Shrinkage-reducing and crack-reducing mass concrete and method for preparing the same

Abstract

The application discloses a shrinkage and crack resistance type mass concrete and a preparation method thereof. The shrinkage and crack resistance type mass concrete is composed of cement, fly ash, mineral powder, fine aggregate, coarse aggregate, a high water absorption and release composite shrinkage reducing agent, an additive and water. The high water absorption and release composite shrinkage reducing agent is prepared by the following steps: polymerization of polyethylene glycol ether acrylate, acrylic acid, acrylamide and 2-acrylamide-2-hydroxypropanesulfonic acid through a free radical polymerization reaction, crosslinking reaction of the obtained polymer and a crosslinking agent N, N-methylenebisacrylamide under the action of hydrochloric acid, and neutralization of the obtained polymer after the crosslinking reaction by adding alkali. The mass concrete has the advantages of meeting the mechanical properties and workability, further solving the problems of easy shrinkage and cracking of traditional mass concrete, and wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of cement concrete technology, and specifically relates to a shrinkage-reducing and crack-resistant mass concrete and its preparation method. Background Technology

[0002] With urbanization, urban land resources are becoming increasingly scarce. To conserve land, super-tall and large-scale construction projects are constantly emerging, placing higher demands on the use of concrete. Concrete is a commonly used material in modern construction, mainly composed of cement, mixed sand and gravel, additives, and aggregates. Concrete is easily affected by environmental, temperature, and technical factors during construction, often resulting in cracks, especially in large-volume concrete. Due to the large volume of concrete, large structural dimensions, complex construction process, and difficult curing, the large amount of heat of hydration generated by the cement inside the structure is not easily dissipated, while the external temperature remains consistent with the ambient temperature, resulting in a large temperature difference between the inside and outside of the concrete, which often leads to cracking. Cracks on the concrete surface reduce the safety of large-volume concrete structures and can even cause serious accidents such as building damage or collapse. Therefore, it is essential to rationally address the problem of cracking in large-volume concrete during construction, implement technical prevention and control measures, and reduce the waste of manpower and resources.

[0003] Patent CN 114397924 B discloses a method for intelligent temperature control of large-volume concrete. This method employs an intelligent control device comprising a main water pipe, a circulating water flow direction converter, a circulating water temperature regulator, a variable frequency pump, a circulating water flow meter, a controller, a first circulating water temperature sensor, a second circulating water temperature sensor, and an ambient temperature sensor. Furthermore, a concrete temperature regulating water pipe, a concrete center temperature sensor, and a concrete surface temperature sensor are embedded within the large-volume concrete structure to be temperature-controlled. After reading and analyzing the detection data from the circulating water flow meter and each temperature sensor, the controller issues control commands to the circulating water flow direction converter, circulating water temperature regulator, and variable frequency pump of the intelligent control device to control the internal temperature of the concrete. This achieves intelligent, dynamic, and efficient temperature control of the concrete and can periodically change the circulating water flow direction, thereby reducing cracking.

[0004] Patent CN 109356160 B discloses a construction method for large-volume concrete. The key technical points include the following steps: (1) Installing structural steel reinforcement and erecting formwork, with the formwork enclosing multiple concrete pouring areas, each separated by a partition joint, and pre-embedded measuring pipes; (2) Pouring concrete into the areas to be poured using a comprehensive layered pouring method; (3) Cooling with water and covering with insulation material; (4) Measuring the concrete temperature at regular intervals, and adjusting the concrete temperature based on the measured temperature difference between the inside and outside of the concrete and the highest internal temperature; (5) Removing the formwork and filling the partition joints. Multiple concrete sections are poured, and each pouring area can be cured separately using different curing methods, facilitating curing, ensuring the temperature and humidity required for cement hydration, and preventing crack formation.

[0005] These methods all use external processes to improve the cracking temperature of large-volume concrete, which is quite cumbersome in practice. Therefore, improving the crack resistance of concrete by addressing its composition and mix proportions is of great significance for modern building construction projects. Summary of the Invention

[0006] The purpose of this invention is to provide a shrinkage-reducing and crack-resistant mass concrete and its preparation method. This shrinkage-reducing and crack-resistant mass concrete, while satisfying mechanical properties and workability, further solves the problem of easy shrinkage and cracking in traditional mass concrete.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] A shrinkage-reducing and crack-resistant mass concrete is provided, comprising the following components by mass parts:

[0009]

[0010] The molecular structure of the superabsorbent and water-releasing composite shrinkage reducer conforms to formula (1):

[0011]

[0012] In the formula, a is a natural number from 0 to 6; m is a natural number from 40 to 140; n is a natural number from 40 to 100; x is a natural number from 20 to 60; y is a natural number from 60 to 120; and z is a natural number from 40 to 80.

[0013] According to the above scheme, the super absorbent and water-releasing composite shrinkage reducer is prepared by free radical polymerization of polyethylene glycol ether acrylate with acrylic acid, acrylamide and 2-acrylamido-2-hydroxypropanesulfonic acid to obtain a polymer, and then crosslinking the obtained polymer with crosslinking agent N,N-methylenebisacrylamide under the action of hydrochloric acid, followed by neutralization with alkali.

[0014] Preferably, the molar ratio of acrylamide, acrylic acid, 2-acrylamide-2-hydroxypropanesulfonic acid and polyethylene glycol ether acrylate is 2-7:2-5:2-4:2-4.

[0015] Preferably, the molar ratio of the crosslinking agent to the obtained polymer is 1 to 1.5:1.

