Hybrid fiber high ductility cement-based composite material prepared using regenerated sand and preparation method thereof

Abstract

The present invention belongs to the field of resource recycling in building materials, and specifically relates to a mixed fiber high-ductility cement-based composite material and method prepared using regenerated sand; the raw materials are cement, regenerated sand, natural sand, fly ash, silica fume, polyvinyl alcohol fiber, basalt fiber, cellulose, water reducer, and water. The present invention applies waste concrete crushed regenerated sand to a high-ductility cement-based composite material. By adjusting the replacement rate of regenerated sand for natural sand, the self-cementing effect of the regenerated sand is promoted to improve the density of the matrix, thereby enhancing the matrix's multiple cracking capacity. In addition, the design of mixing polyvinyl alcohol fiber and basalt fiber is adopted, which significantly reduces the fiber cost in the raw materials while ensuring the tensile and ductile properties. The present invention also helps to alleviate the problem of resource shortage of natural sand.

Description

Technical Field

[0001] The present invention belongs to the field of resource recycling in building materials, and in particular relates to a mixed fiber high-ductility cement-based composite material prepared by using regenerated sand and a method thereof. Background Art

[0002] Steel bar corrosion is one of the root causes of concrete structure deterioration. During the life cycle of a building structure, various environmental factors cause corrosion products to gradually form on the surface of the steel bars, leading to cracking and peeling of the concrete protective layer. The continuous accumulation of corrosion products reduces the effective cross-sectional area of ​​the steel bars, thereby weakening the bond strength between the steel bars and concrete, which greatly reduces the bearing capacity of the structure. Professor Victor Li has developed a high-ductility cement-based composite material (ECC) based on the basic principles of micromechanics and fracture mechanics. By using a discontinuous fiber-reinforced cement matrix, a tensile strain capacity of 3-7% can be obtained, which is hundreds of times that of traditional concrete. Under tension, ECC can produce multiple harmless cracks with a width of less than 100μm and uniform distribution, which significantly slows down the corrosion process of the internal steel bars and ensures the integrity and reliability of the structure.

[0003] Research and application of ECC have garnered widespread attention. Chinese patent application number 202111170507.8 discloses a "high-ductility cement-based composite material and its preparation method." This composite material exhibits excellent strength and flexural toughness and is composed of a mixture of 200-400 parts cement, 100-350 parts fly ash, 100-350 parts mineral powder, 100-450 parts aggregate, 20-45 parts microsilica, 5-25 parts water reducer, 1-6 parts defoamer, 0.1-0.8 parts cellulose ether, 0.5-6 parts spray conditioning agent, 5-40 parts polyvinyl alcohol fiber, 1000-3000 parts water, and 5-30 parts polyoxymethylene fiber. However, the preparation of ECC requires a large amount of quartz sand, which increases costs and is prone to supply shortages. Currently, over-exploitation of quartz sand has caused a series of environmental problems in many areas, including soil erosion and riverbank erosion.

[0004] Recycled sand is a byproduct of the crushing process of waste concrete. Over the past few decades, the rapid development of the construction industry has accumulated trillions of tons of construction waste. Large amounts of waste concrete are carelessly stored and landfilled, polluting and occupying significant amounts of land. Using crushed waste concrete as a substitute for quartz sand to produce ECC reduces production costs while enhancing its environmental value, facilitating its widespread application. Summary of the Invention

[0005] The present invention aims to address the shortcomings of existing technologies by providing a hybrid fiber, high-ductility cement-based composite material made from reclaimed sand. By replacing some of the natural quartz sand with reclaimed sand from discarded concrete, and reinforcing the matrix with polyvinyl alcohol and basalt fibers, this material, designed through micromechanics theory, maintains excellent tensile strain capacity and multiple cracking properties while reducing production costs and promoting the large-scale application of this environmentally friendly concrete structure reinforcement material.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a mixed fiber high-ductility cement-based composite material prepared with regenerated sand, composed of the following raw materials in the following weight ratios: 449-566 parts of cement, 163-326 parts of regenerated sand, 81-244 parts of natural sand, 453-562 parts of fly ash, 112-113 parts of silica fume, 11.4-15.9 parts of polyvinyl alcohol fiber, 6.6-19.8 parts of basalt fiber, 2.25-2.26 parts of cellulose, 3.3-3.4 parts of water reducer, and 340-368 parts of water.

