Low water sensitivity concrete expanding agent and preparation method thereof

Abstract

The application belongs to the technical field of concrete expansion agent, and more particularly relates to a low-water-sensitivity concrete expansion agent and a preparation method thereof. The low-water-sensitivity concrete expansion agent provided by the application comprises a shrinkage compensation component, a regulation component, a ground zeolite powder and a powder carboxylic acid. The shrinkage compensation component comprises modified calcium oxide and light-burned magnesium oxide, and the regulation component comprises at least one of lithium carbonate, sodium sulfate, calcium formate and sodium nitrite. The expansion agent can maintain effective hydration reaction under low-humidity environment (humidity ≤ 50%) or absolute humidity condition, can regulate the expansion process to be synchronous with the shrinkage and strength development process of concrete, and can ensure that the shrinkage compensation stress is matched with the structural constraint condition, so as to generate effective expansion.

Description

Technical Field

[0001] This invention belongs to the field of concrete expansion agent technology, and more specifically relates to a low water-sensitive concrete expansion agent and its preparation method. Background Technology

[0002] With the rapid development of infrastructure construction, large-volume and highly constrained concrete structures are increasingly emerging in water conservancy and hydropower projects, bridge projects, and high-rise and super high-rise buildings. Their durability directly affects the safety and service life of these structures. However, the inherent chemical and drying shrinkage of concrete leads to structural cracking, which not only affects the aesthetics and integrity of buildings but also provides a convenient channel for the intrusion of harmful media, making it a primary cause of durability problems such as steel corrosion, freeze-thaw damage, and sulfate attack. To compensate for concrete shrinkage and inhibit crack formation, expansive agents, as an important functional admixture, are widely used in engineering practice, especially in critical areas such as ultra-long structures, waterproofing projects, and large-volume concrete. The core mechanism of expansive agents lies in the fact that their important active components, such as calcium sulfoaluminate, calcium oxide, or magnesium oxide, react with cement hydration products in the early stages of hydration to generate expansive crystalline products such as ettringite, calcium hydroxide, and magnesium hydroxide. Under the constraint of steel reinforcement and adjacent structures, these products can generate a certain degree of restricted expansion, thereby creating pre-compression stress within the concrete to counteract the tensile stress caused by shrinkage, achieving the purpose of crack resistance and seepage prevention.

[0003] However, the application effect of traditional expansive agents has a key bottleneck: their expansion efficiency is highly dependent on early water curing conditions, and the expansion window is difficult to match with the hydration process of cement-based materials, resulting in a large amount of ineffective expansion. After concrete pouring, if the ambient humidity is insufficient or the surface moisture evaporates too quickly, leading to untimely or insufficient curing, the hydration reaction of the expansive agent will be forced to stop or slow down. The expansion products generated by the hydration reaction of the expansive agent cannot be transferred through rigid constraints to produce expansion deformation, resulting in the loss of the expansive agent's expansion energy. This not only fails to produce the expected shrinkage compensation effect, but may even exacerbate the risk of early plastic cracking of concrete due to the large amount of water consumed by the expansive agent itself. In actual engineering, due to the fast construction pace, large curing work area, difficulty in high-altitude operations, or water scarcity in arid areas, achieving ideal and uninterrupted saturated curing is often quite difficult, and large-volume concrete is actually completely in a moisture-free condition inside. The high sensitivity of traditional expansion agents to the aquatic environment and the difficulty in matching their expansion process with that of cement-based materials severely restrict their stability and reliability, causing their performance in practical applications to often fall short of theoretical expectations, which has long been a problem for engineering technicians.

[0004] To control the reaction process of expansive agents, some researchers have attempted to study the physical or chemical modification of expansive agent particles. Microencapsulation of expansive agent particles with inorganic or organic materials aims to create a "time difference," delaying their hydration reaction and allowing them to expand only after the cement paste has reached a certain strength, thereby improving the utilization rate of effective expansion energy. However, this technical approach faces significant challenges. First, the integrity and stability of the encapsulation are crucial. Second, the rupture mechanism of the encapsulation material is difficult to synchronize with the shrinkage development process of concrete, potentially leading to premature or delayed expansion and failing to achieve the desired compensation effect. Finally, the complex encapsulation process significantly increases the production cost of the expansive agent, hindering its large-scale application in numerous engineering projects. Existing technologies have improved the performance of expansive agents to some extent, but have not yet solved the core problem of water sensitivity. Developing a novel concrete expansive agent that is insensitive to environmental humidity and has a controllable expansion process has become an urgent need to improve the crack resistance and durability of concrete structures. Summary of the Invention

