A calcined mineral-bonded multi-scale steel fiber for UHPC and its preparation method

Abstract

This invention relates to a method for preparing calcined mineral-bonded multi-scale steel fibers for UHPC (Ultra-High-Pressure Polymer) and its composition by weight percentage: 61.13%–68.32% long steel fibers, 15.29%–17.09% short steel fibers, 2.71%–8.95% magnesium bicarbonate, 0.63%–2.18% alumina, 1.11%–3.86% glass powder, 0.04%–0.13% boron oxide, 10% PVA solution, and 0.1% adhesive. This invention uses calcined minerals obtained through high-temperature sintering to bond short steel fibers to the surface of long steel fibers, improving the dispersion and synergistic effect of steel fibers in UHPC. The hard calcined mineral crystals roughen the smooth surface of the steel fibers, improving the physical bonding properties between the cement paste and the fibers, thereby enhancing the mechanical properties of UHPC.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of building engineering materials, in particular to calcined mineral bonded multi-scale steel fibers for UHPC (ultra-high performance concrete) and a preparation method thereof. BACKGROUND

[0002] Due to the excellent performance of UHPC (ultra-high performance concrete) materials, UHPC is increasingly replacing ordinary concrete in major projects such as bridges, high-speed rails and underground engineering. However, as the performance requirements of concrete in many projects are becoming higher and higher, how to further improve the performance of UHPC, especially the mechanical properties, has become a research hotspot in the field of civil engineering. One of the important ways to improve the performance of UHPC is to study the application of fibers.

[0003] The invention patent with the patent number 2022116478003 improves the roughness of the surface of polyformaldehyde (POM) fiber by impacting and rubbing the POM fiber with sand, solves the problem of poor adhesion between the surface of the POM fiber and the cement slurry, and thus improves the dispersion degree and strength of the fiber in the UHPC matrix.

[0004] The invention patent with the patent number 2022105899615 studies hybrid fiber reinforced UHPC. By winding the plant fiber around the waste tire steel fiber, the steel fiber forms a continuous phase in the concrete, thereby improving the mechanical properties of the UHPC. The invention patent with the patent number 202210327781X uses high water absorption non-metallic fibers (flax fiber, jute fiber, green hemp fiber, etc.) to improve the toughness, shrinkage and corrosion resistance of the UHPC, and the water in the high water absorption fiber can also continuously supplement the water required for the hydration of cement and admixtures, further improving the performance of the UHPC.

[0005] The invention patent with the patent number 2022104146632 soaks the steel fiber in a silane coupling agent solution, and then soaks it in a solution of tetraethyl orthosilicate, anhydrous ethanol and deionized water, to obtain a surface hyperbranched modified steel fiber, which strengthens the adhesion of the fiber and improves the toughness, strength, crack resistance and other properties of the UHPC. The invention patent with the patent number 202010474926X uses a method of modifying ultra-high molecular weight polyethylene fiber with a silane coupling agent to enhance the UHPC. The invention patent with the patent number 2018104801717 soaks silica in a solution of ethanol, water, cetyltrimethylammonium bromide and tetraethyl orthosilicate to obtain modified silica, then soaks ultra-fine steel fiber in the modified silica, and after aging, drying and other processes, obtains modified ultra-fine steel fiber, and uses this fiber to prepare high-impedance UHPC.

[0006] The application patent with the patent number 2018105162265 realizes directional arrangement of steel fibers by applying current to UHPC mixture after molding and vibrating, and obtains arrangement information of the fibers in the UHPC matrix in real time through a perspective detector, so that the tensile property and toughness of the UHPC are effectively improved. The application patent with the patent number 2016109795889 also realizes directional distribution of steel fibers in the UHPC matrix by passing direct current.

[0007] Generally, the non-metallic fibers are suitable for the UHPC with a lower strength grade, and the steel fibers are indispensable for the UHPC with a high strength grade, and the method of improving the surface roughness of the steel fibers by mechanical wear is not applicable due to the hard texture of the steel fibers. The modification of the fibers by a coupling agent and the like is a relatively complex process and the chemical drugs used are relatively high in price. The method of using direct current to enhance the UHPC by directional arrangement of the steel fibers increases the construction safety difficulty. SUMMARY

[0008] In view of the problems of the fibers in the existing UHPC preparation process, the purpose of the application is to provide a calcined mineral bonded multi-scale steel fiber for UHPC and a preparation method, which can effectively improve the mechanical properties of the UHPC.

