Basalt fiber magnesia anti-cracking agent and preparation method thereof

Abstract

This invention discloses a basalt fiber magnesium-based crack-resistant agent and its preparation method, belonging to the technical field of building material admixtures. The basalt fiber magnesium-based crack-resistant agent of this invention, by weight, comprises the following raw materials: 5-15 parts of basalt fiber composite material, 80-94 parts of magnesium expansion agent, and 1-5 parts of α-sepiolite; the basalt fiber content in the basalt fiber composite material is 70-90%; the dosage of the basalt fiber magnesium-based crack-resistant agent in concrete is 4-6 kg / m³. 3 The basalt fiber magnesium anti-cracking agent of the present invention aims to significantly enhance the tensile strength, compressive strength, impermeability, frost resistance and impact resistance of concrete by incorporating an appropriate amount of anti-cracking agent with micro-expansion properties, thereby achieving the goal of simultaneously improving the crack resistance and durability of concrete.

Description

Technical Field

[0001] This invention belongs to the technical field of concrete admixtures for building materials, specifically relating to a basalt fiber magnesium anti-cracking agent and its preparation method. Background Technology

[0002] Due to foundation constraints, concrete structures may experience stress concentration; influenced by internal and external temperature differences and age, the temperature stress during the concrete cooling process may exceed the current tensile strength of the concrete; and if curing is not timely, the concrete surface will experience drying shrinkage. All of these situations can lead to large-scale cracking in concrete. With rapid social development, large-volume and ultra-long concrete structures are becoming increasingly common, and high-strength and high-performance concrete is being widely used. The causes of concrete cracking are becoming more complex, and the risk of cracking is becoming increasingly serious, especially in large-volume and ultra-long structures where temperature stress caused by the heat of hydration of concrete leads to cracking.

[0003] In water conservancy and hydropower engineering construction, concrete temperature control measures are diverse: projects can build their own concrete mixing systems; for large-volume concrete, measures such as optimizing mix proportions, selecting high-quality raw materials, and lowering concrete grades are often used to reduce the adiabatic temperature rise; combined with aggregate pre-cooling and ice-water mixing, the temperature of raw materials is reduced to control the temperature at the mixing plant outlet; shading is provided during transportation; a microclimate is created by spraying water on the surface during pouring; and cooling water is used for cooling during curing. Despite such strict temperature control, cracks are still difficult to avoid during construction, hence the saying "no dam, no crack." In municipal and transportation engineering, concrete is mostly commercial concrete supplied by mixing plants, with large supply volumes and relatively fixed raw materials and equipment, making it difficult to provide concrete with ideal temperature, physical and mechanical properties, and thermodynamic indicators for individual projects. Furthermore, municipal and transportation buildings are mainly "slender" and "thin-slab" structures, requiring high-grade concrete with small cross-sections, and cooling water pipes cannot be embedded inside the concrete, meaning the concrete can only cool naturally after pouring. Therefore, improving concrete performance has become an important research direction in concrete temperature control. The ideal concrete should have characteristics such as low heat, low elastic modulus, high tensile-to-compression ratio, and high autogenous volume deformation (ultimate tensile value).

[0004] Researchers in the existing technology have proposed several approaches:

[0005] The first approach involves adjusting the release of heat of hydration in concrete by adding admixtures based on the concrete temperature process curve, thereby reducing the peak temperature. This is exemplified by heat of hydration inhibitors. Studies have found that heat of hydration inhibitors can delay the peak temperature of concrete by approximately 24 hours, but cannot reduce the total heat of the concrete. Adding heat of hydration inhibitors significantly reduces the workability of the mixture, lowers the early strength of the concrete, and increases the later shrinkage deformation of the concrete.

[0006] The second type involves adding admixtures with expansive properties to compensate for surface shrinkage by altering the self-generated volume deformation. Common expansive agents are mostly early-expansion type, represented by calcium sulfoaluminate and calcium oxide. Calcium sulfoaluminate expansive agents, when added to concrete, undergo hydration to form calcium sulfoaluminate hydrate, i.e., ettringite, resulting in volume expansion and compensating for concrete surface shrinkage. During hydration, ettringite (C3A·3CaSO4·32H2O) is formed. The expansion effect of calcium oxide expansive agents is mainly due to the hydration of calcium oxide crystals to form calcium hydroxide crystals, leading to volume increase. These expansive agents have rapid hydration rates and rapid early expansion, resulting in large early plastic deformation of the concrete, absorbing some of the expansion. However, their weak shrinkage compensation ability in the later stages, large dosage requirements, and difficulty in controlling the total alkali content of the concrete also limit their application. Another type of expansive agent is magnesium oxide, which has delayed expansion characteristics. The expansion and deformation of magnesium oxide mainly occur during the cooling and shrinkage stage of concrete (7 days to 90 days). For large-volume, high-grade concrete, the heat of hydration is released very slowly, which better utilizes the delayed expansion characteristics of magnesium oxide-based expansion agents.

[0007] The third method involves enhancing the tensile strength and ultimate tensile value of concrete by adding fiber materials. The most commonly used fiber materials in concrete engineering are polypropylene fibers and steel fibers. Polypropylene fibers have good alkali resistance, but low tensile strength, are prone to aging, are not environmentally friendly, and their raw material sources are somewhat limited. Furthermore, low-modulus synthetic fibers often reduce the compressive strength of concrete. Steel fibers are expensive, have lower bonding strength, lower production efficiency, and higher energy consumption.

