A shrinkage-reducing admixture for concrete, a preparation method and application thereof

Abstract

The present application relates to the technical field of concrete admixtures, in particular to a shrinkage-reducing admixture for concrete, a preparation method and application thereof.The preparation process of the present application overcomes the problems of poor alkali resistance of traditional admixtures and easy cracking of solidified concrete.The present application comprises the following steps: preparing a reducing initiator, a chain transfer agent, an unsaturated acid monomer, a shrinkage-reducing functional monomer and an amide functional monomer solution by step-by-step preparation, controlling the polymerization conditions under nitrogen protection, and obtaining a water reducing agent; using alkyl glycoside as a starter, step-by-step polymerizing propylene oxide and ethylene oxide to obtain a low-foaming polyether; mixing the water reducing agent and the low-foaming polyether with an alkali-resistant additive to obtain a shrinkage-reducing admixture; and significantly improving the water-reducing rate, flow retention and compressive strength of concrete, optimizing the setting time, reducing the dry shrinkage rate and the influence of alkali erosion, and improving the compactness and durability of concrete through hydrogen bond network, low surface tension and alkali resistance protection.The viscosity of the concrete admixture is moderate, which is suitable for concrete application, and the process is stable and easy to industrialize.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete admixtures, in particular to a shrinkage-reducing admixture for concrete, a preparation method and application. BACKGROUND

[0002] Concrete will undergo volume shrinkage during setting and drying, causing concrete cracking, damaging or collapsing the structure, and reducing the safety performance of the building. These cracks not only affect the mechanical properties and aesthetics of the concrete, but also accelerate the intrusion of harmful ions such as chloride ions and sulfate ions, leading to steel corrosion, accelerated carbonation, and even structural damage, severely shortening the service life of the project. The cracking of concrete structures has always been a difficult problem that the engineering community is eager to solve, and shrinkage-reducing admixtures are an important way to control concrete shrinkage and cracking.

[0003] Patent CN117263563A discloses a concrete shrinkage-reducing admixture that reduces the surface tension of the cement concrete pore solution through the synergistic and unified action of the shrinkage-reducing component and the auxiliary component, reduces the driving force for shrinkage stress to occur, and achieves excellent shrinkage-reducing effect. Patent CN118165192A discloses that the synthesized concrete shrinkage-reducing admixture effectively reduces the shrinkage driving force of the cementitious system by significantly reducing the surface tension of the pore solution in the cementitious system and maintaining the relative humidity inside the system at a high level (> 94%), thereby achieving the purpose of shrinkage reduction. Patent CN111454014A discloses a method of introducing amino groups, sulfonic acid groups, amide groups, siloxane structure monomers, and ethylene glycol acrylate monomers into the molecular structure of the polymer to reduce the dry shrinkage rate of cement mortar. Although the above-mentioned shrinkage-reducing admixtures have certain shrinkage-reducing effect, they all ignore the problem that concrete is a strong alkaline environment, and surfactants will hydrolyze and lose their effect in a strong alkaline environment. The mechanism of concrete shrinkage-reducing admixtures is to reduce the surface tension of water in the capillary pores of concrete and reduce the shrinkage force in the water evaporation process to reduce the shrinkage of concrete. Therefore, the development of shrinkage-reducing admixtures that achieve the above performance in a strong alkaline environment can truly achieve the effect of shrinkage reduction.

[0004] High dosage of shrinkage-reducing admixtures increases the number of air bubbles, affecting workability and durability. In addition, shrinkage-reducing admixtures are mostly organic low molecular weight substances, which are prone to volatilization or degradation, and the long-term shrinkage-reducing effect decays. In addition, the adaptability of common admixtures such as water-reducing agents is poor, and when used together, flocculation or separation easily occurs, leading to abnormal viscosity of the slurry, and the dual functions of shrinkage reduction and water reduction cannot be simultaneously considered. The existing improvements mostly sacrifice fluidity or strength.

[0005] Therefore, a shrinkage-reducing admixture for concrete, a preparation method and application are proposed. SUMMARY

[0006] The application aims to provide a shrinkage-reducing admixture for concrete, a preparation method and application. The shrinkage-reducing admixture is prepared by step-by-step preparation of a reducing initiator, a chain transfer agent, an unsaturated acid monomer, a shrinkage-reducing functional monomer and an amide functional monomer solution, control of polymerization conditions under nitrogen protection, preparation of a water-reducing agent, step-by-step polymerization of propylene oxide and ethylene oxide using alkyl glycoside as a starter, preparation of a low-foam polyether, mixing of the two to obtain the shrinkage-reducing admixture, and significant improvement of the water-reducing rate, flow retention and compressive strength of concrete, optimization of the setting time, reduction of the dry shrinkage rate and alkali erosion effect, and improvement of the compactness and durability of concrete through hydrogen bond networks, low surface tension and alkali resistance protection.

