Internal curing agent suitable for ultra-high performance concrete and preparation method of internal curing agent

Abstract

The invention belongs to the technical field of concrete admixtures, and particularly relates to an internal curing agent suitable for ultra-high performance concrete and a preparation method of the internal curing agent. The internal curing agent is prepared from the following components in parts by weight: 3 to 5 parts of tapioca flour, 1 to 2 parts of porous analcime spheres, 1 to 2 parts of gamma-type nano aluminum oxide, 5 to 12 parts of anionic monomers, 55 to 100 parts of nonionic monomers, 0.2 to 0.5 part of an initiator, 0.2 to 0.5 part of a cross-linking agent and 100 to 300 parts of deionized water. The concrete internal curing agent obtained by the preparation method is a spherical anionic-nonionic concrete internal curing agent, the water absorption rate is 80-100, the concrete internal curing agent has hydrophilic and alkali-resistant groups, and the particle size is 20-50 [mu] m; the influence on the mechanical property of the concrete is small, and early shrinkage of the concrete can be effectively inhibited; the volume stability of the concrete is improved; the cracking risk is reduced.

Description

Technical Field

[0001] This invention belongs to the field of concrete admixture technology, and in particular to an internal curing agent suitable for ultra-high performance concrete and its preparation method. Background Technology

[0002] Ultra-high absorbent polymer (UHSAP) is a new type of polymer material that can absorb tens or even hundreds of times its own weight in water. Ultra-high performance concrete has ultra-high durability and ultra-high strength, with a compressive strength exceeding 120 MPa. It is a new type of cement-based material developed in recent years, with a water-cement ratio typically of 0.14-0.20. Due to the low water-cement ratio, its autogenous shrinkage is very large, which can easily lead to early cracking.

[0003] Using internal curing agents is an effective way to solve this problem. However, existing research shows that while adding superabsorbent resins to internal curing agents reduces the autogenous shrinkage of ultra-high performance concrete, it also reduces the concrete strength. Therefore, there is an urgent need to develop new internal curing agents that do not reduce concrete strength. Internal curing agents are added to concrete internally, and they have functions such as reducing shrinkage, inhibiting cracking, and improving water retention. This gives the concrete better pouring performance and achieves long-term internal water retention and curing, significantly reducing the risk of concrete cracking.

[0004] Currently, commercially available superabsorbent polymers are generally synthesized using acrylic acid as a raw material. The products have excessively high water absorption ratios and excessively fast liquid absorption rates. When used as internal curing agents, they easily absorb too much mixing water in the early stages, significantly reducing the workability of concrete and failing to meet actual construction requirements. This limits the application of superabsorbent polymers in the construction field. Therefore, concrete internal curing agents must have slower liquid absorption rates and lower water absorption ratios.

[0005] However, most existing internal curing agents use porous lightweight aggregates, such as kaolin and bentonite. For example, CN201110195132.0 discloses a method for preparing a water-retaining, salt- and alkali-resistant concrete internal curing agent. Using plant starch, layered inorganic powder, anionic monomers, nonionic monomers, and water as main raw materials, under the action of an initiator, crosslinking agent, and a certain temperature, an internal curing agent with a particle size of 75-150 μm is obtained through dissolution, reaction, filtration, washing, drying, and pulverization. This solves the problem of limited internal curing effect caused by the poor salt and alkali resistance of traditional SAP. However, after swelling, the particle size will become at least five times the original size, and the pore size will be too large after water release, leaving large pores inside the concrete, thus adversely affecting the mechanical properties of the concrete. Therefore, how to provide an internal curing agent suitable for ultra-high performance concrete is a pressing technical problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide an internal curing agent suitable for ultra-high performance concrete and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: an internal curing agent suitable for ultra-high performance concrete, wherein the internal curing agent is prepared from the following components in parts by weight: 3-5 parts tapioca flour, 1-2 parts porous zeolite balls, 1-2 parts γ-type nano alumina, 5-12 parts anionic monomer, 55-100 parts nonionic monomer, 0.2-0.5 parts initiator, 0.2-0.5 parts crosslinking agent, and 100-300 parts deionized water.

[0008] Furthermore, the anionic monomer is one or more of sodium methacrylate sulfonate and 2-acrylamido-2-methylpropanesulfonic acid.

[0009] Furthermore, the nonionic monomer is one or more of acrylamide, methacrylamide, N-methylacrylamide, and N,N-dimethylacrylamide.