[0008] The fourth method is compound admixture, which involves mixing the three admixtures mentioned above, hoping to leverage the advantages of each material. However, engineering tests and practices have shown that arbitrary combinations only increase costs and project investment, failing to achieve the desired results. For example, a compound admixture of 1% heat of hydration inhibitor and 5% magnesium expansion agent has a less effective cooling effect than a single admixture, and its self-generated volume deformation is reduced by 15% compared to magnesium oxide alone. Another example is a magnesium-calcium mixed expansion agent, whose main components are magnesium and calcium, with a very small proportion of heat of hydration inhibitor and a small amount of basalt fiber. The enhancement of concrete's mechanical properties is controlled by the magnesium-calcium mixed expansion agent, which provides early and late-stage expansion deformation of the concrete, respectively. The total admixture content is as high as 13%–17%, resulting in high costs.

[0009] Therefore, there is an urgent need to develop a high-performance, low-cost, environmentally friendly, and widely applicable crack-resistant agent. Summary of the Invention

[0010] This invention provides a basalt fiber magnesium anti-cracking agent and its preparation method. Firstly, by combining three commonly used building materials—basalt fiber, magnesium expansion agent, and α-sepiolite—the expansion deformation capacity and tensile strength of the anti-cracking agent can be improved, thereby reducing the cost of the anti-cracking agent. Secondly, by improving the solvent and stirring method, the reaction degree of the anti-cracking agent components can be increased, further improving the physical properties of the anti-cracking agent.

[0011] In a first aspect, the present invention provides a basalt fiber magnesium anti-cracking agent, comprising, by weight, the following raw materials: 5-15 parts of basalt fiber composite material, 80-94 parts of magnesium expansion agent and 1-5 parts of α-sepiolite;

[0012] The basalt fiber composite material contains 70-90% basalt fiber.

[0013] The dosage of the basalt fiber magnesium crack-resistant agent in concrete is 4-6 kg / m³. 3 .

[0014] Based on the above technical solution, the present invention can be further improved as follows.

[0015] Furthermore, by weight, it includes the following raw materials: 8-12 parts basalt fiber composite material, 85-90 parts magnesium expanding agent, and 2-3 parts α-sepiolite.

[0016] Furthermore, by weight, it includes the following raw materials: 10 parts of basalt fiber composite material, 87 parts of magnesium expanding agent, and 3 parts of α-sepiolite.

[0017] Furthermore, the magnesium expanding agent is high-purity lightly calcined magnesium oxide, wherein the magnesium oxide content in the magnesium expanding agent is greater than 85%, the loss on ignition is less than 4%, the water content is less than 1%, the f-CaO content is less than 2%, and the active reaction time is 50s to 300s.

[0018] Furthermore, the basalt fiber composite material is a material prepared by composite modification of basalt fibers and carbon nanotube particles;

[0019] The basalt fiber is a short-cut fiber with a diameter of 15–22 μm and a length of 15–30 mm.

[0020] Furthermore, the basalt fiber composite material is prepared by the following method:

[0021] Activate basalt fibers and carbon nanoparticles;

[0022] The activated basalt fibers were combined with carbon nanoparticles to obtain basalt fiber composite materials.

[0023] Further, the activation includes the following steps:

[0024] After sintering, the basalt fibers are immersed in a mixed acid solution (H2SO4 / HNO3 mixed acid solution) to etch the surface, thus obtaining activated basalt fibers.

[0025] Carbon nanotubes were immersed in a mixed acid solution and ultrasonically dispersed. They were then cleaned with anhydrous ethanol and dried to obtain activated carbon nanotube particles.

[0026] Preferably, the mixed acid solution used to soak the carbon nanotubes is a mixture of concentrated nitric acid and concentrated sulfuric acid solutions, wherein the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, the volume fraction of concentrated sulfuric acid is 98%, and the volume fraction of concentrated nitric acid is 67%.

[0027] Furthermore, the composite modification includes the following steps:

[0028] The activated basalt fibers and carbon nanotube particles were dissolved in acetone solution at a mass ratio of 70-90:10-30 and then ultrasonically dispersed.

[0029] The dispersed solution was kneaded at 160–200°C, and then stamped and calcined to obtain basalt fiber composite material.

[0030] In a second aspect, the present invention provides a method for preparing the basalt fiber magnesium anti-cracking agent as described in any one of the first aspects, comprising the following steps:

[0031] Weigh the raw materials according to the weight proportions, mix the raw materials and add 50-75% anhydrous ethanol by weight of the raw materials. Mix using a three-stage stirring method to obtain basalt fiber magnesium anti-cracking agent.

[0032] The three-stage stirring method includes a first stage of stirring at room temperature, a second stage of stirring with heat, and a third stage of stirring with cooling.

[0033] Furthermore, the stirring speed in the first stage at room temperature is 300-1000 rpm, and the stirring time is 15-30 min;

[0034] The second stage of heating and stirring is carried out at a temperature of 150–180°C for 1–6 hours and at a speed of 4500–6000 rpm.

[0035] The third stage of cooling and stirring is carried out by natural cooling, with a stirring speed of 300-1000 rpm and a stirring time of 30-60 minutes.

