Preparation method of modified recycled coarse aggregate and recycled concrete

Abstract

The invention provides a preparation method of modified recycled coarse aggregate and recycled concrete, and the preparation method comprises the following steps: carrying out vacuum treatment on the recycled coarse aggregate to obtain pretreated recycled coarse aggregate; the preparation method comprises the following steps: adding a nano modifier and a dispersant into water, and stirring to obtain a nano modifier mixed solution; in a vacuum environment, adding and immersing the pretreated recycled coarse aggregate into a nano modifier mixed solution, starting to soak the recycled coarse aggregate, introducing carbon dioxide for carbonization treatment while soaking, taking out the recycled coarse aggregate after a period of time, and drying the recycled coarse aggregate until the weight of the recycled coarse aggregate is constant to obtain modified recycled coarse aggregate; and finally, preparing the recycled concrete by using a mixed solution of the modified recycled coarse aggregate and the nano modifier soaked with the recycled coarse aggregate. The vacuum pretreatment process, the nano-modification process and the carbonization treatment process are effectively integrated, so that the vacuum pretreatment process, the nano-modification process and the carbonization treatment process are mutually assisted, and the performance of the recycled coarse aggregate is jointly optimized, so that the performance of the recycled concrete is improved.

Description

Technical Field

[0001] The invention relates to the technical field of recycled concrete, and in particular to a preparation method of modified recycled coarse aggregate and recycled concrete. Background Art

[0002] At a time when the world is in urgent need of green environmental protection and strict control of carbon emissions, the construction industry faces huge challenges in reducing costs and achieving sustainable development. With the acceleration of urbanization and the booming construction industry, the demand for concrete continues to increase. However, traditional concrete production consumes a lot of natural resources, and waste concrete also brings environmental pressure. These problems need to be solved urgently, so recycled concrete is gradually gaining attention as a sustainable building material. In the application field of recycled concrete, the performance of coarse aggregate is the key to quality. Because the coarse aggregate of recycled concrete has experienced long-term complex stress environment and chemical erosion in previous use, it has been damaged and aged. The old cement slurry on its surface is attached or damaged, resulting in poor bonding with the cement slurry, affecting the mechanical properties. There are also a large number of irregular microcracks and pores inside, the structure is loose, and the alkali-aggregate reaction activity is high, which will reduce the durability of concrete.

[0003] In order to improve the performance of recycled concrete coarse aggregate and improve the quality of recycled concrete, researchers have conducted a lot of exploration and attempts. Traditional treatment methods, such as simple washing and screening, have limited effects and are difficult to meet the increasingly stringent requirements of construction projects. The development of nanotechnology has brought new opportunities to the field of recycled concrete. Nanomaterials have shown great potential in improving the performance of concrete due to their extremely small particle size and unique physical and chemical properties. At the same time, carbonization treatment is also considered to be an effective strengthening method. However, single nano-modification or carbonization treatment still has certain limitations in practical applications. Therefore, exploring a new method of synergistically treating recycled concrete coarse aggregate with nano-modification and carbonization to prepare a new type of recycled concrete with better performance has important practical significance and broad application prospects.

[0004] However, the current method of synergistically treating recycled concrete coarse aggregates with nano-modification and carbonization still has certain limitations. For example, in terms of nano-modification, single nanomaterials are currently used more frequently, and the performance improvement of single nanomaterials on recycled aggregates is limited. For example, nano-TiO2 is mainly outstanding in photocatalysis and antibacterial properties, but the improvement in strength and wear resistance is not significant; at the same time, a single nanomaterial is difficult to meet the complex and changing engineering needs, and cannot adapt to the diverse requirements of concrete in different engineering environments. Similarly, the current main carbonization methods also face many problems. On the one hand, although dry carbonization is relatively simple, the carbonization effect may not be uniform enough. On the other hand, although pressurized carbonization can improve the carbonization efficiency to a certain extent, it has high requirements for equipment and is relatively complex to operate.

