A concrete anti-cracking admixture for highland alpine regions and a preparation method and application thereof

Abstract

The application discloses a kind of highland alpine region concrete anti-cracking admixture and its preparation method and application, it is related to concrete admixture technical field.The components of the highland alpine region concrete anti-cracking admixture include: self-healing material 60~80 parts, slow-release curing agent 10~20 parts, low-temperature reinforcing agent 6~10 parts and workability regulator 4~10 parts by mass fraction;Raw materials of the self-healing material include: healing component, complex component, expansion component, aluminum potassium sulfate dodecahydrate and calcium hydroxide;Raw materials of the slow-release curing agent include: acrylic acid, acrylamide, N,N'-methylene bisacrylamide, ammonium persulfate and surface modifier solution.The highland alpine region concrete anti-cracking admixture is suitable for highland alpine region thin-walled high pier concrete, can reduce early shrinkage crack of thin-walled high pier concrete formed in highland alpine region harsh environment, improve its frost resistance.Meanwhile, it can also improve its mechanical properties, and will not affect its workability.

Description

Technical Field

[0001] This invention relates to the field of concrete admixture technology, and in particular to a crack-resistant concrete admixture for high-altitude and cold regions, its preparation method, and its application. Background Technology

[0002] In high-altitude, frigid regions with harsh climates, such as cold and dry conditions, long hours of sunshine and strong radiation, large diurnal temperature variations, and strong winds, a significant cause of concrete cracking in bridge piers is shrinkage cracking caused by these extreme conditions. This shrinkage primarily includes drying shrinkage, plastic shrinkage, and autogenous shrinkage. When the stress generated by the constrained shrinkage of concrete exceeds its tensile strength, shrinkage cracking occurs. After pouring, the heat of hydration in the cement causes a rapid temperature rise to its peak, followed by volume expansion and contraction as the temperature drops. Simultaneously, the internal heat of hydration is difficult to dissipate, resulting in a high internal temperature, while the surface cools down quickly, creating a significant temperature difference between the interior and exterior. In the early stages of curing, the concrete strength is low, and this large temperature difference makes the surface prone to cracking. In the later stages of curing, the concrete shrinks as it cools, but due to the constraint of the base, the bottom concrete is under tension. When the tensile stress exceeds the concrete's ultimate tensile strength, the resulting cracks propagate upwards, potentially forming through-cracks. Furthermore, freeze-thaw cycles can cause freezing damage cracks. Early-stage freeze-thaw cracking in concrete is caused by the volume expansion of the microstructure due to the freezing of pore water in the cement paste structure, resulting in the formation of fine cracks inside the concrete. Long-term freeze-thaw cracking in concrete occurs in the freeze-thaw environment with large temperature differences at high altitudes, where the hardened cement paste structure is affected by freeze-thaw cycles, resulting in irreversible cracks.

[0003] Thin-walled high piers are the main type of bridge piers for long-span bridges in high-altitude and frigid regions due to their advantages such as lightweight structure, low cost, simple construction, and structural stability. However, the unique environment of high-altitude and frigid regions, characterized by low temperatures, dryness, intense solar radiation, large diurnal temperature variations, and frequent freeze-thaw cycles, leads to widespread and severe cracking in the concrete structures of thin-walled high piers, significantly impacting the structure's durability and even safety. Currently, cracking of thin-walled high piers in high-altitude and frigid regions is one of the most pressing technical challenges to be addressed in practical engineering projects. Summary of the Invention

[0004] The purpose of this invention is to provide a crack-resistant admixture for concrete in high-altitude and cold regions, its preparation method, and its application, so as to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention is: a concrete crack-resistant admixture for high-altitude and cold regions, comprising, by weight, 60-80 parts of self-healing material, 10-20 parts of slow-release curing agent, 6-10 parts of low-temperature strengthening agent, and 4-10 parts of workability modifier;

[0007] The raw materials of the self-healing material include: healing components, complexing components, swelling components, potassium aluminum sulfate dodecahydrate, and calcium hydroxide;

[0008] The raw materials of the slow-release curing agent include: acrylic acid, acrylamide, N,N'-methylenebisacrylamide, ammonium persulfate, and a surface modifier solution.

