Anti-cracking concrete based on response type water sustained-release microcapsules and preparation method of anti-cracking concrete

Abstract

The invention provides anti-cracking concrete based on response type water sustained-release microcapsules and a preparation method of the anti-cracking concrete, and belongs to the technical field of concrete materials. The concrete comprises cement, aggregate, a mineral admixture, water, a water reducing agent and water slow-release microcapsules. The microcapsule takes hydroxypropyl methyl cellulose and chitosan as slow-release carriers, is grafted with a temperature-sensitive monomer N-isopropylacrylamide and a hydrophilic monomer methoxypolyethylene glycol, is coated with a silane coupling agent on the surface, has temperature-sensitive and salt-sensitive dual response characteristics, and can intelligently release water according to the temperature and ion concentration change in the hydration process. The concrete can effectively regulate and control the hydration process, reduce the shrinkage stress and delay the generation of cracks, and has a remarkable anti-cracking enhancing effect and good construction applicability.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to a crack-resistant concrete based on responsive water-release microcapsules and its preparation method. Background Technology

[0002] Concrete, as the most widely used and core structural material in modern construction engineering, directly determines the safety and service life of buildings through its volume stability and long-term durability, playing an irreplaceable role in ensuring the quality of infrastructure and improving the living environment. The crack resistance of concrete components is a key indicator of their durability, mainly regulated by the internal hydration process, microstructure formation, and environmental stress.

[0003] To improve the crack resistance of concrete, various technical approaches have been developed in the industry. Among them, the chemical admixture modification approach has become one of the mainstream solutions due to its ease of engineering application. In particular, the addition of water-reducing agents, expanding agents, and mineral admixtures aims to reduce water consumption, compensate for shrinkage, or fill pores; and the use of fiber reinforcement technology (such as CN118878238A) forms a physical network in the matrix to bridge and confine cracks. These methods have improved certain crack resistance or impermeability properties of concrete to some extent.

[0004] However, these existing technical solutions still have fundamental limitations in dealing with the complex cracking problem of concrete, especially precast concrete: (1) The mechanism of action is passive and delayed: Water-reducing agents, expansion agents and other technologies mainly focus on "reducing shrinkage sources" or "post-compensation", while fiber reinforcement belongs to "physical crack prevention" after crack initiation. Neither actively intervenes in the core process of cement hydration and cannot solve the endogenous stress caused by uneven energy release in the early and late stages of hydration; (2) It cannot achieve precise matching: Concrete hydration is a dynamic process of exothermic and ion concentration change. Existing technologies cannot intelligently respond to the different water requirements of different stages (such as plastic period, early hardening period and service period) in this process, resulting in a mismatch between water supply and consumption in time and space; (3) During the concrete pouring process, due to the asynchronous hydration of new and old concrete and the large humidity gradient, traditional admixtures are difficult to play a continuous and effective role in this area. The interface area between new and old concrete is still a high-risk area for stress concentration and crack initiation.

[0005] Therefore, the key technical bottleneck that urgently needs to be overcome in this field is: how to develop a control technology that can release water as needed based on the internal state of concrete hydration (such as temperature and ion concentration), so as to coordinate the hydration reaction and balance the development of internal stress from the source, thereby achieving full-cycle crack resistance improvement from the plastic stage to the long-term service stage. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a crack-resistant concrete based on responsive water-release microcapsules and its preparation method, thereby solving the technical problem of "passive lag in concrete crack resistance technology and shrinkage cracking caused by water supply and demand mismatch".

[0007] To achieve the above objectives, the present invention is implemented using the following technical solution: In a first aspect, the present invention provides a crack-resistant concrete based on responsive water-release microcapsules, wherein the crack-resistant concrete is formed by mixing and pouring cement, aggregates, mineral admixtures, water, water-reducing agent and water-release microcapsules. The water-release microcapsules comprise: (1) The sustained-release carrier is formed by cross-linking hydroxypropyl methylcellulose and modified chitosan with glutaraldehyde; (2) A temperature-sensitive monomer is cross-linked onto the modified chitosan through a polymerization reaction; (3) A hydrophilic monomer is grafted into the chitosan structure through a carboxylation reaction and introduced into the sustained-release carrier after pre-modification; (4) Silane coupling agent, coated on the surface of microcapsules.

[0008] Specifically, the aggregate is a mixture of continuously graded crushed stone and river sand in a weight ratio of (3~4):1.

[0009] Specifically, the mineral admixture is metakaolin with an activity index of 110-120% and a particle size of 30-45 μm.

[0010] Specifically, the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a solid content of 20-30%, a water reduction rate of 30-40%, and a retarding time of 4-8 hours.