[0010] Acrylamide compounds are nonionic monomers with strong salt and alkali resistance and relatively weak water absorption, but their water absorption rate is faster than that of acrylic compounds. By copolymerizing with acrylic compounds in a certain proportion, the gel strength and strong alkali resistance of the synthetic resin are improved. The concrete internal curing agent obtained by the preparation method of this invention is a spherical anionic nonionic concrete internal curing agent with a water absorption ratio of 80-100. It has both hydrophilic and alkali-resistant groups, and the particle size is between 20-50 μm. After absorbing water and swelling, it is placed in cement filtrate for 24 hours without significant shrinkage or color change. The 24-hour water retention rate is 85%, and it can repeatedly absorb and release water, thus exhibiting good strong alkali resistance. Compared with irregular UHSAP, the spherical internal curing agent and its surrounding hydration products are arc-shaped. This special "micro-arc structure" can effectively disperse and conduct the surrounding compressive stress and has excellent dispersibility. Furthermore, after the internal curing agent of this invention is mixed with cement, as the cement hydrates and hardens, the water retained inside the curing agent is gradually released, forming near-spherical, regular macroscopic pores in the cement paste, thus preparing porous, highly absorbent internal curing agent concrete. Due to the water-releasing curing characteristics of the internal curing agent of this invention, a high-strength arched shell structure with a high degree of hydration and a dense structure is formed around the spherical, regular pores, making this pore structure fundamentally different from the pore structure in conventional foamed concrete.

[0011] Furthermore, the initiator is one or more of potassium persulfate and ammonium persulfate.

[0012] Furthermore, the porous zeolite spheres have a particle size of 10-20 μm and a specific surface area ≥600 m². 2 / g, with a porosity of 50-60%.

[0013] Furthermore, the porous zeolite spheres are prepared through the following steps: (1) Take 50-100 mesh cubic zeolite, soak it in water for 24 hours, then wash it with water 2-3 times, dry it, and roast it at 500℃ for 3 hours; (2) Take the calcined zeolite from step (1), soak it in a 1 mol / L potassium aluminum sulfate solution for 24 hours, wash it, and then dry it at 100°C. (3) According to the weight ratio of 6-10:1, the dried zeolite and pore-forming agent in step (2) are mixed and 2-6% of polyacrylate binder are added to form balls. The balls are then calcined at 600°C for 3 hours. After calcination, the balls are cooled to room temperature. If necessary, the calcined porous zeolite balls are broken up to obtain the porous zeolite balls.

[0014] Furthermore, the pore-forming agent is carbonized peanut shells with a particle size of 2-5 μm. During the high-temperature sintering process, the carbonized peanut shells turn into gas and are discharged, thus avoiding the generation of toxic and harmful gases produced during the sintering of plastic particles. This effectively reduces the health hazards to operators during the preparation of the pore-forming agent and also reduces environmental pollution.

[0015] The internal curing agent of this invention incorporates porous zeolite spheres. These spheres have numerous cavities and channels, exhibiting high adsorption capacity. The porous zeolite spheres can adsorb water-absorbing polymers into their interior or on their surface. This allows the curing agent material to maintain the good water absorption and release performance of the superabsorbent polymer while controlling the water absorption and release rates. This not only reduces the impact on the mechanical properties of concrete but also effectively inhibits early shrinkage of concrete, thereby improving the volume stability of concrete and reducing the risk of cracking.

[0016] Furthermore, the particle size of γ-type nano-alumina is 150-300 nm. Using γ-type nano-alumina as an internal curing agent, leveraging its porous and high-strength properties, nano-alumina exhibits excellent nano-effects. These effects facilitate the hydration of concrete cementitious materials, improve the strength of the concrete after setting, and further reduce shrinkage due to its filling and compacting effect.

[0017] Furthermore, the crosslinking agent is one of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, or ethylene glycol diglycidyl ether.

