet the requirements of high-performance concrete. This limits the application of using recycled sand to prepare concrete in practical engineering. Summary of the Invention

[0004] In order to compensate for the pores inside recycled sand concrete, improve the compactness of recycled sand concrete, and thus enhance the strength and durability of recycled sand concrete, this application provides a high-performance recycled sand concrete and its preparation method.

[0005] In a first aspect, this application provides a high-performance concrete made from recycled sand, employing the following technical solution:

[0006] A high-performance concrete using recycled sand, by weight, comprises 800-900 parts modified recycled sand, 600-650 parts cement, 400-500 parts modified fly ash, 50-80 parts recycled fiber, 30-40 parts MgO expanding agent, 20-30 parts water-reducing agent, and 100-200 parts cenospheres; wherein the modified recycled sand is obtained by modifying recycled sand from waste construction debris after demolition; and the modified fly ash is obtained by modifying fly ash from coal combustion waste.

[0007] Recycled sand is mainly composed of aggregates obtained from the manual crushing of waste construction materials such as waste clay bricks after building demolition. By adopting the above-mentioned technical solutions, modified recycled sand effectively removes impurities such as silicates, metal oxides, and cement particles, improving the purity of the recycled sand. This not only realizes the recycling of construction waste and reduces dependence on natural resources, but also improves the inherent properties of recycled sand, thereby enhancing the overall performance of recycled sand concrete. The use of MgO expansion agent can compensate for the shrinkage of recycled sand concrete, reducing the formation of cracks, thus enhancing the impermeability and durability of recycled sand concrete. In addition, the cement particles in recycled sand undergo a hydration reaction upon contact with water to form a gel-like substance. MgO can act as a catalyst to promote this reaction, thereby enhancing the cementitious properties of recycled sand. The addition of recycled fibers not only enables the recycling of resources but also forms a fiber network structure inside the recycled sand concrete, improving its density and thus enhancing its toughness and crack resistance. Modified fly ash has higher activity and can further react with other raw materials to form compounds with cementitious properties, further filling the pores of the concrete, improving the density of the recycled sand concrete, and enhancing its fluidity and workability. Mixing according to the proportions of this application can yield high-performance recycled sand concrete with good strength, impermeability, and durability.

[0008] Optionally, the method for preparing the modified recycled sand includes the following steps: crushing, screening, magnetic separation, and air separation of the waste construction waste after demolition to obtain recycled sand; adding the recycled sand to a phosphoric acid solution for washing, and then performing sand-liquid separation, and repeatedly washing 3-5 times to obtain primary modified recycled sand; drying and cooling the primary modified recycled sand at 70-80℃ to obtain modified recycled sand.

[0009] By adopting the above technical solution, adding recycled sand to an acid solution for cleaning can effectively remove metallic impurities and carbonate substances from the recycled sand, thereby improving the purity of the recycled sand. Using phosphoric acid solution to clean the recycled sand can not only remove impurities, but also form a phosphate film on the surface of the recycled sand particles, which helps to improve the durability and corrosion resistance of the recycled sand.

[0010] Optionally, the primary modified recycled sand is pretreated as follows before drying: the primary modified recycled sand is soaked in water for 30-40 minutes.

[0011] By adopting the above technical solution, soaking in water after acid washing can further remove the small particles, oil stains or other impurities remaining on the surface of the primary modified recycled sand, making the primary modified recycled sand purer. During the soaking process, water will gradually penetrate into the interior of the primary modified recycled sand particles, making its structure more loose and porous. This structure helps the modified recycled sand to better absorb and retain water in concrete, improving the water absorption and water retention of recycled sand concrete, thereby improving the density and strength of recycled sand concrete.

[0012] Optionally, the preparation method of the modified fly ash includes the following steps: adding coal waste fly ash to a composite solution of NaOH and silane coupling agent in a volume ratio of (1-2):1, stirring for 4-5 hours under water bath heating at 50-60℃ to obtain pretreated fly ash, wherein the mass ratio of the coal waste fly ash to the composite solution is 1:(4-5); filtering and washing the pretreated fly ash, drying it at 150-170℃, and cooling it to obtain modified fly ash.

