Ultrahigh performance concrete for cold regions and preparation method and application thereof

Abstract

This invention relates to, specifically, a high-performance concrete for cold regions, the raw materials of which include: cement 600-900 kg / m³ 3 Silica fume 200-240 kg / m³ 3 Fly ash 100-120 kg / m³ 3 Manufactured sand 1000-1200 kg / m³ 3 Water-reducing agent 20-26 kg / m³ 3 Defoamer 1-5 kg / m³ 3 Water 170-220 kg / m 3 The invention also discloses a method for preparing the aforementioned ultra-high performance concrete for cold regions. Furthermore, the invention discloses the application of the aforementioned ultra-high performance concrete for cold regions as shotcrete.

Description

Technical Field

[0001] This invention relates to the field of ultra-high performance concrete technology, and in particular to an ultra-high performance concrete for cold regions, its preparation method, and its application. Background Technology

[0002] Concrete, as one of the most commonly used materials in civil engineering, boasts advantages such as abundant raw materials, mature production processes, and good economic efficiency, and is widely used in construction, road and bridge engineering, and underground engineering. For aesthetic and practical purposes, thin-walled lightweight structures, large-span structures, and super high-rise buildings are becoming increasingly common.

[0003] Ordinary concrete has its own limitations, such as poor toughness, susceptibility to cracking, and poor durability, which restricts its development in modern structural engineering. With the continuous expansion of highway construction, the main construction areas are gradually shifting from plains to mountainous and hilly regions, leading to an increasing demand for mountain highway tunnels. However, with the completion of a large number of infrastructure projects, many are experiencing corrosion, cracking, and other related problems due to prolonged use or lack of maintenance, resulting in numerous structural defects and short lifespans in current buildings. To address these issues, concrete materials with higher strength and better workability have become crucial factors influencing the further development of new structural engineering and ensuring long-term good structural performance.

[0004] Ultra-high performance concrete (UHPC) is a material that significantly improves the mechanical properties of ordinary concrete based on the theory of the densest packing density and using modern concrete preparation technology. While ensuring workability, it gives concrete ultra-high strength, stability and durability.

[0005] UHPC, a novel concrete material with ultra-high strength, ultra-high durability, ultra-low permeability, and ultra-high toughness, typically exhibits a compressive strength greater than 150 MPa, a flexural strength greater than 20 MPa, a permeability coefficient less than 10⁻¹⁸ m / s, and a toughness index greater than 101. Shotcrete technology is a construction method that delivers concrete or mortar to a nozzle via high-pressure air or other power, and then sprays it at high speed onto the target surface. The combination of shotcrete technology and UHPC can fully utilize the high performance of UHPC while improving its construction efficiency and economy, providing a new option for engineering construction. However, the high performance requirements of UHPC necessitate high fluidity, high consistency, and high viscosity, which makes it prone to problems such as pipe blockage, segregation, and rheological changes during pumping and shotcrete, requiring urgent solutions. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing an ultra-high performance concrete for cold regions, its preparation method, and its application.

[0007] A type of ultra-high performance concrete for cold regions, the raw materials of which include: cement 600-900 kg / m³ 3 Silica fume 200-240kg / m³ 3 Fly ash 100-120kg / m³ 3 Manufactured sand 1000-1200 kg / m³ 3 Water-reducing agent 20-26 kg / m³ 3 Defoamer 1-5kg / m³ 3 Water 170-220kg / m 3 ; and reinforcing fibers; the volume content of reinforcing fibers is 1.0-3.5%, and the reinforcing fibers are at least one of polypropylene fibers, reinforced polypropylene fibers, steel fibers, and reinforced steel fibers.

[0008] Preferably, the defoamer is a polyether-modified silicone defoamer.

