A method of adding attapulgite clay-based conditioner to enhance the workability of concrete for slip-form construction

Abstract

The application discloses a method for improving the workability of concrete for slip-form construction by adding a mixed attapulgite clay-based conditioner, which comprises the following steps: modifying mixed attapulgite clay with quaternary ammonium salt cationic surfactant and fully hydrating the mixed attapulgite clay to obtain a conditioner slurry; and adding and mixing, in steps, cement, fly ash, sand, gravel, water, a functional additive (which is compounded from carbon six polycarboxylic acid water reducing agent, sodium gluconate, glycerol, hydroxypropyl methyl cellulose and fatty alcohol polyoxyethylene ether sodium sulfate) and the conditioner slurry to obtain the concrete for slip-form construction. The application successfully prepares the concrete with excellent workability, small collapse and high strength by adding the mixed attapulgite clay-based conditioner, regulating the components and proportion of the functional additive, optimizing the mixing ratio and mixing in steps, and the concrete has a good application prospect in the fields of slip-form construction, 3D printing and complex component manufacturing.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of concrete for slip-form construction, in particular to a method for improving the workability of concrete for slip-form construction by adding a mixed attapulgite clay-based conditioner, and belongs to the field of green chemistry and low-carbon building materials. BACKGROUND

[0002] It is well known that concrete has excellent plasticity, mechanical properties and durability, and is widely used in the fields of construction, water conservancy engineering, infrastructure engineering and 3D intelligent manufacturing. The workability and quality of concrete are largely determined by the properties, addition amount and compatibility of the component materials, such as the particle shape, surface characteristics and grading of aggregates, which can affect the bonding of cement and aggregates and the fluidity of concrete mixture; concrete mixed with sand having a fineness modulus greater than 3.7 is not easy to control in workability and is not easy to vibrate into shape; concrete mixed with sand having a fineness modulus less than 0.7 requires more cement content and the strength is significantly reduced. At the same time, the workability of concrete is also closely related to the construction process (mixing, forming and curing). With the rapid development of building engineering technology in China, infrastructure engineering structures are becoming more complex, construction equipment is gradually developing towards mechanization, intelligentization and integration, and construction technology is paying more attention to environmental protection and sustainability, and the comprehensive performance requirements of concrete materials are also becoming higher and higher.

[0003] Slipform construction is a concrete paving process that utilizes a complex and comprehensive large-scale mechanized construction system (slipform paver). Characterized by the absence of fixed formwork, the construction process—including spreading, paving, vibrating, and finishing—is completed continuously while the paver is in motion. It has been dubbed a "3D printer for cement concrete" and has gained widespread popularity. Compared to traditional manual formwork, slipform construction offers significant advantages in improving construction quality and efficiency, ensuring safe operations, and enhancing overall profitability, including high mechanization, rapid construction speed, structural integrity, high surface finish, and beautiful, straight lines. Currently, slipform construction of concrete structures such as cement concrete pavements, curbstones, gutters, and retaining walls has been achieved using molds of varying cross-sectional shapes. However, with the widespread adoption of slipform construction technology, issues with concrete product quality and on-site technical issues have arisen. For example, when constructing crash barriers (approximately 1.2 meters high) using slipform construction, a concrete mix with high workability requirements is required, such as low slump, high cohesion, early strength and rapid hardening, and rapid forming. However, in order to facilitate the slipform paving construction of guardrails, dry hard concrete (slump should be controlled at 30±10mm) is often used. The small slump makes it difficult for concrete to enter and exit the tank of the mixer truck. Tank trucks can only be used to transport the concrete mixture to the site and then use excavators to spread the concrete, which greatly increases the difficulty and cost of concrete transportation and spreading. Tank truck transportation may also lead to deterioration of concrete working performance. At the same time, insufficient vibration liquefaction during the paving process will also cause voids to form in the lower part of the guardrail, and even cause the newly paved concrete guardrail to sink. Choosing concrete with too large a slump will cause poor cohesion, rough surface segregation, linear distortion and deformation, and early cracking of hardened concrete, which will increase safety hazards and the economic cost of subsequent maintenance and repair.

[0004] Throughout the entire slipform construction process, the concrete mix must possess excellent fluidity, wrapping, and water retention during transportation and placement, while also maintaining excellent cohesion, compaction, and shape retention during vibration, extrusion, and paving. Given the maturity of slipform construction equipment, the technical challenges of slipform construction lie in designing the concrete mix proportions and controlling working properties such as workability and thixotropy. Only when the working properties of slipform concrete (such as workability, compaction, strength, and stability) meet the requirements of each stage of slipform construction, coupled with the smooth operation of the slipform paver, can the high quality and efficiency of the slipform construction process be fully demonstrated. At the same time, appropriate admixtures should be selected based on transportation distance, environment, climate, and other conditions to ensure and improve the performance of the concrete mixture. However, the high water reduction rate of a single polycarboxylic acid high-performance water-reducing agent gives the concrete a high degree of fluidity, but poor plasticity retention, which seriously affects the construction progress and quality of slipform construction. This requires the optimal combination of functional components with good compatibility and environmental friendliness to obtain a composite admixture that can improve the workability and shape retention of concrete. Therefore, it is of great practical significance to formulate a slipform construction concrete that can meet the performance requirements of slipform construction while also having good plasticity retention and high early strength, and with controllable properties.

