CN117164307A - Hybrid fiber high-ductility cement-based composite material prepared from reclaimed sand and preparation method thereof - Google Patents
Hybrid fiber high-ductility cement-based composite material prepared from reclaimed sand and preparation method thereof Download PDFInfo
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- CN117164307A CN117164307A CN202311111602.XA CN202311111602A CN117164307A CN 117164307 A CN117164307 A CN 117164307A CN 202311111602 A CN202311111602 A CN 202311111602A CN 117164307 A CN117164307 A CN 117164307A
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- 238000002360 preparation method Methods 0.000 title claims description 20
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 135
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 84
- 239000004372 Polyvinyl alcohol Substances 0.000 claims abstract description 69
- 229920002451 polyvinyl alcohol Polymers 0.000 claims abstract description 69
- 229920002748 Basalt fiber Polymers 0.000 claims abstract description 51
- 239000010881 fly ash Substances 0.000 claims abstract description 39
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- 238000003756 stirring Methods 0.000 claims description 28
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- 239000000463 material Substances 0.000 claims description 18
- 239000001866 hydroxypropyl methyl cellulose Substances 0.000 claims description 16
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- UFVKGYZPFZQRLF-UHFFFAOYSA-N hydroxypropyl methyl cellulose Chemical group OC1C(O)C(OC)OC(CO)C1OC1C(O)C(O)C(OC2C(C(O)C(OC3C(C(O)C(O)C(CO)O3)O)C(CO)O2)O)C(CO)O1 UFVKGYZPFZQRLF-UHFFFAOYSA-N 0.000 claims description 16
- 235000010979 hydroxypropyl methyl cellulose Nutrition 0.000 claims description 16
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 10
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/91—Use of waste materials as fillers for mortars or concrete
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- Curing Cements, Concrete, And Artificial Stone (AREA)
Abstract
The invention belongs to the field of resource recycling in building materials, and particularly relates to a hybrid fiber high-ductility cement-based composite material prepared by using reclaimed sand and a method thereof; the raw materials comprise cement, reclaimed sand, natural sand, fly ash, silica fume, polyvinyl alcohol fiber, basalt fiber, cellulose, water reducing agent and water. According to the invention, the waste concrete crushed reclaimed sand is applied to the high-ductility cement-based composite material, and the self-cementing effect of the reclaimed sand is promoted to improve the compactness of the matrix by adjusting the substitution rate of the reclaimed sand on the natural sand, so that the multiple cracking capacity of the matrix is improved. In addition, the design of mixing the polyvinyl alcohol fiber and the basalt fiber is adopted, so that the fiber cost in the raw materials is obviously reduced while the stretching and extending characteristics are ensured. The invention also helps to alleviate the resource shortage problem of the natural sand.
Description
Technical Field
The invention belongs to the field of resource recycling in building materials, and particularly relates to a hybrid fiber high-ductility cement-based composite material prepared from reclaimed sand and a method.
Background
Reinforcement corrosion is one of the root causes of deterioration of concrete structures. During the life cycle of the building structure, various environmental factors promote the gradual formation of corrosion products on the surface of the steel bars, leading to cracking and spalling of the concrete protective layer. The continuous accumulation of corrosion products reduces the effective cross-sectional area of the rebar, thereby weakening the bond strength between the rebar and the concrete and greatly reducing the load-bearing capacity of the structure. Victor Li teaches the development of a high-ductility cement-based composite (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 conventional concrete. The ECC can generate a plurality of harmless cracks with the width within 100 mu m and even distribution under the stretching state, obviously slows down the corrosion process of internal reinforcing steel bars and ensures the structural integrity and reliability.
Research and application of ECC has gained a great deal of attention. The Chinese patent document with application number 202111170507.8 discloses a high-ductility cement-based composite material and a preparation method thereof, wherein the composite material has good strength and bending toughness, and the composite material is prepared by mixing 200-400 parts of cement, 100-350 parts of fly ash, 100-350 parts of mineral powder, 100-450 parts of aggregate, 20-45 parts of silica fume, 5-25 parts of water reducer, 1-6 parts of defoamer, 0.1-0.8 part of cellulose ether, 0.5-6 parts of injection regulator, 5-40 parts of polyvinyl alcohol fiber, 1000-3000 parts of water and 5-30 parts of polyoxymethylene fiber. However, the preparation process of ECC requires a large amount of quartz sand to be consumed, which increases costs and is liable to suffer from a problem of supply shortage. At present, over exploitation of quartz sand has caused a series of environmental problems such as soil erosion and river bank erosion.
