Method for preparing concrete for sliding film construction by adding attapulgite-based thixotropic agent

Abstract

The present invention discloses a method for preparing concrete for synovial construction by adding an attapulgite-based thixotropic agent. First, Mingguang attapulgite is subjected to acid activation and surface micro-hydrophobicization treatment to obtain a thixotropic agent slurry. Then, materials such as cement, fly ash, sand, gravel, water, a composite admixture (formed by a compound of a polycarboxylate water-reducing agent, sodium gluconate, sodium hexametaphosphate, borax, and sodium α-olefin sulfonate) and the thixotropic agent slurry are added and mixed in steps to obtain a concrete material for synovial construction. The present invention successfully prepares concrete with excellent slump retention, workability, and strength by using multiple strategies such as adding Mingguang attapulgite thixotropic agent slurry, regulating the functional components and proportions in the composite admixture, optimizing the mix ratio, and mixing in steps. The concrete has good application prospects in the fields of slipform construction, 3D printing, and complex component manufacturing.

Description

Technical Field

[0001] The invention relates to a method for preparing concrete for sliding film construction, in particular to a method for preparing concrete for sliding film construction by adding an attapulgite-based thixotropic agent, and belongs to the field of green and low-carbon building materials. Background Art

[0002] With the rapid development of my country's social economy and science and technology, infrastructure projects have become more complex and multi-dimensional. Construction techniques are gradually moving towards mechanization, intelligence, and integration. The construction industry is also placing greater emphasis on technological innovation to drive quality, efficiency, upgrades, and high-quality development. Slipform construction is a construction technique for cast-in-place concrete projects. It uses a slipform paver to compact and form fresh concrete delivered to the construction site in one go. It is considered a "3D printer for cement concrete" and is highly favored by all sectors. Slipform construction offers advantages such as a high degree of mechanization, fast construction speed, good structural integrity, high surface finish, and beautiful, straight lines. Compared to traditional manual formwork techniques, it offers unparalleled advantages in reducing labor intensity, reducing material consumption, improving construction quality and efficiency, ensuring safe operations, and enhancing overall benefits.

[0003] Slipform paving has been demonstrated in the construction of concrete pavements, roads, bridge guardrails, curbs, slopes, ditches, and other ancillary structures. However, with the widespread adoption of this technology, issues with concrete product quality and construction site technical issues have arisen. For example, slipform paving of concrete crash barriers with a certain vertical height (approximately 1.2 meters) places high demands on the workability of the concrete mix, requiring low slump, high cohesion, early strength and rapid hardening, and rapid forming. Furthermore, as small-scale components for roads and bridges, concrete guardrails have long continuous longitudinal lengths, necessitating strict control of their appearance, ensuring a solid interior and polished exterior, accurate dimensions, linear alignment, and consistent color. However, in the process of guardrail slipform paving, in order to facilitate construction, dry hard concrete (slump should be controlled at 30±10mm) is often used. Too small slump makes it difficult for concrete to enter and exit the tank of the mixer truck, and it is easy to stick to the tank during transportation, making it difficult to transport it by concrete mixer truck. It can only be transported to the site by tank truck and then spread by excavator, which greatly increases the difficulty and cost of concrete transportation and spreading. In addition, due to insufficient vibration liquefaction during the paving process, it 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, early cracking and shrinkage, etc. The working performance, strength after hardening and durability of the concrete will be reduced, which will pose a safety hazard to traffic safety and increase 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, as well as 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 slipform concrete exhibits excellent working properties (such as workability, compaction, strength, and stability) that meet the requirements of each stage of slipform construction, combined 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. A single polycarboxylic acid high-performance water-reducing agent has a high water-reduction rate, giving the concrete high fluidity, but poor plasticity retention, which seriously affects the construction progress and quality of slipform construction. This requires optimizing compatible, environmentally friendly functional components to create a composite admixture to improve the workability and shape retention of concrete. Therefore, formulating a slipform construction concrete that not only meets the performance requirements of slipform construction but also has good plasticity retention and high early strength is of great practical significance.

