High-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material and preparation method thereof

Abstract

The application discloses a kind of high-performance waste plastic fiber reinforced recycled concrete aggregate base composite materials and preparation method thereof, belong to building material technical field.Composite material with recycled concrete aggregate as matrix, compound waste PET fiber, fly ash, mineral powder, silica fume, Portland cement and other raw materials;Preparation method includes six core steps of raw material grading pretreatment, waste PET fiber reinforced recycled concrete aggregate processing, composite batching gradient stirring, grading compression molding, constant temperature and humidity curing and performance post-processing, and process parameters of each step are accurately controlled.The application solves the problems of low shear strength of recycled concrete aggregate, poor interface bonding of waste PET fiber and aggregate, etc.The prepared composite material has cohesion ≥34.8kPa, internal friction angle ≥46.6°, and the comprehensive performance such as shear strength and compressive strength is significantly improved, which can be widely used in highway pavement base, building roadbed, municipal engineering cushion and other building fields.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material and its preparation method. Background Technology

[0002] The rapid development of the construction industry has generated a large amount of demolition waste, while the widespread use of plastic products has led to a year-on-year increase in the amount of waste plastics. The disorderly dumping of these two types of solid waste not only occupies a large amount of land resources but also easily causes environmental problems such as soil and water pollution, becoming a significant obstacle to ecological environmental protection and sustainable development. Resource recovery from demolition waste to produce recycled concrete aggregate (RCA) and recycling waste plastics into fiber-reinforced materials, and applying both to construction fields such as highway engineering, is an important way to realize the resource utilization of solid waste and also a research and development trend in the field of building materials.

[0003] Recycled concrete aggregates have become one of the core directions of construction solid waste resource utilization due to their advantages such as readily available raw materials, low cost, and ability to replace natural sand and gravel aggregates. However, due to their own structural characteristics, they have problems such as low shear strength and high interfacial porosity. If they are directly applied to the construction of roadbed and pavement base courses, it is easy to cause roadbed structural instability, pavement cracking, subsidence and other defects, which will significantly reduce the service life and safety of road projects. This defect seriously limits the promotion and application of recycled concrete aggregates in high-grade highway pavement base courses and other scenarios with high material performance requirements.

[0004] Waste plastic fibers, especially waste PET fibers, are lightweight, have good tensile strength, and strong corrosion resistance. When incorporated into recycled concrete aggregates as reinforcing materials, they are expected to improve the mechanical properties of the composite materials through the bridging and bonding effects of the fibers, thereby enhancing key indicators such as shear strength and cohesion. Therefore, this has become an important research direction for improving the performance of recycled concrete aggregates. Shear strength is a core indicator determining the bearing capacity and structural stability of pavement base courses, directly affecting the overall quality of road engineering. However, current research on composite materials of recycled concrete aggregates and waste plastic fibers still has many shortcomings: On the one hand, existing studies generally show low interfacial bonding strength and poor compatibility between waste PET fibers and recycled concrete aggregates, failing to fully realize the fiber reinforcement effect. At the same time, the utilization rate of solid waste is low, making it difficult to achieve the synergistic high-value utilization of construction solid waste, plastic solid waste, and industrial solid waste. On the other hand, research on the shear behavior of these composite materials is still in its preliminary stage. Most related experiments are small-scale indoor tests, lacking systematic data support from large-scale direct shear tests (LDST). The influence of key factors such as fiber content and fiber length on the shear performance of recycled concrete aggregates has not yet been clearly and uniformly understood, failing to provide a scientific and reliable theoretical basis for the formulation design and construction application of low-carbon, high-performance pavement materials in practical engineering.

[0005] Against this backdrop, there is an urgent need to conduct systematic research on the effect of waste plastic fibers on the shear properties of recycled concrete aggregates, optimize the formulation system of waste plastic fiber reinforced recycled concrete aggregate matrix composites, develop suitable preparation processes, and solve the problems of insufficient mechanical properties and low solid waste utilization rate of existing composite materials, so as to lay the foundation for the large-scale application of such materials in construction engineering. Summary of the Invention

[0006] To address the technical problems of low solid waste utilization rate and insufficient mechanical properties in existing waste PET fiber reinforced recycled concrete aggregate-based composite materials, this invention provides a high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material and its preparation method. This enables the synergistic high-value utilization of multiple solid wastes, significantly improves the comprehensive properties of the composite material such as shear strength, compressive strength, and cohesion, and meets the usage requirements of different construction projects.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0008] A high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material, by weight, comprises the following raw materials: 600-750 parts recycled concrete aggregate, 3-7.5 parts waste PET fiber, 30-50 parts fly ash, 20-40 parts mineral powder, 5-15 parts silica fume, 40-60 parts P·O42.5 silicate cement, 1-3 parts polycarboxylate-based high-efficiency water-reducing agent, 0.2-1 parts anhydrous sodium sulfate early-strength agent, 0.1-0.5 parts sodium citrate retarder, 0.05-0.2 parts organosilicon defoamer, 80-120 parts deionized water, and 5-10 parts nano-calcium carbonate.

[0009] Furthermore, the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material, by weight, comprises the following raw materials: 680 parts recycled concrete aggregate, 3.4 parts waste PET fiber, 40 parts fly ash, 30 parts mineral powder, 10 parts silica fume, 50 parts P·O42.5 silicate cement, 2 parts polycarboxylate-based high-efficiency water-reducing agent, 0.5 parts anhydrous sodium sulfate early-strength agent, 0.3 parts sodium citrate retarder, 0.1 parts organosilicon defoamer, 100 parts deionized water, and 8 parts nano calcium carbonate.

[0010] Furthermore, the recycled concrete aggregate is derived from waste concrete structures, and after crushing, screening, and impurity removal, its density is 2.60~2.70 g / cm³. 3 Water absorption rate ≤10%, Los Angeles abrasion value ≤30.2%.

[0011] Furthermore, the waste PET fibers are taken from recycled waste plastic bottles, with a length of 5mm to 20mm, a fiber diameter of 40μm to 50μm, and a water absorption rate of <1%.

[0012] This invention also provides a method for preparing a high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material, comprising the following steps:

[0013] (1) Raw material grading and pretreatment: The recycled concrete aggregate is dried, cooled, graded and screened to control the particle size to 2.36~5mm and the moisture content to 5~6%; fly ash, mineral powder and silica fume are ground and passed through a 200-mesh sieve, and nano calcium carbonate is dried to a moisture content ≤0.5%;

[0014] (2) Waste PET fiber reinforced recycled concrete aggregate treatment: Add waste PET fiber to the recycled concrete aggregate that has been pretreated in step (1), and mix for 6 to 14 minutes using a mechanical mixer with a speed of 100 to 300 r / min to ensure that the fiber is evenly dispersed in the recycled concrete aggregate matrix. After mixing, pack it into a sealed plastic bag to obtain waste PET fiber reinforced recycled concrete aggregate.

[0015] (3) Composite batching gradient mixing: A three-stage speed gradient mixing process is adopted. Waste PET fiber reinforced recycled concrete aggregate, fly ash, mineral powder, silica fume, P·O42.5 silicate cement and nano calcium carbonate are pre-mixed at 100~150 r / min for 5~8 min to obtain inorganic mixture; anhydrous sodium sulfate early strength agent, sodium citrate retarder and organosilicon defoamer are added to inorganic mixture and stirred at 200~250 r / min for 8~10 min to obtain fiber-inorganic composite mixture; polycarboxylate-based high-efficiency water-reducing agent and deionized water are added to the above mixture and stirred at 250~300 r / min for 3~5 min. The total mixing time is 16~23 min to obtain composite mixture.

[0016] (4) Graded pressing molding: The composite mixture is filled into the mold in layers, with 3 to 4 layers and each layer having a thickness of 40 to 50 mm. A light compaction hammer is used in conjunction with an automatic loading system to compact the layers. The compaction rate is 0.02 to 0.03 mm / s, the molding pressure is 150 to 200 kPa, and the initial porosity of the mixture is controlled to be 0.60 to 0.70 to obtain the molded blank.

[0017] (5) Constant temperature and humidity curing: The formed blanks are graded and cured at a temperature of 20~25℃ and a relative humidity of ≥90%. For the first 7 days, sealed and moisturized curing is used, and for the next 21 days, natural moisturized curing is used. Deionized water is sprayed onto the surface of the blanks regularly. The total curing time is 28 days to obtain the cured blanks.

[0018] (6) Performance post-treatment: After curing, the green body is demolded and naturally aged for 7 to 10 days. Appearance and performance tests are conducted, and unqualified products are removed to obtain high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite products.

[0019] Further, in step (1), the drying temperature of the recycled concrete aggregate is 100~110℃, the drying time is 45~50h, and it is cooled to ≤25℃ and screened by standard sieve using stripping and reduction technology; the drying temperature of the nano calcium carbonate is 80~90℃, and the drying time is 2~3h.

[0020] Further, in step (2), the fibers are uniformly dispersed in the recycled concrete aggregate matrix. After mixing, the mixture is placed in a sealed plastic bag and left to stand at 21~25℃ for 1.5~2.5h to keep the moisture distribution and fiber-aggregate interface characteristics stable, thereby obtaining recycled concrete aggregate reinforced with waste PET fibers.

[0021] Furthermore, in step (3), the three-stage speed gradient mixing adopts a horizontal twin-shaft mixer. During the mixing process, the temperature of the mixture is controlled to not exceed 30°C, and the method of adding material while mixing is adopted to prevent fiber agglomeration.

[0022] Further, in step (4), the inner wall of the mold is coated with a release agent, which is a mixture of silicone oil and machine oil with a volume ratio of 1:3. After each layer is compacted, the surface is smoothed and then the next layer of mixture is filled in.

[0023] Furthermore, in step (6), the temperature for natural aging is 20~25℃ and the relative humidity is 50~60%.

[0024] Compared with the prior art, the technical advantages of this invention are:

[0025] 1. Co-utilization of multiple solid wastes: low carbon and low cost

[0026] This invention designs a multi-source raw material system composed of recycled concrete aggregate, waste PET fiber, fly ash, mineral powder, and silica fume. The recycled concrete aggregate is construction waste, the waste PET fiber is plastic waste, and the fly ash and mineral powder are industrial waste. The overall solid waste utilization rate exceeds 60%, far higher than the below 50% of existing technologies, effectively solving the problem of pollution from the accumulation of construction waste, plastic waste, and industrial waste. The solid waste raw materials in this multi-source system are widely available and inexpensive, replacing some of the high-priced silicate cement and natural sand and gravel aggregates, reducing the production cost of composite materials by 20-30%. No toxic, harmful, flammable, or explosive components are introduced into the raw materials, and there is no discharge of waste gas, wastewater, or solid waste during the production process, meeting the environmental protection requirements of green building materials.

[0027] 2. Gradient mixing + staged pressing + staged curing, precisely controlling performance.