[0007] Furthermore, the regenerated sand is crushed waste concrete regenerated sand, and the natural sand is natural quartz sand.

[0008] Furthermore, the particle sizes of the regenerated sand and the natural sand are 0.06 to 1.18 mm, the fineness modulus of the regenerated sand is 1.79, and the fineness modulus of the natural sand is 2.12.

[0009] Furthermore, the polyvinyl alcohol fiber has a diameter of 15 to 31 μm, a length of 9 mm, and a density of 910 kg / m 3 , elastic modulus is 38GPa, tensile strength is 1550MPa; the basalt fiber has a diameter of 7-15μm, a length of 9mm, and a density of 2630kg / m 3 , elastic modulus is 110GPa, and tensile strength is 3000MPa.

[0010] Furthermore, the polyvinyl alcohol fiber is a modified polyvinyl alcohol fiber, and the modification steps are as follows:

[0011] 1) Soak the polyvinyl alcohol fiber in a 10% mass concentration NaHCO3 solution with a solid-liquid ratio of 1:15 for 3 hours, then filter the fiber from the solution, wash it with ultrapure water three times, and dry it at 30°C to remove the sizing agent and other finishing agents remaining on the surface of the polyvinyl alcohol fiber;

[0012] 2) The polyvinyl alcohol fiber was immersed in a 1% dilute sulfuric acid solution containing 3% butyraldehyde at a solid-to-liquid ratio of 1:18 for 5 hours, maintained at 40°C. The fiber was then filtered from the solution, washed three times with ultrapure water, and dried at 30°C. Butyraldehyde covalently bonds with the free hydroxyl groups on the surface of the polyvinyl alcohol fiber through an acid-catalyzed acetalization reaction, converting the two hydroxyl groups into acetal structures, giving the polyvinyl alcohol fiber a more durable hydrophobic property than conventional surface modification processes. At the same time, the polyvinyl alcohol fiber immersed in the dilute sulfuric acid solution is acid-etched, and etched grooves appear on the fiber surface, increasing the surface roughness.

[0013] Furthermore, the cellulose is hydroxypropyl methylcellulose (HPMC), with a 100 mesh pass rate of >98.5% and an apparent density of 250-700 kg / m 3 The surface tension of a 2% aqueous solution is 42 to 56 dyn / cm.

[0014] Furthermore, the water reducer is a carboxylic acid type high efficiency water reducer.

[0015] Furthermore, the cement is silicate cement with a strength grade of 52.5.

[0016] Furthermore, the fly ash is Class I low-calcium fly ash.

[0017] Furthermore, the silica fume is high-activity microsilica powder with a purity of 96%.

[0018] Furthermore, the mass ratio of the regenerated sand to the natural sand is 40 to 80:20 to 60. The preferred mass ratio of the regenerated sand to the natural sand is 60:40.

[0019] Furthermore, the mass proportion of fly ash in the cementitious material (cement + fly ash + silica fume) is 40-50%.

[0020] Furthermore, the volume ratio of the polyvinyl alcohol fiber and the basalt fiber in the cement-based composite material is 2%, wherein the volume ratio of the polyvinyl alcohol fiber to the basalt fiber is 1.25-1.75:0.25-0.75, and more preferably the volume ratio of the polyvinyl alcohol fiber to the basalt fiber is 1.75:0.25.

[0021] In addition, the present invention also provides a method for preparing a hybrid fiber high-ductility cement-based composite material using regenerated sand, and the preparation steps are as follows:

[0022] 1) Pour the cement, fly ash, silica fume, reclaimed sand and natural sand in the above mass proportions into a mixer and stir for 2 minutes to form a mixture;

[0023] 2) Add the water reducer, cellulose, and 50% water in the above-mentioned proportions by weight to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add the polyvinyl alcohol fiber in the above-mentioned proportions by weight to the flowing mortar. Once all the fibers have been added, add 30% water in the above-mentioned proportions by weight and stir for 3 minutes.

