Concrete internal curing agent with hydration temperature rise regulation effect, preparation method of concrete internal curing agent and concrete shrinkage-reducing and anti-cracking functional material

Abstract

The invention relates to the field of concrete functional additives, in particular to a concrete internal curing agent with a hydration temperature rise regulation effect, a preparation method of the concrete internal curing agent and a concrete shrinkage-reducing and anti-cracking functional material. Wherein the raw materials comprise a polymeric monomer, a cross-linking monomer, an initiator, a polyhydroxy carbohydrate and water; wherein the polymeric monomer is composed of 70-100% by mass of an acrylamide monomer and the balance of an acrylic acid monomer, the polyhydroxy carbohydrate is a starch hydrolysate dextrin compound, and the DE value of the dextrin compound is greater than 0 but not greater than 15. The internal curing agent effectively solves the problem that an existing commercially available super absorbent polymer (SAP) internal curing material is poor in water absorption and water retention capacity on a cement pore solution containing divalent ions and trivalent ions, and the internal curing agent has the effects of internal curing and cement hydration heat release regulation and control.

Description

Technical Field

[0001] This application relates to the field of functional additives for concrete, and more specifically, to an internal curing agent for concrete with hydration temperature rise regulation function, its preparation method, and functional materials for concrete shrinkage reduction and crack resistance. Background Technology

[0002] Cement concrete is currently the most widely used building material due to its excellent workability, mechanical properties, and price advantage, making it widely used in municipal engineering, bridges, roads, high-speed railways, dams, and other fields. As infrastructure construction expands to coastal and plateau environments, concrete structures are becoming increasingly larger, thicker, and longer. This necessitates that concrete, in addition to good workability and mechanical properties, also possess superior durability. Preventing concrete from cracking is a fundamental prerequisite for its durability. Once cracks occur, they provide a rapid transmission channel for corrosive media, allowing them to penetrate the concrete at rates tens of thousands of times higher than those of ordinary clinker. When these media reach the surface of the reinforcing steel and accumulate to a critical concentration, the steel corrodes and expands, leading to durability problems in the engineering structure. Therefore, preventing concrete cracking is essential for ensuring its durability.

[0003] Deformation and shrinkage are fundamental properties of cement concrete, primarily stemming from the volume reduction and heat release during cement hydration, as well as the self-drying effect caused by the consumption of internal moisture. When the shrinkage stress generated during the contraction of structural concrete exceeds its corresponding tensile strength due to internal and external constraints, cracking occurs. This problem is further exacerbated by the characteristics of modern concrete, such as high cementitious material usage, low water-cement ratio, high admixture proportion, high fluidity, and high strength grade. Therefore, reducing or compensating for concrete shrinkage, lowering concrete temperature rise, and increasing internal humidity are the main directions for preventing cracking. Research on crack resistance can generally be conducted from the perspectives of concrete mix design optimization and construction techniques. In addition, developing and using crack-resistant functional materials is one of the most common and convenient measures for concrete crack resistance. Among these methods, using the expansion effect of calcium or magnesium-based expansive materials to resist concrete shrinkage is a common anti-cracking measure. Examples include calcium oxide expansive materials proposed in patents JP2023028435A, JP2020152610A, and CN104692691B; magnesium oxide expansive materials proposed in CN110066128B; and methods for preparing calcium-magnesium composite expansive agents in CN1412144A and CN110066129B. In earlier years, apart from reducing the amount of adhesive, using low- to medium-heat cement, or implementing cooling water pipes, there were no other methods to reduce the hydration temperature rise of concrete using chemical admixtures. In recent years, a class of functional materials that inhibit the rate of heat release during cement hydration has emerged, such as the technologies disclosed in patents CN104098288B, CN105217994B, JP5881013B2, and JP1984030743A. Superabsorbent polymer (SAP) materials, as a type of internal curing material, are also widely used to solve concrete cracking, as disclosed in patents such as CN101318786A, CN103058566A, and CN104446174A. Besides single-function materials, there are also many patents that combine two crack-resistant functional materials to form a dual crack-resistant technology. For example, patents such as CN101863072A and CN102390951A disclose the technology of combining an expansion agent with SAP, while patents such as CN102674738B, CN111377648B, and CN108147705B disclose the technology of combining calcium-magnesium expansion materials with hydration heat control materials.

