A concrete composition for precast members having improved strength and durability and a method for producing the same

Abstract

The application relates to the technical field of building materials, and particularly discloses a precast component concrete composition with improved strength and durability and a preparation method thereof, which comprises the following raw materials in parts by weight: 60-70 parts of Portland cement, 20-30 parts of slag powder, 1-2 parts of a water reducing agent, 0.2-0.5 parts of anti-cracking fiber, 1-3 parts of composite conductive reinforcing material, 0.5-2.5 parts of early-strength and slump-keeping adjusting agent, 80-90 parts of modified recycled aggregate and 25-35 parts of mixing water; the composite conductive reinforcing material comprises carbon nanotubes and graphene. The composition prepared by the application can be used in more demanding and more complex building structures, and has the advantages of high strength and good durability.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a concrete composition for precast components with improved strength and durability, and a method for preparing the same. Background Technology

[0002] Precast concrete components are increasingly widely used in modern industrialized construction due to their advantages such as factory production, controllable quality, and high construction efficiency. However, as building structures develop towards higher, more complex, and more durable directions, and as the requirements for engineering sustainability continue to increase, traditional precast concrete faces many challenges. On the one hand, while pursuing high strength, conventional concrete often struggles to simultaneously achieve excellent durability, crack resistance, and long-term volume stability, leading to performance degradation of components under harsh environments or long-term loads, affecting structural safety and service life. On the other hand, there is an urgent need for the resource utilization of construction waste, but ordinary recycled aggregates, due to their inherent defects such as high water absorption, low strength, and weak interfacial bonding with cement paste, will significantly degrade the mechanical and durability properties of concrete when directly used in high-performance precast components, limiting their high-value applications.

[0003] In existing technologies, concrete performance is typically improved by using single or combined methods such as adding mineral admixtures, high-efficiency water-reducing agents, fibers, and special admixtures. For example, adding fibers can improve crack resistance, but it is difficult to significantly enhance both early strength and durability simultaneously; adding conductive nanomaterials (such as carbon nanotubes and graphene) is expected to strengthen and toughen the concrete, but their uniform dispersion and interface optimization in the cement matrix remain technical challenges; simple physical or chemical modification of recycled aggregates has limited strengthening effects and cannot meet ultra-high durability requirements. Furthermore, conventional curing processes cannot further optimize the microstructure of concrete and seal harmful pores while improving early strength.

[0004] Therefore, developing a concrete composition specifically for precast components that can systematically solve the above problems, namely, simultaneously achieving ultra-high strength, excellent durability, and superior crack resistance, and efficiently utilizing recycled aggregates, along with its corresponding preparation and curing methods, has become a key technological requirement for promoting the development of building industrialization and green building. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a concrete composition for precast components with improved strength and durability, and a method for preparing the same.

[0006] In a first aspect, this application provides a concrete composition for precast components that improves strength and durability, employing the following technical solution: A concrete composition for improving the strength and durability of precast components comprises the following raw materials in parts by weight: The mixture comprises 60-70 parts silicate cement, 20-30 parts slag powder, 1-2 parts water-reducing agent, 0.2-0.5 parts crack-resistant fiber, 1-3 parts composite conductive reinforcing material, 0.5-2.5 parts early strength-slump retention regulator, 80-90 parts modified recycled aggregate, and 25-35 parts mixing water; the composite conductive reinforcing material includes carbon nanotubes and graphene.

[0007] By employing the above technical solutions, the synergistic hydration reaction of silicate cement and slag powder forms a dense and stable ettringite and CSH gel matrix, significantly improving overall density and chemical stability. The addition of a water-reducing agent further optimizes particle dispersion and water-cement ratio, achieving lower porosity and higher matrix strength. Crack-resistant fibers effectively bridge and inhibit the initiation and propagation of microcracks at the microscale, greatly enhancing the material's toughness and crack resistance, thereby improving long-term durability. Carbon nanotubes and graphene in the composite conductive reinforcing material construct a three-dimensional network structure in the cement matrix through their nanoscale effect, not only filling nanopores and hindering crack extension but also strengthening the aggregate-paste interface transition zone, synergistically improving mechanical properties and impermeability. Early-strength and slump-retaining regulators regulate the hydration process, promoting early strength development while maintaining good workability, ensuring construction quality. Modified recycled aggregates, after surface treatment, enhance their adhesion to the paste, reducing internal defects and water absorption. The synergistic effect of these components enables concrete to exhibit excellent high strength and high durability after hardening. It can effectively resist performance degradation caused by environmental factors such as chloride ion erosion, carbonation, and freeze-thaw cycles, and improve the resistance to deformation and damage under load, thereby providing long-term reliable structural performance for precast components.