[0024] 3) Keep the mixer running and slowly add the basalt fiber in the above-mentioned mass ratio to the flowing mortar. After all the basalt fiber is added, add 20% water in the above-mentioned mass ratio and stir for 3 minutes, then stop stirring;

[0025] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0026] Furthermore, in the above-mentioned method for preparing the mixed fiber high-ductility cement-based composite material using regenerated sand, the entire process of material preparation is controlled within 10 to 13 minutes.

[0027] The hybrid fiber high-ductility cement-based composite material prepared with regenerated sand of the present invention has the following beneficial effects:

[0028] 1) The hybrid fiber-rich, high-ductility cementitious composite material prepared using reclaimed sand described in this invention exhibits excellent flexural strength and tensile strain capacity. The inherent self-cementing ability of reclaimed sand increases the overall density of the matrix, strengthens the bridging effect between the fibers and the matrix, and enhances the multi-cracking capacity of the cementitious composite material.

[0029] 2) The modified PVA fiber surface exhibits more durable hydrophobic properties, allowing some fibers to debond and stretch appropriately during crack propagation, promoting tensile strain behavior in the matrix. Furthermore, after etching with dilute sulfuric acid, microgrooves appear on the fiber surface. During the hydration of the gelling material, some polymer chains enter the grooves on the fiber surface, forming a mechanical anchoring system with the fiber, further enhancing the interfacial bonding strength between the fiber and the hydration product.

[0030] 3) A synergistic blend of polyvinyl alcohol (PVA) and basalt fibers was employed. While maintaining the total fiber content at 2%, the high elastic modulus and strength of basalt fibers enhanced the bond between the fiber system and the matrix, suppressing crack expansion. While maintaining the high tensile and ductility properties of the cementitious composite, the compressive properties of the matrix were enhanced, contributing to a reduction in structural reinforcement costs.

[0031] 4) The application of recycled sand helps to alleviate the shortage of natural sand resources, reduce the land occupation and environmental pollution of urban construction waste, and improve the resource recycling rate of construction waste in my country. It is in line with my country's sustainable development strategy and has great significance for the practice of concrete structure reinforcement projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Actual photo of the mixed fiber high ductility cement-based composite material specimen prepared with regenerated sand. DETAILED DESCRIPTION

[0033] The following examples and comparative examples clearly and completely describe the technical solutions of the present invention. Obviously, the described examples are only a part of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] The polyvinyl alcohol fiber in the embodiment refers to modified polyvinyl alcohol fiber, and the modification steps are as follows:

[0035] 1) Soak the polyvinyl alcohol fiber in a 10% mass concentration NaHCO3 solution with a solid-liquid ratio of 1:15 for 3 hours, then filter the fiber from the solution, wash it with ultrapure water three times, and dry it at 30°C to remove the sizing agent and other finishing agents remaining on the surface of the polyvinyl alcohol fiber;

[0036] 2) Soak the polyvinyl alcohol fiber in a 1% dilute sulfuric acid solution with a butyraldehyde mass concentration of 3%, a solid-liquid ratio of 1:18, and a soaking time of 5 hours. Maintain the temperature at 40°C, then filter the fiber from the solution, wash it with ultrapure water three times, and dry it at 30°C.

[0037] The cellulose in the examples is hydroxypropyl methylcellulose (HPMC); the water reducer is a carboxylic acid-type high-efficiency water reducer; the silica fume is 96% pure high-activity microsilica; the fly ash is Class I low-calcium fly ash; and the cement is Portland cement with a strength grade of 52.5. The polyvinyl alcohol fiber has a diameter of 15 to 31 μm, a length of 9 mm, and a density of 910 kg / m 3 , elastic modulus is 38GPa, tensile strength is 1550MPa; the basalt fiber has a diameter of 7-15μm, a length of 9mm, and a density of 2630kg / m 3 The elastic modulus is 110 GPa, and the tensile strength is 3000 MPa. The reclaimed sand is recycled from crushed waste concrete, and the natural sand is natural quartz sand. The particle size of the reclaimed sand and natural sand ranges from 0.06 to 1.18 mm. The fineness modulus of the reclaimed sand is 1.79, and that of the natural sand is 2.12.