[0005] Natural micro- and nanostructured clay minerals possess excellent surface, volume, size, and filling effects, making them the preferred choice for environmentally friendly functional materials and novel auxiliary fillers. Among them, attapulgite is a magnesium-aluminosilicate clay mineral with regular nanopores and a one-dimensional rod-shaped crystalline morphology. Its unique crystal structure and excellent adsorption, carrier, colloidal, and reinforcing properties enable it to play a vital role in many sectors of the national economy. With the continuous decline in high-quality attapulgite resources, mixed clay minerals associated or symbiotic with various minerals will become a focus of future development. Mixed-dimensional attapulgite clay is a natural nanostructured mineral material composed primarily of one-dimensional rod-shaped attapulgite and two-dimensional flaky illite. It possesses the combined properties of both one- and two-dimensional clay minerals, boasting vast reserves, strong adsorption capacity, and low cost. Similarly, green, environmentally friendly, and low-cost attapulgite can also be used to improve the working performance and application performance of concrete materials. For example, patents such as a slipform concrete for high piers of highway bridges and its preparation method (CN118221399A), an ultra-high performance concrete composition that can be sprayed (CN114075059A), a cementitious material containing modified basalt fiber and its preparation method (CN113173749B), a concrete composite admixture and its preparation method (CN113292273A), a concrete and its preparation method (CN107879690 A), a preparation method of nano-attapulgite recycled concrete (CN113773016A), and a red mud / attapulgite ceramsite concrete hollow insulating block and its preparation method (CN103253907B) all involve the use of attapulgite to prepare slipform concrete as a thixotropic agent, thickener, and to improve concrete strength or thermal insulation properties.

[0006] Existing technical solutions for using attapulgite to improve the working performance of concrete only utilize the high viscosity of attapulgite, its activity after high-temperature calcination, or the increase of surface activity by surface-modified basalt fibers. They do not truly achieve efficient utilization of the unique structural characteristics, physical and chemical properties, and micro-nano effects of attapulgite itself. They also do not combine key process controls such as the selection and quality control of concrete raw materials, mix ratio optimization, functional admixture compounding, and mixing process to give full play to the compatibility and complementary advantages of the various components of concrete to promote and synergistically improve the working performance and quality of concrete materials. In view of the particularity of the sliding membrane construction process and the high performance requirements of the concrete used, the present invention adopts multiple strategies such as adding a mixed-dimensional attapulgite clay-based conditioner slurry, regulating the functional components and proportions in the composite admixture, optimizing the mix ratio and mixing in steps. The structure-activity relationship between key factors such as the addition amount of the mixed-dimensional attapulgite clay-based conditioner, the proportion of key functional components in the composite admixture, the mix ratio and the working performance of the concrete mixture is quantitatively analyzed, and concrete with excellent workability, slump retention and high strength is successfully prepared. The concrete has good application prospects in the fields of sliding form construction, 3D printing and complex component manufacturing. Summary of the Invention

[0007] The working performance of the above-mentioned concrete mixture for synovial construction cannot simultaneously meet the specific requirements in the transportation, distribution, paving and forming stages, which seriously limits the full realization of the advantages of synovial construction in terms of construction speed, construction quality and comprehensive economic benefits. Based on a deep understanding of the synovial construction process, the specific working performance requirements of concrete for synovial construction and the physical and chemical properties of mixed-dimensional attapulgite clay, the present invention provides a method for improving the working performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner. First, the mixed-dimensional attapulgite clay is modified with a quaternary ammonium salt cationic surfactant and fully hydrated to obtain a conditioner slurry. Then, materials such as cement, fly ash, sand, gravel, water, functional admixture (formed by a compound of polycarboxylic acid water reducer and sodium gluconate, glycerin, hydroxypropyl methylcellulose and sodium fatty alcohol polyoxyethylene ether sulfate) and the conditioner slurry are added and mixed in steps to obtain synovial construction concrete.