[0005] In addition, in the current synergistic treatment of nano-modification and carbonization, nano-modification and carbonization are often carried out separately, lacking an effective connection mechanism. In the process of nano-modification, nano-materials are simply applied to the coarse aggregate of recycled concrete, without considering the needs and effects of subsequent carbonization treatment. Similarly, carbonization treatment only focuses on the reaction between CO2 and aggregate, while ignoring the synergistic effect that nano-materials may bring. This relatively isolated treatment method makes it impossible for nano-modification and carbonization to form an organic whole and give full play to their respective advantages. For example, in traditional methods, the addition of nano-materials may only be to improve a certain property of aggregate, without considering the impact on nano-materials during carbonization. At the same time, carbonization treatment simply improves the density and stability of aggregates, without further improving the carbonization effect with the help of the special properties of nano-materials. This lack of interactive treatment method has resulted in certain limitations on the effects of nano-modification and carbonization. Moreover, in the current methods, the time sequence of nano-modification and carbonization is usually fixed. First, nano-material modification is carried out first, and then carbonization treatment is implemented; second, carbonization treatment is carried out first, followed by nano-modification. However, both methods have significant defects. On the one hand, this fixed order limits the possibility of collaboration between the two and cannot be flexibly adjusted according to actual conditions. On the other hand, this process is time-consuming and greatly reduces production efficiency. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for preparing modified recycled coarse aggregate and recycled concrete, wherein the recycled coarse aggregate is vacuum treated, and a method for simultaneously treating the recycled coarse aggregate by nano-modification and carbonization is adopted, thereby effectively integrating the vacuum pretreatment, nano-modification and carbonization treatment processes so that they assist each other and jointly optimize the performance of the recycled coarse aggregate, thereby improving the performance of the recycled concrete.

[0007] In order to solve the above technical problems, the technical solution of the present invention is:

[0008] A method for preparing modified recycled coarse aggregate comprises the following steps:

[0009] S1. Vacuum-treat the recycled coarse aggregate to obtain pre-treated recycled coarse aggregate. By pre-vacuum-treating the recycled coarse aggregate, the air in the pores of the aggregate is effectively removed, which allows the nano-modifier to penetrate deeper into the aggregate and give full play to its performance advantages. It also provides favorable conditions for the carbonization process, allowing CO2 gas to penetrate more smoothly, increasing the carbonization depth and making the carbonization more efficient and uniform.

[0010] S2. Adding a nano-modifier and a dispersant into water and stirring to obtain a nano-modifier mixture, wherein the nano-modifier is composed of nano-TiO2, nano-Al2O3 and nano-ZrO2 in a certain proportion, and the dispersant is a water reducer and PAM; the binary combination of nano-TiO2 and nano-Al2O3 in the nano-modifier can improve the microstructure of the recycled coarse aggregate, making it denser and reducing intermittent pores; and nano-ZrO2 can accelerate the carbonization reaction, increase the amount of calcium carbonate generated, and enhance the carbonization and curing effect of the recycled coarse aggregate; the three nanomaterials in the nano-modifier interact with each other, aiming to achieve the best synergistic effect of the three nanomaterials to maximize the performance of the recycled coarse aggregate;

[0011] S3. In a vacuum environment, the nano-modifier mixture is added to and immersed in the pre-treated recycled coarse aggregate, and carbon dioxide is introduced for carbonization treatment. After a period of time, the modified recycled coarse aggregate is taken out and dried to a constant weight to obtain the modified recycled coarse aggregate.

[0012] The nano-modifier soaking modification and carbonization treatment are carried out simultaneously. At this time, in a high humidity environment, CO2 first reacts with water to generate carbonic acid: CO2+H2O→H2CO3. Then, carbonic acid reacts with calcium hydroxide in the recycled coarse aggregate to generate stable compounds such as calcium carbonate (CaCO3): Ca(OH)2+H2CO3→CaCO3+2H2O. At the same time, hydrated calcium silicate also reacts with carbonic acid: 3CaO·2SiO2·3H2O+3CO2→CaCO3+2SiO2·3H2O. This chemical reaction can fill the pores and microcracks inside the aggregate and enhance the density and strength of the aggregate. Higher humidity helps promote the dissolution and diffusion of CO2, accelerate the chemical reaction, and thus more effectively improve the performance of the aggregate.

[0013] Moreover, each component in the nano-modifier has its own unique performance advantages. Reasonable combination can produce synergistic effects, showing a significant effect of "1+1+1>3". Among them, nano-ZrO2 can reduce the size and orientation of calcium hydroxide (CH) crystals, increase the reactivity of CH, and thus accelerate the carbonization reaction. In addition, nano-ZrO2 can provide more nucleation sites, promote the reaction of CO2 and hydration products, and enable the recycled coarse aggregate to absorb CO2 more effectively during the carbonization process and generate more calcium carbonate. In addition, the nano-modifier can also optimize the microstructure of the coarse aggregate, reduce internal pores, and improve the density of the coarse aggregate, thereby enhancing the stability and durability of the coarse aggregate during the carbonization process.

[0014] Furthermore, before the recycled coarse aggregate is vacuum treated, the recycled coarse aggregate is cleaned and dried to a constant weight.

[0015] Furthermore, the vacuum degree during vacuum treatment in step S1 is 0.1 MPa, and the vacuum treatment time is 30-60 min.