[0005] In the construction industry, the performance of cementitious materials is often enhanced by adding chemical modifiers (such as hydroxyethyl cellulose ether and hydroxypropyl methyl cellulose ether) or polymer additives. Unlike chemical additives, natural micro- and nanostructured clay minerals possess excellent surface effects, volume effects, size effects, and filling effects, making them the preferred choice for environmentally friendly functional materials and novel auxiliary fillers. Among them, attapulgite is a hydrous magnesium-aluminum silicate clay mineral with a layered chain structure. It is a natural one-dimensional nanostructured material. Its unique nanorod-like crystal morphology, pore structure, and charged properties give it excellent colloidal and adsorption properties, as well as the ability to strengthen and toughen polymer materials. It is widely used in various industries such as petroleum, chemical industry, environmental protection, medicine, food, and energy. Studies have shown that green, environmentally friendly, and low-cost attapulgite can improve the working performance and application performance of concrete materials. For example, attapulgite can be used to prepare thixotropic agents for slipform concrete of high bridge piers, attapulgite and other clay minerals can be used to prepare thickeners for concrete, attapulgite can be used as a concrete component to improve concrete strength, or attapulgite can be used to improve the thermal insulation performance of concrete blocks. Patents such as a slipform concrete for high piers of highway bridges and a preparation method thereof (CN118221399A), an ultra-high performance concrete composition capable of spraying (CN114075059A), a cementitious material containing modified basalt fiber and a preparation method thereof (CN113173749B), a nanoporous concrete using a thixotropic colloid as a template and a preparation method thereof (CN105294141A), a concrete composite admixture and a preparation method thereof (CN113292273A), a concrete and a preparation method thereof (CN107879690 A), a preparation method of nano-attapulgite recycled concrete (CN113773016A), and a red mud / attapulgite ceramsite concrete hollow insulation block and a preparation method thereof (CN103253907B) all involve this content. However, the above-mentioned technical solutions for using attapulgite to improve the working performance of concrete only utilize technical characteristics such as the viscosity of attapulgite, the activity of high-temperature calcined attapulgite, or the use of attapulgite to surface-modify basalt fiber to increase surface activity, and fail to achieve truly efficient utilization of the unique structural characteristics, physical and chemical properties, and micro-nano effects of attapulgite itself.

[0006] In fact, not all attapulgite exhibits viscosity-increasing and thixotropic properties at low concentrations. Only the relatively well-developed, pure, high-rod length-to-diameter ratio Mingguang attapulgite with a trioctahedral crystal structure exhibits excellent viscosity-increasing and thixotropic properties. Increasing the amount of attapulgite added inevitably increases the viscosity and thixotropy of the suspension. However, exceeding a certain addition level (e.g., ≥2%) can cause the concrete mixture to instantly become dry and hard, losing fluidity, causing significant problems for subsequent construction. Furthermore, given the specific nature of the slipform construction process and the high requirements for the concrete's performance, key control factors such as the selection and quality control of slipform concrete raw materials, mix ratio design, compounding of functional admixtures, and the mixing process are also crucial. This has important practical implications for the promotion and application of slipform construction technology in the construction industry. Based on this, the present invention adopts multiple strategies such as adding Mingguang attapulgite thixotropic agent slurry, regulating the functional components and proportions in the composite admixture, optimizing the mix ratio and mixing in steps, quantitatively analyzing the structure-activity relationship between key factors such as the amount of attapulgite thixotropic agent added, the proportion of key functional components in the composite admixture, the mix ratio and the working performance of the concrete mixture, and successfully prepares concrete with excellent slump retention, compactness, workability and strength, which has good application prospects in the fields of slipform construction, 3D printing, and complex component manufacturing. Summary of the Invention

[0007] In view of the fact that the above-mentioned concrete mixture cannot simultaneously meet the specific working performance requirements in the transportation, distribution, paving and forming stages of synovial construction, which seriously limits the full realization of the advantages of the synovial construction process in terms of construction speed, construction quality, and comprehensive economic benefits, the present invention, 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 Mingguang attapulgite, provides a method for preparing concrete for synovial construction by adding a attapulgite-based thixotropic agent. First, the Mingguang attapulgite is acid-activated and the surface is micro-hydrophobized to obtain a thixotropic agent slurry. Then, materials such as cement, fly ash, sand, gravel, water, composite admixture (formed by a compound of polycarboxylic acid water reducer, sodium gluconate, sodium hexametaphosphate, borax and sodium α-olefin sulfonate) and the thixotropic agent slurry with optimized ratios are added and mixed step by step to obtain concrete for synovial construction.