[0036] The technical solutions provided in this application have at least the following advantages compared with the prior art:

[0037] 1. The basalt fiber magnesium-based crack-resistant agent of this invention comprises three components: a basalt fiber composite material, lightly calcined magnesium oxide (magnesium-based expanding agent), and α-sepiolite. The modified basalt fiber composite material retains the excellent acid, alkali, and corrosion resistance of basalt fibers while improving tensile and fracture resistance, maintaining good stability over a higher temperature range. Lightly calcined magnesium oxide imparts a micro-expansion property to the crack-resistant agent, improving the durability of concrete. α-sepiolite has a unique fiber bundle structure that can interweave and bind within the basalt fiber structure, increasing the density and strength of the crack-resistant agent and providing mechanical interlocking, further enhancing its acid, alkali, and corrosion resistance.

[0038] 2. The preparation method of the basalt fiber magnesium anti-cracking agent of the present invention utilizes the characteristic of sepiolite itself being easily soluble in polar solvents and forming a network. An ethanol solution is used to mix the three components. During the mixing process, the network formed by the sepiolite can coat the basalt fiber composite material and lightly calcined magnesium oxide, and squeeze the smaller particles of lightly calcined magnesium oxide into the fiber gaps or squeeze the broken fiber ends into the gaps between the lightly calcined magnesium oxide particles. In summary, the most basic effect of the three-stage mixing process is to improve the uniformity of mixing, allow the ethanol to evaporate during the mixing process to avoid its impact on the concrete structure, and prevent particle molecules from agglomerating in a certain local location, thus affecting the performance of the anti-cracking agent and reducing the porosity of the anti-cracking agent.

[0039] 3. The basalt fiber magnesium crack-resistant agent in this invention can comprehensively improve the physical and mechanical properties and durability of concrete. Tests show that adding a very small amount of basalt fiber magnesium crack-resistant agent (4-6 kg / m³) to concrete... 3 It can increase the tensile strength of concrete by 10-20%, the compressive strength of concrete by 5-10%, the frost resistance of concrete by 10-30%, and the impermeability of concrete by about 20%.

[0040] 4. This invention has natural compatibility with concrete matrix, does not affect the workability of concrete mixture, is environmentally friendly and pollution-free, has good alkali resistance, and is well adaptable to both silicate cement and ordinary silicate cement. Attached Figure Description

[0041] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the process for preparing the basalt fiber magnesium anti-cracking agent of the present invention;

[0044] Figure 2 This is a schematic diagram of the cross-section of the concrete after fracture in Experiment Example 1, after the addition of basalt fiber magnesium anti-cracking agent. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0047] In a first aspect, this application provides a basalt fiber magnesium anti-cracking agent, which, by weight, comprises the following raw materials: 5-15 parts of basalt fiber composite material, 80-94 parts of magnesium expansion agent, and 1-5 parts of α-sepiolite;

[0048] The basalt fiber composite material contains 70-90% basalt fiber (which can be understood as the mass fraction of activated basalt fiber);

[0049] The dosage of the basalt fiber magnesium crack-resistant agent in concrete is 4-6 kg / m³. 3 .

[0050] In this invention, basalt fiber is a high-performance inorganic silicate fiber with a green and environmentally friendly production process. It possesses excellent chemical stability, corrosion resistance, high-temperature resistance, seismic performance, and environmental friendliness. In this invention, modified basalt fiber is used as the reinforcement, lightly calcined magnesia as the matrix, and α-sepiolite as the auxiliary material. The crack-resistant agent prepared by mixing these three components exhibits superior mechanical properties and high-temperature resistance. It can induce continuous micro-expansion within the concrete during the concrete molding process, compensating for concrete shrinkage stress and reducing the risk of shrinkage cracking in structures. Simultaneously, it can improve the pore structure of concrete, greatly increasing its density and thus significantly enhancing its crack resistance.

[0051] The magnesium-based expanding agent in this invention is made of high-purity light-burned magnesium oxide, prepared by crushing, grinding, and calcining magnesite. The raw material is crushed and added to a ball mill or tube mill for co-grinding into powder with a particle size of ≤0.088mm. The pre-treated raw material is mixed with magnesium chloride solution and water in a high-pressure sand mixer for 10 minutes. The uniformly mixed material is dried and then placed in a rotary kiln for calcination. The calcination is divided into two stages: (1) calcination at 700~900℃ for 30~60min; (2) calcination at 900~1100℃ for 30~60min. The light-burned magnesium oxide obtained by calcination has a MgO content greater than 85%, a loss on ignition less than 4%, a moisture content less than 1%, an f-CaO content less than 2%, and an active reaction time of 50s~300s. At the same time, its various performance indicators should meet the relevant provisions of DL / T5296-2013 "Technical Specification for Magnesium Oxide Admixture in Hydraulic Concrete".

