High elastic modulus UHPC material and preparation method thereof

Abstract

The invention belongs to the technical field of concrete, and provides a high elastic modulus UHPC material and a preparation method thereof, the preparation method comprises the following steps: S1, uniformly mixing 65-68 parts by weight of cement, 55-60 parts by weight of gravel, 10-12 parts by weight of quartz sand, 11-13 parts by weight of silica fume, 13-15 parts by weight of fly ash and 4.5-6 parts by weight of modified steel fiber to obtain an initial dry material; and S2, adding 30-34 parts of water into the initial dry material obtained in the step S1, then adding 5-6 parts of nano SiO2-copolymerized colloidal particles, 0.8-1.2 parts of a high-efficiency water reducing agent and 0.5-0.7 part of a dispersing agent, and uniformly mixing to obtain the high-elasticity-modulus UHPC material, the modified steel fibers are prepared by modifying steel fibers with a silane coupling agent. The elastic modulus of the prepared UHPC material can be remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and particularly relates to a high elastic modulus UHPC material and a preparation method thereof. Background Art

[0002] The hollow slab bridge is a common beam bridge structure form. It mainly uses hollow concrete slabs (i.e., hollow slabs) as the main load-bearing structure, and supports the weight of the entire bridge and bears the external forces generated by loads such as vehicles through bearings set on the pier caps. The hollow slab usually has a certain span, and its cross-section is rectangular or nearly rectangular in shape, with a hollow part in the middle. This design can effectively reduce the self-weight of the structure on the premise of ensuring the bearing capacity. Compared with solid slab bridges, it can save a large amount of building materials and at the same time reduce the requirements for the lower structure (such as piers and abutments). Hollow slabs are widely used in highway bridges, especially in rural roads, urban secondary roads, branch roads and other roads with relatively small traffic volume. It is also often used in the widening project of bridges, adding hollow slabs beside the original bridge as part of the new bridge deck to improve the traffic capacity of the bridge.

[0003] With the economic development and social progress, the traffic flow is increasing continuously, and the vehicle load is also getting larger and larger. Many early hollow slab bridges have relatively low design standards, and their bearing capacities can no longer meet the existing traffic demands. In addition, during the long-term use of hollow slab bridges, local damage, cracks and other problems may occur in some parts, resulting in a decline in the structural bearing capacity. At this time, it is necessary to reinforce the hollow slab bridge, and UHPC concrete is an ideal choice for reinforcing hollow slab beam bridges.

[0004] The hollow slab bridge mainly bears bending moment during its service life. The UHPC concrete used to reinforce the hollow slab bridge needs to have a high elastic modulus so that it has higher stiffness when bending, can effectively resist bending deformation, reduce the deflection of the hollow slab under load, and then improve the bending resistance of the bridge, effectively ensuring the safety and stability of the bridge during use. Therefore, how to further improve the elastic modulus of UHPC materials is worthy of in-depth study. Summary of the Invention

[0005] To solve the problems in the background art, the present invention provides a high elastic modulus UHPC material and a preparation method thereof, which can significantly improve the elastic modulus of the prepared UHPC material.

[0006] To achieve the above object, in the first aspect, the present invention provides a preparation method of a high elastic modulus UHPC material, including the following steps:

[0007] S1. Mix 65 - 68 parts by weight of cement, 55 - 60 parts of sand and gravel, 10 - 12 parts of quartz sand, 11 - 13 parts of silica fume, 13 - 15 parts of fly ash and 4.5 - 5.5 parts of modified steel fibers to obtain the initial dry material.

[0008] S2. Add 30 - 34 parts of water to the initial dry material obtained in S1, and then add 5 - 6 parts of nano - SiO 2 - copolymer particles, 0.8 - 1.2 parts of high - efficiency water - reducing agent and 0.5 - 0.7 parts of dispersant, and mix them evenly to obtain the high - elastic - modulus UHPC material.

[0009] The modified steel fibers are prepared by modifying steel fibers with a silane coupling agent.

[0010] Furthermore, the preparation method of the modified steel fibers is as follows:

[0011] A1. Clean the steel fibers with an alkaline cleaner to remove organic pollutants such as surface oil stains, then soak the cleaned steel fibers in absolute ethanol for 1 - 1.5 h to remove the residual water film on the surface, and then dry them at room temperature to ensure that the surface of the steel fibers is dry without moisture, obtaining clean steel fibers.