[0013] By adopting the above technical solution, the surface of coal-fired waste fly ash is modified by heating and stirring in a composite solution water bath. This makes the surface of the pretreated fly ash rougher and significantly improves its reactivity. NaOH solution can destroy the glass network structure of coal-fired waste fly ash, making it loose and porous, exposing more active sites. Silane coupling agents can form chemical bonds with the inorganic matter on the surface of coal-fired waste fly ash, improving its compatibility and binding force with organic matter. Washing and drying can remove excess moisture and impurities from the pretreated fly ash, making the modified fly ash purer and more stable. The modified fly ash can more effectively fill the pores of recycled sand concrete, improve the density of recycled sand concrete, reduce the water absorption rate of recycled sand concrete, and improve the strength and durability of recycled sand concrete.

[0014] Optionally, the modified fly ash undergoes the following pretreatment: a pore-forming agent and a binder are added to the modified fly ash and mixed; the mixture is then calcined at 500-600℃ for 2-3 hours and cooled. The mass ratio of the coal waste fly ash to the pore-forming agent and binder is (3-4):(0.5-0.8):0.2.

[0015] By adopting the above technical solution, and by adding a pore-forming agent and calcining at an appropriate temperature, finer pores and channels can be formed inside the fly ash, increasing the specific surface area of ​​the fly ash and greatly improving its activity. The activating components in the fly ash react more easily with the hydration components in the cement to form cementitious compounds, thereby enhancing the density of recycled sand concrete, reducing its water absorption, and significantly improving its strength and durability. The addition of a binder can enhance the bonding force between fly ash particles, improve the interfacial properties between fly ash and recycled sand concrete, reduce interfacial defects, and further improve the overall performance of recycled sand concrete.

[0016] Optionally, the recycled fiber comprises recycled steel fiber and recycled plastic fiber in a mass ratio of (1-2):1.

[0017] By adopting the above technical solutions, recycled steel fibers can effectively disperse and transfer stress in recycled sand concrete, enabling the recycled sand concrete to exhibit better crack resistance and impact resistance when subjected to external loads, reducing the generation and propagation of cracks. Recycled plastic fibers have a relatively low density, which can reduce the density of recycled sand concrete, making it lighter. Both recycled steel fibers and recycled plastic fibers are obtained from waste through treatment and reuse, which meets the requirements of sustainable development and environmental protection. The two fibers are synergistically and evenly distributed in recycled sand concrete, which can effectively improve the compactness, strength and toughness of recycled sand concrete, making it more durable.

[0018] Optionally, the water-reducing agent may be any one of naphthalene-based water-reducing agents, lignin sulfonates, or water-soluble resin sulfonates.

[0019] By adopting the above technical solutions, naphthalene-based water-reducing agents, lignin sulfonate-based or water-soluble resin sulfonate-based water-reducing agents have abundant raw material sources, simple manufacturing processes, and low pollution, meeting environmental protection requirements. They can significantly reduce the amount of water required for concrete preparation and improve the compressive strength and flexural strength of concrete.

[0020] Optionally, the cenospheres have an apparent density of 0.6 × 10⁻⁶. 3 kg / m 3 -0.8×10 3 kg / m 3 Spherical fly ash particles.

[0021] By adopting the above technical solution, 0.6×10 3 kg / m 3 -0.8×10 3 kg / m 3The fly ash spherical cenospheres are lighter, and their spherical shape helps improve the fluidity and workability of concrete. Moreover, fly ash spherical cenospheres are a renewable resource, and their use helps reduce the extraction of new resources and reduce waste generation, which meets the requirements of environmental protection and energy conservation.