[0004] As is well known, cracking during the hardening stage of concrete occurs when the stress caused by deformations such as autogenous shrinkage, thermal shrinkage, and drying shrinkage exceeds the tensile strength of the concrete under constrained conditions. To solve the problem of concrete cracking, a single material technology cannot cover all of these shrinkage deformations; it can only be effective for shrinkage cracking in concrete under certain conditions, but cannot solve the cracking of concrete structures under extreme conditions or with multiple combined effects. While some patents have been published regarding technologies based on the dual regulation of expansion materials and hydration heat control materials or SAP (superabsorbent polymer) materials, SAP has been widely studied and reported as an internal curing material. Commercially available SAP is mainly prepared by polymerization of acrylic monomers and is suitable for rapid water absorption in the hygiene field, exhibiting good water absorption and retention properties for monovalent ionic solutions.

[0005] However, when used in cement concrete, it needs to have a fast water absorption and slow water release capacity for cement pore solutions with high salt and strong alkali. In addition, the salt ions in the cement pore solution are mainly divalent calcium ions and trivalent aluminum ions, etc. Conventional commercially available SAP does not have a good water absorption and slow water release capacity for this ion solution. Summary of the Invention

[0006] This application first provides a concrete internal curing agent with hydration temperature rise regulation function. The internal curing agent of this application forms a network structure of superabsorbent polymer (SAP) resin and polyhydroxy sugar compounds that interpenetrate each other. This effectively solves the problem of poor water absorption and retention capacity of existing commercially available SAP resins for cement pore solutions containing divalent and trivalent ions. This allows the internal curing agent to have both internal curing and cement hydration heat release regulation effects. Moreover, when the internal curing agent of this application is used in combination with expansive materials, it can further increase the expansion efficiency of the expansive materials. Thus, a multifunctional and synergistic concrete crack-resistant material can be obtained that combines expansion to compensate for shrinkage, internal curing and water retention, and regulation of cement hydration heat release.

[0007] In a first aspect, this application provides a concrete internal curing agent with hydration temperature rise regulation function, employing the following technical solution: A concrete internal curing agent with hydration temperature rise regulation function, the raw materials include polymeric monomers, crosslinking monomers, initiators, polyhydroxy sugar compounds and water; wherein the polymeric monomers are composed of 70% to 100% acrylamide monomers and the balance being acrylic monomers by mass percentage, and the polyhydroxy sugar compounds are dextrin compounds, which are hydrolysis products of starch, and the DE value of the dextrin compounds is greater than 0 but not more than 15.

[0008] By adopting the above technical solutions, this application achieves the formation of an interpenetrating network structure of polyhydroxy sugar compounds and SAP resin, enabling the internal curing agent to exhibit excellent water absorption and retention capabilities for cement pore solutions containing divalent and trivalent ions, thus combining the effects of internal curing and cement hydration heat regulation. Specifically, compared to conventional SAP resins, this application uses more amide monomers in its polymer monomers, resulting in better water absorption and retention capabilities for cement pore solutions containing divalent and trivalent ions. Furthermore, this application… The polymerizing monomers and crosslinking monomers can work better with polyhydroxy sugar compounds to construct interpenetrating network structures. The interpenetrating network structure of this application not only has good water absorption and water retention capabilities, but also the internal protective agent of this application will not cause the polyhydroxy sugar compounds to be released too quickly or too early due to excessive water absorption ratio. In addition, this application uses dextrin-like compounds, which are hydrolyzed products of starch with a suitable degree of hydrolysis. This is not only conducive to the construction of interpenetrating network structures with polymerizing monomers and crosslinking monomers, but also conducive to their own slow release. The released polyhydroxy sugar compounds can play a good role in regulating the heat of hydration.

[0009] In summary, while each component in the internal curing agent of this application exerts its own effect, it also works synergistically with the other components, enabling the internal curing agent of this application to have excellent water absorption and retention capacity for cement pore solutions containing divalent and trivalent ions, thus combining the effects of internal curing and cement hydration heat release regulation.

[0010] Furthermore, the crosslinking monomer is composed of 50% to 70% N,N'-methylenebisacrylamide, 20% to 50% trimethylolpropane triacrylate and pentaerythritol triacrylate in any proportion, and the balance pentaerythritol tetraacrylate by mass percentage.

[0011] It should also be noted that the 20% to 40% of trimethylolpropane triacrylate and pentaerythritol triacrylate in any proportion refers to a mixture of trimethylolpropane triacrylate and pentaerythritol triacrylate in any proportion, with the content of the mixture being 20-40%. The balance of pentaerythritol tetraacrylate can be 0.