[0008] The present invention provides a method for preparing concrete for synovial film construction by adding an attapulgite-based thixotropic agent, characterized in that the concrete is prepared by mixing the following raw materials in parts by weight: 315-320 parts of cement, 55-60 parts of fly ash, 840-850 parts of sand (mud content ≤1.0%), 305-315 parts of crushed stone (5-10 mm), 720-725 parts of crushed stone (10-20 mm), 180-190 parts of water, 5-6 parts of a composite admixture, and 1.5-3.0 parts of the attapulgite-based thixotropic agent. 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 2.6-3.2. The flocculant content in the washed sand is ≤0.5%. The composite admixture is a C6 polycarboxylate water-reducing agent (water-reducing rate of 25-35%) mixed with sodium gluconate, sodium hexametaphosphate, borax, and sodium α-olefin sulfonate (AOS) in a mass ratio of 100:2-4:2-3:1-2:0.25-1.0. The 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 addition levels on key concrete properties such as workability, slump, and mechanical strength were systematically examined. Ultimately, the amounts of component materials that meet the required construction conditions, mechanical properties, and other technical and economic indicators 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 functional components in the composite admixture, greatly reducing the efficacy of the composite admixture and the synergistic enhancement effect between the components, and even causing the admixture to fail. Therefore, 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 mainly medium-coarse sand 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, reducing the total void ratio and total surface area. Not only does this reduce the amount of cement slurry used, but it can also improve the density and strength of the concrete; and if washed sand is used, the flocculant content in the washed sand needs to be limited to ≤0.5%. This is because the trace flocculants contained in the sand will reduce the strength of the concrete, resulting in damage to the shape retention of the concrete during slipform construction. Furthermore, the maximum particle size of coarse aggregate is limited by the structural type and reinforcement density. The surface condition of coarse aggregate is also closely related to strength. Considering that the slipform construction process uses a spiral distributor to feed the concrete, and that the concrete passes through the steel mesh during paving, tightly enveloping the rebar, the maximum particle size of the crushed stone in the aggregate is optimized. Two sizes of crushed stone, 5-10 mm and 10-20 mm, are selected and mixed in a mass ratio of 3:7. This ensures both ease of feeding and paving during the slipform construction process while also ensuring sufficient strength and a smooth surface for the slipform concrete. Furthermore, to meet the requirements for slipform concrete to have both fluidity (during transportation) and rapid cohesion and formwork erection (during paving), technical characteristics such as the dosage of desulfurized gypsum and alcoholamine grinding aids in the cement, as well as the water requirement of the fly ash, are specified to ensure excellent workability for slipform concrete.

[0010] The preparation method for a thixotropic agent based on attapulgite is as follows: After pulping and acid activation of Mingguang attapulgite ore and surface micro-hydrophobization treatment, the ore is dispersed in water at a solids content of 5-7% and stirred for at least 12 hours to form a thixotropic agent slurry, which is then added to the ore. The attapulgite ore has a attapulgite content of ≥75%, and its chemical composition, as determined by XRF, has a MgO mass fraction of 10-14%. The pulping and acid activation process involves crushing the Mingguang attapulgite ore to 100 mesh size, ultrasonically dispersing it in a sulfuric acid or phosphoric acid aqueous solution at a pH of 3.5-4.0, and stirring for 4-8 hours. The surface micro-hydrophobicization treatment process is as follows: first, oleic acid glyceride or a silane coupling agent is added to an alcohol-water mixed solution (alcohol / water volume ratio = 8:2) to obtain a uniform modified solution; then, acid-activated attapulgite is ultrasonically dispersed into the above-mentioned modified solution with a solid content of 7%, heated (80-90°C), refluxed and stirred for 6-8 hours, and then centrifuged and dried to obtain a surface micro-hydrophobicized powder, wherein the amount of oleic acid glyceride or silane coupling agent added is 0.5-2.0% of the mass of the acid-activated attapulgite.