[0005] The purpose of this invention is to provide a low water-sensitive concrete expansion agent and its preparation method to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention: provides a low water-sensitive concrete expansion agent, comprising, by weight, the following raw materials: The formula consists of 80-90 parts of shrinkage compensation component, 0.2-0.4 parts of regulating component, 10-20 parts of finely ground zeolite powder, and 1-2 parts of powdered carboxylic acid. The shrinkage compensation component includes modified calcium oxide and lightly calcined magnesium oxide; The regulating components include at least one of lithium carbonate, sodium sulfate, calcium formate, and sodium nitrite.

[0007] Furthermore, the mass ratio of modified calcium oxide to lightly calcined magnesium oxide in the shrinkage compensation component is 60-80:20-40.

[0008] Furthermore, 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%.

[0009] Furthermore, the preparation steps of the modified calcium oxide include: Polyethylene glycol and ethanol are mixed in an equal mass ratio to obtain a polyethylene glycol ethanol solution; Stearic acid and ethanol are mixed at a mass ratio of 1:50 to obtain a stearic acid-ethanol solution; Add calcium oxide clinker to the stearic acid ethanol solution and stir until homogeneous to obtain a calcium oxide suspension; The polyethylene glycol ethanol solution was added to the calcium oxide suspension, and after the reaction, the mixture was dried and ground to obtain the modified calcium oxide.

[0010] Optionally, the mass ratio of the calcium oxide clinker, polyethylene glycol, and stearic acid is 80-90:10-15:5-10.

[0011] Optionally, the reaction temperature is 35-40℃, the rotation speed is 300-400rpm, and the time is 1-2h.

[0012] Optionally, the drying temperature is 60°C.

[0013] Optionally, the grinding is performed to grind to a specific surface area of ​​300-450 m². 2 / kg.

[0014] Optionally, the specific surface area of ​​the calcium oxide clinker is 300-450 m². 2 / kg, free calcium oxide content ≥75%.

[0015] Optionally, the molecular weight of the polyethylene glycol is 1800-2200.

[0016] Furthermore, the average particle size of the ground zeolite powder is 75-150 μm.

[0017] Furthermore, the powdered carboxylic acid is a high-slump-retention powdered polycarboxylic acid high-performance water-reducing agent with a water reduction rate greater than 25%.

[0018] The second technical solution of the present invention provides a method for preparing the above-mentioned low water-sensitive concrete expansion agent, the steps of which include: The low water-sensitive concrete expansion agent is obtained by uniformly mixing the shrinkage compensation component, the regulating component, the finely ground zeolite powder, and the powdered carboxylic acid.

[0019] The third technical solution of the present invention provides an application of the above-mentioned low water sensitivity concrete expansion agent in concrete preparation.

[0020] The present invention discloses the following technical effects: This invention provides a low-water-sensitivity concrete expansion agent. The modified calcium oxide component in this low-water-sensitivity concrete expansion agent employs a unique composite coating modification technology. Stearic acid reacts with the surface of calcium oxide to generate calcium stearate, forming a first dense, chemically hydrophobic coating layer. Then, through the physical adsorption or entanglement of long polyethylene glycol molecular chains, a second hydrophilic spatial protective layer is formed, creating a core-shell structured modified calcium oxide clinker. This allows for staged control of calcium oxide clinker hydration, regulating the onset time and rate of hydration expansion. By controlling the differences in the influence of the component on the shrinkage compensation component itself and the hydration process of cement, expansion is delayed. The hydration rate of the components is improved, and the effect of enhancing the cement hydration process is enhanced. The difference in hydration rates between the two is coordinated, so that the expansion component can generate more effective expansion to compensate for concrete shrinkage under appropriate rigid constraints. The interior of the finely ground zeolite powder is filled with uniformly sized pores and channels, which can adsorb a large number of water molecules in the early stage and play a water storage role in the cement paste. The free water stored in the later stage will be gradually released, slowing down the rate of decrease in internal humidity of the concrete, promoting the hydration of the expansion component, reducing the dependence of the expansion agent on external early water curing, and achieving effective shrinkage compensation under low environmental humidity and internal moisture-free conditions of concrete, thus reducing the risk of concrete cracking. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The expansion process of the expansion agent used as a baseline example and Examples 1-5 in mortar specimens of different ages in a low humidity environment was limited to the expansion rate.