[0052] The basalt fiber in this invention is an inorganic fiber material made from pure natural volcanic volcanic rock. It is a continuous fiber rapidly drawn after being melted at a high temperature of 1450–1500℃. Basalt blocks with a diameter of 50–60 mm, after being crushed and washed, are fed into a furnace using a feeding device. Under the action of a vertical flame, they melt, homogenize, and degas at approximately 1500℃. The melt then passes through a submerged heated tubular flow channel into a passageway. At this point, the melt reaches a suitable forming temperature and is transported by a platinum tube distributor to the corresponding central feeder, flowing into a platinum sprue. The melt flowing out of the sprue is then forcibly cooled by a hot air-cooled fiber cooler to form fibers. Its tensile strength is ≥1050 MPa, elastic modulus ≥34 GPa, elongation at break ≤3.1%, and other performance indicators such as acid resistance, alkali resistance, and UV resistance should meet the relevant requirements of GB / T23265-2009.

[0053] The α-sepiolite in this invention, occurring in large bundles of fibrous crystals, is a pure, natural, non-toxic, odorless, asbestos-free, and radioactive hydrated magnesium silicate clay mineral. It possesses the largest specific surface area and a unique internal pore structure among non-metallic minerals. The channels and pores can adsorb large amounts of water or polar substances. Therefore, it can adsorb ethanol solution during the preparation process of this invention, and further adsorb other polar substances during the subsequent concrete preparation process, improving compatibility and bonding ability. Furthermore, the foaming properties of this invention can enhance the network crosslinking ability of the other two components, thereby improving the mechanical and bonding properties of the crack-resistant agent.

[0054] Preferably, by weight, it comprises the following raw materials: 8-12 parts of basalt fiber composite material, 85-90 parts of magnesium expanding agent, and 2-3 parts of α-sepiolite.

[0055] More preferably, by weight, it includes the following raw materials: 10 parts of basalt fiber composite material, 87 parts of magnesium expansion agent and 3 parts of α-sepiolite.

[0056] In some specific embodiments of the present invention, the magnesium expanding agent is high-purity lightly calcined magnesium oxide, wherein the magnesium oxide content in the magnesium expanding agent is greater than 85%, the loss on ignition is less than 4%, the water content is less than 1%, the f-CaO content is less than 2%, and the active reaction time is 50s to 300s.

[0057] In some specific embodiments of the present invention, the basalt fiber composite material is a material prepared by composite modification of basalt fiber and carbon nanotube particles;

[0058] The basalt fiber is a short-cut fiber with a diameter of 15–22 μm and a length of 15–30 mm.

[0059] In some specific embodiments of the present invention, the basalt fiber composite material is prepared by the following method:

[0060] Activate basalt fibers and carbon nanoparticles;

[0061] The activated basalt fibers were combined with carbon nanoparticles to obtain basalt fiber composite materials.

[0062] In some specific embodiments of the present invention, the activation includes the following steps:

[0063] After sintering basalt fibers, they are soaked in a mixed acid solution (H2SO4 / HNO3 mixed acid solution), stirred and reacted in an oil bath at 75-85℃ for 5 hours, then cooled to room temperature, washed with water until the pH value is 6-7 and dried, and the surface is etched to obtain activated basalt fibers.

[0064] Carbon nanotubes were immersed in a mixed acid solution and ultrasonically dispersed. They were then cleaned with anhydrous ethanol and dried to obtain activated carbon nanotubes.

[0065] Preferably, the sintering temperature is 300–500℃ and the sintering time is 30–45 min. Sintering can remove deposits on the surface of basalt fibers, which is beneficial to increasing the surface activity of basalt fibers; then, etching the surface of basalt fibers with concentrated sulfuric acid and concentrated nitric acid can create pores and grooves on the surface of basalt fibers, thereby improving the adhesion properties of the basalt fiber surface.

[0066] Preferably, the mixed acid solution used to soak the basalt fibers is a mixed solution of sulfuric acid and nitric acid with a concentration of 5-10 wt%, wherein the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid solution is 3:1, the volume fraction of concentrated sulfuric acid is 98%, and the volume fraction of concentrated nitric acid is 67%.

[0067] Preferably, the mixed acid solution used to soak the carbon nanotubes is a mixture of concentrated nitric acid and concentrated sulfuric acid solutions, wherein the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1, the volume fraction of concentrated sulfuric acid is 98%, and the volume fraction of concentrated nitric acid is 67%. The ultrasonic dispersion is performed using an ultrasonic disperser with a power of 300W, and the stirring time is 6–10 hours. The drying temperature is 60–90℃, and the drying time is 6–10 hours. Mixed acid treatment can carboxylate the carbon nanotubes, resulting in more uniform and stable dispersion of the carbon nanotubes in subsequent preparations of crack-resistant agents and concrete. Simultaneously, carboxylated carbon nanotubes in fiber composite structures can alter the fracture properties and fracture direction of the fibers (e.g., ...). Figure 2 As shown in the figure, the basalt fiber composite modification can improve mechanical properties, better transfer stress, delay crack formation, and increase the service life of the composite material.

[0068] In some specific embodiments of the present invention, the composite modification includes the following steps:

[0069] The activated basalt fibers and carbon nanotube particles were co-dissolved in acetone solution and ultrasonically dispersed.

[0070] A small amount of asphalt was added to the dispersed solution and kneaded at 160-200℃. After kneading, the mixture was stamped and calcined to obtain basalt fiber composite material.

[0071] The kneading time is 10-30 minutes, the stamping pressure is 1-10 MPa, the stamping temperature is 100°C, and the calcination temperature is 200-500°C.