[0028] This invention designs a precise preparation process involving gradient mixing, graded pressing and molding, and constant temperature and humidity graded curing. It precisely controls the process parameters at each step, solving problems such as uneven fiber dispersion, uneven internal pore distribution, and insufficient hydration of the cementitious material. Gradient mixing employs three speed levels to ensure uniform fiber dispersion in the mixture, preventing agglomeration and accumulation. Graded pressing and molding uses layered compaction, controlling the compaction rate and pressure of each layer to ensure uniform compaction of the mixture, with an initial porosity controlled at 0.60~0.70, improving the density of the composite material. Graded curing adopts a "7-day sealed moisturizing followed by 21-day natural moisturizing" curing regime, matching the hydration characteristics of cement-based materials, ensuring more complete hydration of the cementitious material and more stable strength development in the later stages.

[0029] 3. Excellent overall performance and significantly expanded application range.

[0030] This invention not only focuses on the shear properties of composite materials, but also achieves a synergistic improvement in comprehensive properties such as shear properties, compressive strength, and flexural strength through optimization of raw material formulation and preparation process. This solves the problems of insufficient comprehensive performance and limited applicability of existing composite materials. Testing shows that the composite material prepared by this invention has a 28-day compressive strength ≥30.2 MPa, a 28-day flexural strength ≥5.1 MPa, a water absorption rate ≤3.8%, and a Los Angeles abrasion value ≤27.8%. All performance indicators exceed the requirements of JTG / T F20-2015 "Technical Specifications for Construction of Highway Pavement Base Course" and GB 50204-2015 "Code for Acceptance of Construction Quality of Concrete Structures". It can be widely used in high-grade highway pavement base courses, building subgrades, and other construction engineering fields, significantly expanding its applicability and demonstrating excellent engineering application prospects. Attached Figure Description

[0031] Figure 1 This is a picture of recycled concrete before it was crushed.

[0032] Figure 2 This is a picture of recycled concrete after it has been crushed.

[0033] Figure 3 This is a picture of 5mm of waste plastic fiber (PET fiber);

[0034] Figure 4 It is a picture of 20mm waste plastic fiber (PET fiber);

[0035] Figure 5 The graph shows the shear stress versus horizontal displacement curves under different normal stresses for a pure RCA sample.

[0036] Figure 6 The graphs show the vertical and horizontal displacement curves under different normal stresses for a pure RCA sample.

[0037] Figure 7The graph shows the shear stress versus horizontal displacement curves under different normal stresses for a 0.5% 5mm RCA sample.

[0038] Figure 8 The graph shows the vertical and horizontal displacement curves under different normal stresses for a 0.5% 5mm RCA sample.

[0039] Figure 9 The graph shows the shear stress versus horizontal displacement curves under different normal stresses for a 1% 5mm RCA sample.

[0040] Figure 10 The graph shows the vertical and horizontal displacement curves under different normal stresses for a 1% 5mm RCA sample.

[0041] Figure 11 The graph shows the shear stress versus horizontal displacement curves under different normal stresses for a 2% 5mm RCA sample.

[0042] Figure 12 The graph shows the vertical and horizontal displacement curves under different normal stresses for a 2% 5mm RCA sample.

[0043] Figure 13 The graph shows the shear stress versus horizontal displacement curves under different normal stresses for a 0.5% 20mm RCA sample.

[0044] Figure 14 The graph shows the vertical and horizontal displacement curves under different normal stresses for a 0.5% 20mm RCA sample.

[0045] Figure 15 The graph shows the shear stress versus horizontal displacement curves under different normal stresses for a 1% 20mm RCA sample.

[0046] Figure 16 The graph shows the vertical and horizontal displacement curves under different normal stresses for a 1% 20mm RCA sample.

[0047] Figure 17 The graph shows the shear stress versus horizontal displacement curves under different normal stresses for a 2% 20mm RCA sample.

[0048] Figure 18 The graph shows the vertical and horizontal displacement curves under different normal stresses for a 2% 20mm RCA sample.

[0049] Figure 19 This is a bar chart comparing the peak shear strength of the examples and comparative examples under 150 kPa normal stress.

[0050] Figure 20 This is a comparison chart of the two indicators, cohesion and internal friction angle, between the examples and the comparative examples;

[0051] Figure 21 This is a comparison chart of the 28-day compressive strength and 28-day flexural strength of the example and the comparative example. Detailed Implementation

[0052] In this invention, the inventors previously conducted research on the shear properties of recycled concrete aggregate reinforced with waste PET fibers, as follows:

[0053] 1. Theoretical basis of shear strength

[0054] The shear strength of a material refers to the maximum stress it can withstand under shear stress. According to the Mohr-Coulomb criterion, the shear strength of a material can be expressed through the friction angle. With cohesion The characterization and calculation formula are as follows:

[0055] In the formula, Normal stress ( ), Shear stress ( ), The friction angle is (°). The cohesive force of the material (Pa).

[0056] The Mohr-Coulomb criterion states that the shear strength of a material consists of two parts: the cohesive force within the material and the frictional force between the material surfaces. Therefore, the shear strength of a material is not only affected by normal stress, but also closely related to the material's inherent viscous characteristics and surface friction properties.

[0057] 2. Experimental Materials and Experimental Design

[0058] (1) Experimental materials

[0059] To systematically investigate the shear properties of recycled concrete aggregate reinforced with waste plastic fibers, this invention selects recycled concrete aggregate (RCA) and polyethylene terephthalate (PET) fibers as the core experimental materials.

[0060] Recycled concrete (RCA) is derived from waste concrete structures. After crushing and screening, the particle size is controlled within the range of 5mm to 20mm. Fine impurities are removed to ensure material purity. Its physical and mechanical properties directly affect the overall performance of the composite material. The results before and after crushing of the recycled concrete are shown in [Figure 1]. Figure 1 , Figure 2 Waste PET fiber is made from recycled waste plastic bottles and cut into two specifications: 5mm short fibers and 20mm long fibers, as shown in the attached images. Figure 3 , Figure 4 The fiber surface has a certain roughness, which is beneficial for forming effective friction and interlocking with RCA, thereby improving the shear properties of the composite material. The basic properties of the two types of experimental materials are shown in Table 1.

[0061]

[0062] (2) Experimental design and equipment

[0063] This experiment used a large direct shear apparatus. The shear box of the apparatus measures 305 mm (length) × 305 mm (width) × 204 mm (depth) and is equipped with an automatic loading system and a displacement sensor with an accuracy of ±0.01 mm. To avoid the interference of boundary effects on the test results, the width of the shear box must be at least 10 times the maximum aggregate size. The present invention further adjusts the sample size to To effectively eliminate the sample size effect (SSE), the maximum normal stress capacity of the test equipment is 200 kPa, and the adjustable shear rate range is 0.01~1.0 mm / s.

[0064] The experiment consisted of 9 sample groups, including pure RCA samples and samples with different fiber reinforcement ratios. The specific grouping is shown in Table 2. The original maximum particle size of RCA (…) The original thickness was 20mm, which was adjusted to 5mm, 3.36mm, and 2.36mm using a stripping and reduction technique. The values ​​were 61, 91, and 129, respectively. Selecting these three particle sizes as the reduction particle sizes ensures the consistency of particle size distribution and engineering representativeness. The mass percentage of particles removed after stripping is approximately 25%, which is within the conventional range of 10% to 30% in engineering practice. Waste PET fibers were formulated according to RCA dry weight with contents of 0%, 0.5%, 1%, and 2%, respectively. Two fiber lengths, 5 mm and 20 mm, were also used to systematically study the effects of fiber content and length on RCA shear strength.

[0065]

[0066] (3) Sample preparation and testing procedures

[0067] 1) Sample preparation

[0068] To ensure the uniformity and stability of the test materials, RCA was first dried in a 105℃ drying oven for 48 hours until constant weight, then cooled to 23℃ room temperature, and deionized water was added at a ratio of 10% of the RCA moisture content. Following the sample ratios in Table 2, PET fibers were added to the RCA batch by batch, and mixed for 10 minutes using a mechanical stirrer at 200 rpm to ensure uniform fiber dispersion within the RCA matrix. After mixing, the samples were placed in sealed plastic bags and allowed to stand at a constant temperature of 23℃ for 2 hours to stabilize the moisture distribution and fiber-aggregate interface properties.

[0069] The removal and reduction of aggregates is completed by sieving using standard sieves with specifications of 5mm, 3.36mm, and 2.36mm. The quality error during the sieving process is controlled within ±1%, ensuring the accuracy of particle size adjustment.

[0070] 2) Test program

[0071] The tests were conducted strictly in accordance with the "Specifications for Testing Geotechnical Engineering for Highways" and ASTM D3080 / D3080M-11 standards. The specific test procedures are as follows:

[0072] a. The prepared fiber-aggregate mixture is layered into a direct shear box, each layer approximately 50mm thick. It is then uniformly compacted to its loosest state using a light compaction hammer, with an initial porosity of [missing value]. Approximately 0.65;

[0073] b. Apply three normal stresses of 50 kPa, 100 kPa and 150 kPa to the sample using an air compressor, stabilize for 5 min after loading, and record the initial vertical displacement of the sample;

[0074] c. Apply a horizontal shear force to the sample at a constant shear rate of 0.025 mm / s until the horizontal displacement reaches 30 mm (approximately 10% of the sample length).

[0075] d. A high-precision sensor with an accuracy of ±0.01mm is used to record shear stress, horizontal displacement and vertical displacement data in real time at a sampling frequency of 10Hz;

[0076] e. Each group of samples was tested three times under each normal stress condition, and the average value of the tests was taken to reduce the influence of random errors.

[0077] The entire experiment was conducted in an indoor environment with a constant temperature of 23℃ and a relative humidity of 50% to eliminate the interference of external environmental conditions on the test results.

[0078] 3. Results and Analysis

[0079] (1) Shearing behavior analysis

[0080] Through large-scale direct shear tests, the shear behavior characteristics of pure recycled concrete aggregate and waste plastic fiber reinforced samples under different normal stresses were systematically revealed. The shear stress-horizontal displacement curves and vertical displacement-horizontal displacement relationships of samples with different mix proportions showed different patterns.

[0081] like Figure 5As shown, the shear stress of the pure RCA sample increases rapidly with increasing horizontal displacement, reaching a peak at approximately 12 mm, then slightly decreases and tends to stabilize. Under normal stresses of 150 kPa, 100 kPa, and 50 kPa, its peak shear strengths are 176 kPa, 112.3 kPa, and 70.1 kPa, respectively. This characteristic indicates that RCA exhibits typical loose, sandy material properties during shearing; initially, particles rearrange, and after fine particles fill the voids, the shear stress tends to stabilize. When the normal stress increases from 50 kPa to 150 kPa, the shear stiffness of the RCA significantly increases, indicating that the contact friction between particles increases with increasing normal stress. From the vertical displacement curve, the sample is in a compressed state during the 0-5 mm horizontal displacement stage, with a maximum vertical displacement of approximately -0.2 mm; after the horizontal displacement reaches 5 mm, the vertical displacement shifts to an expansion state, with a maximum value of 2.1 mm and a fluctuation range of approximately ±0.2 mm, consistent with the shear behavior characteristics of loose granular materials.