[0022] Figure 2 The expansion process of the expansion agent used as a baseline example and Examples 1-5 in mortar specimens of different ages in a moisture-free environment with limited expansion rate. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0027] 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.

[0028] Unless otherwise specified, all raw materials and reagents involved in the specific embodiments of this invention are commercially available products.

[0029] In a specific embodiment of the present invention, the specific surface area of ​​the calcium oxide clinker used is 300-450 m². 2 The free calcium oxide content should be between [value] / kg and ≥75%. It can be a commercially available product or can be homemade, as follows: Limestone and gypsum are mixed and ground into raw meal at a mass ratio of 90:10. The raw meal is then calcined at 1350℃±100℃ and ground to a specific surface area of ​​300~450m². 2 / kg, to obtain calcium oxide clinker.

[0030] Unless otherwise specified, room temperature and ambient temperature in the specific embodiments of this invention refer to 20-30℃.

[0031] 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.

[0032] In some specific embodiments, the present invention provides a method for preparing a low-water-sensitive concrete expansion agent, the steps of which include: S1. Preparation of modified calcium oxide: The mass ratio of the self-made calcium oxide clinker, polyethylene glycol and stearic acid is 80-90:10-15:5-10. S1.1 Add stearic acid to anhydrous ethanol at a mass ratio of 1:50, heat to 35-40℃ and stir until the stearic acid is completely dissolved to obtain a stearic acid-ethanol solution; add dried calcium oxide clinker powder (specific surface area 300-450 m²) 2 / kg, free calcium oxide content ≥75%), is added to stearic acid ethanol solution under continuous stirring, heated to 45-50℃, and stirred at 300-400 rpm for 1 hour to obtain a pretreated calcium oxide suspension; S1.2. Slowly add polyethylene glycol (molecular weight 1800-2200) to anhydrous ethanol while stirring at a low speed of 100-200 rpm. The mass ratio of polyethylene glycol to anhydrous ethanol is 1:1. Heat the reaction vessel to 35-40℃ and keep stirring until the polyethylene glycol is completely dissolved to obtain a clear polyethylene glycol ethanol solution. S1.3. Add all of the prepared polyethylene glycol ethanol solution to the pretreated calcium oxide suspension, heat to 35-40℃, and react at 300-400 rpm for 1-2 hours. Then, dry the resulting suspension at 60℃ for 2-4 hours to remove the organic solvent, and grind it to a specific surface area of ​​300-450 m². 2 / kg, to obtain modified calcium oxide; S2. Mix modified calcium oxide and lightly calcined magnesium oxide at a mass ratio of 60-80:20-40 to obtain a shrinkage compensation component; The magnesium oxide content of 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%. S3. Prepare raw materials by mass: 80-90 parts of the shrinkage compensation component obtained in step S2, 0.2-0.4 parts of the regulating component, 10-20 parts of finely ground zeolite powder, and 1-2 parts of powdered carboxylic acid; The regulating components include at least one of lithium carbonate, sodium sulfate, calcium formate, and sodium nitrite; The average particle size of finely ground zeolite powder is 75-150 μm; Powdered carboxylic acid is a high-slump-retention powdered polycarboxylic acid high-performance water-reducing agent with a water reduction rate of greater than 25%. S4. Mix the shrinkage compensation component, the regulating component, the finely ground zeolite powder and the powdered carboxylic acid evenly to obtain the low water sensitivity concrete expansion agent.

[0033] This invention utilizes the synergistic effect of a modified calcium oxide shrinkage compensation component prepared with a unique composite coating modification technology and finely ground zeolite powder. The shrinkage compensation component can maintain an effective hydration reaction even in low humidity environments (humidity ≤50%) or under absolute humidity conditions. By controlling the components, the expansion process is synchronized with the shrinkage development process of concrete, ensuring that the shrinkage compensation stress matches the structural constraints, thereby generating more effective expansion and reducing the risk of concrete cracking.

[0034] Not only is the production process simple and it has good compatibility with cement-based materials, but it can also effectively compensate for shrinkage and reduce the risk of concrete cracking under low ambient humidity and dry conditions inside concrete.