[0022] Secondly, this application provides a method for preparing high-performance concrete using recycled sand, employing the following technical solution:

[0023] A method for preparing high-performance concrete using recycled sand includes the following steps: mixing modified recycled sand, MgO expansion agent, and cement for 10-15 minutes to obtain a preliminary mixture; adding modified fly ash, recycled fiber, water-reducing agent, and cenospheres to the preliminary mixture and continuing to mix for 10-15 minutes to obtain a medium mixture; adding water to the medium mixture and mixing for 20-30 minutes to obtain high-performance concrete using recycled sand, wherein the mass ratio of the medium mixture to water is (10-15):1.

[0024] By adopting the above technical solution, the modified recycled sand is first mixed with MgO expansion agent and cement to obtain a preliminary mixture, which helps the MgO expansion agent to fully coat the modified recycled sand. Subsequently, the preliminary mixture is mixed with modified fly ash, recycled fiber, water-reducing agent and cenospheres to obtain a medium mixture, which helps the components to be fully mixed and evenly distributed. When the material-to-water ratio is (10-15):1, it helps the components to be fully mixed and obtain concrete with good workability.

[0025] Optionally, the regenerated fiber undergoes the following pretreatment: soaking the regenerated fiber in H2O2 solution for 8-10 hours, washing it with water and drying it; then grinding the dried regenerated fiber for 10-15 minutes.

[0026] By adopting the above technical solution, many impurities exist on the surface of recycled fibers. These impurities may affect the adhesion between recycled fibers and other raw materials, resulting in weak interfacial bonding and thus causing internal defects in recycled sand concrete. H2O2, as a strong oxidant, can effectively remove oxides, greases, and other impurities from the surface of recycled fibers, thereby improving the purity and quality of the recycled fibers. Grinding helps to shorten the longer fibers in the recycled fibers, making the length, diameter, and shape of the recycled fibers more uniform and reducing the occurrence of fiber agglomeration or concentrated distribution. After surface treatment of the recycled fibers by soaking and grinding with H2O2, the recycled fibers are easier to disperse in recycled sand concrete, forming a more uniform and dense fiber network, reducing porosity and concentrated stress in the recycled sand concrete, thereby improving the strength and durability of the recycled sand concrete.

[0027] In summary, this application has the following beneficial effects:

[0028] 1. This application modifies recycled sand to effectively remove impurities such as silicates and metal oxides, thereby improving the purity and performance of the recycled sand. Surface treatment of fly ash from coal combustion waste significantly enhances the activity of the modified fly ash, making it easier to react with other raw materials in recycled sand concrete to form cementitious substances. The mixed use of modified recycled sand and modified fly ash effectively fills the pores of the recycled sand concrete, reduces interface defects, and improves the density of the recycled sand concrete, thus reducing its water absorption and enhancing its strength and durability. Furthermore, the reuse of waste effectively alleviates the shortage of natural sand resources.

[0029] 2. By adding recycled fibers, this application achieves the reuse of waste materials, which enables the recycled sand concrete to form a denser fiber network structure, further compensating for the pore structure inside the recycled sand concrete, enhancing the compactness of the recycled sand concrete, and making the recycled sand concrete exhibit better crack resistance when bearing external loads, thereby enhancing the strength and durability of the recycled sand concrete.

[0030] 3. By adding MgO expansion agent in this application, not only can the shrinkage of recycled sand concrete be compensated and the cracking be reduced, but it can also react with the cement particles in the recycled sand when they come into contact with water to generate cementitious substances, thereby further improving the cementitious properties of the recycled sand and enhancing the overall performance of the recycled sand concrete. Detailed Implementation

[0031] The following embodiments provide a further detailed description of this application.

[0032] Preparation Example

[0033] Preparation Examples of Modified Recycled Sand 1-4

[0034] Preparation Examples 1-4 are examples of the preparation of modified recycled sand. The waste buildings used in the raw materials come from the construction waste demolished in an old building demolition and renovation project in Qingdao, including waste concrete blocks, waste bricks and construction slag; the concentration of the phosphoric acid solution is 85%, industrial grade.