[0009] This invention relates to a concrete crack-resistant admixture suitable for thin-walled, high-pier concrete in high-altitude, cold regions. It addresses shrinkage cracks and freeze-thaw cycle cracks caused by low temperatures, strong solar radiation, large diurnal temperature variations, and frequent freeze-thaw cycles. The slow-release curing agent absorbs and continuously releases moisture, maintaining relative humidity within the cement stone structure and reducing early shrinkage cracks in the harsh environment of high-altitude, cold regions. Simultaneously, it leaves independent, non-connected pores within the concrete, improving the freeze-thaw resistance of thin-walled, high-pier concrete in such environments. The self-healing material diffuses with water within the resulting concrete cracks. When the active substances encounter incompletely hydrated cement particles, they generate hydrated calcium silicate and calcium aluminosilicate, etc., through a cyclical reaction. This enables repeated self-healing of shrinkage cracks and freeze-thaw cycle-induced freezing damage cracks caused by constrained temperature and humidity changes within and outside the concrete during the service life of thin-walled, high-pier concrete. The low-temperature strengthening agent provides nucleation sites during the crystallization and growth stages of hydration products, accelerating the formation of cement hydration products and promoting the humidity-regulating effect of the slow-release curing agent, thereby mitigating drying shrinkage cracking. The workability modifier mitigates the adverse effects of the slow-release curing agent on concrete workability, allowing the concrete to maintain good workability. Therefore, the synergistic effect of these components enables the crack-resistant admixture of this invention to be used in low-temperature environments in high-altitude and cold regions, effectively improving the mechanical properties of thin-walled, high-pier concrete in these areas and maintaining good workability.

[0010] Further, by mass fraction, the raw materials of the self-healing material include: 40-60 parts of healing component, 2-8 parts of complexing component, 20-40 parts of expansion component, 5-10 parts of potassium aluminum sulfate dodecahydrate and 10-20 parts of calcium hydroxide.

[0011] Potassium aluminum sulfate dodecahydrate provides Al 3+ and SO4 2-It can react with calcium hydroxide in concrete to form insoluble ettringite crystals, which block pores. Its water solubility allows the active ions to penetrate deep into the concrete with water, expanding the waterproofing range and depth. Calcium hydroxide can provide the calcium ions necessary for the formation of waterproofing crystals such as ettringite, while ensuring an alkaline environment inside the concrete, providing the necessary conditions for crystal formation and long-term existence.

[0012] Furthermore, the healing component is one or two of anhydrous calcium sulfate, calcium magnesium carbonate, and calcium sulfoaluminate.

[0013] The healing components dissolve quickly upon contact with water and penetrate the water, providing the calcium ions necessary for the formation of waterproof crystals such as ettringite.

[0014] Furthermore, the complexing component is one or two of sodium citrate, sodium tartrate, and tetrasodium ethylenediaminetetraacetate (all of which are soluble carboxylate substances).

[0015] The anionic groups in the complexing component (soluble carboxylate substances) can react with calcium ions present in concrete to form unstable calcium complexes. These complexes diffuse with water in concrete cracks, transporting calcium ions from high concentrations to low concentrations. When they encounter incompletely hydrated cement particles, the active anions in the calcium complexes are replaced by silicate and aluminate ions, forming more stable hydrated calcium silicate and calcium aluminosilicate. The active anions continue to diffuse with water to calcium-rich areas and complex with calcium ions, initiating a new round of reactions. When the concrete is dry, the active anionic substances are dormant; when moist, they are activated, initiating a cyclical reaction and achieving multiple self-healing of concrete cracks.

[0016] Furthermore, by mass fraction, the raw materials of the expanded component include: 20-40 parts of lightly calcined calcium oxide and 60-80 parts of lightly calcined magnesium oxide.

[0017] The expansion component can form a micro-expanding insoluble substance that effectively fills and blocks the micropores inside the concrete. In the early stage, the expansion of lightly calcined calcium oxide compensates for the early shrinkage, and in the later stage, the expansion of lightly calcined magnesium oxide compensates for the medium and long-term shrinkage. This achieves phased and full-process compensation of the shrinkage process of concrete, inhibits the generation of shrinkage cracks, and improves the crack resistance of thin-walled high-pier concrete in high-altitude and cold regions.

[0018] Preferably, the lightly calcined calcium oxide has a calcium oxide content greater than 80 wt% and a residue of less than 4.0 wt% on an 80 μm square-hole sieve.