[0011] Specifically, the mass ratio of hydroxypropyl methylcellulose, modified chitosan, and glutaraldehyde in the sustained-release carrier is (1.4~1.6):1:(0.07~0.13).

[0012] Specifically, the modified chitosan is obtained by reacting and polymerizing pre-modified chitosan and thermosensitive monomer, wherein the mass ratio of pre-modified chitosan to thermosensitive monomer is 1:(0.2~0.3).

[0013] Specifically, the pre-modified chitosan is prepared by reacting a hydrophilic monomer with maleic anhydride and then condensing it with chitosan.

[0014] Specifically, the temperature-sensitive monomer is N-isopropylacrylamide.

[0015] Specifically, the hydrophilic monomer is polyethylene glycol monomethyl ether.

[0016] Secondly, the present invention provides a method for preparing crack-resistant concrete based on responsive water-release microcapsules, comprising the following steps: (1) First, the hydrophilic monomer and maleic anhydride are reacted to obtain carboxylated hydrophilic monomer, and then reacted with chitosan to obtain pre-modified chitosan; the pre-modified chitosan and the thermosensitive monomer are polymerized to obtain modified chitosan, and finally hydroxypropyl methylcellulose and glutaraldehyde are added. The slurry after the reaction is dried and granulated to obtain pre-modified microcapsules, and then coated with silane coupling agent to obtain water-release microcapsules; (2) By weight, mix 100 parts of cement, 300-400 parts of aggregate, and 8-15 parts of mineral admixture. Stir for 1-2 minutes for the first time, add 42-43 parts of water and 0.7-1.0 parts of water-reducing agent, stir for 2-3 minutes for the second time, and finally add 4.5-5.5 parts of water-slow-release microcapsules. Stir for 1-2 minutes for the third time to obtain crack-resistant concrete.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) By introducing temperature-sensitive and salt-sensitive dual-response water slow-release microcapsules, this invention realizes intelligent regulation of water supply during concrete hydration, reduces internal stress caused by hydration heat and water supply-demand mismatch from the source, significantly delays crack initiation, and increases the time to first cracking to more than 80 hours.

[0018] (2) The microcapsules of the present invention are coated with silane coupling agent to ensure that the microcapsules are uniformly dispersed in concrete, enhance the bonding between the microcapsules and the cement matrix, and play the role of intelligent water release and stress buffering.

[0019] (3) The microcapsule morphology design of the present invention is adapted to engineering construction, solving the industry problem of poor compatibility and easy agglomeration of water-release agents with concrete matrix. Attached Figure Description

[0020] Figure 1 This is a diagram of the chemical equations for the synthesis pathway of pre-modified chitosan. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] The core of this invention lies in providing a crack-resistant concrete based on "temperature-sensitive and salt-sensitive dual-response" water-release microcapsules. By designing a microcapsule slow-release system that can synchronously respond to changes in temperature and ion concentration, water can be supplied on demand in time and space, thereby regulating the hydration process from the source, optimizing the microstructure and enhancing the interfacial bonding, and effectively inhibiting various shrinkage cracks caused by the imbalance of water and energy.

[0023] Specifically, the water-release microcapsules use hydroxypropyl methylcellulose and chitosan as sustained-release carriers, and their network strength and anti-swelling ability are enhanced by glutaraldehyde cross-linking. In the system, poly-N-isopropylacrylamide serves as a temperature-sensitive component, with its low critical dissolution temperature designed within the 35-40℃ range, allowing for precise response to hydration exothermic reactions: when the temperature exceeds this threshold, the molecular chains contract and trigger water release. Simultaneously, the hydroxypropyl methylcellulose / chitosan carrier network itself possesses salt-sensitive properties, affecting the Ca2+ content in the cement hydration solution. 2+ It is sensitive to concentration (20-40 mmol / L) and swells in a high calcium ion environment, further accelerating water release, thus constructing a smart water release mechanism with dual temperature-salt response and synergistic effect.

[0024] Based on this, by grafting polyethylene glycol monomethyl ether to enhance the hydrophilicity of the carrier and by using silane coupling agents for surface coating, the chemical bonding between the microcapsules and cement hydration products can be promoted, significantly improving their interfacial adhesion performance with the concrete matrix.

[0025] This system achieves crack prevention through phased water retention and release: In the initial stage (low temperature, low ion concentration), the microcapsule network is stable, locking in water to reduce plastic shrinkage; during the peak of hydration exothermic stage, temperature-sensitive and salt-sensitive effects synergistically trigger rapid water release to meet the hydration reaction requirements and promote the uniform formation of CSH gel and ettringite; in the later stage of hardening, it switches to slow water release to continuously compensate for drying shrinkage. This process not only significantly reduces shrinkage stress at each stage but also disperses internal stress through the elastic particle effect formed by microcapsules in the matrix. Combined with the secondary hydration filling effect of active admixtures such as metakaolin, it jointly achieves matrix densification and interface strengthening, thereby comprehensively improving the crack resistance and durability of concrete.