[0072] In this invention, if the basalt fibers are of varying lengths, the dispersion process preferably involves adding the basalt fibers in four stages: 15–18 mm, 19–24 mm, 25–27 mm, and 28–30 mm in length. First, 15–18 mm basalt fibers are added and mixed thoroughly. Then, longer lengths are added sequentially, mixed thoroughly, and so on, until all basalt fibers are completely added. This dispersion process improves the mixing degree between basalt fibers and carbon nanotubes, enhances the overall bonding and entanglement potential, and improves the stability of the composite material.

[0073] Acetone solution is a high-performance solvent. Ultrasonic dispersion can improve the uniformity of carbon nanotube particles and basalt fibers. The modified carbon nanotubes and basalt fibers will have gaps in their structures to varying degrees. High-temperature kneading can fully combine and react the carbon nanotube particles and activated basalt fibers, combining them in different ways to form a new and complex network structure. Stamping can form a stable structure. After calcination, the composite material can agglomerate, enhancing its stability.

[0074] Secondly, based on a general inventive concept, such as Figure 1 As shown, the present invention provides a method for preparing the basalt fiber magnesium anti-cracking agent according to any one of the first aspects, comprising the following steps:

[0075] Weigh the raw materials according to the weight parts, mix the raw materials and add anhydrous ethanol of the raw material mass. Mix using a three-stage stirring method to obtain basalt fiber magnesium anti-cracking agent.

[0076] The three-stage stirring method includes a first stage of stirring at room temperature, a second stage of stirring with heat, and a third stage of stirring with cooling.

[0077] In some specific embodiments of the present invention, the stirring speed of the first stage at room temperature is 300-1000 rpm, and the stirring time is 15-30 min;

[0078] The second stage of heating and stirring is carried out at a temperature of 150–180°C for 1–6 hours and at a speed of 4500–6000 rpm.

[0079] The third stage of cooling and stirring is carried out by natural cooling, with a stirring speed of 300-1000 rpm and a stirring time of 30-60 minutes.

[0080] The principles and features of the present invention are described below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, specific conditions or manufacturer-recommended conditions should be followed in the embodiments. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0081] In the following examples, the basalt fibers are chopped fibers with a diameter of 15 μm and a length of 18 mm. The average particle size of the magnesium expanding agent is less than 2 μm, and the average particle size of α-sepiolite is less than 2.5 mm.

[0082] Example 1

[0083] This embodiment provides a basalt fiber magnesium-based crack-resistant agent, comprising the following raw materials in parts by weight:

[0084] The mixture consists of 10 parts of basalt fiber composite material, 87 parts of magnesium expanding agent, and 3 parts of α-sepiolite.

[0085] The basalt fiber composite material contains 75% basalt fiber.

[0086] In this embodiment, the basalt fiber composite material is prepared by the following method:

[0087] (1) After sintering the basalt fiber, it is immersed in an 8wt% mixed acid solution and the surface is etched to obtain activated basalt fiber. The sintering temperature is 350℃ and the sintering time is 30min. The mixed acid solution includes concentrated sulfuric acid (98%) and concentrated nitric acid (67%) in a volume ratio of 3:1.

[0088] (2) The carbon nanotubes were immersed in a mixed acid solution and ultrasonically dispersed. Then, they were washed five times with anhydrous ethanol as the cleaning solvent and dried to obtain activated carbon nanotubes. The mixed acid solution was the same as that in step (1). The ultrasonic dispersion was performed using an ultrasonic disperser with a power of 300W and a stirring time of 6 hours. The drying temperature was 75℃ and the drying time was 6 hours.

[0089] (3) The activated basalt fibers and carbon nanotubes were dissolved in acetone solution at a mass ratio of 75:25 and then ultrasonically dispersed.

[0090] A small amount of asphalt was added to the dispersed solution and kneaded at 160℃. After kneading, the mixture was stamped and calcined to obtain a basalt fiber composite material. The kneading time was 20 min, the stamping pressure was 10 MPa, the stamping temperature was 100℃, and the calcination temperature was 300℃.

[0091] In this embodiment, the basalt fiber magnesium anti-cracking agent was prepared by the following method:

[0092] Weigh the raw materials according to the weight proportions, mix the raw materials and add 50% anhydrous ethanol of the raw material mass. Mix using a three-stage stirring method to obtain basalt fiber magnesium anti-cracking agent.

[0093] The three-stage stirring method includes a first stage of stirring at room temperature, a second stage of stirring with heat, and a third stage of stirring with cooling.

[0094] The stirring speed in the first stage at room temperature is 500 rpm, and the stirring time is 30 minutes.

[0095] The second stage of heating and stirring is carried out at a temperature of 180℃ for 2 hours and a speed of 4500 rpm.

[0096] The third stage of cooling and stirring is carried out by natural cooling, with a stirring speed of 500 rpm and a stirring time of 30 minutes.

[0097] Example 2

[0098] This embodiment provides a basalt fiber magnesium-based crack-resistant agent, comprising the following raw materials in parts by weight:

[0099] Five parts of basalt fiber composite material, 93 parts of magnesium expanding agent and 2 parts of α-sepiolite.

[0100] The preparation method of the basalt fiber magnesium anti-cracking agent in this embodiment is the same as that in Example 1.