[0035] Preparation Example 1: A method for preparing modified recycled sand, comprising the following steps:

[0036] S1. 100 kg of construction waste after demolition is crushed and screened by a high-pressure roller press to obtain primary screen material with a particle size of less than 4.75 mm.

[0037] S2. The primary screened material is subjected to magnetic separation to remove iron, and then the material after magnetic separation is subjected to air separation to remove light substances and dust from the material by airflow, thus obtaining recycled sand.

[0038] S3. Add the regenerated sand to the phosphoric acid solution and stir and wash for 40 minutes. Then, perform sand-liquid separation. Repeat the operation 3 times to wash repeatedly to obtain the first modified regenerated sand.

[0039] S4. Soak the first modified recycled sand in water for 30 minutes, then dry it at 70°C for 10 hours, and cool it to room temperature to obtain the final product.

[0040] Preparation Example 2: A method for preparing modified recycled sand, comprising the following steps:

[0041] S1. 100 kg of construction waste after demolition is crushed and screened by a high-pressure roller press to obtain primary screen material with a particle size of less than 4.75 mm.

[0042] S2. The primary screened material is subjected to magnetic separation to remove iron, and then the material after magnetic separation is subjected to air separation to remove light substances and dust from the material by airflow, thus obtaining recycled sand.

[0043] S3. Add the regenerated sand to the phosphoric acid solution and stir and wash for 30 minutes. Then, perform sand-liquid separation. Repeat the operation 5 times to repeatedly wash and obtain the first modified regenerated sand.

[0044] S4. Soak the first modified recycled sand in water for 40 minutes, then dry it at 80°C for 10 hours, and cool it to room temperature to obtain the final product.

[0045] Preparation Example 3: A method for preparing modified recycled sand, comprising the following steps:

[0046] S1. 100 kg of construction waste after demolition is crushed and screened by a high-pressure roller press to obtain primary screen material with a particle size of less than 4.75 mm.

[0047] S2. The primary screened material is subjected to magnetic separation to remove iron, and then the material after magnetic separation is subjected to air separation to remove light substances and dust from the material by airflow, thus obtaining recycled sand.

[0048] S3. Add the regenerated sand to the phosphoric acid solution and stir and wash for 40 minutes. Then, perform sand-liquid separation. Repeat the operation 3 times to wash repeatedly to obtain the first modified regenerated sand.

[0049] S4. Dry the first modified recycled sand at 80℃ for 10 hours, and then cool it to room temperature to obtain the final product.

[0050] Preparation Example 4: A method for preparing modified recycled sand, comprising the following steps:

[0051] S1. 100 kg of construction waste after demolition is crushed and screened by a high-pressure roller press to obtain primary screen material with a particle size of less than 4.75 mm.

[0052] S2. The material from the initial screening is magnetically separated to remove iron, and then the material after magnetic separation is air-separated to remove light substances and dust by airflow.

[0053] Preparation Examples of Modified Fly Ash 5-7

[0054] Preparation Examples 5-7 are examples of the preparation of modified fly ash. The raw materials used include coal combustion waste generated during the combustion process of coal-fired power plants and industrial boilers in Qingdao. The concentration of NaOH solution is 20%, industrial grade. The silane coupling agent is selected from Shandong Yuanjin New Material Co., Ltd., KH-1731. The pore-forming agent is selected from Qingzhou Huazhen Abrasive Technology Co., Ltd., 25-30. The binder is polyvinyl alcohol binder.

[0055] Preparation Example 5: A method for preparing modified fly ash, comprising the following steps:

[0056] S1. Add 30 kg of coal-fired waste fly ash to 120 kg of composite solution and stir for 4 h in a water bath heating environment at 50 °C to obtain pretreated fly ash. The composite solution is a mixture of NaOH and silane coupling agent with a volume ratio of 1:1.

[0057] S2. After filtering the pretreated fly ash and washing it with clean water, dry it at 150℃ for 12 hours and cool it to room temperature to obtain primary modified fly ash.

