High-performance green cement-based grouting material and construction method

Abstract

The invention belongs to the technical field of high-performance grouting materials, and particularly relates to a high-performance green cement-based grouting material and a construction method. The problems that steel fibers of an existing grouting material are prone to sedimentation, porosity caused by regenerated sand is high, and durability is poor are solved. According to the grouting material, a cementing material, modified reclaimed sand compound fine aggregate, nano SiO2 modified composite fibers and the like are used as raw materials, reclaimed sand is subjected to ball milling and dihydric phosphate soaking modification, pores are blocked, and an interface is optimized; the composite fiber is activated, coated and modified to inhibit sedimentation of the steel fiber. The obtained grouting material has the advantages of good fluidity, early strength, high strength, compactness and durability, has the advantage of solid waste utilization, and is suitable for grouting construction of prefabricated buildings and bridge sleeves.

Description

Technical Field

[0001] This invention belongs to the field of high-performance grouting material technology, specifically relating to a high-performance green cement-based grouting material and its construction method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Against the backdrop of the rapid development of prefabricated building construction and intelligent bridge construction technology, sleeve grouting material, as a core material for ensuring reliable connection of reinforcing bars in prefabricated components, directly determines the seismic resistance and overall load-bearing capacity of the structure. Adding steel fibers to high-performance grouting materials can effectively improve the material's crack resistance, toughness, and mechanical strength. Adding modified recycled sand can achieve resource utilization of construction waste, reduce production costs, optimize aggregate gradation, and ensure the density and durability of the grouting material, thus balancing environmental protection and performance. However, the addition of these materials also brings related problems that severely restrict the large-scale application in the industry: Firstly, steel fiber settling leads to performance degradation. To improve crack resistance and long-term strength, steel fibers need to be incorporated into the grout. However, under high fluidity requirements, steel fibers easily settle and stratify within the grout due to density differences. This directly causes two major problems: settling causes fibers to accumulate at the bottom, while the middle and upper parts are lacking, resulting in a significant decrease in the crack resistance and toughening capacity of critical connection areas; weakened interfacial bonding: the loss of homogeneity in the grout after fiber settling weakens the synergistic stress-bearing performance of the reinforcing steel, grout, and sleeve, creating potential for connection failure. Intelligent prefabricated bridge-building machines require sleeve connections to reach design strength and bear dynamic loads in a very short time. The strength dispersion and insufficient long-term reliability of existing grouts due to steel fiber settling seriously hinder the large-scale application of rapid connection technology for precast components. Simultaneously, the incorporation of recycled sand further exacerbates the inhomogeneity of the material's internal structure, making the above problems even more prominent.

[0004] Secondly, the performance defects caused by the addition of recycled sand. While recycled sand, as a recyclable material from crushed construction waste, can effectively reduce production costs when added, its inherent defects also bring many problems. The surface of recycled sand is covered with loose, porous hardened cement stone, resulting in high porosity, high water absorption, and a rough, angular surface. Direct addition will preferentially absorb water and cementitious components from the grout, leading to increased viscosity, decreased fluidity, and poor filling performance of the grout, easily forming pores and weak interfaces internally. Furthermore, the poor interfacial bonding between recycled sand and new grout results in a loose and enriched transition zone. Combined with the inability to effectively fill the original pores of the recycled sand, this leads to an increase in interconnected pores, increased overall porosity, and decreased density after the grout hardens, thus affecting the strength, durability, and volume stability of the grout.

[0005] Therefore, developing a high-performance green cement-based grout that can effectively suppress steel fiber settling, make full use of recycled sand and overcome its inherent defects, and possess high fluidity, micro-expansion, high strength and excellent durability has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides the following technical solution: In a first aspect, a high-performance green cement-based grouting material is provided, wherein the raw materials of the grouting material comprise the following components in parts by weight: 80-120 parts of cementitious material, 55-65 parts of fine aggregate, 3-9 parts of nano-SiO2 modified composite fiber, 20-30 parts of water, and 1-5 parts of admixture.

