Cement-based grouting mortar for reinforcing steel pipe jacket with enlarged section and preparation method and application thereof

Abstract

This invention provides a cement-based grouting mortar for reinforcing enlarged cross-sections of outer steel pipes. By weight, it comprises: 20-40 parts sulfoaluminate cement; 30-40 parts fine aggregate; 10-16 parts water; 6-10 parts rice husk ash; 0.3-0.7 parts modified nano-magnesium oxide; 0.3-0.7 parts modified rice straw fiber; 3-7 parts modified steel fiber; and 6-10 parts composite modified emulsion. This invention also provides a method for preparing the above-mentioned cement-based grouting mortar for reinforcing enlarged cross-sections of outer steel pipes, which has the advantages of simple process flow and easy promotion. Compared with traditional grouting materials, the cement-based grouting mortar prepared by this invention has advantages such as high mechanical strength and impermeability, good toughness, high fluidity, and good volume stability. It can be widely used in reinforcing concrete, steel-concrete composite, steel pipe, and structural steel components with enlarged cross-sections of outer steel pipes. It is particularly suitable for grouting construction when the distance between the outer steel pipe and the original component is small, and has broad prospects for promotion and application.

Description

Technical Field

[0001] This invention belongs to the field of concrete, steel-concrete composite, steel pipe and steel section reinforcement technology, specifically relating to a cement-based grouting mortar for reinforcing steel pipes with enlarged cross-sections, its preparation method and application. Background Technology

[0002] Currently, a significant number of existing building structures, including concrete, steel-concrete composite, steel pipe, and steel profile structures, are facing structural performance degradation due to physical aging and chemical corrosion, structural damage from natural disasters such as floods and fires, or design and construction errors that prevent them from meeting code requirements. These issues have seriously affected the safety and usability of these structures. Demolishing and rebuilding these structures would not only consume substantial manpower and resources but also require a lengthy process, leading to dust and noise pollution, and generating large amounts of non-biodegradable construction waste that severely impacts the environment. Therefore, to ensure safety, guarantee sustainable socio-economic development, and comprehensively eliminate safety hazards, it is crucial to utilize reasonable and effective reinforcement technologies to improve the load-bearing capacity of concrete, steel-concrete composite, steel pipe, and steel profile structures, thereby restoring and extending their service life.

[0003] Among the many research directions on novel structural forms, the steel tube enlargement reinforcement method has broad application prospects. Traditionally, the core concrete material in the steel tube enlargement method is ordinary concrete. In recent years, researchers have attempted to replace ordinary concrete with new concrete materials, such as self-compacting concrete, expansive concrete, high-strength concrete, fiber-reinforced concrete, and recycled concrete. The main purpose of using self-compacting concrete, expansive concrete, high-strength concrete, and fiber-reinforced concrete is to improve the workability and compressive mechanical properties of steel tube concrete. The main purpose of using recycled concrete is to transform construction waste into usable concrete aggregate, thus "turning waste into treasure" through the steel tube concrete structure and achieving resource conservation.

[0004] However, when the distance between the outer steel pipe and the original component is small (less than 25mm), if concrete is used to fill the gap between them, problems such as incomplete compaction or gaps between the steel pipes will usually occur. This weakens the squeezing effect between the concrete and the steel pipe, and the triaxial compressive strength of the concrete cannot be fully utilized, ultimately causing potential engineering hazards.

[0005] Based on this, for working conditions where the distance between the outer steel pipe and the original component is small, it is urgent to study and develop a new type of cement-based grouting mortar for reinforcing the outer steel pipe by increasing its cross-section, so as to achieve effective and reliable filling of the gap between the outer steel pipe and the original component and enhance the overall mechanical strength of the matrix. Summary of the Invention

[0006] One of the objectives of this invention is to provide a novel cement-based grouting mortar for reinforcing enlarged cross-sections of outer steel pipes, which has high compressive strength, good waterproof performance, good flowability, and micro-expansion characteristics, so as to achieve effective and reliable filling of the gap between the outer steel pipe and the original component and enhance the overall mechanical strength of the matrix.