[0101] Example 3

[0102] This embodiment provides a basalt fiber magnesium-based crack-resistant agent, comprising the following raw materials in parts by weight:

[0103] The mixture consists of 10 parts basalt fiber composite material, 87.5 parts magnesium expansion agent, and 2.5 parts α-sepiolite.

[0104] The preparation method of the basalt fiber magnesium anti-cracking agent in this embodiment is the same as that in Example 1.

[0105] Example 4

[0106] This embodiment provides a basalt fiber magnesium-based crack-resistant agent, comprising the following raw materials in parts by weight:

[0107] Eight parts of basalt fiber composite material, 90 parts of magnesium expansion agent and 2 parts of α-sepiolite.

[0108] The preparation method of the basalt fiber magnesium anti-cracking agent in this embodiment is the same as that in Example 1.

[0109] Example 5

[0110] This embodiment provides a basalt fiber magnesium-based crack-resistant agent, comprising the following raw materials in parts by weight:

[0111] The mixture consists of 15 parts of basalt fiber composite material, 80 parts of magnesium expanding agent, and 5 parts of α-sepiolite.

[0112] The preparation method of the basalt fiber magnesium anti-cracking agent in this embodiment is the same as that in Example 1.

[0113] Examples 1-5 are identical except for the weight of the raw materials.

[0114] Example 6

[0115] The difference between this embodiment and Embodiment 1 is that the basalt fiber composite material in this embodiment is prepared by the following method:

[0116] (1) After sintering the basalt fiber, it is immersed in a 10wt% mixed acid solution and the surface is etched to obtain activated basalt fiber. The sintering temperature is 500℃ and the sintering time is 30min. The mixed acid solution includes concentrated sulfuric acid (98%) and concentrated nitric acid (67%) in a volume ratio of 3:1.

[0117] (2) The carbon nanotubes were immersed in a mixed acid solution and ultrasonically dispersed. Then, they were washed five times with anhydrous ethanol as the cleaning solvent and dried to obtain activated carbon nanotubes. The mixed acid solution was the same as that in step (1). The ultrasonic dispersion was performed using an ultrasonic disperser with a power of 300W and a stirring time of 6 hours. The drying temperature was 90℃ and the drying time was 6 hours.

[0118] (3) The activated basalt fibers and carbon nanotubes were dissolved in acetone solution at a mass ratio of 75:25 and then ultrasonically dispersed.

[0119] A small amount of asphalt was added to the dispersed solution and kneaded at 180℃. After kneading, the mixture was stamped and calcined to obtain basalt fiber composite material. The kneading time was 10 min, the stamping pressure was 5 MPa, the stamping temperature was 100℃, and the calcination temperature was 200℃.

[0120] Example 7

[0121] The difference between this embodiment and Embodiment 1 is that the basalt fiber composite material in this embodiment is prepared by the following method:

[0122] (1) After sintering the basalt fiber, it is immersed in a 5wt% mixed acid solution and the surface is etched to obtain activated basalt fiber. The sintering temperature is 300℃ and the sintering time is 45min. The mixed acid solution includes concentrated sulfuric acid (98%) and concentrated nitric acid (37%) in a volume ratio of 3:1.

[0123] (2) The carbon nanotubes were immersed in a mixed acid solution and ultrasonically dispersed. Then, they were washed five times with anhydrous ethanol as the cleaning solvent and dried to obtain activated carbon nanotubes. The mixed acid solution was the same as that in step (1). The ultrasonic dispersion was performed using an ultrasonic disperser with a power of 300W and a stirring time of 6 hours. The drying temperature was 75℃ and the drying time was 6 hours.

[0124] (3) The activated basalt fibers and carbon nanotubes were dissolved in acetone solution at a mass ratio of 75:25 and then ultrasonically dispersed.

[0125] The dispersed solution was mixed with a small amount of asphalt (30% of the mass of the activated basalt fiber, and the rest were the same) at 200℃. After mixing, the mixture was stamped and calcined to obtain the basalt fiber composite material. The mixing time was 30 min, the stamping pressure was 5 MPa, the stamping temperature was 100℃, and the calcination temperature was 300℃.

[0126] Comparative Example 1

[0127] The only difference between this comparative example and Example 1 is that basalt fiber is used instead of basalt fiber composite material.

[0128] Comparative Example 2

[0129] The only difference between this comparative example and Example 1 is that no carbon nanotubes are added during the preparation of the basalt fiber composite material; only the basalt fibers are modified.

[0130] Comparative Example 3

[0131] The only difference between this comparative example and Example 1 is that a magnesium expanding agent is not used.

[0132] Comparative Example 4

[0133] The only difference between this comparative example and Example 1 is that α-sepiolite is replaced with diatomaceous earth of the same specification.

[0134] Comparative Example 5

[0135] The only difference between this comparative example and Example 1 is that the basalt fiber magnesium anti-cracking agent was prepared directly by stirring at room temperature.

[0136] Comparative Example 6

[0137] The only difference between this comparative example and Example 1 is that the basalt fiber magnesium anti-cracking agent was prepared directly by heating and stirring.

[0138] Experimental Example 1

[0139] The materials prepared in Example 1 and Comparative Examples 1-6 were mixed into concrete according to the same proportions, and the concrete was subjected to performance tests, including slump, compressive strength, splitting strength, flexural strength, and autogenous volumetric deformation.

