Long-lasting expansion and crack resistance agent for concrete, preparation method and crack-resistant concrete

Abstract

This application relates to a long-lasting expansive anti-cracking agent for concrete, a preparation method, and crack-resistant concrete. The agent comprises, by mass percentage, 60% to 90% microcapsules A and 10% to 40% microcapsules B. Microcapsules A include core particles A and a capsule wall coating the outer surface of the core particles A. The core particles A include a mixed expansive agent, microcrystalline cellulose, and anhydrous ethanol. The mixed expansive agent includes calcium oxide, a medium-activity magnesium oxide, and a low-activity magnesium oxide. Microcapsules B include core particles B and a capsule wall coating the outer surface of the core particles B. The core particles B include a mixed repair material, microcrystalline cellulose, and anhydrous ethanol. The mixed repair material includes calcium oxide, a high-activity magnesium oxide, sodium silicate, and calcined hydrotalcite. This application addresses the problem of cracking in large-volume concrete, which cannot be fully addressed by relying solely on methods of reducing crack generation or repairing cracks.

Description

Technical Field

[0001] The present application relates to the technical field of concrete admixtures, and in particular to a long-lasting expansion and anti-cracking agent for concrete, a preparation method, and anti-cracking concrete. Background Art

[0002] With the rapid development of my country's infrastructure, concrete is being used on an increasingly large scale in large-scale projects. This type of large-volume concrete exhibits high hydration heat and shrinkage. Shrinkage cracks and temperature cracks are the most common cracks in large-volume concrete. While small microscopic cracks generally pose no short-term threat to the concrete's structure, they can significantly impact its durability. Harmful substances such as chloride ions, sulfate ions, water molecules, and carbon dioxide can easily penetrate the concrete through these cracks, accelerating structural degradation and steel corrosion. Based on the history of crack development, there are two primary technical approaches to improving concrete's crack resistance: reducing the probability of concrete cracking and improving concrete's ability to repair existing cracks.

[0003] Currently, adding expansive agents to compensate for the shrinkage of large-volume concrete is one of the effective measures to reduce the occurrence of cracks and improve the crack resistance of concrete. However, expansive agents have little effect on improving temperature cracks and are less effective in repairing existing cracks. If microcracks are not effectively repaired in the early stages, they will expand into macrocracks, affecting the durability and strength of concrete. In addition, existing single expansive agents are difficult to achieve the purpose of compensating for shrinkage in all stages. Calcium-based expansive agents have a fast hydration rate in the early stage, resulting in a large amount of ineffective expansion in the plastic stage of concrete, and basically no expansion in the later stage. Magnesium-based expansive agents mainly expand in the middle and late stages, but the early expansion is low, and the compensation for shrinkage is limited. Encapsulating repair materials in microcapsules is a relatively efficient way to repair cracks, but a single crack repair method cannot control the occurrence of cracks from the source, and has limited improvement in the crack resistance of concrete. In addition, existing microcapsules often use organic wall materials, which have poor compatibility with concrete. Therefore, cracks often bypass the capsules, making it impossible for the repair material to be released in time.

[0004] The two methods have different action times, action levels, and action principles, and each has certain defects. Therefore, relying solely on reducing the occurrence of cracks or repairing cracks cannot completely solve the cracking problem of large-volume concrete. Summary of the Invention

[0005] The embodiments of the present application provide a long-lasting expansion anti-cracking agent for concrete, a preparation method, and anti-cracking concrete to solve the problem of cracking of large-volume concrete that cannot be completely solved by simply reducing the occurrence of cracks or repairing cracks in the related art.

[0006] In a first aspect, a long-lasting expansion and anti-cracking agent for concrete is provided, which comprises 60% to 90% microcapsules A and 10% to 40% microcapsules B, calculated by mass percentage;

[0007] The microcapsule A comprises a capsule core particle A and a capsule wall coated on the outer surface of the capsule core particle A. The capsule core particle A comprises a mixed swelling agent, microcrystalline cellulose and anhydrous ethanol; the mixed swelling agent comprises a calcium oxide swelling agent, a medium-activity magnesium oxide swelling agent and a low-activity magnesium oxide swelling agent;

[0008] The microcapsule B includes a core particle B and a capsule wall coated on the outer surface of the core particle B. The core particle B includes a mixed repair material, microcrystalline cellulose and anhydrous ethanol; the mixed repair material includes a calcium oxide expander, a high-activity magnesium oxide expander, sodium silicate and calcined hydrotalcite.

[0009] In some embodiments, in the capsule core particle A, the mass ratio of the mixed swelling agent, microcrystalline cellulose and anhydrous ethanol is 1: (0.4-0.8): (0.8-1.4);

[0010] and / or, in the capsule core particle B, the mass ratio of the mixed repair material, microcrystalline cellulose and anhydrous ethanol is 1:(0.4-0.8):(0.8-1.4);

[0011] And / or, in the mixed expansion agent, the mass percentages of calcium oxide expansion agent, medium-activity magnesium oxide expansion agent and low-activity magnesium oxide expansion agent are 30% to 60%, 20% to 40% and 10% to 30% respectively;

[0012] And / or, in the mixed repair material, the mass percentages of calcium oxide expansion agent, high-activity magnesium oxide expansion agent, sodium silicate, and calcined hydrotalcite are 40% to 60%, 20% to 40%, 10% to 30%, and 5% to 15% respectively;

[0013] And / or, the diameter of the microcapsule A is 0.7-1.2 mm, and the diameter of the capsule core particle A is 0.4-0.7 mm;

[0014] And / or, the diameter of the microcapsule B is 0.3-0.6 mm, and the diameter of the capsule core particle B is 0.2-0.5 mm;

[0015] and / or, the melting point of the capsule wall of the microcapsule A is 35° C. to 55° C.;

[0016] And / or, the reaction times of the high-activity magnesium oxide expansion agent, the medium-activity magnesium oxide expansion agent and the low-activity magnesium oxide expansion agent are 40s to 80s, 100s to 140s and 220s to 260s respectively.