[0018] Another object of the present invention is to provide a method for preparing the above-mentioned internal curing agent suitable for ultra-high performance concrete, the preparation method comprising the following steps: (1) Weigh out 3-5 parts of cassava flour, 1-2 parts of porous zeolite balls, 1-2 parts of γ-type nano alumina, 0.2-0.5 parts of initiator, and 0.2-0.5 parts of crosslinking agent, respectively, and dissolve them in 100-150 parts of deionized water. After stirring thoroughly, a mixed solution A is obtained. Add the mixed solution A to a four-necked flask and place it in a water bath at 60-80℃ and stir thoroughly for 0.5-1 hour. (2) Weigh out 5-12 parts of anionic monomer and 55-100 parts of nonionic monomer respectively, dissolve them in 100-150 parts of deionized water, and obtain monomer solution B after thorough stirring. (3) At 60-80℃, the monomer solution B obtained in step (2) is added dropwise to the mixed solution A in step (1) for reaction. The dropwise addition time of monomer solution B is controlled to be 1-2 hours; the reaction time is 4-6 hours, and a gel copolymer is obtained after the reaction. (4) The copolymer obtained in step (3) is filtered and washed, then atomized and dried at 220-250°C for 2-4 hours, and then dried at 70-80°C for 20-24 hours until completely dry. The atomized and dried copolymer is dried to a spherical structure with an average particle size of 20-50 μm to obtain the internal curing agent.

[0019] Compared with the prior art, the present invention has the following technical effects and advantages: 1. The concrete internal curing agent prepared by the method of the present invention is a spherical anionic nonionic concrete internal curing agent with a water absorption ratio of 80-100. It has both hydrophilic and alkali-resistant groups and a particle size between 20-50 μm. After absorbing water and swelling, it is placed in cement filtrate for 24 hours without significant shrinkage or color change. The water retention rate after 24 hours is 85%. It can repeatedly absorb and release water, so it has good resistance to strong alkalis. Compared with irregular HSAP, the spherical internal curing agent and its surrounding hydration products are arc-shaped. This special "micro-arc structure" can effectively disperse and conduct the compressive stress around it and has good dispersibility.

[0020] 2. The internal curing agent of this invention incorporates porous zeolite spheres. The porous zeolite spheres have many cavities and channels in their structure, which have a high adsorption capacity. The porous zeolite spheres can adsorb water-absorbing polymers inside or on their surface. This allows the curing agent material to control the water absorption and release rate while ensuring the good water absorption and release performance of the superabsorbent polymer. This not only reduces the impact on the mechanical properties of concrete, but also effectively inhibits the early shrinkage of concrete. In turn, it improves the volume stability of concrete and reduces the risk of cracking.

[0021] 3. Using γ-type nano-alumina as an internal curing agent, taking advantage of its porous and high-strength properties, nano-alumina has a good nano-effect, which helps with the hydration of concrete cementitious materials, improves the strength of concrete after setting, and further reduces shrinkage value through filling and compaction effect. Detailed Implementation

[0022] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0023] Example 1 A method for preparing an internal curing agent suitable for ultra-high performance concrete, the preparation method comprising the following steps: (1) Weighing 3 parts of cassava flour, 1 part of porous zeolite balls, 1 part of γ-type nano alumina, 0.2 parts of initiator, and 0.2 parts of crosslinking agent respectively, dissolving them in 100 parts of deionized water, and obtaining mixed solution A after thorough stirring; adding mixed solution A into a four-necked flask and placing it in a 60℃ water bath and stirring thoroughly for 0.5 hours; (2) Weigh out 5 parts of anionic monomer and 55 parts of nonionic monomer respectively, dissolve them in 100 parts of deionized water, and obtain monomer solution B after thorough stirring; (3) At 60°C, the monomer solution B obtained in step (2) is added dropwise to the mixed solution A in step (1) for reaction, and the addition time of monomer solution B is controlled to be 1 hour; the reaction time is 4 hours, and a gel copolymer is obtained after the reaction. (4) The copolymer obtained in step (3) is filtered and washed. First, the product is atomized and dried at 220℃ for 2 hours, then dried at 70℃ for 20 hours until completely dry. The atomized product is dried to a spherical structure with an average particle size of 20μm to obtain the internal maintenance agent.

[0024] The anionic monomer is sodium methylpropenesulfonate; The nonionic monomer is acrylamide; The initiator is selected as ammonium persulfate; The porous zeolite spheres have a particle size of 10 μm and a specific surface area of ​​600 m². 2 / g, with a porosity of 50%.

[0025] The particle size of γ-type nano-alumina is 150 nm.