[0007] To achieve the above-mentioned purpose, the application provides the following technical scheme.

[0008] The application provides a preparation method of a shrinkage-reducing admixture for concrete, and the preparation method is as follows: mixing water-reducing agent and low-foam polyether by weight parts, stirring at room temperature until uniform and transparent, and obtaining an intermediate material mixture; adding an alkali-resistant additive to the intermediate material mixture, and stirring again until uniform and transparent to obtain the shrinkage-reducing admixture.

[0009] The alkali-resistant additive is obtained by mixing alkyl triethoxysilane, polyoxyethylene ether, sodium dodecyl diphenyl ether disulfonate, deionized water and citric acid.

[0010] The water-reducing agent is obtained by copolymerization of a chain transfer agent, mercaptoacetic acid, an unsaturated acid monomer, acrylic acid, a shrinkage-reducing functional monomer, butyl acrylate, an amide functional monomer, acrylamide and iso-pentenyl polyoxyethylene ether.

[0011] The iso-pentenyl polyoxyethylene ether has a CAS of 62601-60-9 and a polymerization degree of 54; the C12-C14 alkyl glycoside has a CAS of 157707-88-5; the C8-10 alkyl glycoside has a CAS of 68515-73-1; and the C16-18 alkyl glycoside is Glucopon 600 CSUP.

[0012] The low-foam polyether is obtained by ring-opening addition reaction of alkyl glycoside, propylene oxide and ethylene oxide.

[0013] Preferably, the alkyl length of the alkyl glycoside is C8-C16.

[0014] Further preferably, the alkyl length of the alkyl glycoside is C12-C16.

[0015] Preferably, the copolymerization reaction process is as follows: the polymerization reaction is carried out under the protection of nitrogen; the isopentenyl polyoxyethylene ether is added into a reaction kettle, deionized water is added, stirring is started, and the temperature is increased to completely dissolve; the oxidation initiator is added into the reaction kettle, and solution A and solution B are added dropwise; after the dropwise addition is completed, the water reducing agent is obtained by keeping the reaction; the viscosity of the water reducing agent is 27-44 s, and the surface tension is 45-48 mN / m.

[0016] Preferably, solution A is obtained by dissolving the reducing initiator and mercaptoacetic acid in deionized water; and solution B is obtained by mixing acrylic acid, butyl acrylate and acrylamide. Solution A is used to control the polymer chain growth, avoid abnormal viscosity caused by too high molecular weight, and slightly increase the chain transfer agent after the introduction of acrylamide to prevent branching caused by hydrogen bonds; solution B ensures uniform distribution of monomers, and the amide group of acrylamide is uniformly embedded in the main chain in subsequent polymerization, which is beneficial to the formation of a hydrogen bond network.

[0017] Preferably, the ring-opening addition reaction process is as follows: the alkyl glycoside and potassium hydroxide are put into a high-pressure polymerization kettle, nitrogen protection, temperature increase and preservation are carried out to make the material distribution uniform; propylene oxide is added, the reaction is started, and the remaining propylene oxide is added after the pressure is stabilized; this step ensures uniform activation of the polyhydroxy of APG, which is beneficial to subsequent ring-opening of the epoxy; after the reaction is stabilized, ethylene oxide is added, the reaction is started, and the remaining ethylene oxide is added after the pressure is stabilized; after sufficient reaction, the temperature is reduced to room temperature, and the low-foam polyether is obtained by acid neutralization, the viscosity is 600-1500 Pa·s, and the surface tension is 28-33 mN / m.

[0018] The application further provides a shrinkage-reducing type additive for concrete, wherein the content of the water reducing agent in the shrinkage-reducing type additive for concrete is 83.9wt%-90.0wt%; the content of the low-foam polyether is 0.10wt%-0.28wt%; and the content of the alkali-resistant additive is 4.7wt%-16.0wt%; and the mass ratio of alkyl triethoxysilane, polyoxyethylene ether, sodium dodecyl diphenyl ether disulfonate, water and citric acid in the alkali-resistant additive is 9-12:2-3:1:3-6:1-2.

[0019] The application of the shrinkage-reducing type additive for concrete, wherein the shrinkage-reducing type additive is applied to C40 concrete; and the 7d dry shrinkage rate of the C40 concrete after the application is-231.6×10 -6 to-246.7×10 -6 , and the 28d dry shrinkage rate is-413.4×10 -6 to-431.0×10 -6 .

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] 1、The alkyl polyglycoside chain length and catalyst dosage are optimized in the preparation of low-foam polyether, and through step-by-step polymerization and pressure monitoring, the moderate extension and structural stability of the polyether chain are ensured. The sequential injection of ethylene oxide and propylene oxide balances the hydrophilic and hydrophobic properties, and the low-surface-tension product is prepared. The water-reducing agent and alkali-resistant additive are used in combination to reduce the air bubbles and pore tension in the concrete, improve the compactness and alkali resistance, significantly reduce the drying shrinkage, and improve the overall strength and long-term durability of the concrete.