[0007] The cementitious material is preferably silicate-based cement, and more preferably early-strength type, including but not limited to one or a combination of several of PO42.5R ordinary silicate cement, PO52.5R ordinary silicate cement, PI42.5R silicate cement, PI52.5R silicate cement, and PC42.5R composite silicate cement.

[0008] Fine aggregate is a mixture of natural sand or manufactured sand and recycled sand in a mass ratio of 1 to 4:1. To address the shortcomings of existing technologies where recycled sand affects the overall porosity and reduces durability of grouting materials, this invention involves ball milling and dihydrogen phosphate soaking of the recycled sand. Ball milling aims to break up the loose, hardened cement paste adhering to the surface of the recycled sand through mechanical grinding and impact, resulting in denser particles and a more rounded particle shape. Dihydrogen phosphate reacts with Ca(OH)₂ and cement stone in the recycled sand to generate dense calcium phosphate products, effectively plugging pores, strengthening the aggregate surface, ensuring the fluidity of the grouting material, and reducing the porosity of the hardened grouting material. In some embodiments with better results, the preparation method of the recycled sand is as follows: Construction waste is used as raw material. After sorting and impurity removal, it is first crushed by a jaw crusher to obtain recycled coarse aggregate with a particle size of less than 25 mm, and then crushed by an impact crusher to obtain recycled coarse aggregate with a particle size of less than 10 mm. The aggregate is then sieved, and fine aggregate with a particle size of 0.075 mm to 2.35 mm is retained for ball milling. The ball-milled fine aggregate is then immersed in a 5% to 10% (w / w) solution of dihydrogen phosphate at room temperature for 2 to 4 hours, allowing the solution to fully penetrate into the surface pores and weak hydration product layer of the recycled sand. Afterward, the aggregate is removed, excess solution is filtered off, and it is dried at 60 to 80°C. The dihydrogen phosphate reacts with calcium hydroxide, calcium silicate hydrate, and other products on the surface of the recycled sand to form a dense calcium phosphate mineral phase, which fills and seals the surface pores, thereby achieving surface densification modification of the recycled sand. Further feasible dihydrogen phosphates include sodium dihydrogen phosphate (NaH2PO4) or potassium dihydrogen phosphate (KH2PO4).

[0009] Nano-SiO2 modified composite fiber is a composite fiber with a surface coated with nano-silica. To prevent steel fibers from settling during grouting and mixing, this invention provides a nano-SiO2 modified composite fiber. The main improvement of this method compared to existing technologies is that the composite fiber is pre-etched with an acidic activation solution, thereby enhancing the subsequent nano-SiO2 coating effect, effectively increasing the yield of cementitious substances in the grout, and improving the gel strength of the grout. The preparation method of the nano-SiO2 modified composite fiber includes the following steps: The composite fiber is immersed in an activation solution at 35-45°C for activation, and dried to obtain activated composite fiber. The activated composite fiber is added to an anhydrous ethanol solution of a silane coupling agent and reacted at 35-45°C for 30-40 minutes. Then, nano-SiO2 is slowly added, and the reaction continues at the above temperature for 25-35 minutes, followed by drying to obtain the final product.

[0010] Furthermore, the above-mentioned method for preparing nano-SiO2 modified composite fibers also has the following preferred embodiments: The composite fiber is a mixture of PVA fiber and steel fiber in a mass ratio of 21~25:75~79, wherein the PVA fiber has a length of 11~13mm and a fineness of 1100~1300D, and the steel fiber has a length of 12~14mm and a diameter of 0.18~0.22mm.

[0011] The activation solution is prepared as follows: water and anhydrous ethanol are mixed at a volume ratio of 1:5~10, then polyethylene glycol is added to a mass fraction of 0.5~2%, and hydrogen peroxide is added to a mass fraction of 1~3%.

[0012] The silane coupling agent is KH-550, and an anhydrous ethanol solution of the silane coupling agent is prepared according to a mass ratio of KH-550: anhydrous ethanol: water of 1:8~12:1~3.

[0013] The amount of nano-SiO2 added is 3-8% of the mass of the composite fiber.