[0026] In this invention, carboxylated polyethylene glycol monomethyl ether is first prepared by reacting polyethylene glycol monomethyl ether, maleic anhydride, p-toluenesulfonic acid and toluene. The mass ratio of polyethylene glycol monomethyl ether, maleic anhydride, p-toluenesulfonic acid and toluene is 1:(1~1.05):(0.02~0.05):20. The preparation temperature is 100~110℃ and the reaction time is 6~8h.

[0027] After carboxylating the hydrophilic monomer polyethylene glycol monomethyl ether, chitosan dissolved in acetic acid solution is added. Pre-modified chitosan is prepared through a condensation reaction between the carboxyl groups on the pre-modified chitosan and the amino groups on the chitosan. Unsaturated bonds are introduced into the pre-modified chitosan. During the preparation process, condensing agents 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide are added, along with deionized water. A 5% (w / w) sodium hydroxide aqueous solution is used to adjust the... The pH is 5-6. Chitosan, carboxylated polyethylene glycol monomethyl ether, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, 10% acetic acid aqueous solution and deionized water are mixed in a mass ratio of 1:(0.2-0.3):(0.4-0.5):(0.2-0.4):(0.8-1.5):(10-20). The reaction temperature is 20-30℃ and the reaction time is 1-2 hours.

[0028] Next, the thermosensitive monomer N-isopropylacrylamide was added to the pre-modified chitosan, and the modified chitosan was obtained by in-situ polymerization with ammonium persulfate as a free radical initiator to generate poly-N-isopropylacrylamide crosslinked with the pre-modified chitosan. The mass ratio of pre-modified chitosan, N-isopropylacrylamide, ammonium persulfate and deionized water was 1:(0.2~0.3):(0.05~0.06):(10~20), the reaction temperature was 60~70℃, and the reaction time was 1~2h. Hydroxypropyl methylcellulose and glutaraldehyde were added to modified chitosan. The unreacted amino groups in the modified chitosan continued to participate in the reaction of glutaraldehyde and hydroxypropyl methylcellulose, eventually forming a sustained-release carrier that encapsulates thermosensitive monomers and hydrophilic monomers. The mass ratio of modified chitosan, hydroxypropyl methylcellulose, glutaraldehyde and 10% citric acid aqueous solution was (1.4~1.6):1:(0.07~0.13):(40~50), the reaction temperature was 25~30℃, and the reaction time was 1~2h.

[0029] In this invention, the viscosity of hydroxypropyl methylcellulose is 5 × 10⁻⁶. 4 ~1×10 5 The slurry has a viscosity of 5000-8000 mPa·s, a methoxy content of 28-30%, a degree of deacetylation of chitosan ≥85%, and a molecular weight of 50000-80000 Da; the molecular weight of polyethylene glycol monomethyl ether is 200; and the viscosity of the resulting slurry is 5000-8000 mPa·s. s.

[0030] In this invention, the raw materials for concrete, by weight, include: 100 parts cement, 300-400 parts aggregate, 8-15 parts mineral admixture, 42-43 parts water, 0.7-1.0 parts water-reducing agent, and 4.5-5.5 parts water-slow-release microcapsules.

[0031] The cement used is grade 52.5 silicate cement (specific surface area of ​​380±15m²). 2 / kg, initial setting time ≥45min); the aggregate is a mixture of continuously graded crushed stone (particle size 5~16mm, mud content ≤0.3%) and river sand (fineness modulus 2.5~2.7, mud content ≤0.8%), with a weight ratio of crushed stone to river sand of (3~4):1; the mineral admixture is metakaolin with an activity index of 110~120% and a particle size of 30~45um; the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a solid content of 20~30%, a water reduction rate of 30~40%, and a retarding time of 4~8h.

[0032] In this invention, the pressure spray dryer has an inlet air temperature of 145~155℃. The outlet air temperature is 67~73℃, the atomization pressure is 0.8~1MPa, and the feed rate is 60~70L / h.

[0033] In this invention, the drying temperature of the dryer is 58~62℃ and the drying time is 2~3h.

[0034] In this invention, the fluidized bed coating machine has a fluidization air velocity of 1.5~2m / s, a temperature of 28~32℃, a coating liquid spraying speed of 10~15L / h, and a coating time of 30~45min.

[0035] In this invention, the first stirring time is 1-2 minutes, the second stirring time is 2-3 minutes, and the third stirring time is 1-2 minutes.