[0007] The second objective of this invention is to provide a method for preparing a novel cement-based grouting mortar for reinforcing steel pipes with enlarged cross-sections.

[0008] The third objective of this invention is to provide an application of a new type of cement-based grouting mortar for reinforcing steel pipes with enlarged cross-sections.

[0009] One of the technical solutions adopted to achieve the objective of this invention is: providing a cement-based grouting mortar for reinforcing steel pipes with enlarged cross-sections, comprising the following raw materials by weight:

[0010] 20-40 parts of sulfoaluminate cement; 30-40 parts of fine aggregate; 10-16 parts of water; 6-10 parts of rice husk ash; 0.3-0.7 parts of modified nano-magnesium oxide; 0.3-0.7 parts of modified rice straw fiber; 3-7 parts of modified steel fiber; 6-10 parts of composite modified emulsion.

[0011] The overall concept of this invention for a cement-based grouting mortar used for reinforcing steel pipes with enlarged cross-sections is as follows: To impart better comprehensive performance to the cement-based grouting mortar, this invention starts with the raw materials, screening the types and amounts of raw materials to coordinate and modify the various properties of the cement-based grouting material matrix at multiple scales from the microscale to the mesoscale to the macroscale (nanoscale to microscale to millimeter scale).

[0012] Among them, modified nano-magnesium oxide, as a nanoscale modifying material, has a micro-expansion effect, which can improve the expansion rate of the matrix and help achieve a better filling effect. At the same time, it can also utilize the nano-nucleation effect, nano-filling effect and nano-bridging effect of modified nano-magnesium oxide to promote the degree of hydration reaction of the matrix, optimize the internal pore structure (reduce porosity and increase the proportion of internal gel pores), thereby densifying the internal structure and improving the mechanical strength and impermeability of the matrix.

[0013] Modified rice straw fiber, as a micron-scale modified raw material, has two advantages. First, its excellent elastic modulus enables effective connection of cracks and pores in the matrix, improving the mechanical strength and impermeability of the matrix. Second, modified rice straw fiber can also serve as a grafting carrier for modified nano-magnesium oxide, effectively dispersing nanomaterials, optimizing the proportion of gel pores, and enhancing the mechanical strength of the matrix.

[0014] Modified steel fiber, as a millimeter-scale modifying material, utilizes the strong tensile strength (greater than 100MPa) of steel fiber to dissolve cracks in the matrix into scattered microcracks, avoiding stress concentration and thus enhancing the mechanical strength of the matrix.

[0015] Preferably, the sulfoaluminate cement is selected from self-stressing sulfoaluminate cement with a strength grade of 42.5.

[0016] Preferably, the fine aggregate is selected from sand with a mesh size of 250 to 300.

[0017] Preferably, the rice husk ash is obtained by calcining rice husks at 700-800℃ for 1-2 hours, followed by grinding and sieving, and its particle size is 200-300nm.

[0018] Furthermore, the modified nano-magnesium oxide is prepared by successively modifying nano-magnesium oxide with thionyl chloride and an organic diol; the outer diameter of the nano-magnesium oxide is 10–50 nm, and the length is 1.5–2.5 μm. The nano-magnesium oxide raw material used in this invention is rod-shaped, which has a better nano-bridging effect, and can better bridge pores and voids at the microscale, improving the density and strength of the matrix. The organic diol includes ethylene glycol, propylene glycol, or bisphenol A, etc.

[0019] In some preferred embodiments, the preparation method of the modified nano-magnesium oxide includes: mixing nano-magnesium oxide with an outer diameter of 10-50 nm and a length of 1.5-2.5 μm with thionyl chloride in a solvent at a mass ratio of (1-2):(3-6), treating at 60-80°C for 2-4 h, centrifuging to obtain a solid product, washing and drying to obtain a first product; mixing the first product with pyridine and an organic diol in N,N'-dimethylacetamide, reacting at 50-70°C for 6-8 h, removing the organic solvent and pyridine, washing and drying to obtain modified nano-magnesium oxide; the mass ratio of the first product to the organic diol is (5-10):(2-4).