[0012] A2. Add KH - 550 to the ethanol solution, stir at 200 - 240 r / min at room temperature for 20 - 30 min, mix until the solution changes from turbid to transparent, and then store it sealed for 10 - 15 h to ensure that KH - 550 is fully hydrolyzed to obtain the modified solution.

[0013] A3. Immerse the clean steel fibers obtained in A1 into the modified solution obtained in A2, stir at 120 - 140 r / min for 20 - 30 min to make the clean steel fibers fully contact with the modified solution, ensure that KH - 550 can be evenly adsorbed on the surface of the steel fibers, then filter them out, and dry them at a constant temperature of 90 - 100 °C for 0.8 - 1.5 h to make the KH - 550 adsorbed on the surface of the steel fibers solidify into a film, thus obtaining the modified steel fibers.

[0014] Furthermore, the preparation method of the nano - SiO 2 - copolymer particles is as follows:

[0015] B1. Mix tetraethyl orthosilicate, water, and absolute ethanol in a molar ratio of 1:(3.5 - 4):(7 - 8), add them to a three - necked flask, dropwise add ammonia water, the molar ratio of ammonia water to tetraethyl orthosilicate is (0.4 - 0.5):5, react at 40 °C for 12 - 14 h, then add KH - 570, the molar ratio of tetraethyl orthosilicate to KH - 570 is 1:(6 - 8), and perform surface modification on the silica sol to obtain the modified silica sol.

[0016] B2. The modified silica sol obtained in B1 is centrifuged multiple times (rotation speed: 15,000 rpm, temperature: 4 °C, centrifugation time: 30 min), and then redispersed in an anhydrous ethanol solution for washing to remove residual KH-570 and other impurities. Then it is placed in an oven at 65 - 70 °C for drying for 20 - 24 h to obtain modified SiO 2 ;

[0017] B3. By weight, 2 parts of the modified SiO 2 obtained in B2 are dispersed in 16 - 18 parts of a composite monomer through ultrasonic treatment. The composite monomer includes butyl acrylate, styrene, and acrylic acid, and the mass ratio of the three is 8:8:(1 - 1.2). Then, it is subjected to high-speed shearing with 0.3 - 0.4 parts of a stabilizer, 0.5 - 0.6 parts of a surfactant, and 30 - 34 parts of deionized water to obtain a pre-emulsified product;

[0018] B4. The pre-emulsified product obtained in B3 is added to a four-necked flask, protected by nitrogen, heated to 68 - 72 °C, and then 26 parts of butyl acrylate, 22 parts of styrene, 0.3 - 0.4 parts of a stabilizer, 1.6 - 1.7 parts of a surfactant, 0.2 - 0.25 parts of a buffer, 1 part of an initiator, and 90 - 95 parts of deionized water are added dropwise. After the dropwise addition, the temperature is raised to 75 - 78 °C and reacted for 1.5 h to ensure that the remaining monomers react completely, and then centrifuged to obtain the nano-SiO 2 - copolymer particles.

[0019] Furthermore, the surfactant includes ammonium nonylphenol polyoxyethylene ether sulfate and octylphenol polyoxyethylene ether, and the mass ratio of the two is 1:(1 - 1.5).

[0020] Furthermore, the cement used is P.O52.5 grade cement.

[0021] Furthermore, the gravel includes fine sand and medium sand, and the mass ratio of the two is (2 - 2.5):1;

[0022] The particles with a particle size greater than 0.075 mm in the fine sand exceed 85% of the total weight, and the average particle size is 0.25 mm - 0.125 mm; the particles with a particle size greater than 0.25 mm in the medium sand exceed 50% of the total weight, and the average particle size is 0.5 - 0.25 mm.

[0023] Furthermore, the specification of the quartz sand is 16 - 26 mesh; the particle size of the silica fume is less than 1 μm; the particle size of the fly ash is 1 - 60 μm.

[0024] Furthermore, the high-range water reducer used is a polycarboxylate-based water reducer.

[0025] Furthermore, the dispersant includes triisopropanolamine and / or triethanolamine.

[0026] In a second aspect, the present invention provides a high elastic modulus UHPC material prepared by the above-mentioned preparation method.

[0027] This application has the following beneficial effects:

[0028] The high elastic modulus UHPC material of the present invention includes modified steel fibers and nano-SiO 2 - copolymer particles. Among them, in the preparation of the modified steel fibers, the surface of the steel fibers is modified by a silane coupling agent, which can enhance the adhesion between the steel fibers and the cement paste, thereby reducing the occurrence of (high dosage) steel fiber agglomeration phenomenon, enabling the modified steel fibers to be better dispersed in the UHPC, and improving the overall performance (elastic modulus) of the UHPC material.