[0016] Further, in step S2, the water reducer is an aminosulfonate-based high-efficiency water reducer; PAM is anionic, and the molecular weight of PAM is 10-12 million; the nanoparticles in the nanomodifier have high surface energy and are prone to agglomeration. The aminosulfonate-based high-efficiency water reducer can be adsorbed on the surface of the nanoparticles, and the nanoparticles are dispersed by electrostatic repulsion to reduce agglomeration; at the same time, the water reducer can also reduce the thickness of the water film on the surface of the nanoparticles, release more free water, and further enhance the dispersion effect. As an anionic high molecular polymer, the long chain structure of PAM can form a steric hindrance between the nanoparticles, effectively prevent the aggregation of the nanoparticles, and keep them in a stable dispersed state. In addition, PAM can also interact with the charges on the surface of the nanoparticles, enhance the electrostatic repulsion between the particles, and further promote the stability of the dispersion. The water reducer and PAM work together to effectively disperse the nanoparticles in the nanomodifier and improve the uniform distribution of the nanoparticles in the system, thereby giving full play to the modification effect of the nanoparticles and improving the performance of the recycled coarse aggregate.

[0017] Furthermore, the mass concentration of the nano-modifier in the nano-modifier mixture in step S2 is 2%-4%; the mass ratio of nano-TiO2, nano-Al2O3 and nano-ZrO2 is (32%-36%):(32%-36%):(28%-32%).

[0018] Furthermore, in step S2, the mass concentration of the dispersant in the nano-modifier mixed solution is 2.9%-4.7%, wherein the mass ratio of PAM to the water reducing agent is (0.53%-0.85%):(99.15%-99.47%).

[0019] Furthermore, the time for soaking and simultaneous carbonization in step S3 is 8 to 16 hours.

[0020] Furthermore, the carbonization rate in step S3 is: 100% CO2 gas is introduced at a constant flow rate of 0.1 to 0.3 liters / minute.

[0021] Furthermore, modified recycled coarse aggregate is prepared by a vacuum multi-pipeline aeration integrated carbonization device; the vacuum multi-pipeline aeration integrated carbonization device comprises a closed container, a vacuum pump and a CO2 gas cylinder, the closed container is connected to the vacuum pump through a vacuum pipe, a vacuum pressure gauge for detecting the vacuum degree in the closed container is installed on the closed container, the vacuum pump works to evacuate the closed container, and the vacuum degree in the closed container is displayed by the vacuum pressure gauge; the CO2 gas cylinder is connected to the closed container through a CO2 delivery pipeline, a pressure regulating valve is provided on the CO2 gas cylinder, a gas flowmeter is connected to the CO2 delivery pipeline, and the pressure regulating valve is adjusted to control the introduction of CO2 gas into the closed container.

[0022] The present invention also provides a recycled concrete prepared based on modified recycled coarse aggregate, wherein the specific components of the recycled concrete are as follows: 157-163 parts of natural coarse aggregate, 157-163 parts of modified recycled coarse aggregate, 148-152 parts of natural fine aggregate, 100-105 parts of ordinary Portland cement, and 51-54 parts of a nano-modifier mixed solution obtained by soaking the recycled coarse aggregate.

[0023] When the nano-modifier mixture after soaking the recycled coarse aggregate is added to the recycled concrete, nano-TiO2 has photocatalytic and antibacterial properties, while nano-Al2O3 is beneficial to enhance the hardness and stability of the recycled concrete. The two work together to promote the formation of a denser microstructure of the recycled concrete, thereby reducing the presence of intermittent pores. Nano-ZrO2 can continue to play a role inside the concrete, accelerate the carbonation reaction, increase the amount of calcium carbonate generated, and thus enhance the carbonation curing effect of the concrete. At the same time, nano-ZrO2 can optimize the structure of cement hydration products, promote hydration reactions, increase density, and thus improve the compressive and tensile strength properties of concrete. The nano-TiO2, nano-Al2O3 and nano-ZrO2 in the mixture interact with each other and jointly improve the performance of the recycled concrete, making it significantly improved in terms of strength, durability and wear resistance.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) by pre-vacuuming the recycled coarse aggregate, the air in the pores of the aggregate is effectively removed, so that the nano-modifier can penetrate deeper into the aggregate and give full play to its performance advantages. This also provides favorable conditions for the carbonization process, allowing CO2 gas to penetrate more smoothly, increasing the carbonization depth and making the carbonization more efficient and uniform.

[0025] (2) In the present invention, the immersion modification of the nano-modifier and the carbonization treatment are carried out simultaneously, so that the immersion modification and the carbonization treatment interact with each other. The nanomaterials in the nano-modifier can fully contact with the coarse aggregate and be modified. At the same time, nano-ZrO2 can improve the carbon fixation efficiency of the recycled coarse aggregate due to its unique properties. Moreover, the high humidity environment under the immersion condition promotes the carbonization reaction, and the air disturbance effect makes the nanomaterials better dispersed in the concrete, thereby enhancing the effect of nano-modification.