[0016] Preferably, the initiator used in the free radical polymerization reaction is potassium persulfate.

[0017] Preferably, the amount of initiator used in the free radical polymerization reaction is 3% to 4% of the molar amount of acrylic acid.

[0018] Preferably, 2-acrylamido-2-alkylpropanesulfonic acid is 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-ethylpropanesulfonic acid, 2-acrylamido-2-propylpropanesulfonic acid, 2-acrylamido-2-isopropylpropanesulfonic acid, 2-acrylamido-2-butylpropanesulfonic acid, 2-acrylamido-2-isobutylpropanesulfonic acid, 2-acrylamido-2-sec-butylpropanesulfonic acid, 2-acrylamido-2-tert-butylpropanesulfonic acid, 2-acrylamido-2-pentylpropanesulfonic acid, 2-acrylamido-2-isopentylpropanesulfonic acid, 2-acrylamido-2-neopentylpropanesulfonic acid, 2-acrylamido-2-tert-pentylpropanesulfonic acid, or 2-acrylamido-2-hexylpropanesulfonic acid.

[0019] Preferably, the polyethylene glycol ether acrylate is prepared by esterification of acrylic acid and polyethylene glycol under the combined action of a catalyst and a polymerization inhibitor.

[0020] More preferably, the molar ratio of polyethylene glycol to acrylic acid is 3-6:1-3.

[0021] More preferably, the amount of catalyst is 3% to 5% of the molar amount of polyethylene glycol, and the amount of polymerization inhibitor is 0.4% to 0.5% of the molar amount of acrylic acid.

[0022] More preferably, the catalyst is one of sulfuric acid, concentrated sulfuric acid, aminosulfonic acid, p-toluenesulfonic acid, and heteropoly acid, with concentrated sulfuric acid being preferred.

[0023] More preferably, the polymerization inhibitor is hydroquinone.

[0024] According to the above scheme, the preparation method of the super absorbent and water-releasing composite shrinkage reducer is as follows: using acrylic acid and polyethylene glycol, under the combined action of a catalyst and a polymerization inhibitor, an intermediate polyethylene glycol ether acrylate is generated through an esterification reaction. Then, the obtained intermediate polyethylene glycol ether acrylate is polymerized with acrylic acid, acrylamide and 2-acrylamido-2-hydroxypropanesulfonic acid under the action of an initiator through a free radical polymerization reaction. The resulting polymer and crosslinking agent are then crosslinked under the action of hydrochloric acid, followed by neutralization with alkali. Finally, the super absorbent and water-releasing composite shrinkage reducer is obtained through processes such as shearing, washing, drying, pulverizing and sieving.

[0025] According to the above scheme, the specific steps for preparing the super absorbent and water-releasing composite shrinkage reducing agent are as follows:

[0026] (1) Polymerization reaction

[0027] The mixture is rinsed with N2, then deionized water, acrylic acid and acrylamide are added. The temperature is gradually raised to 50-65°C. The initiator, polyethylene glycol ether acrylate and 2-acrylamide-2-hydroxypropanesulfonic acid aqueous solution are added dropwise over 2-3 hours. After the addition is complete, the mixture is kept at a constant temperature for 2-3 hours. The reaction is then terminated by cooling the reactants.

[0028] (2) Crosslinking reaction

[0029] The hydrochloric acid solution was stirred and heated to 45°C. The polymer and crosslinking agent aqueous solution obtained in step (1) were added dropwise over a period of 2 to 3 hours. The mixture was then kept at a constant temperature for 1.5 to 2 hours.

[0030] (3) Neutralization reaction

[0031] Sodium hydroxide aqueous solution was added dropwise to the reactants prepared in step (2) to carry out a neutralization reaction. The pH value of the solution was adjusted to 7-8. Finally, after processes such as cutting, washing, drying, crushing, and sieving, irregular granular super water-absorbing and water-releasing composite shrinkage reducer with a particle size of 0.1mm-0.15mm was obtained.

[0032] Preferably, in step (1), the polyethylene glycol ether acrylate is prepared by mixing acrylic acid, polyethylene glycol, catalyst and polymerization inhibitor in a certain proportion, stirring and heating to 85-90°C, esterifying for 2-3 hours, and distilling under reduced pressure to obtain polyethylene glycol ether acrylate.

[0033] Preferably, in step (2), the concentration of the hydrochloric acid solution is 25-30%.

[0034] Preferably, in step (3), the concentration of the sodium hydroxide aqueous solution is 10-15%.

[0035] According to the above scheme, the cement has a strength grade of 42.5 and a specific surface area of ​​350-360 m². 2 / kg of low-heat silicate cement; the fly ash is Grade II fly ash with a fineness (0.045mm sieve residue) of 22.5-23.5% and a water requirement ratio of 92-95%; the slag powder has a density of 2.83-2.85 g / cm³. 3 Specific surface area 440-450 m² 2 / kg of S95 grade slag powder; the fine aggregate has a fineness modulus of 2.5-2.7 and an apparent density of 2600-2650 kg / m³. 3 River sand with a mud content of 0.8-1.0%; the coarse aggregate has an apparent density of 2600-2640 kg / cm³. 3 The continuously graded crushed stone has a strength of 2.6-2.8% and a particle size of 5mm-31.5mm; the admixture is a polycarboxylate superplasticizer with a water reduction rate of 28-30%.