[0014] Admixtures used in the above-mentioned grouting materials should be chlorine-free and low-alkali components. Optional admixtures include, but are not limited to, high-performance water-reducing agents (such as polycarboxylic acids), micro-expansion agents (such as ettringite type / calcium sulfoaluminate type), early-strength agents (such as calcium formate, alkanolamines, and sodium sulfate complexes), retarders (such as sodium gluconate, citric acid, or polycarboxylic acid retarder), defoamers (such as organosilicones and polyethers), water-retaining agents / thickening agents (such as low-viscosity HPMC and polyethers), fiber dispersants, anti-permeability agents (organosilicones), and antifreeze agents (sodium nitrite-potassium carbonate composites).

[0015] Secondly, a construction method for the cement-based grouting material described in the first aspect is provided, comprising the following steps: After thoroughly dry-mixing 80-120 parts of cementitious material, 55-65 parts of fine aggregate, and nano-SiO2 modified composite fiber, add water with mixed additives and continue stirring until the slurry becomes fluid. After standing and degassing, use gravity or pressure grouting, and continuously grout in a single batch until full. After initial setting, cover and cure.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. By ball milling and immersion modification of recycled sand with dihydrogen phosphate, the surface pores of aggregate are effectively sealed and the interface transition zone is optimized, which significantly reduces the porosity of the grout after hardening, improves its density and durability, and realizes the resource utilization of construction waste, thereby reducing costs.

[0017] 2. Nano-SiO2 modified composite fibers are used. Surface activation and coating treatments are used to improve fiber dispersion, inhibit steel fiber sedimentation, ensure slurry homogeneity, and enhance crack resistance and structural stress synergy.

[0018] 3. The prepared grouting material has the characteristics of high fluidity, ultra-early strength, micro-expansion and high density, which meets the requirements of rapid connection of prefabricated buildings and intelligent prefabricated bridge building machines. It has stable strength, high reliability and wide applicability. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 The preparation process of the recycled sand described in this invention; Figure 2 The results show the effects of unmodified and modified recycled sand on the porosity of hardened grout. Figure 2 In the figure, A represents the cumulative pore volume of the four groups of samples. Figure 2 In Figure B, the pore size distribution of the four groups of samples is shown. Figure 3 The results of the flowability test of the grout prepared in Example 1; Figure 4 Scanning electron microscope (SEM) images of the hardened grouting materials in Comparative Example 1 and Examples 1-3; in, Figure 4 Image (a) is a scanning electron microscope image of the grout material after hardening in Comparative Example 1. Figure 4 Image (b) is a scanning electron microscope image of the grout material after hardening in Example 1. Figure 4 Image (c) is a scanning electron microscope image of the grout after hardening in Example 2. Figure 4 Image d is a scanning electron microscope image of the grout after hardening in Example 3; Figure 5 These are XRD patterns of the grouting material on day 3 and day 28 of curing in Examples 1-3; where, Figure 5 Image A is the XRD pattern of the grout on the 3rd day of curing. Figure 5 Image B is the XRD pattern of the grout material on day 28 of curing. Detailed Implementation

[0021] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] In the context of this specification, the word "comprising" is considered to mean "particularly including". It should not be interpreted as "consisting only of". In the description of this invention, it should be understood that the term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The symbol " / " in this document indicates an "or" relationship between the related objects; for example, A / B means A or B.

[0024] In the description of embodiments of the present invention, the words "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of the present invention should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0025] In the description of the embodiments of the present invention, unless otherwise stated, "a plurality of" means two or more.

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0027] Example 1 In this embodiment, a high-performance green cement-based grouting material is provided. The raw materials of the cement-based grouting material include the following components in parts by weight: 100 parts of PO42.5R ordinary silicate cement, 60 parts of fine aggregate, 3.35 parts of nano-SiO2 modified composite fiber, 28 parts of water, and 3.9 parts of polycarboxylate-based high-efficiency water-reducing agent.

[0028] The fine aggregate is obtained by mixing natural sand and recycled sand in a 1:1 mass ratio. The recycled sand is a reclaimed material from bridge construction waste. The preparation method is as follows: the pre-treated waste concrete blocks are put into a jaw crusher for preliminary crushing to obtain recycled coarse aggregate with a particle size of less than 25 mm. The recycled coarse aggregate is then fed into a reverse crusher for further crushing to a particle size of less than 10 mm. It is then fed into a ball mill, where mechanical grinding and impact are used to improve the particle morphology of the aggregate to obtain small-particle-size lightweight material. The particles with a particle size between 0.075 mm and 2.35 mm are then collected by multi-stage sieves and immersed in a 6.5% potassium dihydrogen phosphate solution at room temperature for 2-4 hours. After immersion, the material is dried to obtain recycled sand.