[0011]

[0012] From the physical and chemical properties of different attapulgite (Table 1) and SEM images ( Figure 1 ) comparison shows that the Mingguang attapulgite with a trioctahedral rod crystal structure has the characteristics of high purity, large rod crystal length / diameter ratio, high MgO content, large specific surface area and pore volume. Under the same processing conditions (7% solid content, stirring at 11000rpm for 20 minutes), the initial viscosity of the Mingguang attapulgite suspension is 20 and 100 times that of the Xuyi attapulgite and Linze mixed-fiber attapulgite clay suspensions, respectively. At a low addition amount (2%), there is almost no sedimentation within 2 hours, and it shows extremely excellent suspension stability. This is all attributed to the unique properties of Mingguang attapulgite such as high purity, long rod crystals and crystal structure. At the same time, the unique structural characteristics and physicochemical properties of Mingguang attapulgite nanorods and rod bundles facilitate the entanglement and interweaving of these rods in a static state, forming flocculated aggregates. This traps a large number of water molecules within the network, resulting in a low-flow, high-load-bearing gel. Repeated shearing or agitation disrupts the three-dimensional network, releasing the water molecules and enhancing the fluidity of the composite, thus promoting the thixotropy of concrete, a crucial characteristic for slip film construction. The rheological properties of the cement paste were tested using an Anton-Paar MCR102 rheometer. The thixotropy index, defined as the ratio of initial stress to equilibrium stress, quantitatively describes the relationship between static and dynamic yield stresses. A higher thixotropy index indicates a greater tendency for the composite cement paste to thicken in static and thin in shear, and therefore exhibits better thixotropy. The above three types of attapulgite were dispersed at a high speed in cement paste at a mass fraction of 0.5%. It was found that the thixotropy index of the neat cement paste was only 1.93, while the addition of Mingguang attapulgite had the greatest improvement in the thixotropy index of the neat cement paste (about 25%), confirming that the addition of Mingguang attapulgite makes it easier to obtain cement-based cementitious materials with low dynamic yield stress, high static yield stress and thixotropy, which gives it good development potential in thixotropic concrete application fields such as sliding film construction and 3D printing.

[0013] This application selects Mingguang attapulgite, characterized by long rod crystals, high viscosity, and thixotropy, to prepare a thixotropic agent for concrete. It is added as a hydrated slurry (to reduce the impact of bulk water absorption on the water-binder ratio of concrete). This approach does not affect its compatibility with other concrete base materials while fully utilizing the nanocrystalline structure and colloidal properties of the Mingguang attapulgite. However, Mingguang attapulgite's adsorption performance is inferior to that of the other two types of attapulgite. When added to concrete mixes, it has a weaker adsorption capacity for functional components such as water reducers and air-entraining agents, which helps these components function effectively. Acid activation of Mingguang attapulgite removes unstable impurities such as carbonates and soluble salts from the original ore. The conductivity of the acid-activated slurry is significantly reduced, confirming a reduction in the amount of soluble salts. Furthermore, the open pore structure facilitates the binding of the micro-hydrophobic modifier. The pH of the acid-activated solution is limited to 3.5-4.0 to prevent a significant decrease in the viscosity of the attapulgite during the acidification process, which could affect its performance in slipform construction. Acid-activated attapulgite, then subjected to a surface micro-hydrophobic treatment, weakens its strong adsorption of free and unbound water in the concrete system, allowing sufficient water to hydrate, lubricate, and hydrate the system. Furthermore, it transforms the attapulgite into an amphiphilic, highly dispersible thixotropic agent. One end of the mineral is hydrophilic, while the other end of the grafted long-chain organic molecules not only disperses the attapulgite-based thixotropic agent uniformly within the cement paste and aggregate gaps through electrostatic repulsion, but also binds with free components in the composite admixture, enhancing thixotropic and water-retention properties. Finally, after the acid-activated and surface-micro-hydrophobicized Mingguang attapulgite is fully hydrated, it is added to concrete as a thixotropic slurry. This solves the problem of the attapulgite's strong hydrophilicity causing the concrete mix to dry out quickly and lack the fluidity required for slipform construction and transportation. Furthermore, the highly dispersible thixotropic slurry can quickly disperse and act between inorganic and organic materials, exhibiting excellent thixotropic properties, filling effects, and toughening and reinforcement during vibration and paving.