[0022] 2、In the preparation of the water-reducing agent, an amide functional monomer is introduced, the monomer hydrolysis is avoided by extending the dropping time and controlling the heating rate, and the amide group is uniformly embedded in the main chain to form a hydrogen bond network. The molecular weight is regulated and the monomer molar ratio is optimized by using a chain transfer agent to enhance the hydrophilic group distribution, reduce the surface tension and viscosity fluctuation, improve the dispersion efficiency of the water-reducing agent on the cement particles, improve the uniformity and workability of the fresh concrete, inhibit the early shrinkage and crack generation, and significantly enhance the long-term stability and durability of the concrete.

[0023] 3、The water-reducing agent is mixed with the low-foam polyether by normal temperature stirring, and the alkali-resistant additive composed of alkyl triethoxysilane, polyoxyethylene ether, sodium dodecyl diphenyl ether disulfonate, etc. is gradually added to form a uniform and transparent shrinkage-reducing additive. The components work together to enhance the hydrogen bond network and surface tension regulation. The alkali-resistant additive forms a protective layer in the alkaline environment to reduce erosion, improve the water-reducing rate and flow retention of the concrete, delay the hydration reaction, optimize the setting time, significantly improve the compressive strength and alkali resistance, and reduce the drying shrinkage.

[0024] 4、Alkyl polyglycoside is used as a starting agent, the hydroxyl group is activated by inert gas cleaning and controlling the heating rate, and an alkaline catalyst is used. Propylene oxide and ethylene oxide are injected step by step, and the pressure and temperature are strictly controlled to ensure uniform ring-opening polymerization. After the reaction, the temperature is lowered, vacuum distillation is used to remove residual monomers, and the pH is neutralized to prepare a clear and transparent low-foam polyether. The hydrophilic and hydrophobic balance of the polyether chain is regulated, the surface tension is reduced, the molecular weight distribution is optimized, the product has moderate viscosity, the generation of foam in the concrete is significantly reduced, the compactness and surface activity of the mixture are improved, and thus the compressive strength and crack resistance of the concrete are improved.

[0025] 5、By step-by-step preparation of reducing initiator, chain transfer agent and unsaturated acid monomer, shrinkage reducing functional monomer and amide functional monomer solution, combined with nitrogen protection, control the polymerization temperature, drop time and holding reaction, ensure uniform distribution of monomer and moderate growth of polymerization chain, avoid abnormal molecular weight. After the reaction, adjust the solid content, neutralize the pH and filter the impurities, prepare a light yellow transparent water reducing agent; by forming a stable hydrogen bond network, enhancing the intermolecular interaction, reducing the surface tension and viscosity fluctuation, improving the dispersibility and stability of the water reducing agent in the concrete, significantly improving the fluidity and retention of the fresh concrete, reducing the introduction of air bubbles, optimizing the pore structure, thereby improving the workability and durability of the concrete. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Preparation method flow chart of the shrinkage reducing type admixture for concrete of the present application. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0028] Please refer to Figure 1 The present application provides a shrinkage reducing type admixture for concrete, a preparation method and application, and the technical solutions are as follows:

[0029] Preparation example 1 (preparation of water reducing agent)

[0030] S1 solution preparation: 1.8g of reducing initiator vitamin C, 4.2g of chain transfer agent mercaptoacetic acid were added to 60g of deionized water, and dissolved under 400rpm stirring to obtain solution A for standby. 180g of unsaturated acid monomer acrylic acid, 512g of shrinkage reducing functional monomer butyl acrylate and 284g of amide functional monomer acrylamide were mixed and added to 120g of deionized water, and stirred uniformly at 400rpm to obtain solution B for standby.

[0031] S2 polymerization reaction: The polymerization reaction was carried out under nitrogen protection, and the flow rate was 0.5 L / min; 280 g of iso-pentenyl polyoxyethylene ether was added to the reaction kettle, 51 g of deionized water was added, stirring was started, and the temperature was raised from room temperature at a rate of 2 ℃ / min to 50 ℃ until complete dissolution. 12 g of H2O230 wt% aqueous solution was added to the reaction kettle, and immediately the dropping was started: solution A and solution B were dropped at the same time; solution A was dropped for 4 h, and solution B was dropped for 3.5 h, and the dropping rate was uniform. The dropping time was extended to adapt to the activity of acrylamide to ensure uniform copolymerization; after the dropping was completed, the reaction was kept at 50 ℃ for 40 min to ensure that the monomer conversion rate was >96%.