[0058] S3. Add 5 kg of pore-forming agent and 2 kg of binder to the primary modified fly ash, mix and stir, calcine at 500°C for 2 hours, and cool to room temperature to obtain the final product.

[0059] Preparation Example 6: A method for preparing modified fly ash, comprising the following steps:

[0060] S1. Add 40 kg of coal-fired waste fly ash to 120 kg of composite solution and stir for 5 h in a water bath heating environment at 60 °C to obtain pretreated fly ash. The composite solution is a mixture of NaOH and silane coupling agent with a volume ratio of 2:1.

[0061] S2. After filtering the pretreated fly ash and washing it with clean water, dry it at 170℃ for 12 hours and cool it to room temperature to obtain primary modified fly ash.

[0062] S3. Add 8 kg of pore-forming agent and 2 kg of binder to the primary modified fly ash, mix and stir, calcine at 500℃ for 2 hours, and cool to room temperature to obtain the final product.

[0063] Preparation Example 7: A method for preparing modified fly ash, comprising the following steps:

[0064] S1. Add 30 kg of coal-fired waste fly ash to 120 kg of composite solution and stir for 4 h in a water bath heating environment at 50 °C to obtain pretreated fly ash. The composite solution is a mixture of NaOH and silane coupling agent with a volume ratio of 1:1.

[0065] S2. After filtering the pretreated fly ash and washing it with clean water, dry it at 150℃ for 12 hours and cool it to room temperature to obtain the final product.

[0066] Example

[0067] Example 1: A high-performance concrete using recycled sand, the raw materials and dosages of which are shown in Table 1. The modified recycled sand was prepared in Example 1; the modified fly ash was prepared in Example 5; the cement was PO32.5 silicate cement; the average length of the recycled steel fibers was 6.2 mm and the diameter was 15 μm; the average length of the recycled plastic fibers was 3.3 mm and the diameter was 8 μm; the MgO expanding agent was selected from Dechang Weiye Construction Engineering Technology Co., Ltd., 1055; the water-reducing agent was a naphthalene-based water-reducing agent selected from Wanshan Group, xty-042; and the cenospheres had an apparent density of 0.6 × 10⁻⁶. 3 kg / m 3 Spherical fly ash particles.

[0068] Table 1. Raw materials and their quantities in Examples 1-4

[0069] Components Example 1 Example 2 Example 3 Example 4 Modified recycled sand / Kg 800 840 870 900 cement / Kg 620 600 630 650 Modified fly ash / Kg 450 470 400 500 Recycled steel fiber / Kg 25 40 48 40 Recycled plastic fiber / Kg 25 20 24 40 MgO expanding agent / Kg 30 32 36 40 Water-reducing agent / Kg 25 20 22 30 Beads / Kg 120 150 100 200 Water / Kg 150 181 142 160

[0070] The above-mentioned method for preparing high-performance concrete using recycled sand includes the following steps:

[0071] S1. Mix the modified recycled sand, MgO expansion agent, and cement for 10 minutes to obtain the initial mixture;

[0072] S2. Soak the regenerated fiber in H2O2 solution for 8 hours, wash with water and then dry.

[0073] S3. Grind the dried regenerated fibers for 10 minutes to obtain pretreated regenerated fibers;

[0074] S4. Add modified fly ash, pretreated recycled fiber, water-reducing agent and cenospheres to the primary mixture, and continue stirring for 10 minutes to obtain the intermediate mixture.

[0075] S5. Add water to the medium mixture and mix for 30 minutes to obtain recycled sand high-performance concrete.

[0076] Example 2: A high-performance concrete made from recycled sand, which differs from Example 1 in that the raw materials and their amounts are shown in Table 1, the modified recycled sand is prepared from Preparation Example 2, and the modified fly ash is prepared from Preparation Example 6.