[0026] (3) The preparation of the modified recycled aggregate in the present invention is carried out in a vacuum multi-pipe aeration integrated carbonization device, which effectively integrates the vacuum treatment, immersion modification and carbonization treatment processes of the recycled coarse aggregate, so that they promote each other and jointly improve the performance of the recycled coarse aggregate; at the same time, it also improves the processing efficiency, reduces time and cost, and enhances the stability and reliability of the processing.

[0027] (4) In the present invention, a nano-modifier mixture obtained by soaking recycled coarse aggregate is added to the recycled concrete. The nano-TiO2 in the nano-modifier has properties such as photocatalysis and antibacterial properties, which can improve the durability of the concrete to a certain extent. The nano-Al2O3 helps to enhance the hardness and stability of the aggregate, and the nano-ZrO2 can improve the carbonization efficiency. These three nano-materials cooperate with each other and can combine their respective advantages to significantly improve the strength, wear resistance, durability and other capabilities of the recycled concrete. Therefore, the recycled concrete of the present invention is suitable for a variety of projects and different application environments and has a wider applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the vacuum multi-pipeline aeration integrated carbonization device in the present invention;

[0029] In the figure, 1-CO2 gas cylinder, 2-pressure regulating valve, 3-gas flow meter, 4-CO2 main delivery pipeline, 5-porous diverter, 6-CO2 diversion delivery pipeline, 7-pipeline valve, 8-sealed container, 9-nano modifier mixture, 10-recycled coarse aggregate particles, 11-aeration stone, 12-vacuum pressure gauge, 13-vacuum pipeline, 14-vacuum pump. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0031] The modified recycled coarse aggregate provided by the present invention is prepared in a vacuum multi-channel aeration integrated carbonization device. The structure of the vacuum multi-channel aeration integrated carbonization device is as follows: Figure 1The vacuum multi-pipe aeration integrated carbonization device comprises a closed container 8, a vacuum pump 14 and a CO2 gas cylinder 1. The closed container is connected to the vacuum pump through a vacuum pipe 13. A vacuum pressure gauge 12 for detecting the vacuum degree in the closed container is installed on the closed container. When the vacuum pump is working, the closed container is evacuated, and the vacuum degree in the closed container is displayed by the vacuum pressure gauge.

[0032] The CO2 gas cylinder is connected to the closed container through a CO2 delivery pipeline. A pressure regulating valve 2 is provided on the CO2 gas cylinder. A gas flow meter 3 is connected to the CO2 delivery pipeline. The pressure regulating valve is adjusted to control the introduction of CO2 gas into the closed container. Specifically, the CO2 delivery pipeline includes a CO2 main delivery pipeline 4 and multiple CO2 shunt delivery pipelines 6. One end of the CO2 main delivery pipeline is connected to the CO2 gas cylinder, and the other end of the CO2 main delivery pipeline is connected to one end of multiple CO2 shunt delivery pipelines through a porous diverter 5. The other ends of multiple CO2 shunt delivery pipelines are all connected to the closed container to achieve multi-pipeline aeration in the closed container. Furthermore, pipeline valves 7 are installed on the CO2 shunt delivery pipelines to facilitate aeration management. Preferably, one end of the CO2 shunt delivery pipeline located in the closed container is connected to an aeration stone 11, and the aeration stone and CO2 gas work together to form bubble aeration, thereby generating effective gas disturbance. A solution addition port (not shown in the figure) is provided on the closed container.

[0033] The method for preparing the modified recycled coarse aggregate provided by the present invention comprises the following steps:

[0034] S1. Wash the recycled coarse aggregate to remove residual mortar and dust on the surface, and dry it to constant weight;

[0035] Specifically, the recycled coarse aggregate is in two grades, wherein the recycled coarse aggregate with a particle size of 4.75 to 9.5 mm accounts for 71.04%, and the recycled coarse aggregate with a particle size of 9.5 to 16 mm accounts for 28.96%.

[0036] S2. Vacuum-treating the recycled coarse aggregate to obtain pre-treated recycled coarse aggregate, wherein the vacuum degree during vacuum treatment is 0.1 MPa and the vacuum treatment time is 30-60 min;

[0037] Specifically, the vacuum treatment of recycled coarse aggregate is carried out in a vacuum multi-pipeline aeration integrated carbonization device, see Figure 1 , place 10 recycled coarse aggregate particles in a closed container, turn on the vacuum pump until the vacuum degree in the closed container is 0.1MPa, turn off the vacuum pump, and discharge the air in the gaps of the recycled coarse aggregate under a vacuum environment of 0.1MPa. If the vacuum degree drops, continue to turn on the vacuum pump to draw vacuum and maintain the vacuum degree at 0.1MPa. The entire vacuum treatment time is 30-60min to ensure that the air in the gaps of the recycled coarse aggregate is completely discharged.