[0017] In some embodiments, the capsule wall of the microcapsule A comprises modified paraffin;

[0018] Alternatively, the capsule wall of the microcapsule A is obtained by solidifying a capsule wall solution A. The preparation method of the capsule wall solution A comprises: melting modified paraffin into liquid to form the capsule wall solution A.

[0019] In some embodiments, the preparation method of the modified paraffin wax includes: melting paraffin wax at 60°C to 100°C into a liquid, adding three-dimensional porous graphene, stirring evenly, and placing the mixed liquid under vacuum for adsorption for 2h to 3h to obtain the modified paraffin wax.

[0020] In some embodiments, the three-dimensional porous graphene is added in an amount of 2% to 8% by mass of the paraffin wax;

[0021] And / or, the method for preparing the three-dimensional porous graphene comprises:

[0022] Ultrasonic dispersion of graphene oxide in deionized water to form a graphene oxide aqueous solution with a concentration of 2 to 2.5 g / L;

[0023] The graphene oxide aqueous solution is placed in a reactor, heated to 180-220°C and kept constant for 5-7 hours. After natural cooling, columnar graphene hydrogel is obtained. After repeated washing with deionized water, it is freeze-dried for 24-36 hours to obtain three-dimensional porous graphene.

[0024] In some embodiments, the capsule wall of the microcapsule B comprises ethyl cellulose, modified zeolite powder and anhydrous ethanol;

[0025] Alternatively, the capsule wall of the microcapsule B is obtained by solidifying a capsule wall solution B. The preparation method of the capsule wall solution B comprises: dissolving ethyl cellulose in anhydrous ethanol to prepare an ethyl cellulose solution with a concentration of 2-3%, adding modified zeolite powder, and stirring uniformly to form a capsule wall solution B.

[0026] In some embodiments, the modified zeolite powder has a particle size of ≤20 μm;

[0027] And / or, the modified zeolite powder is added in an amount of 30% to 50% of the mass fraction of the ethyl cellulose;

[0028] And / or, the preparation method of the modified zeolite powder comprises: soaking the zeolite powder in a saturated calcium hydroxide solution for 2 to 3 hours, and then drying.

[0029] In a second aspect, a method for preparing a long-lasting expansion and anti-cracking agent for concrete as described above is provided, comprising:

[0030] The mixed swelling agent, microcrystalline cellulose and anhydrous ethanol are uniformly mixed to prepare a wet material, which is then extruded, spheronized, dried and sieved in sequence to obtain capsule core particles A;

[0031] The core particles A are placed in the capsule wall solution A, the core particles A are coated into a film using a fluidized bed, and the film is dried and sieved to obtain microcapsules A;

[0032] The mixed repair material, microcrystalline cellulose and anhydrous ethanol are uniformly mixed to prepare a wet material, which is then extruded, spheronized, dried and sieved in sequence to obtain capsule core particles B;

[0033] The core particles B are placed in the capsule wall solution B, the core particles B are coated into a film using a fluidized bed, and then dried and sieved to obtain microcapsules B;

[0034] The microcapsules A and B are uniformly mixed to obtain a long-lasting expansion and anti-cracking agent for concrete.

[0035] In some embodiments, the preparation method of calcined hydrotalcite includes: calcining calcium aluminum carbonate type hydrotalcite at 480-520° C. for 5-6 hours.

[0036] In a third aspect, a crack-resistant concrete is provided, which includes a gel material and any of the above-described long-lasting expansion anti-cracking agents for concrete, wherein the amount of the anti-cracking agent is 6% to 12% of the mass fraction of the gel material.

[0037] The beneficial effects of the technical solution provided by this application include:

[0038] The long-lasting expansion anti-cracking agent for concrete provided in this application has excellent anti-cracking performance. It can not only compensate for the shrinkage and temperature rise of concrete in all stages, thereby reducing the occurrence of shrinkage cracks and temperature cracks, but also can efficiently self-repair the cracked micro-cracks. The repair effect is significant, and the anti-cracking performance of concrete is improved from many aspects.

[0039] Microcapsule A has a good expansion effect. By mixing calcium oxide and magnesium oxide expansion agents, it not only has high expansion efficiency and can compensate for concrete shrinkage at all stages, but also has strong adaptability. The proportion of expansion agent can be adjusted according to the shrinkage law of concrete, making it suitable for different grades of concrete.

[0040] Microcapsule A uses modified paraffin wax as its wall material, which reduces temperature rise and delays expansion. This effectively inhibits thermal cracking in large concrete volumes and reduces the ineffective shrinkage of calcium oxide expansive agents during the plastic phase. Furthermore, a low dosage of three-dimensional porous graphite forms a continuous thermal conductivity network within the paraffin wax, establishing a bridge between the wax and the concrete matrix. This avoids the problems of poor thermal conductivity, incompatibility, and leakage associated with traditional paraffin wax incorporation into concrete.

[0041] Microcapsule B exhibits excellent mechanical response to microcracks. By incorporating zeolite powder into ethyl cellulose, an organic-inorganic wall material is achieved. The calcium hydroxide within the zeolite participates in the hydration reaction, increasing the adhesion between the wall material and the cement paste. This improves the compatibility of the microcapsules with concrete, enhances their mechanical response to cracks, and reduces the phenomenon of cracks bypassing the capsules, a common phenomenon with traditional organic wall materials.