[0036] Example 1; (1) Under a nitrogen atmosphere, polyethylene glycol monomethyl ether, maleic anhydride, p-toluenesulfonic acid and toluene were mixed in a mass ratio of 1:1:0.02:20 and reacted at 100°C for 6 h. Carboxylated polyethylene glycol monomethyl ether was obtained by vacuum distillation. Chitosan, carboxylated polyethylene glycol monomethyl ether, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, 10% acetic acid aqueous solution and deionized water were mixed and stirred evenly in a mass ratio of 1:0.2:0.4:0.2:0.8:10. The pH was adjusted to 5 with 5% sodium hydroxide aqueous solution and reacted at 20°C for 1 h. Precipitation was carried out in acetone, filtered, and the filter cake was collected to obtain pre-modified chitosan. (2) Under a nitrogen atmosphere, pre-modified chitosan, N-isopropylacrylamide, ammonium persulfate and deionized water were mixed evenly in a mass ratio of 1:0.2:0.05:10 and stirred at 60°C for 1 h to obtain modified chitosan; modified chitosan, hydroxypropyl methylcellulose, glutaraldehyde and 10% citric acid aqueous solution were mixed in a mass ratio of 1.4:1:0.07:40 and reacted at 25°C for 1 h to obtain slurry; the slurry was granulated using a pressure spray dryer with an inlet air temperature of 145°C, an outlet air temperature of 67°C, an atomization pressure of 0.8 MPa and a feed rate of 60 L / h, and dried at 58°C for 2 h to obtain pre-modified microcapsules; (3) 3-glycidyl etheroxypropyltrimethoxysilane and ethanol were mixed at a mass ratio of 1:10 to prepare a coating solution. The pre-modified microcapsules were fed into a fluidized bed coating machine with a fluidization air velocity of 1.5 m / s, a temperature of 28°C, a coating solution spraying speed of 10 L / h, and a coating time of 30 min. Then, the microcapsules were blown with hot air at 40°C for 15 min to obtain water-release microcapsules. (4) By weight, mix 100 parts of cement, 262.5 parts of crushed stone, 87.5 parts of river sand and 11.5 parts of metakaolin. Stir for 1.5 minutes for the first time, add 42.5 parts of water and 0.85 parts of water-reducing agent, stir for 2.5 minutes for the second time, add 5 parts of water-release microcapsules, and stir for 1.5 minutes for the third time to obtain crack-resistant concrete.

[0037] Example 2; (1) Under a nitrogen atmosphere, polyethylene glycol monomethyl ether, maleic anhydride, p-toluenesulfonic acid and toluene were mixed in a mass ratio of 1:1.02:0.03:20 and reacted at 105℃ for 7h. Carboxylated polyethylene glycol monomethyl ether was obtained by vacuum distillation. Chitosan, carboxylated polyethylene glycol monomethyl ether, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, 10% acetic acid aqueous solution and deionized water were mixed and stirred evenly in a mass ratio of 1:0.25:0.45:0.3:1.1:15. The pH was adjusted to 5.5 with 5% sodium hydroxide aqueous solution and reacted at 25℃ for 1.5h. Precipitation was carried out in acetone, filtered, and the filter cake was collected to obtain pre-modified chitosan. (2) Under a nitrogen atmosphere, pre-modified chitosan, N-isopropylacrylamide, ammonium persulfate and deionized water were mixed evenly in a mass ratio of 1:0.25:0.055:15 and stirred at 65°C for 1.5 h to obtain modified chitosan; modified chitosan, hydroxypropyl methylcellulose, glutaraldehyde and 10% citric acid aqueous solution were mixed in a mass ratio of 1.4:1:0.07:45 and reacted at 28°C for 1.5 h to obtain slurry; the slurry was granulated using a pressure spray dryer with an inlet air temperature of 150°C, an outlet air temperature of 70°C, an atomization pressure of 0.9 MPa and a feed rate of 65 L / h, and dried at 60°C for 2.5 h to obtain pre-modified microcapsules; (3) Mix 3-glycidyl etheroxypropyltrimethoxysilane and ethanol at a mass ratio of 1:10 to prepare a coating solution. Send the pre-modified microcapsules into a fluidized bed coating machine with a fluidization air velocity of 1.8 m / s, a temperature of 30°C, a coating solution spraying speed of 12 L / h, and coating for 40 min. Then, purge with hot air at 40°C for 15 min to obtain water-release microcapsules. (4) By weight, mix 100 parts of cement, 262.5 parts of crushed stone, 87.5 parts of river sand and 11.5 parts of metakaolin. Stir for 1.5 minutes for the first time, add 42.5 parts of water and 0.85 parts of water-reducing agent, stir for 2.5 minutes for the second time, add 5 parts of water-release microcapsules, and stir for 1.5 minutes for the third time to obtain crack-resistant concrete.