[0038] S3. Add the nano-modifier and the dispersant into water and stir manually for about 10 minutes to obtain a nano-modifier mixture, wherein the nano-modifier is composed of nano-TiO2, nano-Al2O3 and nano-ZrO2 in a certain proportion, and the dispersant is a water reducer and PAM; specifically, the mass concentration of the nano-modifier in the nano-modifier mixture is 2%-4%; the mass ratio of nano-TiO2, nano-Al2O3 and nano-ZrO2 is (32%-36%):(32%-36%):(28%-32%); the mass concentration of the dispersant in the nano-modifier mixture is 2.9%-4.7%, wherein the mass ratio of PAM to water reducer is (0.53%-0.85%):(99.15%-99.47%).

[0039] Furthermore, the water reducer is an aminosulfonate-based high-efficiency water reducer; PAM is an anionic type, and the molecular weight of PAM is 10-12 million.

[0040] S4. In a vacuum environment, adding the nano-modifier mixture to the pre-treated recycled coarse aggregate and immersing it, starting to immerse the recycled coarse aggregate, introducing carbon dioxide to perform carbonization treatment during the immersion treatment, and taking it out after a period of time and drying it to a constant weight to obtain a modified recycled coarse aggregate;

[0041] Specifically, after the vacuum treatment time in step S1 reaches 30-60 minutes, the nano-modifier mixed solution is injected into the sealed container through the solution addition port on the sealed container until the nano-modifier mixed solution 9 immerses the pre-treated recycled coarse aggregate. Figure 1 . During the entire process of mixed liquid injection, keep the vacuum pumping to ensure that the vacuum degree in the closed container is 0.1MPa. After the mixed liquid is injected, seal the solution inlet, turn off the vacuum pump, open the pressure regulating valve on the CO2 cylinder and the pipeline valve on the CO2 diversion pipeline, and introduce CO2 gas into the closed container to achieve carbonization treatment while soaking. The soaking and synchronous carbonization time is 8 to 16 hours. Multi-channel aeration can ensure that CO2 gas is evenly distributed in the solution for soaking coarse aggregates, improving the uniformity of carbonization; at the same time, bubble aeration is formed under the joint action of the aeration stone, thereby generating effective gas disturbance and helping the dispersion of the nano modifier.

[0042] According to the value of the gas flow meter, adjust the pressure regulating valve to ensure that 100% CO2 gas enters the closed container at a constant flow rate of 0.1 to 0.3 liters / minute.

[0043] Furthermore, in steps S1 and S4, the aggregate is dried to constant weight in a drying oven at 105°C to 110°C for 8 hours, cooled to room temperature and weighed after the initial drying; the aggregate is placed in the drying equipment again for further drying for 2 hours, then cooled to room temperature and weighed again; the weighing results are checked twice, and if the weight change does not exceed 0.1% to 0.2%, it indicates that the aggregate has been dried to constant weight. If the weight change exceeds this range, continue drying until constant weight is reached.

[0044] In the present invention, recycled concrete is prepared based on modified recycled coarse aggregate. The specific components of the recycled concrete are as follows: 157-163 parts of natural coarse aggregate, 157-163 parts of modified recycled coarse aggregate, 148-152 parts of natural fine aggregate, 100-105 parts of ordinary Portland cement, and 51.54-53.66 parts of a nano-modifier mixed solution obtained by soaking the recycled coarse aggregate.

[0045] Example 1

[0046] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0047] In step S3, 40 g of nano modifier (nano-TiO2 14 g, nano-Al2O3 14 g and nano-ZrO2 12 g), 0.5 g of PAM and 58.2 g of water reducer are added into 1901.3 g of water, and stirred to obtain 2000 g of a nano modifier mixed solution with a concentration of 2%;

[0048] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.1 liter / minute, and the soaking and synchronous carbonization time is 8 hours.

[0049] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 773.15g of a nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 22.5g of water reducer, 15.46g of nano-modifier, and 0.19g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then cured for 28 days under standard conditions.

[0050] Example 2

[0051] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0052] In step S3, 60 g of nano modifier (nano-TiO2 21 g, nano-Al2O3 21 g and nano-ZrO2 18 g), 0.5 g of PAM and 76.95 g of water reducer are added to 1862.55 g of water, and stirred to obtain 2000 g of a nano modifier mixed solution with a concentration of 3%;

[0053] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.1 liter / minute, and the soaking and synchronous carbonization time is 16 hours.

[0054] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 789.24g of a nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 30g of a water reducer, 24.04g of a nano-modifier, and 0.20g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then cured for 28 days under standard conditions.

[0055] Example 3

[0056] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0057] In step S3, 80 g of nano modifier (nano-TiO2 28 g, nano-Al2O3 28 g and nano-ZrO2 24 g), 0.5 g of PAM and 93.18 g of water reducer are added to 1826.32 g of water, and stirred to obtain 2000 g of a nano modifier mixed solution with a concentration of 4%;

[0058] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.1 liter / minute, and the soaking and synchronous carbonization time is 24 hours.