[0020] Furthermore, the modified rice straw fiber is prepared by successively modifying rice straw fiber with alkali and silane coupling agent, with a length of 0.6–0.9 cm. Alkali modification softens the rice straw fiber and removes lignocellulose and impurities from its surface. Silane coupling agent is grafted onto the rice straw fiber, bridging the modified rice straw fiber and modified nano-magnesium oxide during the later preparation process. This not only facilitates the dispersion of modified nano-magnesium oxide but also improves the mechanical strength and impermeability of the matrix.

[0021] Preferably, the alkali modification includes: soaking in a 10-20% NaOH aqueous solution for 1-2 hours, followed by rinsing with water, and then drying at 80-100°C for 2-3 hours; the silane coupling agent modification includes: soaking in an acetone solution of a 20-30% silane coupling agent for 2-4 hours. Preferably, the silane coupling agent used is KH570.

[0022] Furthermore, the modified steel fiber is obtained by acid treatment of steel fiber, and has a length of 10-20 mm and a diameter of 0.4-0.5 mm. The modified steel fiber has hooks at both ends. The acid treatment step can remove oxides and impurities from the surface of the steel fiber. Preferably, the acid treatment includes: immersing the steel fiber in a mixed solution of concentrated nitric acid and concentrated sulfuric acid for 1-2 hours, followed by rinsing with a large amount of anhydrous ethanol. Preferably, the volume ratio of concentrated nitric acid to concentrated sulfuric acid in the mixed solution is (2-3):1.

[0023] Furthermore, the composite emulsion is composed of an acrylate microemulsion modified with a silane coupling agent and an epoxy resin emulsion modified with a silane coupling agent; its solid content is 30-40%, and its average particle size is 150-200 nm. Preferably, the mass ratio of the acrylate microemulsion modified with a silane coupling agent to the epoxy resin emulsion modified with a silane coupling agent is (3-6):1.

[0024] In this invention, the addition of the composite emulsion serves two purposes. First, it improves the fluidity of cement-based grouting mortar by entraining air and reducing water content, preventing grout loss and thus significantly enhancing its impermeability. Second, the composite emulsion possesses strong adhesive properties, rapidly filling cracks and effectively preventing their formation. It also exhibits good dispersibility, filling pores and cracks caused by uneven mixing and contributing to the homogenization of the mortar's internal structure. This enhances internal adhesion and forms a network structure, which significantly reduces the settling of fine aggregates, ensuring their uniform dispersion within the matrix and thereby strengthening internal mechanical strength and impermeability.

[0025] The second objective of this invention is achieved by providing a method for preparing cement-based grouting mortar for reinforcing steel pipes with enlarged cross-sections, as described in one objective of this invention, comprising the following steps:

[0026] S1. Prepare the raw materials according to the following weight proportions: 20-40 parts of sulfoaluminate cement; 30-40 parts of fine aggregate; 10-16 parts of water; 6-10 parts of rice husk ash; 0.3-0.7 parts of modified nano-magnesium oxide; 0.3-0.7 parts of modified rice straw fiber; 3-7 parts of modified steel fiber; 6-10 parts of composite modified emulsion.

[0027] S2. Modified nano-magnesium oxide and modified rice straw fiber are placed in water and subjected to ultrasonic treatment to obtain a mixed solution;

[0028] S3. Sulfoaluminate cement, fine aggregate, rice husk ash and modified steel fiber are mixed to obtain a mixture; the mixed solution is added to the mixture and mixed evenly to obtain the grouting mortar.

[0029] S4. Add composite modified emulsion to the grouting mortar, mix well, and then vibrate and cure to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0030] Preferably, in step S2, the ultrasonic treatment power is 700-800W and the ultrasonic treatment time is 0.3-0.5h; in this step, the modified nano-magnesium oxide is grafted onto the modified rice straw fiber with the assistance of ultrasound, and the modified nano-magnesium oxide is uniformly dispersed.

[0031] Preferably, in step S3, the mixing time of the mixture is 180-210 s; the mixing time of adding the mixing solution to the mixture is 180-240 s.