[0036] This invention provides a method for preparing the above-mentioned shrinkage-reducing and crack-resistant mass concrete, comprising the following steps:

[0037] (1) Weigh cement, fly ash, slag powder, water, admixture and fine aggregate in the proportion, mix them evenly to obtain a uniformly mixed cement mortar.

[0038] (2) Add coarse aggregate and high water absorption and water release composite shrinkage reducer to the cement mortar obtained in step (1) in proportion, stir evenly, and you will get a shrinkage-reducing and crack-resistant large-volume concrete with a certain fluidity.

[0039] This invention provides a large-volume concrete, comprising a highly absorbent and water-releasing composite shrinkage-reducing agent, which effectively reduces the autogenous shrinkage of large-volume concrete; wherein:

[0040] The hydration of the carboxylic acid, hydroxyl, sulfonic acid, and amino groups in the superabsorbent and water-releasing composite shrinkage reducer allows for the chemical adsorption of water molecules, absorbing tens to thousands of times its own weight in water. Moreover, the composite shrinkage reducer itself has a three-dimensional cross-linked network structure, which can physically adsorb the absorbed water through capillary action and hydrogen bonding, trapping it inside the network structure. Even under pressure, the water is difficult to escape, resulting in good water retention. When the relative humidity inside the cement stone decreases, the highly absorbent and water-releasing components, acting as a "reservoir," slowly release water under the influence of capillary negative pressure and humidity gradient. This water is easily dispersed to compensate for the water evaporated due to the lower relative humidity of the external environment compared to the internal humidity, ensuring a higher internal relative humidity and thus reducing the drying shrinkage of large-volume concrete. On the other hand, the release of water promotes the hydration of the cement matrix, resulting in more complete hydration and a denser structure. The density of the concrete's pore structure and the amount of water available for evaporation inside the concrete are the main factors affecting shrinkage; that is, the denser the pore structure, the slower the rate of water loss, and therefore the smaller the drying shrinkage.

[0041] Meanwhile, the superabsorbent and water-releasing composite shrinkage reducer is also composed of organic chemical surface-active groups. These surface-active groups contain hydrophilic polar groups (carboxylic acid groups, hydroxyl groups, sulfonic acid groups, and amino groups) and hydrophobic non-polar groups (methyl groups). Water is a strongly polar liquid. When the surfactant dissolves in water, according to the principle of attraction between like polarities and repulsion between dissimilar polarities, the hydrophilic groups attract water molecules and dissolve in water, while the hydrophobic groups repel water molecules and leave the water. As a result, the surface-active group components are adsorbed on the interface between the two phases, which reduces the interfacial tension between the two phases. This reduces the additional pressure on the capillary during the water loss process, reduces the shrinkage stress generated by the capillary pores during water loss, and thus reduces the self-shrinkage of large-volume concrete.

[0042] The beneficial effects of this invention are as follows:

[0043] This invention provides a mass concrete comprising a highly absorbent and water-releasing composite shrinkage-reducing agent with a three-dimensional cross-linked network structure. On one hand, it acts as a "reservoir," slowly releasing moisture as the relative humidity inside the cement paste decreases, thus maintaining internal relative humidity. On the other hand, the moisture release promotes the hydration of the cement matrix, making the concrete structure denser and reducing the drying shrinkage of the mass concrete. Furthermore, the composite shrinkage-reducing agent contains surface-active groups; its hydrophilic polar groups and hydrophobic non-polar groups are beneficial for reducing the autogenous shrinkage of the mass concrete. The shrinkage-reducing and crack-resistant mass concrete obtained by this invention, while satisfying mechanical properties and workability requirements, further solves the problems of large shrinkage and easy cracking inherent in traditional mass concrete, and has significant application prospects. Detailed Implementation

[0044] To better understand the present invention, the following description, in conjunction with embodiments, further illustrates the content of the present invention, but the content of the present invention is not limited to the scope described in the embodiments.

[0045] In the following examples, the specific parameters of the required raw materials are as follows:

[0046] The cement has a strength grade of 42.5 and a specific surface area of ​​360 m². 2 Low-heat silicate cement per kg.

[0047] The fly ash is Class II fly ash with a fineness (0.045mm sieve residue) of 23.5% and a water requirement ratio of 95%.

[0048] The slag powder has a density of 2.85 g / cm³. 3 Specific surface area 450m² 2 / kg of S95 grade slag powder.

[0049] The fine aggregate has a fineness modulus of 2.7 and an apparent density of 2650 kg / m³. 3River sand with a mud content of 1.0%.

[0050] The coarse aggregate has an apparent density of 2640 kg / cm³. 3 Continuously graded crushed stone with a strength of 2.8% and a particle size of 5mm to 31.5mm.

[0051] The admixture is a polycarboxylate superplasticizer with a water reduction rate of 30%.

[0052] Example 1

[0053] The preparation of a superabsorbent and water-releasing composite shrinkage reducing agent includes the following steps:

[0054] (1) Esterification reaction

[0055] 4 mol of acrylic acid, 3 mol of polyethylene glycol, 0.09 mol of concentrated sulfuric acid and 0.016 mol of hydroquinone were mixed, stirred and heated to 90°C, and esterified for 3 hours. Polyethylene glycol ether acrylate was obtained by vacuum distillation.

[0056] (2) Polymerization reaction

[0057] Rinse the four-necked flask with N2, then add 500g of deionized water, 2mol of acrylic acid and 2mol of acrylamide, and gradually raise the temperature to 50℃. Add 0.06mol of potassium persulfate, 2mol of polyethylene glycol ether acrylate obtained in step (1) and 2mol of 2-acrylamide-2-methylpropanesulfonic acid aqueous solution dropwise over a period of 2 hours. After the addition is complete, keep the temperature constant for 2 hours and then cool the reactants to terminate the reaction.