[0019] Preferably, the magnesium oxide content of the lightly calcined magnesium oxide is greater than 90 wt%, the active reaction time is 100-200 s, and the residue on an 80 μm square hole sieve is less than 4.0 wt%.

[0020] Furthermore, the preparation steps of the self-healing material include: mixing the healing component, the complexing component and the swelling component, drying them, and then mixing them with potassium aluminum sulfate dodecahydrate and calcium hydroxide to obtain the self-healing material.

[0021] Further, by mass fraction, the raw materials of the slow-release curing agent include: 130-150 parts of acrylic acid, 50-70 parts of acrylamide, 0.06-0.08 parts of N,N'-methylenebisacrylamide, 0.5-0.6 parts of ammonium persulfate, and 0.5-1.5 parts of surface modifier solution.

[0022] Further, by mass, the surface modifier solution consists of 15-25 parts epichlorohydrin, 50-70 parts polyethylene glycol, and 15-25 parts water.

[0023] The role of surface modifiers is to regulate the water absorption capacity of slow-release curing agents, preventing the rapid formation of soft gels on the particle surface during water absorption, which can lead to particle clumping, hinder water molecules from penetrating the interior of the slow-release curing agent, and affect its water absorption performance. Epichlorohydrin surface crosslinking agents are used to increase the crosslinking density on the surface of the slow-release curing agent particles, solving the surface gelation problem. Meanwhile, the hydrophilic solvent polyethylene glycol promotes the dissolution of epichlorohydrin, allowing it to be sprayed evenly onto the surface of the slow-release curing agent particles.

[0024] Furthermore, the preparation steps of the sustained-release maintenance agent include:

[0025] The acrylic acid was diluted with water to a concentration of 25-35 wt%, and then the degree of neutralization was adjusted to 65-75% with sodium hydroxide solution to obtain a neutralized acrylic acid solution.

[0026] The acrylamide and N,N'-methylenebisacrylamide were added to the acrylic acid neutralization solution to obtain a mixed solution; after adjusting the temperature of the mixed solution to 55~65℃, the ammonium persulfate was added, and after stirring evenly, it was allowed to stand for 2~3 hours to polymerize and form a gel.

[0027] The gel is broken into granules, and then the surface modifier solution is evenly sprayed onto the surface of the granular gel. After the reaction, the gel is dried and pulverized to obtain the slow-release curing agent.

[0028] Slow-release curing agents contain a large number of hydrophilic hydroxyl and carboxyl groups, and their molecules form a complex cross-linked network structure. During the mixing process of thin-walled high-pier concrete, they rapidly enter a water-absorbing state, with free water adsorbed onto the polymer chains and encapsulated within the network structure. The release of moisture from slow-release curing materials requires significant energy and is therefore slow. When stress is generated in the smaller capillaries of the surrounding medium, it drives the smaller particles of slow-release curing material to begin releasing moisture, reducing shrinkage. When the humidity and stress differences inside and outside the capillaries are large, it drives the larger particles of slow-release curing material to continuously release moisture, promoting the secondary hydration of cement particles and mineral admixtures. Slow-release curing materials can effectively regulate the relative humidity inside the cement stone structure of thin-walled high-pier concrete in high-altitude and cold regions, slowing down the drying shrinkage and cracking process caused by harsh climates. At the same time, because they release water during cement hydration to promote hydration, they improve the internal density structure of thin-walled high-pier concrete. The released water leaves independent, non-connected pores inside the concrete and forms a gel film attached to the pore walls, relieving expansion stress and osmotic pressure during freeze-thaw cycles. Thus, the crack resistance and freeze-thaw resistance of thin-walled high-pier concrete in high-altitude and cold regions are improved.

[0029] Preferably, after diluting the acrylic acid with water to a concentration of 25-35 wt%, the process further includes a step of stirring the acrylic acid at 25-30°C and a rotation speed of 250-300 r / min until homogeneous.

[0030] Preferably, the concentration of the sodium hydroxide solution is 25-35 wt%.

[0031] Preferably, the reaction includes standing at room temperature for 1 to 2 hours.

[0032] Preferably, the pulverization specifically refers to pulverizing to the point where it can pass through an 80-100 mesh sieve.

[0033] Furthermore, the low-temperature enhancing agent is one or two of nano-hydrated calcium silicate powder, nano-calcium carbonate powder, and nano-silica powder.