[0059] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 804.89g of the nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 37.5g of water reducer, 32.19g of nano-modifier, and 0.2g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then continued to be cured for 28 days under standard conditions.

[0060] Example 4

[0061] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0062] In step S3, 60 g of nano modifier (nano-TiO2 21 g, nano-Al2O3 21 g and nano-ZrO2 18 g), 0.5 g of PAM and 76.95 g of water reducer are added to 1862.55 g of water, and stirred to obtain 2000 g of a nano modifier mixed solution with a concentration of 3%;

[0063] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.2 liters / minute, and the soaking and synchronous carbonization time is 24 hours.

[0064] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 789.24g of a nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 30g of a water reducer, 24.04g of a nano-modifier, and 0.20g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then cured for 28 days under standard conditions.

[0065] Example 5

[0066] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0067] In step S3, 80 g of nano modifier (nano-TiO2 28 g, nano-Al2O3 28 g and nano-ZrO2 24 g), 0.5 g of PAM and 93.18 g of water reducer are added to 1826.32 g of water, and stirred to obtain 2000 g of a nano modifier mixed solution with a concentration of 4%;

[0068] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.2 liters / minute, and the soaking and synchronous carbonization time is 8 hours.

[0069] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 804.89g of the nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 37.5g of water reducer, 32.19g of nano-modifier, and 0.2g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then continued to be cured for 28 days under standard conditions.

[0070] Example 6

[0071] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0072] In step S3, 40 g of nano modifier (nano-TiO2 14 g, nano-Al2O3 14 g and nano-ZrO2 12 g), 0.5 g of PAM and 58.2 g of water reducer are added into 1901.3 g of water, and stirred to obtain 2000 g of a nano modifier mixed solution with a concentration of 2%;

[0073] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.2 liters / minute, and the soaking and simultaneous carbonization time is 16 hours.

[0074] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 773.15g of a nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 22.5g of water reducer, 15.46g of nano-modifier, and 0.19g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then cured for 28 days under standard conditions.

[0075] Example 7

[0076] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0077] In step S3, 80 g of nano modifier (nano-TiO2 28 g, nano-Al2O3 28 g and nano-ZrO2 24 g), 0.5 g of PAM and 93.18 g of water reducer are added to 1826.32 g of water, and stirred to obtain 2000 g of a nano modifier mixed solution with a concentration of 4%;

[0078] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.3 liters / minute, and the soaking and simultaneous carbonization time is 16 hours.

[0079] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 804.89g of the nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 37.5g of water reducer, 32.19g of nano-modifier, and 0.2g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then continued to be cured for 28 days under standard conditions.

[0080] Example 8

[0081] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0082] In step S3, 40 g of nano modifier (nano-TiO2 14 g, nano-Al2O3 14 g and nano-ZrO2 12 g), 0.5 g of PAM and 58.2 g of water reducer are added into 1901.3 g of water, and stirred to obtain 2000 g of a nano modifier mixed solution with a concentration of 2%;

[0083] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.3 liters / minute, and the soaking and synchronous carbonization time is 24 hours.

[0084] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 773.15g of a nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 22.5g of water reducer, 15.46g of nano-modifier, and 0.19g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then cured for 28 days under standard conditions.

[0085] Example 9

[0086] In this embodiment, the modified recycled coarse aggregate and recycled concrete are prepared according to the above method, wherein in step S2, 2500 g of recycled coarse aggregate is placed in a closed container for vacuum treatment, the vacuum degree of the vacuum treatment is 0.1 MPa, and the vacuum treatment time is 30 min;

[0087] In step S3, 60 g of the novel modifier (nano-TiO2 21 g, nano-Al2O3 21 g and nano-ZrO2 18 g), 0.5 g of PAM and 76.95 g of a water reducer are added to 1862.55 g of water, and stirred to obtain 2000 g of a nano-modifier mixed solution with a concentration of 3%;

[0088] In step S4, the carbonization rate is 100% CO2 gas at a constant flow rate of 0.3 liters / minute, and the soaking and simultaneous carbonization time is 8 hours.

[0089] The specific components of the recycled concrete in this embodiment are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of modified recycled coarse aggregate, 2220g of natural medium sand, and 789.24g of a nano-modifier mixed solution after soaking the recycled coarse aggregate (including 735g of water, 30g of a water reducer, 24.04g of a nano-modifier, and 0.20g of PAM). Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then cured for 28 days under standard conditions.

[0090] Comparative Example 1

[0091] The preparation method of the recycled coarse aggregate obtained in this comparative example is: washing the recycled coarse aggregate to remove residual mortar and dust on the surface, and drying to constant weight to obtain pretreated recycled coarse aggregate.