[0008] The present invention discloses a method for improving the performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner. The method comprises mixing the following raw materials by weight: 320-325 parts cement, 60-65 parts fly ash, 845-855 parts sand (mud content ≤1.0%), 725-730 parts crushed stone (10-20 mm), 300-305 parts crushed stone (20-30 mm), 175-185 parts water, 4-6 parts functional admixture, and 2-6 parts mixed-dimensional attapulgite clay-based conditioner. The cement is a mixture of any one or more of Portland cement, white cement, and sulphoaluminate cement; the desulfurized gypsum and alcoholamine grinding aids are added in amounts of ≤6% and 0.1%, respectively. The fly ash is Class F fly ash with a water requirement ratio (%) of ≤90; and the crushed stone has a mud content of ≤1.0%. The sand is natural sand or washed sand, primarily medium-coarse sand, with a fineness modulus of 2.6 to 3.2. The flocculant content in the washed sand is ≤0.5%. The above mix design is based on the basic technical properties of the raw materials and the specific conditions of slipform construction. Combined with preliminary concrete mix design and laboratory mix testing, the effects of changes in water-binder ratio, specific water consumption, sand ratio, admixture components, and additive amounts on key concrete properties such as workability, slump, and mechanical strength were systematically examined. Ultimately, the amounts of component materials that meet the construction conditions, mechanical properties, and other technical and economic indicators required for slipform construction were determined.

[0009] Among them, if the mud content in the fine aggregate sand is too high, the mud minerals therein will absorb the key components of the functional admixture, greatly reducing the use effect of the functional admixture and the synergistic enhancement effect between the components, and even causing the admixture to fail. The mud content in the sand needs to be controlled to ≤1.0%; at the same time, the particle shape and surface characteristics of the sand will affect its bonding with cement and the fluidity of the concrete mixture. In order to meet the fluidity of concrete in slipform construction, it is preferred to use medium-coarse sand as the main material with a fineness modulus of 2.6 to 3.2, and use an appropriate amount of medium-sized sand to fill the gaps between the coarse sand. The total void ratio and total surface area are reduced, which not only reduces the amount of cement slurry used, but also improves the density and strength of the concrete; if washed sand is used, the flocculant content in the washed sand needs to be limited to ≤0.5%. This is because the trace flocculant contained in the sand will reduce the strength of the concrete, resulting in damage to the concrete's shape retention ability during slipform construction. In addition, the particle size, surface condition, and gradation of coarse aggregate are closely related to density and strength. The aggregate's crushed stone particle size is optimized to be between 10 and 30 mm, and the crushed stone is applied at a mass ratio of 7:3 between 10-20 mm and 20-30 mm. This ensures both fluidity during feeding and paving during slipform construction, while also ensuring sufficient strength and a smooth surface for the paved concrete. Furthermore, to meet the requirements for slipform construction concrete to possess both fluidity during transportation and rapid cohesion and formwork erection during paving, technical features such as the dosage of desulfurized gypsum and alcoholamine grinding aids in the cement, as well as the water requirement ratio of fly ash, are specified to avoid introducing excessive gypsum or alcoholamines that could affect the concrete's cohesiveness and setting time, thus ensuring excellent performance for slipform construction concrete.

[0010] The preparation method of a mixed-dimensional attapulgite clay-based conditioning agent is as follows: mixed-dimensional attapulgite clay is modified with a quaternary ammonium salt cationic surfactant to obtain a modified powder, the modified powder is then uniformly dispersed in water at a solids content of 30-35%, and hydrated for at least 6 hours to obtain a conditioning agent slurry, which is then added in the form of a slurry. The mixed-dimensional attapulgite clay has a mineral composition including clay minerals, quartz, feldspar, dolomite, calcite, and gypsum. The clay component is primarily attapulgite, supplemented by illite, chlorite, and kaolinite. The clay mineral content is 50-55%, and attapulgite accounts for 60-70% of the clay minerals. The quaternary ammonium salt cationic surfactants are dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), and trimethylstearylammonium bromide (STAB), added in an amount of 10-20% by weight of the mixed-dimensional attapulgite clay. The modification reaction is carried out at a temperature of 60-80°C for 4-6 hours. Preferably, the mixed-dimensional attapulgite clay is pretreated with acid activation before organic modification. The acid activation is performed by dispersing the raw ore at a solid-liquid ratio of 1:5 in a sulfuric acid or phosphoric acid aqueous solution with a pH of 3.5-4.0 and stirring for 4-8 hours.

[0011]

[0012] From the physical and chemical properties of mixed-dimensional attapulgite clay (Table 1) and SEM images ( Figure 1 ) It can be seen that the mixed-dimensional attapulgite clay is composed of one-dimensional rod-shaped attapulgite and two-dimensional lamellar clay minerals such as illite and kaolinite, as well as granular quartz, calcite, etc. It is a typical composite material of mixed-dimensional crystal structure mineral symbiosis, wherein the attapulgite content is between 20% and 40%, the rod crystal length is uneven and the length / diameter ratio is small, and the rod crystals with different arrangement directions are entangled and intertwined with the lamellar layers and particles, and further disordered stacking forms a large number of nano-channels. Preferably, acid activation is performed in advance to remove unstable fine particles such as carbonates and dolomite in the mixed-dimensional attapulgite clay, so that after adding it to concrete, it does not affect the corrosion resistance and durability of the concrete, and the unblocked stacked pores further increase the number of binding sites with surfactants. Furthermore, the surface structure parameters can be quantitatively calculated by the N2 adsorption-desorption isotherm, including the specific surface area (S BET ), total pore volume (V total ) and average pore size (P D ), it can be seen that the specific surface area and total pore volume of the mixed-dimensional attapulgite clay have reached 149m 2 / g and 0.2676 cm 3 / g, with a pore diameter of approximately 7.18nm. The large specific surface area, pore volume, and abundant small pores endow the mixed-dimensional attapulgite with excellent adsorption and carrier properties, facilitating the construction of functional composite materials. More importantly, mixed-dimensional attapulgite is abundant and widely distributed in nature, with reserves exceeding 1 billion tons in my country alone. This allows for local access to the material, providing a strong raw material base and supply support for the large-scale and high-value applications of mixed-dimensional attapulgite clay. This also lays a solid foundation for the application of this affordable, environmentally friendly mixed-dimensional attapulgite clay in new concrete technologies, such as slipform construction.