[0058] (3) Crosslinking reaction

[0059] Add a certain amount of hydrochloric acid solution to a three-necked flask, stir and heat to 45°C, and add 1 mol of the polymer obtained in step (2) and 1 mol of N,N-methylenebisacrylamide aqueous solution dropwise over a period of 2.5 h. Then, react at a constant temperature for 1.5 h.

[0060] (4) Neutralization reaction

[0061] While stirring, sodium hydroxide aqueous solution was added dropwise to the reactants prepared in step (3) to carry out a neutralization reaction. The pH value of the solution was adjusted to 7. Finally, after processes such as cutting, washing, drying, crushing, and sieving, irregular granular super water-absorbing and water-releasing composite shrinkage reducer with a particle size of 0.1 mm to 0.15 mm was obtained.

[0062] Example 2

[0063] The preparation of a superabsorbent and water-releasing composite shrinkage reducing agent includes the following steps:

[0064] (1) Esterification reaction

[0065] 4 mol of acrylic acid, 3 mol of polyethylene glycol, 0.09 mol of concentrated sulfuric acid and 0.016 mol of hydroquinone were mixed, stirred and heated to 90°C, and esterified for 3 hours. Polyethylene glycol ether acrylate was obtained by vacuum distillation.

[0066] (2) Polymerization reaction

[0067] Rinse the four-necked flask with N2, then add 500g of deionized water, 2mol of acrylic acid and 2mol of acrylamide, and gradually raise the temperature to 50℃. Add 0.06mol of potassium persulfate, 2mol of polyethylene glycol ether acrylate obtained in step (1) and 2mol of 2-acrylamide-2-ethylpropanesulfonic acid aqueous solution dropwise over a period of 2 hours. After the addition is complete, keep the temperature constant for 2 hours and then cool the reactants to terminate the reaction.

[0068] (3) Crosslinking reaction

[0069] Add a certain amount of hydrochloric acid solution to a three-necked flask, stir and heat to 45°C, and add 1 mol of the polymer obtained in step (2) and 1 mol of N,N-methylenebisacrylamide aqueous solution dropwise over a period of 2.5 h. Then, react at a constant temperature for 1.5 h.

[0070] (4) Neutralization reaction

[0071] While stirring, sodium hydroxide aqueous solution was added dropwise to the reactants prepared in step (3) to carry out a neutralization reaction. The pH value of the solution was adjusted to 7. Finally, after processes such as cutting, washing, drying, crushing, and sieving, irregular granular super water-absorbing and water-releasing composite shrinkage reducer with a particle size of 0.1 mm to 0.15 mm was obtained.

[0072] Example 3

[0073] The preparation of a superabsorbent and water-releasing composite shrinkage reducing agent includes the following steps:

[0074] (1) Esterification reaction

[0075] 4 mol of acrylic acid, 3 mol of polyethylene glycol, 0.09 mol of concentrated sulfuric acid and 0.016 mol of hydroquinone were mixed, stirred and heated to 90°C, and esterified for 3 hours. Polyethylene glycol ether acrylate was obtained by vacuum distillation.

[0076] (2) Polymerization reaction

[0077] Rinse the four-necked flask with N2, then add 500g of deionized water, 2mol of acrylic acid and 2mol of acrylamide, and gradually raise the temperature to 50℃. Add 0.06mol of potassium persulfate, 2mol of polyethylene glycol ether acrylate obtained in step (1) and 2mol of 2-acrylamide-2-butylpropanesulfonic acid aqueous solution dropwise over a period of 2 hours. After the addition is complete, keep the temperature constant for 2 hours and then cool the reactants to terminate the reaction.

[0078] (3) Crosslinking reaction

[0079] Add a certain amount of hydrochloric acid solution to a three-necked flask, stir and heat to 45°C, and add 1 mol of the polymer obtained in step (2) and 1 mol of N,N-methylenebisacrylamide aqueous solution dropwise over a period of 2.5 h. Then, react at a constant temperature for 1.5 h.

[0080] (4) Neutralization reaction

[0081] While stirring, sodium hydroxide aqueous solution was added dropwise to the reactants prepared in step (3) to carry out a neutralization reaction. The pH value of the solution was adjusted to 7. Finally, after processes such as cutting, washing, drying, crushing, and sieving, irregular granular super water-absorbing and water-releasing composite shrinkage reducer with a particle size of 0.1 mm to 0.15 mm was obtained.

[0082] Example 4

[0083] The preparation of a superabsorbent and water-releasing composite shrinkage reducing agent includes the following steps:

[0084] (1) Esterification reaction

[0085] 4 mol of acrylic acid, 3 mol of polyethylene glycol, 0.09 mol of concentrated sulfuric acid and 0.016 mol of hydroquinone were mixed, stirred and heated to 90°C, and esterified for 3 hours. Polyethylene glycol ether acrylate was obtained by vacuum distillation.

[0086] (2) Polymerization reaction

[0087] Rinse the four-necked flask with N2, then add 500g of deionized water, 5mol of acrylic acid and 2mol of acrylamide, and gradually raise the temperature to 50℃. Add 0.15mol of potassium persulfate, 2mol of polyethylene glycol ether acrylate obtained in step (1) and 2mol of 2-acrylamide-2-ethylpropanesulfonic acid aqueous solution dropwise over a period of 2 hours. After the addition is complete, keep the temperature constant for 2 hours and then cool the reactants to terminate the reaction.

