A cast-in-place concrete for reinforcing a jacketed steel pipe with an enlarged section and a method of manufacturing the same

Abstract

The application provides a kind of grouting concrete for reinforcing jacketed steel pipe with enlarged section, by weight fraction, including the following raw materials: sulphoaluminate cement 15-25 parts; fine aggregate 15-25 parts; coarse aggregate 20-30 parts; water 10-16 parts; modified nano-silica 0.4-0.6 parts; modified sodium bentonite 6-8 parts; composite expansion agent 2-8 parts; phosphorous slag 4-6 parts; water reducing agent 0.4-0.6 parts; composite activator 2-6 parts; wherein, the composite expansion agent is mixed by sodium sulphoaluminate, calcium oxide and calcium aluminate in a certain proportion. The application also provides a preparation method of the above grouting concrete. The grouting concrete for reinforcing jacketed steel pipe with enlarged section prepared by the application has good flow performance, high early and late strength, high toughness, good volume stability and other advantages compared with traditional grouting materials, and can be widely applied to jacketed steel pipe with enlarged section, steel pipe concrete, steel pipe and profiled steel components, etc., and has broad popularization and application prospect.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology for building reinforcement, specifically relating to a cast-in-place concrete for reinforcing a steel tube with an enlarged cross-section and its preparation method. Background Technology

[0002] Concrete, steel-concrete composite pipes, steel pipes, and structural steel components are increasingly widely used in practical engineering projects, such as industrial plants, high-rise and super high-rise buildings, and bridge structures, due to their excellent compressive strength, convenient construction procedures, and good fire resistance. However, with the extension of service life, structural damage or design errors caused by physical and chemical factors can seriously affect the safety and usability of building structures. Therefore, improving the service life of existing structures through reasonable and effective reinforcement measures is an urgent problem that needs to be solved for my country's social and economic development. The steel pipe enlargement reinforcement method is a relatively common reinforcement method. Steel pipe reinforcement involves inserting a steel pipe outside the existing steel-concrete composite pipe. Generally, the steel pipe components (such as two semi-circular steel pipes) are welded on-site, and then grout is injected into the gap between the formed steel pipe and the existing structure to reinforce the original component.

[0003] The core purpose of the steel tube enlargement reinforcement method is to utilize the inherent mechanical properties of steel to improve the stress and deformation performance of the specimen. Filling the gap between the steel tube and the existing structural member with a filler (grout, cement mortar, or concrete) ensures that the steel tube and the existing member work together. In this case, the compressive strength and thickness of the interlayer concrete, along with the dimensions and wall thickness of the steel tube, are all important reinforcement design parameters. The contribution of the interlayer concrete to improving the specimen's load-bearing capacity and stiffness may even be greater than that of the steel tube.

[0004] However, in actual reinforcement methods using steel pipes to increase the cross-section, the internal core concrete material (pouring material) often suffers from problems such as non-compactness or gaps between the steel pipes. This weakens the compressive force between the concrete and the steel pipe, making it difficult to fully utilize the triaxial compressive strength of the concrete, ultimately leading to potential engineering hazards.

[0005] Based on this, a type of cast-in-place concrete suitable for reinforcing enlarged cross-sections of outer steel pipes is provided. This concrete not only effectively and reliably fills the gap between the outer steel pipe and the original component when the distance between them is large, but also has advantages such as high compressive strength, good durability, and good flowability. It is easy to construct and can further improve the overall strength of the reinforced building structure, which is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] One of the objectives of this invention is to provide a cast-in-place concrete for reinforcing an enlarged cross-section of an outer steel pipe, which has high compressive strength, good durability, good flowability, and good expansion properties.

[0007] The second objective of this invention is to provide a method for preparing cast-in-place concrete for reinforcing enlarged cross-sections of outer steel pipes, which has high compressive strength, good durability, good flowability, and good expansion properties.

[0008] One of the technical solutions adopted by the present invention to achieve its objective is: to provide a cast-in-place concrete for reinforcing an outer steel pipe with an enlarged cross-section, comprising the following raw materials by weight:

[0009] The mixture comprises: 15-25 parts of sulfoaluminate cement; 15-25 parts of fine aggregate; 20-30 parts of coarse aggregate; 10-16 parts of water; 0.4-0.6 parts of modified nano-silica; 6-8 parts of modified sodium bentonite; 2-8 parts of composite expansive agent; 4-6 parts of phosphorus slag; 0.4-0.6 parts of water-reducing agent; and 2-6 parts of composite activator. The composite expansive agent is composed of sodium sulfoaluminate, calcium oxide, and calcium aluminate mixed in a certain proportion.