[0013]

[0014] This application selects mixed-dimensional attapulgite clay, which has abundant reserves, a mixed-dimensional structure, and excellent adsorption properties, as raw material. After organic modification and sufficient hydration, it is used to prepare a concrete conditioner, which is then added in the form of a slurry (to reduce the effect of water absorption on the water-cement ratio of the concrete). This not only effectively inhibits the weakening or functional masking caused by the adsorption of functional components in the admixture, but also utilizes highly dispersed attapulgite / surfactant micelles to improve the workability, thixotropy, and compactness of concrete materials. As shown in Table 2, the surface of natural mixed-dimensional attapulgite clay is rich in polar silanol groups and negative charges (Zeta potential of -21.6 mV). After modification with quaternary ammonium cationic surfactants, the main chemical composition does not change significantly, indicating that it is still a mixed-dimensional composite mineral composed of one-dimensional and two-dimensional clay minerals. The high calcium content is conducive to increasing the Ca content in the cement paste. 2+ The concentration was increased, which accelerated the hydration and improved the early strength, while the Zeta potential increased to -14.1 mV, which confirmed that the quaternary ammonium salt cationic surfactant and the mixed-dimensional attapulgite clay achieved efficient combination, and increasing the modification reaction temperature was more conducive to the rapid reaction and improved the efficiency of organic modification. After organic modification, the mixed-dimensional attapulgite clay forms a more hydrophobic distribution medium, which can weaken the strong adsorption of the mixed-dimensional attapulgite clay on free water and free water in the concrete system, reduce the aggregation rate of nano-scale cementitious materials, and ensure that there is sufficient water in the system for hydration, hydration and lubrication. It also increases the contact area between the mineral additives and the cementitious materials and aggregates, effectively improving the agglomeration of the cementitious system and enhancing the dispersion and uniformity of the cement paste. On the other hand, using quaternary ammonium salt cationic surfactants as soft templates, the mixed-dimensional attapulgite clay has both inorganic and organic properties. One end of the mineral is hydrophilic, and the other end of the grafted long-chain organic molecules can not only disperse the nano- and mixed-dimensional clay minerals evenly in the gaps between the cement paste and aggregates through electrostatic repulsion, but can also combine with the free components in the functional admixture to adjust the nanostructure, morphology and size of the composite cementitious materials, thereby improving the thixotropy, density and water retention. Finally, the modified mixed-dimensional attapulgite clay was fully hydrated and added to the concrete in the form of a conditioner slurry, which solved the problem that the mixed-dimensional attapulgite clay had strong hydrophilicity, causing the concrete mixture to dry and harden quickly, and did not meet the fluidity requirements for slipform construction and transportation. At the same time, the highly dispersible, nano-mixed-dimensional mineral conditioner can quickly disperse and act between the cement paste and aggregate, showing excellent thixotropy, filling effect and toughening and reinforcement effects during the vibration and paving process.

[0015] The functional admixture comprises a C6 polycarboxylate water reducer (water reduction rate of 25-35%), sodium gluconate, glycerin, hydroxypropyl methylcellulose, and sodium fatty alcohol polyoxyethylene ether sulfate (AES) in a mass ratio of 100:2-4:2-3:3-4:1-2. Specifically, an optimized ratio of retarder, collapse preventer, air entraining agent, and defoamer is added to the high-efficiency C6 polycarboxylate water reducer for compounding. The concrete mixing process is as follows: first, 80% of the total water volume is added to the uniformly mixed dry materials of cement, sand, gravel, and fly ash, and stirred for 1-2 minutes. Then, the functional admixture and 10% of the total water volume are added, and stirred for 2-3 minutes. Finally, a conditioner slurry (containing approximately 10% of the total water volume) is added and stirred again for 2-3 minutes to produce concrete for slip film construction. To improve the mixing efficiency and performance of concrete, a step-by-step mixing strategy is adopted. After the cementitious materials, aggregates, and 80% water are thoroughly mixed, the surfaces of the cementitious materials and aggregates are evenly covered with a water film. Adding diluted functional admixtures allows the functional components to fully function directly within the highly dispersed system formed by the water film. After key components such as high-efficiency water reducers improve the fluidity of the concrete, a high-solids content conditioner slurry is added and stirred again. This allows the nanostructured, amphiphilic, mixed-dimensional mineral materials to be efficiently dispersed and act on the concrete mixture system. Slump, compactness, and strength are key technical indicators for measuring the performance and quality control of concrete mixtures used in slipform construction. Initial slump and the change in slump over time directly reflect the concrete's workability, self-compacting, and shape-retention capabilities. High-strength concrete not only ensures the quality of construction projects but also provides a strong guarantee for building safety.