[0009] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0010] Preferably, the reinforced polypropylene fiber is prepared by the following specific steps: polyethylene and maleic anhydride-grafted polyethylene are mixed evenly and melted to obtain a first preform; polypropylene, sodium polyacrylate, and sodium chloride are mixed evenly and melted to obtain a second preform; the first preform is used as the core material and the second preform is used as the sheath material, which are then spun into fibers by a composite spinning machine, cooled, cut, soaked, ultrasonically washed, vacuum dried, and then ultrasonically dispersed with calcium formate, sodium silicate, and anhydrous ethanol for 1-2 hours. The anhydrous ethanol is then removed, and the fibers are pulverized.

[0011] More preferably, the mass ratio of polyethylene, maleic anhydride-grafted polyethylene, polypropylene, sodium polyacrylate, sodium chloride, calcium formate, and sodium silicate is 1-5:0.01-0.1:10-18:1-2:1-2:1-2:1-2.

[0012] Preferably, the steel fiber reinforcement is prepared by the following specific steps: the steel fiber is added to an aqueous solution of dopamine hydrochloride and stirred for 1-5 minutes, the pH of the system is adjusted to 7.5-8.2, oxygen is introduced for polymerization for 1-5 hours, filtered, washed, and vacuum dried, added to a calcium chloride solution and stirred for 1-10 minutes, sodium polyphosphate is added and stirred for 1-2 hours, carbon dioxide is introduced until the pH of the system is 6.4-6.8, stirred for 1-2 hours, allowed to stand for 1-5 hours, filtered, washed, and vacuum dried.

[0013] More preferably, the mass concentration of the dopamine hydrochloride aqueous solution is 1.5-2 g / L, the concentration of the calcium chloride solution is 0.1-0.5 mol / L, and the mass ratio of steel fiber, dopamine hydrochloride aqueous solution, calcium chloride solution, and sodium polyphosphate is 10-20:40-60:40-60:5-12.

[0014] The preparation method of the aforementioned ultra-high performance concrete for cold regions includes the following steps:

[0015] S1. Mix cement, silica fume, fly ash and reinforcing fibers for 1-4 minutes to obtain reinforcing cementitious material;

[0016] S2. Add manufactured sand and defoamer to the reinforcing cementitious material and continue stirring for 1-5 minutes to obtain dry mix.

[0017] S3. Add water-reducing agent and water to the dry mix and stir for 2-6 minutes.

[0018] The above-mentioned curing method for ultra-high performance concrete in cold regions adopts high-temperature steam curing, with a curing temperature of 90±5℃ and a curing time of 3±0.5 days.

[0019] The above-mentioned cold regions use ultra-high performance concrete as shotcrete.

[0020] Preferably, the concrete raw materials also include: an accelerator and hydroxypropyl methylcellulose, with the accelerator dosage being 20-24 kg / m³. 3 The dosage of hydroxypropyl methylcellulose is 0.20-0.24 kg / m³. 3 .

[0021] Beneficial effects:

[0022] This invention combines polyethylene with maleic anhydride-grafted polyethylene and adds a polypropylene structural layer to the outer layer. The two have high bonding strength. Sodium chloride is removed by ultrasonic washing with water. The resulting porous structure has high adsorption strength for calcium formate and sodium sulfate, and also provides expansion space for sodium polyacrylate to absorb water and expand, ensuring the stable hydration of cement, thereby reducing shrinkage and effectively improving the impermeability and frost resistance of concrete.

[0023] This invention involves bonding a layer of polydopamine to the surface of steel fibers and then depositing a layer of nano-calcium carbonate. This allows the calcium ions on the fibers to crosslink with the silicate ions in the reinforcing polypropylene fibers, creating a uniform network structure on top of the original network structure of the concrete slurry. This not only effectively prevents pipe blockage and delamination during pumping and spraying but also effectively inhibits the propagation of microcracks inside the concrete after curing, thereby effectively enhancing the compressive strength of the system.