[0010] In this invention, to ensure the concrete has a certain degree of expansiveness, a specific ratio of self-stressing sulfoaluminate cement, modified sodium bentonite, and a composite expansive agent is used in the raw materials. The ettringite formed after the hydration of the self-stressing sulfoaluminate cement exhibits micro-expansion characteristics. The modified sodium bentonite is obtained by high-temperature calcination of sodium bentonite, resulting in smaller particle size, increased specific surface area, more complete crystals, a denser structure, higher activity, and consequently, improved expansiveness. The composite expansive agent is a mixture of sodium sulfoaluminate, calcium oxide, and calcium aluminate in a specific ratio. These three raw materials provide sulfur, calcium, and aluminum elements, respectively, and generate high-sulfur hydrated calcium sulfoaluminate and monosulfur hydrated calcium sulfoaluminate with micro-expansion characteristics. By controlling the proportions of these three raw materials, their synergistic effects are achieved, keeping the expansion rate of the concrete matrix within a reasonable range and maintaining stable expansiveness. This also avoids the adverse effects of high expansiveness on the mechanical strength of the matrix.

[0011] Preferably, the sulfoaluminate cement is a self-stressing sulfoaluminate cement with a strength grade of 42.5.

[0012] Preferably, the modified sodium-based bentonite is obtained by calcining sodium-based bentonite at 700-800℃ for 1-2 hours, followed by grinding and sieving, and its particle size is 150-200nm.

[0013] Preferably, the composite expanding agent is a mixture of sodium sulfoaluminate, calcium oxide, and calcium aluminate in a mass ratio of (0.6–0.7):(1.4–1.6):1, with a particle size of 300–500 nm. More preferably, the amount of the composite expanding agent accounts for 2–8 wt.% of the total weight of the raw materials. In this invention, by controlling the amount of each component in the composite expanding agent, the ratio of sulfur, calcium, and aluminum in the matrix can be further regulated, thereby balancing the amounts of high-sulfur hydrated calcium sulfoaluminate and monosulfur hydrated calcium sulfoaluminate. Under these conditions, the matrix can be guaranteed to have micro-expansion characteristics, high and stable mechanical strength, and good impermeability.

[0014] Preferably, the fine aggregate is selected from medium-coarse sand with a mesh size of 200-240; the coarse aggregate is selected from recycled aggregate with a particle size of 5-25mm. Recycled aggregate is inexpensive and avoids the resource consumption caused by manual sand and gravel mining, thus saving resources and protecting the environment, and helping to reduce project costs.

[0015] In some preferred embodiments, the preparation method of coarse aggregate includes: crushing the original C40 strength concrete and grading it by screening into three particle sizes: 0-5 mm, 5-25 mm, and larger than 25 mm. Particles with a size of 5-25 mm are used directly as recycled coarse aggregate; particles with a size of 0-5 mm are discarded, and particles with a size greater than 25 mm are crushed again until their size reaches 5-25 mm. The above crushing operation can be carried out using a jaw concrete crusher.

[0016] Preferably, the modified nano-silica is prepared by successively modifying nano-silica with trichlorotriazine and polyethylene oxide. The above modification process can graft a certain number of hydrophilic functional groups such as hydroxyl and carboxyl groups onto the surface of the nano-silica, thereby significantly improving the mechanical strength and impermeability of the matrix.

[0017] In some preferred embodiments, the method for preparing the modified nano-silica includes: mixing nano-silica and trichlorotriazine in solvent A at a mass ratio of (10-20):(3-4), reacting at room temperature for a certain time, washing and drying to obtain a first product; dissolving the first product in solvent B, adding it to solvent C containing dissolved polyethylene oxide to obtain a mixture; wherein the mass ratio of the first product to polyethylene oxide is (10-20):(2-3); heating the mixture under a protective atmosphere for a certain time to obtain a second product; washing and drying the second product to obtain modified nano-silica.