[0012] Further, the molar ratio of the polymeric monomer to the crosslinking monomer is 20-100; the mass ratio of the sum of the polymeric monomers and crosslinking monomers to the mass of the polyhydroxy sugar compound is 0.5-2; the mass ratio of the total mass of the polymeric monomers, crosslinking monomers, initiator, and polyhydroxy sugar compound to water is 0.5-1; and the molar amount of the initiator is 0.0005-0.002 compared to the sum of the molar amounts of the polymeric monomers and crosslinking monomers.

[0013] Furthermore, the water content of the polyhydroxy sugar compound does not exceed 15%.

[0014] Secondly, this application provides a method for preparing a concrete internal curing agent with hydration temperature rise regulation function, using the following technical solution: A method for preparing a concrete internal curing agent with hydration temperature rise regulation function includes the following steps: The initiator is dissolved in a small amount of water to form an initiator solution. The polyhydroxy sugar compound, polymeric monomer, and crosslinking monomer are dispersed in water and thoroughly mixed and stirred to form a homogeneous solution or suspension with a temperature not exceeding 20°C. Then, the aforementioned initiator solution is added and thoroughly mixed to obtain a prepolymer solution. After repeatedly replacing the oxygen on the surface of the prepolymer solution with nitrogen, the temperature is slowly increased, with a temperature rise of not less than 65°C. After the reaction temperature reaches 65-75°C, it is kept at this temperature for 2±0.2 hours before cooling down to obtain the concrete internal curing agent.

[0015] Thirdly, this application provides a concrete shrinkage-reducing and crack-resistant functional material using a concrete internal curing agent with hydration temperature rise regulation function, employing the following technical solution: A concrete shrinkage-reducing and crack-resistant functional material using a concrete internal curing agent with hydration temperature rise regulation function, the raw materials of which include calcium oxide expanded clinker, lightly calcined magnesium oxide, auxiliary dispersing materials and internal curing agent.

[0016] By adopting the above technical solutions, it is found that various types of concrete shrinkage are not isolated but rather have a coupled effect. Disclosed methods for the synergistic effect of single or two crack-resistant materials on coupled concrete shrinkage deformation are few or ineffective. This application's shrinkage-reducing and crack-resistant functional materials include calcium oxide expanded clinker, lightly calcined magnesia, and an internal curing agent, specifically addressing the cracking problems caused by autogenous shrinkage, drying shrinkage, and temperature shrinkage in modern concrete engineering. On the one hand, the expansion properties of calcium oxide expanded clinker and lightly calcined magnesia compensate for concrete shrinkage; on the other hand, the specially formulated internal curing agent inhibits the exothermic reaction of cement hydration while simultaneously reducing internal autogenous drying shrinkage and further stimulating the calcium-magnesium expansion material; thus producing multiple synergistic effects and solving the problem of shrinkage cracking in modern concrete.

[0017] Furthermore, the calcium oxide expanded clinker has an 80µm sieve residue between 15% and 30% and a 0.315mm sieve residue of no more than 0.5%; in its phase composition, the content of free calcium oxide (f-CaO) is no less than 45%, the content of calcium sulfoaluminate is no less than 8%, and the content of calcium hydroxide is no more than 10%; the loss on ignition is no more than 2%. The calcium oxide expanded clinker can be prepared by calcining and grinding limestone, gypsum, bauxite, etc., in a specific ratio.

[0018] Furthermore, the residue on an 80µm sieve of the light-calcined magnesium oxide is between 5% and 10%, the magnesium oxide content is not less than 85%, and the activation reaction time tested according to DL / T 5296 standard is 100s to 200s; a further activation reaction time is 120s to 180s, and the optimal activation reaction time is 140s to 160s. The light-calcined magnesium oxide can be produced using a suspension process of first pulverizing and then calcining.

[0019] Furthermore, the residue of the internal curing agent on a 0.315mm sieve shall not exceed 5% and the residue on an 80um sieve shall not be less than 30%.

[0020] Furthermore, the raw materials for the concrete shrinkage-reducing and crack-resistant functional materials include, by mass percentage: ≥10% calcium oxide expanded clinker, ≤80% lightly calcined magnesium oxide, 2%~10% internal curing agent, and the remainder being auxiliary dispersing materials.

[0021] In summary, this application has the following beneficial effects: 1. Firstly, this application synthesizes an internal curing agent with an interpenetrating network structure using raw materials such as polymerizable monomers, crosslinking monomers, and polyhydroxy sugar compounds. The construction of the interpenetrating network structure of SAP resin and polyhydroxy sugar compounds not only enables the internal curing agent to have good water absorption and retention capabilities for cement pore solutions containing divalent and trivalent ions, but also facilitates the slow release of polyhydroxy sugar compounds. The released polyhydroxy sugar compounds have excellent hydration heat regulation capabilities, thereby enabling the internal curing agent of this application to also have excellent water absorption and retention capabilities for cement pore solutions containing divalent and trivalent ions, thus combining the effects of internal curing and cement hydration heat release regulation.