[0042] Microcapsule B significantly enhances the resistance of large-volume concrete to harmful molecules, ensuring its long-term durability. By grading the particle size of the repair product, dense accumulation of the repair material within the cracks is achieved, reducing the penetration of harmful molecules into the concrete from these cracks. The structural memory and ion exchangeability of calcined hydrotalcite allow for strong adsorption of harmful molecules such as chloride ions, sulfate ions, and carbon dioxide, further reducing their penetration rate. Furthermore, calcined hydrotalcite increases and maintains the alkalinity of the pore solution, ensuring the long-term stability of the hydration product. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0044] Figure 1 This is a flow chart of the preparation method of the long-lasting expansion and anti-cracking agent for concrete provided in the embodiments of the present application. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0046] The present application provides a long-lasting expansion and anti-cracking agent for concrete, which comprises 60% to 90% microcapsules A and 10% to 40% microcapsules B, calculated by mass percentage;

[0047] The microcapsule A comprises a capsule core particle A and a capsule wall coated on the outer surface of the capsule core particle A. The capsule core particle A comprises a mixed swelling agent, microcrystalline cellulose and anhydrous ethanol; the mixed swelling agent comprises a calcium oxide swelling agent, a medium-activity magnesium oxide swelling agent and a low-activity magnesium oxide swelling agent;

[0048] The microcapsule B includes a core particle B and a capsule wall coated on the outer surface of the core particle B. The core particle B includes a mixed repair material, microcrystalline cellulose and anhydrous ethanol; the mixed repair material includes a calcium oxide expander, a high-activity magnesium oxide expander, sodium silicate and calcined hydrotalcite.

[0049] Among the mixed expansive agents in the microcapsule A, the calcium oxide expansive agent has a fast hydration rate and high expansion efficiency. The hydration reaction is mainly completed within the first three days, and the restricted expansion rate in the first three days can reach over 90%, mainly compensating for the early shrinkage of concrete. The medium-activity magnesium oxide expansive agent has a mild reaction, with a small amount of expansion in the early stage and sustainable expansion in the middle stage, mainly compensating for the medium-term shrinkage of concrete. The low-activity magnesium oxide expansive agent has almost no expansion in the early stage, with the expansion concentrated in the late stage, and the sustainable expansion time is long, mainly compensating for the late shrinkage of concrete. The combination of the calcium oxide expansive agent, the medium-activity magnesium oxide expansive agent, and the low-activity magnesium oxide expansive agent can fully utilize the expansion effects of the different expansive agents at different stages, ensuring compensation for the shrinkage of large-volume concrete at all stages, thereby reducing the occurrence of shrinkage cracks in large-volume concrete.

[0050] In the mixed repair material of microcapsules B, the calcium oxide expander has the fastest hydration rate and the largest expansion volume, first forming calcium hydroxide crystals. The larger calcium hydroxide crystals quickly fill the cracks. The highly active magnesium oxide expander exhibits high early activity, producing smaller magnesium hydroxide crystals that can fill the gaps between calcium hydroxide crystals. Sodium silicate reacts with calcium ions in the solution through a complex precipitation reaction, forming tiny products that fill even smaller gaps and tiny areas at the crack tips. By grading the repair product's particle size, the expanded products are densely packed, ensuring a dense repair at the crack and minimizing the penetration of harmful molecules.

[0051] After cracks appear, harmful substances such as chloride ions, sulfate ions, water molecules, and carbon dioxide can easily penetrate into the concrete through the cracks, causing a decrease in the alkalinity of the solution in the concrete, corrosion of steel bars, expansion cracking, and other hazards, affecting the durability of the structure and service safety. Filling and repairing the cracks can to a certain extent resist the invasion of harmful substances, but for harmful substances with tiny particles, there is still the problem of penetrating into the concrete through the tiny gaps in the cracks. Hydrotalcite is a typical layered structure material. The layers are divalent and trivalent metal cations, and the interlayers are negatively charged anions and water. Due to the exchangeability of anions and the structural memory effect, it has a strong adsorption capacity. The anion exchange order is: CO3 2- >OH - >SO4 2- >HPO4 2- >F - >Cl - >Br - >NO3 -After calcination, hydrotalcite loses its anions and water, and the calcined product returns to its original structure when it encounters anions and water. This calcined hydrotalcite first exhibits structural memory reconstruction when encountering anions, and its adsorption capacity is superior to that of ion exchangeability. After structural reconstruction, it then exhibits ion exchangeability. Therefore, the adsorption capacity of calcined hydrotalcite for harmful substances such as chloride ions is significantly better than that of the original hydrotalcite. In addition, calcined hydrotalcite has stronger alkalinity, which can increase and maintain the alkalinity in the pore solution, promote the hydration reaction of the repair material, achieve the purpose of quickly repairing cracks, and maintain the long-term stability of the hydration product.

[0052] In the capsule core particles A, the mass ratio of the mixed swelling agent, microcrystalline cellulose and anhydrous ethanol is 1: (0.4-0.8): (0.8-1.4).

[0053] In the capsule core particle B, the mass ratio of the mixed repair material, microcrystalline cellulose and anhydrous ethanol is 1: (0.4-0.8): (0.8-1.4);

[0054] In the mixed expansion agent, the mass percentages of the calcium oxide expansion agent, the medium-activity magnesium oxide expansion agent and the low-activity magnesium oxide expansion agent are 30% to 60%, 20% to 40% and 10% to 30% respectively.

[0055] In the mixed repair material, the mass percentages of calcium oxide expansion agent, high-activity magnesium oxide expansion agent, sodium silicate and calcined hydrotalcite are 40% to 60%, 20% to 40%, 10% to 30% and 5% to 15% respectively.