[0038] Example 3; (1) Under a nitrogen atmosphere, polyethylene glycol monomethyl ether, maleic anhydride, p-toluenesulfonic acid and toluene were mixed in a mass ratio of 1:1.05:0.05:20 and reacted at 110°C for 8 h. Carboxylated polyethylene glycol monomethyl ether was obtained by vacuum distillation. Chitosan, carboxylated polyethylene glycol monomethyl ether, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, 10% acetic acid aqueous solution and deionized water were mixed and stirred evenly in a mass ratio of 1:0.3:0.5:0.4:1.5:20. The pH was adjusted to 6 with 5% sodium hydroxide aqueous solution and reacted at 30°C for 2 h. Precipitation was carried out in acetone, filtered, and the filter cake was collected to obtain pre-modified chitosan. (2) Under a nitrogen atmosphere, pre-modified chitosan, N-isopropylacrylamide, ammonium persulfate and deionized water were mixed evenly in a mass ratio of 1:0.3:0.06:20 and stirred at 70°C for 2 hours to obtain modified chitosan; modified chitosan, hydroxypropyl methylcellulose, glutaraldehyde and 10% citric acid aqueous solution were mixed in a mass ratio of 1.4:1:0.07:50 and reacted at 30°C for 2 hours to obtain slurry; the slurry was granulated using a pressure spray dryer with an inlet air temperature of 155°C, an outlet air temperature of 73°C, an atomization pressure of 1MPa and a feed rate of 70L / h, and dried at 62°C for 3 hours to obtain pre-modified microcapsules; (3) Mix 3-glycidyl etheroxypropyltrimethoxysilane and ethanol at a mass ratio of 1:10 to prepare a coating solution. Send the pre-modified microcapsules into a fluidized bed coating machine with a fluidization air velocity of 2 m / s, a temperature of 32°C, a coating solution spraying speed of 15 L / h, and coating for 45 min. Then, purge under 40°C hot air for 15 min to obtain water-release microcapsules. (4) By weight, mix 100 parts of cement, 262.5 parts of crushed stone, 87.5 parts of river sand and 11.5 parts of metakaolin. Stir for 1.5 minutes for the first time, add 42.5 parts of water and 0.85 parts of water-reducing agent, stir for 2.5 minutes for the second time, add 5 parts of water-release microcapsules, and stir for 1.5 minutes for the third time to obtain crack-resistant concrete.

[0039] Example 4; (1) Under a nitrogen atmosphere, polyethylene glycol monomethyl ether, maleic anhydride, p-toluenesulfonic acid and toluene were mixed in a mass ratio of 1:1.02:0.03:20 and reacted at 105℃ for 7h. Carboxylated polyethylene glycol monomethyl ether was obtained by vacuum distillation. Chitosan, carboxylated polyethylene glycol monomethyl ether, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, 10% acetic acid aqueous solution and deionized water were mixed and stirred evenly in a mass ratio of 1:0.25:0.45:0.3:1.1:15. The pH was adjusted to 5.5 with 5% sodium hydroxide aqueous solution and reacted at 25℃ for 1.5h. Precipitation was carried out in acetone, filtered, and the filter cake was collected to obtain pre-modified chitosan. (2) Under a nitrogen atmosphere, pre-modified chitosan, N-isopropylacrylamide, ammonium persulfate and deionized water were mixed evenly in a mass ratio of 1:0.25:0.055:15 and stirred at 65°C for 1.5 h to obtain modified chitosan; modified chitosan, hydroxypropyl methylcellulose, glutaraldehyde and 10% citric acid aqueous solution were mixed in a mass ratio of 1.4:1:0.07:45 and reacted at 28°C for 1.5 h to obtain slurry; the slurry was granulated using a pressure spray dryer with an inlet air temperature of 150°C, an outlet air temperature of 70°C, an atomization pressure of 0.9 MPa and a feed rate of 65 L / h, and dried at 60°C for 2.5 h to obtain pre-modified microcapsules; (3) Mix 3-glycidyl etheroxypropyltrimethoxysilane and ethanol at a mass ratio of 1:10 to prepare a coating solution. Send the pre-modified microcapsules into a fluidized bed coating machine with a fluidization air velocity of 1.8 m / s, a temperature of 30°C, a coating solution spraying speed of 12 L / h, and coating for 40 min. Then, purge with hot air at 40°C for 15 min to obtain water-release microcapsules. (4) By weight, mix 100 parts of cement, 225 parts of crushed stone, 75 parts of river sand and 8 parts of metakaolin. Stir for 1 minute, add 42 parts of water and 0.7 parts of water-reducing agent, stir for 2 minutes, add 4.5 parts of water-slow-release microcapsules, stir for 1 minute, and obtain crack-resistant concrete.