[0026] The crosslinking agent is N,N'-methylenebisacrylamide; Example 2 A method for preparing an internal curing agent suitable for ultra-high performance concrete, the method comprising the following steps: (1) Weigh out 4 parts of cassava flour, 1.5 parts of porous zeolite balls, 1.5 parts of γ-type nano alumina, 0.3 parts of initiator, and 0.3 parts of crosslinking agent, respectively, and dissolve them in 120 parts of deionized water. After stirring thoroughly, a mixed solution A is obtained. Add the mixed solution A to a four-necked flask and place it in a 70°C water bath and stir thoroughly for 0.8 hours. (2) Weigh out 8 parts of anionic monomer and 80 parts of nonionic monomer respectively, dissolve them in 120 parts of deionized water, and obtain monomer solution B after thorough stirring. (3) At 70°C, the monomer solution B obtained in step (2) is added dropwise to the mixed solution A in step (1) for reaction. The dropwise addition time of monomer solution B is controlled at 1.5 hours; the reaction time is 5 hours, and a gel copolymer is obtained after the reaction. (4) The copolymer obtained in step (3) is filtered and washed. The internal maintenance agent is obtained by first atomizing and drying at 235°C for 3 hours, then drying at 75°C for 22 hours until completely dry, and atomizing and drying to a spherical structure with an average particle size of 35μm.

[0027] The anionic monomer is sodium methylpropenesulfonate; The nonionic monomer is acrylamide; The initiator is selected as ammonium persulfate; The porous zeolite spheres have a particle size of 15 μm and a specific surface area ≥700 m². 2 / g, with a porosity of 55%.

[0028] The particle size of γ-type nano-alumina is 220 nm.

[0029] The crosslinking agent is N,N'-methylenebisacrylamide.

[0030] Example 3 A method for preparing an internal curing agent suitable for ultra-high performance concrete, the method comprising the following steps: (1) Weigh out 5 parts of cassava flour, 2 parts of porous zeolite balls, 2 parts of γ-type nano alumina, 0.5 parts of initiator, and 0.5 parts of crosslinking agent, respectively, and dissolve them in 150 parts of deionized water. After stirring thoroughly, a mixed solution A is obtained. Add the mixed solution A to a four-necked flask and place it in an 80°C water bath and stir thoroughly for 1 hour. (2) Weigh out 12 parts of anionic monomer and 100 parts of nonionic monomer respectively, dissolve them in 150 parts of deionized water, and stir thoroughly to obtain monomer solution B; (3) At 80°C, the monomer solution B obtained in step (2) is added dropwise to the mixed solution A in step (1) for reaction. The dropwise addition time of monomer solution B is controlled at 2 hours; the reaction time is 6 hours, and a gel copolymer is obtained after the reaction. (4) The copolymer obtained in step (3) is filtered and washed, then atomized and dried at 250°C for 4 hours, and then dried at 80°C for 24 hours until completely dry. The atomized and dried copolymer has a spherical structure with an average particle size of 50 μm to obtain the internal curing agent.

[0031] The anionic monomer is 2-acrylamido-2-methylpropanesulfonic acid; The nonionic monomer is N-methylacrylamide; The initiator is ammonium persulfate; The porous cubic zeolite spheres have a particle size of 20 μm and a specific surface area ≥800 m². 2 / g, with a porosity of 60%.

[0032] The particle size of γ-type nano-alumina is 300 nm.

[0033] The crosslinking agent is one of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, or ethylene glycol diglycidyl ether.

[0034] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that γ-type nano-alumina was not used, and porous zeolite balls of the same weight were used instead of γ-type nano-alumina. Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that porous zeolite balls were not used; instead, γ-type nano-alumina of the same weight was used instead of porous zeolite balls. Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the same weight proportions of zeolite powder are used instead of porous cubic zeolite balls.

[0035] The concrete internal curing agents obtained in Examples 1-3 and Comparative Examples 1-3 of this invention were applied to ultra-high performance concrete. The specific concrete mix proportions are shown in Table 1. Table 1: Concrete Mix Design Table (Unit: Kg) Commercially available cement sand steel fiber fly ash silica ash Water reducing agent Internal care agent water Blank group 600 1000 157 200 200 20 0 150 experimental group 600 1000 157 200 200 20 10 150 The 3-day, 7-day, and 28-day compressive strengths of the concrete obtained from the blank group and the experimental group (Examples 1-3 and Comparative Examples 1-3) were tested according to GB / T50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete". Simultaneously, the 7-day autogenous shrinkage rate of the concrete obtained was tested according to GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". The test results are shown in Table 2. Table 2: Test Results Experimental Project Blank group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Internal maintenance agent dosage / kg 0 10 10 10 10 10 10 3d compressive strength / MPa 89.2 88.4 88.0 87.8 86.5 86.6 86.4 7d compressive strength / MPa 105.1 102.6 102.1 101.1 100.5 100.8 100.4 28-day compressive strength / MPa 134.2 133.9 132.3 131.8 119.6 134.8 119.3 <![CDATA[7d Self-shrinkage rate / 10 -6 > 612 202 193 212 253 294 282 Slump / mm 250 261 263 268 254 255 253 Expansion / mm 651 663 659 661 653 656 652 As can be seen from the results in Table 2, the internal curing agents obtained in Examples 1-3 of this invention have achieved outstanding results in reducing concrete shrinkage, especially Example 2, whose 7-day autogenous shrinkage rate is only 193 × 10⁻⁶. -6 Furthermore, the compressive strength remains at a high level, and there is no significant decrease in strength when the shrinkage rate is reduced.