The reclaimed sand is a byproduct obtained in the waste concrete crushing process. The rapid development of the construction industry has accumulated tens of trillion tons of construction waste over the past few decades. A large amount of waste concrete is randomly piled up and buried, pollutes and occupies a large amount of land. The broken waste concrete is used as a substitute for quartz sand to prepare the ECC, so that the ecological and environment-friendly value of the ECC is given while the production cost is reduced, and the ECC is promoted and applied.
Disclosure of Invention
The invention aims at overcoming the defects of the prior art and providing a hybrid fiber high-ductility cement-based composite material prepared by using reclaimed sand. The waste concrete crushed reclaimed sand is used for replacing part of natural quartz sand, polyvinyl alcohol fibers and basalt fiber reinforced matrix are used, and the design is based on the mesomechanics theory, so that the production cost is reduced while the good tensile strain capacity and multiple cracking characteristics of the reinforced concrete are ensured, and the reinforced concrete structure reinforcing material is promoted to be applied to the large-scale of the reinforced concrete structure reinforcing material.
In order to solve the technical problems, the invention adopts the following technical scheme: the mixed fiber high-ductility cement-based composite material prepared from reclaimed sand comprises the following raw materials in parts by mass: 449-566 parts of cement, 163-326 parts of reclaimed 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.
Further, the reclaimed sand is crushed reclaimed sand of waste concrete, and the natural sand is natural quartz sand.
Further, the particle size of the reclaimed sand and the natural sand is 0.06-1.18 mm, the fineness modulus of the reclaimed sand is 1.79, and the fineness modulus of the natural sand is 2.12.
Further, the polyvinyl alcohol fiber has a diameter of 15-31 μm, a length of 9mm and a density of 910kg/m 3 The elastic modulus is 38GPa, and the tensile strength is 1550MPa; the basalt fiber has the diameter of 7-15 mu m, the length of 9mm and the density of 2630kg/m 3 The elastic modulus is 110GPa, and the tensile strength is 3000MPa.
Further, the polyvinyl alcohol fiber is a modified polyvinyl alcohol fiber, and the modification steps are as follows:
1) Soaking polyvinyl alcohol fiber in NaHCO with mass concentration of 10% 3 In the solution, the solid-liquid ratio is 1:15, soaking for 3 hours, filtering the fiber from the solution, washing with ultrapure water for 3 times, drying at 30 ℃,to remove the sizing agent and other finishing agents remained on the surface of the polyvinyl alcohol fiber;
2) Polyvinyl alcohol fibers are soaked in 1% dilute sulfuric acid solution with the mass concentration of 3% of butyraldehyde, and the solid-liquid ratio is 1:18, soaking for 5 hours at 40 ℃, filtering the fiber from the solution, washing 3 times with ultrapure water, and drying at 30 ℃. The butyraldehyde is covalently bonded with free hydroxyl groups on the surface of the polyvinyl alcohol fiber through an acid-catalyzed acetal reaction, and the two hydroxyl groups are converted into an acetal structure, so that the polyvinyl alcohol fiber has longer lasting hydrophobic property compared with the common surface modification process. Meanwhile, the polyvinyl alcohol fibers immersed in the dilute sulfuric acid solution are subjected to acid etching, and etching grooves are formed in the surfaces of the fibers, so that the surface roughness is increased.
Further, the cellulose is hydroxypropyl methylcellulose (HPMC), the 100 mesh passing rate is more than 98.5%, and the apparent density is 250-700 kg/m 3 The surface tension of the 2% aqueous solution is 42-56 dyn/cm.
Further, the water reducer is a carboxylic acid type high-efficiency water reducer.
Further, the cement is Portland cement with the strength grade of 52.5.
Further, the fly ash is I-grade low-calcium fly ash.
Furthermore, the silica fume is high-activity micro silica fume with the purity of 96 percent.
Further, the mass ratio of the reclaimed sand to the natural sand is 40-80:20-60. The mass ratio of the preferable regenerated sand to the natural sand is 60:40.
Further, the mass ratio of the fly ash in the cementing material (cement, fly ash and silica fume) is 40-50%.