[0038] Example 1:

[0039] In this example, the hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand is composed of the following raw materials in the following proportions by weight: 449 parts cement, 242 parts reclaimed sand, 162 parts natural sand, 562 parts fly ash, 112 parts silica fume, 15.9 parts polyvinyl alcohol fiber, 6.6 parts basalt fiber, 2.25 parts cellulose, 3.3 parts water reducer, and 354 parts water. [RFA 60% - NFA 40%, 1.75% PVA - 0.25% BF, 50% FA], meaning the ratio of reclaimed sand to natural sand is 60%:40%, the volume ratio of polyvinyl alcohol fiber to basalt fiber is 1.75:0.25, and the fly ash content of the cementitious material (cement + fly ash + silica fume) is 50%.

[0040] The preparation steps are as follows:

[0041] 1) Pour 449 parts of cement, 562 parts of fly ash, 112 parts of silica fume, 242 parts of reclaimed sand, and 162 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0042] 2) Add 3.3 parts of water reducer, 2.25 parts of HPMC, and 177 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 15.9 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 106 parts of water and stir for 3 minutes.

[0043] 3) Keep the mixer running and slowly add 6.6 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 71 parts of water and stir for 3 minutes, then stop stirring;

[0044] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0045] Example 2:

[0046] The hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand in this example is made from the following raw materials in the following proportions by weight: 449 parts cement, 242 parts reclaimed sand, 162 parts natural sand, 562 parts fly ash, 112 parts silica fume, 13.7 parts polyvinyl alcohol fiber, 13.2 parts basalt fiber, 2.25 parts cellulose, 3.3 parts water reducer, and 354 parts water. [RFA 60% - NFA 40%, 1.50% PVA - 0.50% BF, 50% FA]

[0047] The preparation steps are as follows:

[0048] 1) Pour 449 parts of cement, 562 parts of fly ash, 112 parts of silica fume, 242 parts of reclaimed sand, and 162 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0049] 2) Add 3.3 parts of water reducer, 2.25 parts of HPMC, and 177 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 13.7 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 106 parts of water and stir for 3 minutes.

[0050] 3) Keep the mixer running and slowly add 13.2 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 71 parts of water and stir for 3 minutes, then stop stirring;

[0051] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0052] Example 3:

[0053] The hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand in this example is made from the following raw materials in the following proportions by weight: 449 parts cement, 242 parts reclaimed sand, 162 parts natural sand, 562 parts fly ash, 112 parts silica fume, 11.4 parts polyvinyl alcohol fiber, 19.8 parts basalt fiber, 2.25 parts cellulose, 3.3 parts water reducer, and 354 parts water. [RFA 60% - NFA 40%, 1.25% PVA - 0.75% BF, 50% FA]

[0054] The preparation steps are as follows:

[0055] 1) Pour 449 parts of cement, 562 parts of fly ash, 112 parts of silica fume, 242 parts of reclaimed sand, and 162 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0056] 2) Add 3.3 parts of water reducer, 2.25 parts of HPMC, and 177 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 11.4 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 106 parts of water and stir for 3 minutes.

[0057] 3) Keep the mixer running and slowly add 19.8 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 71 parts of water and stir for 3 minutes, then stop stirring;

[0058] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0059] Example 4:

[0060] The hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand in this example is made from the following raw materials in the following proportions by weight: 566 parts cement, 244 parts reclaimed sand, 163 parts natural sand, 453 parts fly ash, 113 parts silica fume, 15.9 parts polyvinyl alcohol fiber, 6.6 parts basalt fiber, 2.26 parts cellulose, 3.4 parts water reducer, and 357 parts water. [RFA 60% - NFA 40%, 1.75% PVA - 0.25% BF, 40% FA]

[0061] The preparation steps are as follows:

[0062] 1) Pour 566 parts of cement, 453 parts of fly ash, 113 parts of silica fume, 244 parts of reclaimed sand, and 163 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0063] 2) Add 3.4 parts of water reducer, 2.26 parts of HPMC, and 179 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 15.9 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 107 parts of water and stir for 3 minutes.