[0032] Preferably, in step S4, the mixing time for adding the composite modified emulsion is 240–300 s; the curing is carried out under normal temperature conditions.

[0033] The third objective of this invention is achieved by providing an application of cement-based grouting mortar for reinforcing the outer steel pipe with an enlarged cross-section, as described in one of the objectives of this invention, comprising: filling the gap between the outer steel pipe and the outer surface of the original component using the cement-based grouting mortar for reinforcing the outer steel pipe with an enlarged cross-section.

[0034] Preferably, the gap between the outer steel pipe and the outer surface of the original component is less than 25mm.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) The present invention provides a cement-based grouting mortar for reinforcing the cross section of an outer steel pipe. It adopts a certain proportion of modified nano magnesium oxide, modified rice straw fiber and modified steel fiber in combination, and the multi-scale interactive design from nano to micro to millimeter significantly improves the flow performance, expansion performance and compressive strength of the cement-based grouting mortar for reinforcing the cross section of an outer steel pipe.

[0037] (2) The present invention provides a cement-based grouting mortar for reinforcing the cross section of an outer steel pipe. Its raw materials are low-cost industrial or agricultural waste such as rice husk ash and rice straw fiber, which can reduce the project cost and effectively solve the problem of centralized stacking of industrial or agricultural waste, and has the advantage of turning waste into treasure.

[0038] (3) The present invention provides a method for preparing cement-based grouting mortar for reinforcing steel pipes with enlarged cross-sections. The preparation process is simple and easy to promote. Compared with traditional grouting materials, the cement-based grouting mortar prepared by the present invention has advantages such as high strength, good toughness, high fluidity, and good volume stability. It can be widely used in reinforcing concrete, steel pipe concrete, steel pipe and structural steel components with enlarged cross-sections of steel pipes. It is particularly suitable for grouting construction when the distance between the steel pipe and the original component is small (less than 25mm), and has broad prospects for promotion and application. Attached Figure Description

[0039] Figure 1 This is a schematic flowchart illustrating a method for preparing cement-based grouting mortar for reinforcing an outer steel pipe with an enlarged cross-section, as provided in an embodiment of the present invention. Detailed Implementation

[0040] 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.

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0042] 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.

[0043] The mass fractions of the main raw materials involved in Examples 1-7 and Comparative Examples 1-3 of the present invention are shown in Table 1 below.

[0044] Table 1

[0045]

[0046]

[0047] In the above table,

[0048] The cement is selected from 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 250-300; the rice husk ash is obtained by calcining rice husks at 700-800℃ for 1-2 hours, followed by grinding and sieving, with a particle size of 200-300 nm; the modified rice straw fiber is obtained by successively modifying rice straw fiber with alkali and silane coupling agent, with a length of 0.6-0.9 cm. The modified steel fiber is obtained by acid treatment of steel fiber, with a length of 10-20 mm and a diameter of 0.4-0.5 mm, and the modified steel fiber has hooks at both ends; the composite emulsion is a mixture of silane coupling agent modified acrylate microemulsion and epoxy resin emulsion in a mass ratio of (3-6):1; its solid content is 15-20%, and the average particle size is 150-200 nm.

[0049] The preparation method of modified nano-magnesium oxide is as follows:

[0050] (1) Select 2-4g of nano-magnesium oxide and ball mill it for 12-18h at a speed of 500-800rpm with automatic rotation direction change every 10-20min to obtain nano-magnesium oxide with an average outer diameter of 10-50nm and an average length of 1.5-2.5um; wash it with water and vacuum dry it at 50-70℃ for 15-25h before use.

[0051] (2) Mix 0.5-1g of nano magnesium oxide treated in step (1) above with 1.5-3g of thionyl chloride in 3-5mL of N-methylpyrrolidone organic solvent, stir at 60-80℃ for 2-4h, centrifuge at 4000-5000rpm for 20-30min to separate the solid, wash the separated solid with tetrahydrofuran organic solvent, and then vacuum dry at 40-50℃ for 10-15h.