Further, 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 to 0.75; it is further preferable that the volume ratio of the polyvinyl alcohol fiber to the basalt fiber is 1.75:0.25.
In addition, the invention also provides a method for preparing the hybrid fiber high-ductility cement-based composite material by using the reclaimed sand, which comprises the following preparation steps:
1) Pouring cement, fly ash, silica fume, reclaimed sand and natural sand according to the mass ratio into a stirrer, and stirring for 2 minutes to form a mixture;
2) And adding the water reducer, the cellulose and 50% water according to the mass ratio into a stirrer, and stirring for 2 minutes to form the flowing mortar. Meanwhile, slowly adding the polyvinyl alcohol fibers in the mass part ratio into the flowing mortar, and adding 30% water in the mass part ratio into the flowing mortar for stirring for 3 minutes after the complete addition;
3) Maintaining the continuous operation of the stirrer, slowly adding basalt fibers according to the mass part ratio into the flowing mortar, adding 20% water according to the mass part ratio into the flowing mortar for stirring for 3 minutes after all the basalt fibers are added, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Further, according to the method for preparing the hybrid fiber high-ductility cement-based composite material by using the reclaimed sand, the whole preparation process of the material is controlled to be 10-13 minutes.
The hybrid fiber high-ductility cement-based composite material prepared from the reclaimed sand has the following beneficial effects:
1) The hybrid fiber high-ductility cement-based composite material prepared from the reclaimed sand has good bending strength and tensile strain capacity. The inherent self-cementing capability of the reclaimed sand improves the total compactness of the matrix, enhances the bridging effect between the fiber and the matrix, and improves the multiple cracking capability of the cement-based composite material.
2) The modified polyvinyl alcohol fiber surface has longer lasting hydrophobic property, so that partial fiber is properly debonded and stretched in the crack growth process, and the tensile strain behavior of the matrix is promoted. Meanwhile, after the fiber is etched by dilute sulfuric acid, a fine groove appears on the surface. In the hydration process of the cementing material, part of the high polymer chain segment enters the fiber surface groove to form a mechanical anchoring system with the fiber, so that the interface bonding strength between the fiber and a hydration product is further improved.
3) The polyvinyl alcohol fiber and basalt fiber mixed mode based on the synergistic effect is adopted, so that the high elastic modulus and high strength of the basalt fiber are utilized to enhance the bonding strength between a fiber system and a matrix and inhibit crack expansion under the condition that the total fiber mixed amount is 2% unchanged. The compressive property of the matrix is improved while the tensile expansion property of the high-ductility cement-based composite material is ensured, and the reduction of the structural reinforcement cost is facilitated.
4) The application of the reclaimed sand is beneficial to relieving the resource shortage problem of the natural sand, reducing the stacking occupation and environmental pollution problems of urban building wastes, improving the recycling rate of the building wastes in China, conforming to the sustainable development strategy in China and having great significance to concrete structure reinforcement engineering practice.
Drawings
FIG. 1 is a physical diagram of a hybrid fiber high-ductility cement-based composite material specimen prepared by reclaimed sand.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below by means of examples and comparative examples, and it is apparent that the described examples are only some examples of the present invention. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the invention, are within the scope of the invention.
The polyvinyl alcohol fiber in the examples refers to a modified polyvinyl alcohol fiber, and the modification steps are as follows:
1) Soaking polyvinyl alcohol fiber in NaHCO with mass concentration of 10% 3 In the solution, the solid-liquid ratio is 1:15, soaking for 3 hours, filtering the fiber from the solution, washing the fiber with ultrapure water for 3 times, and drying the fiber at 30 ℃ to remove the sizing agent and other finishing agents remained on the surface of the polyvinyl alcohol fiber;
2) Polyvinyl alcohol fibers are soaked in 1% dilute sulfuric acid solution with the mass concentration of 3% of butyraldehyde, and the solid-liquid ratio is 1:18, soaking for 5 hours at 40 ℃, filtering the fiber from the solution, washing 3 times with ultrapure water, and drying at 30 ℃.