[0014] The composite admixture is prepared by adding optimized proportions of retarder, collapse preventer, air entraining agent and defoaming agent to high-efficiency C6 polycarboxylic acid water reducer. The concrete mixing process is as follows: first, add 80% of water and composite admixture to the evenly mixed cement, sand, crushed stone and fly ash dry materials and stir for 2 to 3 minutes, then add attapulgite-based thixotropic agent slurry and stir again for 2 to 3 minutes to obtain concrete for slipform construction. The slump, density and strength are the key technical indicators for measuring the working performance and quality control of concrete mixtures for slipform construction. Among them, the initial slump and the change of slump over time intuitively reflect the workability, self-compacting and shape-retaining ability of concrete, and high-strength concrete can not only ensure the quality of construction projects, but also provide strong protection for building safety. From the change of the slump of the prepared concrete over time ( Figure 2) It can be seen that the comparative example 1 uses the mix ratio used in the on-site formwork casting method, and the concrete mixture prepared will have slight bleeding. The slump becomes 30mm after 1 hour, and there are some small depressions on the surface of the concrete specimen. The fluidity and self-compacting properties of this concrete are poor, and it cannot meet the requirements of slip-form construction concrete. Comparative example 2 is to add Mingguang attapulgite (0.5% of the mass of the cementitious material) slurry under the same mix ratio. The workability of the concrete mixture is significantly improved. Although the slump loss after 1 hour is large and still cannot meet the construction requirements of slip-form construction concrete, the surface of the concrete specimen after collapse is smoother and denser, indicating that the addition of attapulgite can significantly improve the workability and compactness of concrete. Further, from the time-dependent changes in the slump of the concrete of Examples 1 to 3 ( Figure 2 ) It can be clearly seen that the concrete mixtures added with the slightly hydrophobized Mingguang attapulgite thixotropic agent slurry and the composite admixture did not show rapid cohesion or dry hardening, but always showed excellent workability, cohesion and shape retention within 2 hours, the slump was maintained between 130 and 190 mm, and the cement paste and aggregate had good wrapping properties. In particular, the stacking morphology of the concrete specimens after collapse in Example 3 was approximately an ideal truncated cone, the specimen surface was smoother, denser, and had no collapse, and had excellent thixotropy and self-compacting ability, which can fully meet the working performance requirements of slipform construction concrete.

[0015] CT scanning technology is an innovative and non-destructive way to deeply study the microstructure of concrete. It can better reflect the spatial distribution of aggregates and pores in concrete and the characteristics of pore structure. In addition, due to the different densities of cement mortar and stone materials in concrete and the pores inside, 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 is also greater. From the CT scanning images of different concrete ( Figure 3 and 4 ) It can be seen that the addition of Mingguang attapulgite slurry can increase the cohesion of concrete, while the center of the test block has more cementitious materials and relatively less aggregates, while the aggregate distribution on the outside is relatively more uniform. When the layer thickness is 6 and 9 cm, the number of large-diameter pores is large and concentrated ( Figure 3 The addition of attapulgite-based thixotropic agents and composite admixtures makes the cementitious materials and aggregates in each fault of the concrete uniformly distributed and tightly wrapped, and the number of pores in the entire section is significantly reduced and most of them are small pores that are not connected ( Figure 4), which means that the two work together to improve the spatial distribution uniformity of aggregates and pores in concrete, as well as the pore structure characteristics. The attapulgite-based thixotropic agent grafted with long-chain organic molecules can efficiently and quickly fill the micro-gaps between cement paste and aggregate, and combine with the free components in the composite admixture to improve the workability, thixotropic properties and water retention of concrete, which is more conducive to forming a stable dense structure and improving the strength of concrete. 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 are 1721.52 Hu and 40.62 Mpa, respectively. After adding the attapulgite-based thixotropic agent and the composite admixture in Example 3, the CT value and compressive strength of the concrete increased to 1905.36 Hu and 46.21 Mpa, respectively, which are much higher than the strength requirements of the crash barrier C30. The other examples also show the same trend, showing excellent density and toughening and reinforcement properties.

[0016] In summary, the present invention has the following advantages compared with the prior art:

[0017] 1. The present invention successfully prepares concrete with excellent thixotropy, slump retention, workability, and compactness by introducing a Mingguang attapulgite thixotropic agent slurry and a multifunctional composite admixture into concrete materials, and further combining multiple strategies such as component quality control, optimized mix ratio, and step-by-step mixing. 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, enhancing overall benefits, reducing labor intensity, and reducing material consumption.