[0034] In high-altitude and cold regions, the cement hydration reaction of thin-walled high-pier concrete is relatively slow under low-temperature conditions. The water retention and release modes of slow-release curing agents cannot fully regulate the internal moisture of concrete in the early stages. However, low-temperature strengthening agents can provide crystal nucleus growth points during the crystallization and growth stages of hydration products, accelerate the generation of cement hydration products, promote the regulation of relative humidity by slow-release curing agents, and thus slow down drying shrinkage cracking.

[0035] Preferably, the average particle size of the low-temperature enhancing agent is less than 300 nm.

[0036] Furthermore, by weight, the raw materials of the workability regulator include: 60-70 parts of calcium lignosulfonate and 30-40 parts of polycarboxylate superplasticizer.

[0037] Slow-release curing agents adsorb some of the free water in concrete into their own network structure, resulting in a less soluble gelling state. However, the reduction of free water leads to decreased fluidity of the cement paste and accelerated slump loss in thin-walled high-pier concrete, affecting the workability of the concrete. Workability modifiers can mitigate the adverse effects of slow-release curing agents on concrete workability. Simultaneously, calcium lignosulfonate can adsorb onto the surface of cement particles, delaying the hydration reaction of tricalcium aluminate and tricalcium silicate, promoting heat dissipation between the thin-walled high-pier concrete and the environment, reducing temperature rise, minimizing the internal and external temperature difference, and thus reducing the occurrence of temperature cracks.

[0038] Preferably, the polycarboxylate superplasticizer is a high-slump-retention powdered polycarboxylate superplasticizer with a water reduction rate greater than 25%.

[0039] The second technical solution of the present invention: a method for preparing the above-mentioned concrete crack-resistant admixture for high-altitude and cold regions, comprising the following steps:

[0040] The self-healing material, the slow-release curing agent, the low-temperature strengthening agent, and the workability modifier are mixed to obtain the concrete crack-resistant admixture for high-altitude and cold regions.

[0041] The third technical solution of the present invention: the application of the above-mentioned concrete crack-resistant admixture for high-altitude and cold regions in the preparation of thin-walled high-pier concrete in high-altitude and cold regions.

[0042] The term "thin-walled high-pier concrete in high-altitude and frigid regions" specifically refers to concrete piers in the form of thin-walled high piers used in high-altitude and frigid regions. High-altitude and frigid regions are defined as areas with altitudes above 1000 meters, characterized by harsh climates, low temperatures and dryness, strong solar radiation, large diurnal temperature variations, and frequent freeze-thaw cycles. In these regions, thin-walled high-pier concrete is susceptible to drying shrinkage cracks due to changes in internal relative humidity and ambient humidity, and is also prone to temperature difference cracks due to changes in ambient temperature.

[0043] Furthermore, the dosage of the anti-cracking admixture for concrete in high-altitude and cold regions is 1 to 3% of the total mass of cementitious materials in the thin-walled high-pier concrete in high-altitude and cold regions.

[0044] The present invention discloses the following technical effects:

[0045] The concrete crack-resistant admixture for high-altitude and cold regions of this invention can absorb and continuously release moisture, maintaining the relative humidity inside the cement stone structure and reducing early shrinkage cracks formed in the harsh environment of high-altitude and cold regions. Simultaneously, it leaves independent, non-connected pores within the concrete, improving the freeze-thaw resistance of thin-walled high-pier concrete in high-altitude and cold environments. Furthermore, the concrete crack-resistant admixture of this invention can achieve multiple self-healing of shrinkage cracks and freeze-thaw damage cracks caused by the constrained temperature and humidity changes inside and outside the concrete during the service phase. In addition, the concrete crack-resistant admixture of this invention can improve the mechanical properties of thin-walled high-pier concrete in low-temperature environments of high-altitude and cold regions without affecting the workability of the concrete. Detailed Implementation

[0046] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0047] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0048] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0049] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0050] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0051] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0052] In the following embodiments, comparative examples, and effect verifications of the present invention, room temperature specifically refers to 20~30℃.