[0035] Based on the temperature and hydration process of concrete, the autogenous shrinkage and temperature drop shrinkage generated in the early and middle stages are relatively large, while the autogenous shrinkage and drying shrinkage in the later stages are relatively small. A multi-component composite of different expansion components is used to prepare a shrinkage compensation component. Modified calcium oxide expansion component is used to achieve early and middle stage expansion, and low-activity magnesium oxide expansion component is used to achieve micro-expansion in the later stage to prevent shrinkage and stabilize the expansion prestress formed in the early stage.

[0036] In the preparation of modified calcium oxide, calcium stearate is generated by the reaction of stearic acid with the surface of calcium oxide, forming a dense, chemically hydrophobic coating layer. This coating provides moisture protection, extends the storage time of calcium oxide clinker, and slows down calcium oxide hydration. Secondly, polyethylene glycol is coated onto the outer layer of calcium oxide. Its long molecular chains form a second hydrophilic protective layer through physical adsorption or entanglement. This layer exhibits good water solubility and dispersibility, facilitating the uniform distribution of the expansion agent particles in the cement slurry. Its chain structure creates a steric hindrance effect, preventing particle agglomeration, while the hydrophilic layer regulates the rate of water molecule entry, achieving delayed but unimpeded hydration. By modifying the core-shell structure of calcium oxide clinker, staged control of its hydration is achieved. Initially, the polyethylene glycol (PEG) layer dissolves rapidly in water, effectively dispersing the stearic acid-coated calcium oxide particles into the cement paste, preventing agglomeration and uneven expansion. In the middle stage, after the PEG layer dissolves, water molecules begin to contact the hydrophobic and dense calcium stearate layer, delaying hydration expansion and thus regulating the expansion window. In the later stage, as cement hydration progresses, the system's pH and ionic strength increase, gradually destroying or penetrating the calcium stearate coating, allowing the calcium oxide clinker to hydrate and generate effective expansion stress to compensate for shrinkage. By controlling the thickness and ratio of the two coating layers, the onset time and rate of hydration expansion can be more precisely controlled, better matching the expansion window with the plastic-to-hardening hydration process of the cement paste.

[0037] During the plastic stage of concrete, the calcium oxide clinker in the shrinkage compensation component undergoes rapid hydration to generate expansion products, but it cannot effectively expand and deform through rigid constraints, resulting in a loss of expansion energy of the calcium oxide expansive agent. To improve the effective expansion of the calcium oxide expansive agent, its expansion window needs to be matched with the cement hydration process. By controlling the difference in the component's influence on the calcium oxide clinker's own hydration process and on the cement hydration process, the component can help slow down the hydration rate of calcium oxide clinker while enhancing the cement hydration process, thus coordinating the difference in hydration rates between the two. This allows the calcium oxide clinker to effectively expand under the rigid constraints of concrete to compensate for concrete shrinkage.

[0038] Finely ground zeolite powder has a highly porous interior with uniformly sized pores and channels, resulting in a large internal surface area. This allows it to adsorb a significant amount of water molecules and facilitate ion exchange, effectively storing water within the cement paste. As the hydration level of cement and shrinkage-compensating components increases, the internal humidity of the concrete gradually decreases, as does the hydration level of the shrinkage-compensating components. Meanwhile, the free water stored in the zeolite powder is gradually released, slowing the rate of internal humidity reduction, increasing the hydration level of the shrinkage-compensating components, and reducing reliance on early external water curing. Simultaneously, finely ground zeolite powder contains a large amount of active SiO2 and Al2O3, whose pozzolanic activity can improve the strength and durability of concrete and reduce drying shrinkage. Furthermore, finely ground zeolite powder improves the pore structure of the paste and enhances the expansion performance of the shrinkage-compensating components.

[0039] The addition of shrinkage-compensating components and finely ground zeolite powder to concrete can affect its early workability. The addition of powdered carboxylic acid can improve the slump of concrete after discharge and reduce slump loss over time.