[0029] In the preparation of nano-SiO 2 - copolymer particles, the nano-particles have a small particle size and a large specific surface area, which can rigidly fill the voids between the steel fibers and the matrix, improve the microstructure of the interfacial transition zone, and enhance the interfacial bonding strength, thereby weakening the problem of elastic modulus decline caused by the increased inhomogeneity of the interfacial transition zone due to the high dosage of steel fibers; the latex layer can play a soft filling role, forming a polymer film in the interfacial transition zone, further enhancing the adhesion between the steel fibers and the matrix, and at the same time improving the compactness and uniformity of the interfacial transition zone, and further improving the overall performance (elastic modulus) of the UHPC material.

[0030] The silane coupling agent on the surface of the modified steel fibers will also change the morphology of the adjacent organic copolymer (the latex layer of nano-SiO 2 - copolymer particles), thereby improving the bonding effect. The deformable layer theory believes that a flexible resin layer can be generated to relieve the interfacial stress; while the constrained layer theory believes that the silane can "tighten" the polymer structure in the interphase region. Thus, a synergistic effect is generated between the two, synergistically improving the overall performance (elastic modulus) of the UHPC material. Brief Description of the Drawings

[0031] Figure 1 、Comparison trend chart of the elastic modulus test data of the UHPC materials prepared in Examples 1 - 3 and Comparative Examples 1 - 7 in the test examples of the present invention. Detailed Embodiments

[0032] The following further elaborates on this application in conjunction with the embodiments.

[0033] The raw materials of the examples and comparative examples of this application are all ordinary commercially available products unless otherwise specified.

[0034] Example 1: (1) Preparation of modified steel fibers, and the preparation method is as follows:

[0035] A1. Clean the steel fibers with commercially available alkaline cleaners to remove organic pollutants such as surface oil stains. Then soak the cleaned steel fibers in absolute ethanol for 1.2 h to remove the residual water film on the surface, and then air-dry at room temperature to ensure that the surface of the steel fibers is dry and free of moisture, obtaining clean steel fibers.

[0036] A2. Add KH-550 to the ethanol solution, which is prepared by mixing absolute ethanol and water at a volume ratio of 1:2; the mass ratio of KH-550 to the ethanol solution is 1:5; at room temperature, stir at 220 r / min for 25 min, mix until the solution changes from turbid to transparent, and seal and store for 12 h to ensure that KH-550 is fully hydrolyzed, obtaining a modified solution.

[0037] A3. Immerse the clean steel fibers obtained in A1 into the modified solution obtained in A2, stir at 130 r / min for 25 min to make the clean steel fibers fully contact with the modified solution, ensure that KH-550 can be evenly adsorbed on the surface of the steel fibers, then filter out, and bake at a constant temperature of 95 °C for 1.2 h to cure the KH-550 adsorbed on the surface of the steel fibers into a film, obtaining modified steel fibers.

[0038] Among them, the steel fibers are corrugated steel fibers (c), purchased from Henan Fengkai Refractory Materials Co., Ltd. KH-550, purchased from Dongguan Kangjin New Material Technology Co., Ltd.

[0039] (2) Preparation of nano-SiO 2 - copolymer particles, and the preparation method is as follows:

[0040] B1. Mix tetraethyl orthosilicate, water, and absolute ethanol at a molar ratio of 1:3.8:7.5, add them to a three-necked flask, dropwise add ammonia water, and the molar ratio of ammonia water to tetraethyl orthosilicate is 0.45:5. After reacting at 40 °C for 13 h, add KH-570, and the molar ratio of tetraethyl orthosilicate to KH-570 is 1:7 to perform surface modification on the silica sol, obtaining a modified silica sol.

[0041] B2. Perform multiple centrifugation treatments on the modified silica sol obtained in B1. The specific operation of the centrifugation treatment is a rotation speed of 15000 rpm, a temperature of 4 °C, and a centrifugation time of 30 min, and disperse and wash in an absolute ethanol solution to remove residual KH-570 and other impurities, and then place in an oven at 68 °C and dry for 22 h to obtain modified SiO 2 .