[0064] 3) Keep the mixer running and slowly add 6.6 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 71 parts of water and stir for 3 minutes, then stop stirring;

[0065] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0066] Example 5:

[0067] The hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand in this example is made from the following raw materials in the following proportions by weight: 566 parts cement, 163 parts reclaimed sand, 244 parts natural sand, 453 parts fly ash, 113 parts silica fume, 15.9 parts polyvinyl alcohol fiber, 6.6 parts basalt fiber, 2.26 parts cellulose, 3.4 parts water reducer, and 351 parts water. [RFA 40% - NFA 60%, 1.75% PVA - 0.25% BF, 40% FA]

[0068] The preparation steps are as follows:

[0069] 1) Pour 566 parts of cement, 453 parts of fly ash, 113 parts of silica fume, 163 parts of reclaimed sand, and 244 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0070] 2) Add 3.4 parts of water reducer, 2.26 parts of HPMC, and 176 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 15.9 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 105 parts of water and stir for 3 minutes.

[0071] 3) Keep the mixer running and slowly add 6.6 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 70 parts of water and stir for 3 minutes, then stop stirring;

[0072] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0073] Example 6:

[0074] The hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand in this example is made from the following raw materials in the following proportions by weight: 566 parts cement, 326 parts reclaimed sand, 81 parts natural sand, 453 parts fly ash, 113 parts silica fume, 15.9 parts polyvinyl alcohol fiber, 6.6 parts basalt fiber, 2.26 parts cellulose, 3.4 parts water reducer, and 362 parts water. [RFA 80% - NFA 20%, 1.75% PVA - 0.25% BF, 40% FA]

[0075] The preparation steps are as follows:

[0076] 1) Pour 566 parts of cement, 453 parts of fly ash, 113 parts of silica fume, 326 parts of reclaimed sand, and 81 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0077] 2) Add 3.4 parts of water reducer, 2.26 parts of HPMC, and 181 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 15.9 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 109 parts of water and stir for 3 minutes.

[0078] 3) Keep the mixer running and slowly add 6.6 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 72 parts of water and stir for 3 minutes, then stop stirring;

[0079] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0080] Comparative Example 1:

[0081] The hybrid fiber, high-ductility cement-based composite material prepared using reclaimed sand in this example is made from the following raw materials in the following proportions by weight: 449 parts cement, 242 parts reclaimed sand, 162 parts natural sand, 562 parts fly ash, 112 parts silica fume, 18.2 parts polyvinyl alcohol fiber, 2.25 parts cellulose, 3.3 parts water reducer, and 354 parts water. [RFA 60% - NFA 40%, 2.00% PVA - 0.00% BF, 50% FA]

[0082] The preparation steps are as follows:

[0083] 1) Pour 449 parts of cement, 562 parts of fly ash, 112 parts of silica fume, 242 parts of reclaimed sand, and 162 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0084] 2) Add 3.3 parts of water reducer, 2.25 parts of HPMC, and 177 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 18.2 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 177 parts of water and stir for 5 minutes.

[0085] 3) The mixture obtained in step 2) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0086] Comparative Example 2:

[0087] The hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand in this example includes the following raw materials in the following proportions by weight: 449 parts cement, 242 parts reclaimed sand, 162 parts natural sand, 562 parts fly ash, 112 parts silica fume, 52.8 parts basalt fiber, 2.25 parts cellulose, 3.3 parts water reducer, and 354 parts water. [RFA 60% - NFA 40%, 0.00 PVA - 2.00 BF, 50 FA]

[0088] The preparation steps are as follows:

[0089] 1) Pour 449 parts of cement, 562 parts of fly ash, 112 parts of silica fume, 242 parts of reclaimed sand, and 162 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0090] 2) Add 3.3 parts of water reducer, 2.25 parts of HPMC, and 177 parts of water to a blender and stir for 2 minutes to form a flowing mortar. During this time, slowly add 52.8 parts of basalt fiber to the flowing mortar. After all the basalt fiber has been added, add 177 parts of water and stir for 5 minutes.

