High-strength self-compacting concrete for complex steel structure and preparation method thereof

Abstract

This application relates to a high-strength self-compacting concrete for complex steel structures and its preparation method. The raw materials for preparation include the following components by weight: 400-415 parts cement, 85-95 parts fly ash, 85-95 parts mineral powder, 820-860 parts coarse aggregate, 800-820 parts fine aggregate, 6.5-7.5 parts admixture, and 145-155 parts water. The coarse aggregate includes crushed stone with a particle size of 5-10 mm and crushed stone with a particle size of 10-20 mm. The admixture includes a polycarboxylate superplasticizer. This application, by blending crushed stone with a particle size of 5-10 mm and crushed stone with a particle size of 10-20 mm, achieves continuous gradation of the coarse aggregate, reduces porosity, and optimizes particle packing. This unexpectedly results in a self-compacting concrete that synergistically improves high fluidity, low viscosity, high slump retention, high strength, and excellent appearance quality, meeting the comprehensive requirements of complex steel structures for high-strength self-compacting concrete.

Description

Technical Field

[0001] This application relates to the field of building materials technology, and in particular to a high-strength self-compacting concrete for complex steel structures and a method for preparing the same. Background Technology

[0002] With the development of modern architecture towards larger spans, more irregular shapes, and higher load-bearing capacities, steel-concrete composite structures have been increasingly widely used. These structures feature extremely dense reinforcement and often include complex geometries such as inclined columns and beams with large inclination angles. Traditional concrete, due to its insufficient fluidity and poor filling performance, is difficult to compact through vibration. Self-compacting concrete, with its high fluidity, high resistance to segregation, and excellent filling capacity, has become a key material for solving these problems.

[0003] However, existing high-strength self-compacting concrete faces significant technical challenges in practical applications: on the one hand, the required strength grades necessitate low water-cement ratios and high cementitious material content, resulting in high plastic viscosity and a rapid decrease in spread during transportation and construction waiting periods, making it difficult to meet on-site pouring requirements; on the other hand, complex structures impose extremely stringent conditions on the concrete's filling capacity, gap clearance, and surface quality. Furthermore, in actual engineering projects, special components such as sloping long steel trusses and "E"-shaped inclined columns are frequently encountered, where ordinary self-compacting concrete is prone to problems such as segregation, aggregate accumulation, and surface color differences during pouring.

[0004] In summary, there is an urgent need to develop a self-compacting concrete that combines low viscosity, high flow retention, high homogeneity, and good appearance quality. Summary of the Invention

[0005] In order to make self-compacting concrete have low viscosity, high flow retention, high homogeneity and good appearance quality, this application provides a high-strength self-compacting concrete for complex steel structures and a method for preparing the same.

[0006] In a first aspect, this application provides a high-strength self-compacting concrete for complex steel structures, employing the following technical solution: A high-strength self-compacting concrete for complex steel structures is prepared by means of the following components in parts by weight: 400-415 parts cement, 85-95 parts fly ash, 85-95 parts mineral powder, 820-860 parts coarse aggregate, 800-820 parts fine aggregate, 6.5-7.5 parts admixture, and 145-155 parts water. The coarse aggregate includes crushed stone with a particle size of 5-10 mm and crushed stone with a particle size of 10-20 mm. The admixture includes polycarboxylate superplasticizer.

[0007] The inventors discovered that by blending crushed stone with a particle size of 5-10mm and crushed stone with a particle size of 10-20mm, the coarse aggregate achieves continuous gradation, significantly reduces porosity, and optimizes particle packing. Compared to single-size crushed stone or poorly graded coarse aggregate: single-size crushed stone has high porosity, requiring more mortar to fill, resulting in high plastic viscosity of concrete, rapid loss of spread over time, high pumping resistance, and a tendency for aggregate segregation; however, by blending 5-10mm and 10-20mm crushed stone, the smaller-size crushed stone fills the voids between the larger-size crushed stone, resulting in a denser aggregate skeleton. Simultaneously, it reduces point contact friction between coarse aggregates, allowing the slurry to uniformly coat the aggregate surface even at lower viscosity.

[0008] Specifically, continuously graded coarse aggregates reduce the yield stress and plastic viscosity of the mixture, allowing self-compacting concrete to flow smoothly under its own weight and fill densely reinforced areas, achieving compaction without vibration. After gradation optimization, the total specific surface area of ​​the aggregates tends to be more reasonable, and the interface transition zone between the paste and aggregates is denser, effectively suppressing segregation and bleeding. After hardening, the surface has fewer pores and a more uniform color. In addition, the dense aggregate skeleton and the low water-cement ratio paste work synergistically to ensure stable early strength development and sufficient later strength reserves in concrete, while reducing the risk of shrinkage cracking.

[0009] This application achieves a comprehensive performance breakthrough in high-strength self-compacting concrete by combining coarse aggregate gradation with the synergy of cementitious materials and admixtures, achieving breakthroughs in three aspects: rheological control, homogeneity assurance, and strength enhancement. Continuously graded coarse aggregate reduces the flow resistance of the paste, enabling the concrete to achieve high scalability and long-term slump retention at low viscosity. The filling effect of small-diameter crushed stone inhibits aggregate segregation, ensuring the homogeneity of the mixture and the appearance quality after hardening. The dense aggregate skeleton and optimized paste work together to impart high compressive strength and durability to the concrete. Therefore, the high-strength self-compacting concrete for complex steel structures provided by this application can overcome the construction difficulties of densely reinforced and irregularly shaped structures where vibration compaction is impossible, meeting the stringent requirements for self-compacting concrete in projects such as large stadiums and super high-rise transfer floors.