[0042] B3. By weight, ultrasonically treat 2 parts of the modified SiO obtained in B2 2Dispersed in 17 parts of composite monomers, the composite monomers include butyl acrylate, styrene and acrylic acid, and the mass ratio of the three is 8:8:1. Then, it is subjected to high-speed shearing with 0.35 parts of stabilizer, 0.55 parts of surfactant and 32 parts of deionized water to obtain a pre-emulsified product.

[0043] B4. Add the pre-emulsified product obtained in B3 to a four-necked flask, protect it with nitrogen, heat it to 70 °C, and then dropwise add 26 parts of butyl acrylate, 22 parts of styrene, 0.35 parts of stabilizer, 1.65 parts of surfactant, 0.22 parts of buffer, 1 part of initiator and 94 parts of deionized water. After the dropping is completed, heat it to 76 °C and react for 1.5 h to completely react the remaining monomers, and then perform centrifugation to obtain nano-SiO 2 - copolymerized rubber particles.

[0044] Among them, the surfactant includes ammonium nonylphenol polyoxyethylene ether sulfate and octylphenol polyoxyethylene ether, and the mass ratio of the two is 1:1.2. The stabilizer is polyacrylic acid. The buffer is sodium bicarbonate. The initiator is ammonium persulfate.

[0045] Tetraethyl orthosilicate, purchased from Yajie Chemical Trading Co., Ltd., Zhangjiagang Free Trade Zone. KH-570, purchased from Dongguan Kangjin New Material Technology Co., Ltd. Butyl acrylate, purchased from Chuangyida (Shandong) Biotechnology Co., Ltd. Styrene, purchased from Langcheng Chemical Industry. Acrylic acid, purchased from Shandong Kejian Chemical Industry Co., Ltd. Ammonium nonylphenol polyoxyethylene ether sulfate (CO436 TX-4SA), purchased from Jiangsu Haian Petrochemical Factory. Octylphenol polyoxyethylene ether (OP-40), purchased from Jining Tangyi Chemical Co., Ltd. Polyacrylic acid (CH-10912), purchased from Dongguan Baihong Environmental Protection Technology Co., Ltd.

[0046] (3) A preparation method of a high elastic modulus UHPC material, comprising the following steps:

[0047] S1. By weight, mix 66 parts of cement, 56 parts of grit, 11 parts of quartz sand, 12 parts of silica fume, 14 parts of fly ash and 5 parts of modified steel fiber to obtain an initial dry material.

[0048] S2. Add 32 parts of water to the initial dry material obtained in S1, and then add 5.5 parts of nano-SiO 2 - copolymerized rubber particles, 1 part of high-efficiency water reducer and 0.6 part of dispersant, and mix well to obtain a high elastic modulus UHPC material.

[0049] Among them, P.O52.5 grade cement is used. The gravel includes fine sand and medium sand, and the mass ratio of the two is (2 - 2.5):1. The particles with a particle size greater than 0.075 mm in the fine sand exceed 85% of the total weight, and the average particle size is 0.25 mm - 0.125 mm; the particles with a particle size greater than 0.25 mm in the medium sand exceed 50% of the total weight, and the average particle size is 0.5 - 0.25 mm. The specification of the quartz sand is 16 - 26 mesh. The particle size of the silica fume is less than 1 μm. The particle size of the fly ash is 1 - 60 μm. The high-range water reducing agent uses a polycarboxylate-based water reducing agent. The dispersant includes triisopropanolamine and triethanolamine, and the mass ratio of the two is 1:1.

[0050] The polycarboxylate-based water reducing agent is purchased from Shandong Hongteng Biotechnology Co., Ltd. Triisopropanolamine (85%), triethanolamine (85%), both are purchased from Jinan Youshengyuan Chemical Co., Ltd.

[0051] Example 2: The difference between this example and Example 1 is as follows: A preparation method of a high elastic modulus UHPC material includes the following steps:

[0052] S1. By weight, 65 parts of cement, 55 parts of gravel, 10 parts of quartz sand, 11 parts of silica fume, 13 parts of fly ash and 4.5 parts of modified steel fiber are mixed evenly to obtain the initial dry material.

[0053] S2. 30 parts of water are added to the initial dry material obtained in S1, and then 5 parts of nano-SiO 2 - copolymer particles, 0.8 part of high-range water reducing agent and 0.5 part of dispersant are added and mixed evenly to obtain the high elastic modulus UHPC material.