[0088] (3) Crosslinking reaction

[0089] Add a certain amount of hydrochloric acid solution to a three-necked flask, stir and heat to 45°C, and add 1 mol of the polymer obtained in step (2) and 1 mol of N,N-methylenebisacrylamide aqueous solution dropwise over a period of 2.5 h. Then, react at a constant temperature for 1.5 h.

[0090] (4) Neutralization reaction

[0091] While stirring, sodium hydroxide aqueous solution was added dropwise to the reactants prepared in step (3) to carry out a neutralization reaction. The pH value of the solution was adjusted to 7. Finally, after processes such as cutting, washing, drying, crushing, and sieving, irregular granular super water-absorbing and water-releasing composite shrinkage reducer with a particle size of 0.1 mm to 0.15 mm was obtained.

[0092] Example 5

[0093] The preparation of a superabsorbent and water-releasing composite shrinkage reducing agent includes the following steps:

[0094] (1) Esterification reaction

[0095] 4 mol of acrylic acid, 3 mol of polyethylene glycol, 0.09 mol of concentrated sulfuric acid and 0.016 mol of hydroquinone were mixed, stirred and heated to 90°C, and esterified for 3 hours. Polyethylene glycol ether acrylate was obtained by vacuum distillation.

[0096] (2) Polymerization reaction

[0097] Rinse the four-necked flask with N2, then add 500g of deionized water, 2mol of acrylic acid and 7mol of acrylamide, and gradually raise the temperature to 50℃. Add 0.06mol of potassium persulfate, 2mol of polyethylene glycol ether acrylate obtained in step (1) and 2mol of 2-acrylamide-2-ethylpropanesulfonic acid aqueous solution dropwise over a period of 2 hours. After the addition is complete, keep the temperature constant for 2 hours and then cool the reactants to terminate the reaction.

[0098] (3) Crosslinking reaction

[0099] Add a certain amount of hydrochloric acid solution to a three-necked flask, stir and heat to 45°C, and add 1 mol of the polymer obtained in step (2) and 1 mol of N,N-methylenebisacrylamide aqueous solution dropwise over a period of 2.5 h. Then, react at a constant temperature for 1.5 h.

[0100] (4) Neutralization reaction

[0101] While stirring, sodium hydroxide aqueous solution was added dropwise to the reactants prepared in step (3) to carry out a neutralization reaction. The pH value of the solution was adjusted to 7. Finally, after processes such as cutting, washing, drying, crushing, and sieving, irregular granular super water-absorbing and water-releasing composite shrinkage reducer with a particle size of 0.1 mm to 0.15 mm was obtained.

[0102] Example 6

[0103] The preparation of a superabsorbent and water-releasing composite shrinkage reducing agent includes the following steps:

[0104] (1) Esterification reaction

[0105] 4 mol of acrylic acid, 3 mol of polyethylene glycol, 0.09 mol of concentrated sulfuric acid and 0.016 mol of hydroquinone were mixed, stirred and heated to 90°C, and esterified for 3 hours. Polyethylene glycol ether acrylate was obtained by vacuum distillation.

[0106] (2) Polymerization reaction

[0107] Rinse the four-necked flask with N2, then add 500g of deionized water, 5mol of acrylic acid and 2mol of acrylamide, and gradually raise the temperature to 50℃. Add 0.06mol of potassium persulfate, 2mol of polyethylene glycol ether acrylate obtained in step (1) and 2mol of 2-acrylamide-2-butylpropanesulfonic acid aqueous solution dropwise over a period of 2 hours. After the addition is complete, keep the temperature constant for 2 hours, and then cool the reactants to terminate the reaction.

[0108] (3) Crosslinking reaction

[0109] Add a certain amount of hydrochloric acid solution to a three-necked flask, stir and heat to 45°C, and add 1 mol of the polymer obtained in step (2) and 1 mol of N,N-methylenebisacrylamide aqueous solution dropwise over a period of 2.5 h. Then, react at a constant temperature for 1.5 h.

[0110] (4) Neutralization reaction

[0111] While stirring, sodium hydroxide aqueous solution was added dropwise to the reactants prepared in step (3) to carry out a neutralization reaction. The pH value of the solution was adjusted to 7. Finally, after processes such as cutting, washing, drying, crushing, and sieving, irregular granular super water-absorbing and water-releasing composite shrinkage reducer with a particle size of 0.1 mm to 0.15 mm was obtained.

[0112] Example 7

[0113] The preparation of a superabsorbent and water-releasing composite shrinkage reducing agent includes the following steps:

[0114] (1) Esterification reaction

[0115] 4 mol of acrylic acid, 3 mol of polyethylene glycol, 0.09 mol of concentrated sulfuric acid and 0.016 mol of hydroquinone were mixed, stirred and heated to 90°C, and esterified for 3 hours. Polyethylene glycol ether acrylate was obtained by vacuum distillation.

[0116] (2) Polymerization reaction

[0117] Rinse the four-necked flask with N2, then add 500g of deionized water, 2mol of acrylic acid and 7mol of acrylamide, and gradually raise the temperature to 50℃. Add 0.06mol of potassium persulfate, 2mol of polyethylene glycol ether acrylate obtained in step (1) and 2mol of 2-acrylamide-2-tert-butylpropanesulfonic acid aqueous solution dropwise over 2 hours. After the addition is complete, keep the temperature constant for 2 hours and then cool the reactants to terminate the reaction.