[0010] In one specific implementation, the mass ratio of the crushed stone with a particle size of 5-10 mm to the crushed stone with a particle size of 10-20 mm is 1:(2.5-3.5).

[0011] The inventors verified through experiments that by controlling the mass ratio within the range of 1:2.5-3.5, the small-diameter crushed stone can just densely fill the gaps between the large-diameter crushed stone, and the aggregate system reaches the most compact packing state. At this time, the mortar can fully coat the surface of the aggregate without increasing the viscosity due to excess. The concrete slump expansion, pouring time, time loss, and hardened appearance quality all reach the optimal balance.

[0012] When the mass ratio of 5-10mm crushed stone to 10-20mm crushed stone is less than 1:3.5 (i.e., too little small-diameter crushed stone), the voids formed by the skeleton of large-diameter crushed stone cannot be fully filled, the contact points between aggregates increase, the flow resistance is high, the concrete spread is insufficient, and crushed stone accumulation is easy to occur. When the mass ratio is higher than 1:2.5 (i.e., too much small-diameter crushed stone), the small-diameter crushed stone will expand the skeleton of large-diameter particles, which will increase the porosity, increase the amount of mortar required, make the slurry viscosity too high, and significantly prolong the pouring time.

[0013] In one specific implementation, the polycarboxylate superplasticizer is a polycarboxylate superplasticizer modified with vinylimidazole grafting.

[0014] Preferably, the polycarboxylate superplasticizer modified with vinylimidazole is prepared as follows: S1. Disperse 1-vinylimidazole in water to form an aqueous solution of 1-vinylimidazole; S2. Under nitrogen protection, the 1-vinylimidazol aqueous solution and initiator prepared in step S1 are added dropwise to the polycarboxylate superplasticizer to react and obtain the polycarboxylate superplasticizer modified with vinylimidazolium grafting.

[0015] The inventors discovered that, compared with unmodified polycarboxylate superplasticizer, the use of vinylimidazolium-grafted polycarboxylate superplasticizer resulted in a moderate increase in the viscosity of the concrete paste and a significant improvement in the suspension stability of the aggregates when the concrete was in a static state. Under pumping or pouring shearing action, the viscosity decreased rapidly and the fluidity was restored. At the same time, after hardening, the surface bubbles were reduced and the color was more uniform.

[0016] Specifically, unmodified polycarboxylate superplasticizers rely solely on carboxyl anchoring and the steric hindrance of polyether side chains for dispersion. In low water-cement ratio, high-strength self-compacting concrete, cement particles readily hydrate and encapsulate superplasticizer molecules, leading to a loss of spread over time. Furthermore, this results in a significant density difference between the paste and aggregate, causing coarse aggregates to settle and surface bleeding during static standing. However, when vinylimidazole is grafted onto the polycarboxylate molecular side chains, the nitrogen atom in the imidazole group contains a lone pair of electrons, which can interact with the Ca in the cement paste. 2+ Fe 3+The metal ions form reversible coordination bonds. Under static conditions such as transportation and waiting, multiple modified polycarboxylate molecules construct a loose three-dimensional network structure through imidazole-metal ion coordination, which moderately increases the yield stress of the slurry, effectively inhibiting aggregate settling and slurry bleeding. At the same time, this network does not excessively increase plastic viscosity, ensuring initial fluidity. When concrete is subjected to high shear forces during pumping or pouring, the coordination bonds break, the network rapidly dissociates, the system viscosity decreases, and the concrete returns to a high-flow state, enabling it to smoothly fill complex structures with dense reinforcement. After pouring, the shear force disappears, the coordination bonds reform, the network partially recovers, and the slurry further consolidates the encapsulation of aggregates. In addition, the imidazole group also has certain defoaming and foam-stabilizing functions, which can reduce large, inferior air bubbles on the concrete surface, resulting in a smoother surface after hardening.

[0017] This application utilizes vinylimidazole-grafted modified polycarboxylate superplasticizer to achieve synergistic effects with a continuously graded coarse aggregate and cementitious material system. The reversible coordination and crosslinking effect provided by the modified superplasticizer inhibits segregation during the settling period and ensures flowability during the shearing period, resolving the contradiction between "high fluidity and anti-segregation" in high-strength self-compacting concrete. Combined with the optimized aggregate gradation, the paste uniformly coats the aggregate, resulting in strong interfacial bonding. After hardening, the strength meets the C50-60 design requirements, and the appearance quality is excellent. Therefore, the self-compacting concrete of this application can achieve self-leveling and self-compacting without vibration in the construction of densely reinforced and complex steel structures, while also possessing low viscosity, high fluidity retention, high homogeneity, and good appearance quality.

[0018] In one specific implementation, the amount of 1-vinylimidazole used is 1.5%-5.0% of the solid content of the polycarboxylate superplasticizer.

[0019] Through experiments, the inventors verified that by controlling the amount of 1-vinylimidazole within the range of 1.5%-5.0%, the grafting density is moderate. The polycarboxylic acid molecules retain their original dispersion and steric hindrance capabilities, while introducing a sufficient number of imidazole coordination sites. During the standing period, a moderately cross-linked network is formed to achieve anti-segregation. During the shearing period, the network can reversibly dissociate to ensure flow. At the same time, the imidazole groups work together to defoam, so that the overall performance of the concrete reaches the optimal balance.