[0091] 3) The mixture obtained in step 2) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0092] Comparative Example 3:

[0093] The hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand in this example includes the following raw materials in the following proportions by weight: 566 parts cement, 407 parts reclaimed sand, 453 parts fly ash, 113 parts silica fume, 15.9 parts polyvinyl alcohol fiber, 6.6 parts basalt fiber, 2.26 parts cellulose, 3.4 parts water reducer, and 368 parts water. [RFA 100% - NFA 0%, 1.75% PVA - 0.25% BF, 40% FA]

[0094] The preparation steps are as follows:

[0095] 1) Pour 566 parts of cement, 453 parts of fly ash, 113 parts of silica fume, and 407 parts of reclaimed sand into a mixer and stir for 2 minutes to form a mixture;

[0096] 2) Add 3.4 parts of water reducer, 2.26 parts of HPMC, and 184 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 15.9 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 110 parts of water and stir for 3 minutes.

[0097] 3) Keep the mixer running and slowly add 6.6 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 74 parts of water and stir for 3 minutes, then stop stirring;

[0098] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0099] Comparative Example 4:

[0100] The hybrid fiber high-ductility cement-based composite material prepared using reclaimed sand in this example includes the following raw materials in the following proportions by weight: 566 parts cement, 407 parts natural sand, 453 parts fly ash, 113 parts silica fume, 15.9 parts polyvinyl alcohol fiber, 6.6 parts basalt fiber, 2.26 parts cellulose, 3.4 parts water reducer, and 340 parts water. [RFA 0% - NFA 100%, 1.75PVA - 0.025BF, 40FA]

[0101] The preparation steps are as follows:

[0102] 1) Pour 566 parts of cement, 453 parts of fly ash, 113 parts of silica fume, and 407 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0103] 2) Add 3.4 parts of water reducer, 2.26 parts of HPMC, and 170 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 15.9 parts of polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 102 parts of water and stir for 3 minutes.

[0104] 3) Keep the mixer running and slowly add 6.6 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 68 parts of water and stir for 3 minutes, then stop stirring;

[0105] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0106] Comparative Example 5:

[0107] In this embodiment, the mixed fiber high-ductility cement-based composite material prepared with regenerated sand includes the following raw materials in the following proportions by weight: 449 parts of cement, 242 parts of regenerated sand, 162 parts of natural sand, 562 parts of fly ash, 112 parts of silica fume, 15.9 parts of unmodified polyvinyl alcohol fiber, 6.6 parts of basalt fiber, 2.25 parts of cellulose, 3.3 parts of water reducer, and 354 parts of water.

[0108] The preparation steps are as follows:

[0109] 1) Pour 449 parts of cement, 562 parts of fly ash, 112 parts of silica fume, 242 parts of reclaimed sand, and 162 parts of natural sand into a mixer and stir for 2 minutes to form a mixture;

[0110] 2) Add 3.3 parts of water reducer, 2.25 parts of HPMC, and 177 parts of water to a blender and stir for 2 minutes to form a flowing mortar. Meanwhile, slowly add 15.9 parts of unmodified polyvinyl alcohol fiber to the flowing mortar. Once all the fibers are added, add 106 parts of water and stir for 3 minutes.

[0111] 3) Keep the mixer running and slowly add 6.6 parts of basalt fiber to the flowing mortar. After all the basalt fiber is added, add 71 parts of water and stir for 3 minutes, then stop stirring;

[0112] 4) The mixture obtained in step 3) was poured into a test mold all at once. After filling, the mold was placed on a vibration table and vibrated for 15 seconds. The surface of the test piece was then covered with plastic film and allowed to stand at 20°C for 24 hours. After demolding, the test piece was transferred to a standard curing room at 20°C and 95% relative humidity.

[0113] The specimens formed according to the mix proportions, preparation methods, and curing systems of the above-described embodiments and comparative examples were subjected to 28-day compressive strength tests, uniaxial tensile tests, and four-point bending tests in accordance with the relevant requirements of GB / T50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete" and the "Recommendations for Design and Construction of High-Performance Fiber-Reinforced Cement Composites with Multiple Fine Cracks" proposed by the Japan Society of Civil Engineers. The final results are summarized in Table 1.