[0029] The preparation method of nano-SiO2 modified composite fibers includes the following steps: (1) Fiber pretreatment Steel fibers and PVA fibers were mixed evenly at a mass ratio of 78:22 to obtain composite fibers. Deionized water and anhydrous ethanol were added to a stirred reactor at a volume ratio of 1:5 and stirred at 300 rpm for 3 minutes to mix thoroughly. Glacial acetic acid was added to adjust the pH of the system to 4.0-4.5. Then, 1.5% of PEG-400 polyethylene glycol and 2% of low-concentration hydrogen peroxide (by mass of the total activation solution) were added, and the mixture was stirred at a constant temperature for 10 minutes to obtain the activation solution, which was then set aside for later use.

[0030] The composite fibers were simultaneously added to the activation solution at a ratio of 1:10 (total mass of composite fibers to mass of activation solution). The solution was heated to 40°C and stirred at a low speed of 200 rpm for 15 minutes to complete the activation of the composite fibers. After activation, the composite fibers were removed, drained through a filter screen to remove residual liquid, and then pre-dried in a 50°C forced-air drying oven for 30 minutes to remove free moisture, yielding surface-activated composite fibers for later use.

[0031] (2) Activation treatment with silane coupling agent A hydrolysate was prepared by mixing KH-550 silane coupling agent, anhydrous ethanol, and deionized water in a ratio of 1:10:2 (mass ratio). The pH was adjusted to 9-10 with dilute ammonia, and the mixture was stirred for 15 minutes. The surface-activated composite fibers were then immersed in the hydrolysate and stirred in a 60°C water bath for 30 minutes. After removal, the fibers were dried at 80°C to obtain the coupling agent-activated composite fibers.

[0032] (3) Preparation of nano-SiO2 coating solution Using deionized water as the dispersion medium, polycarboxylate dispersant was added, followed by nano-SiO2. The amount of nano-SiO2 added was 5% of the mass of the composite fiber. The mixture was ultrasonically dispersed for 20 minutes to form a uniform and stable nano-SiO2 suspension.

[0033] (4) In-situ composite coating and curing The coupling agent-activated composite fiber obtained in step (2) was added to the nano-SiO2 suspension and stirred at 60°C for 30 min to allow the nano-SiO2 to uniformly coat the steel fiber and PVA fiber surface through chemical bonding and physical adsorption of the silane coupling agent. After filtration and washing, it was dried at 105°C and cured at 120°C for 1 h to obtain the nano-SiO2 modified composite fiber.

[0034] The construction method for the above-mentioned cement-based grouting material is as follows: Thoroughly clean the grouting area, removing loose dust, oil, debris, and standing water from the base surface to ensure a clean and impurity-free interface. Add PO42.5R ordinary silicate cement, fine aggregate, and nano-SiO2 modified composite fibers to a mixing device and dry mix for 2-3 minutes to ensure thorough mixing of all solid components and uniform fiber dispersion without clumping. Then add water mixed with the polycarboxylate superplasticizer and wet mix for 3-4 minutes until the grout is uniformly fluid, with good flowability, no lumps, and no air bubbles. After mixing, allow it to stand for 1-2 minutes to release air.

[0035] Gravity grouting is used. After grouting is completed, excess grout that overflows should be removed in time, and curing should be carried out for no less than 7 days.

[0036] Example 2 In this embodiment, another high-performance green cement-based grouting material is provided. The raw materials of the cement-based grouting material include the following components in parts by weight: 120 parts of PI52.5R ordinary Portland cement, 65 parts of fine aggregate, 8.52 parts of nano-SiO2 modified composite fiber, 30 parts of water, and 4.8 parts of calcium sulfoaluminate expansion agent.