[0082] like Figures 6-18 As shown, after introducing PET fibers, the shear stress-displacement curves of all fiber-reinforced samples exhibited similar trends, with peak values ​​appearing at approximately 9 mm of horizontal displacement. Both shear stress and shear stiffness were significantly higher than those of pure RCA samples, but the improvement effects varied depending on the fiber length and content. For example, the sample containing 1% 20 mm long fibers had a peak shear strength of 190.31 kPa under a normal stress of 150 kPa, an increase of approximately 8.13% compared to pure RCA. Under normal stresses of 50 kPa and 100 kPa, the peak shear strengths were 69.1 kPa and 137.2 kPa, respectively, with a decrease in shear stress of approximately 5% after the peak. In contrast, the sample containing 0.5% 20 mm fibers had a peak shear strength of 172.6 kPa, a decrease of 1.93% compared to pure RCA, with slightly smaller fluctuations in shear stress.

[0083] The effect of increasing fiber content on the shear behavior of the samples showed a clear pattern: for samples with 0.5% and 1% fiber content, the shear strength increased linearly with increasing fiber content; however, when the fiber content increased to 2%, the increase in shear strength slowed down significantly. For example, the peak shear strength of a sample containing 2% 20mm fiber under a normal stress of 150kPa was 217.6kPa, only 14.35% higher than that of a sample of the same length with 1% fiber content. This phenomenon may be due to excessive fiber accumulation at high content, leading to local slippage in the sample.

[0084] Regarding vertical displacement, the fiber-reinforced samples exhibited significant expansion characteristics, with the expansion effect being more pronounced in the long-fiber samples. For example, the sample containing 2% 20mm fibers had a maximum vertical displacement of 2.5mm under a normal stress of 150kPa, which was 108% higher than that of pure RCA (1.2mm). This result reflects the bridging effect of the fibers, enhancing the volumetric effect within the shear band.

[0085] (2) Calculation of shear parameters

[0086] Based on the Mohr-Coulomb criterion, linear regression was used to analyze the normal stress of each sample. By fitting the peak shear strength data, the cohesion of each sample was calculated. and internal friction angle The results are shown in Table 3.

[0087]

[0088] Based on the data in Table 3, the shear parameter patterns of samples with different ratios are analyzed as follows:

[0089] 1) Cohesion of pure RCA kPa, internal friction angle The internal friction angle is within the range of typical loose granular materials (40°-48°), indicating that pure RCA has typical granular material characteristics, while the low cohesion reflects its insufficient tensile strength.

[0090] 2) In the 5mm short fiber reinforced sample, as the fiber content increased from 0.5% to 2%, the cohesion... The internal friction angle decreased from 27.7 kPa to 19.1 kPa. The angle of internal friction increased from 43.4° to 47.1°. The decrease in cohesion may be due to the fact that the fibers were not fully embedded in the RCA matrix under high fiber content, resulting in a decrease in the bond strength between the fiber and aggregate. The increase in the internal friction angle is due to the fibers filling the gaps between aggregate particles, which enhances the friction between particles.

[0091] 3) In the 20mm long fiber-reinforced sample, as the fiber content increased from 0.5% to 2%, the cohesion... The internal friction angle decreased from 34.6 kPa to 27.6 kPa. The cohesion increased from 46.4° to 49.9°. The long-fiber samples generally exhibited higher cohesion than the short-fiber samples with the same dosage, indicating a more significant bridging effect of the long fibers. The decrease in cohesion at higher dosages followed the same pattern as the short-fiber samples. Furthermore, the internal friction angle of the long-fiber reinforced samples was close to the upper limit (48°) for gravel materials, meeting the mechanical performance requirements of highway pavement base courses.

[0092] 4) Shear parameter analysis of 1% 20mm fiber-reinforced samples with maximum particle sizes of 5mm, 3.36mm, and 2.36mm showed that their internal friction angles were 47.3°, 46.4°, and 45.9°, respectively, and their cohesion was 33.4kPa, 32.4kPa, and 31.8kPa, respectively. As... The reduction in aggregate size, with changes in both the internal friction angle and cohesion less than 2%, indicates that the reduction in maximum aggregate size has a relatively small impact on shear parameters. This result verifies the reliability of the stripping method in characterizing the shear properties of recycled concrete aggregates and provides a theoretical basis for the optimized design of recycled concrete aggregate size in engineering applications.

[0093] (3) Analysis of fiber reinforcement mechanism

[0094] The enhancing effect of PET waste plastic fibers on the shear properties of RCA can be explained by the following mechanical mechanism, which has been verified by theoretical models and experimental data:

[0095] 1) Friction and interlocking action

[0096] The main function of short fibers (5mm) is to fill the gaps between RCA particles, increase the frictional resistance at the particle contact surface, and thus improve the internal friction angle of the sample. For example, the internal friction angle of a 1% 5mm fiber-reinforced sample increased to 45.9°; long fibers (20mm) formed a network constraint structure through cross-particle bridging, significantly improving the cohesion of the sample. For example, the cohesion of a sample reinforced with 0.5% 20mm fiber reaches 34.6 kPa. Theoretical models indicate that the shear resistance at the fiber-particle interface... With fiber surface roughness ( and normal stress The results showed that the peak shear strength of the sample increased proportionally with the normal stress in the experiment, verifying the rationality of the theoretical model.

[0097] 2) Tensile resistance

[0098] PET fibers possess a high tensile strength of 450 MPa, effectively resisting aggregate particle displacement within the shear band of the sample. This effect is particularly significant under low normal stress (50 kPa). For example, a sample containing 1% 20 mm fibers exhibits a peak shear strength of 89.5 kPa under 50 kPa normal stress, a 42% improvement compared to pure RCA (62.8 kPa). (Fiber tensile increment) With fiber count and orientation angle Relatedly, this invention assumes that the fibers are uniformly oriented in the aggregate (average) The calculated tensile increment matches the measured increment well.

[0099] 3) Fiber length and content effect

[0100] Bridging distance of long fibers (20mm) This can more effectively enhance the binding effect between aggregate particles; while the bridging distance of short fibers (5mm) The effect is mainly limited to enhancing the local frictional effect of the particles. When the fiber content increases to 2%, the increase in peak shear strength slows down, and the cohesion decreases. This is because excessive fiber accumulation at high content leads to slippage at the fiber-aggregate interface. This trend conforms to a quadratic function model. In the formula: Fiber content; The fitting coefficients are used; the fitting parameters for this experiment are set to [value]. , goodness of fit .

[0101] 4) Expansion characteristics

[0102] The expansion behavior of fiber-reinforced samples stems from the restrictive effect of fibers on aggregate particle rearrangement, leading to an increased volume expansion rate of the shear band. The vertical displacement of long-fiber samples is significantly greater than that of short-fiber samples and pure RCA samples (e.g., the vertical displacement of 2% 20mm fiber samples is 2.5mm), further validating the theory that the bridging reinforcement effect of long fibers is superior to that of short fibers.

[0103] 4. Conclusion

[0104] This invention systematically evaluated the enhancing effect of waste plastic (PET) fibers on the shear properties of recycled concrete aggregate (RCA) through large-scale direct shear tests (LDST). Based on the experimental results and mechanism analysis, the following main conclusions were drawn:

[0105] 1) PET fiber can significantly improve the shear properties of RCA. Among them, 20mm long fiber has the best reinforcing effect at a dosage of 0.5%~1%. The cohesion of the sample at this ratio can reach 34.6kPa and the internal friction angle exceeds 40°, which meets the mechanical performance requirements of highway pavement base course.

[0106] 2) Higher fiber content is not always better. When the fiber content reaches 2%, excessive fiber accumulation will cause a slippage effect, which will reduce the enhancement effect on the shear properties of RCA.

[0107] 3) When the maximum RCA particle size was reduced from 5 mm to 2.36 mm using the stripping reduction technique, the change in the shear parameters (cohesion and internal friction angle) of the sample was less than 2%, indicating that the reduction in aggregate particle size had little impact on its shear performance. At the same time, it verified the reliability of the stripping method in the laboratory characterization of the shear performance of recycled concrete aggregates, and provided theoretical support for the particle size design of recycled concrete aggregates in engineering practice.

[0108] Based on previous research findings on the shear properties of waste PET fiber-reinforced recycled concrete aggregate, the inventors have developed a high-performance waste plastic fiber-reinforced recycled concrete aggregate-based composite material, which comprises the following components by weight:

[0109] The composition includes: 600-750 parts recycled concrete aggregate, 3-7.5 parts waste PET fiber, 30-50 parts fly ash, 20-40 parts mineral powder, 5-15 parts silica fume, 40-60 parts P·O42.5 silicate cement, 1-3 parts polycarboxylate-based high-efficiency water-reducing agent, 0.2-1 parts anhydrous sodium sulfate early-strength agent, 0.1-0.5 parts sodium citrate retarder, 0.05-0.2 parts organosilicon defoamer, 80-120 parts deionized water, and 5-10 parts nano calcium carbonate.

[0110] The recycled concrete aggregate is derived from waste concrete structures, and after crushing, screening, and impurity removal, its density is 2.60~2.70 g / cm³. 3 The water absorption rate is ≤10%, and the Los Angeles abrasion value is ≤30.2%. The waste PET fiber is taken from recycled waste plastic bottles, and is cut into 5mm short fibers and 20mm long fibers, with a fiber diameter of 40μm~50μm, a tensile strength of ≥450MPa, and a density of 1.35~1.40g / cm³. 3 Water absorption rate <1%.

[0111] The preparation method of the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material includes the following steps:

[0112] (1) Raw material classification and pretreatment

[0113] Recycled concrete aggregates are dried in an oven at 100-110℃ for 45-50 hours until constant weight is achieved. After cooling to ≤25℃, they are graded and sieved through standard sieves (2.36mm, 3.36mm, 5mm) using a stripping and reduction technique to adjust the particle size to 2.36-5mm and control the moisture content to 5-6%, thus completing the pretreatment. Fly ash, mineral powder, and silica fume are ground and then sieved through a 200-mesh sieve to remove coarse impurities. Nano-calcium carbonate is dried in an oven at 80-90℃ for 2-3 hours to remove water until the moisture content is ≤0.5%. P·O42.5 silicate cement is stored in a dry environment for later use to prevent moisture absorption and clumping.

[0114] (2) Treatment of waste PET fiber reinforced recycled concrete aggregate

[0115] Waste PET fibers are added to the recycled concrete aggregate that has undergone pretreatment in step (1). The waste PET fibers are prepared according to the dry weight of the recycled concrete aggregate and have a content of 0.5% to 1%. The mixture is stirred for 6 to 14 minutes using a mechanical mixer with a speed of 100 to 300 r / min to ensure that the fibers are evenly dispersed in the recycled concrete aggregate matrix. After mixing, the sample is placed in a sealed plastic bag and left to stand for 1.5 to 2.5 hours under constant temperature conditions of 21 to 25°C to keep the moisture distribution and fiber-aggregate interface characteristics stable, thereby obtaining recycled concrete aggregate reinforced with waste PET fibers.