[0024] The concrete of this invention has good fluidity and, under the premise of high pumpability, effectively increases the spraying thickness. The product far surpasses the performance of ordinary high-performance concrete in terms of performance and technical indicators. Moreover, it can strengthen the microstructure of concrete, improve aggregate-mortar interface defects to a certain extent, effectively enhance its density, improve the low-temperature mechanical properties of ultra-high performance concrete, and further improve concrete durability. At the same time, the invention has good construction performance, which is more conducive to its promotion and application in practical engineering. Attached Figure Description

[0025] Figure 1 This is a comparison chart of the flowability of the mortars obtained in Examples 1-4.

[0026] Figure 2 The graph shows a comparison of the flexural strength and compressive strength of the concrete obtained in Examples 1-4 after high-temperature steam curing.

[0027] Figure 3 Photograph of the SPB0608 shotcrete pump used in this invention.

[0028] Figure 4 This is a schematic diagram of the nozzle used in this invention.

[0029] Figure 5 This is a photograph of the surface being sprayed during the spray test.

[0030] Figure 6 This is a photograph of the sprayed surface after the spraying test was completed.

[0031] Figure 7 This is a photograph showing the maximum thickness of the top spray during the spray test.

[0032] Figure 8 This is a photograph showing the maximum thickness of the sprayed material on a vertical surface during the spraying test. Detailed Implementation

[0033] The present invention will be further explained below with reference to specific embodiments.

[0034] The cement used below is Xinjiang Tianshan 42.5 ordinary Portland cement, the silica fume used below was purchased locally in Xinjiang, and the fly ash used below is a new type of ultrafine volcanic ash powder microspheres produced by Beijing Zhengyuan Yiqing New Material Technology Co., Ltd.

[0035] The parameters of the manufactured sand used are as follows: apparent density 2.64 kg / m³ 3 Bulk density (compact) 1.71 kg / m³ 3 Bulk density (loose) 1.64 kg / m³ 3 The mud content is 1.60%, the water content is 0.36%, the gradation zone is super 1, and the fineness modulus is 3.81.

[0036] The steel fibers used below are straight copper-plated steel fibers produced by Ganzhou Daye Metal Fiber Co., Ltd., with the following parameters: length 13mm, diameter 0.2mm, aspect ratio 65, shape qualification rate ≥98%, smooth surface, impurities <0.1%, and tensile strength ≥2850MPa.

[0037] The polypropylene fiber parameters used are as follows: tensile strength ≥400MPa, initial modulus ≥5000MPa, elongation at break ≤30%, equivalent diameter 0.1-0.4mm, length 10±1mm, and alkali resistance (ultimate tensile strength retention rate) ≥95%.

[0038] Example 1

[0039] A type of ultra-high performance concrete for cold regions, the raw materials of which include: 720 kg / m³ of cement. 3 Silica fume 200kg / m 3 100kg / m³ of fly ash 3 1070 kg / m³ of manufactured sand 3 Polycarboxylate superplasticizer 24kg / m 3 Polyether-modified silicone defoamer 1kg / m³ 3 184 kg / m³ of water 3 ; and polypropylene fibers with a volume content of 2.0%.

[0040] The preparation method of the aforementioned ultra-high performance concrete for cold regions includes the following steps:

[0041] S1. Cement, silica fume, fly ash and polypropylene fiber are fed into a mixer and stirred at 40 r / min for 3 min to obtain a reinforcing cementitious material.

[0042] S2. Add manufactured sand and defoamer to the reinforcing cementitious material and continue stirring for 3 minutes to obtain dry mix;

[0043] S3. Add water-reducing agent and water to the dry mix, and stir at 20 r / min for 2 min, then stir at 55 r / min for 2 min.

[0044] Example 2

[0045] A type of ultra-high performance concrete for cold regions, the raw materials of which include: 770 kg / m³ of cement. 3 Silica fume 220kg / m 3 110 kg / m³ of fly ash 3 1050kg / m³ of manufactured sand 3 Polycarboxylate superplasticizer 24kg / m 3 Polyether-modified silicone defoamer 1kg / m³ 3 187 kg / m³ of water 3; and steel fibers with a volume content of 1.5%.