[0037] The fine aggregate is obtained by mixing natural sand and recycled sand at a mass ratio of 2:1. The preparation method of the recycled sand is the same as in Example 1, except that the concentration of potassium dihydrogen phosphate solution is 9.8%.

[0038] The preparation method of nano-SiO2 modified composite fibers includes the following steps: (1) Fiber pretreatment Steel fibers and PVA fibers were mixed evenly at a mass ratio of 75:25 to obtain composite fibers. Deionized water and anhydrous ethanol were added sequentially to a stirred reactor at a volume ratio of 1:10 and stirred at 300 rpm for 3 minutes to mix thoroughly. Glacial acetic acid was added to adjust the pH of the system to 4.0-4.5. Then, 0.5% of PEG-400 polyethylene glycol and 1% of low-concentration hydrogen peroxide (by mass of the total activation solution) were added, and the mixture was stirred at a constant temperature for 10 minutes to obtain the activation solution, which was then set aside for later use.

[0039] The composite fibers were simultaneously added to the activation solution at a ratio of 1:10 (total mass of composite fibers to mass of activation solution). The solution was heated to 40°C and stirred at a low speed of 200 rpm for 15 minutes to complete the activation of the composite fibers. After activation, the composite fibers were removed, drained through a filter screen to remove residual liquid, and then pre-dried in a 50°C forced-air drying oven for 30 minutes to remove free moisture, yielding surface-activated composite fibers for later use.

[0040] (2) Activation treatment with silane coupling agent A hydrolysate was prepared by mixing KH-550 silane coupling agent, anhydrous ethanol, and deionized water in a ratio of 1:8:1 (mass ratio). The pH was adjusted to 9-10 with dilute ammonia, and the mixture was stirred for 15 minutes. The surface-activated composite fibers were then immersed in the hydrolysate and stirred in a 60°C water bath for 30 minutes. After removal, the fibers were dried at 80°C to obtain the coupling agent-activated composite fibers.

[0041] (3) Preparation of nano-SiO2 coating solution Using deionized water as the dispersion medium, polycarboxylate dispersant was added, followed by nano-SiO2. The amount of nano-SiO2 added was 5% of the mass of the composite fiber. The mixture was ultrasonically dispersed for 30 minutes to form a uniform and stable nano-SiO2 suspension.

[0042] (4) In-situ composite coating and curing The coupling agent-activated composite fiber obtained in step (2) was added to a nano-SiO2 suspension and stirred at 40°C for 60 min. This allowed the nano-SiO2 to uniformly coat the steel and PVA fibers through chemical bonding and physical adsorption by the silane coupling agent. After filtration and washing, the fiber was dried at 105°C and cured at 120°C for 1 h to obtain the nano-SiO2 modified composite fiber.

[0043] The remaining settings are the same as in Example 1.

[0044] Example 3 In this embodiment, another high-performance green cement-based grouting material is provided. The raw materials of the cement-based grouting material include the following components in parts by weight: 80 parts of PI52.5R ordinary Portland cement, 55 parts of fine aggregate, 3.2 parts of nano-SiO2 modified composite fiber, 20 parts of water, and 1.2 parts of UEA expansion agent.

[0045] The fine aggregate is obtained by mixing manufactured sand and recycled sand in a mass ratio of 1:1. The preparation method of the recycled sand is the same as in Example 1, except that the concentration of potassium dihydrogen phosphate solution is 5.2%.

[0046] The preparation method of nano-SiO2 modified composite fibers includes the following steps: (1) Fiber pretreatment Steel fibers and PVA fibers were mixed evenly at a mass ratio of 79:21 to obtain composite fibers. Deionized water and anhydrous ethanol were added sequentially to a stirred reactor at a volume ratio of 1:10 and stirred at 300 rpm for 3 minutes to mix thoroughly. Glacial acetic acid was added to adjust the pH of the system to 4.0-4.5. Then, 2% of the total mass of PEG-400 polyethylene glycol and 3% of low-concentration hydrogen peroxide were added, and the mixture was stirred at a constant temperature for 10 minutes to obtain the activation solution, which was then set aside for later use.