[0016] The slump of the prepared concrete changes over time ( Figure 2) It can be seen that in Comparative Example 1, the mix ratio used in the on-site formwork casting method was used, and the concrete mixture prepared exhibited slight bleeding, which may be caused by slight differences in the materials or water quality used. After 1 hour, the slump became 50 mm, and a small amount of slurry was found to flow out from the bottom of the slump cone after lifting it, indicating that the concrete had poor fluidity and water retention and could not meet the requirements of slipform construction concrete. Comparative Example 2, using the same mix ratio, added a slurry of mixed attapulgite clay (1.0% by weight of the cementitious material). The workability of the concrete mixture was significantly improved, and the initial slump was reduced to 180 mm. Although the slump loss after 1 hour was still as high as 130 mm, which still did not meet the construction requirements of slipform construction concrete, the surface of the concrete specimen after slump was smoother and denser, indicating that the addition of attapulgite can significantly improve the workability and forming ability of concrete. Furthermore, from the time-dependent changes in the slump of the concrete in Examples 1 to 3, it can be seen that the concrete mixtures to which the mixed-dimensional attapulgite clay-based conditioner slurry and the functional admixture were added did not show rapid cohesion or dry hardening, but always exhibited excellent workability, cohesion and shape retention within 2 hours, and the slump was maintained between 130 and 200 mm. The cement slurry and aggregate had good encapsulation properties. In particular, the stacking morphology of the concrete specimens after collapse in Example 2 was approximately an ideal truncated cone, and the specimen surface was smoother, denser, and had no collapse. It had excellent workability and self-compacting ability, and could fully meet the working performance requirements of slipform construction concrete.

[0017] Unlike conventional concrete structure detection methods, CT scanning technology uses an innovative, non-destructive approach to deeply study the microstructure of concrete, which can better reflect the spatial distribution of aggregates and pores within the concrete, as well as the characteristics of the pore structure. In addition, due to the different densities of cement mortar and stone materials in concrete and the pores contained within, the absorption coefficient of concrete to X-rays is different, that is, the CT value is different. The size of the CT value directly reflects the density and density of the concrete material. The larger the CT value, the greater the density and density of the concrete material, and the corresponding mechanical strength will also increase. From the CT scanning images of different concretes ( Figure 3 and 4 ) can be seen from the results that adding mixed-dimensional attapulgite clay slurry can increase the cohesiveness of concrete, while the center of the specimen has more cementitious materials and relatively less aggregate, while the aggregate distribution outside is relatively more uniform. When the layer thickness is 6 and 9 cm, the number of large-diameter pores is more and more concentrated ( Figure 3 The addition of mixed-dimensional attapulgite clay-based conditioner slurry and functional admixtures makes the cementitious materials and aggregates in each fault of the concrete uniformly distributed and tightly combined, and the number of pores in the cross section is significantly reduced and small pores are scattered ( Figure 4), indicating that the two synergistically improve the spatial uniformity of aggregate and pore distribution and pore structure characteristics of concrete; the mixed-dimensional attapulgite clay-based conditioner grafted with long-chain organic molecules has a nano-, mixed-dimensional crystal structure and amphiphilic properties, efficiently and quickly filling the micro-gaps between cement paste and aggregate. It also combines with the free components in the functional admixture to improve the workability, thixotropy, and water retention of concrete, further facilitating the formation of a stable, dense structure and enhancing concrete strength. This is fully reflected in the changes in the CT value and compressive strength of the concrete. The CT value and compressive strength of the concrete prepared in Comparative Example 2 were 1711.91 Hu and 40.8 MPa, respectively. However, after adding the mixed-dimensional attapulgite clay-based conditioner and functional admixture in Example 2, the CT value and compressive strength of the concrete increased to 1906.08 Hu and 45.31 MPa, respectively, far exceeding the strength requirements of the C30 crash barrier. The other examples also showed the same trend, demonstrating excellent density and toughening and reinforcement properties.

[0018] In summary, the present invention has the following advantages compared with the prior art:

[0019] 1. By introducing a mixed-dimensional attapulgite clay-based conditioner and functional admixtures into concrete materials, and further combining multiple strategies such as component quality control, optimized mix ratio, and step-by-step mixing, this invention successfully produces concrete with excellent slump retention, workability, and high strength. This concrete can meet the specific working properties of concrete used in slipform construction, 3D printing, and the construction of complex structures, and has outstanding advantages in improving construction quality and efficiency, reducing labor intensity, reducing material consumption, and enhancing overall benefits.