[0020] When the dosage of 1-vinylimidazole is less than 1.5% of the solid content of polycarboxylate superplasticizer, the density of imidazole groups grafted onto the side links of the polycarboxylate molecules is insufficient. Under static conditions, there are too few coordination crosslinking points between imidazole and metal ions, resulting in a weak three-dimensional network structure. This makes it difficult to effectively inhibit aggregate settling and slurry bleeding, and the anti-segregation effect is not obvious. Simultaneously, due to the limited number of imidazole groups, its control effect on air bubbles is weak, and many large air bubbles are still visible on the surface of hardened concrete. When the dosage of 1-vinylimidazole is higher than 5.0%, the imidazole grafting density is too high, leading to overcrowding of the polycarboxylate molecular side chains. On the one hand, crosslinking and gelation easily occur during synthesis, reducing product stability. On the other hand, excessive imidazole groups form an overly dense coordination network under static conditions, resulting in excessive slurry yield stress, significantly reduced initial expansion, prolonged pouring time, and even bottoming out, ultimately sacrificing the core flow properties of self-compacting concrete.

[0021] In one specific feasible implementation, step S2-1 involves adjusting the pH of the reaction solution to 6.5-7.5 after the reaction is completed.

[0022] Adjusting the pH of the reaction solution to 6.5-7.5 after the reaction is complete is crucial for the stability and application performance of the grafted product. When the pH of the reaction solution is below 6.5, the system is acidic, and the carboxyl groups on the side chains of polycarboxylic acid molecules mainly exist in the form of -COOH, enhancing hydrogen bonding and making the molecular chains prone to coiling and aggregation. This leads to stratification or precipitation of the modified polycarboxylic acid water-reducing agent during storage. Furthermore, under acidic conditions, residual initiators or unreacted monomers may slowly hydrolyze, producing odorous or corrosive byproducts. Simultaneously, excessively low pH accelerates the protonation of imidazole groups, weakening their subsequent coordination ability with metal ions in cement paste and affecting the dynamic cross-linking effect of concrete. When the pH of the reaction solution is above 7.5, the system is alkaline, which may trigger hydrolysis of polycarboxylic acid ester bonds or ring-opening side reactions of the imidazole ring, leading to the destruction of the grafted structure. This significantly reduces the dispersion and slump retention properties of the water-reducing agent, resulting in poor storage stability. Adjusting the pH to a neutral range of 6.5-7.5 ensures that the carboxyl groups exist in the -COO⁻ form, resulting in extended molecular chains, good solubility, and a uniform and stable product. Simultaneously, it maintains a suitable proportion of unprotonated imidazole groups, enabling reversible coordination bonds with metal ions without affecting initial dispersibility due to excessive coordination. Consequently, the pH-adjusted modified polycarboxylate superplasticizer exhibits significantly improved storage stability and good compatibility with the ionic environment of cement paste. When applied to high-strength self-compacting concrete, it stably performs its dual functions of water reduction, dispersion, and dynamic crosslinking.

[0023] In one specific implementation, the admixture further includes a nano-montmorillonite dispersion.

[0024] Preferably, the mass ratio of the effective solid content of the nano-montmorillonite dispersion to the effective solid content of the polycarboxylate superplasticizer modified with vinylimidazole is 1:(3-8).

[0025] The inventors discovered that the introduction of nano-montmorillonite dispersion, when combined with polycarboxylate superplasticizer grafted with vinylimidazole, produced a significant synergistic effect.

[0026] Specifically, nano-montmorillonite is a two-dimensional layered silicate mineral with a surface rich in silanol groups and negatively charged lamellae. In the alkaline environment of cement paste, the lamellae in the nano-montmorillonite dispersion can form hydrogen bonds with the nitrogen atoms of the imidazole groups and the ether oxygen atoms of the polycarboxylic acid side chains. Simultaneously, the negative charge on the lamellae surface and the positive charge sites generated after the protonation of the imidazole groups generate electrostatic attraction. This synergistic effect of hydrogen bonding and electrostatic interaction anchors the nano-montmorillonite lamellae around the modified polycarboxylic acid molecules, forming dynamic cross-linking points of organic-inorganic hybrid. This hybrid network interpenetrates and synergistically enhances the imidazole-metal ion coordination network: under static conditions, the dual network significantly increases the yield stress of the paste, effectively suppressing aggregate settling and paste bleeding; under shear conditions, both networks can reversibly dissociate, and the fluidity is rapidly restored. In addition, nano-montmorillonite also has cation exchange capacity, which can adsorb or release Ca²⁺ ions in cement paste, playing an "ion buffer" role and dynamically regulating the coordination density of imidazole-metal ions, so that concrete maintains a suitable rheological state at different ambient temperatures and hydration stages.