[0008] Optionally, the mass ratio of carbon nanotubes to graphene in the composite conductive reinforcing material is 1:1-5.

[0009] By employing the above technical solutions, carbon nanotubes and graphene form a multi-scale, multi-dimensional synergistic reinforced composite network structure in the concrete matrix. Carbon nanotubes, with their extremely high aspect ratio, interlock in three-dimensional space, forming a pervasive fibrous reinforcing skeleton. This not only effectively transfers and disperses stress but also significantly improves the material's electrical conductivity, providing a physical basis for potential intelligent monitoring. Meanwhile, sheet-like graphene, with its huge specific surface area and two-dimensional planar structure, tightly adheres to the interface between cement hydration products and aggregates. On the one hand, it efficiently fills nanoscale pores, blocking the diffusion channels of micro-cracks and greatly improving the density and impermeability of the matrix; on the other hand, its strong physical barrier effect effectively delays the intrusion path of corrosive media. More importantly, the two complement each other: graphene sheets provide a stable anchoring platform for carbon nanotubes, preventing their aggregation and maximizing their dispersion and reinforcing efficiency; while carbon nanotubes bridge adjacent graphene sheets, repairing their potential sheet defects, making the entire conductive reinforcement network more complete and stable. This synergistic effect not only significantly enhances the toughness, crack resistance, and overall mechanical strength of cement paste, but also comprehensively improves the durability of concrete by improving the microstructure and charge transport pathways in the interface transition zone, enabling it to resist the damage of complex environmental stresses for a longer period of time.

[0010] Optionally, the modified recycled aggregate is CO2 mineralized curing aggregate, and its preparation includes the following steps: placing the recycled aggregate in a pressure reactor, and under the conditions of a temperature of 50-80℃ and a relative humidity of 60-80%, introducing CO2 gas and maintaining the pressure inside the reactor at 0.2-0.5MPa, and curing for 12-48 hours.

[0011] By employing the above-mentioned technical solution, under suitable temperature, humidity, and pressure conditions, CO2 gas reacts with the active calcium components (such as calcium hydroxide and unhydrated calcium silicate) on the surface and within the pores of the aggregate, generating calcium carbonate crystals that provide both binding and filling effects. This process significantly seals the inherent microcracks and pores of the aggregate at the microscopic level, roughening and densifying its surface, thereby substantially reducing the aggregate's water absorption and crushing index, and enhancing its inherent mechanical strength. More importantly, the mineralized calcium carbonate layer optimizes the interfacial transition zone between the aggregate and the cement paste, strengthening their chemical bonding and mechanical interlocking, effectively reducing stress concentration and microcrack initiation caused by defects in the recycled aggregate. In terms of macroscopic performance, concrete using this modified aggregate exhibits significantly reduced internal defects and a marked improvement in uniformity and density. This not only directly enhances the compressive and flexural strength of the components but also systematically improves their durability, manifesting as superior resistance to chloride ion penetration, freeze-thaw cycles, and carbonation. Consequently, it provides precast components with long-term stable volume stability and load-bearing capacity. Simultaneously, this technology also offers environmental benefits such as carbon sequestration and emission reduction.

[0012] Optionally, the crack-resistant fiber is a composite of polypropylene fiber and polyvinyl alcohol microfiber, with lengths of 30-50 mm and 6-12 mm respectively, and a mass ratio of 1-2:1.

