Anti-crack functional material for ballastless track roadbed slab concrete and preparation method thereof

Abstract

The invention belongs to the technical field of high-speed railway ballastless track construction, and particularly discloses an anti-crack functional material for ballastless track roadbed slab concrete and a preparation method of the anti-crack functional material. The anti-cracking functional material provides a whole-course expansion effect and delays early expansion by means of a mode of coating calcium oxide with calcium carbonate and compounding magnesium oxide; the protein modified starch is used as a hydration heat regulation and control layer, so that the regulation and control effect of single starch on cement hydration heat is improved, and a compound expanding agent is slowly released; carbonized and expanded rice husks are used as a biomass water-absorbing and anti-releasing material, so that the self-shrinkage and drying shrinkage of the concrete are reduced; the temperature-sensitive microgel material is used as the outermost layer component, the highest temperature value of the roadbed slab concrete is reduced, the temperature drop shrinkage stress of the concrete is improved, and the temperature shrinkage cracking risk of the roadbed slab concrete is inhibited. Various shrinkage stresses of the roadbed slab are accurately regulated and controlled, the limiting and restraining stress of the prefabricated sleeper and the base on the concrete of the roadbed slab is effectively compensated and improved, and the anti-cracking performance of the concrete of the ballastless track roadbed slab is fundamentally improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-speed railway ballastless track construction, and specifically discloses an anti-cracking functional material for ballastless track bed slab concrete and a preparation method thereof. Background Art

[0002] Tracks are a vital component of rail transit systems, directly impacting the normal operation and driving safety of the lines. Tracks are primarily composed of rails, fasteners, sleepers, roadbeds, switches, and track ancillary equipment. The roadbed is the foundation of the track, bearing vehicle loads transmitted through the sleepers and distributing them downward. Ballastless track, with its advantages of excellent stability, simple construction methods, and minimal maintenance, has been widely used in my country's high-speed railway construction. The roadbed of ballastless track is a cast-in-place concrete structure, distributed along the line in long strips or continuous structures. Due to inherent defects such as the continuous strip shape and the combination of cast-in-place and precast (sleeper) concrete, post-cast concrete shrinkage can lead to numerous defects such as transverse through-hole cracks in the roadbed surface and splayed cracks around the sleepers. These defects severely impact construction quality acceptance, increase operational maintenance workload, and reduce the durability of the ballastless track structure. The current ballastless track construction industry can only address the problem of cracking in ballastless track concrete through post-repair, but is unable to predict, prevent, or pre-treat the problem. Research has shown that temperature and humidity are the primary factors affecting shrinkage cracking in ballastless track concrete, with their impact on surface cracking being particularly pronounced. Cement dosage, aggregate gradation, and the use of anti-cracking functional materials are key material factors in addressing shrinkage cracking in ballastless track concrete. Therefore, the selection and development of suitable anti-cracking functional materials based on the structural form and cracking characteristics of ballastless track concrete to formulate low-shrinkage, highly crack-resistant concrete, and thereby fundamentally suppress the risk of cracking in ballastless track concrete, is a current research hotspot in the field of ballastless track concrete construction.

[0003] There are many studies on anti-cracking solutions for ballastless track bed concrete, but all of them have certain drawbacks.

[0004] For example, Chinese patent CN 108149526A discloses a method for crack-resistant construction of CRTS I type two-block ballastless track slabs. This method controls cracking of the slab concrete by adding an expansive agent to the slab concrete and combining it with dynamic monitoring using strain gauges embedded in the slab concrete. However, this method, which utilizes only an expansive agent, cannot effectively compensate for the various shrinkages of the slab concrete and therefore cannot suppress the risk of cracking.

[0005] For example, Chinese patent CN 116674052A discloses a method for controlling cracking in ballastless track slab concrete. Finite element analysis (FEM) numerical simulations are used to calculate the concrete cracking risk factor under different operating conditions based on various concrete performance indicators. The method then incorporates an anti-cracking agent, representing 5% to 10% of the cementitious material weight, into the slab concrete. The concrete mold temperature and pouring method are then regulated. Finally, a moisture evaporation inhibitor is sprayed on the slab concrete, and the concrete is covered with plastic film and thermal insulation materials for curing. This method, which only uses an expansive agent as an anti-cracking agent and combines it with other factors such as the mold temperature, pouring method, and curing method, has some positive effects on crack prevention. However, the construction process is complex and has limited its widespread application.

[0006] For example, Chinese patent CN 110184864A discloses a method for reducing the crack rate of bi-block ballastless track slabs. This method incorporates an expansive agent into the slab concrete to control the risk of slab cracking in nine areas: ① geotextile laying and construction layout, ② bottom reinforcement installation, ③ sleeper assembly and rough adjustment, ④ formwork installation, ⑤ track fine-tuning, ⑥ concrete pouring, ⑦ concrete vibration, ⑧ concrete curing, and ⑨ concrete dynamic monitoring. This approach focuses more on controlling the construction process, rather than using conventional expansive agents to compensate for slab concrete shrinkage, focusing on material improvement. This approach fails to control cracks in the slab concrete at the source, making it difficult to precisely control the concrete's crack resistance.