[0040] Example 1 The preparation steps of a low-water-sensitivity concrete expansion agent include: S1. Preparation of modified calcium oxide: The self-made calcium oxide clinker (specific surface area 395m²) 2 / kg, free calcium oxide content ≥75%), the mass ratio of polyethylene glycol and stearic acid is 80:12:8; S1.1 Add stearic acid to anhydrous ethanol at a mass ratio of 1:50, heat to 35°C and stir until the stearic acid is completely dissolved to obtain a stearic acid ethanol solution; add dried calcium oxide clinker powder to the stearic acid ethanol solution under continuous stirring, heat to 45°C and stir at 350 rpm for 1 hour to obtain a pretreated calcium oxide suspension; S1.2. Polyethylene glycol (molecular weight 2200) is slowly added to anhydrous ethanol at a low speed of 150 rpm with stirring. The mass ratio of polyethylene glycol to anhydrous ethanol is 1:1. The reaction vessel is heated to 35°C and stirred until the polyethylene glycol is completely dissolved to obtain a clear polyethylene glycol ethanol solution. S1.3. Add all of the prepared polyethylene glycol ethanol solution to the pretreated calcium oxide suspension, heat to 35°C, and react at 350 rpm for 1.5 hours. Then, dry the resulting suspension at 60°C for 3 hours to remove the organic solvent, and grind it to a specific surface area of ​​395 m². 2 / kg, to obtain modified calcium oxide; S2. Mix modified calcium oxide and lightly calcined magnesium oxide at a mass ratio of 70:30 to obtain a shrinkage compensation component; The lightly calcined magnesium oxide had a magnesium oxide content of 95 wt%, an active reaction time of 165 s, and a residue of 2.8 wt% on an 80 μm square-hole sieve. S3. Prepare raw materials by mass: 85 parts of the shrinkage compensation component, 0.3 parts of the regulating component, 15 parts of finely ground zeolite powder, and 1.5 parts of powdered carboxylic acid obtained in step S2; The regulating components are sodium sulfate and calcium formate in equal mass ratio; The average particle size of finely ground zeolite powder is between 75-150 μm; The powdered carboxylic acid is a high-slump-retention powdered polycarboxylic acid high-performance water-reducing agent with a water reduction rate of 32%. S4. Mix the shrinkage compensation component, the regulating component, the finely ground zeolite powder and the powdered carboxylic acid evenly to obtain the low water sensitivity concrete expansion agent.

[0041] Example 2 Compared with Example 1, the difference is that the raw material mass ratio in step S3 is: 90 parts of shrinkage compensation component, 0.4 parts of regulating component, 10 parts of finely ground zeolite powder and 2 parts of powdered carboxylic acid.

[0042] Example 3 Compared with Example 1, the difference is that the raw material mass ratio in step S3 is: 80 parts of shrinkage compensation component, 0.2 parts of regulating component, 20 parts of finely ground zeolite powder and 1 part of powdered carboxylic acid.

[0043] Example 4 The difference from Example 1 is that in step S2, the modified calcium oxide and lightly calcined magnesium oxide are in a mass ratio of 60:40.

[0044] Example 5 The difference from Example 1 is that in step S2, the modified calcium oxide and lightly calcined magnesium oxide are in a mass ratio of 80:20.

[0045] Comparative Example 1 Compared with Example 1, the difference is that the raw material mass ratio in step S3 is: 85 parts of shrinkage compensation component, 15 parts of finely ground zeolite powder and 1.5 parts of powdered carboxylic acid (reducing the control component).

[0046] Comparative Example 2 Compared with Example 1, the difference is that the raw material mass ratio in step S3 is: 85 parts of shrinkage compensation component, 0.3 parts of regulating component and 15 parts of finely ground zeolite powder (to reduce the carboxylic acid powder).

[0047] Comparative Example 3 Compared with Example 1, the difference lies in the following: the raw material mass ratio in step S3 is as follows: 95 parts of shrinkage compensation component, 0.3 parts of regulating component, 5 parts of finely ground zeolite powder, and 1.5 parts of powdered carboxylic acid. Comparative Example 4 The difference from Example 1 is that the mass ratio of calcium oxide clinker, polyethylene glycol and stearic acid in step S1 is 70:10:20.

[0048] Comparative Example 5 The difference compared to Example 1 is that the specific surface area of ​​the self-made modified calcium oxide in step S2 is 540 m². 2 / kg.

[0049] Comparative Example 6 The difference from Example 1 is that the average particle size of the zeolite powder ground in step S3 is 240 μm.