[0056] The diameter of the microcapsule A is 0.7-1.2 mm, and the diameter of the capsule core particle A is 0.4-0.7 mm.

[0057] The diameter of the microcapsule B is 0.3-0.6 mm, and the diameter of the capsule core particle B is 0.2-0.5 mm.

[0058] The melting point of the capsule wall of the microcapsule A is 35°C to 55°C. When the temperature rise caused by the hydration heat release of the bulk concrete reaches the melting point of the capsule wall, the capsule wall begins to melt, releasing the encapsulated expansive agent, thereby reducing the ineffective expansion of the highly active calcium oxide expansive agent during the plastic phase and simultaneously reducing temperature cracks caused by the rapid temperature rise within the bulk concrete. During the cooling phase of the bulk concrete, the molten capsule wall resolidifies, thereby slowing the cooling rate within the concrete and reducing temperature drop cracks.

[0059] The reaction times of the high-activity magnesium oxide expansion agent, medium-activity magnesium oxide expansion agent, and low-activity magnesium oxide expansion agent are 40s to 80s, 100s to 140s, and 220s to 260s, respectively, and preferably 60s, 120s, and 240s. The reaction time of the magnesium oxide expansion agent is the main indicator for evaluating its activity. The shorter the reaction time, the higher the activity. The expansion of the high-activity magnesium oxide in microcapsule B is mainly concentrated in the early stage, which plays a role in quickly repairing cracks; the expansion of the medium-activity magnesium oxide and low-activity magnesium oxide in microcapsule A is mainly concentrated in the middle and late stages, respectively compensating for the shrinkage of large-volume concrete in the middle and late stages.

[0060] The capsule wall of the microcapsule A includes at least one of paraffin wax and modified paraffin wax.

[0061] Preferably, the capsule wall of the microcapsule A comprises modified paraffin.

[0062] Modified paraffin wax, the wall material for microcapsules A, offers reduced temperature rise, excellent mechanical properties, and delayed expansion. As a phase-change material, paraffin wax exhibits high latent heat, a wide temperature range, no overcooling, and stable performance. It can reduce the temperature rise and fall rates and peak temperatures of concrete, minimizing temperature cracking caused by the large temperature difference between the interior and surface of concrete during the hydration exothermic temperature rise and cooling phases. Its excellent mechanical properties ensure a low breakage rate for the microcapsules during mixing. Furthermore, the expansive agent encapsulated in the paraffin wax is released only when the internal temperature of the concrete reaches the melting point of the modified paraffin wax, thereby reducing the ineffective contraction of the calcium oxide expansive agent during the plastic phase and increasing the effective expansion rate of the expansive agent.

[0063] Specifically, the capsule wall of the microcapsule A is obtained by solidifying a capsule wall solution A. The preparation method of the capsule wall solution A includes: melting modified paraffin into liquid to form the capsule wall solution A.

[0064] The preparation method of the modified paraffin wax comprises: melting paraffin wax at 60° C. to 100° C. into liquid, adding three-dimensional porous graphene, stirring evenly, and placing the mixed liquid under vacuum for adsorption for 2 to 3 hours to obtain the modified paraffin wax.

[0065] The traditional paraffin wax added to concrete has the problems of low thermal conductivity and easy leakage of liquid paraffin. Compared with two-dimensional graphene, the use of three-dimensional porous graphene to modify paraffin wax, on the one hand, has a macroscopic three-dimensional structure, and the graphene sheets support each other, avoiding the easy agglomeration of two-dimensional graphene. It has a larger specific surface area and better thermal conductivity. It can form a continuous thermal conductive network in the paraffin phase at a low dosage, which is more excellent in improving the thermal conductivity and temperature sensitivity of paraffin wax, so that paraffin wax can sense temperature changes in time and release expansion agent; on the other hand, porous graphene establishes a paraffin wax connection to the concrete base. The porous graphene bridges the gap between the two bodies, alleviating the leakage problem of traditional liquid paraffin added to concrete. The principle is as follows: the large specific surface area of porous graphene provides adsorption sites for paraffin, and the paraffin is deeply embedded in the graphene pores by vacuum adsorption. The porous structure and strong adsorption properties create a strong physical bond between graphene and paraffin. At the same time, a large number of unreduced oxygen-containing groups such as carboxyl groups are attached to the three-dimensional porous graphene prepared by the hydrothermal method. When these oxygen-containing groups are exposed to cement paste, they are deprotonated under the action of strong alkali and ionize into H + , making the porous graphene surface negatively charged, attracting Ca in concrete 2+ This promotes an orderly hydration reaction on the porous graphene surface, resulting in a strong chemical bond between the porous graphene and the slurry. Furthermore, 3D porous graphene retains the excellent mechanical properties of 2D graphene. Its incorporation into the wall material can improve its mechanical strength and reduce the breakage rate of microcapsules during stirring.

[0066] The three-dimensional porous graphene is added in an amount of 2% to 8% of the mass fraction of the paraffin.

[0067] The three-dimensional porous graphene is prepared by a hydrothermal self-assembly method of graphene oxide. The specific preparation method includes: ultrasonically dispersing graphene oxide in deionized water to form a graphene oxide aqueous solution with a concentration of 2 to 2.5 g / L; placing the graphene oxide aqueous solution in a reactor, heating it to 180 to 220° C. and keeping the temperature constant for 5 to 7 hours, and obtaining a columnar graphene hydrogel after natural cooling. After repeatedly rinsing with deionized water, the hydrogel is freeze-dried for 24 to 36 hours to obtain the three-dimensional porous graphene.