[0032] S3 post-treatment: After the reaction was completed, deionized water was added to a total mass of 1000 g, and the solid content was adjusted to 42 wt%; stirring was continued at 200 rpm for 30 min to complete the residual monomer polymerization; cooled to room temperature, neutralized to pH=7 with 10 wt% NaOH solution, slowly titrated to avoid local high alkalinity leading to degradation of amide group; filtered with a 200 mesh screen to remove impurities, and a light yellow transparent shrinkage reducing PCE mother liquor was obtained.

[0033] Preparation of Comparative Example 1 (preparation of water reducing agent)

[0034] Different from Preparation Example 1, all raw materials were directly mixed to obtain a mixed solution for standby during the preparation of S1 solution.

[0035] Preparation of Comparative Example 2 (preparation of water reducing agent)

[0036] Different from Preparation Example 1, no amide functional monomer acrylamide was added.

[0037] Preparation of Comparative Example 3 (preparation of water reducing agent)

[0038] Different from Preparation Example 1, the temperature rising rate of S2 polymerization reaction was 5 ℃ / min; and the reaction temperature was 70 ℃, and the reaction time remained unchanged.

[0039] Preparation Example 2 (preparation of low-foaming polyether)

[0040] Put 45.6 g of C12-C14 alkyl glycoside and 0.574 g of potassium hydroxide into a high-pressure polymerization reactor, start stirring at 200 rpm, and seal the reactor. Use inert gas nitrogen to clean the reactor cavity three times, each time filling to 0.2 MPa, emptying, and removing oxygen and moisture. Increase the temperature from 25°C to 120°C at a rate of 5°C / min, keep the temperature at 120°C for 10 min, and make the potassium hydroxide uniformly dispersed in the alkyl glycoside to form a basic starting system. At 120°C, quickly inject 2 g of propylene oxide as an initiator through a feeding pump, complete within 5 min, and observe the pressure drop and temperature rise to indicate that the reaction has started. After the pressure stabilizes (drops to <0.1 MPa), ensure that the pressure is ≤0.5 MPa, and then start continuously adding the remaining 104.6 g of propylene oxide at a uniform drop rate, complete within 2 h. If the pressure approaches 0.5 MPa, pause the feeding until the pressure drops to 0.1 MPa. The reaction temperature is controlled at 130°C, and the stirring speed is 200 rpm. After the addition of propylene oxide is complete, keep the temperature at 130°C for 120 min until the pressure no longer drops (<0.05 MPa) to ensure a conversion rate of >98%. Ensure that the reactor temperature is 130°C, quickly inject 2 g of ethylene oxide as an initiator within 5 min, and observe the pressure drop and temperature rise. After the pressure stabilizes, it drops to 0.1 MPa. Ensure that the pressure is ≤0.5 MPa, and then start continuously adding the remaining 37.2 g of ethylene oxide, complete within 1 h. The pressure control is the same as above. The reaction temperature is controlled at 140°C, and the stirring speed is 200 rpm. After the addition of ethylene oxide is complete, keep the temperature at 140°C for 60 min until the pressure <0.05 MPa no longer drops to ensure a conversion rate of >98%.

[0041] After the reaction is complete, stop heating, slowly cool to room temperature <40°C at a rate of 5°C / min to avoid product sticking to the wall, open the reactor, discharge the inert gas, and discharge the product to obtain a clear and transparent low-foam polyether product, a light yellow viscous liquid containing a small amount of residual monomer, which is removed by vacuum distillation at -0.09 MPa, 80°C for 30 min. Adjust the product pH to 6-8 to neutralize the remaining potassium hydroxide with dilute acetic acid. Store in a sealed container, avoid light, and store at room temperature, with a stability of >6 months.

[0042] Preparation Example 3 (low-foam polyether preparation)

[0043] The difference from Preparation Example 2 is that the amount of potassium hydroxide is 0.813 g, and the remaining 161.1 g of propylene oxide is added dropwise within 3 h. The remaining 59.8 g of ethylene oxide is added dropwise within 1.5 h.

[0044] Preparation Example 4 (low-foam polyether preparation)

[0045] Different from Preparation Example 2, C12-C14 alkyl glycoside was replaced by C8-C10 alkyl glycoside, and the amount was 37.4 g, and the amount of potassium hydroxide was adjusted to 0.549 g.

[0046] Preparation of Comparative Example 4 (low-foam polyether preparation)

[0047] Different from Preparation Example 2, C12-C14 alkyl glycoside was replaced by C8-C10 alkyl glycoside, and the amount was 37.4 g, and the amount of potassium hydroxide was adjusted to 0.549 g.

[0048] Preparation of Comparative Example 5 (low-foam polyether preparation)

[0049] Different from Preparation Example 2, the amount of potassium hydroxide was 1.039 g, the remaining 215.5 g of propylene oxide was added dropwise within 4 h, the remaining 80.4 g of ethylene oxide was added dropwise within 2 h, and the temperature was kept at 150 ℃ after the addition of propylene oxide was completed, and the temperature was kept at 80 ℃ after the addition of ethylene oxide was completed.