[0027] By controlling the mass ratio within the range of 1:3 to 1:8, nano-montmorillonite sheets can be uniformly dispersed in the slurry in a single layer or a few layers. The abundant silanol groups on their surface form hydrogen bonds with the imidazole nitrogen atoms and polyether oxygen atoms of the imidazole-modified polycarboxylate molecular side chains. Simultaneously, the negative charge between the montmorillonite layers and the positive charge of the imidazole groups generate electrostatic attraction, constructing an organic-inorganic hybrid dual dynamic cross-linking network. The relative amount of nano-montmorillonite and the imidazole-modified polycarboxylate superplasticizer significantly affects the overall performance of concrete. However, when the mass ratio of the effective solid content of nano-montmorillonite to the effective solid content of the modified polycarboxylate superplasticizer is less than 1:8, the number of montmorillonite sheets is too small, making it difficult to form a sufficient density of hydrogen bonds or electrostatic cross-linking points with the imidazole groups. The organic-inorganic hybrid network is incomplete, resulting in limited improvement in the slurry yield stress and insignificant improvement in anti-segregation effect. Furthermore, the nano-filling effect of montmorillonite is weak, and its contribution to the strength and impermeability of hardened concrete is negligible. When the mass ratio is higher than 1:3, the excessive amount of montmorillonite sheets can easily cause self-aggregation and stacking. Not only can they not be evenly dispersed, but they will also adsorb a large amount of free water and water-reducing agent molecules, resulting in a sharp increase in the viscosity of the slurry, a significant decrease in the initial slump expansion, a prolonged pouring time, and even false setting, thus losing the high fluidity advantage of self-compacting concrete.

[0028] Therefore, by limiting the appropriate ratio of nano-montmorillonite to imidazole-modified polycarboxylate superplasticizer, this application achieves a synergistic improvement in high fluidity, strong anti-segregation, high strength, and excellent appearance quality.

[0029] In one specific implementation, the additive further includes a polyether-modified silicone defoamer.

[0030] The polyether-modified silicone defoamer used in this application has both polyether and silicone segments in its molecular structure. The polyether segments endow the defoamer with good hydrophilicity and self-emulsifying ability, allowing it to be uniformly dispersed in cement paste. It exhibits no adverse interactions with the vinylimidazole-grafted modified polycarboxylate superplasticizer and does not affect the superplasticizer's adsorption, dispersion, and dynamic coordination crosslinking functions. The silicone segments, on the other hand, have extremely low surface tension, enabling them to rapidly spread on the bubble surface, reduce bubble film strength, and promote bubble rupture and discharge from the paste. A synergistic defoaming effect also exists between the polyether-modified silicone defoamer and the imidazole groups: the imidazole groups themselves have certain surface activity, enabling them to adsorb at the bubble interface, weakening the bubble film stability and providing favorable conditions for the defoamer's intervention; the combined effect of both results in more thorough bubble elimination.

[0031] Meanwhile, the introduction of nano-montmorillonite dispersion further enhances the defoaming effect. During mixing, the nano-montmorillonite flakes physically puncture or compress large air bubbles, achieving mechanical defoaming, forming a dual mechanism with the chemical defoaming of the polyether-modified silicone defoamer. After the air bubbles are eliminated, the paste becomes denser, the interface between the aggregate and the paste is more firmly bonded, and the compressive strength and impermeability of the concrete are correspondingly improved.

[0032] Therefore, this application, through the synergistic effect of polyether-modified organosilicon defoamer, imidazole-modified polycarboxylate superplasticizer, and nano-montmorillonite dispersion, effectively eliminates inferior air bubbles inside and on the surface of concrete while maintaining the high fluidity, low viscosity, high slump retention, and high segregation resistance of concrete. This results in a smooth, uniformly colored, and honeycomb-free concrete surface after hardening, meeting the stringent requirements of complex steel structures for the appearance quality of self-compacting concrete, while further improving the density and durability of concrete.

[0033] Secondly, this application provides a method for preparing high-strength self-compacting concrete for complex steel structures, employing the following technical solution: A method for preparing high-strength self-compacting concrete for complex steel structures includes the following steps: After cement, fly ash, mineral powder, coarse aggregate, and fine aggregate are mixed evenly, admixtures and water are added and mixed evenly to obtain the high-strength self-compacting concrete.

[0034] By adopting the above steps, high-strength self-compacting concrete with low viscosity, high flow retention, high homogeneity, high strength, and excellent appearance quality can be stably produced, meeting the stringent requirements of complex steel structures for construction performance and forming quality. First, cement, fly ash, mineral powder, coarse aggregate, and fine aggregate are dry-mixed to ensure initial uniform contact between the powder and aggregate, preventing powder agglomeration or localized powder accumulation on the aggregate surface. Then, admixtures and water are added and mixing continues. At this point, the liquid components uniformly penetrate into the dry mix. Under stirring, the admixtures (especially vinylimidazole-grafted modified polycarboxylate superplasticizers and nano-montmorillonite dispersions) can be rapidly adsorbed onto the cement particles and aggregate surface, fully exerting their water-reducing, dispersing, dynamic coordination, cross-linking, and nano-filling effects.

[0035] In summary, this application includes at least one of the following beneficial technical effects: 1. This application combines crushed stone with a particle size of 5-10mm and crushed stone with a particle size of 10-20mm in a certain proportion to form a continuous gradation of coarse aggregate, which significantly reduces the porosity and point contact friction between aggregates, thereby reducing the plastic viscosity of concrete, improving the spreadability retention, and inhibiting aggregate segregation and bleeding. This results in fewer pores and a uniform color on the hardened surface, achieving a balance between high fluidity, low viscosity and excellent appearance quality.

[0036] 2. This application utilizes a polycarboxylate superplasticizer grafted with vinylimidazolium to reversibly coordinate the imidazolium groups with metal ions in the cement paste. During the settling period, a moderate three-dimensional network is constructed to inhibit aggregate settling and paste bleeding. During the shearing period, the network reversibly dissociates to restore high fluidity. This solves the contradiction between high fluidity and segregation resistance in high-strength self-compacting concrete, while also possessing ultra-long slump retention and low viscosity characteristics.