[0077] The above-mentioned method for preparing high-performance concrete using recycled sand includes the following steps:

[0078] S1. Mix the modified recycled sand, MgO expansion agent, and cement for 15 minutes to obtain the initial mixture;

[0079] S2. Soak the regenerated fibers in H2O2 solution for 10 hours, wash with water and then dry.

[0080] S3. Grind the dried regenerated fibers for 15 minutes to obtain pretreated regenerated fibers;

[0081] S4. Add modified fly ash, pretreated recycled fiber, water-reducing agent and cenospheres to the primary mixture, and continue stirring for 15 minutes to obtain the intermediate mixture.

[0082] S5. Add water to the medium mixture and mix for 20 minutes to obtain recycled sand high-performance concrete.

[0083] Example 3: A high-performance concrete made from recycled sand, which differs from Example 1 in that the raw materials and their quantities are shown in Table 1, while the other steps are the same as in Example 1.

[0084] Example 4: A high-performance concrete made from recycled sand, which differs from Example 1 in that the raw materials and their quantities are shown in Table 1, while the other steps are the same as in Example 1.

[0085] Example 5: A high-performance concrete made from recycled sand, which differs from Example 1 in that the modified recycled sand is prepared by Preparation Example 3, while the other steps are the same as in Example 1.

[0086] Example 6: A high-performance concrete made from recycled sand, which differs from Example 1 in that the modified fly ash is prepared by Example 7, while the other steps are the same as in Example 1.

[0087] Example 7: A high-performance concrete made from recycled sand, which differs from Example 1 in that no recycled steel fiber is added, and the amount of recycled plastic fiber added is 50 kg. All other steps are the same as in Example 1.

[0088] Example 8: A high-performance concrete made from recycled sand, which differs from Example 1 in that no recycled plastic fiber is added, and the amount of recycled steel fiber added is 50 kg. All other steps are the same as in Example 1.

[0089] Example 9: A high-performance concrete made from recycled sand, differing from Example 1 in that it is prepared by the following method:

[0090] S1. Mix the modified recycled sand, MgO expansion agent, and cement for 10 minutes to obtain the initial mixture;

[0091] S2. Add modified fly ash, recycled fiber, water-reducing agent and cenospheres to the primary mixture, and continue stirring for 10 minutes to obtain the intermediate mixture;

[0092] S3. Add water to the medium mixture and mix for 30 minutes to obtain recycled sand high-performance concrete.

[0093] Example 10: A high-performance concrete made from recycled sand, differing from Example 1 in that it is prepared by the following method:

[0094] S1. Mix the modified recycled sand, MgO expansion agent, and cement for 10 minutes to obtain the initial mixture;

[0095] S2. Soak the regenerated fiber in H2O2 solution for 8 hours, wash with water and then dry.

[0096] S3. Add modified fly ash, the recycled fiber obtained in step S2, water-reducing agent and cenospheres to the primary mixture, and continue stirring for 10 minutes to obtain the intermediate mixture.

[0097] S4. Add water to the intermediate mixture and mix for 30 minutes to obtain recycled sand high-performance concrete.

[0098] Comparative Example

[0099] Comparative Example 1: A high-performance concrete made from recycled sand, which differs from Example 1 in that the modified recycled sand was prepared by Example 4, and the modified fly ash was replaced with an equal mass of coal-fired waste fly ash. All other steps were the same as in Example 1.

[0100] Comparative Example 2: A high-performance concrete made from recycled sand, which differs from Example 1 in that the modified fly ash is replaced with an equal mass of coal-fired waste fly ash, while all other steps are the same as in Example 1.

[0101] Comparative Example 3: A high-performance concrete made from recycled sand, which differs from Example 1 in that no recycled steel fibers and recycled plastic fibers are added, while all other steps are the same as in Example 1.

[0102] Comparative Example 4: A high-performance concrete made from recycled sand, which differs from Example 1 in that no MgO expansion agent was added, while all other steps were the same as in Example 1.