[0013] By employing the above technical solution, longer polypropylene fibers can effectively bridge and constrain visible cracks on a macroscopic scale. Their higher elastic modulus distributes the load, significantly improving the material's deformation capacity and fracture toughness under stress, and preventing the propagation of cracks. Shorter polyvinyl alcohol microfibers, with their fine diameter and large quantity, are uniformly dispersed within the slurry in the early stages of cement hydration. They can suppress initial microcracks caused by plastic shrinkage and drying shrinkage, and in hardened concrete, they form a stronger chemical bond and mechanical anchoring effect with the matrix, refining the pore structure at the microscopic level and hindering the propagation of nanoscale defects. The two are combined in a specific ratio to achieve functional complementarity and synergistic effect: the long fibers provide the overall structural support, preventing structural damage; the short fibers fill the microscopic areas not covered by the long fiber network, eliminating stress concentration points, thus blocking the propagation paths of cracks from the nanometer, micrometer, to millimeter scale layer by layer. This multi-level defense mechanism not only greatly improves the crack resistance and impact toughness of concrete, but also fundamentally cuts off the rapid intrusion channels of water and corrosive media by inhibiting cracks, thereby significantly enhancing the impermeability, corrosion resistance and long-term durability of the components.

[0014] Optionally, the early strength-slump retention regulator is a complex of lithium sulfate, lithium silicate and modified lignin sulfonate, wherein the mass ratio of lithium sulfate to lithium silicate is 1:1-3, the total amount of the two accounts for 40%-60% of the mass of the early strength-slump retention regulator, and the remainder is modified lignin sulfonate.

[0015] By employing the above-mentioned technical solution, the activity of silicate and aluminate minerals is efficiently stimulated under the synergistic effect of lithium sulfate and lithium silicate, significantly accelerating the formation and interweaving of key strength phases such as CSH gel and ettringite. This rapidly constructs a dense early-stage framework structure at the molecular scale, providing excellent early-stage strength development momentum for concrete. Simultaneously, the compounded modified lignin sulfonate, through adsorption on the surface of cement particles and hydration products, forms a stable steric hindrance and solvation film, effectively delaying the excessively rapid increase in hydration rate and locking in free water in the mixture. This significantly inhibits slump loss over time within several hours, ensuring that precast components have a sufficient and stable working window during production and casting. More importantly, the specific ratio of lithium sulfate to lithium silicate enables precise control over the hydration exothermic process and microstructure formation, avoiding microstructure defects caused by premature and rapid hydration. The presence of modified lignin sulfonate achieves good regulation of hydration speed. This synergistic effect ensures that the concrete can meet the early strength requirements for rapid demolding and lifting. Moreover, because the early structure formed is more uniform and has fewer defects, it lays a solid microscopic foundation for the continuous growth of subsequent strength and long-term durability.

[0016] Secondly, this application provides a method for preparing a concrete composition for precast components with improved strength and durability, employing the following technical solution: A method for preparing a concrete composition for precast components with improved strength and durability includes the following steps: S1. Add silicate cement, slag powder, and composite conductive reinforcing material into a mixer and dry mix at a speed of 60-80 r / min for 3-5 minutes; S2. Slowly add the mixed water containing the dissolved water-reducing agent to the dry material from step S1, increase the rotation speed to 120-150 r / min, and stir for 2-4 minutes to form a uniform conductive slurry. S3. Add modified recycled aggregate, crack-resistant fiber and early strength-slump retention modifier to the slurry in step S2 in sequence, adjust the speed to 100-120 r / min, stir for 3-5 minutes, add the remaining mixing water during the process, and form a uniform concrete mixture. S4. Pour the mixture into the mold, vibrate to compact it, and let it stand for 12-24 hours under standard curing conditions. After demolding, move it to an environment with a relative humidity of 60±5%, a temperature of 20±2℃, and a CO2 concentration of more than 20% for secondary carbonation curing for 7-14 days to obtain the concrete composition.