[0047] The composite fibers were simultaneously added to the activation solution at a ratio of 1:20 (total mass of composite fibers to mass of activation solution). The solution was heated to 45°C and stirred at a low speed of 150 rpm for 20 minutes to complete the activation of the composite fibers. After activation, the composite fibers were removed, drained through a filter screen to remove residual liquid, and then pre-dried in a 55°C forced-air drying oven for 25 minutes to remove free moisture, yielding surface-activated composite fibers for later use.

[0048] (2) Activation treatment with silane coupling agent A hydrolysate was prepared by mixing KH-550 silane coupling agent, anhydrous ethanol, and deionized water in a ratio of 1:12:3 (mass ratio). The pH was adjusted to 9-10 with dilute ammonia, and the mixture was stirred for 15 minutes. The surface-activated composite fibers were then immersed in the hydrolysate and stirred in a 60°C water bath for 30 minutes. After removal, the fibers were dried at 80°C to obtain the coupling agent-activated composite fibers.

[0049] (3) Preparation of nano-SiO2 coating solution Using deionized water as the dispersion medium, polycarboxylate dispersant was added, followed by nano-SiO2. The amount of nano-SiO2 added was 5% of the mass of the composite fiber. The mixture was ultrasonically dispersed for 30 minutes to form a uniform and stable nano-SiO2 suspension.

[0050] (4) In-situ composite coating and curing The coupling agent-activated composite fiber obtained in step (2) was added to a nano-SiO2 suspension and stirred at 40°C for 60 min. This allowed the nano-SiO2 to uniformly coat the steel and PVA fibers through chemical bonding and physical adsorption by the silane coupling agent. After filtration and washing, the fiber was dried at 105°C and cured at 120°C for 1 h to obtain the nano-SiO2 modified composite fiber.

[0051] The remaining settings are the same as in Example 1.

[0052] Comparative Example 1 In this embodiment, another cement-based grouting material is provided. The difference from Embodiment 1 lies in the method for preparing the nano-SiO2 modified composite fibers, where the fiber pretreatment method is as follows: Steel fibers and PVA fibers were mixed evenly at a mass ratio of 78:22 to obtain composite fibers. Deionized water and anhydrous ethanol were added to a stirred reactor at a volume ratio of 1:5 and stirred at 300 r / min for 3 min to mix evenly. Glacial acetic acid was added to adjust the pH of the system to 4.0-4.5, and epoxy emulsion at 1.5% of the total mass of the activation solution was added.

[0053] The remaining settings are the same as in Example 1.

[0054] Performance testing 1. Porosity testing This test was conducted to investigate whether the incorporation of recycled sand would affect the porosity of the hardened grout. Based on the raw material composition of Example 1, the proportion of fine aggregate was as follows: RS0: Fine aggregate is 100% recycled sand that has not been soaked in potassium dihydrogen phosphate solution; RS1: The fine aggregate is 100% recycled sand soaked in 6.5% potassium dihydrogen phosphate solution (prepared in Example 1). RS1:1: The fine aggregate is a mixture of recycled sand (prepared in Example 1) and natural sand at a mass ratio of 1:1; RS1:2: The fine aggregate is a mixture of recycled sand (prepared in Example 1) and natural sand at a mass ratio of 1:2.

[0055] Porosity was tested using mercury intrusion porosimetry (MIP). Standard test blocks (40mm × 40mm × 160mm) were prepared according to the composition and proportions of Example 1, excluding fine aggregate. After 28 days of standard curing, the porosity was tested and calculated. The average value of three test blocks in each group was taken. The test results are as follows: Figure 2 As shown.

[0056] Based on the above results, none of the four groups of samples produced significant pores of 50 nm or larger, demonstrating that ball milling helps reduce the porosity of the recycled sand. The recycled sand without dihydrogen phosphate treatment (RS0, green) exhibited a higher distribution in the 20-50 nm range, and its cumulative pore volume was significantly larger than other samples, proving the necessity of dihydrogen phosphate soaking modification. RS1 used 100% potassium dihydrogen phosphate-modified recycled sand, which showed a significantly lower porosity than RS0. The surface pores of the modified recycled sand were effectively filled, the interfacial transition zone structure was optimized, and the bonding density with the cement matrix was greatly improved, mitigating the adverse effects of the recycled sand's inherent defects.