[0037] 3. This application introduces nano-montmorillonite dispersion, which forms a dual dynamic cross-linked network of organic-inorganic hybrid with imidazole-modified polycarboxylate superplasticizer through hydrogen bonding and electrostatic synergy. The coordination density is dynamically controlled by utilizing the cation exchange capacity of nano-montmorillonite, and a polyether-modified organosilicon defoamer is added to eliminate inferior bubbles. This achieves a synergistic improvement in multiple properties in five aspects: low viscosity, high flow retention, high anti-segregation, high strength, and excellent appearance quality, thus meeting the stringent requirements of self-compacting concrete for complex steel structures. Detailed Implementation

[0038] The present application will be further described in detail below with reference to embodiments and comparative examples: Some of the raw materials used in the examples and comparative examples: Cement: Purchased from Wuxi Tianshan, grade P·042.5, specific surface area 345m² / kg, initial setting time 230min, final setting time 290min, 3d compressive strength 25.1MPa, 28d compressive strength 50.2MPa.

[0039] Fly ash: purchased from Huacheng, grade II, fineness 22.4%, water requirement ratio 98%.

[0040] Mineral powder: purchased from Changzhou Zhongtian, grade S95, density 2.9g / cm³ 3 It has a specific surface area of ​​420 m² / kg, an activity index of 85% at 7 days, and an activity index of 102% at 28 days.

[0041] Fine aggregate: Purchased from Dongting Lake, type is natural sand, specification is medium sand, fineness modulus is 2.7, apparent density is 2610 kg / m³ 3 The mud content is 1.0%.

[0042] Coarse aggregate: Purchased from Kangcheng Mining, crushed stone with a particle size of 5-10mm and an apparent density of 2920kg / m³. 3 The mud content is 0.4%, and the crushing value is 5.5%; the apparent density of the crushed stone with a particle size of 10-20mm is 2920kg / m³. 3 The mud content is 0.6%, and the crushing value is 6.5%.

[0043] Polycarboxylate superplasticizer: Purchased from Kezhijie, model Point-330HS, a high-efficiency polycarboxylate superplasticizer with a water reduction rate of 22%, an air content of 2.9%, and a solid content of 40%.

[0044] 1-Vinylimidazole (CAS: 1072-63-5), hydrogen peroxide aqueous solution (CAS: 7722-84-1, 30% aqueous solution), L-ascorbic acid (CAS: 50-81-7), and nano-montmorillonite (product code: 682632) were all purchased from Sigma-Aldrich.

[0045] Polyether modified silicone defoamer (item number: W-745, purchased from Guangzhou Zhongwan New Materials Co., Ltd.)

[0046] Unless otherwise specified, all raw materials used in the examples and comparative examples are commercially available products.

[0047] Preparation Example 1 The preparation of polycarboxylate superplasticizer modified with vinylimidazole grafting is as follows: S1. Disperse 1 kg of 1-vinylimidazole in 10 kg of water to form an aqueous solution of 1-vinylimidazole; S2. Under nitrogen protection, the above-mentioned 1-vinylimidazole aqueous solution and initiator (the initiator is a redox initiation system composed of hydrogen peroxide and L-ascorbic acid, wherein 0.8 kg of hydrogen peroxide aqueous solution is dissolved in 5 kg of water, and 0.2 kg of L-ascorbic acid is dissolved in 5 kg of water) are added dropwise to 83.3 kg of polycarboxylate superplasticizer (corresponding to a solid content of 33.3 kg). The temperature is raised to 40°C and the reaction is carried out for 2 hours. After the reaction is completed, the mixture is cooled to room temperature, and the pH of the reaction solution is adjusted to 7.0 with 30% sodium hydroxide solution. The solution is then filtered through a 200-mesh filter to obtain the vinylimidazole grafted superplasticizer.

[0048] The effective solids content of the vinylimidazole-grafted polycarboxylate superplasticizer prepared in this example was found to be 36%.

[0049] Preparation Example 2 The only difference between Preparation Example 2 and Preparation Example 1 is that in step S1 of Preparation Example 2, instead of dispersing 1 kg of 1-vinylimidazole in 10 kg of water, 0.333 kg of 1-vinylimidazole is dispersed in 3.33 kg of water.

[0050] The effective solids content of the vinylimidazole-grafted polycarboxylate superplasticizer prepared in this example was found to be 35%.

[0051] Preparation Example 3 The only difference between Preparation Example 3 and Preparation Example 1 is that in step S1 of Preparation Example 3, instead of dispersing 1 kg of 1-vinylimidazole in 10 kg of water, 2 kg of 1-vinylimidazole is dispersed in 20 kg of water.

[0052] The effective solids content of the vinylimidazole-grafted polycarboxylate superplasticizer prepared in this example was found to be 37%.

[0053] Preparation Example 4 The preparation of the nano-montmorillonite dispersion is as follows: 1 kg of nano-montmorillonite was slowly added to 19 kg of water and ultrasonically treated. After standing for 24 hours, the large particles at the bottom were removed. The upper uniform colloid was then taken to obtain a nano-montmorillonite dispersion with a solid content of 5%. Example

[0054] Example 1 Taking the preparation of C60 grade high-strength self-compacting concrete as an example, the preparation of high-strength self-compacting concrete for complex steel structures is as follows: After mixing 407 parts by weight of cement, 87 parts by weight of fly ash, 87 parts by weight of mineral powder, 210 parts by weight of crushed stone with a particle size of 5-10mm, 631 parts by weight of crushed stone with a particle size of 10-20mm, and 810 parts by weight of fine aggregate evenly, 7 parts by weight of polycarboxylate superplasticizer and 150 parts by weight of water are added and mixed evenly to obtain high-strength self-compacting concrete.