[0018] 2. Based on the application scenarios and on-site construction requirements of slipform construction, the present invention uses Mingguang attapulgite, which has thixotropy, a large rod crystal length / diameter ratio, and high suspension stability, as raw material. A thixotropic agent slurry is obtained through acid activation and surface micro-hydrophobicization treatment. Furthermore, a functional composite admixture is prepared by compounding multiple components such as a slump preventer, a retarder, and an air-entraining agent with a high-efficiency water reducer. This synergistically regulates the macroscopic properties (slump change, strength) and microscopic characteristics (internal aggregate distribution, pore space distribution) of concrete, producing a concrete material with a slump maintained between 130 and 190 mm within 2 hours, high density, and high strength.

[0019] 3. The concrete preparation method of the present invention utilizes minor adjustments to conventional concrete mixing processes. By adding a small amount of attapulgite-based thixotropic agents and functional admixtures, the method produces concrete with specialized performance characteristics without increasing equipment investment. This concrete can be applied to slipform construction and other applications of thixotropic concrete. While these minor adjustments increase the cost of concrete by 70 to 100 yuan per cubic meter, they address several practical technical challenges associated with slipform construction, such as transportation, distribution, and paving. This approach minimizes environmental pollution and ecological damage, resulting in significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 SEM images of Mingguang attapulgite (upper left), Xuyi attapulgite (upper right), and Linze mixed-fiber attapulgite clay (lower).

[0021] Figure 2 The slump of the prepared concrete changes over time.

[0022] Figure 3 and 4 The following are CT scan images of the concrete specimens prepared in Comparative Example 2 and Example 3, respectively. The concrete specimens used were 15 cm x 15 cm in size. The CT scanning equipment used was a Brilliance 16 spiral CT machine. The specific CT scanning conditions were: 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. The corresponding aggregate distribution maps (top) and pore distribution maps (bottom) were obtained. 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.

[0023] Figure 5 CT values ​​of the concrete test blocks prepared in Comparative Example 2 and Example 3.

[0024] Figure 6 is the compressive strength of the prepared concrete after 28 days of curing. DETAILED DESCRIPTION

[0025] The following examples further illustrate the method for preparing concrete for slip film construction by adding an attapulgite-based thixotropic agent. Slump and specimen strength were tested in accordance with the Standard for Testing Methods for Ordinary Concrete Mixtures (GB / T50080-2016) and the Test Procedure for Cement and Cement Concrete for Highway Engineering (JTG3420-2020).

[0026] Comparative Example 1

[0027] Accurately weigh the following raw materials in parts by weight: 315 parts of Portland cement, 55 parts of Class F fly ash, 840 parts of sand (mud content of 1.0%), 310 parts of crushed stone (5-10mm), 720 parts of crushed stone (10-20mm), 168 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 .

[0028] Comparative Example 2

[0029] Accurately weigh the following raw materials in parts by weight: 320 parts Portland cement, 60 parts Class F fly ash, 850 parts sand (1.0% mud content), 315 parts crushed stone (5-10 mm), 720 parts crushed stone (10-20 mm), 154 parts water, 5 parts C6 polycarboxylate superplasticizer, and 28 parts Mingguang attapulgite slurry. The Mingguang attapulgite slurry is prepared by dispersing Mingguang attapulgite ore (75% attapulgite content and 10% MgO by mass) in water at a solids content of 7% 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 polycarboxylate superplasticizer 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 Mingguang attapulgite 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 .

[0030] Example 1

[0031] (1) Construction of attapulgite-based thixotropic agent: First, the Mingguang attapulgite ore (attapulgite content of 75% and MgO mass fraction of 10%) was crushed to 100 mesh, ultrasonically dispersed in a phosphoric acid aqueous solution with a pH value of 4.0 and stirred for 8 hours. After filter pressing and centrifugation, the solid phase filter cake was dispersed in an alcohol / water mixed solution containing oleic acid glyceride, wherein the mass of oleic acid glyceride was 0.5% of the mass of acid-activated attapulgite. After reflux stirring at 80°C for 6 hours, centrifugation and drying were performed to obtain a surface slightly hydrophobicized powder. The powder was dispersed in water with a solid content of 5% and stirred for 24 hours to obtain a thixotropic agent slurry for use.