[0053] Unless otherwise specified, all raw materials used in the following embodiments, comparative examples, and effect verifications of this invention are commercially available products. Specifically, the light-burned calcium oxide has a calcium oxide content of 89 wt% and a residue of 2.6 wt% on an 80 μm square-hole sieve; the light-burned magnesium oxide has a magnesium oxide content of 92 wt%, an active reaction time (obtained by the citric acid reaction time method) of 150 s, and a residue of 3.2 wt% on an 80 μm square-hole sieve; the polycarboxylate superplasticizer is a high-slump-retaining powdered polycarboxylate superplasticizer with a water reduction rate of 28%, provided by Hebei Chang'an Yucai Technology Co., Ltd.; the cement is P·O 42.5 ordinary Portland cement; the fly ash is Grade II fly ash; the manufactured sand is medium sand with a fineness modulus of 2.7 and a methylene blue value of 1.1; the graded crushed stone has a particle size of 5-20 mm, a mud content of less than 0.5 wt%, and a needle-like / flaky content of less than 5.0 wt%; the retarded polycarboxylate superplasticizer is provided by Hebei Chang'an Yucai Technology Co., Ltd., and conforms to GB standards for concrete admixtures. The 8076-2008 standard requires that the workability and mechanical properties of concrete meet the technical specifications of GB 8076-2008 "Concrete Admixtures".

[0054] In the following embodiments, comparative examples, and effect verifications of this invention, the term "number of parts" refers to "parts by mass".

[0055] Example 1

[0056] A type of concrete crack-resistant admixture for high-altitude and cold regions, comprising: 70 parts of self-healing material, 15 parts of slow-release curing agent, 8 parts of low-temperature strengthening agent, and 7 parts of workability modifier.

[0057] The self-healing material consists of the following raw materials: 50 parts of healing component (anhydrous calcium sulfate), 5 parts of complexing component (sodium tartrate), 25 parts of expansion component, 8 parts of potassium aluminum sulfate dodecahydrate and 12 parts of calcium hydroxide; the expansion component is composed of 30 parts of lightly calcined calcium oxide and 70 parts of lightly calcined magnesium oxide.

[0058] The raw material composition of the slow-release curing agent is: 140 parts acrylic acid, 60 parts acrylamide, 0.07 parts N,N'-methylenebisacrylamide, 0.5 parts ammonium persulfate, and 1 part surface modifier solution; the surface modifier solution is composed of 20 parts epichlorohydrin, 60 parts polyethylene glycol, and 20 parts water.

[0059] The low-temperature enhancer is a white powder of nano-hydrated calcium silicate with an average particle size of 260 nm.

[0060] The raw material composition of the workability regulator is: 65 parts calcium lignosulfonate and 35 parts polycarboxylate superplasticizer.

[0061] The preparation steps for the above-mentioned concrete crack-resistant admixtures in high-altitude and cold regions are as follows:

[0062] S1. Preparation of self-healing materials

[0063] The healing component, complexing component, and swelling component are mixed and dried, and then mixed with potassium aluminum sulfate dodecahydrate and calcium hydroxide to obtain a self-healing material.

[0064] S2, Preparation of sustained-release maintenance agent

[0065] S2.1 Add 140 parts of acrylic acid to a four-necked flask, dilute with water to a concentration of 30 wt%, and mechanically stir (250 r / min) in a constant temperature water bath at 25℃ until homogeneous. Then add 30 wt% sodium hydroxide solution to adjust the degree of neutralization to 70% to obtain a neutralized acrylic acid solution.

[0066] S2.2 Add 60 parts of acrylamide and 0.07 parts of N,N'-methylenebisacrylamide to the acrylic acid neutralization solution and stir until homogeneous to obtain a mixed solution; then adjust the constant temperature water bath temperature to 60℃, add 0.5 parts of initiator ammonium persulfate, stir until homogeneous, and let stand at 60℃ for 2.5h to polymerize and form a gel.

[0067] S2.3. The obtained gel is crushed into granules, and then 1 part of surface modifier solution (a mixture of 20 parts epichlorohydrin, 60 parts polyethylene glycol and 20 parts water) is evenly sprayed onto the surface of the granular gel. It is left to stand at room temperature for 1 hour, then dried in a vacuum drying oven at 80°C, and then pulverized with a pulverizer until it can pass through a 90-mesh sieve to obtain powdered particles, which are the slow-release curing agent.

[0068] S3. Preparation of anti-cracking admixtures for concrete in high-altitude and cold regions

[0069] The self-healing material, slow-release curing agent, low-temperature strengthening agent and workability modifier are mixed evenly to obtain a crack-resistant admixture for concrete in high-altitude and cold regions.