[0040] Example 5; (1) Under a nitrogen atmosphere, polyethylene glycol monomethyl ether, maleic anhydride, p-toluenesulfonic acid and toluene were mixed in a mass ratio of 1:1.02:0.03:20 and reacted at 105℃ for 7h. Carboxylated polyethylene glycol monomethyl ether was obtained by vacuum distillation. Chitosan, carboxylated polyethylene glycol monomethyl ether, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, 10% acetic acid aqueous solution and deionized water were mixed and stirred evenly in a mass ratio of 1:0.25:0.45:0.3:1.1:15. The pH was adjusted to 5.5 with 5% sodium hydroxide aqueous solution and reacted at 25℃ for 1.5h. Precipitation was carried out in acetone, filtered, and the filter cake was collected to obtain pre-modified chitosan. (2) Under a nitrogen atmosphere, pre-modified chitosan, N-isopropylacrylamide, ammonium persulfate and deionized water were mixed evenly in a mass ratio of 1:0.25:0.055:15 and stirred at 65°C for 1.5 h to obtain modified chitosan; modified chitosan, hydroxypropyl methylcellulose, glutaraldehyde and 10% citric acid aqueous solution were mixed in a mass ratio of 1.4:1:0.07:45 and reacted at 28°C for 1.5 h to obtain slurry; the slurry was granulated using a pressure spray dryer with an inlet air temperature of 150°C, an outlet air temperature of 70°C, an atomization pressure of 0.9 MPa and a feed rate of 65 L / h, and dried at 60°C for 2.5 h to obtain pre-modified microcapsules; (3) Mix 3-glycidyl etheroxypropyltrimethoxysilane and ethanol at a mass ratio of 1:10 to prepare a coating solution. Send the pre-modified microcapsules into a fluidized bed coating machine with a fluidization air velocity of 1.8 m / s, a temperature of 30°C, a coating solution spraying speed of 12 L / h, and coating for 40 min. Then, purge with hot air at 40°C for 15 min to obtain water-release microcapsules. (4) By weight, mix 100 parts of cement, 240 parts of crushed stone, 80 parts of river sand and 9.5 parts of metakaolin. Stir for 1.5 minutes for the first time, add 42.2 parts of water and 0.8 parts of water-reducing agent, stir for 2.5 minutes for the second time, and finally add 4.8 parts of water-slow-release microcapsules. Stir for 1.5 minutes for the third time to obtain crack-resistant concrete.

[0041] Example 6; (1) Under a nitrogen atmosphere, polyethylene glycol monomethyl ether, maleic anhydride, p-toluenesulfonic acid and toluene were mixed in a mass ratio of 1:1.02:0.03:20 and reacted at 105℃ for 7h. Carboxylated polyethylene glycol monomethyl ether was obtained by vacuum distillation. Chitosan, carboxylated polyethylene glycol monomethyl ether, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, 10% acetic acid aqueous solution and deionized water were mixed and stirred evenly in a mass ratio of 1:0.25:0.45:0.3:1.1:15. The pH was adjusted to 5.5 with 5% sodium hydroxide aqueous solution and reacted at 25℃ for 1.5h. Precipitation was carried out in acetone, filtered, and the filter cake was collected to obtain pre-modified chitosan. (2) Under a nitrogen atmosphere, pre-modified chitosan, N-isopropylacrylamide, ammonium persulfate and deionized water were mixed evenly in a mass ratio of 1:0.25:0.055:15 and stirred at 65°C for 1.5 h to obtain modified chitosan; modified chitosan, hydroxypropyl methylcellulose, glutaraldehyde and 10% citric acid aqueous solution were mixed in a mass ratio of 1.4:1:0.07:45 and reacted at 28°C for 1.5 h to obtain slurry; the slurry was granulated using a pressure spray dryer with an inlet air temperature of 150°C, an outlet air temperature of 70°C, an atomization pressure of 0.9 MPa and a feed rate of 65 L / h, and dried at 60°C for 2.5 h to obtain pre-modified microcapsules; (3) Mix 3-glycidyl etheroxypropyltrimethoxysilane and ethanol at a mass ratio of 1:10 to prepare a coating solution. Send the pre-modified microcapsules into a fluidized bed coating machine with a fluidization air velocity of 1.8 m / s, a temperature of 30°C, a coating solution spraying speed of 12 L / h, and coating for 40 min. Then, purge with hot air at 40°C for 15 min to obtain water-release microcapsules. (4) By weight, mix 100 parts of cement, 320 parts of crushed stone, 80 parts of river sand and 15 parts of metakaolin. Stir for 2 minutes for the first time, add 43 parts of water and 1 part of water-reducing agent, stir for 3 minutes for the second time, and finally add 5.5 parts of water-release microcapsules. Stir for 2 minutes for the third time to obtain crack-resistant concrete.