[0055] Example 2 The only difference between Example 2 and Example 1 is that in the preparation steps of Example 2, 7 parts by weight of polycarboxylate superplasticizer are replaced with 6.95 parts by weight of the polycarboxylate superplasticizer prepared in Example 1 and 0.05 parts by weight of polyether modified silicone defoamer.

[0056] Example 3 The only difference between Example 3 and Example 1 is that in the preparation steps of Example 3, 7 parts by weight of polycarboxylate superplasticizer are replaced with 6.95 parts by weight of the polycarboxylate superplasticizer prepared in Example 2 and 0.05 parts by weight of polyether modified silicone defoamer.

[0057] Example 4 The only difference between Example 4 and Example 1 is that in the preparation steps of Example 4, 7 parts by weight of polycarboxylate superplasticizer are replaced with 6.95 parts by weight of the polycarboxylate superplasticizer prepared in Example 3 and 0.05 parts by weight of polyether modified silicone defoamer.

[0058] Example 5 The only difference between Example 5 and Example 2 is that in the preparation steps of Example 5, 6.95 parts by weight of the polycarboxylate superplasticizer and 0.05 parts by weight of the polyether-modified silicone defoamer prepared in Example 1 are replaced with 2.95 parts by weight of the polycarboxylate superplasticizer prepared in Example 1, 4 parts by weight of the nano-montmorillonite dispersion prepared in Example 4, and 0.05 parts by weight of the polyether-modified silicone defoamer.

[0059] Example 6 The only difference between Example 6 and Example 5 is that in the preparation steps of Example 6, 2.95 parts by weight of the polycarboxylate superplasticizer prepared in Example 1, 4 parts by weight of the nano-montmorillonite dispersion prepared in Example 4, and 0.05 parts by weight of the polyether-modified silicone defoamer are replaced with 6.5 parts by weight of the polycarboxylate superplasticizer prepared in Example 1, 0.45 parts by weight of the nano-montmorillonite dispersion prepared in Example 4, and 0.05 parts by weight of the polyether-modified silicone defoamer.

[0060] Example 7 The only difference between Example 7 and Example 5 is that in the preparation steps of Example 7, 2.95 parts by weight of the polycarboxylate superplasticizer prepared in Example 1, 4 parts by weight of the nano-montmorillonite dispersion prepared in Example 4, and 0.05 parts by weight of the polyether-modified silicone defoamer are replaced with 1.5 parts by weight of the polycarboxylate superplasticizer prepared in Example 1, 5.45 parts by weight of the nano-montmorillonite dispersion prepared in Example 4, and 0.05 parts by weight of the polyether-modified silicone defoamer.

[0061] Example 8 The only difference between Example 8 and Example 5 is that in the preparation steps of Example 8, 210 parts by weight of crushed stone with a particle size of 5-10 mm and 631 parts by weight of crushed stone with a particle size of 10-20 mm are replaced with 310 parts by weight of crushed stone with a particle size of 5-10 mm and 531 parts by weight of crushed stone with a particle size of 10-20 mm.

[0062] Example 9 The only difference between Example 9 and Example 5 is that in the preparation steps of Example 9, 210 parts by weight of crushed stone with a particle size of 5-10 mm and 631 parts by weight of crushed stone with a particle size of 10-20 mm are replaced with 110 parts by weight of crushed stone with a particle size of 5-10 mm and 731 parts by weight of crushed stone with a particle size of 10-20 mm.

[0063] Comparative Example 1 The only difference between Comparative Example 1 and Example 5 is that in the preparation steps of Comparative Example 1, 210 parts by weight of crushed stone with a particle size of 5-10 mm and 631 parts by weight of crushed stone with a particle size of 10-20 mm are replaced with 841 parts by weight of crushed stone with a particle size of 5-10 mm.

[0064] Comparative Example 2 The only difference between Comparative Example 2 and Example 5 is that in the preparation steps of Comparative Example 2, 210 parts by weight of crushed stone with a particle size of 5-10 mm and 631 parts by weight of crushed stone with a particle size of 10-20 mm are replaced with 841 parts by weight of crushed stone with a particle size of 10-20 mm.