[0068] The capsule wall of the microcapsule B comprises ethyl cellulose, modified zeolite powder and anhydrous ethanol.

[0069] Specifically, the capsule wall of the microcapsule B is obtained by solidifying a capsule wall solution B. The preparation method of the capsule wall solution B includes: dissolving ethyl cellulose in anhydrous ethanol to prepare an ethyl cellulose solution with a concentration of 2-3%, adding modified zeolite powder, and stirring uniformly to form a capsule wall solution B.

[0070] Wherein, the particle size of the modified zeolite powder is ≤20 μm.

[0071] The modified zeolite powder is added in an amount of 30% to 50% of the mass fraction of the ethyl cellulose.

[0072] The preparation method of the modified zeolite powder comprises: soaking the zeolite powder in a saturated calcium hydroxide solution for 2 to 3 hours, and then drying.

[0073] The wall material of the microcapsule B adopts an organic-inorganic combination to improve the compatibility of the microcapsules with concrete and enhance the mechanical response ability of the microcapsules. Due to their good film-forming properties and moderate mechanical strength, most microcapsules use organic wall materials. However, organic materials have poor compatibility with concrete, and cracks often bypass the capsules and extend along the interface between the capsules and the concrete matrix, making it impossible for the capsules to rupture and release the repair agent in time. Zeolite powder is added to ethyl cellulose. The porous structure of the zeolite powder has good adsorption capacity for ethyl cellulose, ensuring a good combination of the two. The inorganic material zeolite powder has good compatibility with the concrete matrix. The calcium hydroxide remaining in the pores of the zeolite powder participates in the hydration reaction in the concrete, which can further enhance the interfacial adhesion between the ethyl cellulose-zeolite wall material and the concrete matrix, and enhance the sensitivity of the microcapsules to cracks.

[0074] The preparation method of calcined hydrotalcite comprises the following steps: placing calcium aluminum carbonate type hydrotalcite at 480-520 DEG C and calcining for 5-6 hours.

[0075] like Figure 1 As shown, the present application also provides a method for preparing a long-lasting expansion and anti-cracking agent for concrete, which comprises the following steps:

[0076] 101: A mixed expander, microcrystalline cellulose, and anhydrous ethanol are uniformly mixed to prepare a wet material, which is then extruded, spheronized, dried, and sieved in sequence to obtain capsule core particles A; the capsule core particles A are placed in capsule wall solution A, and the capsule core particles A are coated into a film using a fluidized bed, which is then dried and sieved to obtain microcapsules A.

[0077] 102: The mixed repair material, microcrystalline cellulose and anhydrous ethanol are uniformly mixed to prepare a wet material, which is then extruded, spheronized, dried and sieved in sequence to obtain capsule core particles B; the capsule core particles B are placed in capsule wall solution B, and the capsule core particles B are coated into a film using a fluidized bed, which is then dried and sieved to obtain microcapsules B.

[0078] 103: Microcapsules A and B are uniformly mixed to obtain a long-lasting expansion and anti-cracking agent for concrete.

[0079] It should be noted that there is no strict order between the step 101 of preparing microcapsules A and the step 102 of preparing microcapsules B. They can be performed simultaneously, or microcapsules B can be prepared first and then microcapsules A.

[0080] The present application also provides a crack-resistant concrete, which includes a gel material and the above-mentioned long-lasting expansion anti-cracking agent for concrete, wherein the amount of the anti-cracking agent is 6% to 12% of the mass fraction of the gel material.

[0081] The specific implementation of this application is described below with reference to examples.

[0082] Anti-cracking agent examples and comparative examples

[0083] Example 1

[0084] The preparation method of the long-lasting expansion and anti-cracking agent for concrete provided in this embodiment comprises the following steps:

[0085] 1) uniformly mixing the mixed expander of microcapsule A, microcrystalline cellulose, and anhydrous ethanol in a mass ratio of 1:(0.4-0.8):(0.8-1.4) to prepare a wet material, and sequentially extruding, spheronizing, drying, and sieving to obtain capsule core particles A;

[0086] 2) melting the modified paraffin wax at 60° C. to form a capsule wall solution A;

[0087] 3) coating the capsule core particles A in a fluidized bed, drying, and sieving to obtain microcapsules A;

[0088] 4) uniformly mixing the mixed repair material of microcapsule B, microcrystalline cellulose, and anhydrous ethanol at a mass ratio of 1:(0.4-0.8):(0.8-1.4) to prepare a wet material, and sequentially extruding, spheronizing, drying, and sieving to obtain capsule core particles B;

[0089] 5) dissolving ethyl cellulose in anhydrous ethanol to prepare a 2.5% ethyl cellulose solution, adding modified zeolite powder, and stirring uniformly to form a capsule wall solution B;

[0090] 6) coating the core particles B using a fluidized bed apparatus, drying, and sieving to obtain microcapsules B;

[0091] 7) Microcapsules A and microcapsules B are uniformly mixed in a ratio of 70%:30% by mass to prepare a long-lasting expansion and anti-cracking agent for concrete.

[0092] Among them, the calcium oxide expander, the medium-activity magnesium oxide expander and the low-activity magnesium oxide expander in the mixed expander account for 50%, 30% and 20% respectively by mass.

[0093] In the mixed repair material, the calcium oxide expansion agent, the high-activity magnesium oxide expansion agent, the sodium silicate and the calcined hydrotalcite account for 50%, 25%, 15% and 10% respectively by mass.

[0094] The diameter of the microcapsule A is 0.7-1.2 mm, and the diameter of the capsule core particle A is 0.4-0.7 mm; the diameter of the microcapsule B is 0.3-0.6 mm, and the diameter of the capsule core particle B is 0.2-0.5 mm.