The cellulose in the examples is hydroxypropyl methylcellulose (HPMC); the water reducer is carboxylic acid type high-efficiency water reducer; the silica fume is high-activity micro silica powder with the purity of 96%; the fly ash is I-grade low-calcium fly ash; the cement was Portland cement with a strength grade of 52.5. The polyvinyl alcohol fiber has a diameter of 15-31 mu m, a length of 9mm and a density of 910kg/m 3 The elastic modulus is 38GPa, and the tensile strength is 1550MPa; the basalt fiber has the diameter of 7-15 mu m, the length of 9mm and the density of 2630kg/m 3 The elastic modulus is 110GPa, and the tensile strength is 3000MPa. The reclaimed sand is crushed reclaimed sand of waste concrete, and the natural sand is natural quartz sand. The grain diameter of the reclaimed sand and the natural sand is 0.06-1.18 mm, the fineness modulus of the reclaimed sand is 1.79, and the fineness modulus of the natural sand is 2.12.
Example 1:
the mixed fiber high-ductility cement-based composite material prepared by using the reclaimed sand in the embodiment is prepared from the following raw materials in parts by mass: 449 parts of cement, 242 parts of reclaimed sand, 162 parts of natural sand, 562 parts of fly ash, 112 parts of silica fume, 15.9 parts of 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. [ RFA60% -NFA40%,1.75PVA-0.25BF,50FA ], namely the proportion of the reclaimed sand and the natural sand is 60%:40 percent of polyvinyl alcohol fiber and basalt fiber with a volume ratio of 1.75:0.25, the mass ratio of the fly ash in the cementing material (cement, fly ash and silica fume) is 50%.
The preparation method comprises the following steps:
1) 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 are poured into a stirrer, and stirred for 2 minutes to form a mixture;
2) 3.3 parts of water reducer, 2.25 parts of HPMC and 177 parts of water were added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 15.9 parts of polyvinyl alcohol fibers are slowly added into the flowing mortar, and 106 parts of water is added into the flowing mortar for 3 minutes after the complete addition;
3) Keeping the stirrer continuously running, slowly adding 6.6 parts of basalt fibers into the flowing mortar, adding 71 parts of water into the flowing mortar for stirring for 3 minutes after all the basalt fibers are added, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Example 2:
the mixed fiber high-ductility cement-based composite material prepared by using the reclaimed sand in the embodiment is prepared from the following raw materials in parts by mass: 449 parts of cement, 242 parts of reclaimed sand, 162 parts of natural sand, 562 parts of fly ash, 112 parts of silica fume, 13.7 parts of polyvinyl alcohol fiber, 13.2 parts of basalt fiber, 2.25 parts of cellulose, 3.3 parts of water reducer and 354 parts of water. [ RFA60% -NFA40%,1.50PVA-0.50BF,50FA ]
The preparation method comprises the following steps:
1) 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 are poured into a stirrer, and stirred for 2 minutes to form a mixture;
2) 3.3 parts of water reducer, 2.25 parts of HPMC and 177 parts of water were added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 13.7 parts of polyvinyl alcohol fibers are slowly added into the flowing mortar, and 106 parts of water is added into the flowing mortar for 3 minutes after the complete addition;
3) Maintaining the continuous operation of the stirrer, slowly adding 13.2 parts of basalt fiber into the flowing mortar, adding 71 parts of water into the flowing mortar for stirring for 3 minutes after the complete addition, and then stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Example 3:
the mixed fiber high-ductility cement-based composite material prepared by using the reclaimed sand in the embodiment is prepared from the following raw materials in parts by mass: 449 parts of cement, 242 parts of reclaimed sand, 162 parts of natural sand, 562 parts of fly ash, 112 parts of silica fume, 11.4 parts of polyvinyl alcohol fiber, 19.8 parts of basalt fiber, 2.25 parts of cellulose, 3.3 parts of water reducer and 354 parts of water. [ RFA60% -NFA40%,1.25PVA-0.75BF,50FA ]
The preparation method comprises the following steps:
1) 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 are poured into a stirrer, and stirred for 2 minutes to form a mixture;
2) 3.3 parts of water reducer, 2.25 parts of HPMC and 177 parts of water were added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, slowly adding 11.4 parts of polyvinyl alcohol fibers into the flowing mortar, and adding 106 parts of water into the flowing mortar for stirring for 3 minutes after the complete addition;