[0017] By adopting the above technical solution, the cementitious materials and nanoscale conductive materials are first thoroughly dry-mixed to ensure the pre-dispersion of carbon nanotubes and graphene in the powder, laying the foundation for the subsequent formation of a stable and uniform three-dimensional conductive reinforcing network in water. Under optimized rotation speed, the water-reducing agent solution and functional components are added stepwise. This not only achieves efficient dispersion of cement particles by polycarboxylate superplasticizer and the formation of a low water-cement ratio slurry, but also allows for the uniform distribution of crack-resistant fibers and early-strength-slump-maintaining regulators, enabling them to exert their functions of crack resistance and hydration regulation, respectively. The final addition of modified recycled aggregate maximizes the protection of its surface mineralization layer and pre-formed reinforced interface. The core of the entire mixing process is to construct a multi-scale synergistic reinforcement system from nanoscale conductive networks and micron-sized fiber networks to millimeter-level reinforced aggregate skeletons. Subsequently, a unique secondary carbonation curing process utilizes a CO2-rich environment after component molding to promote the continued carbonation reaction of unhydrated cement particles and active minerals in the slurry, generating calcium carbonate crystals that further fill capillary pores and interfacial transition zones, achieving comprehensive microstructure densification from the inside to the surface. The synergy between this preparation and curing process ultimately enables the concrete composition to achieve extremely high density and low defect sensitivity at the microscopic level, while simultaneously achieving ultra-high strength, excellent toughness, extremely low permeability, and excellent volume stability at the macroscopic level, fully meeting the comprehensive requirements of high-performance precast components for rapid production, early strength, long-term durability, and sustainability.

[0018] Optionally, the mixing water contains 0.5-2% nano-silica dispersant by mass of the mixing water.

[0019] By employing the above-mentioned technical solution, the adsorption of dispersant molecules on the surface of nano-silica and other nanomaterials generates strong steric hindrance and electrostatic repulsion, effectively preventing the agglomeration of nanoparticles from the initial mixing stage. This ensures that these highly active components can be uniformly distributed in the cement paste in a monodisperse or ideal multi-scale network form. This not only allows the pozzolanic activity and nucleation effect of nano-silica to be fully utilized, significantly increasing the amount of hydration product CSH gel and refining its microstructure, but also creates ideal conditions for constructing a continuous and uniform three-dimensional reinforcing network for conductive reinforcing materials. This highly homogenized nanoscale dispersion state fundamentally optimizes the rheological properties of the paste, improves the homogeneity and stability of the mixture, and enables all reinforcing phases to achieve a tighter chemical and physical bond with the cement matrix, thereby achieving a comprehensive improvement in compressive strength and durability.

[0020] In summary, this application has the following beneficial effects: 1. This application optimizes concrete structures at multiple levels, from molecular and microscopic, through the synergistic design of silicate cement-slag micropowder system, CO2 mineralized recycled aggregate, nano-conductive reinforcing materials, and multi-scale crack-resistant fibers. This not only endows components with ultra-high strength, toughness, and crack resistance far exceeding conventional products, but also constructs a strong physicochemical barrier through an extremely dense matrix and reinforced interfaces, giving it excellent resistance to chloride ion penetration, carbonation, and freeze-thaw cycles, thus ensuring an ultra-long service life.

[0021] 2. This application employs carbon nanotubes and graphene to construct a nanoscale reinforcing and conductive network. A cross-scale crack-resistant and toughening network is formed through the combination of long and short fibers. Furthermore, the millimeter-level interface is optimized by mineralizing recycled aggregates with CO2, and the rheological and hardening processes are precisely controlled by combining a high-efficiency water-reducing agent and an early-strength, slump-retaining regulator. Under optimized preparation processes, these components achieve a synergistic effect of multiple mechanisms: nanofilling and reinforcement, microfiber crack resistance, macro-aggregate strengthening, and full-process performance control. This fundamentally solves the industry challenge of simultaneously achieving high strength and high durability, and early strength and good workability. Detailed Implementation

[0022] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0023] Silicate cement, purchased from Qianfu Mineral Products Processing Plant in Lingshou County, strength grade 32.5; slag powder is granulated blast furnace slag powder with a glass content ≥85% and a specific surface area ≥450 m². 2 / kg, of which CaO 35%-45%, SiO2 30%-38%, Al2O3 8%-15%, MgO≤8%, sulfides≤2%; the recycled aggregate is obtained by crushing construction demolition waste into crushed stone with a particle size of 5mm-10mm and 10mm-20mm in a mass ratio of 3:17, with a crushing value ≤12%; the nano silica dispersion was purchased from Nanjing Baiju Technology Co., Ltd. BG1900.