[0052] (3) Under argon protection, 0.5-1g of nano magnesium oxide, 1-1.5mL of pyridine and 0.2-0.4g of organic diol after the above step (2) are mixed in 50-80mL of N,N'-dimethylacetamide organic solvent and reacted at 50-70℃ for 6-8h. The N,N'-dimethylacetamide organic solvent and pyridine are removed by vacuum evaporation, and then washed with tetrahydrofuran solvent. After that, the mixture is dried under vacuum at 40-50℃ for 12-18h to obtain modified nano magnesium oxide.

[0053] Example 1

[0054] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0055] Step 2: Place 0.5 parts of modified nano magnesium oxide and 0.5 parts of modified rice straw fiber in 13 parts of water, stir for 180s, and then sonicate at 750W for 0.4h to obtain a uniform mixed solution.

[0056] Step 3: Mix 30 parts of sulfoaluminate cement, 35 parts of medium-coarse sand, 8 parts of rice husk ash and 5 parts of modified steel fiber and dry stir for 180 seconds. Then add the mixture to the above uniform solution and stir for 200 seconds to obtain the grouting mortar.

[0057] Step 4: Add 8 parts of composite modified emulsion to the grouting mortar, stir for 270 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0058] Example 2

[0059] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0060] Step 2: Place 0.4 parts of modified nano magnesium oxide and 0.6 parts of modified rice straw fiber into 13 parts of water, stir for 210s, and then sonicate under an ultrasonic power of 800W for 0.5h to obtain a uniform mixed solution.

[0061] Step 3: Mix 35 parts of sulfoaluminate cement, 30 parts of medium-coarse sand, 8 parts of rice husk ash and 6 parts of modified steel fiber and dry stir for 180 seconds. Then add the mixture to the above uniform solution and stir for 200 seconds to obtain the grouting mortar.

[0062] Step 4: Add 7 parts of composite modified emulsion to the grouting mortar, stir for 300 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0063] Example 3

[0064] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0065] Step 2: Place 0.5 parts of modified nano magnesium oxide and 0.5 parts of modified rice straw fiber in 14 parts of water, stir for 180s, and then sonicate at 750W for 0.4h to obtain a uniform mixed solution.

[0066] Step 3: Mix 25 parts of sulfoaluminate cement, 40 parts of medium-coarse sand, 7 parts of rice husk ash and 5 parts of modified steel fiber and dry stir for 210 seconds. Then add the mixture to the above uniform solution and stir for 240 seconds to obtain the grouting mortar.

[0067] Step 4: Add 8 parts of composite modified emulsion to the grouting mortar, stir for 270 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0068] Example 4

[0069] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0070] Step 2: Place 0.4 parts of modified nano magnesium oxide and 0.6 parts of modified rice straw fiber into 16 parts of water, stir for 180s, and then sonicate under 750W ultrasonic power for 0.3h to obtain a uniform mixed solution.

[0071] Step 3: Mix 32 parts of sulfoaluminate cement, 33 parts of medium and coarse sand, 8 parts of rice husk ash and 4 parts of modified steel fiber and dry stir for 210 seconds. Then add the mixture to the above uniform solution and stir for 180 seconds to obtain the grouting mortar.

[0072] Step 4: Add 6 parts of composite modified emulsion to the grouting mortar, stir for 270 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0073] Example 5

[0074] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0075] Step 2: Place 0.6 parts of modified nano magnesium oxide and 0.4 parts of modified rice straw fiber into 10 parts of water, stir for 180s, and then sonicate under 700W ultrasonic power for 0.5h to obtain a uniform mixed solution.

[0076] Step 3: Mix 40 parts of sulfoaluminate cement, 33 parts of medium and coarse sand, 6 parts of rice husk ash and 3 parts of modified steel fiber and dry stir for 200 seconds. Then add the mixture to the above uniform solution and stir for 210 seconds to obtain the grouting mortar.

[0077] Step 4: Add 7 parts of composite modified emulsion to the grouting mortar, stir for 260 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0078] Example 6

[0079] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0080] Step 2: Place 0.7 parts of modified nano magnesium oxide and 0.3 parts of modified rice straw fiber into 13 parts of water, stir for 180s, and then sonicate under 750W ultrasonic power for 0.4h to obtain a uniform mixed solution.