3) Maintaining the continuous operation of the stirrer, slowly adding 19.8 parts of basalt fiber into the flowing mortar, adding 71 parts of water into the flowing mortar for stirring for 3 minutes after the complete addition, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Example 4:
the mixed fiber high-ductility cement-based composite material prepared by using the reclaimed sand in the embodiment is prepared from the following raw materials in parts by mass: 566 parts of cement, 244 parts of reclaimed sand, 163 parts of natural sand, 453 parts of fly ash, 113 parts of silica fume, 15.9 parts of polyvinyl alcohol fiber, 6.6 parts of basalt fiber, 2.26 parts of cellulose, 3.4 parts of water reducer and 357 parts of water. [ RFA60% -NFA40%,1.75PVA-0.25BF,40FA ]
The preparation method comprises the following steps:
1) 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 are poured into a stirrer and stirred for 2 minutes to form a mixture;
2) 3.4 parts of water reducer, 2.26 parts of HPMC and 179 parts of water are added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 15.9 parts of polyvinyl alcohol fibers are slowly added into the flowing mortar, and 107 parts of water is added into the flowing mortar for 3 minutes after the complete addition;
3) Keeping the stirrer continuously running, slowly adding 6.6 parts of basalt fibers into the flowing mortar, adding 71 parts of water into the flowing mortar for stirring for 3 minutes after all the basalt fibers are added, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Example 5:
the mixed fiber high-ductility cement-based composite material prepared by using the reclaimed sand in the embodiment is prepared from the following raw materials in parts by mass: 566 parts of cement, 163 parts of reclaimed sand, 244 parts of natural sand, 453 parts of fly ash, 113 parts of silica fume, 15.9 parts of polyvinyl alcohol fiber, 6.6 parts of basalt fiber, 2.26 parts of cellulose, 3.4 parts of water reducer and 351 parts of water. [ RFA40% -NFA60%,1.75PVA-0.25BF,40FA ]
The preparation method comprises the following steps:
1) 566 parts of cement, 453 parts of fly ash, 113 parts of silica fume and 163 parts of reclaimed sand, 244 parts of natural sand are poured into a stirrer, and stirred for 2 minutes to form a mixture;
2) 3.4 parts of water reducer, 2.26 parts of HPMC and 176 parts of water are added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 15.9 parts of polyvinyl alcohol fibers are slowly added into the flowing mortar, and 105 parts of water is added into the flowing mortar for 3 minutes after the complete addition;
3) Keeping the stirrer continuously running, slowly adding 6.6 parts of basalt fibers into the flowing mortar, adding 70 parts of water into the flowing mortar for stirring for 3 minutes after all the basalt fibers are added, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Example 6:
the mixed fiber high-ductility cement-based composite material prepared by using the reclaimed sand in the embodiment is prepared from the following raw materials in parts by mass: 566 parts of cement, 326 parts of reclaimed sand, 81 parts of natural sand, 453 parts of fly ash, 113 parts of silica fume, 15.9 parts of polyvinyl alcohol fiber, 6.6 parts of basalt fiber, 2.26 parts of cellulose, 3.4 parts of water reducer and 362 parts of water. [ RFA80% -NFA20%,1.75PVA-0.25BF,40FA ]
The preparation method comprises the following steps:
1) 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 are poured into a stirrer and stirred for 2 minutes to form a mixture;
2) 3.4 parts of water reducer, 2.26 parts of HPMC and 181 parts of water were added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 15.9 parts of polyvinyl alcohol fibers are slowly added into the flowing mortar, and 109 parts of water is added into the flowing mortar for 3 minutes after the complete addition;
3) Keeping the stirrer continuously running, slowly adding 6.6 parts of basalt fibers into the flowing mortar, adding 72 parts of water into the flowing mortar for stirring for 3 minutes after all the basalt fibers are added, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Comparative example 1:
the mixed fiber high-ductility cement-based composite material prepared by using the reclaimed sand in the embodiment is prepared from the following raw materials in parts by mass: 449 parts of cement, 242 parts of reclaimed sand, 162 parts of natural sand, 562 parts of fly ash, 112 parts of silica fume, 18.2 parts of polyvinyl alcohol fiber, 2.25 parts of cellulose, 3.3 parts of water reducer and 354 parts of water. [ RFA60% -NFA40%,2.00PVA-0.00BF,50FA ]