[0020] 2. Based on the slipform construction process and technical requirements, the present invention uses calcium-rich mixed-dimensional attapulgite clay, which is abundant in reserves, has a mixed-dimensional structure, excellent adsorption properties, and is rich in calcium, as raw material. After modification with a quaternary ammonium salt cationic surfactant, a conditioning agent slurry is obtained. Furthermore, a functional composite admixture is obtained by compounding multiple components such as a slump preventer, a retarder, and an air-entraining agent with a high-efficiency water reducer. The two components synergistically regulate the macroscopic properties (slump and strength) and microscopic properties (internal aggregate distribution and pore space distribution) of concrete, thereby producing a concrete material with a slump maintained at 130 to 200 mm within 2 hours and excellent cohesion and strength.

[0021] 3. The concrete preparation method of the present invention is a fine-tuned version of the conventional concrete mixing process. By adding a small amount of clay-based conditioners and functional admixtures, a concrete with specific working properties is obtained without increasing equipment investment. This method can be applied to many fields related to thixotropic concrete. Moreover, the above-mentioned fine-tuning only increases the concrete cost by approximately 70 to 100 yuan per cubic meter. 3It solves many application technical problems in the transportation, distribution and paving of slipform construction concrete, has little environmental pollution and ecological damage, and has good economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM (top) and TEM (bottom) images of mixed-dimensional attapulgite clay.

[0023] Figure 2 The slump of the prepared concrete changes over time.

[0024] Figure 3 and 4 The following are CT scan images of concrete specimens prepared in Comparative Example 2 and Example 2, respectively. The concrete specimens used were 15 cm x 15 cm in size. The CT scanning equipment was a Brilliance 16 spiral CT machine, and the CT scanning conditions were as follows: slice thickness: 3 mm; scanning voltage: 120 kV; reconstruction matrix: 1024 × 1024; magnification: 1; CT value range: -1024 to +3071. After scanning, plots were made at thicknesses of 3, 6, 9, and 12 cm, respectively, to obtain the corresponding aggregate distribution maps (top) and pore distribution maps (bottom). In the aggregate distribution map, white represents aggregate and gray represents hardened cement paste. In the pore distribution map, black spots represent pores, and the spot size represents the pore diameter.

[0025] Figure 5 CT values ​​of the concrete test blocks prepared in Comparative Example 2 and Example 2.

[0026] Figure 6 is the compressive strength of the prepared concrete after 28 days of curing. DETAILED DESCRIPTION

[0027] The following is a detailed description of the method for improving the performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner. Slump and block strength were tested in accordance with the "Standard for Testing Methods of Ordinary Concrete Mixtures (GB / T50080-2016)" and the "Testing Procedures for Cement and Cement Concrete for Highway Engineering (JTG3420-2020)."

[0028] Comparative Example 1

[0029] Accurately weigh the following raw materials in parts by weight: 325 parts of Portland cement, 65 parts of Class F fly ash, 845 parts of sand (mud content of 1.0%), 725 parts of crushed stone (10-20mm), 305 parts of crushed stone (20-30mm), 170 parts of water, and 5 parts of C6 polycarboxylic acid water reducer. Among them, the sand is natural sand with a mud content of 1.0% and a fineness modulus of 2.8; the mud content of crushed stone is 1.0%; and the water reduction rate of the C6 polycarboxylic acid water reducer is 30%. The concrete mixing process is as follows: First, mix the above-mentioned dry materials such as cement, sand, crushed stone, and fly ash with water and stir for 2 minutes, then add the water reducer and stir for 3 minutes to obtain concrete. The slump change of the concrete over time and the strength data of the test block after 28 days of curing are shown in Figure 2 and 6 .

[0030] Comparative Example 2

[0031] Accurately weigh the following raw materials in parts by weight: 325 parts Portland cement, 65 parts Class F fly ash, 845 parts sand (1.0% mud content), 725 parts crushed stone (10-20 mm), 305 parts crushed stone (20-30 mm), 166 parts water, 5 parts C6 polycarboxylic acid-based water reducer, and 13 parts mixed-dimensional attapulgite clay slurry. The mixed-dimensional attapulgite clay slurry is prepared by dispersing mixed-dimensional attapulgite clay (30% attapulgite) in water at a solids content of 30% and stirring for 12 hours. The sand is natural sand with a mud content of 1.0% and a fineness modulus of 2.8. The crushed stone has a mud content of 1.0%. The C6 polycarboxylic acid-based water reducer has a water-reducing rate of 30%. The concrete mixing process is as follows: first, add water and water reducer to the uniformly mixed cement, sand, crushed stone, and fly ash dry materials and stir for 2 minutes. Then, add the mixed attapulgite clay slurry and stir again for 3 minutes to obtain concrete. The slump change of this concrete over time and the strength data of the test block after 28 days of curing are shown in Figure 2 and 6 , the CT scan images and CT values ​​of the concrete specimens are shown in Figure 3 and 5 .