[0054] Example 3: The difference between this example and Example 1 is as follows: A preparation method of a high elastic modulus UHPC material includes the following steps:

[0055] S1. By weight, 68 parts of cement, 60 parts of gravel, 12 parts of quartz sand, 13 parts of silica fume, 15 parts of fly ash and 5.5 parts of modified steel fiber are mixed evenly to obtain the initial dry material.

[0056] S2. 34 parts of water are added to the initial dry material obtained in S1, and then 6 parts of nano-SiO 2 - copolymer particles, 1.2 parts of high-range water reducing agent and 0.7 part of dispersant are added and mixed evenly to obtain the high elastic modulus UHPC material.

[0057] Comparative Example 1: The difference between this comparative example and Example 1 is that the modified steel fiber and nano-SiO 2 - copolymer particles are deleted.

[0058] Specifically, a preparation method of a high elastic modulus UHPC material includes the following steps:

[0059] S1. Mix 66 parts by weight of cement, 56 parts of grit, 11 parts of quartz sand, 12 parts of silica fume and 14 parts of fly ash to obtain the initial dry material.

[0060] S2. Add 32 parts of water to the initial dry material obtained in S1, then add 1 part of high-range water reducer and 0.6 part of dispersant, and mix evenly to obtain the high elastic modulus UHPC material.

[0061] Comparative Example 2: The difference between this comparative example and Example 1 is that the nano-SiO 2 - copolymer particles are deleted; and 5 parts of modified steel fibers are replaced with 2.5 parts of steel fibers.

[0062] Specifically, a preparation method of a high elastic modulus UHPC material includes the following steps:

[0063] S1. Mix 66 parts by weight of cement, 56 parts of grit, 11 parts of quartz sand, 12 parts of silica fume, 14 parts of fly ash and 2.5 parts of steel fibers to obtain the initial dry material.

[0064] S2. Add 32 parts of water to the initial dry material obtained in S1, then add 1 part of high-range water reducer and 0.6 part of dispersant, and mix evenly to obtain the high elastic modulus UHPC material.

[0065] Comparative Example 3: The difference between this comparative example and Example 1 is that the nano-SiO 2 - copolymer particles are deleted; and 5 parts of modified steel fibers are replaced with 5 parts of steel fibers.

[0066] Specifically, a preparation method of a high elastic modulus UHPC material includes the following steps:

[0067] S1. Mix 66 parts by weight of cement, 56 parts of grit, 11 parts of quartz sand, 12 parts of silica fume, 14 parts of fly ash and 5 parts of steel fibers to obtain the initial dry material.

[0068] S2. Add 32 parts of water to the initial dry material obtained in S1, then add 1 part of high-range water reducer and 0.6 part of dispersant, and mix evenly to obtain the high elastic modulus UHPC material.

[0069] Comparative Example 4: The difference between this comparative example and Example 1 is that the modified steel fibers are deleted.

[0070] Specifically, a preparation method of a high elastic modulus UHPC material includes the following steps:

[0071] S1. Mix 66 parts by weight of cement, 56 parts of grit, 11 parts of quartz sand, 12 parts of silica fume and 14 parts to obtain the initial dry material.

[0072] S2. Add 32 parts of water to the initial dry material obtained in S1, and then add 5.5 parts of nano-SiO 2 - copolymer particles, 1 part of high-range water reducer, and 0.6 part of dispersant, and mix evenly to obtain the high elastic modulus UHPC material.

[0073] Comparative Example 5: The difference between this comparative example and Example 1 is that: the nano-SiO 2 - copolymer particles are deleted.

[0074] Specifically, a preparation method of a high elastic modulus UHPC material includes the following steps:

[0075] S1. By weight, mix 66 parts of cement, 56 parts of grit, 11 parts of quartz sand, 12 parts of silica fume, 14 parts of fly ash, and 5 parts of modified steel fiber to obtain the initial dry material.

[0076] S2. Add 32 parts of water to the initial dry material obtained in S1, and then add 1 part of high-range water reducer and 0.6 part of dispersant, and mix evenly to obtain the high elastic modulus UHPC material.

[0077] Comparative Example 6: The difference between this comparative example and Example 1 is that: 5 parts of modified steel fiber are replaced by 5 parts of steel fiber.

[0078] Specifically, a preparation method of a high elastic modulus UHPC material includes the following steps:

[0079] S1. By weight, mix 66 parts of cement, 56 parts of grit, 11 parts of quartz sand, 12 parts of silica fume, 14 parts of fly ash, and 5 parts of steel fiber to obtain the initial dry material.