The preparation method comprises the following steps:
1) 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 are poured into a stirrer, and stirred for 2 minutes to form a mixture;
2) 3.3 parts of water reducer, 2.25 parts of HPMC and 177 parts of water were added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 18.2 parts of polyvinyl alcohol fibers are slowly added into the flowing mortar, and 177 parts of water is added into the flowing mortar for 5 minutes after the complete addition;
3) And (3) pouring the mixture obtained in the step (2) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is finished. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Comparative example 2:
the hybrid fiber high-ductility cement-based composite material prepared from the reclaimed sand in the embodiment comprises the following raw materials in parts by mass: 449 parts of cement, 242 parts of reclaimed sand, 162 parts of natural sand, 562 parts of fly ash, 112 parts of silica fume, 52.8 parts of basalt fiber, 2.25 parts of cellulose, 3.3 parts of water reducer and 354 parts of water. [ RFA60% -NFA40%,0.00PVA-2.00BF,50FA ]
The preparation method comprises the following steps:
1) 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 are poured into a stirrer, and stirred for 2 minutes to form a mixture;
2) 3.3 parts of water reducer, 2.25 parts of HPMC and 177 parts of water were added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 52.8 parts of basalt fiber is slowly added into the flowing mortar, and 177 parts of water is added into the flowing mortar for 5 minutes after the complete addition;
3) And (3) pouring the mixture obtained in the step (2) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is finished. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Comparative example 3:
the hybrid fiber high-ductility cement-based composite material prepared from the reclaimed sand in the embodiment comprises the following raw materials in parts by mass: 566 parts of cement, 407 parts of reclaimed sand, 453 parts of fly ash, 113 parts of silica fume, 15.9 parts of polyvinyl alcohol fiber, 6.6 parts of basalt fiber, 2.26 parts of cellulose, 3.4 parts of water reducer and 368 parts of water. [ RFA100% -NFA0%,1.75PVA-0.25BF,40FA ]
The preparation method comprises the following steps:
1) 566 parts of cement, 453 parts of fly ash, 113 parts of silica fume and 407 parts of reclaimed sand are poured into a stirrer and stirred for 2 minutes to form a mixture;
2) 3.4 parts of water reducer, 2.26 parts of HPMC and 184 parts of water are added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 15.9 parts of polyvinyl alcohol fibers are slowly added into the flowing mortar, and 110 parts of water is added into the flowing mortar for 3 minutes after the complete addition;
3) Keeping the stirrer continuously running, slowly adding 6.6 parts of basalt fibers into the flowing mortar, adding 74 parts of water into the flowing mortar for stirring for 3 minutes after all the basalt fibers are added, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Comparative example 4:
the hybrid fiber high-ductility cement-based composite material prepared from the reclaimed sand in the embodiment comprises the following raw materials in parts by mass: 566 parts of cement, 407 parts of natural sand, 453 parts of fly ash, 113 parts of silica fume, 15.9 parts of polyvinyl alcohol fiber, 6.6 parts of basalt fiber, 2.26 parts of cellulose, 3.4 parts of water reducer and 340 parts of water. [ RFA0% -NFA100%,1.75PVA- & lt025 BF,40FA ]
The preparation method comprises the following steps:
1) 566 parts of cement, 453 parts of fly ash, 113 parts of silica fume and 407 parts of natural sand are poured into a stirrer and stirred for 2 minutes to form a mixture;
2) 3.4 parts of water reducer, 2.26 parts of HPMC and 170 parts of water were added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 15.9 parts of polyvinyl alcohol fibers are slowly added into the flowing mortar, and 102 parts of water is added into the flowing mortar for 3 minutes after the complete addition;
3) Keeping the stirrer continuously running, slowly adding 6.6 parts of basalt fibers into the flowing mortar, adding 68 parts of water into the flowing mortar for stirring for 3 minutes after all the basalt fibers are added, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Comparative example 5:
the hybrid fiber high-ductility cement-based composite material prepared from the reclaimed sand in the embodiment comprises the following raw materials in parts by mass: 449 parts of cement, 242 parts of reclaimed 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.