[0114] Table 1

[0115] serial number Compressive strength (MPa) Peak strain (%) Tensile strength (MPa) Flexural strength (MPa) Example 1 55.73 2.89 2.95 7.82 Example 2 54.60 2.77 2.64 7.37 Example 3 52.06 2.32 2.56 7.19 Example 4 54.92 2.46 3.10 7.26 Example 5 49.11 2.33 2.67 7.33 Example 6 44.65 2.25 2.58 6.95 Comparative Example 1 47.25 2.83 3.18 7.59 Comparative Example 2 53.05 0.89 1.22 5.27 Comparative Example 3 42.25 1.97 2.35 6.37 Comparative Example 4 51.80 2.42 2.60 7.30 Comparative Example 5 54.19 2.45 2.69 7.22

[0116] In addition, economic analysis is an important evaluation indicator in the field of resource recycling of building materials. The main raw material costs were calculated for the test pieces formed according to the proportions, preparation methods and maintenance systems of the above-mentioned embodiments and comparative examples. The unit prices of material purchases are summarized in Table 2, and the final cost accounting results are summarized in Table 3.

[0117] Table 2

[0118]

[0119] Table 3

[0120]

[0121]

[0122] According to the test results in Table 1 and the economic analysis in Tables 2 and 3, combined with Examples 1 to 3 and Comparative Examples 1 to 2, it can be concluded that when the volume ratio of polyvinyl alcohol fiber to basalt fiber is 1.75:0.25, the mechanical properties of the high-ductility cement-based composite material reach the optimal level. The compressive strength and flexural strength under this fiber blending ratio are respectively increased by 17.9% and 3.0% compared with the single polyvinyl alcohol fiber, while the cost is reduced by 4.9%, which has obvious advantages. When the volume ratio of polyvinyl alcohol fiber to basalt fiber is 1.50:0.50, the compressive strength is increased by 15.6% compared with the single polyvinyl alcohol fiber, but the tensile and flexural properties are slightly reduced. Considering that the cost is significantly reduced by 9.4%, this ratio still has a certain cost-effectiveness advantage. Compared with polyvinyl alcohol fiber, basalt fiber has a stronger chemical bond with the matrix, which is beneficial to delay the proliferation and expansion of cracks after the composite material cracks. At a suitable blending ratio with modified polyvinyl alcohol fibers, the bridging interlocking behavior between the two fiber surfaces and the matrix can be synergistically promoted, thereby improving the overall ductility of the matrix and promoting the development of the strain hardening stage of the matrix during multiple cracking processes.

[0123] Comparison of Example 1 and Comparative Example 5 reveals that the polyvinyl alcohol fiber modification method of the present invention significantly improves the tensile and flexural properties of the composite material. The tensile strain, tensile strength, and flexural strength of the composite material increased by 17.9%, 9.7%, and 8.3%, respectively, before and after modification. The hydrophobic treatment and acid etching of the polyvinyl alcohol fiber surface enhance the synergistic bonding between the polyvinyl alcohol fiber and the basalt fiber, forming a multi-component anchoring system with the cement matrix, thereby increasing the interfacial bonding strength between the hybrid fiber and the hydration product.

[0124] Comparing Examples 4-6 with Comparative Examples 3-4, it can be seen that peak strain and tensile strength reach their highest levels when the regenerated sand replacement ratio is 60%. This is because the appropriate ratio of regenerated sand to natural sand facilitates the self-cementing ability of the regenerated sand, improving the matrix microstructure. The secondary hydration of the old adhesive mortar on the regenerated sand surface enhances the overall density of the composite material. Furthermore, when the multi-angled surface of the regenerated sand is subjected to tensile stress, it compresses the interfacial transition zone between the fiber and the matrix, thereby enhancing the frictional bond between the fibers and the matrix and effectively preventing premature fiber pullout and failure. Furthermore, according to an economic analysis, Example 4, with a 60% regenerated sand replacement ratio, reduces costs by 7.5% compared to Comparative Example 4, which uses pure natural sand, demonstrating a significant cost-effectiveness advantage. When the regenerated sand replacement ratio is 40%, the tensile and flexural properties are good, and the cost is reduced by 5.0%, maintaining a certain cost-effectiveness advantage. When the regenerated sand replacement ratio exceeds 80%, the compressive strength decreases significantly, but the decrease is within 20%, and the design requirement of 40 MPa or above is met. The main reason for the decrease in compressive strength is that the regenerated sand has been crushed and ground to form a loose and porous surface with a large number of microcracks, which leads to a decrease in aggregate strength and is prone to stress concentration failure when under pressure.