[0009] The technical scheme of the application is: a calcined mineral bonded multi-scale steel fiber for UHPC, which comprises the following raw materials in percentage by weight: long steel fiber 61.13% to 68.32%, short steel fiber 15.29% to 17.09%, magnesium bicarbonate 2.71% to 8.95%, aluminum oxide 0.63% to 2.18%, glass powder 1.11% to 3.86%, boron oxide 0.04% to 0.13%, PVA solution 10%, and glue 0.1%.

[0010] The magnesium bicarbonate is of an industrial grade or above.

[0011] The aluminum oxide is nano gamma-Al2O3 powder of an industrial grade or above.

[0012] The glass powder is low-melting-point nano glass powder with a melting point of 550 DEG C to 600 DEG C and of an industrial grade or above.

[0013] The boron oxide is powder of an industrial grade or above.

[0014] The long steel fiber is a steel fiber with a diameter of 0.2 mm to 0.3 mm and a length of 20 mm to 25 mm, and the short steel fiber is a steel fiber with a diameter of 0.2 mm to 0.3 mm and a length of 3 mm to 13 mm.

[0015] The PVA in the PVA solution is cold water instant PVA-1788 type, industrial grade and above grade, and the mass concentration of the PVA solution is 1.00%.

[0016] The glue is 502 glue.

[0017] The preparation method of the calcined mineral bonded multi-scale steel fiber comprises the following steps:

[0018] (1) brushing glue on different parts of the long steel fiber;

[0019] (2) bonding short steel fibers at the parts of the long steel fiber where the glue is coated;

[0020] (3) mixing magnesium bicarbonate, aluminum oxide, glass powder, boron oxide and PVA solution into a paste;

[0021] (4) coating the paste on the bonding parts of the long and short steel fibers;

[0022] (5) placing the steel fiber of step (4) in a crucible paved with kaolin clay, placing the crucible into a high-temperature furnace, turning off the high-temperature furnace after calcining at 1000 DEG C for 30 min, and cooling the furnace to room temperature, thereby obtaining the calcined mineral bonded multi-scale steel fiber.

[0023] The method for preparing UHPC comprises the following steps:

[0024] (1) placing cement, slag, silica fume and quartz sand into a concrete mixer and dry mixing for 1 min;

[0025] (2) injecting half of the water and water reducing agent into the concrete mixer and stirring for 2 min;

[0026] (3) injecting the remaining water and water reducing agent into the concrete mixer and stirring for 6 min;

[0027] (4) adding the above calcined mineral bonded multi-scale steel fiber and stirring for 2 min, thereby obtaining UHPC mixture;

[0028] (5) pouring the UHPC mixture into a 100mm*100mm*100mm cubic mold, smoothing the surface, and standing indoors for 24 h to demold, and slowly cooling the test block to room temperature after steam curing at 90 DEG C for 48 h;

[0029] (6) testing the compressive strength of the UHPC test block, and taking the average value of the compressive strength of three test blocks as the final result.

[0030] The cement is Portland cement of P·Ⅱ 52.5 and above strength grade;

[0031] The slag is S95 and above grade;

[0032] The silica fume SiO2 content is more than 95%;

[0033] The quartz sand is 40 mesh to 140 mesh;

[0034] The water is tap water;

[0035] The polycarboxylic acid water reducing agent contains solid content of 50%, and water reducing rate is more than 30.0%.

[0036] Compared with the prior art, the application has the beneficial effects that: (1) the calcined mineral prepared by high-temperature sintering bonds the short steel fibers on the surface of the long steel fibers, improves the dispersity and synergistic effect of the steel fibers in the UHPC; (2) the hard calcined mineral crystals roughen the smooth surface of the steel fibers, improve the physical bonding performance of the cement paste and the fibers, and the obtained minerals are all common minerals in natural stone and can be stably present for a long time; (3) the raw materials are all non-toxic and easy to obtain, and the preparation method is simple. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The figure is the XRD pattern of the calcined mineral after the embodiment 10 of the application is calcined.

[0038] Figure 2 The figure is the schematic diagram of the calcined mineral bonding the multi-scale steel fibers, 1. long steel fiber; 2. short steel fiber; 3. calcined mineral. DETAILED DESCRIPTION

[0039] Combination Figure 2 First, the calcined mineral bonding the multi-scale steel fibers is prepared, the glue is brushed on different parts of the long steel fiber 1; the short steel fiber 2 is bonded on the part of the long steel fiber 1 coated with the glue; the magnesium bicarbonate, aluminum oxide, glass powder, boron oxide and PVA solution are mixed into a paste; the long and short steel fibers are coated with the paste; the steel fibers are placed in the crucible paved with kaolin clay, the crucible is put into the high-temperature furnace, the high-temperature furnace is turned off after calcination at 1000 DEG C for 30 min, and the furnace is cooled to room temperature, at this time, the paste is sintered into the calcined mineral 3, that is, the calcined mineral bonding the multi-scale steel fibers is prepared.