[0032] (2) Preparation of composite admixture: accurately weigh the following raw materials in parts by weight: C6 polycarboxylic acid water reducer (water reduction rate 35%) and sodium gluconate, sodium hexametaphosphate, borax and sodium α-olefin sulfonate in a mass ratio of 100:2:2:2:0.5 and stir (stirring speed 600 rpm, stirring time 15 min) to obtain a composite admixture and set aside;

[0033] (3) Preparation of concrete mixture: Accurately weigh the following raw materials in parts by weight: 320 parts of Portland cement, 60 parts of Class F fly ash, 850 parts of sand (natural sand, mud content 1.0%, fineness modulus 2.6), 315 parts of crushed stone (5-10mm), 720 parts of crushed stone (10-20mm), 154 parts of water, 5 parts of composite admixture, and 28 parts of attapulgite-based thixotropic agent slurry. The concrete mixing process is as follows: First, add water and composite admixture to the uniformly mixed cement, sand, crushed stone, and fly ash dry materials and stir for 2 minutes, then add attapulgite-based thixotropic agent slurry and stir again for 3 minutes to obtain concrete for sliding film 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 .

[0034] Example 2

[0035] (1) Construction of attapulgite-based thixotropic agent: First, the Mingguang attapulgite ore (attapulgite content of 75% and MgO mass fraction of 10%) was crushed to 100 mesh, ultrasonically dispersed in a sulfuric acid aqueous solution with a pH value of 3.5 and stirred for 4 hours. After filter pressing and centrifugal separation, the solid phase filter cake was dispersed in an alcohol / water mixed solution containing a silane coupling agent, wherein the mass of the silane coupling agent KH570 was 2.0% of the mass of the acid-activated attapulgite. After reflux stirring at 90°C for 8 hours, centrifugation and drying were performed to obtain a surface slightly hydrophobicized powder. The powder was dispersed in water with a solid content of 7% and stirred for hydration for 12 hours to obtain an attapulgite-based thixotropic agent slurry for use.

[0036] (2) Preparation of composite admixture: Accurately weigh the following raw materials in parts by weight: C6 polycarboxylic acid water reducer (water reduction rate 25%) and sodium gluconate, sodium hexametaphosphate, borax and sodium α-olefin sulfonate in a mass ratio of 100:4:2:1:0.25 and stir (stirring speed 600 rpm, stirring time 15 min) to obtain a uniform composite admixture for use;

[0037] (3) Preparation of concrete mixture: Accurately weigh the following raw materials in parts by weight: 315 parts of a mixture of Portland cement and sulfoaluminate cement (mass ratio 8:2), 55 parts of Class F fly ash, 840 parts of sand (washed sand, with a mud content and flocculant content of 1.0% and 0.5% respectively, and a fineness modulus of 3.2), 315 parts of crushed stone (5-10 mm), 720 parts of crushed stone (10-20 mm), 154 parts of water, 6 parts of composite admixture, and 26 parts of attapulgite-based thixotropic agent slurry. The concrete mixing process is as follows: First, add water and composite admixture to the uniformly mixed cement, sand, crushed stone, and fly ash dry materials and stir for 2 minutes. Then, add the attapulgite-based thixotropic agent slurry and stir again for 3 minutes to obtain concrete for slip film construction. The slump change of this concrete over time and the strength data of the test blocks after 28 days of curing are shown in Figures 2 and 6.

[0038] Example 3

[0039] (1) Construction of attapulgite-based thixotropic agent: First, the Mingguang attapulgite ore (attapulgite content of 80% and MgO mass fraction of 14%) was crushed to 100 mesh, ultrasonically dispersed in a sulfuric acid aqueous solution with a pH value of 4.0 and stirred for 4 hours. After filter pressing and centrifugation, the solid phase filter cake was dispersed in an alcohol / water mixed solution containing 1.0% oleic acid glyceride, where the mass of oleic acid glyceride was 1.0% of the mass of acid-activated attapulgite. After reflux stirring at 90°C for 8 hours, centrifugation and drying were performed to obtain a surface slightly hydrophobicized powder. The powder was dispersed in water with a solid content of 7% and stirred for hydration for 24 hours to obtain an attapulgite-based thixotropic agent slurry for use.