[0046] The preparation method of the aforementioned ultra-high performance concrete for cold regions includes the following steps:

[0047] S1. Cement, silica fume, fly ash and steel fibers are fed into a mixer and stirred at 40 r / min for 3 min to obtain a reinforcing cementitious material.

[0048] S2. Add manufactured sand and defoamer to the reinforcing cementitious material and continue stirring for 3 minutes to obtain dry mix;

[0049] S3. Add water-reducing agent and water to the dry mix, and stir at 20 r / min for 2 min, then stir at 55 r / min for 2 min.

[0050] Example 3

[0051] A type of ultra-high performance concrete for cold regions, the raw materials of which include: 770 kg / m³ of cement. 3 Silica fume 220kg / m 3 110 kg / m³ of fly ash 3 1050kg / m³ of manufactured sand 3 Polycarboxylate superplasticizer 24kg / m 3 Polyether-modified silicone defoamer 1kg / m³ 3 187 kg / m³ of water 3 ; and reinforced steel fibers with a volume fraction of 1.5%.

[0052] The steel fiber reinforcement is prepared using the following specific steps: 15 kg of steel fiber is added to 50 kg of a 1.8 g / L dopamine hydrochloride aqueous solution and stirred at 300 r / min for 3 min. The pH of the system is adjusted to 7.5-8.2 using a 1.4 mol / L sodium hydroxide solution. Oxygen is introduced for polymerization for 3 h. The mixture is then filtered, washed, and vacuum dried. The fiber is then added to 50 kg of a 0.3 mol / L calcium chloride solution and stirred at 300 r / min for 5 min. 8 kg of sodium polyphosphate is then added and stirring is continued for 1.5 h. Carbon dioxide is introduced until the pH of the system reaches 6.4-6.8, and stirring is continued for 1.5 h. The mixture is allowed to stand for 3 h, then filtered, washed, and vacuum dried.

[0053] The preparation method of the aforementioned ultra-high performance concrete for cold regions includes the following steps:

[0054] S1. Cement, silica fume, fly ash and reinforcing steel fibers are fed into a mixer and stirred at 40 r / min for 3 min to obtain a reinforcing cementitious material.

[0055] S2. Add manufactured sand and defoamer to the reinforcing cementitious material and continue stirring for 3 minutes to obtain dry mix;

[0056] S3. Add water-reducing agent and water to the dry mix, and stir at 20 r / min for 2 min, then stir at 55 r / min for 2 min.

[0057] Example 4

[0058] A type of ultra-high performance concrete for cold regions, the raw materials of which include: 800 kg / m³ of cement. 3 Silica fume 240kg / m 3 120 kg / m³ of fly ash 3 1000 kg / m³ of manufactured sand 3 Polycarboxylate superplasticizer 24kg / m 3 Polyether-modified silicone defoamer 1kg / m³ 3 187 kg / m³ of water 3 ; and reinforced steel fibers with a volume fraction of 1.0% and reinforced polypropylene fibers with a volume fraction of 1.5%.

[0059] The steel fiber reinforcement is prepared using the following specific steps: 15 kg of steel fiber is added to 50 kg of a 1.8 g / L dopamine hydrochloride aqueous solution and stirred at 300 r / min for 3 min. The pH of the system is adjusted to 7.5-8.2 using a 1.4 mol / L sodium hydroxide solution. Oxygen is introduced for polymerization for 3 h. The mixture is then filtered, washed, and vacuum dried. The fiber is then added to 50 kg of a 0.3 mol / L calcium chloride solution and stirred at 300 r / min for 5 min. 8 kg of sodium polyphosphate is then added and stirring is continued for 1.5 h. Carbon dioxide is introduced until the pH of the system reaches 6.4-6.8, and stirring is continued for 1.5 h. The mixture is allowed to stand for 3 h, then filtered, washed, and vacuum dried.