[0057] Comparing RS1:1 and RS1:2, the porosity of the two groups is significantly lower than that of RS1, and the pore size distribution and cumulative pore volume of the two groups are similar, proving that the modified recycled sand is very close to natural sand. The combination of the two can further optimize the aggregate gradation and improve the internal compactness.

[0058] 2. Liquidity Test The truncated cone mold method was employed, conducted at room temperature (20±5℃) in an environment free from direct wind and sunlight. The testing equipment included a standard truncated cone mold, a 500mm×500mm horizontal glass plate, a ruler, and a stopwatch. Before testing, the inner wall of the mold and the glass plate were moistened with a damp cloth. The slurry was prepared according to the predetermined ratio, stirred, allowed to stand, and then allowed to degas. The slurry was then filled into the truncated cone mold and leveled. The mold was lifted vertically at a uniform speed and allowed to stand for 30 seconds. The diameter of the slurry spread in two vertical directions was measured, and the average value was taken as the initial flowability. Each group was measured twice in parallel; a difference ≤10mm was considered valid. The acceptable initial flowability for this grout was 300~380mm, and the flowability after 30 minutes should not be less than 260mm. Strict adherence to operational procedures was required to avoid human error affecting the results.

[0059] The results are as follows Figure 3 As shown, the grout spreads out in a regular and rounded shape, with no obvious stratification or segregation, and no bleeding or water separation. The nano-SiO2 modified composite fibers are evenly dispersed without clumping. The measured average spread diameter is within the qualified range of 300~380mm. After 30 minutes, the fluidity decays slowly and is not lower than 260mm, which meets the fluidity requirements of self-leveling grouting construction. The overall fluidity performance is excellent and the workability meets the standards. It can meet the needs of dense filling and self-leveling construction for bridge engineering grouting operations, without the risk of construction blockage or incomplete filling.

[0060] 3. Phase testing Grouting materials were prepared according to the methods of Comparative Example 1 (NS0), Example 1 (NS1), Example 2 (NS2), and Example 3 (NS3). X-ray diffraction measurements were performed on hardened grouting material specimens after 3 days and 28 days of standard curing, respectively. Small samples were cut from the specimen after 28 days of standard curing and observed using a scanning electron microscope. The results are as follows: Figure 4 and Figure 5 As shown.

[0061] according to Figure 4 In Comparative Example 1 (NS0), the microstructure was relatively loose, with obvious microcracks and pores observed. In Examples 1-3, a denser CSH gel was formed in the microstructure; these hydration products effectively filled the internal pores, resulting in a more compact overall microstructure of the samples.

[0062] according to Figure 5 X-ray diffraction (XRD) tests were used to further analyze the composition of the hydration products of the material. XRD patterns at 3d and 28d confirmed that the hydration products of the grout mainly included CSH gel, calcium hydroxide (Ca(OH)2), and ettringite.

[0063] 4. Compressive and flexural strength tests The grouting material was mixed according to the proportions of Examples 1-3 and Comparative Example 1, and then poured into a 40mm×40mm×160mm triple mold at once. After vibration compaction, the material was leveled and cured in an environment of 20±2℃ and humidity ≥95% for 24 hours before demolding. The molded material was then transferred to a standard curing room to the specified age. A cement mortar flexural strength tester was used to load the specimen at a rate of 50N / s±10N / s until the specimen broke. The failure load was recorded and the flexural strength was calculated. The average value of 3 specimens in each group was taken. The flexed half specimen was placed in the center of the bearing plate of the compressive strength tester and loaded at a rate of 2400N / s±200N / s until failure. The load was recorded and the compressive strength was calculated. The average value of 6 specimens in each group was taken after removing outliers.