[0080] S2. Add 32 parts of water to the initial dry material obtained in S1, and then add nano-SiO 2 - copolymer particles, 1 part of high-range water reducer, and 0.6 part of dispersant, and mix evenly to obtain the high elastic modulus UHPC material.

[0081] Comparative Example 7: The difference between this comparative example and Example 1 is that: 5 parts of modified steel fiber are replaced by 2.5 parts of modified steel fiber.

[0082] Specifically, a preparation method of a high elastic modulus UHPC material includes the following steps:

[0083] S1. By weight, mix 66 parts of cement, 56 parts of grit, 11 parts of quartz sand, 12 parts of silica fume, 14 parts of fly ash, and 2.5 parts of modified steel fiber to obtain the initial dry material.

[0084] S2. Add 32 parts of water to the initial dry material obtained in S1, and then add nano-SiO 2- 5.5 parts of copolymer particles, 1 part of high-range water reducer and 0.6 part of dispersant are mixed evenly to obtain the UHPC material with high elastic modulus.

[0085] Test example: Test object: UHPC materials prepared in Examples 1 - 3 and Comparative Examples 1 - 7.

[0086] Test item: Static compressive elastic modulus.

[0087] Test basis: Test Method Standard for Ultra-High Performance Concrete T / CECS 864 - 2021 (5.3).

[0088] Test results: See Table 1.

[0089] Table 1. Test data of test examples

[0090] Elastic modulus / GPa Example 1 69.2 Example 2 69.7 Example 3 68.9 Comparative Example 1 50.3 Comparative Example 2 59.2 Comparative Example 3 57.2 Comparative Example 4 50.7 Comparative Example 5 63.3 Comparative Example 6 61.7 Comparative Example 7 61.1

[0091] Result analysis: Analyzing Examples 1 - 3 and combining with the data in Table 1 and Figure 1 , it can be seen that the test data of the elastic modulus of the UHPC materials prepared in the present invention (Examples 1 - 3) is as high as above 68.9 GPa, indicating that the UHPC materials prepared in the present invention (Examples 1 - 3) are UHPC materials with high elastic modulus.

[0092] Analyzing Example 1 and Comparative Examples 1 - 7 and combining with the data in Table 1 and Figure 1 , by comparing Comparative Example 1 and Comparative Example 2, it can be known that compared with Comparative Example 1, 2.5 parts of steel fibers are added in Comparative Example 2. As a result, the test data of the elastic modulus of the UHPC material prepared in Comparative Example 2 is 59.2 GPa, which is significantly greater than 50.3 GPa of Comparative Example 1, indicating that the addition of steel fibers can improve the elastic modulus of the prepared UHPC material.

[0093] This is because when the content of steel fibers is relatively low, as its content increases, the steel fibers can be evenly distributed in the UHPC matrix, and the bonding force with the matrix gradually increases. When subjected to external forces, the steel fibers can effectively prevent the expansion of microcracks inside the UHPC, restrict the deformation ability of the material, and thus improve the stiffness and elastic modulus of the UHPC material.

[0094] By comparing Comparative Example 2 and Comparative Example 3, it can be known that compared with 2.5 parts of steel fibers in Comparative Example 2, the addition amount of steel fibers in Comparative Example 3 is increased to 5 parts. As a result, the test data of the elastic modulus of the UHPC material prepared in Comparative Example 3 is 57.2 GPa, which is significantly less than 59.2 GPa of Comparative Example 2, indicating that continuously increasing the amount of steel fibers to an excessive amount will instead have a negative impact on the elastic modulus of the prepared UHPC material.

[0095] This is because when the dosage of steel fibers exceeds a certain limit, excessive steel fibers will cause agglomeration in the UHPC matrix, which is prone to stress concentration during loading, and instead reduces the overall performance of the material, including the elastic modulus. Moreover, high-dosage steel fibers may also affect the microstructure of UHPC, leading to an increase in the inhomogeneity of the interfacial transition zone; the interfacial transition zone is the transition area between the matrix and aggregates, fibers, etc., and its performance has an important impact on the mechanical properties of the overall material. When the performance of the interfacial transition zone is disturbed due to too high a dosage of steel fibers, the synergy between the matrix and steel fibers will be weakened, resulting in a decrease in the elastic modulus.