[0022] 2. The internal curing agent of this application can be used in combination with the expansion material to further enhance the expansion efficiency of the expansion material, thereby obtaining a multifunctional and synergistic concrete crack-resistant material that combines expansion to compensate for shrinkage, internal curing to retain water and regulate the heat release of cement hydration.

[0023] 3. The crack-resistant material of this application can be applied to various cast-in-place concrete projects, especially suitable for walls or roofs with high confinement; it can be mixed with sand, stone, adhesives, etc. when preparing concrete. Detailed Implementation

[0024] The present application will be further described in detail below with reference to the embodiments.

[0025] Example The embodiments of this application first provide a concrete internal curing agent with hydration temperature rise regulation function, the raw materials of which include polymer monomers, crosslinking monomers, initiators, polyhydroxy sugar compounds and water.

[0026] The molar ratio of polymeric monomer to crosslinking monomer is 20-100; the mass ratio of the sum of the total mass of polymeric monomer and crosslinking monomer to the mass of polyhydroxy sugar compound is 0.5-2, preferably 1.5-2; the mass ratio of the total mass of polymeric monomer, crosslinking monomer, initiator and polyhydroxy sugar compound to water is 0.5-1; and the ratio of the molar amount of initiator to the sum of the molar amounts of polymeric monomer and crosslinking monomer is 0.0005-0.002.

[0027] The polymer monomers consist of 70%–100% acrylamide monomers and the balance being acrylic monomers by mass percentage. The polyhydroxy sugar compounds are dextrin compounds, which are hydrolyzed products of starch. The dextrin compounds have a DE value greater than 0 but not exceeding 15, and a water content not exceeding 15%.

[0028] The crosslinking monomers consist of 50%–70% N,N'-methylenebisacrylamide, 20%–50% trimethylolpropane triacrylate and pentaerythritol triacrylate in any proportion, and the balance pentaerythritol tetraacrylate by mass percentage. The initiator is potassium persulfate, sodium persulfate, or ammonium persulfate in any proportion. The conductivity of the water used does not exceed 0.50 mS / m (25°C).

[0029] The preparation method of the above-mentioned internal maintenance agent includes the following steps: The initiator is dissolved in a small amount of water to form an initiator solution. The aforementioned polyhydroxy sugar compound, polymeric monomer, and crosslinking monomer are dispersed in water, thoroughly mixed and stirred to form a homogeneous solution or suspension with a temperature not exceeding 20°C. The aforementioned initiator solution is then added and thoroughly mixed to obtain a prepolymer solution. After repeatedly replacing the oxygen on the surface of the prepolymer solution with nitrogen, the temperature is slowly increased, with a temperature rise not lower than 65°C. Once the reaction temperature reaches 65-75°C, it is held at this temperature for 2±0.2 hours before cooling. The solution is then crushed, dried, and pulverized to form the internal curing agent of this application. The total amount of water in the initiator solvent and the water used to disperse the monomer constitutes the total water content in the formulation of this application.

[0030] This application also provides a concrete shrinkage-reducing and crack-resistant functional material, the raw materials of which include calcium oxide expanded clinker, lightly calcined magnesium oxide, auxiliary dispersing materials, and internal curing agents. The raw materials of the concrete shrinkage-reducing and crack-resistant functional material, by mass percentage, include: calcium oxide expanded clinker ≥10%, lightly calcined magnesium oxide ≤80%, internal curing agent 2%~10%, and the balance being auxiliary dispersing materials.

[0031] The calcium oxide expanded clinker has an 80µm sieve residue of 15% to 30% and a 0.315mm sieve residue of no more than 0.5%; in terms of phase composition, the content of free calcium oxide (f-CaO) is no less than 45%, the content of calcium sulfoaluminate is no less than 8%, and the content of calcium hydroxide is no more than 10%; the loss on ignition is no more than 2%. The calcium oxide expanded clinker can be prepared by calcining limestone, gypsum, bauxite, etc. in a certain proportion and then grinding them.