[0050] Test Example 1

[0051] The viscosity and surface tension of the water-reducing agent and low-foam polyether obtained from Preparation Examples 1-4 and Comparative Examples 1-5 were tested; the specific test method is as follows: the viscosity of the water-reducing agent was determined according to GB / T 1723-1993 “Paint Viscosity Determination Method”, using a P-4 cup method, and the flow time (s) was determined at 25 ℃ to reflect the dynamic viscosity of the sample; the viscosity of the low-foam polyether was determined according to GB / T 2794-2022 “Determination of Adhesive Viscosity”, using a rotary viscometer to determine the dynamic viscosity of the sample at 25 ℃, and the unit was mPa·s;

[0052] The surface tension of the water-reducing agent and low-foam polyether was tested according to GB / T 22237-2008 “Determination of Surface Tension of Surfactants”; the test results are shown in Table 1.

[0053] Table 1 Viscosity and Surface Tension Test Results of Water-Reducing Agent and Low- Foam Polyether

[0054]

[0055] The water reducing agent and low-foam polyether prepared by the method of the present application have moderate viscosity and surface tension. In the preparation of the water reducing agent, in preparation example 1, solution A and solution B are prepared by step-by-step preparation to ensure uniform distribution of monomers, control of polymer chain growth, effective control of molecular weight by mercaptoacetic acid chain transfer agent, avoidance of abnormal viscosity caused by excessively high molecular weight, formation of hydrogen bond network by acrylamide amide group to moderately increase viscosity, and reduction of surface tension by hydrophilic groups such as carboxyl and amide group of butyl acrylate and acrylamide in the PCE mother liquor; in preparation comparative example 1, all raw materials are directly mixed without step-by-step preparation of solution A and B, which leads to uneven distribution of monomers, partial rapid polymerization, wide molecular weight distribution, increased branching, and high viscosity; in preparation comparative example 2, acrylamide is not added, and the hydrogen bond network of amide group is lacking, the interaction between molecular chains is weakened, and the viscosity is low; without the amide group of acrylamide, the hydrophilicity is slightly reduced, and the surface tension is slightly higher than that of preparation example 1; in preparation comparative example 3, rapid heating rate and high temperature lead to hydrolysis or side reactions of acrylamide, partial branching or degradation of polymer chains, uneven molecular weight distribution, and high viscosity; but the surface tension is not greatly affected.

[0056] In the preparation of the low-foam polyether, in preparation example 2, C12-C14 alkyl glycoside is used as a starter, and step-by-step ring-opening polymerization is carried out with propylene oxide and ethylene oxide under KOH catalysis to form a polyether chain. Moderate KOH dosage and control of dropwise addition time ensure moderate molecular weight; the alkyl chain of the alkyl glycoside and the polyether chain (ethylene oxide is hydrophilic, and propylene oxide is hydrophobic) synergistically reduce the surface tension, which is better than that of ordinary polyether and is suitable for low-foam applications. In preparation examples 3 and 4, the viscosity is higher than that of preparation example 2 by adjusting the length of the alkyl side chain of the alkyl glycoside, and the surface tension is stable. In preparation comparative example 4, the C8-C10 alkyl glycoside has a shorter chain length, the molecular weight is reduced, the viscosity is low, the KOH dosage is reduced, and the degree of polymerization is low; the short-chain alkyl glycoside enhances the surface activity, and the surface tension is further reduced. In preparation comparative example 5, the increased raw material dosage and the increased reaction temperature significantly increase the viscosity, and the surface tension is higher than that of preparation example 2.

[0057] Example 1

[0058] The shrinkage-reducing admixture has a mass percentage composition of 90wt% of water reducing agent, 0.1wt% of low-foam polyether, and 9.9wt% of alkali-resistant additive. The alkali-resistant additive is obtained by mixing alkyl triethoxysilane, polyoxyethylene ether, sodium dodecyl diphenyl ether disulfonate, water, and citric acid at a mass ratio of 10:2:1:6:1.

[0059] See Figure 1 , the preparation method of the shrinkage-reducing admixture is as follows:

[0060] a) Mix the water reducing agent and the low-foam polyether by weight parts, without heating or cooling, at a natural temperature, stir until uniform and transparent, and obtain an intermediate material mixture;

[0061] b) adding the alkali-resistant additive into the mixture obtained in step a) while stirring, and stirring again until uniform and transparent to obtain the shrinkage-reducing admixture.

[0062] The shrinkage-reducing admixture prepared in the examples and comparative examples was added to C40 concrete, and the performance of the concrete was tested. The addition of the shrinkage-reducing admixture in the examples and comparative examples is shown in Table 2. The mixing ratio in Table 2 is the mass mixing ratio of alkyl triethoxysilane, polyoxyethylene ether, sodium dodecyl diphenyl ether disulfonate, water, and citric acid.