[0096] By comparing Comparative Example 1 and Comparative Example 4, it can be seen that compared with Comparative Example 1, 5.5 parts of nano-SiO 2 - copolymer particles were added in Comparative Example 4. As a result, the elastic modulus test data of the UHPC material prepared in Comparative Example 4 was 50.7 GPa, which was similar to 50.3 GPa of Comparative Example 1, indicating that the addition of the nano-SiO 2 - copolymer particles alone had no obvious effect on the elastic modulus of the prepared UHPC material.

[0097] By comparing Comparative Example 3 and Comparative Example 5, it can be seen that on the premise that the addition amount of steel fibers in Comparative Example 3 was excessive and was 5 parts, modifying the steel fibers with a silane coupling agent could significantly increase the elastic modulus of the prepared UHPC material.

[0098] This is because modifying the surface of steel fibers with a silane coupling agent can enhance their adhesion to the cement paste, thereby reducing the occurrence of (high-dosage) steel fiber agglomeration, enabling the modified steel fibers to be better dispersed in UHPC, and further increasing the elastic modulus of the UHPC material.

[0099] By comparing Comparative Example 3 and Comparative Example 6, it can be seen that on the premise that the addition amount of steel fibers in Comparative Example 3 was excessive and was 5 parts, adding the nano-SiO 2 - copolymer particles of the present invention could also significantly increase the elastic modulus of the prepared UHPC material.

[0100] This is because on the premise of a high dosage of steel fibers, in the preparation of the added nano-SiO 2 - copolymer particles, the nano-particles have a small particle size and a large specific surface area, can rigidly fill the voids between the steel fibers and the matrix, improve the microstructure of the interfacial transition zone, and increase the interfacial bonding strength, thereby weakening the problem of elastic modulus decrease caused by the increased inhomogeneity of the interfacial transition zone due to a high dosage of steel fibers; the latex layer can play a soft filling role, form a polymer film in the interfacial transition zone, further enhance the adhesion between the steel fibers and the matrix, and at the same time improve the compactness and uniformity of the interfacial transition zone, and further increase the elastic modulus of the UHPC material.

[0101] Combined with Example 1 for comparison, it can be seen that on the premise that the addition amount of steel fibers in Comparative Example 3 is excessive and is 5 parts, the steel fibers are modified with a silane coupling agent, and then the nano-SiO 2 - copolymer particles are added, then a synergistic effect can be generated between the modified steel fibers and the nano-SiO 2 - copolymer particles, and the elastic modulus of the prepared UHPC material is synergistically improved.

[0102] This is because the silane coupling agent on the surface of the modified steel fibers will change the morphology of the adjacent organic copolymer (the latex layer of the nano-SiO 2 - copolymer particles), thereby improving the bonding effect. The deformable layer theory believes that a flexible resin layer can be generated to relieve the interfacial stress; while the constraint layer theory believes that the silane can "tighten" the polymer structure in the interfacial region. Thus, a synergistic effect is generated between the two, and the elastic modulus of the UHPC material is synergistically improved.

[0103] By comparing Example 1 and Comparative Example 7, it can be seen that compared with 2.5 parts of modified steel fibers in Comparative Example 7 (there are 5.5 parts of nano-SiO 2 - copolymer particles) in the system, the addition amount of the modified steel fibers in Example 1 is increased to 5 parts. As a result, the test data of the elastic modulus of the UHPC material prepared in Example 1 is 69.2 GPa, which is significantly greater than 61.1 GPa of Comparative Example 7.

[0104] Moreover, 61.1 GPa of Comparative Example 7 is only slightly greater than 59.2 GPa of Comparative Example 2, indicating that when the content of steel fibers is not high (only 2.5 parts), the modification of steel fibers with a silane coupling agent and the addition of nano-SiO 2 - copolymer particles have little effect on the elastic modulus of the prepared UHPC material. Only when the content of steel fibers is high enough / excessive (reaching about 5 parts), the modification of steel fibers with a silane coupling agent and the addition of nano-SiO 2 - copolymer particles can significantly improve the elastic modulus of the prepared UHPC material, and the two can work better synergistically.

[0105] In addition, it should be noted that among the various specific technical features described in the above specific embodiments, without contradiction, they can be combined in any suitable way. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0106] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a high elastic modulus UHPC material, characterized in that: The steps include: S1. Mix 65-68 parts of cement, 55-60 parts of gravel, 10-12 parts of quartz sand, 11-13 parts of silica fume, 13-15 parts of fly ash and 4.5-5.5 parts of modified steel fiber by weight to obtain an initial dry material; S2, adding 30-34 parts of water to the initial dry material obtained in S1, and then adding 5-6 parts of nano-SiO2-copolymer particles, 0.8-1.2 parts of high-efficiency water reducer and 0.5-0.7 parts of dispersant, and mixing well to obtain the high elastic modulus UHPC material; The modified steel fiber is prepared by modifying the steel fiber with a silane coupling agent.