[0024] Preparation examples of raw materials and / or intermediates Preparation Example 1 A modified recycled aggregate, prepared by the following steps: The washed and dried recycled aggregate was placed in a pressure reactor with a filling coefficient of 60%. The reactor was sealed, the heating system was started, and the temperature of the reaction system was raised to 65°C. Under the condition that the relative humidity inside the reactor was adjusted to 70%, CO2 gas with a purity of ≥99% was introduced. The pressure inside the reactor was controlled to be maintained at 0.35MPa by the pressure regulating valve. After curing for 28 hours, the pressure inside the reactor was slowly released to atmospheric pressure. The reactor door was opened, the aggregate was taken out and cooled to room temperature to obtain the modified recycled aggregate.

[0025] Preparation Example 2 A modified recycled aggregate, prepared by the following steps: The washed and dried recycled aggregate was placed in a pressure reactor with a filling coefficient of 60%. The reactor was sealed, the heating system was started, and the temperature of the reaction system was raised to 50°C. Under the condition that the relative humidity inside the reactor was adjusted to 80%, CO2 gas with a purity of ≥99% was introduced. The pressure inside the reactor was controlled to be maintained at 0.2MPa through the pressure regulating valve. After curing for 48 hours, the pressure inside the reactor was slowly released to atmospheric pressure. The reactor door was opened, the aggregate was taken out and cooled to room temperature to obtain the modified recycled aggregate.

[0026] Preparation Example 3 A modified recycled aggregate, prepared by the following steps: The washed and dried recycled aggregate was placed in a pressure reactor with a filling coefficient of 60%. The reactor was sealed, the heating system was started, and the temperature of the reaction system was raised to 70°C. Under the condition that the relative humidity inside the reactor was adjusted to 60%, CO2 gas with a purity of ≥99% was introduced. The pressure inside the reactor was controlled to be maintained at 0.5MPa through the pressure regulating valve. After curing for 12 hours, the pressure inside the reactor was slowly released to atmospheric pressure. The reactor door was opened, the aggregate was taken out and cooled to room temperature to obtain the modified recycled aggregate.

[0027] Example

[0028] Example 1

[0029] A concrete composition for precast components with improved strength and durability is prepared by the following steps: S1. Add 65kg of silicate cement, 25kg of slag powder, and 2kg of composite conductive reinforcing material to a mixer and dry mix at 70r / min for 4 minutes; the composite conductive reinforcing material is obtained by mixing carbon nanotubes and graphene at a mass ratio of 1:2.5. S2. Dissolve 1.5 kg of polycarboxylate superplasticizer in 20 kg of mixing water, then add it to the dry material from step S1. Increase the rotation speed to 135 r / min and stir for 3 minutes to form a uniform conductive slurry. S3. Add 85 kg of the modified recycled aggregate prepared in Preparation Example 1, 0.35 kg of crack-resistant fiber, and 1.2 kg of early strength-slump retention regulator to the slurry from step S2 in sequence. Adjust the rotation speed to 100-120 r / min and stir for 3-5 minutes. During this period, add the remaining 10 kg of mixing water to form a uniform concrete mixture. The crack-resistant fiber is a composite of polypropylene fiber and polyvinyl alcohol microfiber, with lengths of 30-50 mm and 6-12 mm, respectively, and a mass ratio of 1:1. The early strength-slump retention regulator is a composite of lithium sulfate, lithium silicate, and modified lignin sulfonate, wherein the mass ratio of lithium sulfate to lithium silicate is 1:1, and the total amount of the two accounts for 50% of the mass of the early strength-slump retention regulator, with the remainder being modified lignin sulfonate. S4. Pour the mixture into the mold, vibrate to compact it, and let it stand for 24 hours under standard curing conditions. After demolding, move it to an environment with a relative humidity of 60±5%, a temperature of 20±2℃, and a CO2 concentration of more than 20% for secondary carbonation curing for 7 days to obtain the concrete composition.