[0063] Table 2: Addition ratio of shrinkage-reducing admixture in examples and comparative examples

[0064]

[0065] Comparative Example 1

[0066] Unlike Example 4, no low-foaming polyether and alkali-resistant additive were added, and only a water-reducing agent was added to the cement, i.e., the water-reducing agent was 100 wt%, and the addition amount of the shrinkage-reducing admixture in the cement was 1.2%.

[0067] Comparative Example 2

[0068] Unlike Example 4, the addition amount of the shrinkage-reducing admixture in the cement was 2.0%.

[0069] Comparative Example 3

[0070] Unlike Example 4, the water-reducing agent prepared in Comparative Example 1 was used, and the amount of the water-reducing agent was 83.9 wt%, the amount of the low-foaming polyether was 0.17 wt%, and the amount of the alkali-resistant additive was 16.0 wt%.

[0071] Comparative Example 4

[0072] Unlike Example 4, the water-reducing agent prepared in Comparative Example 2 was used.

[0073] Comparative Example 5

[0074] Unlike Example 4, the water-reducing agent prepared in Comparative Example 3 was used.

[0075] Comparative Example 6

[0076] Unlike Example 4, the low-foaming polyether prepared in Comparative Example 4 was used.

[0077] Comparative Example 7

[0078] Unlike Example 4, the low-foaming polyether prepared in Comparative Example 5 was used.

[0079] Experimental Example 1

[0080] After mixing with concrete, the water-reducing property and the flow retention property of Examples 1-5, Comparative Examples 1-5 were tested; the specific testing methods are as follows: the water-reducing property test was performed according to the method specified in GB 8076-2008 “Concrete Admixtures”, under the standard C40 concrete proportioning, the water-reducing admixture was mixed into the concrete and mixed uniformly. The initial slump (mm) of the fresh concrete was determined by the slump test, compared with the benchmark sample of the commercial water-reducing agent, the water-reducing rate (%) was calculated, the water-reducing rate (%) = [(water consumption of the benchmark sample - water consumption of the test sample) / water consumption of the benchmark sample] x 100%.

[0081] The flow retention property test method is as follows: after the water-reducing property test, the slump (mm) of the fresh concrete at 30 minutes, 60 minutes and 90 minutes was continuously determined to evaluate the flow retention property. Generally, the 60-minute slump loss rate (%) is taken as the main indicator; the slump loss rate (%) = [(initial slump - 60-minute slump) / initial slump] x 100%. The final test results are shown in Table 3.

[0082] Table 3 Water-reducing property and flow retention property test results

[0083]

[0084] The water-reducing rate under the conditions of Examples 1-5 is relatively high and the 60-minute slump loss rate is small. Under the conditions of Examples 1-5, by adjusting the type and amount of the water-reducing agent, the type and amount of the low-foaming polyether, and the mixed glass and amount of the alkali-resistant additive, the hydrogen bond network and the low surface tension are synergistic, the water-reducing rate is high, and the flow retention property is good. Comparative Example 1 only adds the water-reducing agent without polyether and additive, the water-reducing rate is low, and the flow retention property is poor; Comparative Example 2 increases the mixing amount of the water-reducing admixture in the cement to 2.0%, the water-reducing rate is high, but the flow retention property is general; Comparative Example 3 is prepared by the method of Comparative Example 1, the water-reducing agent is not uniformly polymerized, so that the water-reducing rate is low and the flow retention property is poor; Comparative Examples 4 and 5 respectively use the water-reducing agent obtained by the methods of Comparative Examples 2 and 3, due to the lack of amide bonds and high temperature hydrolysis, the water-reducing property and the flow retention property are both poor.

[0085] Experimental Example 2

[0086] The setting time, compressive strength at normal pH and compressive strength at pH 11 of the shrinkage reducing admixture-concrete mixtures obtained from Examples 1-5 and Comparative Examples 1-7 were tested; the specific test methods are as follows: The setting time of cement concrete mixture was determined by penetration resistance method. The shrinkage reducing admixture was mixed into standard C40 concrete, and after uniform mixing, it was placed in a standard mold, and the penetration resistance of the concrete mixture was determined periodically using a Vicat apparatus or a penetration resistance apparatus. When the resistance reached the initial setting standard of 0.5 MPa, the initial setting time was recorded, and when the resistance reached the final setting standard of 4.0 MPa, the final setting time was recorded. The results were expressed in terms of initial setting time and final setting time, and the unit was min.