[0032] The residue on an 80µm sieve for light-calcined magnesium oxide is between 5% and 10%, with a magnesium oxide content of not less than 85%. The activation reaction time, tested according to DL / T 5296 standard, is 100-200 seconds; a further activation reaction time is 120-180 seconds, with the optimal activation reaction time being 140-160 seconds. Light-calcined magnesium oxide can be produced using a suspension process involving powdering followed by calcination. The residue on a 0.315mm sieve for the internal curing agent does not exceed 5%, and the residue on an 80µm sieve is not less than 30%.

[0033] In addition, the auxiliary dispersing material in the embodiments of this application is an anhydrous gypsum powder, fly ash, limestone powder and other powder materials in any proportion, with a moisture content of no more than 1.0% and a residue of no more than 10% on an 80um sieve.

[0034] The above-mentioned concrete shrinkage-reducing and crack-resistant functional material is prepared by mixing the above-mentioned calcium oxide expanded clinker, lightly calcined magnesium oxide, auxiliary dispersing material and internal curing agent in a certain proportion.

[0035] The following explanation is provided through specific examples.

[0036] Example 1 This embodiment provides a concrete internal curing agent with hydration temperature rise regulation function. The raw materials include polymer monomers, crosslinking monomers, initiators, polyhydroxy sugar compounds and water.

[0037] The monomers are: 2.0 mol acrylamide (WM=71) 142 g, 0.1 mol methacrylamide (WM=85) 8.5 g, and 0.9 mol acrylic acid (WM=72) 64.8 g.

[0038] The crosslinking monomers are: 0.021 mol N,N'-methylenebisacrylamide (WM=154) 3.234 g and 0.01 mol trimethylolpropane triacrylate 2.96 g (WM=296).

[0039] The initiator was 0.003 mol potassium persulfate (0.81 g, WM=270).

[0040] The polyhydroxy saccharide compound is: 150g of commercially available dextrin with a DE value of 10.

[0041] 700g of water.

[0042] The preparation process of the internal oxidant in this embodiment includes the following steps: According to the above raw material dosage, the initiator solution prepared by mixing the initiator and 50g of water is added to the remaining (650g) of water. The polyhydroxy sugar compound, polymeric monomer, and crosslinking monomer are then added and thoroughly mixed and stirred to form a homogeneous solution or suspension with a temperature not exceeding 20°C. The aforementioned initiator solution is then added, and the mixture is stirred for 0.5 hours until all the solids are dissolved, yielding a prepolymer solution. Next, the initiator solution is added, and after stirring for 5 minutes, the mixture is purged three times with high-purity nitrogen. The solution is then placed in a water bath and gradually heated to 65°C for the reaction. As the temperature rises, the reaction solution gradually becomes gel-like. After maintaining this temperature for 2 hours, the gel is broken up, dried in an oven, and pulverized through a 0.3mm sieve to obtain the internal curing agent SAP-1.

[0043] This embodiment also provides a concrete shrinkage-reducing and crack-resistant functional material, the raw materials of which include calcium oxide expanded clinker, lightly calcined magnesium oxide, auxiliary dispersing materials, and internal curing agents. Specifically, the above-mentioned SAP-1, lightly calcined magnesium oxide (with an activation reaction time of 140s) produced by the suspension process of Jiangsu Subote New Material Co., Ltd., calcium oxide expanded clinker powder, commercially available gypsum powder, and commercially available Class II fly ash are mixed in a ratio of 25:350:400:125:100 to obtain the concrete shrinkage-reducing and crack-resistant functional material.

[0044] Example 2 This embodiment provides a concrete internal curing agent with hydration temperature rise regulation function. The raw materials include polymer monomers, crosslinking monomers, initiators, polyhydroxy sugar compounds and water.

[0045] The monomers are: 2.0 mol acrylamide (WM=71) 142 g, 0.1 mol methacrylamide (WM=85) 8.5 g, and 0.9 mol acrylic acid (WM=72) 64.8 g.

[0046] The crosslinking monomers are: 15.4 g of 0.1 mol N,N'-methylenebisacrylamide (WM=154) and 14.8 g of 0.05 mol trimethylolpropane triacrylate (WM=296).

[0047] The initiator was 0.005 mol potassium persulfate 1.35 g (WM=270).

[0048] The polyhydroxy saccharide compound is: 130g of commercially available dextrin with a DE value of 5.

[0049] The water level is 650.