[0060] The reinforced polypropylene fiber is prepared by the following specific steps: 3 kg of polyethylene and 0.05 kg of maleic anhydride-grafted polyethylene are mixed evenly and melted to obtain the first preform; 14 kg of polypropylene, 1.5 kg of sodium polyacrylate, and 1.5 kg of sodium chloride are mixed evenly and melted to obtain the second preform; the first preform is used as the core material and the second preform is used as the sheath material, which are then spun into fibers by a composite spinning machine, cooled, cut, soaked in water, ultrasonically washed, vacuum dried, and then 1.5 kg of calcium formate, 1.5 kg of sodium silicate, and 90 kg of anhydrous ethanol are added and ultrasonically dispersed for 1.5 h at an ultrasonic frequency of 12 kHz. The anhydrous ethanol is then removed, and the fibers are pulverized.

[0061] The preparation method of the aforementioned ultra-high performance concrete for cold regions includes the following steps:

[0062] S1. Cement, silica fume, fly ash, reinforcing steel fiber, and reinforcing polypropylene fiber are fed into a mixer and stirred at 40 r / min for 3 min to obtain a reinforcing cementitious material.

[0063] S2. Add manufactured sand and defoamer to the reinforcing cementitious material and continue stirring for 3 minutes to obtain dry mix;

[0064] S3. Add water-reducing agent and water to the dry mix, and stir at 20 r / min for 2 min, then stir at 55 r / min for 2 min.

[0065] The corresponding mortars were prepared in Xinjiang according to the raw materials and methods provided in Examples 1-4.

[0066] The fluidity of the mortars obtained in Examples 1-4 was determined using a cement mortar fluidity tester in accordance with GB / T 2419-2005 "Method for Determination of Flowability of Cement Mortar".

[0067] Referring to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", the mortar obtained in Examples 1-4 was used to cast 40mm×40mm×160mm specimens. These specimens were then cured in a high-temperature steam curing chamber at 90℃ for 3 days. After curing, a flexural strength test was performed first, followed by a compressive strength test on the broken prism. The compression surfaces were the two sides of the specimen during molding, with an area of ​​40mm×40mm.

[0068] Flexural strength was tested on a SANS YAW-100 compression-flexure testing machine. The side of the specimen was placed on the fixture, and the loading rate of the testing machine was 50±10 N / s. Then, the side of the broken specimen end was placed on the fixture, and the loading rate was set to 2400±200 N / s, and uniform loading was applied until the specimen failed.

[0069] like Figure 1 and Figure 2 As shown, the mortar obtained in Example 1 had the lowest fluidity and strength, while the mortar obtained in Example 4 had the highest fluidity and strength, which were significantly better than Examples 1-3 (P<0.05).

[0070] SPB0608 shotcrete pump (e.g.) Figure 3 and Figure 4 The basic parameters of the SPB0608 shotcrete pump for the shotcrete test are as follows:

[0071]

[0072]

[0073] Adjust the parameters of the SPB0608 shotcrete pump as follows: air pipe diameter 35mm, pumping pipe diameter 50mm, jetting air pressure 0.6-1MPa, jetting air volume 8-10m³ / h. 3 / h, spray distance 0.6-1m.

[0074] The mortars obtained in Examples 1-4 were used for vertical wall spraying and top spraying, respectively. Each group of nozzles was supplemented with an alkali-free quick-setting agent and hydroxypropyl methylcellulose. The dosage of the alkali-free quick-setting agent was 22 kg / m². 3 The dosage of hydroxypropyl methylcellulose is 0.22 kg / m³. 3 The maximum spray thickness on the vertical sprayed surface in Example 1 reached 100 mm, and the maximum spray thickness at the top was 91 mm; the maximum spray thickness on the vertical sprayed surface in Example 1 was 73 mm, and the maximum spray thickness at the top was 46 mm; the maximum spray thickness on the vertical sprayed surface in Example 4 was 95 mm, and the maximum spray thickness at the top was 83 mm, confirming that the ultra-high performance concrete obtained by this invention can be used for shotcrete.