[0087] The shrinkage reducing admixture was mixed into standard C40 concrete, and 150 mm x 150 mm x 150 mm cubic specimens were prepared, and standard curing (neutral water curing with pH ≈ 7) was performed until the specified age of 28 d. Using a universal material testing machine, an axial compressive force was applied at a constant loading rate of 0.5-1.0 MPa / s until the specimen was destroyed, the failure load was recorded, and the compressive strength MPa was calculated. The strength formula is: compressive strength = failure load / pressure area;

[0088] Similar to the pH 7 test, but the specimens were cured or soaked in an alkaline solution with pH = 11 to simulate an alkaline environment. After molding, the specimens were initially cured for 24 h under standard conditions, then transferred to a pH = 11 solution for curing until 28 d, and then tested. The temperature of the above tests was 20 ± 2°C, and the humidity was ≥ 95%. The test results are shown in Table 4.

[0089] Table 4 Setting time and compressive strength test results of Examples 1-5 and Comparative Examples 1-7

[0090]

[0091] In Examples 1-5, by adjusting the amount of water reducing agent, the molecular weight is moderate and there is an amide hydrogen bond network, which ensures uniform dispersion of cement particles, delays hydration reaction, and makes the setting time moderate; the low foam polyether proportion reduces the surface tension and cooperatively reduces the introduction of bubbles, optimizes the pore structure, and improves the compressive strength at pH 7; at the same time, various substances in the alkali-resistant additive synergize to form a protective layer in the pH 11 alkaline environment, reducing alkali erosion and maintaining high compressive strength. The initial setting time and final setting time of the above groups are moderate, among which, under the conditions of Example 4, the proportion of water reducing agent is the highest at 95.0 wt%, the hydrogen bond network is strong, the dispersibility is the best, the setting time is the shortest but moderate, the low foam polyether is Preparation Example 4, the C10-C16 alkyl glycoside chain length is increased, the surface tension is the lowest, the bubbles are significantly reduced, and the compactness is improved; the proportion of alkali-resistant additive is the lowest at 4.7 wt%, but the silane component is effective in protecting the cement hydration products at pH 11, and the strength remains optimal among the five examples.

[0092] Comparative Example 1 has no low-foam polyether and alkali-resistant additive, poor dispersibility, many bubbles leading to shortened setting time, non-dense hydration product, low strength at pH 7, no additive protection, severe alkali erosion, and greatly decreased strength; Comparative Example 2 has high water-reducing agent ratio, good initial dispersibility, moderate setting time, high strength at pH 7, but excessive water introduced by the excess additive, increased porosity, accelerated alkali reaction at pH 11, and greatly decreased strength; Comparative Example 3 has a water-reducing agent prepared in Comparative Example 1, wide molecular weight distribution, increased branching, poor dispersibility, shortened setting time, and easy alkali corrosion; Comparative Example 4 has no amide group hydrogen bond network, weak intermolecular interaction, poor dispersibility, the shortest setting time, and significantly decreased strength due to accelerated alkali hydrolysis; Comparative Example 5 has high temperature and rapid heating leading to amide group hydrolysis, unstable structure, decreased setting time and alkali resistance; Comparative Example 6 has a low-foam polyether prepared in Comparative Example 4, low molecular weight of C8-C10 short-chain alkyl glycoside, excessive foaming due to excessively low surface tension, prolonged setting time, increased porosity due to increased foam at pH 11, and decreased strength; Comparative Example 7 has a low-foam polyether prepared in Comparative Example 5, excessively large molecular weight due to high KOH and high temperature, high viscosity, poor dispersibility, the longest setting time, and greatly decreased strength due to the influence of high-temperature polymerization by-products on alkali.

[0093] Experimental Example 3

[0094] The shrinkage-reducing admixtures-concrete mixtures obtained in Examples 1-5 and Comparative Examples 1-7 were subjected to 7d and 28d dry shrinkage tests; the specific test method is as follows: the length change method was used to determine the dry shrinkage rate of the concrete.

[0095] The shrinkage-reducing admixtures were mixed into standard C40 concrete, and after uniform mixing, prismatic test pieces with a size of 100mmx100mmx515mm were formed. After the test pieces were formed, they were cured under standard conditions at a temperature of 20±2℃ and a humidity of ≥95% for 24h, the initial length was measured after demolding with an accuracy of 0.001mm, and then the test pieces were placed in a dry environment at a temperature of 20±3℃ and a relative humidity of 60±5%, and the length change was measured at 7d and 28d, respectively. The dry shrinkage rate = (L0-L t ) / (L0-2xL g ); L0 is the initial length (mm), L t is the length at t days (mm), and L g is the length of the measuring head (mm); the negative value represents shrinkage, and the test results are shown in Table 5.

[0096] Table 5 Dry shrinkage test results

[0097]

[0098] Examples 1-5 have lower shrinkage at 7d and 28d by optimizing the water reducer hydrogen bonding network, low foaming polyether surface tension, and alkali resistant additive ratio. Example 4 has the best performance. Example 5 has a low foaming polyether of Preparation 4, and long chain alkyl glycoside to enhance hydrophobicity, reduce surface water tension, and inhibit early stage shrinkage. At 28d, the alkali resistant additive is the same ratio, and synergistically reduces long-term drying cracks.