[0050] The preparation process of the internal oxidant in this embodiment includes the following steps: According to the above raw material dosage, the initiator solution prepared by mixing the initiator and 50g of water is added to the remaining water along with the polyhydroxy sugar compound, polymeric monomer, and crosslinking monomer. The mixture is thoroughly mixed and stirred to form a homogeneous solution or suspension with a temperature not exceeding 20°C. Then, the aforementioned initiator solution is added, and the mixture is stirred for 0.5 hours until all the solids are dissolved, yielding a prepolymer solution. Next, the initiator solution is added, and after stirring for 5 minutes, the mixture is purged three times with high-purity nitrogen. The solution is then placed in a water bath and gradually heated to 65°C for the reaction. As the temperature rises, the reaction solution gradually becomes gel-like. After maintaining this temperature for 2 hours, the gel is broken up, dried in an oven, and pulverized through a 0.3mm sieve to obtain the internal curing agent SAP-2.

[0051] This embodiment also provides a concrete shrinkage-reducing and crack-resistant functional material, the raw materials of which include calcium oxide expanded clinker, lightly calcined magnesium oxide, auxiliary dispersing materials, and internal curing agents. Specifically, the above-mentioned SAP-1, lightly calcined magnesium oxide (with an activation reaction time of 120s) produced by the suspension process of Jiangsu Subote New Material Co., Ltd., calcium oxide expanded clinker powder, commercially available gypsum powder, and commercially available Class II fly ash are mixed in a ratio of 25:350:400:125:100 to obtain the concrete shrinkage-reducing and crack-resistant functional material.

[0052] Example 3 This embodiment provides a concrete internal curing agent with hydration temperature rise regulation function. The raw materials include polymer monomers, crosslinking monomers, initiators, polyhydroxy sugar compounds and water.

[0053] The monomers are: 3.0 mol acrylamide (WM=71) 213 g, 0.1 mol methacrylamide (WM=85) 8.5 g, and 0.8 mol acrylic acid (WM=72) 57.6 g.

[0054] The crosslinking monomers are: 7.7 g of 0.05 mol N,N'-methylenebisacrylamide (WM=154) and 5.92 g of 0.02 mol trimethylolpropane triacrylate (WM=296).

[0055] The initiator was 0.008 mol potassium persulfate 21.6 g (WM=270).

[0056] The polyhydroxy saccharide compound is: 180g of commercially available dextrin with a DE value of 15.

[0057] 500g of water.

[0058] The preparation process of the internal oxidant in this embodiment includes the following steps: Following the above-mentioned raw material dosages, an initiator solution prepared with initiator and 50g of water was added. The polyhydroxy sugar compound, polymeric monomer, and crosslinking monomer were then added to the remaining water. The mixture was thoroughly mixed and stirred to form a homogeneous solution or suspension with a temperature not exceeding 20°C. The aforementioned initiator solution was then added, and the mixture was stirred for 0.5 hours until all the solids dissolved, yielding a prepolymer solution. Next, the initiator solution was added, and the mixture was stirred for 5 minutes. After purging with high-purity nitrogen three times, the solution was placed in a water bath and gradually heated to 65°C for the reaction. As the temperature increased, the reaction solution gradually became gel-like. After maintaining this temperature for 2 hours, the gel was broken up, dried in an oven, and pulverized through a 0.3mm sieve to obtain the internal curing agent SAP-3.

[0059] This embodiment also provides a concrete shrinkage-reducing and crack-resistant functional material, the raw materials of which include calcium oxide expanded clinker, lightly calcined magnesium oxide, auxiliary dispersing materials, and internal curing agents. Specifically, the above-mentioned SAP-1, lightly calcined magnesium oxide (with an activation reaction time of 140s) produced by the suspension process of Jiangsu Subote New Material Co., Ltd., calcium oxide expanded clinker powder, commercially available gypsum powder, and commercially available Class II fly ash are mixed in a ratio of 25:350:400:125:100 to obtain the concrete shrinkage-reducing and crack-resistant functional material.

[0060] Comparative Example The difference between Comparative Example 1 and Example 1 is that commercially available NR-511 SAP is used instead of Example SAP-1. Commercially available NR-511 SAP is mixed with lightly calcined magnesium oxide (active reaction time of 140s) produced by the suspension process of Jiangsu Subote New Material Co., Ltd., as well as calcium oxide expanded clinker powder, commercially available gypsum powder, and commercially available Class II fly ash in a ratio of 25:350:400:125:100 to obtain a shrinkage-reducing and crack-resistant functional material.

[0061] The difference between Comparative Example 2 and Example 1 is that the monomers used for polymerization are: 71g of 1.0mol acrylamide (WM=71), 8.5g of 0.1mol methacrylamide (WM=85), and 136.8g of 1.9mol acrylic acid (WM=72).