[0018] Furthermore, in the above formulation system, the dosage and type of water-reducing agent will also have a certain impact on the fluidity, mechanical strength, and impermeability of the matrix. In this invention, the water-reducing agent is a compound of inorganic and organic water-reducing agents. Sodium carbonate is an inorganic water-reducing agent, which can increase both the fluidity and mechanical strength of the poured concrete. Calcium lignosulfonate and sodium alkyl sulfate are organic water-reducing agents, which have good antifreeze properties and can effectively inhibit matrix shrinkage.

[0019] Preferably, the water-reducing agent is a mixture of sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate in a mass ratio of (0.7–0.8):(1.1–1.3):1, with a particle size of 700–900 nm. Compared with conventional water-reducing agents, the composite water-reducing agent used in this invention not only improves the fluidity of cast-in-place concrete but also significantly enhances its mechanical strength and impermeability. Preferably, the sodium alkyl sulfate is selected from sodium hexadecyl sulfate or sodium octadecyl sulfate.

[0020] Preferably, the phosphorus slag has a particle size of 10–14 μm and a specific surface area determined by nitrogen adsorption of 400–600 m². 2 / kg, with a mass coefficient K of 1.3 to 1.4.

[0021] Preferably, the composite activator is a mixture of sodium silicate and sodium hydroxide powder.

[0022] Furthermore, in this invention, by optimizing the particle size of each raw material, the matrix system has a certain gradation, ensuring that the matrix has high mechanical strength and good impermeability.

[0023] The second objective of this invention is achieved by providing a method for preparing cast-in-place concrete for reinforcing an outer steel pipe with an enlarged cross-section, comprising the following steps:

[0024] S1. Prepare the following raw materials according to the following mass proportions: 15-25 parts sulfoaluminate cement; 15-25 parts fine aggregate; 20-30 parts coarse aggregate; 10-16 parts water; 0.4-0.6 parts modified nano-silica; 6-8 parts modified sodium bentonite; 2-8 parts composite expansive agent; 4-6 parts phosphorus slag; 0.4-0.6 parts water-reducing agent; 2-6 parts composite activator; Place the modified nano-silica in water and treat it with ultrasound to obtain a mixed solution.

[0025] S2. Mix cement, fine aggregate, coarse aggregate, and phosphorus slag to obtain mixture A; calcine modified sodium bentonite, water-reducing agent, and composite activator to obtain mixture B.

[0026] S3. Mix the mixture A and the mixture B evenly, then add the mixed solution and mix evenly to obtain a mixed slurry;

[0027] S4. Add a composite expansion agent to the mixed slurry, mix well, and then vibrate and cure to obtain the grouting concrete for reinforcing the outer steel pipe with an enlarged cross section.

[0028] Preferably, in step S1, the ultrasonic treatment power is 400-500W and the ultrasonic treatment time is 0.1-0.2h.

[0029] Preferably, in step S2, the calcination temperature is 500–600°C, and the calcination time is 3–5 hours. In the above preparation method, by calcining the modified sodium-based bentonite, water-reducing agent, and composite activator, on the one hand, the activity of the three can be increased; on the other hand, the calcination process can reduce the particle size of the three, increase their specific surface area, accelerate the reaction rate of the poured concrete, and thus increase the mechanical strength and impermeability of the matrix.

[0030] Preferably, in step S3, the mixing time for adding the mixed solution and mixing it to obtain a mixed slurry is 240-300 seconds.

[0031] Preferably, in step S4, the time for adding the composite expanding agent to the mixed slurry and mixing is 60-90 seconds; the curing is carried out under normal temperature conditions.

[0032] Among the main raw materials mentioned above, the components of the composite expansive agent can react rapidly with water, as can sulfoaluminate cement. When both react with water simultaneously, a competitive interference mechanism exists. To prevent the composite expansive agent from preferentially reacting with water, the resulting high-sulfur hydrated calcium sulfoaluminate and monosulfur hydrated calcium sulfoaluminate rapidly coat the surface of unreacted sulfoaluminate cement particles, thereby inhibiting the cement's hydration reaction and causing internal defects in the matrix. Therefore, preferably, the final step of the composite expansive agent preparation method is added to the reaction system to ensure that the matrix has better mechanical strength and impermeability.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The present invention provides a type of cast-in-place concrete for reinforcing an outer steel pipe with an enlarged cross section. The raw materials are made of a certain proportion of sulfoaluminate cement, modified sodium bentonite and composite expansive agent, which controls the expansion rate of the concrete matrix within a reasonable range and maintains stable expansibility. At the same time, it avoids the adverse effects of high expansibility on the mechanical strength of the matrix. Meanwhile, by adding modified nano silica, phosphorus slag and water-reducing agent to the raw materials, it also plays a positive role in the compressive strength and impermeability of the matrix. By optimizing the proportion of each raw material, the cast-in-place concrete not only has high compressive strength, good durability and good flowability, but also has good expansibility, which can effectively meet the application requirements of reinforcing an outer steel pipe with an enlarged cross section.