[0070] Example 2

[0071] Compared with Example 1, the only difference is that the composition of the crack-resistant admixture is: 60 parts of self-healing material, 20 parts of slow-release curing agent, 10 parts of low-temperature strengthening agent and 10 parts of workability regulator.

[0072] Example 3

[0073] Compared with Example 1, the only difference is that the composition of the crack-resistant admixture is: 80 parts of self-healing material, 10 parts of slow-release curing agent, 6 parts of low-temperature strengthening agent and 4 parts of workability regulator.

[0074] Comparative Example 1

[0075] Compared with Example 1, the only difference is that the composition of the crack-resistant admixture is: 70 parts of self-healing material, 5 parts of slow-release curing agent, 8 parts of low-temperature strengthening agent and 7 parts of workability regulator.

[0076] Comparative Example 2

[0077] Compared with Example 1, the only difference is that the composition of the crack-resistant admixture is: 70 parts of self-healing material, 30 parts of slow-release curing agent, 8 parts of low-temperature strengthening agent, and 7 parts of workability modifier.

[0078] Comparative Example 3

[0079] Compared to Example 1, the only difference is that the crack-resistant admixture consists of: 70 parts self-healing material, 15 parts slow-release curing agent, and 7 parts workability modifier. That is, no low-temperature strengthening agent is added.

[0080] Comparative Example 4

[0081] Compared to Example 1, the only difference is that the crack-resistant admixture consists of: 70 parts self-healing material, 15 parts slow-release curing agent, and 8 parts low-temperature strengthening agent. That is, no workability modifier is added.

[0082] Comparative Example 5

[0083] The only difference from Example 1 is that potassium aluminum sulfate dodecahydrate is not added to the self-healing material.

[0084] Comparative Example 6

[0085] The only difference from Example 1 is that calcium hydroxide is not added to the self-healing material.

[0086] Comparative Example 7

[0087] Compared to Example 1, the only difference is that no expanding component is added to the self-healing material.

[0088] Comparative Example 8

[0089] Compared with Example 1, the only difference is that the expansion component of the self-healing material is replaced by an equal mass of lightly calcined calcium oxide instead of lightly calcined magnesium oxide, that is, the expansion component in the self-healing material is 25 parts of lightly calcined calcium oxide.

[0090] Comparative Example 9

[0091] Compared with Example 1, the only difference is that the expansion component of the self-healing material is replaced with an amount of light-burned magnesium oxide instead of light-burned calcium oxide, that is, the expansion component in the self-healing material is 25 parts of light-burned magnesium oxide.

[0092] Comparative Example 10

[0093] Compared with Example 1, the only difference is that the raw materials of the slow-release curing agent do not include a surface modifier solution, and the preparation method of the slow-release curing agent is as follows:

[0094] S1. Add 140 parts of acrylic acid to a four-necked flask, dilute with water to a concentration of 30 wt%, and mechanically stir (250 r / min) in a constant temperature water bath at 25℃ until homogeneous. Then add 30 wt% sodium hydroxide solution to adjust the degree of neutralization to 70% to obtain a neutralized acrylic acid solution.

[0095] S2. Add 60 parts of acrylamide and 0.07 parts of N,N'-methylenebisacrylamide to the acrylic acid neutralization solution and stir until homogeneous to obtain a mixed solution; then adjust the constant temperature water bath temperature to 60℃, add 0.5 parts of initiator ammonium persulfate, stir until homogeneous, and let stand for 2.5h to polymerize and form a gel.

[0096] S3. The obtained gel is broken into granules, dried in a vacuum drying oven at 80°C, and then pulverized with a pulverizer until it can pass through a 90-mesh sieve to obtain powdered particles, which is the slow-release maintenance agent.

[0097] Effect verification

[0098] 1. Performance and mechanical property testing

[0099] Concrete mixtures were prepared using the crack-resistant admixtures prepared in each embodiment and comparative example, and tests were conducted in accordance with the standards GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" and GB / T 18445-2025 "Cement-based Penetrating Crystalline Waterproofing Materials". The composition of the concrete mixtures was: cement 348 kg / m³ 3 60kg / m³ of fly ash 3 768 kg / m³ of manufactured sand 3 Graded crushed stone 1060kg / m³ 3 164 kg / m³ of water 3 Admixture 4.08 kg / m 3 The experiment group (designed according to C35) and the crack-resistant admixture (where the admixture is a retarding polycarboxylate high-performance water-reducing agent, and the dosage of the crack-resistant admixture is 2% of the total mass of cementitious materials in the concrete) were used as the control group. The experiment group without crack-resistant admixture was used as the control group. The experiment group was cured in a constant temperature room at low temperature (5℃) to compare the effects of different crack-resistant admixtures on the workability and mechanical properties of concrete. The results are shown in Table 1.