[0040] To prepare and test calcined mineral-bonded multi-scale steel fiber UHPC, the raw materials for UHPC were weighed. Cement, slag, silica fume, and quartz sand were placed in a concrete mixer and dry-mixed for 1 min. Half of the water and water-reducing agent were added to the concrete mixer and mixed for 2 min. The remaining water and water-reducing agent were added to the concrete mixer and mixed for 6 min. Calcined mineral-bonded multi-scale steel fibers were added and mixed for 2 min to obtain the UHPC mixture. The UHPC mixture was poured into a 100 mm × 100 mm × 100 mm cube mold, the surface was smoothed, and the mold was removed after standing indoors for 24 h. The specimens were steam-cured at 90 °C for 48 h and then slowly cooled to room temperature. The compressive strength of the UHPC specimens was tested, and the average compressive strength of three specimens was taken as the final result.

[0041] Magnesium bicarbonate, industrial grade, produced by Guangdong Huasheng Food Co., Ltd.; Nano γ-Al2O3 powder, produced by Shanghai Maclean Biochemical Technology Co., Ltd.; Low melting point glass powder, melting point 550℃~600℃, produced by Jiangsu Ruixin New Materials Co., Ltd.; Boron oxide, analytical grade, produced by Sinopharm Group Pharmaceutical Co., Ltd.; Cement, P·Ⅱ52.5 grade, produced by Taizhou Conch Cement Co., Ltd.; Slag, S95 grade, produced by Shandong Kangjing New Materials Technology Co., Ltd.; Silica fume, silicon dioxide content 95%, produced by Lingshou County Tuyun Mineral Products Processing Plant; Long and short steel fibers, produced by Ganzhou Daye Metal Fiber Co., Ltd.; Quartz sand, 40 mesh~140 mesh, produced by Fengyang County Shengli Quartz Sand Co., Ltd.; PVA, cold water quick-dissolving PVA-1788 type, produced by Shanghai Qichen Chemical Technology Co., Ltd.; 502 glue, produced by Huizhou Tongxing Adhesive Co., Ltd.; Polycarboxylate superplasticizer, solid content 50.0%, water reduction rate ≥30.0%, produced by Jiangsu Subote New Materials Co., Ltd.

[0042] [Example 1]

[0043] Prepare the ingredients according to the formula in Table 1.

[0044] Calcined mineral-bonded multi-scale steel fibers and their UHPCs were prepared according to the following steps:

[0045] (1) Apply adhesive to different parts of the long steel fiber;

[0046] (2) Bond short steel fibers to the parts of the long steel fibers coated with adhesive;

[0047] (3) Mix magnesium bicarbonate, aluminum oxide, glass powder, boron oxide and PVA solution into a paste;

[0048] (4) Cover the bonding area of ​​the long and short steel fibers with a paste;

[0049] (5) Place the above steel fibers in a crucible lined with kaolin clay, place the crucible in a high-temperature furnace, calcine at 1000°C for 30 minutes, then turn off the high-temperature furnace and cool it to room temperature to obtain calcined mineral-bonded multi-scale steel fibers.

[0050] (6) Place cement, slag, silica fume and quartz sand in a concrete mixer and dry mix for 1 minute;

[0051] (7) Pour half of the water and water-reducing agent into the concrete mixer and mix for 2 minutes;

[0052] (8) Pour the remaining water and water-reducing agent into the concrete mixer and mix for 6 minutes;

[0053] (9) Add calcined mineral-bonded multi-scale steel fibers and stir for 2 minutes to obtain UHPC mixture;

[0054] (10) Pour the UHPC mixture into a 100mm×100mm×100mm cube mold, smooth the surface, let it stand indoors for 24 hours to demold, steam the test block at 90℃ for 48 hours and then slowly cool it to room temperature.

[0055] (11) The UHPC test block was subjected to compressive strength test, and the average compressive strength of the three test blocks was taken as the final result.

[0056] Table 1. Mixing ratio of UHPC used in the experiment (kg / m³) 3 )

[0057] Cement Silica fume Slag Quartz sand Water Water reducing agent Steel fibers 700 200 100 1000 180 11 156

[0058] [Example 1] - [Example 11]

[0059] The formula is shown in Table 2, and the preparation process is the same.

[0060] Figure 1 The image shown is an XRD pattern of minerals after calcination in Example 10 of the present invention. The calcined minerals are nepheline, orthoclase, spinel, and forsterite.