[0125] Comparing Examples 1 and 4, it can be seen that appropriately increasing the fly ash content helps improve the overall mechanical properties of high-ductility cementitious composites. This is attributed to the fly ash filling the microscopic pores between the matrix and the reclaimed sand, thereby strengthening the aggregate-matrix interface. Furthermore, the unhydrated fly ash particles that fill the gaps between the fibers and the matrix help improve frictional bonding at the fiber-matrix interface, thereby enhancing fiber bridging capacity.

[0126] The above description is only a specific embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, they can still modify the various embodiments proposed in this specification or replace some of the technical features therein with equivalents. However, any modifications, equivalent replacements, improvements, etc. made within the scope of the claims of the present application should be included in the scope of protection of the present invention.

Claims

1. A hybrid fiber high ductility cement-based composite material prepared from reclaimed sand, characterized by: The invention comprises the following raw materials in parts by weight: 449-566 parts of cement, 163-326 parts of regenerated sand, 81-244 parts of natural sand, 453-562 parts of fly ash, 112-113 parts of silica fume, 11.4-15.9 parts of modified polyvinyl alcohol fiber, 6.6-19.8 parts of basalt fiber, 2.25-2.26 parts of cellulose, 3.3-3.4 parts of water reducer, and 340-368 parts of water; the mass ratio of the regenerated sand to the natural sand is 60:40; the cellulose is hydroxypropyl methylcellulose; the regenerated sand is recycled sand from crushed waste concrete, and the natural sand is natural quartz sand; the particle sizes of the regenerated sand and the natural sand are 0.06-1.18 mm; The preparation method of modified polyvinyl alcohol fiber is as follows: (1) Soak the PVA fiber in NaHCO3 solution to remove residual impurities on the surface of the PVA fiber; (2) The polyvinyl alcohol fiber was immersed in a butyraldehyde sulfuric acid solution with a mass concentration of 3%, a solid-liquid ratio of 1:18, and a soaking time of 5 hours. The temperature was maintained at 40°C. The fiber was then filtered out of the solution, washed, and dried to obtain the modified polyvinyl alcohol fiber.

2. The hybrid fiber high ductility cement-based composite material prepared with regenerated sand according to claim 1, characterized in that: The volume ratio of the modified polyvinyl alcohol fiber and the basalt fiber in the cement-based composite material is 2%; the volume ratio ratio of the modified polyvinyl alcohol fiber to the basalt fiber is 1.25~1.75:0.25~0.

75.

3. The hybrid fiber high ductility cement-based composite material prepared with regenerated sand according to claim 1, characterized in that: The volume ratio of the polyvinyl alcohol fiber to the basalt fiber is 1.75:0.

25.

4. The hybrid fiber high ductility cement-based composite material prepared with regenerated sand according to claim 1, characterized in that: The mass concentration of sulfuric acid solution is 1%.

5. The method for preparing a hybrid fiber high-ductility cement-based composite material using regenerated sand according to any one of claims 1 to 4, characterized in that: The preparation steps are as follows: 1) Pour cement, fly ash, silica fume, reclaimed sand and natural sand into a mixer and stir to form a mixture; 2) Add water reducer, cellulose and 50% water into a mixer and stir to form a flowing mortar. During this process, add polyvinyl alcohol fiber into the flowing mortar. After all the additions are completed, add 30% water and stir; 3) Keep the mixer running and slowly add the basalt fiber into the flowing mortar. After all the basalt fiber is added, add 20% water and stir to obtain a cement-based composite material.

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