The preparation method comprises the following steps:
1) 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 are poured into a stirrer, and stirred for 2 minutes to form a mixture;
2) 3.3 parts of water reducer, 2.25 parts of HPMC and 177 parts of water were added to a mixer and stirred for 2 minutes to form a flowing mortar. Meanwhile, 15.9 parts of unmodified polyvinyl alcohol fibers are slowly added into the flowing mortar, and 106 parts of water is added into the flowing mortar for 3 minutes after the complete addition;
3) Keeping the stirrer continuously running, slowly adding 6.6 parts of basalt fibers into the flowing mortar, adding 71 parts of water into the flowing mortar for stirring for 3 minutes after all the basalt fibers are added, and stopping stirring;
4) And 3) pouring the mixture obtained in the step 3) into a test mould at one time, and placing the test mould on a vibrating table to vibrate for 15 seconds after the material filling is completed. Then, the surface of the test piece is covered with a plastic film, and the test piece is kept stand for 24 hours in an environment with the temperature of 20 ℃. After demoulding, the test piece is transferred into a standard curing chamber with a temperature of 20 ℃ and a relative humidity of 95%.
Test pieces molded according to the above examples and comparative examples in proportion, preparation method and maintenance system were subjected to a compressive strength test at 28 days of age, a uniaxial tensile test and a four-point bending test with reference to the related requirements of GB/T50081-2019 "test method Standard for physical mechanical Properties of concrete" and "Recommendations for design and construction ofhigh-performance fiber reinforced cement composites with multiple fine cracks" by the society of civil engineering, japan, and the final results are summarized in Table 1.
TABLE 1
| Numbering device | 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 |
In addition, the economic analysis is an important evaluation index in the field of recycling of resources of building materials, the cost of main raw materials is calculated for test pieces molded according to the above examples and comparative examples, the preparation method and the maintenance system, the purchase unit price of materials is summarized in table 2, and the final cost calculation result is summarized in table 3.
TABLE 2
TABLE 3 Table 3
From the test results of table 1 and the economic analysis of table 2, table 3, in combination 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: and at 0.25, the mechanical property of the high-ductility cement-based composite material is optimal. The compressive strength and the bending strength of the fiber in the blending ratio are respectively improved by 17.9 percent and 3.0 percent compared with those of the single-doped polyvinyl alcohol fiber, and meanwhile, the cost is reduced by 4.9 percent, so that the fiber has obvious advantages. When the volume ratio of the polyvinyl alcohol fiber to the basalt fiber is 1.50: at 0.50, the compressive strength is improved by 15.6% compared with that of the single-doped polyvinyl alcohol fiber, but the tensile property and the bending property are slightly reduced, and the cost is obviously reduced by 9.4%, so that the ratio still has a certain cost performance advantage. Compared with polyvinyl alcohol fibers, the basalt fibers have stronger chemical bonding with the matrix, and are beneficial to delaying the proliferation and expansion of cracks after the composite material is cracked. Under the proper mixing ratio with the modified polyvinyl alcohol fiber, the bridging and interlocking actions between the two fiber surfaces and the matrix can be synergistically promoted, so that the whole ductility of the matrix is improved, and the development of the matrix in a strain hardening stage in the multiple cracking process is promoted.
As can be seen from the comparison of example 1 and comparative example 5, the modification method of the polyvinyl alcohol fiber in the present invention is remarkable in improvement of the tensile and bending properties of the composite material. The tensile strain, tensile strength and bending strength of the composite material are respectively improved by 17.9%,9.7% and 8.3% before and after modification. After the surface of the polyvinyl alcohol fiber is subjected to hydrophobic treatment and acid etching, the synergistic bonding effect between the polyvinyl alcohol fiber and the basalt fiber is enhanced, and a multi-element anchoring system is formed with a cement matrix, so that the interface bonding strength between the hybrid fiber and a hydration product is improved.
As can be seen from the comparison of examples 4 to 6 and comparative examples 3 to 4, the peak strain and tensile strength reached the highest when the reclaimed sand substitution rate was 60%. The reason is that the proper proportion of the reclaimed sand to the natural sand is beneficial to promoting the self-cementing capacity of the reclaimed sand to improve the microstructure of the matrix, and the secondary hydration of the old adhesive mortar on the surface of the reclaimed sand improves the total compactness of the composite material. And when the multi-edge surface of the reclaimed sand is subjected to tensile stress, the interface transition area between the fiber and the matrix is extruded, so that the friction combination between the fiber and the matrix is enhanced, and the fiber is effectively prevented from being pulled out prematurely to fail. And according to economic analysis, the cost of the example 4 with the substitution rate of the regenerated sand of 60% is reduced by 7.5% compared with that of the comparative example 4 with pure natural sand, and the cost performance advantage is obvious. When the substitution rate of the reclaimed sand is 40%, the reclaimed sand has good tensile property and bending property, the cost is reduced by 5.0%, and the reclaimed sand still has a certain cost performance advantage. When the substitution rate of the reclaimed sand is higher than 80%, the compressive strength is obviously reduced, but the reduction amplitude is within 20%, and the design requirement of more than 40MPa is met. The main reason for the decrease in compressive strength is: the reclaimed sand is crushed and ground to form a loose and porous surface, and a large number of microcracks exist, so that the strength of the aggregate is reduced, and the aggregate is easy to be damaged by stress concentration when being pressed.