[0062] The difference between Comparative Example 3 and Example 1 is that the dextrin-like compounds, which are hydrolysates of starch, are replaced with unhydrolyzed starch.

[0063] The difference between Comparative Example 4 and Example 1 is that the DE value of the dextrin compound is 20.

[0064] Performance testing It should be noted that in the product performance testing of this application, the liquid absorption ratio was tested in accordance with JC / T 2551-2019 "Concrete High Water Absorbency Resin Internal Curing Agent"; the mortar restricted expansion rate was tested in accordance with GB / T 23439-2017 "Concrete Expansion Agent"; and the hydration heat performance was tested in accordance with JC / T 2608-2021 "Concrete Hydration Temperature Rise Inhibitor", with a dosage of 10% as an internal admixture.

[0065] (1) For the internal curing agent / SAP resin obtained in the examples and comparative examples, the liquid absorption ratio in deionized water and saturated calcium hydroxide solution was tested by the tea bag method. The test results are shown in Table 1.

[0066] Table 1. Liquid uptake ratio (g / g) of internal maintenance agent / SAP tree in comparative and example cases. As shown in Table 1, the commercially available SAP exhibits a significantly higher absorption rate and absorption ratio in deionized water than the sample from Example 1. The former rapidly reaches 200 g / g or even over 300 g / g, while the latter, even after 24 hours of water absorption, only achieves an absorption ratio of 149 g / g, less than half that of the former, indicating a significantly lower absorption ratio. However, in saturated calcium hydroxide solution, commonly used as a simulation solution for cement pores, the difference is even more pronounced. The commercially available SAP achieves an absorption ratio of 130 g / g within the first 15 minutes, but this ratio decreases rapidly and continuously with prolonged soaking time, reaching only 8 g / g after 24 hours. The SAP-1 sample from Example 1, on the other hand, demonstrates a slower absorption and liquid retention capacity, achieving an absorption ratio of 55 g / g at 15 minutes, 45 g / g even after 180 minutes, and 35 g / g after 24 hours. As is well known, to ensure concrete has certain workability, it needs to maintain a flowable plastic state for several hours. During this period, the internal moisture is sufficient, and continuous water release from SAP is not required. This is why commercially available SAP is not suitable for concrete. Compared with Example 1, the liquid absorption ratio of Comparative Example 2 is basically consistent with that of Comparative Example 1. The liquid absorption ratio in deionized water is significantly higher than that of Example 1, while in saturated calcium hydroxide solution, the liquid absorption ratio reaches 86 g / g in 15 minutes, but only 19 g / g in 24 hours. Compared with Example 1, the data of Comparative Example 3 shows that, when reacting with unhydrolyzed starch, the liquid absorption ratio in both saturated calcium hydroxide solution and deionized water is significantly lower than that of Example 1. Similarly, Comparative Example 4, which reacts with overly hydrolyzed dextrin, also shows a lower liquid absorption ratio than that of Example 1.

[0067] (2) For the shrinkage-reducing and crack-resistant functional materials of the examples and comparative examples, the heat reduction rate of mortar hydration when 10% is added was tested according to JC / T 2608, and the free expansion rate of mortar with 10% added under sealed conditions was tested according to GB / T 23439-2017. The test results are shown in Table 2.

[0068] Table 2. Mortar properties of shrinkage-reducing and crack-resistant functional materials in the examples and comparative examples. As shown in Table 2, Comparative Example 1, formulated with commercially available SAP, does not have the function of regulating the heat release of cement hydration. In fact, the heat release of hydration in the early 24 hours is higher than that of the baseline, resulting in a 24-hour heat reduction rate of -5%, but it has virtually no impact on the heat release of hydration at 7 days. In contrast, the sample of Example 1 can regulate the heat release process of cement hydration, reducing the heat release by 35% in 24 hours, and accounting for 92% of the heat release in the baseline at 7 days. It has little impact on the heat release in the later stages, which means that it has little impact on long-term strength. Regarding expansion deformation, the difference in expansion deformation under sealed conditions is also very obvious. The mortar with Comparative Example 1 has a 3-day restricted expansion rate of 0.015%, and the expansion deformation only increases by 0.001% from 3 days to 7 days. At 28 days, it decreases by 0.003% compared to 7 days. This process is a typical autogenous volume expansion deformation process, that is, although it generally exhibits expansion in the long term, and the early expansion is obvious, it will soon turn into shrinkage. The mortar process of the sample in Example 1 differed. Not only did it exhibit large overall expansion over a long period, but this expansion was continuous, with no shrinkage observed within 28 days. This expansion process is similar to that under water-grown conditions, and the reason for this continuous large expansion is the continuous water release from Example SAP-1. Similarly, Comparative Example 2, due to its similar absorption rate in saturated calcium hydroxide solution as Example 1, also showed shrinkage at 28 days compared to 7 days, and the shrinkage was smaller than that of Example 1 at the same age. Compared to Example 1, Comparative Example 3 introduced unhydrolyzed starch, which essentially lacked hydration heat regulation properties. Compared to Example 1, Comparative Example 4 introduced dextrin with a DE value of 20. Although the 24-hour hydration heat reduction rate was good, the 7-day hydration heat reduction rate was excessively high, reaching 19%, which is detrimental to the development of later strength. Based on the above test results, the above examples have good shrinkage reduction and crack resistance.