[0032] Example 1

[0033] (1) Constructing a mixed-dimensional attapulgite clay-based conditioning agent: First, the mixed-dimensional attapulgite clay (attapulgite content is 30%) is dispersed in a sulfuric acid aqueous solution with a pH value of 3.5 at a solid-liquid ratio of 1:5 and stirred for 8 hours. After filter pressing and centrifugation, the solid phase filter cake is dispersed in a trimethyl stearyl ammonium bromide aqueous solution, wherein the mass of trimethyl stearyl ammonium bromide is 10% of the mass of the acid-activated mixed-dimensional attapulgite clay. After reflux stirring at 60°C for 6 hours, centrifugation and drying are performed to obtain a modified powder. The modified powder is dispersed in water with a solid content of 30% and stirred for 6 hours to obtain a conditioning agent slurry for use.

[0034] (2) Preparation of functional admixture: accurately weigh the following raw materials in parts by weight: C6 polycarboxylic acid water reducer (water reduction rate 35%) and sodium gluconate, glycerol, hydroxypropyl methylcellulose and sodium fatty alcohol polyoxyethylene ether sulfate in a mass ratio of 100:2:2:3:2 and stir (stirring speed 600 rpm, stirring time 15 min) to obtain the functional admixture and set aside;

[0035] (3) Preparation of concrete mixture: Accurately weigh the following raw materials in parts by weight: 325 parts of Portland cement, 65 parts of Class F fly ash, 855 parts of sand (natural sand, mud content 1.0%, fineness modulus 2.6), 730 parts of crushed stone (10-20mm), 300 parts of crushed stone (20-30mm), 171 parts of water, 4 parts of functional admixture, and 13 parts of mixed attapulgite clay-based conditioner slurry. The concrete mixing process is as follows: First, add 154 parts of water to the evenly mixed cement, sand, crushed stone, and fly ash dry materials and stir for 2 minutes, then add the functional admixture and 17 parts of water and stir for 2 minutes, finally add the conditioner slurry and stir again for 3 minutes to obtain concrete for sliding membrane construction. The slump change of this concrete over time and the strength data of the test block after 28 days of curing are shown in Figure 2 and 6 .

[0036] Example 2

[0037] (1) Constructing a mixed-dimensional attapulgite clay-based conditioning agent: First, the mixed-dimensional attapulgite clay (attapulgite content is 30%) is dispersed in an aqueous solution of dodecyltrimethylammonium bromide at a solid-liquid ratio of 1:5, wherein the mass of dodecyltrimethylammonium bromide is 15% of the mass of the mixed-dimensional attapulgite clay. After stirring and refluxing at 80°C for 6 hours, the modified powder is centrifuged and dried to obtain a modified powder. The modified powder is dispersed in water with a solid content of 33% and stirred and hydrated for 8 hours to obtain a conditioning agent slurry for use.

[0038] (2) Preparation of functional admixture: accurately weigh the following raw materials in parts by weight: C6 polycarboxylic acid water reducer (water reduction rate 30%) and sodium gluconate, glycerol, hydroxypropyl methylcellulose and sodium fatty alcohol polyoxyethylene ether sulfate in a mass ratio of 100:4:3:4:1 and stir (stirring speed 600 rpm, stirring time 15 min) to obtain the functional admixture and set aside;

[0039] (3) Preparation of concrete mixture: the raw materials in the following weight parts were accurately weighed, Portland cement 320 parts, F-grade fly ash 60 parts, sand (natural sand, containing 1.0% of mud, fineness modulus of 2.6) 850 parts, gravel (10-20mm) 725 parts, gravel (20-30mm) 305 parts, water 173 parts, functional additive 6 parts, 6 parts of mixed attapulgite clay-based conditioner slurry. The concrete mixing process is as follows: first, add 156 parts of water to the mixed uniform cement, sand, gravel, fly ash dry materials, stir for 2 min, then add functional additive and 17 parts of water, stir for 2 min, finally add conditioner slurry and stir for 3 min again, get the concrete for slip film construction. The slump loss of the concrete and the strength data of the test block after 28 days of curing are shown in Figure 2 and 6 , CT scan image and CT value are shown in Figure 4 and 5 .