[0035] (2) The present invention provides a method for preparing cast-in-place concrete for reinforcing steel pipes with enlarged cross-sections. This method involves calcining modified sodium-based bentonite, a water-reducing agent, and a composite activator to increase the activity of the raw materials and improve the reaction rate of the cast-in-place concrete, thereby increasing the mechanical strength and impermeability of the matrix. The preparation process is simple, and the resulting cast-in-place concrete, compared with traditional casting materials, has advantages such as good flowability, high early and late strength, high toughness, and good volume stability. It can be widely used in reinforced concrete for enlarged cross-sections of steel pipes, steel-concrete composite structures, steel pipes, and structural steel components, and has broad prospects for promotion and application. Attached Figure Description

[0036] Figure 1 This is a schematic flowchart illustrating a method for preparing cast-in-place concrete for reinforcing an outer steel pipe with an enlarged cross-section, as provided by the present invention. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0039] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0040] The raw materials and their weight proportions involved in the various embodiments and comparative examples of the present invention are shown in Table 1 below:

[0041] Table 1

[0042]

[0043]

[0044] In the above table,

[0045] The cement is self-stressing sulfoaluminate cement with a strength grade of 42.5; the fine aggregate is selected from medium-coarse sand with a mesh size of 200-240; the coarse aggregate is selected from recycled aggregate with a particle size of 5-25 mm; the modified sodium-based bentonite is obtained by calcining sodium-based bentonite at 700-800℃ for 1-2 hours, followed by grinding and sieving, with a particle size of 150-200 nm; the composite expansive agent is a mixture of sodium sulfoaluminate, calcium oxide and calcium aluminate in a mass ratio of (0.6-0.7):(1.4-1.6):1, with a particle size of 300-500 nm. The water-reducing agent is a mixture of sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate in a mass ratio of (0.7–0.8):(1.1–1.3):1, with a particle size of 700–900 nm. The sodium alkyl sulfate is selected from sodium hexadecyl sulfate or sodium octadecyl sulfate. The phosphorus slag has a particle size of 10–14 μm, and its specific surface area determined by nitrogen adsorption is 400–600 m². 2 / kg, with a mass coefficient K of 1.3 to 1.4; the composite activator is a mixture of sodium silicate and sodium hydroxide powder in a mass ratio of (0.5 to 0.7):1.

[0046] The preparation method of modified nano-silica is as follows:

[0047] (1) Mix 1-2g of nano-silica and 0.3-0.4g of trichlorotriazine in 30-50mL of acetone, stir at 20-30℃ for 3-4h, then react at 20-25℃ for 60-80h, wash with acetone and then vacuum dry at 15-20℃ for 5-10h.

[0048] (2) Dissolve 1-2g of nano-silica treated in step (1) above in 50-70mL of N,N'-dimethylformamide, and then add it to 10-15mL of xylene solution containing 0.2-0.3g of polyethylene oxide. Stir at 10-20℃ for 4-8h, then raise the temperature to 50-70℃ under nitrogen protection and react at a constant temperature for 10-16h, then raise the temperature to 70-80℃ and react at a constant temperature for 10-16h; the polyethylene oxide needs to be vacuum dried at 40-50℃ for 35-45h before use.

[0049] (3) After the reaction is complete, the solvent is removed by vacuum evaporation, the mixture is washed with xylene and acetone, and then vacuum dried at 40-60℃ for 10-18h to obtain modified nano-silica.

[0050] Example 1

[0051] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.5 parts of modified nano silica in 13 parts of water, stir for 270s, and then sonicate under an ultrasonic power of 450W for 0.15h to obtain a uniform mixed solution.