[0050] Experimental Example 1 Expansion performance test The concrete expansive agents prepared in Examples 1-5 and Comparative Examples 1-6 were used to form cement mortar specimens with the expansive agents according to the standards GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" and GB / T 23439-2017 "Concrete Expansive Agent". The curing chamber and laboratory temperature were adjusted to 20±2℃. The mortar specimens were placed in a curing chamber with a low humidity environment of (45±5)% for curing. In addition, the mortar specimens were placed in a laboratory and tightly wrapped with polyethylene film to simulate the moisture-free environment inside the concrete. The changes in the restricted expansion rate of cement mortar at different ages under different humidity curing conditions were measured. The benchmark example was a high-performance expansive agent purchased from Chongqing Beibei District Sansheng New Material Technology Co., Ltd. The results are shown in Tables 1 and 2.

[0051] Table 1. Restricted expansion rates of mortar test blocks of various ages in a low-humidity curing chamber. As shown in Table 1, a comparison between Examples 1-5 and the baseline example reveals that, through the unique composite coating modification technology of calcium oxide, the restricted expansion rate of the mortar in Example 1 was reduced by more than 30% compared to the commercially available high-performance expansive agent. In the baseline example, the restricted expansion rate continuously increased in the first 3 days and then stabilized relatively. In contrast, the restricted expansion rate of the examples continued to increase in the first 5 days and then stabilized relatively, with a significantly higher restricted expansion rate at 28 days compared to the commercially available high-performance expansive agent. This indicates that the modification of calcium oxide in the examples controlled the onset time and rate of hydration expansion, achieving phased control of the hydration of the expansion component, thus resulting in the continuous increase in the restricted expansion rate in the first 5 days. The control component coordinated the difference in hydration rates between the expansive agent and cement, optimizing the expansion process. Under the rigid constraint of concrete, the calcium oxide clinker produced more effective expansion, leading to the increase in the restricted expansion rate at 28 days. Furthermore, curing the mortar blocks in a low-humidity environment gradually released the free water stored in the zeolite powder, slowing down the rate of internal humidity reduction and reducing the dependence of the expansion component on early external water curing. A comparison of Example 1 and Comparative Example 1 demonstrates the beneficial effects of the control component on the expansion process and performance. Comparing Example 1 with Comparative Example 4, it is shown that excessive stearic acid coating modification of calcium oxide will reduce the expansion performance of the expanding agent. Comparing Example 1 with Comparative Examples 5 and 6, it is shown that the fineness of the modified calcium oxide and the particle size of the ground zeolite powder will affect the performance of the expanding agent.

[0052] Table 2. Restricted expansion rates of mortar specimens at different ages in a moisture-free environment. A polyethylene film was used to tightly wrap the mortar test blocks to simulate the moisture-free environment inside concrete. Comparing the baseline examples in Tables 1 and 2, it can be seen that ambient humidity affects the performance of the expansive agent, and that commercially available expansive agents rely on early moisture curing. In the examples, by adding zeolite powder, the stored free water is gradually released, slowing down the rate of decrease in internal humidity, increasing the hydration degree of the shrinkage-compensating component, reducing the expansive agent's dependence on external early water curing, and improving the expansive agent's expansion performance.

[0053] This invention is in Figure 1 and Figure 2 The paper presents the expansion history of the expansion agents prepared in different embodiments and comparative examples in mortar specimens of different ages under low humidity or absolute moisture conditions. It can be seen that through the unique composite coating modification technology of calcium oxide, the expansion history of each embodiment is significantly improved compared with the baseline example in both low humidity and absolute moisture conditions. The expansion performance is improved, the ineffective expansion in the plastic stage is reduced, and the limited expansion rate increases continuously in the first five days. This can better compensate for the shrinkage of concrete during the temperature drop stage and reduce the risk of cracking.

[0054] Experimental Example 2 The concrete expansion agents prepared in Examples 1-5 and Comparative Examples 1-6 were used to mix concrete according to the standard GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" to evaluate their workability and mechanical properties. A C35 mix proportion for a tunnel secondary lining concrete was used, with 240 kg / m³ of cement. 3 160 kg / m³ of fly ash 3 Fine aggregate 706 kg / m 3 Coarse aggregate 1152 kg / m³ 3 134 kg / m³ of water 3 and water-reducing agent 4.8 kg / m 3 2.8 kg / m³ of entraining agent 3 The expanding agent is 32 kg / m³. 3 The cement used was P·O 42.5, produced by Sichuan Esheng Cement Co., Ltd.; the fly ash was Grade II, produced by Yibin Power Plant; the fine aggregate was medium sand with a methylene blue value of 1.2; the coarse aggregate had good gradation, with a particle size of 5-20mm, a mud content of less than 0.5%, and a needle-like and flaky content of less than 5.0%; the admixture was a retarding polycarboxylate high-performance water-reducing agent, provided by Hebei Chang'an Yucai Technology Co., Ltd., which met the technical specifications of GB 8076-2008 "Concrete Admixtures". The benchmark example was a high-performance expansive agent purchased from Chongqing Beibei District Sansheng New Material Technology Co., Ltd. The results are shown in Table 3.