[0116] (3) Gradient mixing of compound ingredients

[0117] A three-stage speed gradient mixing process was adopted. Waste PET fiber-reinforced recycled concrete aggregate, fly ash, mineral powder, silica fume, P·O42.5 silicate cement, and nano-calcium carbonate were added to a horizontal twin-shaft mixer. The mixing speed was controlled at 100~150 r / min, and the mixture was pre-mixed for 5~8 min to obtain an inorganic mixture. Anhydrous sodium sulfate early strength agent, sodium citrate retarder, and organosilicon defoamer were added to the inorganic mixture, and the mixing speed was increased to 200~250 r / min. The mixture was stirred for 8~10 min to obtain a fiber-inorganic composite mixture. Polycarboxylate-based high-efficiency water-reducing agent and deionized water were added to the above mixture, and the mixing speed was increased again to 250~300 r / min. The mixture was stirred for 3~5 min, and the total mixing time was controlled at 16~23 min. During the mixing process, the temperature of the mixture was controlled not to exceed 30℃ to obtain a uniform composite mixture. During the mixing process, the materials were added while mixing to prevent fiber agglomeration.

[0118] (4) Graded pressing molding

[0119] Apply a layer of release agent (a mixture of silicone oil and machine oil, volume ratio 1:3) to the inner wall of the direct shear box forming mold to prevent the mixture from sticking to the mold; fill the mold with the composite mixture in layers, 3 to 4 layers, each layer 40 to 50 mm thick, and use a light compaction hammer with an automatic loading system to compact each layer, controlling the compaction rate at 0.02 to 0.03 mm / s and the forming pressure at 150 to 200 kPa. After each layer is compacted, scrape the surface smooth before filling in the next layer of mixture; after all compaction is completed, control the initial porosity of the mixture to be 0.60 to 0.70 to obtain the formed blank.

[0120] (5) Constant temperature and humidity maintenance

[0121] The shaped green body, together with the mold, is placed in a constant temperature and humidity curing chamber for graded curing. The curing temperature is controlled at 20~25℃ and the relative humidity is ≥90%. The first 7 days are sealed and moisturized curing, and the next 21 days are natural moisturizing curing. Deionized water is sprayed on the surface of the green body regularly to ensure that the cementitious material is fully hydrated. The total curing time is 28 days to obtain the cured green body.

[0122] (6) Performance post-processing

[0123] After curing, the green body is demolded from the mold and placed in an environment of 20~25℃ and 50~60% relative humidity for natural aging for 7~10 days to stabilize the performance of the green body. After aging, the green body is subjected to appearance and performance testing, and unqualified products are removed to obtain high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite material.

[0124] Technical principle of the invention:

[0125] This composite material uses recycled aggregate from waste concrete as the core framework and waste PET fiber as the flexible reinforcing phase. It is compounded with cementitious materials, chemical admixtures, and nanofillers to form a multi-component system. Through precise raw material pretreatment, gradient mixing, graded pressing, and graded curing processes, the multi-scale synergistic effects of each raw material are achieved, ultimately producing a high-performance building composite material. Its technical principles revolve around the roles of each raw material, the synergistic effects between them, and the necessity of selecting process parameters, ultimately achieving technical effects exceeding those of conventional recycled concrete. These are described in detail below:

[0126] I. The core role of each raw material

[0127] The raw materials of this composite material can be divided into six categories according to their functions: skeleton phase, reinforcing phase, cementing system, chemical admixtures, nanofillers, and hydration media. The proportions and parameters of each raw material are precise ranges after performance optimization. Their core functions are as follows:

[0128] 1. Skeletal phase

[0129] It is a recycled concrete aggregate, with a mix proportion of 600-750 parts, and the key parameter is a density of 2.60-2.70 g / cm³. 3 It has a water absorption rate of ≤10%, a Los Angeles abrasion value of ≤30.2%, and a particle size of 2.36~5mm. It serves as the macroscopic rigid skeleton of composite materials, bearing the main load, while also enabling the reuse of waste concrete solid waste, reducing the consumption of natural aggregates, and reducing carbon emissions during the production process.

[0130] 2. Enhanced phase

[0131] It is made from waste PET fiber, with a ratio of 3~7.5 parts, accounting for 0.5%~1% of the dry weight of aggregate. The key parameters are a combination of 5mm short fibers and 20mm long fibers, fiber diameter of 40~50μm, tensile strength ≥450MPa, and water absorption rate <1%. It can achieve bridging and crack prevention at the micro level, inhibit the propagation of microcracks in aggregate, effectively improve the toughness, flexural strength and impact resistance of composite materials, and at the same time, it can absorb recycled waste plastic bottles, realizing the dual solid waste utilization of waste concrete and waste plastics.

[0132] 3. Main cementing material

[0133] It is P·O42.5 silicate cement, with a mix ratio of 40-60 parts. It is the core of the cementitious system, providing core hydration products such as CSH gel and Ca(OH)2. These hydration products bind aggregates and fibers to form the strength basis of composite materials, ensuring the normal development of early strength of the material.

[0134] 4. Auxiliary cementitious materials

[0135] The mixture consists of fly ash, mineral powder, and silica fume, in proportions of 30-50 parts, 20-40 parts, and 5-15 parts, respectively, all of which must pass through a 200-mesh sieve. Fly ash exhibits a pozzolanic effect, filling matrix pores and reducing heat of hydration; mineral powder undergoes active hydration reactions, improving the later-stage strength and impermeability of the composite material; silica fume possesses a high specific surface area, filling the microscopic gaps in hydration products, densifying the cementitious matrix, and enhancing the interfacial adhesion between the matrix and aggregates / fibers.

[0136] 5. Chemical admixtures

[0137] This mixture is a blend of polycarboxylate superplasticizer, anhydrous sodium sulfate accelerator, sodium citrate retarder, and silicone defoamer, with proportions of 1-3 parts, 0.2-1 parts, 0.1-0.5 parts, and 0.05-0.2 parts, respectively. The polycarboxylate superplasticizer reduces the water-cement ratio, improves the workability of the mixture, and prevents fiber agglomeration. The anhydrous sodium sulfate accelerator accelerates cement hydration, compensating for insufficient early strength caused by recycled aggregates. The sodium citrate retarder regulates the cement hydration rate, preventing uneven temperature rise and internal cracks in the mixture caused by the accelerator. The silicone defoamer eliminates air bubbles generated during mixing, reducing matrix porosity defects.

[0138] 6. Nanofillers

[0139] It is nano-calcium carbonate, with a ratio of 5-10 parts and a moisture content of ≤0.5%. It fills the nano-pores of the cementitious matrix with nano-sized particles, refines the hydration product grains, and can also act as a heterogeneous nucleation core to promote cement hydration and improve the interfacial bonding effect among fiber, aggregate and cementitious matrix.

[0140] 7. Hydration medium

[0141] Deionized water is used, with a mixing ratio of 80-120 parts. As a necessary medium for cement hydration, it provides the conditions for the hydration reaction. At the same time, precise mixing controls the water-cement ratio, adjusts the workability of the mixture, ensures sufficient cement hydration, and prevents excessive porosity due to excessive water.

[0142] II. Synergistic Effects Among Raw Materials

[0143] This composite material is not a simple mixture of raw materials, but rather forms a multi-scale synergistic system of "rigid skeleton - flexible reinforcement - cementation bonding - admixture regulation - nano-densification". Each raw material compensates for defects and enhances performance. The core synergistic effects are divided into five categories, achieving structural optimization from the macroscopic to the nanoscale:

[0144] (a) Rigid-flexible synergy between skeletal phase and reinforcing phase

[0145] Recycled concrete aggregates, acting as a rigid skeleton, bear the main load, but suffer from defects such as internal micro-cracks and poor interfacial bonding. Waste PET fibers, distributed uniformly in the aggregate gaps and cementitious matrix in a composite pattern of long and short lengths, achieve bridging and crack prevention through their high tensile strength, inhibiting the propagation of micro-cracks in the aggregates. Their low water absorption rate prevents the fibers from reducing interfacial bonding due to water absorption. At the same time, the mechanical interlocking between the fibers and aggregates enhances the interfacial bonding force of the skeleton, transforming the originally "rigid and brittle" recycled aggregate skeleton into a "rigid and tough" fiber-aggregate composite skeleton, thus solving the core problem of high brittleness in traditional recycled concrete.

[0146] (II) Synergistic effect of graded hydration in cementitious systems

[0147] Cement, fly ash, mineral powder, and silica fume form a gradient gradation system of "primary cementitious material + auxiliary cementitious material," achieving a dual synergistic effect of hydration reaction and micro-filling.

[0148] 1. The Ca(OH)2 generated during cement hydration provides reactants for the pozzolanic reaction of fly ash and mineral powder. The two undergo secondary hydration to generate more CSH gel, which fills the pores of the matrix and improves the later strength.

[0149] 2. Silica fume fills the microscopic gaps between cement, fly ash / mineral powder hydration products with ultrafine particles, achieving a graded filling of "coarse cement particles → medium fly ash / mineral powder particles → fine silica fume particles", resulting in a significantly denser cementitious matrix;

[0150] 3. The low heat of fly ash and mineral powder offsets the heat of cement hydration, preventing temperature cracks in the matrix due to uneven temperature rise. Silica fume improves the interfacial bonding between the cementitious system and aggregates and fibers, ultimately achieving sufficient early-stage hydration and continuous late-stage hydration of the cementitious system, resulting in a dense microstructure without temperature cracks.

[0151] (III) Complementary Regulation and Synergistic Effect of Chemical Admixtures

[0152] The four admixtures form a complementary system of "hydration regulation + compaction optimization," precisely ensuring the workability of the mixture and its structural performance after hardening.

[0153] 1. Hydration rate control: Anhydrous sodium sulfate, an early-strength agent, accelerates the formation of ettringite, thereby increasing early strength; sodium citrate, a retarder, complexes Ca... 2+ It slows down hydration, counteracts the excessively rapid hydration effect of the early strength agent, ensures a smooth hydration process, and avoids internal micro-cracks.

[0154] 2. Density optimization: Polycarboxylate superplasticizer reduces the water-cement ratio and ensures uniform fiber dispersion; silicone defoamer eliminates air bubbles introduced during stirring due to fiber dispersion and additives. The two work together to achieve "water-reducing densification + defoaming densification", reducing pore defects.

[0155] 3. The combined use of admixtures avoids the limitations of single admixtures. For example, water-reducing agents solve the problem of fiber agglomeration, defoamers make up for the defects of water-reducing agents in introducing air bubbles, and the combination of early strength agents and retarders allows the composite material to meet the early strength requirements of demolding during construction and ensure the stable development of strength in the later stage.

[0156] (iv) Micro-nano synergy between nano-calcium carbonate and the gelation system

[0157] Nano-calcium carbonate, as a nanofiller, forms a synergistic effect with the cementation system of "nanofilling + crystal nucleation induction":

[0158] 1. Nanoscale particles fill the nanoscale pores of the cementitious matrix, achieving secondary densification on the basis of fine particle filling of silica fume, further reducing the porosity of the matrix;

[0159] 2. As a heterogeneous nucleation core, it promotes the directional growth of cement hydration products on its surface, refines CSH gel grains, and improves the crystallinity of hydration products;

[0160] 3. Improve the interfacial compatibility of fiber-cement matrix, reduce microcracks in the interfacial transition zone, enhance interfacial bonding strength, and allow the bonding force of the cement system to be better transferred to aggregates and fibers.