[0065] 1. The self-compacting concrete prepared in each embodiment and comparative example was subjected to slump flow, T500 (expansion time), and flow loss over time performance tests according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures"; and the pouring time and segregation rate were tested according to JGJ / T 283-2012 "Technical Specification for Application of Self-Compacting Concrete". The measured values ​​were the average of 10 tests and summarized in Table 1: Table 1. Test data on the spread and other properties of self-compacting concrete obtained in each embodiment and comparative example. Group Initial expansion (mm) T500(s) 2h expansion loss (mm) Reversing time (s) Segregation rate (after standing for 1 hour) Example 1 700 3.0 0 13 No segregation Example 2 710 2.8 3 12 No segregation Example 3 695 3.2 6 14 slight segregation Example 4 680 3.8 8 17 Mild oozing Example 5 720 2.5 2 9 Completely without segregation Example 6 690 3.5 8 14 slight segregation Example 7 650 5.0 12 22 Severe segregation Example 8 670 4.0 7 15 slight segregation Example 9 675 3.8 6 14 Mild oozing Comparative Example 1 620 6.5 18 25 Severe segregation Comparative Example 2 630 6.0 15 23 Severe urination 1. The self-compacting concrete test blocks prepared on-site according to the various embodiments and comparative examples were tested for appearance quality by visual inspection after 28 days. The compressive strength performance at 7 days and 28 days was tested according to GB / T 50081-2019. The average values ​​of 10 tests are summarized in Table 2. Table 2. Apparent quality and compressive strength data of self-compacting concrete obtained in each embodiment and comparative example. Group Apparent quality 7-day compressive strength (MPa) 28-day compressive strength (MPa) Example 1 The surface is smooth and free of obvious bubbles. 62 75 Example 2 Smooth surface 64 78 Example 3 A small number of bubbles on the surface 62 75 Example 4 The surface is relatively smooth 63 76 Example 5 The surface is extremely smooth and free of visible bubbles. 67 82 Example 6 A small number of bubbles on the surface 63 76 Example 7 Rough surface with honeycomb 58 70 Example 8 The surface is relatively rough 60 73 Example 9 Slightly pitted surface 61 74 Comparative Example 1 Rough surface, obvious honeycomb 55 66 Comparative Example 2 Rough surface, water stains 56 67 A comparison of Examples 1 to 9 shows that the coarse aggregate gradation, the modification method of polycarboxylate superplasticizer, and the synergistic effect of nano-montmorillonite compounding have a decisive influence on the comprehensive performance of high-strength self-compacting concrete.

[0066] Regarding coarse aggregate gradation, when 5-10mm and 10-20mm crushed stone are blended in an appropriate ratio, the smaller-diameter crushed stone precisely fills the gaps between the larger-diameter crushed stone, achieving the most compact packing state in the aggregate system. This results in an optimal balance between initial spread of the concrete, pouring time, time loss, and hardened surface quality. If the proportion of smaller-diameter crushed stone is too high, it will stretch the larger-diameter skeleton, increasing porosity, leading to excessively high paste viscosity and decreased fluidity. Conversely, if the proportion of smaller-diameter crushed stone is too low, the voids formed by the larger-diameter crushed stone cannot be fully filled, increasing the contact points between aggregates, increasing flow resistance, resulting in insufficient spread and a tendency for bleeding. When using only a single-diameter crushed stone, whether only small-diameter or large-diameter, the excessive porosity or loose skeleton leads to poor fluidity, severe segregation, and low strength. This indicates that only by blending two grades of crushed stone in an appropriate ratio to form a continuous gradation can a synergistic balance of high fluidity, low viscosity, and high strength be achieved.

[0067] Regarding the modification of polycarboxylate superplasticizers, in low water-cement ratio, high-strength self-compacting concrete, unmodified polycarboxylate superplasticizers cause cement particles to hydrate rapidly and encapsulate superplasticizer molecules, resulting in significant loss of spread over time. Furthermore, the density difference between the paste and aggregate is obvious, leading to easy settling of coarse aggregate and surface bleeding during static settling. After using polycarboxylate superplasticizers grafted with vinylimidazolium, the nitrogen atoms in the imidazolium groups contain lone pairs of electrons, enabling reversible coordination bonds with metal ions in the cement paste. This constructs a suitable three-dimensional network during static settling to inhibit aggregate settling and paste bleeding, and the network reversibly dissociates during shearing to restore high fluidity. When the grafting density is moderate, the overall performance of the concrete is optimal. Too low a grafting density results in insufficient coordination crosslinking points and insignificant anti-segregation effect; too high a grafting density leads to an overly dense coordination network, excessive paste yield stress, decreased initial fluidity, and even bottoming out. This indicates that only by controlling the grafting density within a suitable range can a dynamic balance between static anti-segregation and shear-resistance fluidity be achieved.

[0068] In terms of synergistic effects of nano-montmorillonite in compound formulations, nano-montmorillonite is a two-dimensional layered silicate mineral with a surface rich in silanol groups and negatively charged lamellae. In the alkaline environment of cement paste, nano-montmorillonite lamellae can form hydrogen bonds with the nitrogen atoms of imidazole groups and the ether oxygen atoms of polycarboxylic acid side chains. Simultaneously, the negative charge on the lamellae surface and the positive charge sites generated after the protonation of imidazole groups generate electrostatic attraction, forming dynamic cross-linking points of organic-inorganic hybrids. This hybrid network interpenetrates and synergistically enhances the imidazole-metal ion coordination network. When the effective solid content ratio of nano-montmorillonite to imidazole-modified polycarboxylic acid superplasticizer is within a suitable range, the montmorillonite lamellae can be uniformly dispersed in a single layer or a few layers, constructing a complete dual network, significantly improving the fluidity, segregation resistance, strength, and appearance quality of concrete. If the proportion of montmorillonite is too low, it will be difficult to form a sufficient density of cross-linking points, resulting in a weak synergistic effect. If the proportion of montmorillonite is too high, the sheets are prone to self-aggregation and adsorption of free water and water-reducing agent molecules, leading to a sharp increase in viscosity, decreased flowability, reduced strength, and deterioration of apparent quality. This indicates that only by controlling the ratio of the two within an appropriate range can the synergistic effect of the organic-inorganic hybrid dynamic network be fully utilized.