[0118] (3) Crosslinking reaction

[0119] Add a certain amount of hydrochloric acid solution to a three-necked flask, stir and heat to 45°C, and add 1 mol of the polymer obtained in step (2) and 1 mol of N,N-methylenebisacrylamide aqueous solution dropwise over a period of 2.5 h. Then, react at a constant temperature for 1.5 h.

[0120] (4) Neutralization reaction

[0121] While stirring, sodium hydroxide aqueous solution was added dropwise to the reactants prepared in step (3) to carry out a neutralization reaction. The pH value of the solution was adjusted to 7. Finally, after processes such as cutting, washing, drying, crushing, and sieving, irregular granular super water-absorbing and water-releasing composite shrinkage reducer with a particle size of 0.1 mm to 0.15 mm was obtained.

[0122] Example 8

[0123] A method for preparing shrinkage-reducing and crack-resistant mass concrete includes the following steps:

[0124] 1) Weigh 350 parts cement, 60 parts fly ash, 120 parts slag powder, 150 parts water, 12 parts admixture and 720 parts fine aggregate and add them to the mixer. Mix them evenly to obtain a uniformly mixed cement mortar.

[0125] 2) Add 1150 parts of coarse aggregate and 20 parts of the high water absorption and water release composite shrinkage reducer obtained in Example 1 to the cement mortar obtained in step (1) and stir evenly to obtain a shrinkage-reducing and crack-resistant large-volume concrete with a certain fluidity.

[0126] Example 9

[0127] A method for preparing shrinkage-reducing and crack-resistant mass concrete includes the following steps:

[0128] 1) Weigh 350 parts cement, 60 parts fly ash, 120 parts slag powder, 150 parts water, 12 parts admixture and 720 parts fine aggregate and add them to the mixer. Mix them evenly to obtain a uniformly mixed cement mortar.

[0129] 2) Add 1150 parts of coarse aggregate and 20 parts of the high water absorption and water release composite shrinkage reducer obtained in Example 2 to the cement mortar obtained in step (1) and stir evenly to obtain a shrinkage-reducing and crack-resistant large-volume concrete with a certain fluidity.

[0130] Example 10

[0131] A method for preparing shrinkage-reducing and crack-resistant mass concrete includes the following steps:

[0132] 1) Weigh 350 parts cement, 60 parts fly ash, 120 parts slag powder, 150 parts water, 12 parts admixture and 720 parts fine aggregate and add them to the mixer. Mix them evenly to obtain a uniformly mixed cement mortar.

[0133] 2) Add 1150 parts of coarse aggregate and 20 parts of the high water absorption and water release composite shrinkage reducer obtained in Example 3 to the cement mortar obtained in step (1) and stir evenly to obtain a shrinkage-reducing and crack-resistant large-volume concrete with a certain fluidity.

[0134] Example 11

[0135] A method for preparing shrinkage-reducing and crack-resistant mass concrete includes the following steps:

[0136] 1) Weigh 350 parts cement, 60 parts fly ash, 120 parts slag powder, 150 parts water, 12 parts admixture and 720 parts fine aggregate and add them to the mixer. Mix them evenly to obtain a uniformly mixed cement mortar.

[0137] 2) Add 1150 parts of coarse aggregate and 20 parts of the high water absorption and water release composite shrinkage reducer obtained in Example 4 to the cement mortar obtained in step (1) and stir evenly to obtain a shrinkage-reducing and crack-resistant large-volume concrete with a certain fluidity.

[0138] Example 12

[0139] A method for preparing shrinkage-reducing and crack-resistant mass concrete includes the following steps:

[0140] 1) Weigh 350 parts cement, 60 parts fly ash, 120 parts slag powder, 150 parts water, 12 parts admixture and 720 parts fine aggregate and add them to the mixer. Mix them evenly to obtain a uniformly mixed cement mortar.

[0141] 2) Add 1150 parts of coarse aggregate and 20 parts of the high water absorption and water release composite shrinkage reducer obtained in Example 5 to the cement mortar obtained in step (1) and stir evenly to obtain a shrinkage-reducing and crack-resistant large-volume concrete with a certain fluidity.

[0142] Example 13

[0143] A method for preparing shrinkage-reducing and crack-resistant mass concrete includes the following steps:

[0144] 1) Weigh 350 parts cement, 60 parts fly ash, 120 parts slag powder, 150 parts water, 12 parts admixture and 720 parts fine aggregate and add them to the mixer. Mix them evenly to obtain a uniformly mixed cement mortar.

[0145] 2) Add 1150 parts of coarse aggregate and 20 parts of the high water absorption and water release composite shrinkage reducer obtained in Example 6 to the cement mortar obtained in step (1) and stir evenly to obtain a shrinkage-reducing and crack-resistant large-volume concrete with a certain fluidity.

[0146] Example 14

[0147] A method for preparing shrinkage-reducing and crack-resistant mass concrete includes the following steps:

[0148] 1) Weigh 350 parts cement, 60 parts fly ash, 120 parts slag powder, 150 parts water, 12 parts admixture and 720 parts fine aggregate and add them to the mixer. Mix them evenly to obtain a uniformly mixed cement mortar.

[0149] 2) Add 1150 parts of coarse aggregate and 20 parts of the high water absorption and water release composite shrinkage reducer obtained in Example 7 to the cement mortar obtained in step (1) and stir evenly to obtain a shrinkage-reducing and crack-resistant large-volume concrete with a certain fluidity.