[0030] Example 2

[0031] A concrete composition for precast components with improved strength and durability is prepared by the following steps: S1. Add 60kg of silicate cement, 30kg of slag powder, and 1kg of composite conductive reinforcing material to a mixer and dry mix at a speed of 60-80r / min for 3-5 minutes; the composite conductive reinforcing material is obtained by mixing carbon nanotubes and graphene at a mass ratio of 1:1. S2. Dissolve 2 kg of polycarboxylate superplasticizer in 20 kg of mixing water, then add it to the dry material from step S1. Increase the rotation speed to 120-150 r / min and stir for 2-4 minutes to form a uniform conductive slurry. S3. Add 80 kg of the modified recycled aggregate prepared in Preparation Example 1, 0.5 kg of crack-resistant fiber, and 0.5 kg of early strength-slump retention regulator to the slurry in step S2 in sequence. Adjust the rotation speed to 100-120 r / min and stir for 3-5 minutes. During this period, add the remaining 5 kg of mixing water to form a uniform concrete mixture. The crack-resistant fiber is a composite of polypropylene fiber and polyvinyl alcohol microfiber, with lengths of 30-50 mm and 6-12 mm, respectively, and a mass ratio of 2:1. The early strength-slump retention regulator is a composite of lithium sulfate, lithium silicate, and modified lignin sulfonate, wherein the mass ratio of lithium sulfate to lithium silicate is 1:4, and the total amount of the two accounts for 60% of the mass of the early strength-slump retention regulator, with the remainder being modified lignin sulfonate. S4. Pour the mixture into the mold, vibrate to compact it, and let it stand for 12 hours under standard curing conditions. After demolding, move it to an environment with a relative humidity of 60±5%, a temperature of 20±2℃, and a CO2 concentration of more than 20% for secondary carbonation curing for 14 days to obtain the concrete composition.

[0032] Example 3

[0033] A concrete composition for precast components with improved strength and durability is prepared by the following steps: S1. Add 70kg of silicate cement, 20kg of slag powder, and 3kg of composite conductive reinforcing material to a mixer and dry mix at a speed of 60-80r / min for 3-5 minutes; the composite conductive reinforcing material is obtained by mixing carbon nanotubes and graphene at a mass ratio of 1:5. S2. Dissolve 1 kg of polycarboxylate superplasticizer in 20 kg of mixing water, then add it to the dry material from step S1. Increase the rotation speed to 120-150 r / min and stir for 2-4 minutes to form a uniform conductive slurry. S3. Add 90 kg of the modified recycled aggregate prepared in Preparation Example 1, 0.2 kg of crack-resistant fiber, and 2.5 kg of early strength-slump retention regulator to the slurry from step S2 in sequence. Adjust the rotation speed to 100-120 r / min and stir for 3-5 minutes. During this period, add the remaining 15 kg of mixing water to form a uniform concrete mixture. The crack-resistant fiber is a composite of polypropylene fiber and polyvinyl alcohol microfiber, with lengths of 30-50 mm and 6-12 mm, respectively, and a mass ratio of 1:1. The early strength-slump retention regulator is a composite of lithium sulfate, lithium silicate, and modified lignin sulfonate, wherein the mass ratio of lithium sulfate to lithium silicate is 1:2, and the total amount of the two accounts for 40% of the mass of the early strength-slump retention regulator, with the remainder being modified lignin sulfonate. S4. Pour the mixture into the mold, vibrate to compact it, and let it stand for 18 hours under standard curing conditions. After demolding, move it to an environment with a relative humidity of 60±5%, a temperature of 20±2℃, and a CO2 concentration of more than 20% for secondary carbonation curing for 11 days to obtain the concrete composition.

[0034] Example 4

[0035] A concrete composition for precast components with improved strength and durability differs from Example 1 in that an equal amount of carbon nanotubes is used instead of the composite conductive reinforcing material in this example.

[0036] Example 5

[0037] A concrete composition for precast components with improved strength and durability, which differs from Example 1 in that an equal amount of unmodified recycled aggregate is added instead of modified recycled aggregate in this example.

[0038] Example 6

[0039] A concrete composition for precast components with improved strength and durability, which differs from Example 1 in that the crack-resistant fiber added in this example is polypropylene fiber.

[0040] Example 7

[0041] A concrete composition for precast components with improved strength and durability, which differs from Example 1 in that the crack-resistant fiber added in this example is polyvinyl alcohol fiber.

[0042] Example 8

[0043] A concrete composition for precast components with improved strength and durability, which differs from Example 1 in that the early strength-slump retention modifier added in this example is lithium sulfate.