[0140] Specifically, the concrete components include crushed stone, sand, cement, and crack-resistant agent, selected according to the requirements of "Mix Design of Ordinary Concrete" (JGJ55-2011). The trial concrete strength grade is C50, and the cement strength is 542 kg / m³. 3 Water 168kg / m 3 Sand 680kg / m 3 1020 kg / m³ of crushed stone 3 .

[0141] Concrete is prepared by the following methods:

[0142] S1: Use a forced mixer. During mixing, add the crack-resistant agent, sand, gravel, and cement to the mixer simultaneously. Dry mix first, then wet mix, extending the mixing time by 10-20 seconds to ensure the crack-resistant agent is evenly mixed in the concrete. The crack-resistant agent concrete mixture should be uniformly mixed, with a consistent color, and free from segregation, bleeding, or clumping of the basalt fiber magnesium crack-resistant agent.

[0143] S2: The uniformity and consistency of the mixture should be checked at least once per work shift, and the deviation should not exceed ±10% of the mix proportion requirements; if necessary, the volume fraction of the crack-resistant agent should be checked, and the deviation should not exceed ±15% of the mix proportion requirements.

[0144] S3: The slump of fiber-reinforced concrete should be strictly controlled. If the slump is too small, the concrete will stick to the chute, making it difficult to vibrate during placement, resulting in high resistance during slipforming and easy cracking. If the slump is too large, the concrete will easily separate when sliding in the chute, and the concrete will easily collapse after demolding, resulting in poor surface smoothness.

[0145] S4: Crack-resistant concrete should be vibrated with a plate vibrator or an external vibrator to ensure that the basalt fiber magnesium crack-resistant concrete is dense and that the basalt fiber magnesium crack-resistant agent is evenly distributed to avoid the basalt fiber magnesium crack-resistant agent being exposed on the surface of the structure.

[0146] S5: Try to pour continuously to reduce construction joints; if this is unavoidable, the concrete at the joints can be roughened immediately after the concrete has set, or its impact can be reduced by structural reinforcement.

[0147] In this experiment, the dosage of the basalt fiber magnesium crack-resistant agent from Example 1 added to the concrete was ensured to be 6 kg / m³. 3 The dosage of crack-resistant agent in Comparative Examples 1-6 was 6 kg / m³. 3 .

[0148] The detection results of Example 1 and Comparative Examples 1-5 are shown in Table 1.

[0149] Table 1 Statistical Table of Concrete Performance Test Results

[0150]

[0151] It can be seen that, taking the dosage of basalt fiber magnesium anti-cracking agent as the standard, compared with the blank group without any anti-cracking agent, the dosage of basalt fiber magnesium anti-cracking agent prepared in this invention (4-6 kg / m³) is significantly higher. 3 After processing, the tensile strength of concrete can be increased by 10-20%, the compressive strength by 5-10%, the frost resistance by 10-30%, and the impermeability by about 20%.

[0152] In Comparative Example 1, no modification treatment was performed on the basalt fiber, so the activity and dispersion performance of the basalt fiber could not be improved, and a complex network structure could not be obtained. Therefore, the subsequent combination of basalt fiber with lightly calcined magnesium oxide and α-sepiolite was only a physical combination, which could not improve the stability and dispersibility of the crack-resistant agent. As a result, the bonding inside the concrete was relatively weak, and it only had some crack-resistant and waterproof functions.

[0153] In Comparative Example 2, no carbon nanotubes were added to form a network with basalt fibers. Only the basalt itself was etched and kneaded. Therefore, the modified basalt fibers only improved some stability properties and could not improve the bonding ability with lightly calcined magnesia and α-sepiolite. Thus, it had an impact on the performance of concrete, but it was not significant.

[0154] The absence of lightly calcined magnesium oxide in Comparative Example 3 has a certain impact on the micro-expansion capacity of concrete, resulting in a relatively high risk of shrinkage cracking in the prepared concrete, and also has a certain negative impact on the density of the concrete.

[0155] In Comparative Example 4, α-sepiolite was replaced with diatomaceous earth, which has similar properties. Although diatomaceous earth can improve the frost resistance of concrete to a certain extent, its presence will affect the continuity of the internal structure of the concrete. When basalt fibers are stretched, the diatomaceous earth particles will disperse, reducing the compressive and flexural strength of the concrete and having a significant impact on the slump.

[0156] Comparative Examples 5 and 6 used a one-time mixing method to prepare crack-resistant agents. Although this method can mix the raw materials evenly, it will affect the degree of structural cross-linking of the product during the mixing process, resulting in unstable structure of the prepared crack-resistant agent itself. After being used in concrete, it will affect the stability and slump of the concrete.

[0157] Experimental Example 2

[0158] Based on the basalt fiber composite material prepared in Example 1, the content of basalt fiber composite material and lightly calcined magnesium oxide was studied. The method for preparing concrete was the same as that in Example 1.

[0159] The experimental group was divided into experimental groups 1-4, and the control group was divided into control groups 1-4. The dosage of basalt fiber composite material in concrete was 3 kg / m³. 3 3kg / m 3 3kg / m 3 3kg / m 3 0kg / m 3 2.5kg / m 3 3.5kg / m 3 4kg / m 3 The dosage of lightly calcined magnesium oxide is 7.5 kg / m³. 3 7kg / m 3 6.5kg / m 3 6kg / m 3 0kg / m 3 6kg / m 3 6kg / m 3 6kg / m 3 The α-sepiolite content was 0.1 kg / m³. 3 .