[0036] Comparative Examples 1 and 3 did not use γ-type nano-alumina, which is detrimental to the development of concrete strength, and their strength is significantly lower compared to Examples 1-3. Comparative Example 2, which did not use porous zeolite balls, showed a significantly higher 7-day autogenous shrinkage rate than Examples 1-3. Comparative Example 3, which used the same weight proportions of zeolite powder instead of porous zeolite balls, also achieved a relatively high 7-day autogenous shrinkage rate. Clearly, porous zeolite balls have an inhibitory effect on concrete shrinkage.

[0037] This demonstrates that the use of γ-type alumina powder and porous zeolite balls plays a crucial role in the effective production of the internal curing agent.

[0038] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An internal curing agent suitable for ultra-high performance concrete, characterized in that: The internal maintenance agent is prepared from the following components in parts by weight: 3-5 parts tapioca flour, 1-2 parts porous zeolite balls, 1-2 parts γ-type nano alumina, 5-12 parts anionic monomer, 55-100 parts nonionic monomer, 0.2-0.5 parts initiator, 0.2-0.5 parts crosslinking agent, and 100-300 parts deionized water.

2. The internal curing agent for ultra-high performance concrete as described in claim 1, characterized in that: The anionic monomer is one or more of sodium methacrylate sulfonate and 2-acrylamido-2-methylpropanesulfonic acid.

3. The internal curing agent for ultra-high performance concrete as described in claim 1, characterized in that: The nonionic monomer is one or more of acrylamide, methacrylamide, N-methylacrylamide and N,N-dimethylacrylamide.

4. The internal curing agent for ultra-high performance concrete as described in claim 1, characterized in that: The initiator is one or more of potassium persulfate and ammonium persulfate.

5. The internal curing agent for ultra-high performance concrete as described in claim 1, characterized in that: The porous zeolite spheres have a particle size of 10-20 μm and a specific surface area ≥600 m². 2 / g, with a porosity of 50-60%.

6. The internal curing agent for ultra-high performance concrete as described in claim 1, characterized in that: The particle size of γ-type nano-alumina is 150-300 nm.

7. The internal curing agent for ultra-high performance concrete as described in claim 1, characterized in that: The crosslinking agent is one of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, or ethylene glycol diglycidyl ether.

8. A method for preparing an internal curing agent suitable for ultra-high performance concrete as described in any one of claims 1-7, characterized in that: The preparation method includes the following steps: (1) Weigh out 3-5 parts of cassava flour, 1-2 parts of porous zeolite balls, 1-2 parts of γ-type nano alumina, 0.2-0.5 parts of initiator, and 0.2-0.5 parts of crosslinking agent, respectively, and dissolve them in 100-150 parts of deionized water. After stirring thoroughly, a mixed solution A is obtained. Add the mixed solution A to a four-necked flask and place it in a water bath at 60-80℃ and stir thoroughly for 0.5-1 hour. (2) Weigh out 5-12 parts of anionic monomer and 55-100 parts of nonionic monomer respectively, dissolve them in 100-150 parts of deionized water, and obtain monomer solution B after thorough stirring. (3) At 60-80℃, the monomer solution B obtained in step (2) is added dropwise to the mixed solution A in step (1) to carry out the reaction, and the dropwise addition time of monomer solution B is controlled to be 1-2 hours; the reaction time is 4-6 hours. (4) The copolymer obtained in step (3) is filtered and washed, then atomized and dried at 220-250°C for 2-4 hours, and then dried at 70-80°C for 20-24 hours until completely dry. The atomized and dried copolymer is dried to a spherical structure with an average particle size of 20-50 μm to obtain the internal curing agent.