[0069] A comparison of Example 5 with Comparative Examples 1 and 2 shows that coarse aggregate gradation plays a crucial role in improving the overall performance of high-strength self-compacting concrete. Example 5 uses two grades of crushed stone mixed in appropriate proportions to form a continuous gradation. The small-diameter crushed stone densely fills the gaps between the large-diameter crushed stone, achieving the most compact packing state in the aggregate system. Combined with the synergistic effect of imidazole-modified polycarboxylate superplasticizer and nano-montmorillonite dispersion, the concrete achieves comprehensive performance with low viscosity, high fluidity retention, high anti-segregation, high strength, and excellent appearance quality. In contrast, when Comparative Example 1 replaces the coarse aggregate with a single small-diameter crushed stone, the porosity is high, requiring more mortar to fill, resulting in high slurry viscosity, unstable aggregate skeleton, poor fluidity, severe segregation, rough appearance, and low strength. In Comparative Example 2, when the coarse aggregate is replaced with a single large-diameter crushed stone, the skeleton is loose, the slurry easily flows out from the aggregate gaps, resulting in severe bleeding, a rough appearance, and similarly low strength. The above comparison shows that continuously graded coarse aggregate reduces the flow resistance of the paste, enabling concrete to achieve high spread and long-term slump retention at low viscosity; the filling effect of small-diameter crushed stone inhibits aggregate segregation, ensuring the homogeneity of the mixture and the appearance quality after hardening; the dense aggregate skeleton and optimized paste work together to endow concrete with high compressive strength and durability. Therefore, there is a good synergistic match between the continuously graded coarse aggregate compound, the imidazole-modified polycarboxylate superplasticizer, and the nano-montmorillonite dispersion: the continuously graded aggregate provides a stable packing skeleton for the paste, the imidazole-modified superplasticizer provides dynamic coordination and cross-linking to resist segregation and retain slump, and the nano-montmorillonite further strengthens the dual network and fills it densely; together, the three achieve a synergistic improvement in multiple properties.

[0070] This application utilizes a suitable ratio of 5-10mm and 10-20mm crushed stone to form a continuously graded coarse aggregate, achieving the densest packing state of the aggregate system and reducing porosity and slurry flow resistance. Simultaneously, it employs a vinylimidazolium-grafted modified polycarboxylate superplasticizer, leveraging the reversible coordination between imidazolium groups and metal ions to construct a dynamic response network, achieving intelligent response to static anti-segregation and shear-resistant flow. Further compounding with nano-montmorillonite dispersion, through hydrogen bonding and electrostatic interactions, constructs an organic-inorganic hybrid dual dynamic... The cross-linked network, supplemented by polyether-modified silicone defoamer to eliminate inferior bubbles, enables C60 high-strength self-compacting concrete to possess extremely low plastic viscosity, ultra-long flow retention, excellent anti-segregation, high compressive strength, and excellent appearance quality in complex steel structure construction. It achieves a unity of low viscosity, high flow retention, high homogeneity, high strength, and excellent appearance quality, and can be widely used in engineering fields with stringent requirements for concrete workability and molding quality, such as large stadiums, super high-rise transfer floors, and nuclear power plant containment structures.

[0071] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-strength self-compacting concrete for complex steel structures, characterized in that, The raw materials for preparation include the following components in parts by weight: 400-415 parts cement, 85-95 parts fly ash, 85-95 parts mineral powder, 820-860 parts coarse aggregate, 800-820 parts fine aggregate, 6.5-7.5 parts admixture, and 145-155 parts water. The coarse aggregate includes crushed stone with a particle size of 5-10 mm and crushed stone with a particle size of 10-20 mm. The admixture includes polycarboxylate superplasticizer.

2. The high-strength self-compacting concrete for complex steel structures according to claim 1, characterized in that, The mass ratio of the crushed stone with a particle size of 5-10 mm to the crushed stone with a particle size of 10-20 mm is 1:(2.5-3.5).

3. The high-strength self-compacting concrete for complex steel structures according to claim 1, characterized in that, The polycarboxylate superplasticizer is a polycarboxylate superplasticizer modified with vinylimidazole grafting.

4. The high-strength self-compacting concrete for complex steel structures according to claim 3, characterized in that, The polycarboxylate superplasticizer modified with vinylimidazolium grafting is prepared as follows: S1. Disperse 1-vinylimidazole in water to form an aqueous solution of 1-vinylimidazole; S2. Under nitrogen protection, the 1-vinylimidazol aqueous solution and initiator prepared in step S1 are added dropwise to the polycarboxylate superplasticizer to react and obtain the polycarboxylate superplasticizer modified with vinylimidazolium grafting.

5. The high-strength self-compacting concrete for complex steel structures according to claim 4, characterized in that, The amount of 1-vinylimidazole used is 1.5%-5.0% of the solid content of the polycarboxylate superplasticizer.

6. The high-strength self-compacting concrete for complex steel structures according to claim 4, characterized in that, Step S2-1: After the reaction is complete, adjust the pH of the reaction solution to 6.5-7.

5.

7. The high-strength self-compacting concrete for complex steel structures according to claim 3, characterized in that, The additives also include nano-montmorillonite dispersion.

8. The high-strength self-compacting concrete for complex steel structures according to claim 7, characterized in that, The mass ratio of the effective solid content of the nano-montmorillonite dispersion to the effective solid content of the polycarboxylate superplasticizer modified with vinylimidazolium graft is 1:(3-8).

9. The high-strength self-compacting concrete for complex steel structures according to claim 1, characterized in that, The additives also include polyether-modified silicone defoamers.

10. A method for preparing high-strength self-compacting concrete for complex steel structures according to any one of claims 1-9, characterized in that, Includes the following steps: After cement, fly ash, mineral powder, coarse aggregate, and fine aggregate are mixed evenly, admixtures and water are added and mixed evenly to obtain the high-strength self-compacting concrete.