2. The method for preparing a high elastic modulus UHPC material according to claim 1, characterized in that: The preparation method of the modified steel fiber is as follows: A1. Use an alkaline detergent to clean the steel fiber, then soak the cleaned steel fiber in anhydrous ethanol for 1-1.5 hours, and then dry it at room temperature to obtain clean steel fiber; A2. Add KH-550 to the ethanol solution, stir at 200-240r / min for 20-30min at room temperature, mix well, seal and store for 10-15h to obtain the modified solution; A3. Soak the clean steel fiber obtained in A1 into the modified solution obtained in A2, stir at 120-140r / min for 20-30min, then filter it out, and dry it at a constant temperature of 90-100℃ for 0.8-1.5h to obtain the modified steel fiber.

3. The method for preparing a high elastic modulus UHPC material according to claim 1, characterized in that: The preparation method of the nano-SiO2-copolymerized granules is as follows: B1. Mix tetraethyl orthosilicate, water and anhydrous ethanol in a molar ratio of 1:(3.5-4):(7-8), add into a three-necked flask, dropwise add ammonia water, the molar ratio of ammonia water to tetraethyl orthosilicate is (0.4-0.5):5, react at 40°C for 12-14h, add KH-570, the molar ratio of tetraethyl orthosilicate to KH-570 is 1:(6-8), and obtain modified silica sol; B2, the modified silica sol obtained in B1 was subjected to multiple centrifugal treatments (rotation speed 15000 rpm, temperature 4°C, centrifugation time 30 min), then dispersed in an anhydrous ethanol solution for washing, and then placed in an oven at 65-70°C for drying for 20-24 h to obtain modified SiO2; B3, by weight, dispersing 2 parts of the modified SiO2 obtained in B2 in 16-18 parts of a composite monomer by ultrasonic treatment, wherein the composite monomer includes butyl acrylate, styrene and acrylic acid, and the mass ratio of the three is 8:8:(1-1.2), and then high-speed shearing with 0.3-0.4 parts of a stabilizer, 0.5-0.6 parts of a surfactant and 30-34 parts of deionized water to obtain a pre-emulsified product; B4. Add the pre-emulsified product obtained in B3 into a four-necked flask, pass nitrogen protection, heat to 68-72°C, then drop 26 parts of butyl acrylate, 22 parts of styrene, 0.3-0.4 parts of stabilizer, 1.6-1.7 parts of surfactant, 0.2-0.25 parts of buffer, 1 part of initiator and 90-95 parts of deionized water. After the dropwise addition is completed, heat to 75-78°C, react for 1.5 hours, and centrifuge to obtain the nano-SiO2-copolymer particles.

4. The method for preparing a high elastic modulus UHPC material according to claim 3, characterized in that: The surfactant comprises nonylphenol polyoxyethylene ether ammonium sulfate and octylphenol polyoxyethylene ether, and the mass ratio of the two is 1:(1-1.5).

5. The method for preparing a high elastic modulus UHPC material according to claim 1, characterized in that: The cement used is P.O52.5 grade cement.

6. The method for preparing a high elastic modulus UHPC material according to claim 1, characterized in that: The gravel includes fine sand and medium sand, and the mass ratio of the two is (2-2.5):1; In fine sand, particles with a diameter greater than 0.075mm account for more than 85% of the total weight, and the average particle size is 0.25mm-0.125mm; in medium sand, particles with a diameter greater than 0.25mm account for more than 50% of the total weight, and the average particle size is 0.5-0.25mm.

7. The method for preparing a high elastic modulus UHPC material according to claim 1, characterized in that: The specification of the quartz sand is 16-26 mesh; the particle size of the silica fume is less than 1 μm; and the particle size of the fly ash is 1-60 μm.

8. The method for preparing a high elastic modulus UHPC material according to claim 1, characterized in that: The high-efficiency water reducer is a polycarboxylic acid water reducer.

9. The method for preparing a high elastic modulus UHPC material according to claim 1, characterized in that: The dispersant includes triisopropanolamine and / or triethanolamine.

10. A high elastic modulus UHPC material, characterized in that: The method is prepared according to any one of claims 1 to 9.

Images