[0095] The melting point of the modified paraffin wax is 35°C to 55°C; the paraffin modification method is as follows: paraffin is placed at 60°C to melt into a liquid, three-dimensional porous graphene with a paraffin mass fraction of 4% is added, stirred evenly, and the mixed liquid is placed under vacuum for adsorption for 2 hours; the three-dimensional porous graphene is prepared by a hydrothermal self-assembly method of graphene oxide, and the preparation steps are as follows: graphene oxide is ultrasonically dispersed in deionized water to form a graphene oxide aqueous solution with a concentration of 2g / L; the graphene oxide aqueous solution is placed in a reactor, heated to 200°C and kept at a constant temperature for 6 hours, and after natural cooling, a columnar graphene hydrogel is obtained, which is repeatedly rinsed with deionized water and freeze-dried for 24 hours to obtain the three-dimensional porous graphene.

[0096] The reaction times of the high-activity magnesium oxide expansion agent, the medium-activity magnesium oxide expansion agent and the low-activity magnesium oxide expansion agent are 60s, 120s and 240s respectively.

[0097] The particle size of the zeolite powder is ≤20 μm. The modification method of the zeolite powder is: soaking the zeolite powder in a saturated calcium hydroxide solution for 2 hours and then drying it. The modified zeolite powder is added in an amount of 40% of the mass fraction of ethyl cellulose.

[0098] The calcined hydrotalcite is prepared by calcining calcium aluminum carbonate type hydrotalcite at 500° C. for 5 hours.

[0099] A crack-resistant concrete comprises a gel material and the above-mentioned long-lasting expansion anti-cracking agent for concrete, wherein the amount of the anti-cracking agent is 8% of the mass fraction of the gel material.

[0100] Example 2

[0101] The difference between this embodiment and Example 1 is that in the long-durable expansion and anti-cracking agent for concrete provided in this embodiment, the calcium oxide expansion agent, the medium-activity magnesium oxide expansion agent, and the low-activity magnesium oxide expansion agent in the mixed expansion agent account for 40%, 40%, and 20% by mass, respectively.

[0102] Comparative Example 1

[0103] The difference between this comparative example and Example 1 is that the long-lasting expansion and crack-resistant agent for concrete provided in this comparative example is prepared by directly mixing the mixed expansion agent powder and microcapsules B, and the mixed expansion agent is not subjected to granulation and film-forming treatment, that is, no microcapsules A are formed.

[0104] Comparative Example 2

[0105] The difference between this comparative example and Example 1 is that in the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example, the wall material of the microcapsule A is original paraffin wax without modification.

[0106] Comparative Example 3

[0107] The difference between this comparative example and Example 1 is that in the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example, the wall materials of the microcapsule B are ethyl cellulose and original zeolite powder, and the original zeolite powder is not soaked in a saturated calcium hydroxide solution.

[0108] Comparative Example 4

[0109] The difference between this comparative example and Example 1 is that in the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example, the wall material of the microcapsule B is prepared by using ethyl cellulose, and no zeolite powder is added.

[0110] Comparative Example 5

[0111] The difference between this comparative example and Example 1 is that the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example is prepared by directly mixing the mixed expansion agent powder and microcapsule B, the mixed expansion agent is not subjected to granulation and film-forming treatment, and the wall material of the microcapsule B is prepared by ethyl cellulose without the addition of zeolite powder.

[0112] Comparative Example 6

[0113] The difference between this comparative example and Example 1 is that the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example consists of microcapsules A, without microcapsules B.

[0114] Comparative Example 7

[0115] The difference between this comparative example and Example 1 is that the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example consists of microcapsules B, without microcapsules A.

[0116] Comparative Example 8

[0117] The difference between this comparative example and Example 1 is that the dosage of the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example is 4% of the mass fraction of the cementitious material.

[0118] Comparative Example 9

[0119] The difference between this comparative example and Example 1 is that the content of the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example is 16% of the mass fraction of the cementitious material.

[0120] Comparative Example 10

[0121] The difference between this comparative example and Example 2 is that the long-lasting expansion and crack-resistant agent for concrete provided in this comparative example is prepared by directly mixing the mixed expansion agent powder and microcapsules B, and the mixed expansion agent is not subjected to granulation and film-forming treatment, that is, no microcapsules A are formed.

[0122] Comparative Example 11

[0123] The difference between this comparative example and Example 2 is that in the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example, the wall material of the microcapsule A is original paraffin wax without modification.

[0124] Comparative Example 12

[0125] The difference between this comparative example and Example 2 is that in the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example, the wall materials of the microcapsule B are ethyl cellulose and original zeolite powder, and the original zeolite powder is not soaked in a saturated calcium hydroxide solution.

[0126] Comparative Example 13

[0127] The difference between this comparative example and Example 2 is that in the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example, the wall material of the microcapsule B is prepared by using ethyl cellulose, and no zeolite powder is added.

[0128] Comparative Example 14

[0129] The difference between this comparative example and Example 2 is that the long-lasting expansion and crack-resistant agent for concrete provided in this comparative example is prepared by directly mixing the mixed expansion agent powder and microcapsule B, the mixed expansion agent is not subjected to granulation and film-forming treatment, and the wall material of the microcapsule B is prepared by ethyl cellulose without the addition of zeolite powder.

[0130] Comparative Example 15

[0131] The difference between this comparative example and Example 2 is that the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example consists of microcapsules A, without microcapsules B.

[0132] Comparative Example 16

[0133] The difference between this comparative example and Example 2 is that the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example consists of microcapsules B, without microcapsules A.

[0134] Comparative Example 17

[0135] The difference between this comparative example and Example 2 is that the dosage of the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example is 4% of the mass fraction of the cementitious material.