[0161] (v) Multi-scale overall synergy of all components

[0162] Each raw material complements the other at different scales: recycled aggregate forms the macroscopic (mm-level) skeleton, waste PET fiber forms the microscopic (μm-level) reinforcement, the cementing system forms the mesoscopic (μm~nm-level) binder, nano-calcium carbonate forms the nanoscopic (nm-level) densification, and chemical admixtures provide full-scale control. Ultimately, this achieves simultaneous improvement in macroscopic mechanical properties, microscopic structural integrity, and microscopic density, while also enabling high-volume utilization of both waste concrete and waste plastics, balancing performance and environmental protection.

[0163] III. Necessity and Importance of Selecting Preparation Process Parameters

[0164] The preparation process of this composite material consists of six steps: raw material grading and pretreatment, waste PET fiber reinforced aggregate treatment, composite batching and gradient stirring, grading and pressing molding, constant temperature and humidity curing, and performance post-treatment. The process parameters for each step are precisely selected based on the characteristics of the raw materials and performance requirements, without redundancy or deviation. This is crucial for achieving synergistic effects of the raw materials and ensuring the high performance of the composite material. If the parameters deviate from the range, it will directly lead to uneven dispersion of raw materials, structural defects, and performance degradation. The necessity of selecting parameters for each step is as follows:

[0165] (i) Raw material grading and pretreatment: laying the foundation for defect-free raw materials for subsequent processes

[0166] Key parameters: Recycled aggregate is dried at 100~110℃ for 45~50h to constant weight, cooled to ≤25℃, with a particle size of 2.36~5mm and a moisture content of 5~6%; fly ash and other materials are sieved through a 200-mesh sieve; nano calcium carbonate is dried at 80~90℃ for 2~3h to a moisture content of ≤0.5%.

[0167] 1. After the recycled aggregate is dried to constant weight, the moisture content is adjusted to 5-6% to avoid the water-cement ratio from being out of control due to fluctuations in the original water absorption rate. This moisture content can ensure the interfacial bonding between the aggregate and the cementitious matrix, and will not produce pores due to excessive moisture. The drying temperature of 100-110℃ avoids thermal decomposition of the aggregate, and 45-50h ensures thorough drying.

[0168] 2. The aggregate is graded and screened to 2.36~5mm to optimize the particle size distribution, increase the aggregate bulk density, reduce the amount of cementitious materials, and provide uniform gaps for fiber dispersion;

[0169] 3. Fly ash and other materials are passed through a 200-mesh sieve to remove coarse impurities and ensure the activity of pozzolanic ash; nano-calcium carbonate is dried to a low moisture content to avoid moisture introduction that could cause changes in the water-cement ratio and ensure the nano-filling effect;

[0170] 4. This step eliminates defects in the raw materials such as moisture content, particle size, and impurities, avoiding performance fluctuations in subsequent processes due to uneven raw material composition.

[0171] (II) Treatment of waste PET fiber reinforced aggregate: Achieving effective pre-bonding of fiber and aggregate

[0172] Key parameters: fiber content 0.5%~1% (dry weight of aggregate), mixer speed 100~300r / min, mixing time 6~14min, constant temperature standing at 21~25℃ for 1.5~2.5h.

[0173] 1. The critical reinforcement concentration is 0.5% to 1%. Below 0.5%, a continuous bridging and crack-preventing network cannot be formed, while above 1%, the fibers are prone to agglomeration, resulting in pore defects.

[0174] 2. A gradient rotation speed of 100~300r / min avoids fiber entanglement, and a mixing time of 6~14min ensures that the fibers are evenly dispersed in the gaps between the aggregates. If the mixing time is too long, the fibers will be sheared and broken, and the reinforcing effect will be lost.

[0175] 3.21~25℃ constant temperature static setting allows the surface moisture of the aggregate to fully contact with the fiber, stabilizes the fiber-aggregate interface properties, and prevents the fiber from separating from the aggregate during subsequent mixing, forming a stable fiber-aggregate composite skeleton, which is the core step in improving the toughness of composite materials.

[0176] (III) Gradient mixing of compound ingredients: to achieve uniform mixing of multiple components without agglomeration or segregation.

[0177] Key parameters: three-stage speed (100~150→200~250→250~300r / min), total mixing time 16~23min, mixed material temperature ≤30℃, and material is added while mixing.

[0178] 1. The core design features a three-stage gradient speed: low-speed pre-mixing of inorganic materials to prevent aggregate breakage and fiber agglomeration; medium-speed mixing to add admixtures and ensure uniform dispersion; and high-speed mixing to add water-reducing agents and water, improving workability and initiating initial hydration.

[0179] 2. The total mixing time is 16~23 minutes. If it is too short, the mixing will be uneven; if it is too long, the temperature of the mixture will rise too high (>30℃), which will cause the polycarboxylate superplasticizer to fail and the PET fibers to soften and deform.

[0180] 3. Adding materials while stirring prevents fiber agglomeration at the source. Temperature control ≤30℃ ensures the activity of admixtures and fiber properties. This step achieves fully uniform mixing of multiple components, which is the basis for the consistency of composite material performance.

[0181] (iv) Staged compression molding: determines the molding density and structural integrity of composite materials.

[0182] Key parameters: Release agent silicone oil: machine oil = 1:3, 3~4 layers (each layer 40~50mm), compaction rate 0.02~0.03mm / s, molding pressure 150~200kPa, initial porosity ratio 0.60~0.70.

[0183] 1. The release agent has a 1:3 volume ratio, which balances lubrication and adhesion, effectively releasing the mold without contaminating the mixture or affecting the interfacial bonding.

[0184] 2. Compact the mixture in 3-4 layers to avoid uneven stress during one-time feeding. Each layer should be 40-50mm to ensure that the mixture is fully compacted and free of delamination defects.

[0185] 3.0.02~0.03mm / s low-speed compaction allows for full expulsion of internal air and avoids air bubble encapsulation; 150~200kPa molding pressure is the optimal value for "density-skeleton integrity". Too low a pressure will result in insufficient density, while too high a pressure will result in aggregate breakage and fiber breakage.

[0186] 4. An initial void ratio of 0.60 to 0.70 balances density and hydration space. If it is too low, the cement will lack space for hydration and the hydration will be insufficient; if it is too high, the matrix porosity will be high and the mechanical properties will be low.

[0187] (v) Constant temperature and humidity curing: to achieve full hydration and stable strength development of the gelling system.

[0188] Key parameters: maintenance temperature 20~25℃, relative humidity ≥90%, sealed moisturizing for the first 7 days, natural moisturizing for the next 21 days, total maintenance 28 days.

[0189] 1. 20~25℃ is the optimal temperature for cement hydration, avoiding the problems of slow hydration at low temperature and low crystallinity of hydration products at high temperature, while also preventing PET fibers from aging due to heat;

[0190] 2. Relative humidity ≥90% ensures sufficient moisture for hydration and avoids surface shrinkage cracks in the billet;

[0191] 3. Graded curing design: The first 7 days are sealed and moisturized to promote early and rapid hydration of cement, forming an initial strength and fixed green body structure; the next 21 days are naturally moisturized to allow fly ash, mineral powder and silica fume to undergo secondary hydration, generate more CSH gel, improve later strength and durability, and at the same time slowly release internal stress to avoid cracking.

[0192] The 4.28-day total curing period meets the concrete industry standards, ensuring sufficient hydration of the cementitious system and achieving the design requirements for mechanical properties and durability.

[0193] (vi) Post-processing of performance: to ensure the performance stability and engineering applicability of the finished product.

[0194] Key parameters: Natural aging at 20~25℃ and 50~60% relative humidity for 7~10 days, appearance and performance testing.

[0195] 1. The temperature, humidity and aging time allow the moisture inside the blank to evaporate slowly, further releasing internal stress and preventing shrinkage cracking during later use, thus stabilizing the mechanical properties and volume stability of the composite material.

[0196] 2. Appearance and performance testing eliminates substandard products, ensuring consistent finished product quality and meeting the requirements of industrialized construction in building engineering.

[0197] IV. Unexpected Technical Effects Achieved

[0198] Through multi-scale synergy of the aforementioned raw materials and precise control of process parameters, this composite material overcomes the industry bottlenecks of traditional recycled concrete, such as difficulty in balancing solid waste content and performance, high brittleness, low early strength, and poor durability. It achieves technical effects exceeding those of conventional recycled concrete, specifically:

[0199] 1. Mechanical properties: “Strong and tough”: With a high content of recycled aggregate (600~750 parts), not only is the compressive strength significantly improved, but the flexural strength, impact strength and fracture toughness are also greatly improved, which solves the core problem of traditional recycled concrete being “strong but not tough” and achieves dual optimization of rigidity and toughness.

[0200] 2. High performance retention under high content of dual solid waste: Simultaneously consumes waste concrete and waste plastic bottles, with high solid waste content and no need to add high-quality natural aggregates, breaking through the bottleneck of "performance trade-off" in solid waste recycled materials and achieving a win-win situation for environmental protection and performance;

[0201] 3. Synchronous and efficient development of early and late strength: Through the regulation of the hydration rate of admixtures and the secondary hydration of the cementitious system, the early strength of the composite material develops rapidly (meeting the requirements for demolding during construction), and the later strength continues to improve without shrinkage, solving the problems of low early strength and slow development of later strength in traditional recycled concrete.

[0202] 4. Excellent volume stability and significantly improved durability: Nano-dense, fiber crack-resistant and precise process control significantly reduce the dry shrinkage and thermal shrinkage of the composite material, greatly reduce the number of internal micro-cracks, and improve durability indicators such as impermeability and frost resistance, making it suitable for various building engineering scenarios such as roofs, walls, and roads.

[0203] 5. Excellent workability and finished product consistency: The mixture has excellent workability, with no fiber agglomeration or component segregation; the finished product has uniform density and high quality consistency, meeting the requirements of industrialized construction in building engineering.

[0204] 6. Significant comprehensive benefits: Using solid waste to replace natural aggregates and traditional reinforcing fibers significantly reduces raw material costs; the process requires no complex equipment and is highly feasible for industrial production; the improved durability of composite materials extends the service life of building components, reduces subsequent maintenance costs, and combines economic, environmental, and engineering benefits.

[0205] To make the present invention more fully disclosed, more specific embodiments are described below.

[0206] Example 1

[0207] A high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material, by weight, comprises the following raw materials: 600 parts recycled concrete aggregate, 3 parts waste PET fiber, 30 parts fly ash, 20 parts mineral powder, 5 parts silica fume, 40 parts P·O42.5 silicate cement, 1 part polycarboxylate-based high-efficiency water-reducing agent, 0.2 parts anhydrous sodium sulfate early-strength agent, 0.1 parts sodium citrate retarder, 0.05 parts organosilicon defoamer, 80 parts deionized water, and 5 parts nano-calcium carbonate.

[0208] The recycled concrete aggregate is derived from waste concrete structures and undergoes crushing, screening, and impurity removal processes, resulting in a density of 2.65 g / cm³. 3 The water absorption rate is 5.8%, and the Los Angeles abrasion value is 30.2%. The waste PET fiber is taken from recycled waste plastic bottles, cut into 20mm long fibers, with a tensile strength of 450MPa and a density of 1.38g / cm³. 3 The water absorption rate is 0.9%.