[0103] Comparative Example 5: Preparation of a low-cost, high-performance recycled sand concrete, comprising the following steps:

[0104] S1. The coarse aggregate of construction waste with a particle size of 5-50mm is crushed by a high-pressure roller press and then separated by a drum screen to remove sand or lightweight impurities with a particle size greater than 5mm. The recycled concrete sand with a particle size less than 5mm is recycled. The fine aggregate of recycled bricks is obtained by crushing and screening waste bricks, with a particle size range of 0.075-4.75mm.

[0105] S2. Mix cement, recycled brick fine aggregate, recycled concrete sand and waste rubber particles in a certain proportion, wherein the percentage of cement in the total solid mass is 17.1%, recycled brick fine aggregate is 16.1%, recycled concrete sand is 64.4% and waste rubber particles is 2.4%, and water accounts for 100% of the cement content.

[0106] S3. Pour the above-prepared recycled brick fine aggregate, recycled concrete sand and waste rubber particles into a mixer and mix them evenly to obtain mixed aggregate. Then pour cement into the obtained mixed aggregate and mix evenly for 10 minutes. Then pour in water and continue mixing for 15 minutes to obtain the final product.

[0107] Performance testing

[0108] The high-performance concrete specimens made from recycled sand in Examples 1-10 and Comparative Examples 1-5 were tested for compressive strength, flexural strength, impermeability and water absorption. Each test was divided into three groups, and the average value of the test results of the three groups was recorded as the final result in Table 2.

[0109] Compressive strength and flexural strength were tested according to GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete"; the permeability was tested using the penetration height method on recycled sand high-performance concrete, referring to the provisions of SL352-2020 "Test Procedure for Hydraulic Concrete". The method of single pressurization was used, and after constant pressure stabilization for 24 hours, the concrete specimens were split open and the water penetration height of each group of specimens was measured. The average value of the three groups was taken to represent the water permeability resistance of the concrete; the water absorption rate was tested according to GB / T11969-2020 "Test Methods for Performance of Autoclaved Aerated Concrete".

[0110] Table 2. Test data for compressive strength, flexural strength, impermeability, and water absorption.

[0111]

[0112]

[0113] As can be seen from the performance test data of Examples 1-10 and Comparative Examples 1-5, the recycled sand concrete made by mixing modified recycled sand, modified fly ash and recycled fiber after treatment has high performance. Compared with recycled sand concrete made by traditional methods of treating construction waste, the pores inside the recycled sand high-performance concrete of this application are better filled and the interface defects are reduced, which significantly improves the compactness of the recycled sand high-performance concrete of this application, and has excellent compressive and flexural strength, significantly improved impermeability and significantly reduced water absorption.

[0114] The performance test data from Examples 1-6 and Comparative Examples 1-2 show that unmodified recycled sand contains a lot of residual impurities, has low purity, and poor inherent properties, which seriously affects the performance of recycled sand concrete. Soaking the recycled sand in water after acid leaching helps to further improve its performance. Although unmodified fly ash from coal combustion waste can still be activated and react with other raw materials to form gel-like substances, its low activity results in low utilization rate and inability to effectively fill the pores inside the recycled sand concrete to form a dense structure. Under the same mass ratio, the overall performance of the recycled sand concrete is poor, and the water absorption rate is high. Modified fly ash that has undergone further pore-forming modification has a porous structure and its activity is further enhanced, which can further improve the overall performance of high-performance recycled sand concrete.

[0115] As can be seen from the performance test data of Examples 1-4 and Comparative Example 4, the addition of MgO expansive agent can improve the strength and impermeability of recycled sand concrete to a certain extent, reduce the water absorption rate of recycled sand concrete, and MgO can react with other raw materials to generate Mg(OH)2, which plays an expansion role to make up for the pores and defects inside the recycled sand concrete, reduce the generation of cracks, and make the concrete more durable.