[0099] Comparative Examples 1-7 have increased shrinkage due to lack of synergistic components or preparation defects. Comparative Example 1 has no low foaming polyether and alkali resistant additive, poor dispersion, and many bubbles that increase capillary tension, resulting in high 7d shrinkage. At 28d, there is no additive to fill pores, and water evaporation is severe, resulting in a large increase in shrinkage. Comparative Example 2 has a high water reducer ratio, good initial dispersion, and low 7d shrinkage, but excessive water introduction increases late stage evaporation, resulting in high 28d shrinkage. Comparative Example 3 has a water reducer of Preparation Comparative Example 1, a wide molecular weight distribution due to uneven polymerization, and increased branching that results in uneven dispersion, high 7d shrinkage, and easy formation of microcracks that exacerbate shrinkage. Comparative Example 4 has no amide group hydrogen bonding network, weak intermolecular interaction, poor dispersion, and the highest 7d shrinkage. At 28d, there is no hydrogen bond to inhibit uneven hydration, and shrinkage is significantly increased. Comparative Example 5 has a water reducer of Preparation Comparative Example 3, and high temperature and rapid heating that leads to amide group hydrolysis, unstable structure, increasing pores due to hydrolysis products as time increases, and increased drying shrinkage. Comparative Example 6 has a low foaming polyether of Preparation Comparative Example 4, short C8-C10 chain, low molecular weight, and excessive foaming due to excessively low surface tension, resulting in high 7d shrinkage and increased pores and water evaporation at 28d. Comparative Example 7 has a low foaming polyether of Preparation Comparative Example 5, high KOH, and high temperature that leads to excessively large molecular weight, high viscosity, and uneven dispersion, resulting in high shrinkage.

[0100] The above examples are merely examples for clearly illustrating the application, and are not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and here, all embodiments are not required or possible to be exhausted, and thus the changes or variations that are inferred are still within the protection scope of the application.

Claims

1. A method for preparing a shrinkage-reducing admixture for concrete, characterized in that, The preparation method is as follows: water-reducing agent and low-foaming polyether are mixed according to the weight parts and stirred at room temperature until uniform and transparent to obtain intermediate material mixture; alkali-resistant additive is added to the intermediate material mixture and stirred again until uniform and transparent to obtain the shrinkage-reducing additive; The alkali-resistant additive is obtained by mixing alkyltriethoxysilane, polyoxyethylene ether, sodium dodecyl diphenyl ether disulfonate, deionized water and citric acid; the mass ratio of the alkyltriethoxysilane, polyoxyethylene ether, sodium dodecyl diphenyl ether disulfonate, deionized water and citric acid in the alkali-resistant additive is 9-12:2-3:1:3-6:1-2. The water-reducing agent is obtained by copolymerization of chain transfer agent mercaptoacetic acid, unsaturated acid monomer acrylic acid, shrinkage functional monomer butyl acrylate, amide functional monomer acrylamide, and isopentenyl polyoxyethylene ether. The low-foaming polyether is obtained by a ring-opening addition reaction of alkyl glycosides, propylene oxide, and ethylene oxide.

2. The method for preparing a shrinkage-reducing admixture for concrete according to claim 1, characterized in that, The alkyl glycoside has an alkyl length of C12-C16.

3. The method for preparing a shrinkage-reducing admixture for concrete according to claim 1, characterized in that, The copolymerization process is as follows: the polymerization reaction is carried out under nitrogen protection; the isopentenyl polyoxyethylene ether is added to the reaction vessel, the deionized water is added, stirring is started, the temperature is raised to dissolve completely, the oxidation initiator is added to the reaction vessel, and solutions A and B are added dropwise; after the dropwise addition is completed, the reaction is kept at the temperature to obtain the water-reducing agent; Solution A is obtained by dissolving a reducing initiator and mercaptoacetic acid in deionized water; Solution B is obtained by mixing acrylic acid, butyl acrylate and acrylamide.

4. The method for preparing a shrinkage-reducing admixture for concrete according to claim 1, characterized in that, The ring-opening addition reaction process is as follows: the alkyl glycoside and potassium hydroxide are added to a high-pressure polymerization reactor, protected with nitrogen, and heated to ensure uniform material distribution; propylene oxide is added to start the reaction, and after the pressure stabilizes, the remaining propylene oxide is added; after the reaction stabilizes, ethylene oxide is added to start the reaction, and after the pressure stabilizes, the remaining ethylene oxide is added, and the reaction is allowed to proceed fully, cooled to room temperature, and neutralized with acid.

5. A shrinkage-reducing admixture for concrete, characterized in that, The shrinkage-reducing admixture for concrete is prepared by the preparation method described in any one of claims 1-4.

6. An application of a shrinkage-reducing admixture for concrete prepared by the method described in claim 1, characterized in that, Application of shrinkage-reducing admixtures in C40 concrete.

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