[0081] Step 3: Mix 29 parts of sulfoaluminate cement, 30 parts of medium-coarse sand, 10 parts of rice husk ash and 7 parts of modified steel fiber and dry stir for 180 seconds. Then add the mixture to the above uniform solution and stir for 220 seconds to obtain the grouting mortar.

[0082] Step 4: Add 10 parts of composite modified emulsion to the grouting mortar, stir for 280 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0083] Example 7

[0084] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0085] Step 2: Place 0.3 parts of modified nano magnesium oxide and 0.7 parts of modified rice straw fiber into 16 parts of water, stir for 180s, and then sonicate under an ultrasonic power of 800W for 0.3h to obtain a uniform mixed solution.

[0086] Step 3: Mix 20 parts of sulfoaluminate cement, 40 parts of medium-coarse sand, 10 parts of rice husk ash and 5 parts of modified steel fiber and dry stir for 190 seconds. Then add the mixture to the above uniform solution and stir for 220 seconds to obtain the grouting mortar.

[0087] Step 4: Add 8 parts of composite modified emulsion to the grouting mortar, stir for 280 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0088] Comparative Example 1

[0089] Compared with Example 1, this comparative example does not contain 0.5 parts of modified nano-magnesium oxide in the raw materials. The specific preparation method is as follows:

[0090] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0091] Step 2: Place 0.5 parts of modified rice straw fiber in 13 parts of water, stir for 180s, and then sonicate at 750W for 0.4h to obtain a uniform mixed solution.

[0092] Step 3: Mix 30 parts of sulfoaluminate cement, 35 parts of medium-coarse sand, 8 parts of rice husk ash and 5 parts of modified steel fiber and dry stir for 180 seconds. Then add the mixture to the above uniform solution and stir for 200 seconds to obtain the grouting mortar.

[0093] Step 4: Add 8 parts of composite modified emulsion to the grouting mortar, stir for 270 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0094] Comparative Example 2

[0095] Compared with Example 1, this comparative example does not contain 0.5 parts of modified rice straw fiber in its raw materials. The specific preparation method is as follows:

[0096] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0097] Step 2: Place 0.5 parts of modified nano magnesium oxide in 13 parts of water, stir for 180s, and then sonicate at 750W for 0.4h to obtain a homogeneous mixed solution.

[0098] Step 3: Mix 30 parts of sulfoaluminate cement, 35 parts of medium-coarse sand, 8 parts of rice husk ash and 5 parts of modified steel fiber and dry stir for 180 seconds. Then add the mixture to the above uniform solution and stir for 200 seconds to obtain the grouting mortar.

[0099] Step 4: Add 8 parts of composite modified emulsion to the grouting mortar, stir for 270 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0100] Comparative Example 3

[0101] Compared to Example 1, this comparative example does not contain 5 parts of modified steel fiber in the raw materials. The specific preparation method is as follows:

[0102] Step 1: Prepare each raw material according to the weight proportions shown in Table 1;

[0103] Step 2: Place 0.5 parts of modified nano magnesium oxide and 0.5 parts of modified rice straw fiber in 13 parts of water, stir for 180s, and then sonicate at 750W for 0.4h to obtain a uniform mixed solution.

[0104] Step 3: Mix 30 parts of sulfoaluminate cement, 35 parts of medium and coarse sand and 8 parts of rice husk ash and dry stir for 180 seconds. Then add the mixture to the above uniform solution and stir for 200 seconds to obtain the grouting mortar.

[0105] Step 4: Add 8 parts of composite modified emulsion to the grouting mortar, stir for 270 seconds, vibrate, and cure at room temperature to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

[0106] Performance testing

[0107] The present invention uses GB50081-2002, GB / T2419-2005, GB / T 23439 and JC / T984-2011 standards to test the relevant performance of Examples 1-7 and Comparative Examples 1-3. The specific test results are shown in Table 2.