[0136] Comparative Example 18

[0137] The difference between this comparative example and Example 2 is that the content of the long-lasting expansion and anti-cracking agent for concrete provided in this comparative example is 16% of the mass fraction of the cementitious material.

[0138] Anti-cracking concrete examples and comparative examples

[0139] The crack-resistant concrete was prepared by adding the above-prepared anti-cracking agent to concrete. The crack-resistant concrete used in Examples 1 to 2 and Comparative Examples 1 to 18 was prepared using the same anti-cracking agent as in Examples 1 to 2 and Comparative Examples 1 to 18, respectively. The blank was prepared using concrete without the anti-cracking agent. The mix ratios for the various crack-resistant concretes are shown in Table 1. The crack-resistant concrete preparation process was as follows:

[0140] 1) Mix cement, fly ash, crushed stone, river sand, and water reducing agent to form a first mixture;

[0141] 2) adding water and stirring evenly to form a second mixture;

[0142] 3) Add anti-cracking agent and stir evenly to obtain anti-cracking concrete.

[0143] The present application conducts working performance, limited expansion rate, total crack area and thermal insulation temperature rise performance tests on crack-resistant concrete examples 1 to 2, comparative examples 1 to 18 and blank test pieces.

[0144] In addition, this application also performs pre-damage treatment on the specimens to evaluate the self-repairing ability of crack-resistant concrete. The steps are as follows:

[0145] 1) After curing for 28 days, the formed concrete specimens were subjected to compressive strength and RCM tests, and the compressive strength and chloride ion migration coefficient results were recorded as f cu and D;

[0146] 2) The specimens that were formed and cured for 28 days were placed at 50% f cu The specimens were pre-pressed for 3 minutes under a load of 1000 to induce the generation of internal microcracks, and the compressive strength and chloride ion migration coefficient of the specimens after pre-pressing were tested. The test results were recorded as f cu1 and D1;

[0147] 3) Place the pre-stressed specimen in air for 3 days to self-repair, and test the compressive strength and chloride ion migration coefficient of the repaired specimen. The test results are recorded as f cu2 and D2.

[0148] Table 1: Mix ratio of crack-resistant concrete (kg / m) for Examples 1 to 2, Comparative Examples 1 to 18 and Blank Example 3 )

[0149]

[0150]

[0151] Table 2 Working performance, limited expansion rate, total crack area and adiabatic temperature rise of crack-resistant concrete of Examples 1-2, Comparative Examples 1-18 and Blank Example

[0152]

[0153] Table 3 Strength repair efficiency of crack-resistant concrete in Examples 1 to 2, Comparative Examples 1 to 18 and Blank Example

[0154]

[0155]

[0156] Table 4 Chloride ion penetration resistance and repair efficiency of crack-resistant concrete in Examples 1 to 2, Comparative Examples 1 to 18 and Blank Example

[0157]

[0158] The results in Tables 2, 3, and 4 demonstrate that the crack-resistant concrete prepared using this application exhibits excellent crack resistance. The mixture of calcium and magnesium expansive agents compensates for concrete shrinkage throughout its entire lifespan, reducing the occurrence of shrinkage cracks. The delayed expansion effect created by the paraffin wax wall material encapsulating the expansive agent significantly reduces the ineffective expansion of the calcium oxide expansive agent during the plastic phase. The phase change properties of paraffin wax reduce the temperature rise and fall rates of large-volume concrete, minimizing the occurrence of temperature cracks.

[0159] The results in Tables 2, 3, and 4 demonstrate that the crack-resistant concrete prepared using this application exhibits excellent self-healing capabilities and durability. The organic-inorganic combined wall material significantly improves the compatibility of the microcapsules with concrete, increasing their mechanical response and triggering efficiency. The dense accumulation of the repair product at the cracks and the strong adsorption properties of the calcined hydrotalcite significantly reduce the penetration pathways of harmful molecules.

[0160] In summary, this application achieves the function of gradient compensation for shrinkage and temperature rise of the anti-cracking agent in the early, middle and late stages by compounding magnesium-based expansion agents and calcium-based expansion agents and adopting capsule encapsulation technology of modified paraffin wall materials. The compatibility of the capsule and concrete is improved by combining organic-inorganic wall materials, and the density of the crack repair material is improved by utilizing the particle size grading characteristics of the repair product, so that the anti-cracking agent can not only reduce the occurrence of shrinkage cracks and temperature cracks in concrete, but also efficiently self-repair existing cracks, thereby improving the crack resistance of concrete from two aspects.

[0161] The anti-cracking agent provided in this application can adjust the ratio of the expansive agent and the capsule according to the shrinkage law of the concrete, and is suitable for concrete of different grades; the capsule has high strength while ensuring the triggering efficiency, which can reduce the breakage rate of the capsule during transportation and mixing, and reduce the amount of capsule used; the capsule can be mass-produced, and its excellent anti-cracking performance can reduce the maintenance and reinforcement costs of concrete structures caused by cracking problems, and has high engineering application value and potential economic value in various large-volume concrete structures.