[0040] Example 3

[0041] (1) Construction of mixed attapulgite clay-based conditioner: first, disperse mixed attapulgite clay (attapulgite content is 40%) in pH value of 4.0 phosphoric acid aqueous solution with solid-liquid ratio of 1:5, stir for 6h, centrifugal separation after pressure filtration, disperse the solid phase filter cake into cetyltrimethylammonium bromide aqueous solution, wherein the mass fraction of cetyltrimethylammonium bromide is 20% of the acid-activated mixed attapulgite clay, reflux and stir for 4h at 80℃, then centrifugal and dry to obtain modified powder; disperse the powder in water with solid content of 33% and stir for 12h after hydration, get the conditioner slurry and reserve;

[0042] (2) Preparation of functional additive: accurately weigh the following weight parts of raw materials: carbon six polycarboxylic acid water reducer (water reducing rate is 35%) and sodium gluconate, glycerol, hydroxypropyl methyl cellulose and fatty alcohol polyoxyethylene ether sodium sulfate are compounded by stirring (stirring speed is 600rpm, stirring time is 15min) with mass ratio of 100:4:2:3:2, get the functional additive and reserve;

[0043] (3) Preparation of concrete mixture: Accurately weigh the following raw materials in parts by weight: 325 parts of Portland cement, 65 parts of Class F fly ash, 850 parts of sand (natural sand, mud content 1.0%, fineness modulus 2.6), 730 parts of crushed stone (10-20mm), 305 parts of crushed stone (20-30mm), 171 parts of water, 6 parts of functional admixture, and 18 parts of mixed attapulgite clay-based conditioner slurry. The concrete mixing process is as follows: First, add 156 parts of water to the evenly mixed cement, sand, crushed stone, and fly ash dry materials and stir for 2 minutes, then add the functional admixture and 17 parts of water and stir for 3 minutes, finally add the conditioner slurry and stir again for 3 minutes to obtain concrete for sliding membrane construction. The slump change of this concrete over time and the strength data of the test block after 28 days of curing are shown in Figure 2 and 6 .

Claims

1. A method for improving the working performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner, characterized in that: The concrete is prepared by mixing the following raw materials in parts by weight: 320-325 parts of cement, 60-65 parts of fly ash, 845-855 parts of sand, 725-730 parts of 10-20 mm crushed stone, 300-305 parts of 20-30 mm crushed stone, 175-185 parts of water, 4-6 parts of functional admixture, and 2-6 parts of mixed-dimensional attapulgite clay-based conditioning agent; wherein, the preparation method of the mixed-dimensional attapulgite clay-based conditioning agent is as follows: first, the mixed-dimensional attapulgite clay is prepared. The modified powder is modified with a quaternary ammonium salt cationic surfactant to obtain a modified powder, which is then uniformly dispersed in water with a solid content of 30-35%, hydrated for at least 6 hours to obtain a conditioner slurry, and added in the form of a slurry; the functional admixture is a C6 polycarboxylic acid water reducer, sodium gluconate, glycerin, hydroxypropyl methylcellulose, and sodium fatty alcohol polyoxyethylene ether sulfate (AES) mixed in a mass ratio of 100:(2-4):(2-3):(3-4):(1-2); The concrete mixing process is as follows: first, add 80% of the total water volume to the evenly mixed cement, sand, gravel, and fly ash dry materials and stir for 1 to 2 minutes, then add functional admixtures and 10% of the total water volume and stir for 2 to 3 minutes, and finally add conditioner slurry and stir again for 2 to 3 minutes to obtain concrete for sliding membrane construction.

2. The method for improving the working performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner according to claim 1, characterized in that: The mixed-dimensional attapulgite clay is composed of attapulgite and illite as main minerals, accompanied by montmorillonite, chlorite, kaolinite, illite-montmorillonite mixed-layer minerals and quartz minerals, wherein the content of attapulgite is 20-40%.

3. The method for improving the working performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner according to claim 1, characterized in that: The mixed-dimensional attapulgite clay is pre-treated with acid activation, wherein the raw ore is dispersed in a sulfuric acid or phosphoric acid aqueous solution with a pH value of 3.5 to 4.0 at a solid-liquid ratio of 1:5 and stirred for reaction for 4 to 8 hours.

4. The method for improving the working performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner according to claim 1, characterized in that: The quaternary ammonium salt cationic surfactant is dodecyltrimethylammonium bromide (DTAB), hexadecyltrimethylammonium bromide (CTAB) and trimethylstearyl ammonium bromide (STAB), and the addition amount is 10-20% of the mass of the mixed-dimensional attapulgite clay. The modification reaction is carried out at a temperature of 60-80°C for 4-6 hours.

5. The method for improving the working performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner according to claim 1, characterized in that: The cement is any one of silicate cement, white cement and sulphoaluminate cement or a mixture of the above, wherein the content of desulfurized gypsum and alcohol amine grinding aids is ≤6% and 0.1% respectively; the fly ash is Class F fly ash with a water requirement ratio of ≤90%; and the mud content in the crushed stone is ≤1.0%.

6. The method for improving the working performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner according to claim 1, characterized in that: The sand is natural sand or washed sand, mainly medium-coarse sand, with a fineness modulus of 2.6 to 3.2, wherein the flocculant content in the washed sand is ≤0.5%.

7. The method for improving the working performance of concrete for synovial construction by adding a mixed-dimensional attapulgite clay-based conditioner according to claim 1, characterized in that: The slump of the concrete mixture for sliding membrane construction is maintained between 130 and 200 mm within 2 hours.

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