[0209] The preparation method of the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material includes the following steps:

[0210] S1. Raw material grading and pretreatment: The recycled concrete aggregate is dried in a 100℃ oven for 50 hours to constant weight. After cooling to 25℃, it is graded and sieved using a standard sieve to adjust the particle size to 2.36~5mm, and its moisture content is controlled to be 5.8%. Fly ash, mineral powder, and silica fume are ground by grinding equipment and then passed through a 200-mesh sieve to remove coarse particle impurities. Nano calcium carbonate is dried in an 80℃ oven for 3 hours to remove water until the moisture content is 0.5%.

[0211] S2. Waste PET fiber reinforced recycled concrete aggregate treatment: Waste PET fiber is added to the recycled concrete aggregate that has been pretreated in step (1). The waste PET fiber is prepared according to the dry weight of the recycled concrete aggregate and has a content of 0.5%. The mixture is mixed for 10 minutes using a mechanical mixer with a speed of 200 r / min to ensure that the fiber is evenly dispersed in the recycled concrete aggregate matrix. After mixing, the sample is placed in a sealed plastic bag and left to stand for 2 hours under constant temperature of 23℃ to keep the moisture distribution and fiber-aggregate interface characteristics stable, so as to obtain waste PET fiber reinforced recycled concrete aggregate.

[0212] S3. Composite Ingredient Gradient Mixing: A three-stage speed gradient mixing process is adopted. Waste PET fiber reinforced recycled concrete aggregate, fly ash, mineral powder, silica fume, P·O42.5 silicate cement, and nano calcium carbonate are added to a horizontal twin-shaft mixer. The mixing speed is controlled at 100 r / min, and the mixture is pre-mixed for 8 min to obtain an inorganic mixture. Anhydrous sodium sulfate early strength agent, sodium citrate retarder, and organosilicon defoamer are added to the inorganic mixture. The mixing speed is increased to 200 r / min, and the mixture is stirred for 10 min to obtain a fiber-inorganic composite mixture. Polycarboxylate-based high-efficiency water-reducing agent and deionized water are added to the above mixture. The mixing speed is increased again to 250 r / min, and the mixture is stirred for 5 min. During the mixing process, the temperature of the mixture is controlled not to exceed 30℃ to obtain a uniform composite mixture.

[0213] S4. Graded pressing molding: Apply a layer of release agent (a mixture of silicone oil and machine oil, volume ratio 1:3) to the inner wall of the direct shear box molding die; fill the mold with the composite mixture in layers, with 3 layers and each layer being 50mm thick; use a light compaction hammer in conjunction with an automatic loading system to compact each layer, controlling the compaction rate at 0.02mm / s and the molding pressure at 200kPa; after each layer is compacted, scrape the surface smooth before filling in the next layer of mixture; after all compaction is completed, control the initial porosity of the mixture to be 0.60 to obtain the molded blank.

[0214] S5. Constant temperature and humidity curing: The formed green body, together with the mold, is placed in a constant temperature and humidity curing chamber for graded curing. The curing temperature is controlled at 20℃ and the relative humidity is ≥90%. For the first 7 days, sealed moist curing is used, and for the next 21 days, natural moist curing is used. Deionized water is sprayed onto the surface of the green body regularly to ensure that the cementitious material is fully hydrated. The total curing time is 28 days to obtain the cured green body.

[0215] S6. Post-treatment of performance: After curing, the green body is demolded from the mold and placed in an environment of 20℃ and 50% relative humidity for natural aging for 10 days to stabilize the performance of the green body; after aging, the green body is subjected to appearance and performance testing, and unqualified products are removed to obtain high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite material.

[0216] Example 2

[0217] A high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material, by weight, comprises the following raw materials: 680 parts recycled concrete aggregate, 3.4 parts waste PET fiber, 40 parts fly ash, 30 parts mineral powder, 10 parts silica fume, 50 parts P·O42.5 silicate cement, 2 parts polycarboxylate-based high-efficiency water-reducing agent, 0.5 parts anhydrous sodium sulfate early-strength agent, 0.3 parts sodium citrate retarder, 0.1 parts organosilicon defoamer, 100 parts deionized water, and 8 parts nano-calcium carbonate.

[0218] The recycled concrete aggregate is derived from waste concrete structures and undergoes crushing, screening, and impurity removal processes, resulting in a density of 2.65 g / cm³. 3 The water absorption rate is 5.8%, and the Los Angeles abrasion value is 30.2%. The waste PET fiber is taken from recycled waste plastic bottles, cut into 20mm long fibers, with a tensile strength of 450MPa and a density of 1.38g / cm³. 3 The water absorption rate is 0.9%.

[0219] The preparation method of the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material includes the following steps:

[0220] S1. Raw material grading and pretreatment: The recycled concrete aggregate is dried in a 105℃ oven for 48 hours to constant weight, cooled to 25℃, and then sieved using a standard sieve to adjust the particle size to 2.36~5mm, controlling its moisture content to 5.8%; fly ash, mineral powder, and silica fume are ground by grinding equipment and then passed through a 200-mesh sieve to remove coarse particle impurities; nano calcium carbonate is dried in an 85℃ oven for 2.5 hours to remove water until the moisture content is 0.5%.

[0221] S2. Waste PET fiber reinforced recycled concrete aggregate treatment: Waste PET fiber is added to the recycled concrete aggregate that has been pretreated in step (1). The waste PET fiber is prepared according to the dry weight of the recycled concrete aggregate and has a content of 0.5%. The mixture is mixed for 10 minutes using a mechanical mixer with a speed of 200 r / min to ensure that the fiber is evenly dispersed in the recycled concrete aggregate matrix. After mixing, the sample is placed in a sealed plastic bag and left to stand for 2 hours under constant temperature of 23℃ to keep the moisture distribution and fiber-aggregate interface characteristics stable, so as to obtain waste PET fiber reinforced recycled concrete aggregate.

[0222] S3. Composite Ingredient Gradient Mixing: A three-stage speed gradient mixing process is adopted. Waste PET fiber-reinforced recycled concrete aggregate, fly ash, mineral powder, silica fume, P·O42.5 silicate cement, and nano calcium carbonate are added to a horizontal twin-shaft mixer. The mixing speed is controlled at 125 r / min, and the mixture is pre-mixed for 6.5 min to obtain an inorganic mixture. Anhydrous sodium sulfate early strength agent, sodium citrate retarder, and organosilicon defoamer are added to the inorganic mixture. The mixing speed is increased to 225 r / min, and the mixture is stirred for 9 min to obtain a fiber-inorganic composite mixture. Polycarboxylate-based high-efficiency water-reducing agent and deionized water are added to the above mixture. The mixing speed is increased again to 275 r / min, and the mixture is stirred for 4 min. During the mixing process, the temperature of the mixture is controlled not to exceed 30℃ to obtain a uniform composite mixture.

[0223] S4. Graded pressing molding: Apply a layer of release agent (a mixture of silicone oil and machine oil, volume ratio 1:3) to the inner wall of the direct shear box molding die; fill the mold with the composite mixture in layers, with 3 layers and each layer being 45mm thick; use a light compaction hammer in conjunction with an automatic loading system to compact each layer, controlling the compaction rate at 0.025mm / s and the molding pressure at 175kPa; after each layer is compacted, scrape the surface smooth before filling in the next layer of mixture; after all compaction is completed, control the initial porosity of the mixture to be 0.63 to obtain the molded blank.

[0224] S5. Constant temperature and humidity curing: The formed green body, together with the mold, is placed in a constant temperature and humidity curing chamber for graded curing. The curing temperature is controlled at 23℃ and the relative humidity is ≥90%. For the first 7 days, sealed moist curing is used, and for the next 21 days, natural moist curing is used. Deionized water is sprayed onto the surface of the green body regularly to ensure that the cementitious material is fully hydrated. The total curing time is 28 days to obtain the cured green body.

[0225] S6. Post-treatment of performance: After curing, the green body is demolded from the mold and placed in an environment of 23℃ and 55% relative humidity for natural aging for 8.5 days to stabilize the performance of the green body; after aging, the green body is subjected to appearance and performance testing, and unqualified products are removed to obtain high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite material.

[0226] Example 3

[0227] A high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material, by weight, comprises the following raw materials: 750 parts recycled concrete aggregate, 7.5 parts waste PET fiber, 50 parts fly ash, 40 parts mineral powder, 15 parts silica fume, 60 parts P·O42.5 silicate cement, 3 parts polycarboxylate-based high-efficiency water-reducing agent, 1 part anhydrous sodium sulfate early-strength agent, 0.5 parts sodium citrate retarder, 0.2 parts organosilicon defoamer, 120 parts deionized water, and 10 parts nano-calcium carbonate.

[0228] The recycled concrete aggregate is derived from waste concrete structures and undergoes crushing, screening, and impurity removal processes, resulting in a density of 2.65 g / cm³. 3 The water absorption rate is 5.8%, and the Los Angeles abrasion value is 30.2%. The waste PET fiber is taken from recycled waste plastic bottles, cut into 20mm long fibers, with a tensile strength of 450MPa and a density of 1.38g / cm³. 3 The water absorption rate is 0.9%.

[0229] The preparation method of the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material includes the following steps:

[0230] S1. Raw material grading and pretreatment: The recycled concrete aggregate is dried in a 110℃ oven for 48 hours to constant weight. After cooling to 25℃, it is graded and sieved using a standard sieve to adjust the particle size to 2.36~5mm, and its moisture content is controlled to be 5.8%. Fly ash, mineral powder, and silica fume are ground by grinding equipment and then passed through a 200-mesh sieve to remove coarse particle impurities. Nano calcium carbonate is dried in a 90℃ oven for 2 hours to remove water until the moisture content is 0.5%.

[0231] S2. Waste PET fiber reinforced recycled concrete aggregate treatment: Waste PET fiber is added to the recycled concrete aggregate that has been pretreated in step (1). The waste PET fiber is prepared according to the dry weight of the recycled concrete aggregate and the content is 1%. The mixture is mixed for 10 minutes using a mechanical mixer with a speed of 200 r / min to ensure that the fiber is evenly dispersed in the recycled concrete aggregate matrix. After mixing, the sample is placed in a sealed plastic bag and left to stand for 2 hours under constant temperature of 23℃ to keep the moisture distribution and fiber-aggregate interface characteristics stable, so as to obtain waste PET fiber reinforced recycled concrete aggregate.

[0232] S3. Composite Ingredient Gradient Mixing: A three-stage speed gradient mixing process is adopted. Waste PET fiber reinforced recycled concrete aggregate, fly ash, mineral powder, silica fume, P·O42.5 silicate cement, and nano calcium carbonate are added to a horizontal twin-shaft mixer. The mixing speed is controlled at 150 r / min, and the mixture is pre-mixed for 5 min to obtain an inorganic mixture. Anhydrous sodium sulfate early strength agent, sodium citrate retarder, and organosilicon defoamer are added to the inorganic mixture. The mixing speed is increased to 250 r / min, and the mixture is stirred for 8 min to obtain a fiber-inorganic composite mixture. Polycarboxylate-based high-efficiency water-reducing agent and deionized water are added to the above mixture. The mixing speed is increased again to 300 r / min, and the mixture is stirred for 3 min. During the mixing process, the temperature of the mixture is controlled not to exceed 30℃ to obtain a uniform composite mixture.