[0044] Example 9

[0045] A concrete composition for precast components with improved strength and durability, which differs from Example 1 in that the early strength-slump retention modifier added in this example is lithium silicate.

[0046] Example 10

[0047] A concrete composition for precast components with improved strength and durability, which differs from Example 1 in that the early strength-slump retention modifier added in this example is a modified lignin sulfonate.

[0048] Example 11

[0049] A concrete composition for precast components with improved strength and durability differs from Example 1 in that the mixing water in this example contains 1.2% by mass of nano-silica dispersant pre-dissolved in the mixing water.

[0050] Example 12

[0051] A concrete composition for precast components with improved strength and durability differs from Example 1 in that the mixing water in this example contains 0.5% by mass of nano-silica dispersant pre-dissolved in the mixing water.

[0052] Example 13

[0053] A concrete composition for precast components with improved strength and durability differs from Example 1 in that the mixing water in this example contains a nano-silica dispersant at a mass of 2% of the mixing water.

[0054] Comparative Example Comparative Example 1 A concrete composition for precast components with improved strength and durability, which differs from Example 1 in that the recycled aggregate added in this comparative example is unmodified.

[0055] Comparative Example 2 A concrete composition for precast components with improved strength and durability, which differs from Example 1 in that no composite conductive reinforcing material is added in this comparative example.

[0056] Performance testing Detection methods Compressive strength: The specimens were tested according to the methods shown in GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete"; Slump and retention value: After testing the initial slump according to the relevant methods in GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the composition was allowed to stand for 1 hour, and its slump was measured again to calculate the 1-hour slump retention value. Chloride ion diffusion coefficient: According to Appendix C (RCM method) of JGJ / T 193-2009 "Standard for Testing and Evaluation of Concrete Durability", cylindrical specimens with a diameter of 100×50mm are used and cured for 56 days. The specimens are sealed on the sides and placed in an RCM testing device, with one end immersed in NaCl solution (cathode) and the other end immersed in NaOH solution (anode), and a certain DC voltage is applied. By measuring the migration depth of chloride ions in the concrete over a certain period, the chloride ion diffusion coefficient is calculated according to the Nernst-Planck equation to evaluate the chloride ion penetration resistance of the concrete. Carbonation depth: According to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", 100mm×100mm×400mm prism specimens were used. The water-saturated specimens were placed in a rapid freeze-thaw test chamber and their core temperature was cyclically maintained between -18℃ and +5℃. Each cycle lasted for 2-4 hours. The test was terminated when 300 cycles were reached, and the data after 300 cycles was used as the evaluation index.

[0057] Table 1 Experimental test data

[0058] Combining Examples 1-3 and Comparative Example 1 with Table 1, it can be seen that the data of Examples 1-3 are better than those of Comparative Example 1. This indicates that modifying recycled aggregates using the CO2 mineralization curing process can effectively strengthen the aggregates themselves and optimize the aggregate-paste interface, thereby significantly improving the overall performance of concrete, especially its strength and durability.

[0059] Combining Examples 1-3 and Comparative Example 2 with Table 1, it can be seen that the data of Examples 1-3 are better than those of Comparative Example 2, indicating that the addition of composite conductive reinforcing materials, namely carbon nanotubes and graphene, has a significant synergistic reinforcing effect on improving the mechanical properties and durability of concrete, and its role is indispensable.

[0060] Combining Examples 1-4 with Table 1, it can be seen that the data of Examples 1-3 are better than those of Example 4, indicating that the synergistic enhancement effect of carbon nanotubes and graphene compounded in a specific ratio is better than that of using carbon nanotubes alone. The two play a complementary role in constructing multi-scale reinforcement networks, leveraging the advantages of "lines" and "surfaces".

[0061] Combining Examples 1-3 and Example 5 with Table 1, it can be seen that the data of Examples 1-3 are better than those of Example 5, indicating that using CO2 mineralized modified recycled aggregate can more effectively improve the density, interfacial bond strength and long-term durability of concrete compared with using unmodified recycled aggregate.