As can be seen from comparative examples 1 and 4, properly increasing the fly ash content helps to fully increase the mechanical properties of the high-ductility cement-based composite. The reason is attributed to the fact that the fly ash fills microscopic pore channels between the matrix and the reclaimed sand, thereby reinforcing the aggregate-matrix interface. At the same time, unhydrated fly ash particles filled in the interstices between the fibers and the matrix help improve the frictional bonding at the fiber-matrix interface, thereby improving the fiber bridging ability.
The foregoing description is only specific embodiments of the present invention, and is not intended to limit the invention, and it is possible for those skilled in the art to make modifications to the embodiments set forth in the present specification or to make equivalent substitutions for some technical features thereof, but any modifications, equivalent substitutions, improvements, etc. made within the scope of the claims of the present application are intended to be included in the scope of the present invention.
Claims (8)
1. A hybrid fiber high-ductility cement-based composite prepared from reclaimed sand, characterized by: the material comprises the following raw materials in parts by weight: 449-566 parts of cement, 163-326 parts of reclaimed 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 preparation method of the modified polyvinyl alcohol fiber comprises the following steps: and (3) immersing the polyvinyl alcohol fibers in a butyraldehyde sulfuric acid solution for treatment, filtering the polyvinyl alcohol fibers after treatment, washing and drying to obtain the modified polyvinyl alcohol fibers.
2. The hybrid fiber high-ductility cement-based composite material prepared with reclaimed sand of claim 1, wherein the reclaimed sand is waste concrete crushed reclaimed sand and the natural sand is natural quartz sand.
3. The hybrid fiber high-ductility cement-based composite material prepared with reclaimed sand of claim 1 wherein the cellulose is hydroxypropyl methylcellulose.
4. The hybrid fiber high ductility cement-based composite material prepared with reclaimed sand of claim 1 wherein the modified polyvinyl alcohol fiber and basalt fiber are present in the cement-based composite material in a volume ratio of 2%; wherein the volume ratio of the modified polyvinyl alcohol fiber to the basalt fiber is 1.25-1.75: 0.25 to 0.75.
5. The hybrid fiber high ductility cement-based composite material made with reclaimed sand of claim 4 wherein the volume ratio of polyvinyl alcohol fibers to basalt fibers is 1.75:0.25.
6. The hybrid fiber high-ductility cement-based composite material prepared with reclaimed sand of claim 1 wherein the mass ratio of reclaimed sand to natural sand is 60:40.
7. The hybrid fiber high-ductility cement-based composite material prepared with reclaimed sand of claim 1,
(1) Soaking polyvinyl alcohol fiber in NaHCO 3 Removing residual impurities on the surface of the polyvinyl alcohol fiber in the solution;
(2) Polyvinyl alcohol fibers are soaked in butyraldehyde sulfuric acid solution with the mass concentration of 3%, and the solid-liquid ratio is 1:18, soaking for 5 hours, keeping the temperature at 40 ℃, filtering the fiber from the solution, washing, and drying to obtain modified polyvinyl alcohol fiber; wherein the mass concentration of the sulfuric acid solution is 1%.
8. The method for producing a hybrid fiber high-ductility cement-based composite material produced with reclaimed sand as claimed in any one of claims 1 to 7, wherein the production steps are as follows:
1) Pouring cement, fly ash, silica fume, reclaimed sand and natural sand into a stirrer, and stirring to form a mixture;
2) Adding the water reducer, cellulose and 50% of water into a stirrer for stirring to form flowing mortar, wherein polyvinyl alcohol fibers are added into the flowing mortar, and after all the adding is completed, 30% of water is added for stirring;
3) And (3) keeping the mixer continuously running, slowly adding basalt fibers into the flowing mortar, and adding and stirring 20% of water after all the basalt fibers are added to obtain the cement-based composite material.
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