[0092] The specific components of the recycled concrete in this comparative example are as follows: 1500g of ordinary Portland cement, 2355g of natural coarse aggregate, 2355g of pretreated recycled coarse aggregate, 2220g of natural medium sand, and 735g of water. Recycled concrete with a size of 10cm×10cm×10cm was prepared, cured in a mold for 1 day, then demolded, and then continued to be cured for 28 days under standard conditions.

[0093] Comparative Example 2

[0094] The preparation method of the modified recycled coarse aggregate in this comparative example is basically the same as that in Example 1, the only difference is that in this comparative example, the vacuum-treated recycled coarse aggregate is first soaked in a nano-modifier mixed solution alone, then taken out and dried to constant weight, and then carbonized to obtain the modified recycled coarse aggregate.

[0095] The preparation method of the recycled concrete in this comparative example is also basically the same as that in Example 1, the only difference being that the preparation method of the modified recycled coarse aggregate in this comparative example is different from that in Example 1.

[0096] Comparative Example 3

[0097] The preparation method of the modified recycled coarse aggregate in this comparative example is basically the same as that in Example 1, except that no vacuum treatment is performed in this comparative example.

[0098] The preparation method of the recycled concrete in this comparative example is also basically the same as that in Example 1, the only difference being that the preparation method of the modified recycled coarse aggregate in this comparative example is different from that in Example 1.

[0099] Comparative Example 4

[0100] The preparation method of the modified recycled coarse aggregate in this comparative example is consistent with that in Example 1.

[0101] The preparation method of the recycled concrete in this comparative example is also basically the same as that in Example 1, except that the modified agent mixture after the immersion treatment is not added to the recycled concrete in this comparative example.

[0102] Comparative Example 5

[0103] The preparation method of the modified recycled coarse aggregate in this comparative example is basically the same as that in Example 5, the only difference is that the nano-modifier in this comparative example does not contain nano-ZrO2, and the nano-modifier in this comparative example is composed of nano-TiO2 and nano-Al2O3, and the mass ratio of the two is 50%:50%.

[0104] The preparation method of the recycled concrete in this comparative example is also basically the same as that in Example 5, the only difference being that the preparation method of the modified recycled coarse aggregate in this comparative example is different from that in Example 5.

[0105] The properties of the recycled concrete obtained in the above examples and comparative examples were tested, and the results are shown in the following table:

[0106] Compressive strength(MPa) Methyl orange degradation rate (%) Wear rate (%) Frost resistance strength loss rate (%) Example 1 51.33 11.82 3.47 9.21 Example 2 54.2 14.25 2.93 7.6 Example 3 55.8 16.55 2.62 6.87 Example 4 56.5 13.5 2.79 7.03 Example 5 57.75 12.67 3.0 7.84 Example 6 51.5 13.23 2.85 7.47 Example 7 52.85 17.29 2.74 6.79 Example 8 53.21 12.57 3.1 8.09 Example 9 48.36 13.8 2.7 7.21 Comparative Example 1 46.7 0 4.88 12.5 Comparative Example 2 48.58 10.59 3.8 10.5 Comparative Example 3 47.27 11.21 4.29 11.87 Comparative Example 4 45.86 0 4.56 12.22 Comparative Example 5 50.5 12.87 3.2 8.8

[0107] It can be seen from the above results that the recycled concrete prepared by the present invention has improved strength, wear resistance and frost resistance, and the recycled concrete also has photocatalytic properties, which can improve the durability of concrete to a certain extent.

[0108] Test method for methyl orange degradation rate: (1) Prepare a 100 mg / L methyl orange solution as a pollutant; (2) Place a 10 cm × 10 cm × 10 cm recycled concrete sample in a container containing the methyl orange solution; (3) Use a light source (ultraviolet lamp) to irradiate the solution to simulate lighting conditions; (4) Take a sample after 60 minutes and use a spectrophotometer to measure the absorbance of methyl orange in the solution; (5) Calculate the degradation rate of methyl orange based on the change in absorbance. The calculation formula for the degradation rate is: (initial absorbance - absorbance at a certain moment) / initial absorbance × 100%; (6) Repeat the measurement multiple times and take the average value to improve the accuracy of the result.

[0109] Test method for frost resistance strength loss rate: (1) Place a test piece of 10cm×10cm×10cm in a freezing device and conduct a freeze-thaw cycle test. The number of freeze-thaw cycles and temperature conditions are determined according to the standard. Generally, the freezing temperature is -18±2℃, the melting temperature is 5±2℃, and the number of freeze-thaw cycles is 25 times; the time for each freeze-thaw cycle is 12 hours, of which the freezing time is 8 hours and the melting time is 4 hours. After the specified number of freeze-thaw cycles, take out the test piece and conduct a compressive strength test; (2) Calculate the frost resistance strength loss rate, the formula is: frost resistance strength loss rate = (strength before freeze-thaw - strength after freeze-thaw) / strength before freeze-thaw × 100%; (3) Conduct multiple tests and take the average value as the final strength loss rate result.