[0100] Table 1. Workability and Mechanical Properties of Concrete Mixtures

[0101]

[0102] Among them, the compressive strength ratio, shrinkage ratio, and anti-seepage pressure ratio refer to the ratio of compressive strength, shrinkage ratio, and anti-seepage pressure of each test group with different anti-cracking admixtures to the control group, respectively.

[0103] Table 1 shows that the concrete with the anti-cracking admixtures prepared in Examples 1-3 exhibits good workability, with no significant decrease in 2-hour slump; the mechanical properties of the concrete are improved, with a slight increase in the compressive strength ratios after 7 days and 28 days of low-temperature curing; the shrinkage of the concrete is significantly reduced, and the impermeability pressure ratios after 28 days and 56 days are significantly increased, indicating improved crack resistance. Comparing Example 1 and Comparative Example 1, it can be seen that significantly reducing the amount of slow-release curing agent increases concrete shrinkage, decreases the impermeability pressure ratio, and reduces crack resistance. Comparing Example 1 and Comparative Example 2, it can be seen that significantly increasing the amount of slow-release curing agent affects both the workability and mechanical properties of the concrete. Comparing Example 1 and Comparative Example 3, it can be seen that without the addition of the low-temperature strengthening agent, the 7-day compressive strength ratio of the concrete decreases, indicating that early strength is affected in low-temperature environments. Comparing Example 1 and Comparative Example 4, it can be seen that without the addition of the workability modifier, the 2-hour slump of the concrete decreases significantly, leading to pouring difficulties and affecting the workability of the concrete. Comparing Example 1 with Comparative Examples 5 and 6, it can be seen that the 28-day and 56-day permeability pressure ratios of Comparative Examples 5-6 are both reduced, indicating that the addition of potassium aluminum sulfate dodecahydrate and calcium hydroxide to the self-healing material affects its healing performance at 28 days and 56 days. Comparing Example 1 with Comparative Examples 7, 8, and 9, it can be seen that the 28-day shrinkage ratio of Comparative Examples 7-9 is significantly increased, indicating that the expansion component in the self-healing material can effectively compensate for concrete shrinkage and reduce the risk of concrete shrinkage cracking. The staged expansion and shrinkage compensation effect of lightly calcined calcium oxide and lightly calcined magnesium oxide in the expansion component can reduce the risk of concrete shrinkage cracking. Therefore, when the expansion component is omitted or only one of lightly calcined calcium oxide and lightly calcined magnesium oxide is used, the 28-day shrinkage ratio will significantly increase. Comparing Example 1 with Comparative Example 10, it can be seen that the permeability pressure ratio of Comparative Example 10 is significantly reduced, indicating that the surface modifier can improve the performance of the slow-release curing agent.

[0104] 2. Crack resistance test

[0105] The early crack resistance of concrete samples was tested according to the early crack resistance test method in the standard GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete". The composition of the concrete samples was: cement 348 kg / m³. 360kg / m³ of fly ash 3 768 kg / m³ of manufactured sand 3 Graded crushed stone 1060kg / m³ 3 164 kg / m³ of water 3 Additives 4.08 kg / m 3 (Among them, the admixture is a retarding polycarboxylate high-performance water-reducing agent, and the dosage of the crack-resistant admixture is 2% of the total mass of cementitious materials in the concrete). The test group without the addition of the concrete crack-resistant admixture was used as the control group (designed according to C35) to compare the effect of the concrete crack-resistant admixture on the early crack resistance of the concrete sample under constrained conditions.