[0052] Step 2: Add 20 parts of sulfoaluminate cement, 20 parts of fine aggregate, 25 parts of coarse aggregate, and 5 parts of phosphorus slag to a mixer and mix for 220 seconds to obtain mixture A; add 7 parts of modified sodium bentonite, 0.5 parts of water-reducing agent (sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate in a mass ratio of 0.7:1.3:1), and 4 parts of composite activator to a muffle furnace and calcine for 4 hours at a calcination temperature of 550℃. After cooling, sieve to obtain mixture B.

[0053] Step 3: Add mixture A and mixture B into the mixing pot and stir for 210 seconds, then add the mixed solution and continue stirring for 270 seconds to obtain a mixed slurry;

[0054] Step 4: Add 5 parts of composite expansion agent (sodium sulfoaluminate, calcium oxide and calcium aluminate mixed in a mass ratio of 0.6:1.6:1) to the mixed slurry, stir for 75 seconds, vibrate, and cure at room temperature to obtain the grouting concrete for increasing the cross-section of the outer steel pipe.

[0055] Example 2

[0056] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.4 parts of modified nano silica in 16 parts of water, stir for 300s, and then sonicate under an ultrasonic power of 400W for 0.1h to obtain a uniform mixed solution.

[0057] Step 2: Add 20 parts of sulfoaluminate cement, 20 parts of fine aggregate, 25 parts of coarse aggregate, and 4 parts of phosphorus slag to a mixer and mix for 220 seconds to obtain mixture A; add 7 parts of modified sodium bentonite, 0.6 parts of water-reducing agent (sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate in a mass ratio of 0.8:1.1:1), and 3 parts of composite activator to a muffle furnace and calcine for 3 hours at a calcination temperature of 500℃. After cooling, sieve to obtain mixture B.

[0058] Step 3: Add mixture A and mixture B into the mixing pot and stir for 240 seconds. Then add the mixed solution and continue stirring for 240 seconds to obtain a mixed slurry.

[0059] Step 4: Add 4 parts of composite expansion agent (sodium sulfoaluminate, calcium oxide and calcium aluminate mixed in a mass ratio of 0.7:1.4:1) to the mixed slurry, stir for 90 seconds, vibrate, and cure at room temperature to obtain the grouting concrete for increasing the cross-section of the outer steel pipe.

[0060] Example 3

[0061] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.5 parts of modified nano silica in 13 parts of water, stir for 240s, and then sonicate under an ultrasonic power of 500W for 0.15h to obtain a uniform mixed solution.

[0062] Step 2: Add 25 parts of sulfoaluminate cement, 15 parts of fine aggregate, 25 parts of coarse aggregate, and 5 parts of phosphorus slag to a mixer and mix for 220 seconds to obtain mixture A; add 8 parts of modified sodium bentonite, 0.5 parts of water-reducing agent (sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate in a mass ratio of 0.7:1.2:1), and 3 parts of composite activator to a muffle furnace and calcine for 5 hours at a calcination temperature of 550℃. After cooling, sieve to obtain mixture B.

[0063] Step 3: Add mixture A and mixture B into the mixing pot and stir for 180 seconds, then add the mixed solution and continue stirring for 240 seconds to obtain a mixed slurry;

[0064] Step 4: Add 5 parts of composite expansion agent (sodium sulfoaluminate, calcium oxide and calcium aluminate mixed in a mass ratio of 0.6:1.5:1) to the mixed slurry, stir for 60 seconds, vibrate, and cure at room temperature to obtain the grouting concrete for increasing the cross-section of the outer steel pipe.

[0065] Example 4

[0066] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.6 parts of modified nano silica in 13 parts of water, stir for 270s, and then sonicate under an ultrasonic power of 450W for 0.2h to obtain a uniform mixed solution.

[0067] Step 2: Add 15 parts of sulfoaluminate cement, 25 parts of fine aggregate, 22 parts of coarse aggregate, and 6 parts of phosphorus slag to a mixer and mix for 220 seconds to obtain mixture A; add 8 parts of modified sodium bentonite, 0.4 parts of water-reducing agent (sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate in a mass ratio of 0.75:1.2:1), and 5 parts of composite activator to a muffle furnace and calcine for 3 hours at a temperature of 600℃. After cooling, sieve to obtain mixture B.

[0068] Step 3: Add mixture A and mixture B into the mixing pot and stir for 180 seconds. Then add the mixed solution and continue stirring for 300 seconds to obtain a mixed slurry.