[0110] The wear rate test is carried out according to the following steps: (1) Prepare a recycled concrete specimen of 10cm×10cm×10cm; (2) Use a wear tester to perform a wear test on the specimen. Fix the specimen on the tester so that its surface contacts the wear medium (such as a grinding wheel or a steel ball). Wear the specimen under a certain pressure (0.5-1.5MPa) and wear time (10-30 minutes). The wear time and pressure can be set according to relevant standards or experimental requirements; (3) After the wear test, take out the specimen, clean it and dry it; (4) Measure the mass of the specimen before and after wear, calculate the mass loss, and the wear rate calculation formula is: wear rate = (mass before wear - mass after wear) / mass before wear × 100%; (5) Repeat the test multiple times and take the average value as the final wear rate result.

Claims

1. A method for preparing modified recycled coarse aggregate, characterized in that The following steps are involved: S1. Vacuum-treating the recycled coarse aggregate to obtain pre-treated recycled coarse aggregate; S2, adding a nano-modifier and a dispersant into water, stirring to obtain a nano-modifier mixed solution, wherein the nano-modifier is composed of nano-TiO2, nano-Al2O3 and nano-ZrO2 in a certain proportion, and the dispersant is a water reducer and PAM; S3. In a vacuum environment, the nano-modifier mixture is added to the pre-treated recycled coarse aggregate and immersed to start soaking the recycled coarse aggregate. During the soaking treatment, carbon dioxide is introduced for carbonization treatment. After a period of time, the modified recycled coarse aggregate is taken out and dried to a constant weight to obtain the modified recycled coarse aggregate.

2. The method for preparing modified recycled coarse aggregate according to claim 1, characterized in that: Before the recycled coarse aggregate is vacuum treated, the recycled coarse aggregate is cleaned and dried to constant weight.

3. The method for preparing modified recycled coarse aggregate according to claim 1, characterized in that: The vacuum degree during vacuum treatment in step S1 is 0.1 MPa, and the vacuum treatment time is 30-60 min.

4. The method for preparing modified recycled coarse aggregate according to claim 1, characterized in that: The water reducing agent in step S2 is an aminosulfonate-based high-efficiency water reducing agent; PAM is an anionic type, and the molecular weight of PAM is 10-12 million.

5. The method for preparing modified recycled coarse aggregate according to claim 1, characterized in that: The mass concentration of the nano-modifier in the nano-modifier mixed solution in step S2 is 2%-4%; the mass ratio of nano-TiO2, nano-Al2O3 and nano-ZrO2 is (32%-36%): (32%-36%): (28%-32%).

6. The method for preparing modified recycled coarse aggregate according to claim 1, characterized in that: The mass concentration of the dispersant in the nano-modifier mixed solution in step S2 is 2.9%-4.7%, wherein the mass ratio of PAM to water reducer is (0.53%-0.85%):(99.15%-99.47%).

7. The method for preparing modified recycled coarse aggregate according to claim 1, characterized in that: The time for soaking and simultaneous carbonization in step S3 is 8 to 16 hours.

8. The method for preparing modified recycled coarse aggregate according to claim 1, characterized in that: The carbonization rate in step S3 is: 100% CO2 gas is introduced at a constant flow rate of 0.1 to 0.3 liters / minute.

9. The method for preparing modified recycled coarse aggregate according to claim 1, characterized in that: Modified recycled coarse aggregate is prepared by a vacuum multi-pipeline aeration integrated carbonization device; the vacuum multi-pipeline aeration integrated carbonization device comprises a closed container, a vacuum pump and a CO2 gas cylinder, the closed container is connected to the vacuum pump through a vacuum pipe, a vacuum pressure gauge for detecting the vacuum degree in the closed container is installed on the closed container, when the vacuum pump works, the closed container is evacuated, and the vacuum degree in the closed container is displayed by the vacuum pressure gauge; the CO2 gas cylinder is connected to the closed container through a CO2 delivery pipeline, a pressure regulating valve is provided on the CO2 gas cylinder, a gas flowmeter is connected to the CO2 delivery pipeline, and the pressure regulating valve is adjusted to control the introduction of CO2 gas into the closed container.

10. A recycled concrete prepared based on the modified recycled coarse aggregate according to claim 1, characterized in that: The specific components of the recycled concrete are as follows: 157-163 parts of natural coarse aggregate, 157-163 parts of modified recycled coarse aggregate, 148-152 parts of natural fine aggregate, 100-105 parts of ordinary Portland cement, and 51-54 parts of nano-modifier mixed liquid after soaking the recycled coarse aggregate.

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