[0150] Blank example

[0151] A method for preparing large-volume concrete includes the following steps:

[0152] 1) Weigh 350 parts cement, 60 parts fly ash, 120 parts slag powder, 150 parts water, 12 parts admixture and 720 parts fine aggregate and add them to the mixer. Mix them evenly to obtain a uniformly mixed cement mortar.

[0153] 2) Add 1150 parts of coarse aggregate to the cement mortar obtained in step (1) and stir evenly to obtain large-volume concrete with a certain degree of fluidity.

[0154] The compressive strength of the shrinkage-reducing and crack-resistant mass concrete prepared in Examples 8-14 and the blank example was tested, and the results are shown in Table 1.

[0155] Table 1. Compressive strength (MPa) of the shrinkage-reducing and crack-resistant mass concrete prepared in Examples 8-14 and the blank example.

[0156]

[0157]

[0158] As shown in Table 1, the experimental results indicate that, compared with the blank example, the addition of the superabsorbent and water-releasing composite shrinkage-reducing agent reduces the compressive strength of mass concrete at various ages to varying degrees. Specifically, compared with Example 8 in Examples 9 and 10, and with Example 11 in Examples 13 and 14 in Examples 12, it can be seen that the compressive strength of mass concrete at various ages decreases with the increase of the anti-self-shrinkage component (i.e., hydrophobic non-polar groups, such as methyl groups). This is because the incorporation of the anti-self-shrinkage component prolongs the setting time of the mass concrete, affecting cement hydration, hindering the increase of pH value in the cement paste pore solution, and delaying cement hydration, which reduces the heat release during cement hydration and delays the time of the heat release peak, thus affecting the mechanical properties of the mass concrete. Simultaneously, the anti-self-shrinkage component... The incorporation of the components has a certain air-entraining effect. Under the effect of air entrainment, the fluidity and pore structure of the mass concrete paste will change, which will have an adverse effect on the strength of the mass concrete. On the other hand, compared with Example 9, Examples 11 and 12, and Examples 13 and 14, compared with Example 10, all show that with the increase of the anti-drying shrinkage component (i.e., strong hydrophilic groups such as carboxylic acid group, hydroxyl group, sulfonic acid group and amino group), the compressive strength of the mass concrete at all ages increases. This is because when the relative humidity inside the mass concrete decreases, the anti-drying shrinkage component will release water into the cement matrix for a longer period of time, so that the cement hydration is more complete, the degree of cement hydration is improved, and the adverse effect of the anti-self-shrinkage component on cement hydration is greatly mitigated.

[0159] The drying shrinkage values ​​of the shrinkage-reducing and crack-resistant mass concrete prepared in Examples 8-14 and the blank example at various ages were tested, and the results are shown in Table 2.

[0160] Table 2. Drying shrinkage values ​​(μm / m) of the shrinkage-reducing and crack-resistant mass concrete prepared in Examples 8-14 and the blank example.

[0161]

[0162] As shown in Table 2, the experimental results indicate that, compared with the blank example, the addition of the superabsorbent and water-releasing composite shrinkage-reducing agent reduces the drying shrinkage of mass concrete at various ages to varying degrees. Specifically, compared with Example 8 in Examples 9 and 10, and with Example 11 in Examples 13 and 14 in Examples 12, the drying shrinkage values ​​of mass concrete at various ages decrease to varying degrees with the increase of the anti-self-shrinkage component. Furthermore, compared with Example 9 in Examples 11 and 12, and with Example 10 in Examples 13 and 14, the drying shrinkage value of mass concrete also decreases to varying degrees with the increase of the anti-drying shrinkage component. Moreover, compared with Example 9 in Examples 13 and 14, the simultaneous increase of both the anti-self-shrinkage component and the anti-drying shrinkage component further reduces the drying shrinkage value of mass concrete, and its value is lower than that of adding either the anti-self-shrinkage component alone. This demonstrates that the anti-self-shrinkage component and the anti-drying shrinkage component not only exhibit good compatibility in reducing the drying shrinkage of mass concrete but also produce a good synergistic effect.

[0163] The 28-day autogenous shrinkage rate and crack resistance of the shrinkage-reducing and crack-resistant mass concrete prepared in Examples 8-14 and the blank example were tested. The results are shown in Table 3.

[0164] Table 3 shows the 28-day autogenous shrinkage rate and crack resistance of the shrinkage-reducing and crack-resistant mass concrete prepared in Examples 8-14 and the blank example.

[0165]

[0166] As shown in Table 3, compared with the blank example, the addition of the superabsorbent and water-releasing composite shrinkage-reducing agent reduces the 28-day autogenous shrinkage rate of mass concrete and improves its crack resistance to varying degrees. Specifically, compared with Example 8, Examples 9 and 10, Examples 13 and 11, and Examples 14 and 12 all show that with the increase of the anti-shrinkage component, the 28-day autogenous shrinkage rate and the total crack area per unit area of ​​the mass concrete decrease to varying degrees. Furthermore, compared with Example 9, Examples 11 and 12, and Examples 13 and 14, and Example 10, all show that with the increase of the anti-drying shrinkage component, the overall... The 28-day autogenous shrinkage rate and total crack area per unit area of ​​the large-volume concrete were also reduced to varying degrees. On the other hand, compared with Example 9, Examples 13 and 14 show that with the simultaneous increase of the autogenous shrinkage resistance component and the drying shrinkage resistance component, the 28-day autogenous shrinkage rate and total crack area per unit area of ​​the large-volume concrete were further reduced. Their 28-day autogenous shrinkage rate and total crack area per unit area were lower than those achieved by increasing the autogenous shrinkage resistance component or the drying shrinkage resistance component alone. This indicates that the autogenous shrinkage resistance component and the drying shrinkage resistance component not only showed good compatibility in reducing the 28-day autogenous shrinkage rate and total crack area per unit area of ​​the large-volume concrete, but also produced a good synergistic effect.