[0116] The performance test data from Examples 1-4, Examples 7-10, and Comparative Example 3 show that the addition of recycled steel fibers and recycled plastic fibers plays a positive role in the strength and toughness of recycled sand concrete. Moreover, the synergistic use of the two as raw materials has a more significant effect on improving the performance of recycled sand concrete. Pretreatment of recycled fibers with H2O2 can effectively remove impurities from the surface of recycled fibers and improve their purity. Grinding can effectively shorten the long fibers in recycled fibers, making the length, diameter, and shape of the recycled fibers more uniform. This promotes more uniform dispersion of recycled fibers in the recycled sand concrete, forming a more uniform and dense fiber network, resulting in better strength and durability of recycled sand high-performance concrete and reduced water absorption.

[0117] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-performance concrete made from recycled sand, characterized in that, By weight, it comprises 800-900 parts modified recycled sand, 600-650 parts cement, 400-500 parts modified fly ash, 50-80 parts recycled fiber, 30-40 parts MgO expanding agent, 20-30 parts water-reducing agent, and 100-200 parts cenospheres; the modified recycled sand is made by modifying recycled sand obtained from waste construction waste after building demolition. The modified fly ash is made from coal-fired waste fly ash after processing and modification; The method for preparing the modified recycled sand includes the following steps: crushing, screening, magnetic separation, and air separation of the waste construction waste after demolition to obtain recycled sand; adding the recycled sand to a phosphoric acid solution for washing, and then performing sand-liquid separation, and repeatedly washing 3-5 times to obtain primary modified recycled sand; drying and cooling the primary modified recycled sand at 70-80℃ to obtain modified recycled sand. The method for preparing the modified fly ash includes the following steps: adding coal waste fly ash to a composite solution of NaOH and silane coupling agent in a volume ratio of (1-2):1, stirring for 4-5 hours in a water bath at 50-60℃ to obtain pretreated fly ash, wherein the mass ratio of the coal waste fly ash to the composite solution is 1:(4-5); filtering and washing the pretreated fly ash, drying it at 150-170℃, and cooling it to obtain modified fly ash; The modified fly ash undergoes the following pretreatment: a pore-forming agent and a binder are added to the modified fly ash and mixed and stirred. The mixture is then calcined at 500-600℃ for 2-3 hours and cooled. The mass ratio of the coal waste fly ash to the pore-forming agent and binder is (3-4):(0.5-0.8):0.

2.

2. The high-performance concrete made from recycled sand according to claim 1, characterized in that, The primary modified recycled sand undergoes the following pretreatment before drying: the primary modified recycled sand is soaked in water for 30-40 minutes.

3. The high-performance concrete made from recycled sand according to claim 1, characterized in that: The recycled fiber comprises recycled steel fiber and recycled plastic fiber in a mass ratio of (1-2):

1.

4. The high-performance concrete made from recycled sand according to claim 1, characterized in that: The water-reducing agent is any one of naphthalene-based water-reducing agents, lignin sulfonates, or water-soluble resin sulfonates.

5. The high-performance concrete made from recycled sand according to claim 1, characterized in that: The cenospheres have an apparent density of 0.6 × 10⁻⁶. 3 kg / m 3 -0.8×10 3 kg / m 3 Spherical fly ash particles.

6. A method for preparing high-performance concrete using recycled sand according to any one of claims 1-5, characterized in that, Includes the following steps: Modified recycled sand, MgO expanding agent, and cement are mixed and stirred for 10-15 minutes to obtain a preliminary mixture; Add modified fly ash, recycled fiber, water-reducing agent and cenospheres to the primary mixture, and continue stirring for 10-15 minutes to obtain the intermediate mixture; Add water to the intermediate mixture and mix for 20-30 minutes to obtain recycled sand high-performance concrete. The mass ratio of the intermediate mixture to water is (10-15):

1.

7. The method for preparing high-performance concrete using recycled sand according to claim 6, characterized in that, The regenerated fibers undergo the following pretreatment: The regenerated fibers were soaked in H2O2 solution for 8-10 hours, washed with water, and dried. Grind the dried regenerated fibers for 10-15 minutes.

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