[0160] The results of the autogenous volume deformation test of concrete prepared with crack-resistant agents in experimental groups 1-4 and control groups 1-4 are shown in Table 2.

[0161] Table 2 Statistical Table of Test Results for Self-Generating Volume Deformation of Concrete

[0162]

[0163] As shown in Table 2, the self-generated volumetric deformation of concrete without the basalt fiber magnesium crack-resistant agent of this invention is shrinkage-type; in a 20℃ environment, the self-generated volumetric deformation expansion of concrete with basalt fiber magnesium crack-resistant agent (Example 1) at 180 days is approximately (50-60) × 10 -6 Furthermore, the expansion exhibits a continuous and slow growth trend, primarily occurring during the temperature drop phase of large-volume concrete (i.e., 7-90 days after curing). This suggests that, based on the standard dosage of either basalt fiber composite material or lightly calcined magnesia alone, only 2.5-4 kg / m³ of basalt fiber composite material needs to be added externally. 3 This can improve the micro-expansion capacity of concrete and compensate for concrete shrinkage stress. Compared with the total dosage of magnesium expansive agent in existing technologies, which reaches 13-17%, the cost of raw materials has been greatly reduced.

[0164] In summary, the incorporation of the basalt fiber magnesium anti-cracking agent of this invention has no negative impact on the workability and mechanical properties of concrete, and will not lead to super-retarded setting; it can provide continuous micro-expansion, reducing the risk of concrete shrinkage cracking; and it can comprehensively improve the physical and mechanical properties and durability of concrete. The basalt fiber magnesium anti-cracking agent of this invention allows for adjustable dosage ratios and activation reaction times, thereby adapting to the crack resistance and seepage prevention needs of various concrete structures.

[0165] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A basalt fiber magnesium-based crack-resistant agent, characterized in that, By weight, it includes the following raw materials: 5-15 parts of basalt fiber composite material, 80-94 parts of magnesium expansion agent and 1-5 parts of α-sepiolite; The basalt fiber composite material contains 70-90% basalt fiber. The magnesium-based expanding agent is lightly calcined magnesium oxide; The dosage of the basalt fiber magnesium crack-resistant agent in concrete is 4~6 kg / m³. 3 ; The basalt fiber composite material is prepared by the following method: Basalt fibers and carbon nanotubes were activated, and the activated basalt fibers and carbon nanotubes were combined and modified at a mass ratio of 70~90:10~30 to obtain basalt fiber composite materials. The composite modification includes the following steps: The activated basalt fibers and carbon nanotubes were co-dissolved in acetone solution and ultrasonically dispersed. The dispersed solution is mixed with a small amount of asphalt at 160~200℃, and then stamped and fired. The activation includes the following steps: After sintering, basalt fibers are immersed in a mixed acid solution to etch the surface and obtain activated basalt fibers. Carbon nanotubes were immersed in a mixed acid solution and ultrasonically dispersed to carboxylate them. After washing with anhydrous ethanol, they were dried to obtain activated carbon nanotubes.

2. The basalt fiber magnesium crack-resistant agent according to claim 1, characterized in that, By weight, it includes the following raw materials: 8-12 parts of basalt fiber composite material, 85-90 parts of magnesium expansion agent and 2-3 parts of α-sepiolite.

3. The basalt fiber magnesium anti-cracking agent according to claim 1 or 2, characterized in that, By weight, it includes the following raw materials: 10 parts basalt fiber composite material, 87 parts magnesium expansion agent and 3 parts α-sepiolite.

4. The basalt fiber magnesium anti-cracking agent according to claim 1, characterized in that, The lightly calcined magnesia contains more than 85% magnesia, less than 4% loss on ignition, less than 1% moisture, less than 2% f-CaO content, and has an active reaction time of 50s to 300s.

5. The basalt fiber magnesium crack-resistant agent according to claim 1, characterized in that, The mixed acid solution comprises a 98% concentrated sulfuric acid solution and a 67% concentrated nitric acid solution in a volume ratio of 3:

1.

6. The basalt fiber magnesium anti-cracking agent according to claim 1, characterized in that, The basalt fiber is a short-cut fiber with a diameter of 15~22μm and a length of 15~30mm.

7. A method for preparing a basalt fiber magnesium-based crack-resistant agent according to any one of claims 1 to 6, characterized in that, Includes the following steps: Weigh the raw materials according to the weight proportions, mix the raw materials and add 50-75% anhydrous ethanol by weight of the raw materials. Mix using a three-stage stirring method to obtain basalt fiber magnesium anti-cracking agent. The three-stage stirring method includes a first stage of stirring at room temperature, a second stage of stirring with heat, and a third stage of stirring with cooling.

8. The preparation method of the basalt fiber magnesium anti-cracking agent according to claim 7, characterized in that, The stirring speed in the first stage at room temperature is 300~1000 rpm, and the stirring time is 15~30 min; The second stage of heating and stirring is carried out at a temperature of 150~180℃ for 1~6 hours and at a speed of 4500~6000 rpm. The third stage of cooling and stirring is carried out by natural cooling, with a stirring speed of 300~1000 rpm and a stirring time of 30~60 min.

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