[0167] The specific performance testing experiments refer to the following standards:

[0168] Compressive strength test method: Specimens shall be prepared and cured in accordance with Part 4 of the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019). After reaching the specified age, the compressive strength shall be tested in accordance with Part 5 of the "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0169] Shrinkage performance testing method: Shrinkage testing shall be conducted according to Part 8 of the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082-2009).

[0170] Cracking detection method: The total crack area per unit area is detected according to Part 9 of the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082-2009).

[0171] 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; therefore, any obvious variations or modifications derived therefrom remain within the scope of protection of this invention.

[0172] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A shrinkage-reducing and crack-resistant mass concrete, characterized in that, By mass, it includes the following components: Cement: 320-350 parts Water: 140-150 parts Fly ash: 50-60 parts Slag powder: 100-120 parts Fine aggregate: 700-720 parts Coarse aggregate: 980~1150 parts Additive: 10-12 parts Superabsorbent and water-releasing composite shrinkage reducer: 15-20 parts; The superabsorbent and water-releasing composite shrinkage reducing agent is prepared by free radical polymerization of polyethylene glycol ether acrylate with acrylic acid, acrylamide, and 2-acrylamide-2-hydroxypropanesulfonic acid. The resulting polymer is then crosslinked with the crosslinking agent N,N-methylenebisacrylamide under hydrochloric acid, followed by neutralization with alkali. Wherein: The molar ratio of acrylamide, acrylic acid, 2-acrylamide-2-hydroxypropanesulfonic acid and polyethylene glycol ether acrylate is 2~7:2~5:2~4:2~4; 2-Acrylamido-2-alkylpropanesulfonic acid is 2-acrylamido-2-ethylpropanesulfonic acid, 2-acrylamido-2-propylpropanesulfonic acid, 2-acrylamido-2-isopropylpropanesulfonic acid, 2-acrylamido-2-butylpropanesulfonic acid, 2-acrylamido-2-isobutylpropanesulfonic acid, 2-acrylamido-2-sec-butylpropanesulfonic acid, 2-acrylamido-2-tert-butylpropanesulfonic acid, 2-acrylamido-2-pentylpropanesulfonic acid, 2-acrylamido-2-isopentylpropanesulfonic acid, 2-acrylamido-2-neopentylpropanesulfonic acid, 2-acrylamido-2-tert-pentylpropanesulfonic acid, or 2-acrylamido-2-hexylpropanesulfonic acid.

2. The shrinkage-reducing and crack-resistant mass concrete according to claim 1, characterized in that, The molar ratio of crosslinking agent to the resulting polymer is 1~1.5:

1.

3. The shrinkage-reducing and crack-resistant mass concrete according to claim 1, characterized in that, The initiator used in the free radical polymerization reaction is potassium persulfate.

4. The shrinkage-reducing and crack-resistant mass concrete according to claim 1, characterized in that, The amount of initiator used in the free radical polymerization reaction is 3% to 4% of the molar amount of acrylic acid.

5. The shrinkage-reducing and crack-resistant mass concrete according to claim 1, characterized in that, The polyethylene glycol ether acrylate is prepared by esterification of acrylic acid and polyethylene glycol under the combined action of a catalyst and a polymerization inhibitor.

6. The shrinkage-reducing and crack-resistant mass concrete according to claim 1, characterized in that, The specific steps for preparing the superabsorbent and water-releasing composite shrinkage reducing agent are as follows: (1) Polymerization reaction The mixture is rinsed with N2, then deionized water, acrylic acid and acrylamide are added. The temperature is gradually raised to 50-65°C. The initiator, polyethylene glycol ether acrylate and 2-acrylamide-2-hydroxypropanesulfonic acid aqueous solution are added dropwise over 2-3 hours. After the addition is complete, the mixture is kept at a constant temperature for 2-3 hours. The reaction is then terminated by cooling the reactants. (2) Crosslinking reaction The hydrochloric acid solution was stirred and heated to 45°C. The polymer obtained in step (1) and the crosslinking agent aqueous solution were then added dropwise. The dropping time is 2-3 hours, followed by a constant temperature reaction for 1.5-2 hours; (3) Neutralization reaction An aqueous solution of sodium hydroxide was added dropwise to the reactants prepared in step (2) to carry out a neutralization reaction and adjust the pH of the solution. With a value of 7~8, the product undergoes shearing, washing, drying, crushing, and sieving processes to finally obtain irregular granular superabsorbent and water-releasing composite shrinkage reducer with a particle size of 0.1mm~0.15mm.

7. A method for preparing shrinkage-reducing and crack-resistant mass concrete according to any one of claims 1-6, characterized in that, Includes the following steps: 1) Weigh out cement, fly ash, slag powder, water, admixtures and fine aggregates in the correct proportions, mix them evenly to obtain a uniformly mixed cement mortar; 2) Add coarse aggregate and high water absorption and water release composite shrinkage reducer to the cement mortar obtained in step 1) in proportion, stir evenly, and you will get a shrinkage-reducing and crack-resistant mass concrete with a certain fluidity.

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