[0040] (2) Preparation of composite admixture: Accurately weigh the following raw materials in parts by weight: C6 polycarboxylic acid water reducer (water reduction rate 30%) and sodium gluconate, sodium hexametaphosphate, borax and sodium α-olefin sulfonate in a mass ratio of 100:3:3:1:1.0 and stir (stirring speed 500 rpm, stirring time 20 min) to obtain a uniform composite admixture for use;

[0041] (3) Preparation of concrete mixture: Accurately weigh the following raw materials in parts by weight: 320 parts of Portland cement, 60 parts of Class F fly ash, 850 parts of sand (natural sand, mud content 0.8%, fineness modulus 2.8), 315 parts of crushed stone (5-10 mm), 720 parts of crushed stone (10-20 mm), 131 parts of water, 6 parts of composite admixture, and 54 parts of attapulgite-based thixotropic agent slurry. The concrete mixing process is as follows: First, add water and composite admixture to the uniformly mixed cement, sand, crushed stone, and fly ash dry materials and stir for 2 minutes, then add attapulgite-based thixotropic agent slurry and stir again for 3 minutes to obtain concrete for sliding film 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 , CT scan images and CT values ​​are shown in Figure 4 and 5 .

Claims

1. A method for preparing concrete for synovial construction by adding an attapulgite-based thixotropic agent, characterized in that: The concrete is prepared by mixing the following raw materials in parts by weight: 315-320 parts of cement, 55-60 parts of fly ash, 840-850 parts of sand, 305-315 parts of 5-10 mm crushed stone, 720-725 parts of 10-20 mm crushed stone, 180-190 parts of water, 5-6 parts of composite admixture, and 1.5-3.0 parts of attapulgite-based thixotropic agent. The preparation method of the attapulgite-based thixotropic agent is as follows: after pulping acid activation and surface micro-hydrophobicization treatment of Mingguang attapulgite ore, it is dispersed in water with a solid content of 5-7%, and stirred and hydrated for at least 12 hours. A thixotropic agent slurry is obtained and added in the form of a slurry; a composite admixture is prepared by mixing and compounding a C6 polycarboxylic acid water reducer, sodium gluconate, sodium hexametaphosphate, borax, and sodium α-olefin sulfonate (AOS) in a mass ratio of 100:2-4:2-3:1-2:0.25-1.0; and a concrete mixing process is as follows: first, 80% of water and the composite admixture are added to a uniform mixture of cement, sand, gravel, and fly ash dry materials, followed by stirring for 2-3 minutes, and then the attapulgite-based thixotropic agent slurry is added and stirred again for 2-3 minutes to obtain concrete for sliding film construction.

2. The method for preparing concrete for synovial construction by adding an attapulgite-based thixotropic agent according to claim 1, wherein: The cement is a mixture of any one or more of silicate cement, white cement and sulphoaluminate cement, 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, and the water requirement ratio is ≤90%; the mud content in the crushed stone is ≤1.0%.

3. The method for preparing concrete for synovial construction by adding an attapulgite-based thixotropic agent according to claim 1, wherein: The attapulgite content in the Mingguang attapulgite ore is ≥75%, and the mass fraction of MgO in the chemical composition tested by XRF is between 10 and 14%.

4. The method for preparing concrete for synovial film construction by adding an attapulgite-based thixotropic agent according to claim 1, wherein: 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%.

5. The method for preparing concrete for synovial construction by adding an attapulgite-based thixotropic agent according to claim 1, wherein: The pulping acid activation is to crush the Mingguang attapulgite ore into 100 meshes, and then ultrasonically disperse it in a sulfuric acid or phosphoric acid aqueous solution with a pH value of 3.5 to 4.0 and stir the reaction for 4 to 8 hours.

6. The method for preparing concrete for synovial film construction by adding an attapulgite-based thixotropic agent according to claim 1, wherein: The surface micro-hydrophobicization treatment process is as follows: first, oleic acid glyceride or a silane coupling agent is added to an alcohol-water mixed solution to obtain a uniform modified solution; then, acid-activated attapulgite is ultrasonically dispersed in the above-mentioned modified solution, heated to 80-90°C, refluxed and stirred for 6-8 hours, and then centrifuged and dried to obtain a surface micro-hydrophobicized powder, wherein the amount of oleic acid glyceride or the silane coupling agent added is 0.5-2.0% of the mass of the acid-activated attapulgite.

7. The method for preparing concrete for synovial construction by adding an attapulgite-based thixotropic agent according to claim 6, wherein: In the alcohol-water mixed solution, the volume ratio of alcohol to water is 8:

2.

8. The method for preparing concrete for synovial construction by adding an attapulgite-based thixotropic agent according to claim 1, wherein: The slump of the concrete mixture for sliding membrane construction is maintained between 130 and 190 mm within 2 hours.

Images