[0162] In the description of this application, it should be noted that the terms "upper" and "lower" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0163] It should be noted that, in this application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0164] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present 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 the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A long-lasting expansion and anti-cracking agent for concrete, characterized in that: Calculated by mass percentage, it includes 60% to 90% microcapsule A and 10% to 40% microcapsule B; The microcapsule A comprises a capsule core particle A and a capsule wall coated on the outer surface of the capsule core particle A. The capsule core particle A comprises a mixed swelling agent, microcrystalline cellulose and anhydrous ethanol; the mixed swelling agent comprises a calcium oxide swelling agent, a medium-activity magnesium oxide swelling agent and a low-activity magnesium oxide swelling agent; The microcapsule B includes a capsule core particle B and a capsule wall coated on the outer surface of the capsule core particle B, wherein the capsule core particle B includes a mixed repair material, microcrystalline cellulose and anhydrous ethanol; the mixed repair material includes a calcium oxide expansion agent, a high-activity magnesium oxide expansion agent, sodium silicate and calcined hydrotalcite; The capsule wall of the microcapsule A includes modified paraffin wax, and the preparation method of the modified paraffin wax includes: melting the paraffin wax at 60° C. to 100° C. into a liquid, adding three-dimensional porous graphene, stirring evenly, and placing the mixed liquid under vacuum for adsorption for 2 h to 3 h to obtain the modified paraffin wax; The capsule wall of the microcapsule B comprises ethyl cellulose, modified zeolite powder and anhydrous ethanol; the preparation method of the modified zeolite powder comprises: soaking the zeolite powder in a saturated calcium hydroxide solution for 2 to 3 hours, and then drying.

2. The long-lasting expansion and anti-cracking agent for concrete according to claim 1, characterized in that: In the capsule core particle A, the mass ratio of the mixed swelling agent, microcrystalline cellulose and anhydrous ethanol is 1: (0.4-0.8): (0.8-1.4); And / or, in the capsule core particle B, the mass ratio of the mixed repair material, microcrystalline cellulose and anhydrous ethanol is 1: (0.4-0.8): (0.8-1.4); And / or, in the mixed expansion agent, the mass percentages of calcium oxide expansion agent, medium-activity magnesium oxide expansion agent and low-activity magnesium oxide expansion agent are 30% to 60%, 20% to 40% and 10% to 30% respectively; And / or, in the mixed repair material, the mass percentages of calcium oxide expansion agent, high-activity magnesium oxide expansion agent, sodium silicate, and calcined hydrotalcite are 40% to 60%, 20% to 40%, 10% to 30%, and 5% to 15%, respectively; And / or, the diameter of the microcapsule A is 0.7-1.2 mm, and the diameter of the capsule core particle A is 0.4-0.7 mm; And / or, the diameter of the microcapsule B is 0.3-0.6 mm, and the diameter of the capsule core particle B is 0.2-0.5 mm; And / or, the melting point of the capsule wall of the microcapsule A is 35°C to 55°C; And / or, the reaction times of the high-activity magnesium oxide expansion agent, the medium-activity magnesium oxide expansion agent and the low-activity magnesium oxide expansion agent are 40s-80s, 100s-140s and 220s-260s respectively.

3. The long-lasting expansion and anti-cracking agent for concrete according to claim 1, characterized in that: The capsule wall of the microcapsule A is obtained by solidifying a capsule wall solution A. The preparation method of the capsule wall solution A comprises: melting modified paraffin into liquid to form the capsule wall solution A.

4. The long-lasting expansion and anti-cracking agent for concrete according to claim 1, characterized in that: The three-dimensional porous graphene content is 2% to 8% of the mass fraction of the paraffin; And / or, the method for preparing the three-dimensional porous graphene comprises: Ultrasonic dispersion of graphene oxide in deionized water to form a graphene oxide aqueous solution with a concentration of 2-2.5 g / L; The graphene oxide aqueous solution is placed in a reactor, heated to 180-220°C and kept constant for 5-7 hours. After natural cooling, columnar graphene hydrogel is obtained. After repeated washing with deionized water, it is freeze-dried for 24-36 hours to obtain three-dimensional porous graphene.

5. The long-lasting expansion and anti-cracking agent for concrete according to claim 1, characterized in that: The capsule wall of the microcapsule B is obtained by solidifying a capsule wall solution B. The preparation method of the capsule wall solution B comprises: dissolving ethyl cellulose in anhydrous ethanol to prepare an ethyl cellulose solution with a concentration of 2-3%, adding modified zeolite powder, and stirring uniformly to form the capsule wall solution B.

6. The long-lasting expansion and anti-cracking agent for concrete according to claim 1, characterized in that: The modified zeolite powder has a particle size of ≤20 μm; And / or, the modified zeolite powder is added in an amount of 30% to 50% of the mass fraction of the ethyl cellulose.

7. A method for preparing a long-lasting expansion and anti-cracking agent for concrete according to any one of claims 1 to 6, characterized in that: It includes: The mixed swelling agent, microcrystalline cellulose and anhydrous ethanol are uniformly mixed to prepare a wet material, which is then extruded, spheronized, dried and sieved in sequence to obtain capsule core particles A; The core particles A are placed in the capsule wall solution A, the core particles A are coated into a film using a fluidized bed, and the film is dried and sieved to obtain microcapsules A; The mixed repair material, microcrystalline cellulose and anhydrous ethanol are uniformly mixed to prepare a wet material, which is then extruded, spheronized, dried and sieved in sequence to obtain capsule core particles B; The core particles B are placed in the capsule wall solution B, the core particles B are coated into a film using a fluidized bed, and then dried and sieved to obtain microcapsules B; The microcapsules A and B are uniformly mixed to obtain a long-lasting expansion and anti-cracking agent for concrete.

8. The method for preparing a long-lasting expansion and anti-cracking agent for concrete according to claim 7, wherein: The preparation method of calcined hydrotalcite comprises the following steps: placing calcium aluminum carbonate type hydrotalcite at 480-520 DEG C and calcining for 5-6 hours.

9. A crack-resistant concrete, characterized in that: The invention comprises a gel material and the long-lasting expansion anti-cracking agent for concrete as claimed in any one of claims 1 to 6, wherein the amount of the anti-cracking agent is 6% to 12% of the mass fraction of the gel material.

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