[0042] Comparative Example 1; The difference between Comparative Example 1 and Example 2 is that water-release microcapsules are not added, and step (4) is modified as follows: by weight, 100 parts of cement, 262.5 parts of crushed stone, 87.5 parts of river sand and 11.5 parts of metakaolin are mixed, stirred for 1.5 min for the first time, 42.5 parts of water and 0.85 parts of water-reducing agent are added, and stirred for 2.5 min for the second time to obtain crack-resistant concrete; the remaining steps are the same as in Example 2.

[0043] Comparative Example 2; The difference between Comparative Example 2 and Example 2 is that step (3) is omitted, and step (4) is modified as follows: by weight, 100 parts of cement, 262.5 parts of crushed stone, 87.5 parts of river sand and 11.5 parts of metakaolin are mixed, stirred for 1.5 min for the first time, 42.5 parts of water and 0.85 parts of water-reducing agent are added, stirred for 2.5 min for the second time, and finally 5 parts of pre-modified microcapsules are added, stirred for 1.5 min for the third time to obtain crack-resistant concrete; the remaining steps are the same as in Example 2.

[0044] Comparative Example 3; The difference between Comparative Example 3 and Example 2 lies in step (4). Step (4) is modified as follows: by weight, 100 parts of cement, 262.5 parts of crushed stone, 87.5 parts of river sand, 11.5 parts of metakaolin, 42.5 parts of water, 0.85 parts of water-reducing agent, and 5 parts of water-slow-release microcapsules are mixed and stirred for 3 minutes to obtain crack-resistant concrete; the remaining steps are the same as in Example 2.

[0045] Test method: compressive strength Concrete blocks of 150mm×150mm×150mm were prepared according to the standard method of GB / T50081-2019, and their compressive strength was tested after standard curing for 7 days and 28 days. The specific results are shown in Table 1.

[0046] Crack resistance Free shrinkage crack resistance test: The concrete of each embodiment and comparative example was poured in two layers into a 100mm×100mm×400mm prism mold. The first layer was vibrated and compacted. After curing in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95%RH for 24 hours, the second layer was filled and vibrated and compacted. The specimens were then transferred to a temperature and humidity controlled chamber (temperature 20±2℃, relative humidity 90±5%). All exposed surfaces of the specimens (except the bottom surface) were uniformly coated with polyurethane sealant to simulate unidirectional drying conditions. The specimens were continuously monitored using a fixed-position high-definition CCD camera. The time from the start of drying to the appearance of the first crack with a width of ≥0.02mm on the surface of the specimen was recorded as the first crack time. Monitoring continued for 7 days. The total crack area within 7 days was calculated using image analysis software. The specific results are shown in Table 1.

[0047] Constrained shrinkage crack resistance test: Following the standard constrained shrinkage test method, a steel circular ring constrained test frame was used. The inner ring was a rigid constraint. Concrete was poured in two layers into the annular cavity formed by the inner and outer molds as described above. After 24 hours of standard curing, the outer mold was removed, allowing the concrete ring to generate shrinkage stress under the constraint of the inner ring. After sealing the top surface of the specimen, circumferential shrinkage strain was monitored. Images were periodically acquired using a high-definition CCD camera, and the first crack time (crack width ≥ 0.02 mm) was recorded. Using the first crack time of Comparative Example 1 as the baseline, the other examples and comparative examples were used as experimental groups. The delay rate was calculated as follows: Delay rate = (First crack time of experimental group - First crack time of Comparative Example 1) / First crack time of experimental group × 100%. To comprehensively characterize the crack resistance of concrete, the key results obtained from the two test methods are listed in Table 1 below. Among them, "First crack time" and "Total crack area at 7 days" are the results of the free shrinkage crack resistance test; "Delay rate" is calculated based on the first crack time of the constrained shrinkage crack resistance test, using Comparative Example 1 as the baseline. Specific results are shown in Table 1.

[0048] Table 1

[0049] Data from Examples 1-6 collectively demonstrate that the crack-resistant concrete containing fully responsive water-release microcapsules provided by this invention achieves significant improvements in key properties such as compressive strength (up to 30.4 MPa at 7 days and 47.3 MPa at 28 days), time to first cracking during free shrinkage (extended to 81.3-83.5 h), and restrained shrinkage delay rate (all above 62%). This verifies the comprehensive effectiveness of the temperature-sensitive and salt-sensitive dual-response microcapsule system in intelligently regulating hydration and enhancing crack resistance.