[0106] Table 2 Early-stage crack resistance of concrete

[0107]

[0108] Table 2 shows that the concrete with the added anti-cracking admixtures prepared in Examples 1-3 exhibits a reduction rate of over 70% in total crack area per unit area, indicating a significant improvement in early-stage crack resistance. Comparing Example 1 and Comparative Example 1 reveals that significantly reducing the amount of the slow-release curing agent significantly reduces the reduction rate of total crack area per unit area, resulting in a significant decrease in early-stage crack resistance. Comparing Example 1 and Comparative Example 7 shows that without the addition of an expansion component to the self-healing material, the reduction rate of total crack area per unit area is significantly reduced, leading to a significant decrease in early-stage crack resistance. Comparing Example 1 and Comparative Example 2, and considering Table 1, it can be seen that significantly increasing the amount of the slow-release curing agent affects both the workability and mechanical properties of the concrete, but has a relatively small impact on its early-stage crack resistance. Comparing Example 1 and Comparative Example 3, and considering Table 1, it can be seen that without the addition of a low-temperature strengthening agent, the early strength in low-temperature environments decreases, but the impact on the early-stage crack resistance of the concrete is relatively small. Comparing Example 1 with Comparative Examples 4, 5, 6, 8, 9, and 10, it can be seen that the reduction rate of total crack area per unit area decreased slightly. This indicates that the addition or absence of workability regulators, the addition or absence of potassium aluminum sulfate dodecahydrate and calcium hydroxide in the self-healing material, the specific composition of the expansion component, and whether or not surface modifiers are used in the slow-release curing agent all affect the crack resistance of concrete.

[0109] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A crack-resistant admixture for concrete in high-altitude and cold regions, characterized in that, By weight, the components include: 60-80 parts of self-healing material, 10-20 parts of slow-release curing agent, 6-10 parts of low-temperature enhancer, and 4-10 parts of workability modifier; The self-healing material comprises, by weight, 40-60 parts of healing component, 2-8 parts of complexing component, 20-40 parts of expansion component, 5-10 parts of potassium aluminum sulfate dodecahydrate and 10-20 parts of calcium hydroxide. The healing component is one or two of anhydrous calcium sulfate, calcium magnesium carbonate, and calcium sulfoaluminate. The complexing component is one or two of sodium citrate, sodium tartrate and tetrasodium ethylenediaminetetraacetate; The raw materials of the expanded component, by mass parts, include: 20-40 parts of light-burned calcium oxide and 60-80 parts of light-burned magnesium oxide; The preparation steps of the self-healing material include: mixing the healing component, the complexing component and the swelling component, drying them, and then mixing them with potassium aluminum sulfate dodecahydrate and calcium hydroxide to obtain the self-healing material; The raw materials of the slow-release curing agent, by weight, include: 130-150 parts acrylic acid, 50-70 parts acrylamide, 0.06-0.08 parts N,N'-methylenebisacrylamide, 0.5-0.6 parts ammonium persulfate, and 0.5-1.5 parts surface modifier solution; The surface modifier solution, by weight, consists of 15-25 parts epichlorohydrin, 50-70 parts polyethylene glycol, and 15-25 parts water; The low-temperature enhancing agent is one or two of nano-hydrated calcium silicate powder, nano-calcium carbonate powder, and nano-silica powder.

2. The anti-cracking admixture for concrete in high-altitude and cold regions as described in claim 1, characterized in that, The preparation steps of the sustained-release maintenance agent include: The acrylic acid was diluted with water to a concentration of 25-35 wt%, and then the degree of neutralization was adjusted to 65-75% with sodium hydroxide solution to obtain a neutralized acrylic acid solution. The acrylamide and N,N'-methylenebisacrylamide were added to the acrylic acid neutralization solution to obtain a mixed solution; after adjusting the temperature of the mixed solution to 55~65℃, the ammonium persulfate was added, and after stirring evenly, it was allowed to stand for 2~3 hours to polymerize and form a gel. The gel is broken into granules, and then the surface modifier solution is evenly sprayed onto the surface of the granular gel. After the reaction, the gel is dried and pulverized to obtain the slow-release curing agent.

3. The anti-cracking admixture for concrete in high-altitude and cold regions as described in claim 1, characterized in that, The workability modifier comprises, by weight, 60-70 parts of calcium lignosulfonate and 30-40 parts of polycarboxylate superplasticizer.

4. A method for preparing a crack-resistant concrete admixture for high-altitude and cold regions as described in any one of claims 1-3, characterized in that, Includes the following steps: The self-healing material, the slow-release curing agent, the low-temperature strengthening agent, and the workability modifier are mixed to obtain the concrete crack-resistant admixture for high-altitude and cold regions.

5. The application of the anti-cracking admixture for concrete in high-altitude and cold regions as described in any one of claims 1-3 in the preparation of thin-walled high-pier concrete in high-altitude and cold regions.

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