[0069] Step 4: Add 5 parts of composite expansion agent (sodium sulfoaluminate, calcium oxide and calcium aluminate mixed in a mass ratio of 0.65:1.5:1) to the mixed slurry, stir for 90 seconds, vibrate, and cure at room temperature to obtain the grouting concrete for increasing the cross-section of the outer steel pipe.

[0070] Example 5

[0071] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.5 parts of modified nano silica in 10 parts of water, stir for 270s, and then sonicate under an ultrasonic power of 450W for 0.15h to obtain a uniform mixed solution.

[0072] Step 2: Add 15 parts of sulfoaluminate cement, 20 parts of fine aggregate, 30 parts of coarse aggregate, and 4 parts of phosphorus slag to a mixer and mix for 220 seconds to obtain mixture A; add 6 parts of modified sodium bentonite, 0.5 parts of water-reducing agent (sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate in a mass ratio of 0.7:1.1:1), and 6 parts of composite activator to a muffle furnace and calcine for 4 hours at a calcination temperature of 550℃. After cooling, sieve to obtain mixture B.

[0073] Step 3: Add mixture A and mixture B into the mixing pot and stir for 210 seconds, then add the mixed solution and continue stirring for 270 seconds to obtain a mixed slurry;

[0074] Step 4: Add 8 parts of composite expansion agent (sodium sulfoaluminate, calcium oxide and calcium aluminate mixed in a mass ratio of 0.6:1.4:1) to the mixed slurry, stir for 75 seconds, vibrate, and cure at room temperature to obtain the grouting concrete for increasing the cross-section of the outer steel pipe.

[0075] Example 6

[0076] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.5 parts of modified nano silica in 13 parts of water, stir for 270s, and then sonicate under an ultrasonic power of 450W for 0.15h to obtain a uniform mixed solution.

[0077] Step 2: Add 25 parts of sulfoaluminate cement, 15 parts of fine aggregate, 30 parts of coarse aggregate, and 5 parts of phosphorus slag to a mixer and mix for 220 seconds to obtain mixture A; add 7 parts of modified sodium bentonite, 0.6 parts of water-reducing agent (sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate in a mass ratio of 0.8:1.2:1), and 2 parts of composite activator to a muffle furnace and calcine for 4 hours at a calcination temperature of 550℃. After cooling, sieve to obtain mixture B.

[0078] Step 3: Add mixture A and mixture B into the mixing pot and stir for 210 seconds, then add the mixed solution and continue stirring for 270 seconds to obtain a mixed slurry;

[0079] Step 4: Add 2 parts of composite expansion agent (sodium sulfoaluminate, calcium oxide and calcium aluminate mixed in a mass ratio of 0.7:1.4:1) to the mixed slurry, stir for 75 seconds, vibrate, and cure at room temperature to obtain the grouting concrete for increasing the cross-section of the outer steel pipe.

[0080] Example 7

[0081] The difference between this embodiment and Embodiment 6 is that the order of adding the composite expanding agent in the preparation method has been adjusted. The specific preparation method is as follows:

[0082] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.5 parts of modified nano silica in 13 parts of water, stir for 270s, and then sonicate under an ultrasonic power of 450W for 0.15h to obtain a uniform mixed solution.

[0083] Step 2: Pour 25 parts of sulfoaluminate cement, 15 parts of fine aggregate, 30 parts of coarse aggregate, 5 parts of phosphorus slag, and 2 parts of composite expansive agent (sodium sulfoaluminate, calcium oxide, and calcium aluminate mixed in a mass ratio of 0.7:1.4:1) into a mixer and stir for 220 seconds to obtain mixture A; add 7 parts of modified sodium bentonite, 0.6 parts of water-reducing agent (sodium carbonate, calcium lignosulfonate, and sodium alkyl sulfate mixed in a mass ratio of 0.8:1.2:1), and 2 parts of composite activator into a muffle furnace and calcine for 4 hours at a calcination temperature of 550℃. After cooling, sieve to obtain mixture B;

[0084] Step 3: Add mixture A and mixture B into the mixing pot and stir for 210 seconds. Then add the mixed solution and continue stirring for 270 seconds to obtain a mixed slurry. Vibrate the mixed slurry and cure it at room temperature to obtain the cast-in-place concrete for reinforcing the outer steel pipe with an enlarged cross-section.