[0233] S4. Graded pressing molding: Apply a layer of release agent (a mixture of silicone oil and machine oil, volume ratio 1:3) to the inner wall of the direct shear box molding die; fill the mold with the composite mixture in layers, with 4 layers and each layer being 50mm thick; use a light compaction hammer in conjunction with an automatic loading system to compact each layer, controlling the compaction rate at 0.03mm / s and the molding pressure at 200kPa; after each layer is compacted, scrape the surface smooth before filling in the next layer of mixture; after all compaction is completed, control the initial porosity of the mixture to be 0.68 to obtain the molded blank.

[0234] S5. Constant temperature and humidity curing: The formed green body, together with the mold, is placed in a constant temperature and humidity curing chamber for graded curing. The curing temperature is controlled at 25℃ and the relative humidity is ≥90%. For the first 7 days, sealed moist curing is used, and for the next 21 days, natural moist curing is used. Deionized water is sprayed onto the surface of the green body regularly to ensure that the cementitious material is fully hydrated. The total curing time is 28 days to obtain the cured green body.

[0235] S6. Post-treatment of performance: After curing, the green body is demolded from the mold and placed in an environment of 25℃ and 55% relative humidity for natural aging for 7 days to stabilize the performance of the green body; after aging, the green body is subjected to appearance and performance testing, and unqualified products are removed to obtain high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite material.

[0236] Example 4

[0237] A high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material, by weight, comprises the following raw materials: 650 parts recycled concrete aggregate, 6.5 parts waste PET fiber, 35 parts fly ash, 25 parts mineral powder, 8 parts silica fume, 45 parts P·O42.5 silicate cement, 1.5 parts polycarboxylate-based high-efficiency water-reducing agent, 0.4 parts anhydrous sodium sulfate early-strength agent, 0.2 parts sodium citrate retarder, 0.08 parts organosilicon defoamer, 90 parts deionized water, and 6 parts nano-calcium carbonate.

[0238] The recycled concrete aggregate is derived from waste concrete structures and undergoes crushing, screening, and impurity removal processes, resulting in a density of 2.65 g / cm³. 3 The water absorption rate is 5.8%, and the Los Angeles abrasion value is 30.2%. The waste PET fiber is taken from recycled waste plastic bottles, cut into 20mm long fibers, with a tensile strength of 450MPa and a density of 1.38g / cm³. 3 The water absorption rate is 0.9%.

[0239] The preparation method of the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material includes the following steps:

[0240] S1. Raw material grading and pretreatment: The recycled concrete aggregate is dried in an oven at 103℃ for 46 hours to constant weight. After cooling to 25℃, it is graded and sieved using a standard sieve to adjust the particle size to 2.36~5mm, and its moisture content is controlled to be 5.8%. Fly ash, mineral powder, and silica fume are ground by grinding equipment and then passed through a 200-mesh sieve to remove coarse particle impurities. Nano calcium carbonate is dried in an oven at 82℃ for 2.2 hours to remove water until the moisture content is 0.5%.

[0241] S2. Waste PET fiber reinforced recycled concrete aggregate treatment: Waste PET fiber is added to the recycled concrete aggregate that has been pretreated in step (1). The waste PET fiber is prepared according to the dry weight of the recycled concrete aggregate and the content is 1%. The mixture is mixed for 10 minutes using a mechanical mixer with a speed of 200 r / min to ensure that the fiber is evenly dispersed in the recycled concrete aggregate matrix. After mixing, the sample is placed in a sealed plastic bag and left to stand for 2 hours under constant temperature of 23℃ to keep the moisture distribution and fiber-aggregate interface characteristics stable, so as to obtain waste PET fiber reinforced recycled concrete aggregate.

[0242] S3. Composite Ingredient Gradient Mixing: A three-stage speed gradient mixing process is adopted. Waste PET fiber-reinforced recycled concrete aggregate, fly ash, mineral powder, silica fume, P·O42.5 silicate cement, and nano calcium carbonate are added to a horizontal twin-shaft mixer. The mixing speed is controlled at 110 r / min, and the mixture is pre-mixed for 6 min to obtain an inorganic mixture. Anhydrous sodium sulfate early strength agent, sodium citrate retarder, and organosilicon defoamer are added to the inorganic mixture, and the mixing speed is increased to 210 r / min. The mixture is stirred for 8.5 min to obtain a fiber-inorganic composite mixture. Polycarboxylate-based high-efficiency water-reducing agent and deionized water are added to the above mixture, and the mixing speed is increased again to 260 r / min. The mixture is stirred for 3.5 min. During the mixing process, the temperature of the mixture is controlled not to exceed 30℃ to obtain a uniform composite mixture.

[0243] S4. Graded pressing molding: Apply a layer of release agent (a mixture of silicone oil and machine oil, volume ratio 1:3) to the inner wall of the direct shear box molding die; fill the mold with the composite mixture in layers, with 3 layers and each layer being 42mm thick; use a light compaction hammer in conjunction with an automatic loading system to compact each layer, controlling the compaction rate at 0.022mm / s and the molding pressure at 160kPa; after each layer is compacted, scrape the surface smooth before filling in the next layer of mixture; after all compaction is completed, control the initial porosity of the mixture to be 0.61 to obtain the molded blank.

[0244] S5. Constant temperature and humidity curing: The formed green body, together with the mold, is placed in a constant temperature and humidity curing chamber for graded curing. The curing temperature is controlled at 22℃ and the relative humidity is ≥90%. For the first 7 days, sealed moist curing is used, and for the next 21 days, natural moist curing is used. Deionized water is sprayed onto the surface of the green body regularly to ensure that the cementitious material is fully hydrated. The total curing time is 28 days to obtain the cured green body.

[0245] S6. Post-treatment of performance: After curing, the green body is demolded from the mold and placed in an environment of 22℃ and 55% relative humidity for natural aging for 7 days to stabilize the performance of the green body; after aging, the green body is subjected to appearance and performance testing, and unqualified products are removed to obtain high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite material.

[0246] Example 5

[0247] A high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material, by weight, comprises the following raw materials: 700 parts recycled concrete aggregate, 3.5 parts waste PET fiber, 45 parts fly ash, 35 parts mineral powder, 12 parts silica fume, 55 parts P·O42.5 silicate cement, 2.5 parts polycarboxylate-based high-efficiency water-reducing agent, 0.8 parts anhydrous sodium sulfate early-strength agent, 0.4 parts sodium citrate retarder, 0.15 parts organosilicon defoamer, 110 parts deionized water, and 9 parts nano-calcium carbonate.

[0248] The recycled concrete aggregate is derived from waste concrete structures and undergoes crushing, screening, and impurity removal processes, resulting in a density of 2.65 g / cm³. 3 The water absorption rate is 5.8%, and the Los Angeles abrasion value is 30.2%. The waste PET fiber is taken from recycled waste plastic bottles, cut into 20mm long fibers, with a tensile strength of 450MPa and a density of 1.38g / cm³. 3 The water absorption rate is 0.9%.

[0249] The preparation method of the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material includes the following steps:

[0250] S1. Raw material grading and pretreatment: The recycled concrete aggregate is dried in an oven at 108℃ for 47 hours to constant weight. After cooling to 25℃, it is graded and sieved using a standard sieve to adjust the particle size to 2.36~5mm, and its moisture content is controlled to be 5.8%. Fly ash, mineral powder, and silica fume are ground by grinding equipment and then passed through a 200-mesh sieve to remove coarse particle impurities. Nano calcium carbonate is dried in an oven at 88℃ for 2.8 hours to remove water until the moisture content is 0.5%.

[0251] S2. Waste PET fiber reinforced recycled concrete aggregate treatment: Waste PET fiber is added to the recycled concrete aggregate that has been pretreated in step (1). The waste PET fiber is prepared according to the dry weight of the recycled concrete aggregate and has a content of 0.5%. The mixture is mixed for 10 minutes using a mechanical mixer with a speed of 200 r / min to ensure that the fiber is evenly dispersed in the recycled concrete aggregate matrix. After mixing, the sample is placed in a sealed plastic bag and left to stand for 2 hours under constant temperature of 23℃ to keep the moisture distribution and fiber-aggregate interface characteristics stable, so as to obtain waste PET fiber reinforced recycled concrete aggregate.

[0252] S3. Composite Ingredient Gradient Mixing: A three-stage speed gradient mixing process is adopted. Waste PET fiber-reinforced recycled concrete aggregate, fly ash, mineral powder, silica fume, P·O42.5 silicate cement, and nano calcium carbonate are added to a horizontal twin-shaft mixer. The mixing speed is controlled at 140 r / min, and the mixture is pre-mixed for 7 min to obtain an inorganic mixture. Anhydrous sodium sulfate early strength agent, sodium citrate retarder, and organosilicon defoamer are added to the inorganic mixture. The mixing speed is increased to 240 r / min, and the mixture is stirred for 9.5 min to obtain a fiber-inorganic composite mixture. Polycarboxylate-based high-efficiency water-reducing agent and deionized water are added to the above mixture. The mixing speed is increased again to 290 r / min, and the mixture is stirred for 4.5 min. During the mixing process, the temperature of the mixture is controlled not to exceed 30℃ to obtain a uniform composite mixture.

[0253] S4. Graded pressing molding: Apply a layer of release agent (a mixture of silicone oil and machine oil, volume ratio 1:3) to the inner wall of the direct shear box molding die; fill the mold with the composite mixture in layers, with 4 layers and each layer being 48mm thick; use a light compaction hammer in conjunction with an automatic loading system to compact each layer, controlling the compaction rate at 0.028mm / s and the molding pressure at 190kPa; after each layer is compacted, scrape the surface smooth before filling in the next layer of mixture; after all compaction is completed, control the initial porosity of the mixture to be 0.64 to obtain the molded blank.

[0254] S5. Constant temperature and humidity curing: The formed green body, together with the mold, is placed in a constant temperature and humidity curing chamber for graded curing. The curing temperature is controlled at 24℃ and the relative humidity is ≥90%. The first 7 days are for sealed moist curing, and the next 21 days are for natural moist curing. Deionized water is sprayed onto the surface of the green body regularly to ensure that the cementitious material is fully hydrated. The total curing time is 28 days to obtain the cured green body.

[0255] S6. Post-treatment of performance: After curing, the green body is demolded from the mold and placed in an environment of 24℃ and 55% relative humidity for natural aging for 7 days to stabilize the performance of the green body; after aging, the appearance and performance of the green body are tested, and unqualified products are removed to obtain the finished product of high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite material.

[0256] Comparative Example 1 (lacking nano-calcium carbonate)

[0257] The nano-calcium carbonate was removed from the raw materials, and the proportions of the remaining raw materials were completely consistent with those in Example 2; the preparation method was completely consistent with that in Example 2.

[0258] Comparative Example 2 (using a single high-speed rotation of 350 r / min)

[0259] The raw material ratio is completely consistent with that of Example 2; the gradient stirring in step S4 of the preparation method is changed to a single stirring at 350 r / min for 20 min, and the rest of the preparation process is completely consistent with that of Example 2.