[0062] Combining Examples 1-3 and Examples 6-7 with Table 1, it can be seen that the data of Examples 1-3 are better than those of Examples 6-7. This indicates that the combined use of polypropylene fiber and polyvinyl alcohol microfiber can form a more effective multi-scale crack-resistant and toughening network compared to using either fiber alone, thereby more comprehensively improving the crack resistance, toughness and durability of concrete.

[0063] Combining Examples 1-3 and Examples 8-10 with Table 1, it can be seen that the data of Examples 1-3 are better than those of Examples 8-10. This indicates that the early strength-slump retention modifier composed of lithium sulfate, lithium silicate and modified lignin sulfonate has unique advantages in balancing the early strength development and workability maintenance of concrete, and its effect is better than that of each component used alone.

[0064] Combining Examples 1-3 and Examples 11-13 with Table 1, it can be seen that the data of Examples 11-13 are better than those of Examples 1-3. This indicates that adding nano-silica dispersant to the mixing water in advance can further promote the uniform dispersion of nanomaterials in the slurry, thereby giving fuller play to their reinforcing and filling effects and achieving additional improvement in concrete performance.

Claims

1. A concrete composition for precast components with improved strength and durability, characterized in that... It includes the following raw materials by weight: The mixture comprises 60-70 parts silicate cement, 20-30 parts slag powder, 1-2 parts water-reducing agent, 0.2-0.5 parts crack-resistant fiber, 1-3 parts composite conductive reinforcing material, 0.5-2.5 parts early strength-slump retention regulator, 80-90 parts modified recycled aggregate, and 25-35 parts mixing water; the composite conductive reinforcing material includes carbon nanotubes and graphene.

2. The concrete composition for improving the strength and durability of precast components according to claim 1, characterized in that: The mass ratio of carbon nanotubes to graphene in the composite conductive reinforcing material is 1:1-5.

3. The concrete composition for improving the strength and durability of precast components according to claim 1, characterized in that: The modified recycled aggregate is a CO2 mineralized curing aggregate, and its preparation includes the following steps: placing the recycled aggregate in a pressure reactor, and under the conditions of a temperature of 50-80℃ and a relative humidity of 60-80%, introducing CO2 gas and maintaining the pressure inside the reactor at 0.2-0.5MPa, and curing for 12-48 hours.

4. The concrete composition for improving the strength and durability of precast components according to claim 1, characterized in that: The crack-resistant fiber is a composite of polypropylene fiber and polyvinyl alcohol microfiber, with lengths of 30-50 mm and 6-12 mm respectively, and a mass ratio of 1-2:

1.

5. The concrete composition for improving the strength and durability of precast components according to claim 1, characterized in that: The water-reducing agent is a polycarboxylate water-reducing agent with a water reduction rate of ≥30%.

6. The concrete composition for improving the strength and durability of precast components according to claim 1, characterized in that: The early strength-slump retention regulator is a complex of lithium sulfate, lithium silicate and modified lignin sulfonate, wherein the mass ratio of lithium sulfate to lithium silicate is 1:1-3, and the total amount of the two accounts for 40%-60% of the mass of the early strength-slump retention regulator, with the remainder being modified lignin sulfonate.

7. A method for preparing a concrete composition for precast components with improved strength and durability as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Add silicate cement, slag powder, and composite conductive reinforcing material into a mixer and dry mix at a speed of 60-80 r / min for 3-5 minutes; S2. Slowly add the mixed water containing the dissolved water-reducing agent to the dry material from step S1, increase the rotation speed to 120-150 r / min, and stir for 2-4 minutes to form a uniform conductive slurry. S3. Add modified recycled aggregate, crack-resistant fiber and early strength-slump retention modifier to the slurry in step S2 in sequence, adjust the speed to 100-120 r / min, stir for 3-5 minutes, add the remaining mixing water during the process, and form a uniform concrete mixture. S4. Pour the mixture into the mold, vibrate to compact it, and let it stand for 12-24 hours under standard curing conditions. After demolding, move it to an environment with a relative humidity of 60±5%, a temperature of 20±2℃, and a CO2 concentration of more than 20% for secondary carbonation curing for 7-14 days to obtain the concrete composition.

8. The concrete composition for improving the strength and durability of precast components according to claim 7, characterized in that: The mixing water contains 0.5-2% nano-silica dispersant by mass of the mixing water.

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