[0061] [Comparative Example-1]-[Comparative Example-8]

[0062] The formula is shown in Table 2, and the preparation process is the same.

[0063] The results of each embodiment and comparative example are shown in Table 3.

[0064] Compressive strength is one of the main properties of UHPC, and its compressive strength should not be less than 120 MPa. Comparative Examples 1, 2, 3, and 1 show that a long steel fiber weight percentage of 76.00%–68.00% and a short steel fiber weight percentage of 19.00%–17.00% are beneficial to compressive strength; below this range, the UHPC compressive strength decreases. Comparative Examples 3, 4, 5, 2, and 3 show that when the magnesium bicarbonate weight percentage is 8.13%–9.95%, the UHPC compressive strength increases with the increase of the magnesium bicarbonate percentage; when the magnesium bicarbonate weight percentage is less than 8.13% or more than 9.95%, the UHPC compressive strength decreases. Comparative Examples 3, 6, and 7 show that an alumina weight percentage of 2.00%–2.42% has a positive effect on the UHPC compressive strength. Advantages; In Comparative Examples-3,-8,-9,-6, and-7, when the weight of glass powder was 3.34% to 4.08%, the compressive strength of UHPC increased with the increase of glass powder content; Boron oxide plays a catalytic role in the sintering of calcined minerals. In Comparative Examples-10,-11, and-8, when the weight of boron oxide was 0.15% to 0.30%, the compressive strength of UHPC increased, and when the boron oxide content exceeded 0.30%, the compressive strength decreased.

[0065] Table 2 Formulations of Examples and Comparative Examples

[0066]

[0067] Table 3 Test Results

[0068]

[0069]

Claims

1. A calcined mineral bonded multiscale steel fiber for UHPC, characterized in that, The following raw materials are included in percentage by weight: long steel fiber 61.13%~68.32%, short steel fiber 15.29%~17.09%, magnesium bicarbonate 2.71%~8.95%, alumina 0.63%~2.18%, glass powder 1.11%~3.86%, boron oxide 0.04%~0.13%, PVA solution 10%, glue 0.1%; The following steps are adopted to prepare: (1) brushing glue on different parts of the long steel fiber; (2) bonding short steel fiber at the part of the long steel fiber where glue is coated; (3) mixing magnesium bicarbonate, alumina, glass powder, boron oxide, and PVA solution into paste; (4) covering the paste on the bonding part of the long and short steel fiber; (5) placing the steel fiber of step (4) in a crucible paved with kaolin clay, putting the crucible into a high-temperature furnace, turning off the high-temperature furnace after calcining at 1000℃ for 30 min, and cooling to room temperature with the furnace, to obtain calcined mineral-bonded multi-scale steel fiber.

2. The calcined mineral bonded multiscale steel fiber of claim 1, wherein, The alumina is nano γ-Al2O3 powder, industrial grade and above.

3. The calcined mineral bonded multiscale steel fiber of claim 1, wherein, The glass powder is low-melting-point nano glass powder, with a melting point of 550℃~600℃, industrial grade and above.

4. The calcined mineral bonded multiscale steel fiber of claim 1, wherein, The long steel fiber is steel fiber with a diameter of 0.2mm~0.3mm and a length of 20mm~25mm, and the short steel fiber is steel fiber with a diameter of 0.2mm~0.3mm and a length of 3mm~13mm.

5. The calcined mineral bonded multiscale steel fiber of claim 1, wherein, The PVA in the PVA solution is cold-water instant PVA-1788 type, industrial grade and above, and the mass concentration of the PVA solution is 1.00%.

6. The calcined mineral bonded multiscale steel fiber of claim 1, wherein, The glue is 502 glue.

7. The method of producing a calcined mineral bonded multiscale steel fiber according to any one of claims 1 to 6, wherein The following steps are adopted to prepare: (1) brushing glue on different parts of the long steel fiber; (2) bonding short steel fiber at the part of the long steel fiber where glue is coated; (3) mixing magnesium bicarbonate, alumina, glass powder, boron oxide, and PVA solution into paste; (4) covering the paste on the bonding part of the long and short steel fiber; (5) placing the steel fiber of step (4) in a crucible paved with kaolin clay, putting the crucible into a high-temperature furnace, turning off the high-temperature furnace after calcining at 1000℃ for 30 min, and cooling to room temperature with the furnace, to obtain calcined mineral-bonded multi-scale steel fiber.

8. Use of the calcined mineral-bonded multi-scale steel fiber according to any one of claims 1-6 in the preparation of UHPC.

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