[0069] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A concrete internal curing agent having a hydration temperature rise regulating effect, characterized by comprising: a water-soluble polymer; and a water-soluble inorganic substance. The raw materials include polymerization monomers, cross-linking monomers, initiators, polyhydroxy sugar compounds and water; wherein the polymerization monomers are composed of 70-100% acrylamide monomers and the rest acrylic monomers by mass percentage, the polyhydroxy sugar compounds are dextrin compounds which are hydrolysis products of starch, and the DE value of the dextrin compounds is greater than 0 but not more than 15.

2. The internal curing agent for concrete according to claim 1, wherein The cross-linking monomers are composed of 50-70% N,N'-methylenebisacrylamide, 20-50% trimethylolpropane triacrylate and pentaerythritol triacrylate in any proportion, and the rest pentaerythritol tetraacrylate by mass percentage.

3. The internal curing agent for concrete according to claim 1, wherein The molar ratio of the polymerization monomers to the cross-linking monomers is 20-100; the mass ratio of the total mass of the polymerization monomers and the cross-linking monomers to the mass of the polyhydroxy sugar compounds is 0.5-2; the mass ratio of the total mass of the polymerization monomers, the cross-linking monomers, the initiators and the polyhydroxy sugar compounds to the mass of water is 0.5-1; and the molar ratio of the molar amount of the initiators to the sum of the molar amounts of the polymerization monomers and the cross-linking monomers is 0.0005-0.

002.

4. The internal curing agent for concrete according to claim 1, wherein The water content of the polyhydroxy sugar compounds is not more than 15%.

5. A method for producing a concrete internal curing agent having a hydration temperature rise regulating effect according to any one of claims 1 to 4, characterized by, The method comprises the following steps: The initiators are dissolved in a small amount of water to form an initiator solution, the polyhydroxy sugar compounds, the polymerization monomers and the cross-linking monomers are dispersed in water, and then mixed and stirred to form a uniform solution or suspension with a temperature not higher than 20℃, followed by adding the initiator solution, and then mixing thoroughly to obtain a pre-polymer solution; the surface oxygen of the pre-polymer solution is replaced by nitrogen multiple times, and then slowly heated to a temperature not lower than 65℃, and then kept at 65-75℃ for 2±0.2h to start cooling to obtain the concrete internal curing agent.

6. A concrete shrinkage and crack control material using the concrete internal curing agent having the hydration temperature rise control effect according to any one of claims 1 to 4, characterized by, The raw materials include calcium oxide expanded clinker, light-burned magnesium oxide, auxiliary dispersing materials and the internal curing agent according to any one of claims 1-4.

7. The concrete shrinkage and crack control material according to claim 6, characterized in that, The calcium oxide expanded clinker has an 80µm sieve residue of 15% to 30% and a 0.315mm sieve residue of no more than 0.5%; in the phase composition, free calcium oxide ( f The content of α-CaO is not less than 45%, the content of calcium sulfoaluminate is not less than 8%, the content of calcium hydroxide is not more than 10%, and the loss on ignition is not more than 2%.

8. The concrete shrinkage and crack control material according to claim 6, characterized in that, The light-burned magnesium oxide has a 80um screen residue of 5-10% and a magnesium oxide content of not less than 85%, and the active reaction time is 100-200s according to the DL / T 5296 standard.

9. The concrete shrinkage and crack control material according to claim 6, characterized in that, The internal curing agent has a 0.315mm screen residue of not more than 5% and an 80um screen residue of not less than 30%.

10. The concrete shrinkage and crack control material according to claim 7, wherein The raw materials of the concrete shrinkage-reducing and anti-cracking functional material include calcium oxide expanded clinker≥10%, light-burned magnesium oxide≤80%, internal curing agent 2-10%, and the rest auxiliary dispersing materials by mass percentage.

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