[0108] Table 2 Performance Test Results of Cement-Based Grouting Material for Enlarging Cross-Section Reinforcement of Outer Steel Pipe

[0109]

[0110] As can be seen from the above table,

[0111] Compared to Example 1, Comparative Examples 1-3, which removed modified nano-magnesium oxide, modified rice straw fiber, and modified steel fiber from their raw materials, exhibited problems such as low compressive strength and impermeability, poor fluidity, and poor expansion properties in their cement-based grouting mortars. This indicates that the synergistic effect of modified nano-magnesium oxide, modified rice straw fiber, and modified steel fiber, working at multiple scales from nanometer to micrometer to millimeter, plays a positive role in improving the fluidity, expansion properties, and compressive strength of cement-based grouting mortars.

[0112] The cement-based grouting mortars prepared in Examples 1-7 of this invention exhibit a 28-day compressive strength of 80-98 MPa and a seepage resistance of 5.6-7.6 MPa, demonstrating high mechanical strength and impermeability. Furthermore, these mortars possess good fluidity (205-235 mm) and certain expansion characteristics (28-day restricted expansion rate of 0.35%-0.52%), enabling them to effectively and reliably fill narrow gaps between the outer steel pipe and the outer surface of the original component, thereby improving the overall strength and performance of the building structure.

[0113] 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 cement-based grouting mortar for reinforcing an outer steel pipe with an enlarged cross-section, characterized in that, By weight, it includes the following ingredients: 20-40 parts of sulfoaluminate cement; 30-40 parts of fine aggregate; 10-16 parts of water; 6-10 parts of rice husk ash; 0.3-0.7 parts of modified nano-magnesium oxide; 0.3-0.7 parts of modified rice straw fiber; 3-7 parts of modified steel fiber; 6-10 parts of composite modified emulsion; The modified nano-magnesium oxide is prepared by successively modifying nano-magnesium oxide with thionyl chloride and organic diol; the outer diameter of the nano-magnesium oxide is 10-50 nm and the length is 1.5-2.5 μm.

2. The cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section as described in claim 1, characterized in that, The sulfoaluminate cement is selected from self-stressing sulfoaluminate cement with a strength grade of 42.

5.

3. The cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section as described in claim 1, characterized in that, The fine aggregate is selected from sand with a mesh size of 250-300.

4. The cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section as described in claim 1, characterized in that, The rice husk ash is obtained by calcining rice husks at 700-800℃ for 1-2 hours, followed by grinding and sieving, with a particle size of 200-300nm.

5. The cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section according to claim 1, characterized in that, The modified rice straw fiber is obtained by successively modifying rice straw fiber with alkali and silane coupling agent, and its length is 0.6-0.9cm.

6. The cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section according to claim 1, characterized in that, The modified steel fiber is obtained by acid treatment of steel fiber, and its length is 10-20 mm and its diameter is 0.4-0.5 mm. The modified steel fiber has hooks at both ends.

7. The cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section according to claim 1, characterized in that, The composite modified emulsion is composed of an acrylate microemulsion modified with a silane coupling agent and an epoxy resin emulsion modified with a silane coupling agent; the solid content of the composite modified emulsion is 30%-40%, and the average particle size is 150-200nm.

8. A method for preparing cement-based grouting mortar for reinforcing an outer steel pipe with an enlarged cross-section according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Prepare each raw material according to the weight proportions described in claim 1; S2. Modified nano-magnesium oxide and modified rice straw fiber are placed in water and subjected to ultrasonic treatment to obtain a mixed solution; S3. Sulfoaluminate cement, fine aggregate, rice husk ash and modified steel fiber are mixed to obtain a mixture; the mixed solution is added to the mixture and mixed evenly to obtain the grouting mortar. S4. Add composite modified emulsion to the grouting mortar, mix well, and then vibrate and cure to obtain cement-based grouting mortar for reinforcing the outer steel pipe with increased cross-section.

9. An application of cement-based grouting mortar for reinforcing enlarged cross-sections of outer steel pipes according to any one of claims 1-7, characterized in that, The gap between the outer steel pipe and the outer surface of the original component is filled with cement-based grouting mortar to increase the cross-section of the outer steel pipe for reinforcement.

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