[0050] Comparative Example 1 shows that, without the addition of the microcapsules of this invention, the time to first cracking of concrete during free shrinkage is only 41.2 hours, and the total crack area after 7 days reaches 75.3 mm. 2 Furthermore, the constraint contraction has no delay effect.

[0051] The data from Comparative Example 2 show that, although the crack resistance enhancement effect of pre-modified microcapsules without silane coupling agent coating is better than that of Comparative Example 1, it is significantly lower than that of the complete example. This proves that the surface coating of silane coupling agent is crucial for ensuring the uniform dispersion of microcapsules in concrete, avoiding agglomeration failure, enhancing the interfacial bonding between microcapsules and cement matrix, and fully utilizing the intelligent water release and stress buffering functions.

[0052] Comparative Example 3 shows that even with the addition of complete microcapsules, the crack resistance of concrete using a one-time mixing process is still lower than that of the step-mixing example. The step-mixing process is crucial for protecting the structural integrity of the microcapsules during vigorous mixing and maintaining their intelligent response and slow-release function.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A crack-resistant concrete based on responsive water-release microcapsules, characterized in that, The crack-resistant concrete is made by mixing and pouring cement, aggregates, mineral admixtures, water, water-reducing agents, and water-slow-release microcapsules. The water-release microcapsules comprise: (1) The sustained-release carrier is formed by cross-linking hydroxypropyl methylcellulose and modified chitosan with glutaraldehyde; (2) A temperature-sensitive monomer is cross-linked onto the modified chitosan through a polymerization reaction; (3) A hydrophilic monomer is grafted into the chitosan structure through a carboxylation reaction and introduced into the sustained-release carrier after pre-modification; (4) Silane coupling agent, coated on the surface of microcapsules.

2. The crack-resistant concrete based on responsive water-release microcapsules according to claim 1, characterized in that, The aggregate is made by mixing continuously graded crushed stone and river sand in a weight ratio of (3~4):

1.

3. The crack-resistant concrete based on responsive water-release microcapsules according to claim 1, characterized in that, The mineral admixture is metakaolin with an activity index of 110-120% and a particle size of 30-45 μm.

4. The crack-resistant concrete based on responsive water-release microcapsules according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a solid content of 20-30%, a water reduction rate of 30-40%, and a retarding time of 4-8 hours.

5. The crack-resistant concrete based on responsive water-release microcapsules according to claim 1, characterized in that, The mass ratio of hydroxypropyl methylcellulose, modified chitosan, and glutaraldehyde in the sustained-release carrier is (1.4~1.6):1:(0.07~0.13).

6. The crack-resistant concrete based on responsive water-release microcapsules according to claim 1, characterized in that, The modified chitosan is obtained by reacting and polymerizing pre-modified chitosan and thermosensitive monomer, wherein the mass ratio of pre-modified chitosan to thermosensitive monomer is 1:(0.2~0.3).

7. The crack-resistant concrete based on responsive water-release microcapsules according to claim 6, characterized in that, The pre-modified chitosan is prepared by reacting a hydrophilic monomer with maleic anhydride and then condensing it with chitosan.

8. The crack-resistant concrete based on responsive water-release microcapsules according to claim 1, characterized in that, The temperature-sensitive monomer is N-isopropylacrylamide.

9. The crack-resistant concrete based on responsive water-release microcapsules according to claim 1, characterized in that, The hydrophilic monomer is polyethylene glycol monomethyl ether.

10. A method for preparing crack-resistant concrete based on responsive water-release microcapsules as described in any one of claims 1-9, characterized in that, Includes the following steps: (1) First, react the hydrophilic monomer with maleic anhydride, and then react it with chitosan to obtain pre-modified chitosan; Pre-modified chitosan and thermosensitive monomers are polymerized to obtain modified chitosan. Finally, hydroxypropyl methylcellulose and glutaraldehyde are added. The slurry after reaction is dried and granulated to obtain pre-modified microcapsules, which are then coated with silane coupling agents to obtain water-release microcapsules. (2) By weight, mix 100 parts of cement, 300-400 parts of aggregate, and 8-15 parts of mineral admixture. Stir for 1-2 minutes for the first time, add 42-43 parts of water and 0.7-1.0 parts of water-reducing agent, stir for 2-3 minutes for the second time, and finally add 4.5-5.5 parts of water-slow-release microcapsules. Stir for 1-2 minutes for the third time to obtain crack-resistant concrete.

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