[0260] Comparative Example 3 (containing only RCA + waste PET fiber binary system)

[0261] The raw materials are 680 parts of recycled concrete aggregate and 5 parts of waste PET fiber, with no other raw materials. The preparation method only includes drying the raw materials, pressing and molding, and simple curing (natural curing at 23℃ for 28 days), without modification, activation, gradient stirring and other steps.

[0262] Performance testing:

[0263] To verify the superior performance of the high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite material prepared by this invention, performance tests were conducted on samples from Examples 1-5 and Comparative Examples 1-3. Shear strength was tested according to JTG 3430-2020 "Specifications for Geotechnical Tests for Highways". Cohesion c and internal friction angle φ were analyzed using the Mohr-Coulomb criterion linear regression fitting method. Compressive strength and flexural strength were tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". Water absorption was tested according to GB / T50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". Los Angeles abrasion value was tested according to JTG3432-2024 "Specifications for Test of Aggregates in Highway Engineering". All samples were tested in parallel three times, and the average value was taken as the final test result.

[0264] 1. Performance test results

[0265] The performance test results of the samples from Examples 1-5 and Comparative Examples 1-3 of this invention are shown in Table 4. All indicators are the average values ​​of three parallel tests.

[0266]

[0267] 2. Visual analysis of performance test results (based on Table 4)

[0268] To more intuitively demonstrate the performance advantages of the samples of this invention, a performance comparison chart was drawn based on the test results. Figure 19 , Figure 20 , Figure 21 The following charts compare the peak shear strength of the examples and comparative examples under 150 kPa normal stress: bar chart; comparison chart of cohesion and internal friction angle between the examples and comparative examples; and comparison chart of 28-day compressive strength and 28-day flexural strength between the examples and comparative examples.

[0269] (1) Comparison of peak shear strength under 150 kPa normal stress

[0270] The peak shear strength of Examples 1 to 5 is in the range of 192.5 to 205.8 kPa, with Example 2 reaching the maximum value of 205.8 kPa; the peak shear strength of Comparative Examples 1 to 3 is all below 176.0 kPa. The overall trend shows that the shear strength of the samples in the present invention is significantly higher than that of all comparative examples, and the improvement effect of Example 2 is the most obvious.

[0271] (2) Comparison of cohesion and internal friction angle as dual indicators

[0272] Examples 1-5 all exhibited cohesion ≥34.8 kPa and internal friction angle ≥46.6°, with minimal fluctuations in both indicators (cohesion fluctuation ≤1.4 kPa, internal friction angle fluctuation ≤0.9°). In the comparative examples, Comparative Example 3 (containing only the RCA + waste PET fiber binary system) showed a cohesion of only 10.4 kPa, the lowest among all samples. Comparative Examples 1-3, due to raw material shortages / deviations in process parameters, had cohesion ≤25.3 kPa and internal friction angle ≤42.6°, lower than all examples of this invention.

[0273] (3) Comparison of 28d compressive strength and 28d flexural strength

[0274] The 28-day compressive strength of Examples 1-5 was ≥30.2 MPa and the 28-day flexural strength was ≥5.1 MPa. Example 2 achieved the maximum values ​​of 33.5 MPa for compressive strength and 5.6 MPa for flexural strength. The compressive and flexural strengths of Comparative Example 3 (containing only the binary system of RCA and waste PET fiber) were the lowest among all samples (18.6 MPa and 3.0 MPa). The mechanical properties of Comparative Examples 1-3 were significantly lower than those of the present invention. Among them, the compressive strength of Comparative Example 3 was only 18.6 MPa, which was 14.9% lower than that of Example 2.

[0275] 3. Comparative Analysis of Example and Comparative Data

[0276] Combining the detection data in Table 1 and Figures 19-21 Visual analysis was used to compare and analyze the performance differences between the embodiments of the present invention and various comparative examples:

[0277] (1) Internal comparison of Examples 1-5

[0278] All performance indicators in Examples 1-5 were at a high level with minimal fluctuations. Among them, Example 2 exhibited the best performance in all aspects, with a peak shear strength of 205.8 kPa, cohesion of 36.2 kPa, and 28-day compressive strength of 33.5 MPa, verifying the rationality of the optimal values ​​of the raw material ratio and process parameters of the present invention. Examples 1-5 correspond to different nodes in the range of raw material ratio and process parameters, covering the key parameter combinations within the scope of protection of the present invention. Their performance stability further demonstrates that the range of raw material dosage and process parameters set by the present invention has good adaptability.

[0279] (2) Example vs. Comparative Example

[0280] Comparative Example 1 lacked nano-calcium carbonate, and its performance was significantly lower than that of Example 2: the 28-day compressive strength decreased by 20.9%, and the water absorption rate increased by 23.8%. Due to the lack of nano-sized pore filling and grain refinement, the density of the composite material was reduced, and the hydration products did not crystallize sufficiently.

[0281] Comparative Example 2 used a single high-speed stirring method, which resulted in a 17.2% decrease in peak shear strength. This was because the high speed of 350 r / min caused some PET fibers to be sheared and broken, and the aggregate particles were broken, the matrix skeleton was damaged, and the fiber dispersion uniformity was greatly reduced.

[0282] Comparative Example 3 is a conventional RCA+PET fiber binary system. Compared with Example 2, the peak shear strength of Comparative Example 3 is reduced by 14.5%, the cohesion is reduced by 71.3%, and the 28-day compressive strength is reduced by 44.5%. This proves that the aggregate modification, fiber activation, multi-raw material synergy, and precise process control of the present invention can achieve a secondary improvement in performance and solve the technical bottleneck.

[0283] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-performance waste plastic fiber-reinforced recycled concrete aggregate-based composite material, characterized in that, By weight, the raw materials include: 600-750 parts recycled concrete aggregate, 3-7.5 parts waste PET fiber, 30-50 parts fly ash, 20-40 parts mineral powder, 5-15 parts silica fume, 40-60 parts P·O42.5 silicate cement, 1-3 parts polycarboxylate-based high-efficiency water-reducing agent, 0.2-1 parts anhydrous sodium sulfate early strength agent, 0.1-0.5 parts sodium citrate retarder, 0.05-0.2 parts organosilicon defoamer, 80-120 parts deionized water, and 5-10 parts nano calcium carbonate.

2. The high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material according to claim 1, characterized in that, By weight, the raw materials include: 680 parts recycled concrete aggregate, 3.4 parts waste PET fiber, 40 parts fly ash, 30 parts mineral powder, 10 parts silica fume, 50 parts P·O42.5 silicate cement, 2 parts polycarboxylate-based high-efficiency water-reducing agent, 0.5 parts anhydrous sodium sulfate early strength agent, 0.3 parts sodium citrate retarder, 0.1 parts organosilicon defoamer, 100 parts deionized water, and 8 parts nano calcium carbonate.

3. The high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material according to claim 1 or 2, characterized in that, The recycled concrete aggregate is taken from waste concrete structures and processed through crushing, screening, and impurity removal, with a density of 2.60~2.70 g / cm³. 3 Water absorption rate ≤10%, Los Angeles abrasion value ≤30.2%.

4. The high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material according to claim 1 or 2, characterized in that, The waste PET fibers are taken from recycled waste plastic bottles, with a length of 5mm to 20mm, a fiber diameter of 40μm to 50μm, and a water absorption rate of <1%.

5. A method for preparing a high-performance waste plastic fiber-reinforced recycled concrete aggregate-based composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Raw material grading and pretreatment: The recycled concrete aggregate is dried, cooled, graded and screened to control the particle size to 2.36~5mm and the moisture content to 5~6%; fly ash, mineral powder and silica fume are ground and passed through a 200-mesh sieve, and nano calcium carbonate is dried to a moisture content ≤0.5%; (2) Waste PET fiber reinforced recycled concrete aggregate treatment: Add waste PET fiber to the recycled concrete aggregate that has been pretreated in step (1), and mix for 6 to 14 minutes using a mechanical mixer with a speed of 100 to 300 r / min to ensure that the fiber is evenly dispersed in the recycled concrete aggregate matrix. After mixing, pack it into a sealed plastic bag to obtain waste PET fiber reinforced recycled concrete aggregate. (3) Composite batching gradient mixing: A three-stage speed gradient mixing process is adopted. Waste PET fiber reinforced recycled concrete aggregate, fly ash, mineral powder, silica fume, P·O42.5 silicate cement and nano calcium carbonate are pre-mixed at 100~150 r / min for 5~8 min to obtain inorganic mixture; anhydrous sodium sulfate early strength agent, sodium citrate retarder and organosilicon defoamer are added to inorganic mixture and stirred at 200~250 r / min for 8~10 min to obtain fiber-inorganic composite mixture; polycarboxylate-based high-efficiency water-reducing agent and deionized water are added to the above mixture and stirred at 250~300 r / min for 3~5 min. The total mixing time is 16~23 min to obtain composite mixture. (4) Graded pressing molding: The composite mixture is filled into the mold in layers, with 3 to 4 layers and each layer having a thickness of 40 to 50 mm. A light compaction hammer is used in conjunction with an automatic loading system to compact the layers. The compaction rate is 0.02 to 0.03 mm / s, the molding pressure is 150 to 200 kPa, and the initial porosity of the mixture is controlled to be 0.60 to 0.70 to obtain the molded blank. (5) Constant temperature and humidity curing: The formed blanks are graded and cured at a temperature of 20~25℃ and a relative humidity of ≥90%. For the first 7 days, sealed and moisturized curing is used, and for the next 21 days, natural moisturized curing is used. Deionized water is sprayed onto the surface of the blanks regularly. The total curing time is 28 days to obtain the cured blanks. (6) Performance post-treatment: After curing, the green body is demolded and naturally aged for 7 to 10 days. Appearance and performance tests are conducted, and unqualified products are removed to obtain high-performance waste plastic fiber reinforced recycled concrete aggregate matrix composite products.

6. The method for preparing the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material according to claim 5, characterized in that, The recycled concrete aggregate in step (1) is dried at a temperature of 100~110℃ for 45~50h, cooled to ≤25℃, and then sieved through a standard sieve using a stripping and reduction technique; the nano-calcium carbonate is dried at a temperature of 80~90℃ for 2~3h.

7. The method for preparing the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material according to claim 5, characterized in that, In step (2), the fibers are uniformly dispersed in the recycled concrete aggregate matrix. After mixing, the mixture is placed in a sealed plastic bag and left to stand at 21~25℃ for 1.5~2.5h to keep the moisture distribution and fiber-aggregate interface characteristics stable, thereby obtaining recycled concrete aggregate reinforced with waste PET fibers.

8. The method for preparing the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material according to claim 5, characterized in that, In step (3), the three-stage speed gradient mixing uses a horizontal twin-shaft mixer. During the mixing process, the temperature of the mixture is controlled to not exceed 30°C. The method of adding material while mixing is adopted to prevent fiber agglomeration.

9. The method for preparing the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material according to claim 5, characterized in that, In step (4), the inner wall of the mold is coated with a release agent, which is a mixture of silicone oil and machine oil in a volume ratio of 1:

3. After each layer is compacted, the surface is smoothed and then the next layer of mixture is filled in.

10. The method for preparing the high-performance waste plastic fiber reinforced recycled concrete aggregate-based composite material according to claim 5, characterized in that, In step (6), the natural aging temperature is 20~25℃ and the relative humidity is 50~60%.

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