[0085] Comparative Example 1

[0086] The difference between this comparative example and Example 1 is that the modified nano-silica is removed. The specific steps are as follows:

[0087] Step 1: Prepare the raw materials according to the weight proportions shown in Table 1; pour 20 parts of sulfoaluminate cement, 20 parts of fine aggregate, 25 parts of coarse aggregate, and 5 parts of phosphorus slag into a mixer and mix for 220 seconds to obtain mixture A; add 7 parts of modified sodium bentonite, 0.5 parts of water-reducing agent, and 4 parts of composite activator into a muffle furnace and calcine for 4 hours at a calcination temperature of 550℃. After cooling, sieve to obtain mixture B.

[0088] Step 2: Add mixture A and mixture B into the mixing pot and stir for 210 seconds. Then add 13 parts water and continue stirring for 270 seconds to obtain a mixed slurry.

[0089] Step 3: Add 5 parts of composite expansion agent to the mixed slurry, stir for 75 seconds, vibrate, and cure at room temperature to obtain the cast-in-place concrete for reinforcing the outer steel pipe with increased cross-section.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Example 1 is that the modified sodium-based bentonite is removed. The specific steps are as follows:

[0092] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.5 parts of modified nano silica in 13 parts of water, stir for 270s, and then sonicate under an ultrasonic power of 450W for 0.15h to obtain a uniform mixed solution.

[0093] Step 2: Pour 20 parts of sulfoaluminate cement, 20 parts of fine aggregate, 25 parts of coarse aggregate, and 5 parts of phosphorus slag into a mixer and mix for 220 seconds to obtain mixture A; add 0.5 parts of water-reducing agent and 4 parts of composite activator into a muffle furnace and calcine for 4 hours at a calcination temperature of 550℃. After cooling, sieve to obtain mixture B.

[0094] Step 3: Add mixture A and mixture B into the mixing pot and stir for 210 seconds, then add the mixed solution and continue stirring for 270 seconds to obtain a mixed slurry;

[0095] Step 4: Add 5 parts of composite expansion agent to the mixed slurry, stir for 75 seconds, vibrate, and cure at room temperature to obtain the cast-in-place concrete for reinforcing the outer steel pipe with increased cross-section.

[0096] Comparative Example 3

[0097] The difference between this comparative example and Example 1 is that the composite expanding agent is removed. The specific steps are as follows:

[0098] Step 1: Prepare each raw material according to the weight proportions shown in Table 1; place 0.5 parts of modified nano silica in 13 parts of water, stir for 270s, and then sonicate under an ultrasonic power of 450W for 0.15h to obtain a uniform mixed solution.

[0099] Step 2: Add 20 parts of sulfoaluminate cement, 20 parts of fine aggregate, 25 parts of coarse aggregate, and 5 parts of phosphorus slag to a mixer and mix for 220 seconds to obtain mixture A; add 7 parts of modified sodium bentonite, 0.5 parts of water-reducing agent, and 4 parts of composite activator to a muffle furnace and calcine for 4 hours at a calcination temperature of 550℃. After cooling, sieve to obtain mixture B.

[0100] Step 3: Add mixture A and mixture B into the mixing pot and stir for 210 seconds, then add the mixed solution and continue stirring for 270 seconds to obtain a mixed slurry;

[0101] Step 4: Vibrate the mixed slurry and cure it at room temperature to obtain the cast-in-place concrete for reinforcing the outer steel pipe with an enlarged cross-section.

[0102] Comparative Example 4

[0103] The difference between this comparative example and Example 1 is that the amount of composite expansion agent is adjusted to 10 parts, while the amount of other raw materials and preparation steps remain the same as in Example 1, and the resulting cast-in-place concrete for reinforcing the outer steel pipe with an enlarged cross-section is prepared.

[0104] Performance testing

[0105] The present invention uses GB50081-2002, GB / T8077-2000, GB / T 23439 and JC / T984-2011 standards to test the relevant performance of each embodiment and comparative example. The specific test results are shown in Table 2.