[0075] However, the spraying effect in Example 2 was not ideal, with occasional clogging and pulse "fireback" phenomena.

[0076] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A type of ultra-high performance concrete for cold regions, characterized in that, Its raw materials include: cement 600-900 kg / m³ 3 Silica fume 200-240 kg / m³ 3 100-120 kg / m³ of fly ash 3 Manufactured sand 1000-1200 kg / m³ 3 Water-reducing agent 20-26 kg / m 3 Defoamer 1-5 kg / m³ 3 Water 170-220 kg / m 3 ; and reinforcing fibers; The volumetric content of the reinforcing fiber is 1.0-3.5%, and the reinforcing fiber is composed of reinforcing polypropylene fiber and reinforcing steel fiber; The reinforced polypropylene fiber is prepared by the following specific steps: polyethylene and maleic anhydride-grafted polyethylene are mixed evenly and melted to obtain the first preform; polypropylene, sodium polyacrylate, and sodium chloride are mixed evenly and melted to obtain the second preform; the first preform is used as the core material and the second preform is used as the sheath material, which are then spun into fibers by a composite spinning machine, cooled, cut, soaked, ultrasonically washed, vacuum dried, and then ultrasonically dispersed with calcium formate, sodium silicate, and anhydrous ethanol for 1-2 hours. The anhydrous ethanol is then removed, and the fibers are pulverized. The steel fiber reinforcement is prepared by the following specific steps: add the steel fiber to the dopamine hydrochloride aqueous solution and stir for 1-5 minutes. Adjust the pH of the system to 7.5-8.2, introduce oxygen and polymerize for 1-5 hours. Filter, wash, and vacuum dry. Add the fiber to the calcium chloride solution and stir for 1-10 minutes. Then add sodium polyphosphate and continue stirring for 1-2 hours. Introduce carbon dioxide until the pH of the system is 6.4-6.

8. Continue stirring for 1-2 hours. Let stand for 1-5 hours, filter, wash, and vacuum dry.

2. The ultra-high performance concrete for cold regions according to claim 1, characterized in that, The defoamer is a polyether-modified silicone defoamer.

3. The ultra-high performance concrete for cold regions according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent.

4. The ultra-high performance concrete for cold regions according to claim 1, characterized in that, In the production of reinforced polypropylene fibers, the mass ratio of polyethylene, maleic anhydride-grafted polyethylene, polypropylene, sodium polyacrylate, sodium chloride, calcium formate, and sodium silicate is 1-5:0.01-0.1:10-18:1-2:1-2:1-2:1-2:1-2.

5. The ultra-high performance concrete for cold regions according to claim 1, characterized in that, In the process of producing reinforced steel fibers, the mass concentration of dopamine hydrochloride aqueous solution is 1.5-2 g / L, the concentration of calcium chloride solution is 0.1-0.5 mol / L, and the mass ratio of steel fibers, dopamine hydrochloride aqueous solution, calcium chloride solution, and sodium polyphosphate is 10-20:40-60:40-60:5-12.

6. A method for preparing ultra-high performance concrete for cold regions as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix cement, silica fume, fly ash and reinforcing fibers for 1-4 minutes to obtain reinforcing cementitious material; S2. Add manufactured sand and defoamer to the reinforcing cementitious material and continue stirring for 1-5 minutes to obtain dry mix. S3. Add water-reducing agent and water to the dry mix and stir for 2-6 minutes.

7. An application of ultra-high performance concrete as shotcrete in cold regions as described in any one of claims 1-5.

8. The application according to claim 7, characterized in that, Concrete raw materials also include: accelerators and hydroxypropyl methylcellulose, with the accelerator dosage being 20-24 kg / m³. 3 The dosage of hydroxypropyl methylcellulose is 0.20-0.24 kg / m³. 3 .

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