[0055] Table 3 Test results of workability and mechanical properties of concrete mixtures As shown in Table 3, a comparison of the workability of the examples and the baseline examples reveals that the commercially available expansive agent in the baseline example exacerbates the loss of concrete fluidity, affecting on-site pouring and construction. In contrast, the initial and 2-hour concrete slumps in the examples are normal, and the 7-day and 28-day compressive strength ratios are slightly improved. This indicates that the low-water-sensitive expansive agent provided by this invention has no adverse effect on the workability of concrete and even improves its mechanical properties. A comparison of Example 1 and Comparative Example 2 shows that the addition of powdered carboxylic acid is beneficial in mitigating the time-dependent slump loss of concrete over 2 hours.

[0056] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0057] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. 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 invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A low-water-sensitivity concrete expansion agent, characterized in that, By weight, the raw materials include: The formula consists of 80-90 parts of shrinkage compensation component, 0.2-0.4 parts of regulating component, 10-20 parts of finely ground zeolite powder, and 1-2 parts of powdered carboxylic acid. The shrinkage compensation component includes modified calcium oxide and lightly calcined magnesium oxide; The regulating components include at least one of lithium carbonate, sodium sulfate, calcium formate, and sodium nitrite.

2. The low water-sensitive concrete expansion agent as described in claim 1, characterized in that, The mass ratio of modified calcium oxide to lightly calcined magnesium oxide in the shrinkage compensation component is 60-80:20-40.

3. The low water-sensitive concrete expansion agent as described in claim 1, characterized in that, The lightly calcined magnesium oxide has a magnesium oxide content greater than 90 wt%, an active reaction time of 100-200 s, and a residue of less than 4.0 wt% on an 80 μm square hole sieve.

4. The low water-sensitive concrete expansion agent as described in claim 1, characterized in that, The preparation steps of the modified calcium oxide include: Polyethylene glycol and ethanol are mixed in an equal mass ratio to obtain a polyethylene glycol ethanol solution; Stearic acid and ethanol are mixed at a mass ratio of 1:50 to obtain a stearic acid-ethanol solution; Add calcium oxide clinker to the stearic acid ethanol solution and stir until homogeneous to obtain a calcium oxide suspension; The polyethylene glycol ethanol solution was added to the calcium oxide suspension, and after the reaction, the mixture was dried and ground to obtain the modified calcium oxide.

5. The low water-sensitive concrete expansion agent as described in claim 4, characterized in that, The mass ratio of calcium oxide clinker, polyethylene glycol, and stearic acid is 80-90:10-15:5-10; And / or, the specific surface area of ​​the calcium oxide clinker is 300-450 m². 2 / kg, free calcium oxide content ≥75%; And / or, the molecular weight of the polyethylene glycol is 1800-2200.

6. The low water-sensitive concrete expansion agent as described in claim 4, characterized in that, The reaction temperature is 35-40℃, the rotation speed is 300-400rpm, and the time is 1-2h; And / or, the drying temperature is 60°C; And / or, the grinding is to grind to a specific surface area of ​​300-450 m². 2 / kg.

7. The low water-sensitive concrete expansion agent as described in claim 1, characterized in that, The average particle size of the ground zeolite powder is 75-150 μm.

8. The low water-sensitive concrete expansion agent as described in claim 1, characterized in that, The powdered carboxylic acid is a high-slump-retaining powdered polycarboxylic acid high-performance water-reducing agent with a water reduction rate greater than 25%.

9. A method for preparing a low water-sensitive concrete expansion agent according to any one of claims 1-8, characterized in that the step... include: The low water-sensitive concrete expansion agent is obtained by uniformly mixing the shrinkage compensation component, the regulating component, the finely ground zeolite powder, and the powdered carboxylic acid.

10. The application of the low water-sensitive concrete expansion agent according to any one of claims 1-8 in concrete preparation.

Images