[0106] Table 2. Performance Test Results of Cast-in-Place Concrete for Enlarged Cross-Section Reinforcement of Outer Steel Pipe

[0107]

[0108] As can be seen from the above table,

[0109] Compared to Example 1, Comparative Examples 1-3 removed the modified nano-silica, modified sodium-based bentonite, and composite expansive agent from the raw materials, respectively. The resulting cast-in-place concrete showed a significant decrease in mechanical strength, fluidity, micro-expansion, and impermeability compared to Example 1. This indicates that the synergistic effect of a certain proportion of modified nano-silica, modified sodium-based bentonite, and composite expansive agent in the raw materials of this invention is a necessary prerequisite for ensuring the excellent application performance of the cast-in-place concrete. Comparative Example 4, based on Example 1, used an excessive amount of composite expansive agent. Although the resulting cast-in-place concrete still maintained good fluidity and expansive characteristics, its mechanical properties and impermeability were significantly reduced.

[0110] The cast-in-place concrete prepared in Examples 1-7 of this invention has a 28-day compressive strength of 60–94 MPa, a fluidity of 185–235 mm, a 28-day restricted expansion rate of 0.16%–0.42%, and a seepage pressure resistance of 4.3–7.2 MPa. When applied to the construction of the steel pipe enlargement reinforcement method, the above-mentioned cast-in-place concrete can reliably and densely fill the gap between the steel pipe and the original component, allowing the concrete to fully exert its compressive force, thereby improving the overall strength and performance of the building.

[0111] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A type of cast-in-place concrete for reinforcing an enlarged cross-section of an outer steel pipe, characterized in that, By weight, it includes the following ingredients: 15-25 parts sulfoaluminate cement; 15-25 parts fine aggregate; 20-30 parts coarse aggregate; Water 10-16 parts; modified nano-silica 0.4-0.6 parts; modified sodium bentonite 6-8 parts; composite expanding agent 2-8 parts; phosphorus slag 4-6 parts; water reducing agent 0.4-0.6 parts; composite activator 2-6 parts; The composite expanding agent is composed of sodium sulfoaluminate, calcium oxide and calcium aluminate mixed in a mass ratio of (0.6-0.7):(1.4-1.6):1, and its particle size is 300-500 nm. The modified nano-silica was prepared by successively modifying nano-silica with trichlorotriazine and polyethylene oxide. The modified sodium-based bentonite is obtained by calcining sodium-based bentonite at 700-800℃ for 1-2 hours, followed by grinding and sieving, with a particle size of 150-200nm.

2. The cast-in-place concrete for reinforcing the outer steel pipe with increased cross-section according to claim 1, characterized in that, The sulfoaluminate cement is a self-stressing sulfoaluminate cement with a strength grade of 42.

5.

3. The cast-in-place concrete for reinforcing the outer steel pipe with increased cross-section according to claim 1, characterized in that, The fine aggregate is selected from sand with a mesh size of 200-240; the coarse aggregate is selected from recycled aggregate with a particle size of 5-25mm.

4. The cast-in-place concrete for reinforcing the outer steel pipe with increased cross-section according to claim 1, characterized in that, The water-reducing agent is a mixture of sodium carbonate, calcium lignosulfonate and sodium alkyl sulfate in a mass ratio of (0.7-0.8):(1.1-1.3):1, and has a particle size of 700-900 nm.

5. The cast-in-place concrete for reinforcing the outer steel pipe with increased cross-section according to claim 1, characterized in that, The phosphorus slag has a particle size of 10-14 μm and a specific surface area of ​​400-600 m² as determined by nitrogen adsorption. 2 / kg, with a mass coefficient K of 1.3-1.

4.

6. The cast-in-place concrete for reinforcing the outer steel pipe with increased cross-section according to claim 1, characterized in that, The composite activator is a mixture of sodium silicate and sodium hydroxide powder.

7. A method for preparing cast-in-place concrete for reinforcing an outer steel pipe with an enlarged cross-section according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Prepare each raw material according to the weight proportions described in claim 1, place the modified nano-silica in water, and treat it with ultrasound to obtain a mixed solution; S2. Mix cement, fine aggregate, coarse aggregate, and phosphorus slag to obtain mixture A; calcine modified sodium bentonite, water-reducing agent, and composite activator to obtain mixture B. S3. Mix the mixture A and the mixture B evenly, then add the mixed solution and mix evenly to obtain a mixed slurry; S4. Add a composite expansion agent to the mixed slurry, mix well, and then vibrate and cure to obtain the grouting concrete for reinforcing the outer steel pipe with an enlarged cross section.

Images