[0064] Table 1. Flexural and compressive strengths of the grouting materials after hardening in Examples 1-3 and Comparative Example 1 As shown in Table 1, the flexural strength and compressive strength of the grout obtained in Examples 1-3 after hardening significantly exceeded those of Comparative Example 1, proving that the pre-activation treatment of composite fibers can effectively improve the strength of the grout after hardening.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-performance green cement-based grouting material, characterized in that, The raw materials of the grouting material include the following components in parts by weight: The silicate system cement contains 80-120 parts, fine aggregate 55-65 parts, nano-SiO2 modified composite fiber 3-9 parts, water 20-30 parts, and admixture 1-5 parts. The fine aggregate is a mixture of natural sand or manufactured sand and recycled sand in a mass ratio of 1 to 4:

1. The recycled sand is modified by the following method: immersing it in a 5% to 10% dihydrogen phosphate solution at room temperature for 2 to 4 hours, removing it, filtering off excess solution, and drying it at 60 to 80°C to obtain the final product. The nano-SiO2 modified composite fiber is a composite fiber with nano-silica coated on the surface. The composite fiber is pre-etched with an activation solution. The activation solution is prepared as follows: water and anhydrous ethanol are mixed at a volume ratio of 1:5~10, then polyethylene glycol is added to a mass fraction of 0.5~2%, and hydrogen peroxide is added to a mass fraction of 1~3%.

2. The high-performance green cement-based grouting material as described in claim 1, characterized in that, The silicate system cement is one or a combination of several of the following: PO42.5R ordinary silicate cement, PO52.5R ordinary silicate cement, PI42.5R silicate cement, PI52.5R silicate cement, and PC42.5R composite silicate cement.

3. The high-performance green cement-based grouting material as described in claim 1, characterized in that, The preparation method of the recycled sand is as follows: Construction waste is used as raw material and sorted. After sorting and removing impurities, it is first crushed by a jaw crusher to obtain recycled coarse aggregate with a particle size of less than 25 mm, and then crushed by an impact crusher to obtain recycled coarse aggregate with a particle size of less than 10 mm. The aggregate is then sieved and fine aggregate with a particle size of 0.075 mm to 2.35 mm is retained and ball-milled. The ball-milled fine aggregate is then modified by immersing it in a dihydrogen phosphate solution. The dihydrogen phosphate is selected from sodium dihydrogen phosphate or potassium dihydrogen phosphate.

4. The high-performance green cement-based grouting material as described in claim 1, characterized in that, The preparation method of the nano-SiO2 modified composite fiber includes the following steps: the composite fiber is immersed in an activation solution at 35~45℃ for activation, and after drying, the activated composite fiber is obtained. The activated composite fiber is added to an anhydrous ethanol solution of silane coupling agent and reacted at 35~45℃ for 30~40 min. Then, nano-SiO2 is slowly added, and the reaction is continued at the above temperature for 25~35 min. After drying, the composite fiber is obtained.

5. The high-performance green cement-based grouting material as described in claim 4, characterized in that, The composite fiber is a mixture of PVA fiber and steel fiber in a mass ratio of 21~25:75~79, wherein the PVA fiber has a length of 11~13mm and a fineness of 1100~1300D, and the steel fiber has a length of 12~14mm and a diameter of 0.18~0.22mm.

6. The high-performance green cement-based grouting material as described in claim 4, characterized in that, The silane coupling agent is KH-550, and an anhydrous ethanol solution of the silane coupling agent is prepared according to a mass ratio of KH-550: anhydrous ethanol: water of 1:8~12:1~3; the amount of nano-SiO2 added is 3~8% of the mass of the composite fiber.

7. The high-performance green cement-based grouting material as described in claim 1, characterized in that, The admixture is selected from one or more of the following: polycarboxylate superplasticizer, ettringite-type or calcium sulfoaluminate micro-expansion agent, early strength agent, sodium gluconate or citric acid or polycarboxylate retarder, organosilicon or polyether defoamer, water-retaining agent, polyether thickener, fiber dispersant, organosilicon antipermeable agent, and sodium nitrite-potassium carbonate composite antifreeze agent.

8. A method for constructing the cement-based grouting material according to any one of claims 1-7, characterized in that, Includes the following steps: After thoroughly dry-mixing 80-120 parts of cementitious material, 55-65 parts of fine aggregate, and nano-SiO2 modified composite fiber, add water with mixed additives and continue stirring until the slurry becomes fluid. After standing and degassing, use gravity or pressure grouting, and continuously grout in a single batch until full. After initial setting, cover and cure.

Images