[0007] Chinese patent CN 103603236A discloses a method for controlling cracks in a twin-block ballastless track slab. This method only controls the process of slab concrete pouring, vibration, finishing, and maintenance. It does not analyze how to reduce the shrinkage stress of the slab concrete at the source. It also lacks the necessary anti-cracking functional materials, making it difficult to fundamentally address the risk of slab concrete cracking.

[0008] Chinese patent CN 115043610A discloses a concrete anti-cracking agent, crack-resistant concrete, and a preparation method thereof. By optimizing the combination of a composite expansive agent, a hydration heat inhibitor, an internal curing agent, chopped fibers, and a composite anti-seepage agent, the anti-cracking agent works together in concrete, complementing and promoting each other's components to address the problem of concrete's susceptibility to cracking. This method has a certain positive effect on concrete crack resistance, but the duration of the anti-cracking functional components (composite expansive agent, hydration heat inhibitor, internal curing agent, chopped fibers, and composite anti-seepage agent) in concrete cannot be precisely controlled, making it impossible to completely inhibit concrete shrinkage deformation, and can cause shrinkage cracks.

[0009] Chinese patent CN 115403288A discloses a concrete anti-cracking agent, its preparation method, and its use. The agent is prepared using 40-60 parts of ECS1 active powder, 40-60 parts of microbially modified polypropylene fiber, and 4-5 parts of limestone powder. This method significantly improves the workability of the mix and reduces cracks caused by water evaporation by adding a hydrophobic powder to improve the mix's uniformity and water retention. However, while this solution improves the cementitious material's crack resistance, it also reduces its compressive strength, making it unable to meet the load-bearing requirements of ballastless track concrete and fatigue losses during high-speed rail operation.

[0010] For example, a Chinese journal article (Research on Shrinkage Reduction and Crack Prevention Measures for Ballastless Track Concrete in Plateau, He Niangzhe, Li Yongliang, Zeng Xiaohui, etc., Journal of Railway Engineering Society, Issue 10, 2022) disclosed a study on the use of internal curing agent and polypropylene fiber to improve the crack resistance of track bed concrete in plateau environment. The internal curing agent or polypropylene fiber is combined with mineral admixtures such as fly ash powder to improve the crack resistance of track bed concrete by reducing the drying shrinkage of track bed concrete. However, this method only uses a shrinkage-reducing material alone, which only has a certain effect on the shrinkage reduction effect of track bed concrete drying shrinkage; because track bed concrete is not only affected by concrete shrinkage stress in actual engineering structures, but also by the restrictions and constraints of prefabricated sleepers and bases, the single addition of internal curing agent or single addition of polypropylene fiber cannot really solve the cracking problem of track bed concrete in actual engineering.

[0011] Therefore, there is an urgent need to develop an anti-cracking functional material that can essentially match the bearing stress and shrinkage stress of ballastless track bed concrete, so as to fundamentally solve the cracking problem of ballastless track bed concrete. Summary of the Invention

[0012] In view of the defects of the prior art, the present invention provides an anti-cracking functional material for ballastless track bed slab concrete and a preparation method thereof, so as to solve the cracking problems of ballastless track bed slab concrete in the prior art, such as cracks, splayed cracks at the four corners of the sleepers, and transverse through-cracks on the slab surface, thereby achieving the goals of simple operation, economic efficiency, and good crack control effect.

[0013] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0014] A crack-resistant functional material for ballastless track slab concrete comprises a microgel coating layer and loaded microspheres coated inside the microgel coating layer; the loaded microspheres comprise carbonized puffed rice husks and core-shell structured microspheres loaded in the pores of the carbonized puffed rice husks; the core-shell structured microspheres comprise a protein-modified starch coating layer and a composite expansion agent coated inside the protein-modified starch coating layer; wherein the composite expansion agent is obtained by thoroughly and uniformly mixing a magnesium oxide expansion agent and a modified calcium oxide expansion agent.

[0015] Specifically, the mass of the composite expander is 60 to 75 parts; the mass of the protein-modified starch coating layer is 5 to 10 parts; the mass of the carbonized puffed rice husk is 15 to 20 parts; and the mass of the microgel coating layer is 5 to 10 parts; all of the above are parts by mass.

[0016] Specifically, the modified calcium oxide expansion agent is a calcium oxide expansion agent whose surface is coated with calcium carbonate.

[0017] Furthermore, the encapsulation amount of calcium carbonate is 5% to 10% of the mass of the calcium oxide expansion agent.

[0018] Preferably, the modified calcium oxide expansion agent is obtained by subjecting CO2 to a gas phase suspension carbonation reaction with calcium oxide clinker powder.

[0019] Further preferably, CO2 is obtained by filtering, pressurizing and concentrating the high-temperature CO2 flue gas generated during the preparation of magnesium oxide expansion agent by calcining magnesite in a suspension kiln.

[0020] Further preferably, CO2 and calcium oxide clinker powder are subjected to gas phase suspension carbonation reaction in a fluidized bed furnace.

[0021] Preferably, the magnesium oxide expansion agent is light-burned MgO with a hydration activity of 100s to 150s, which is produced by calcining magnesite in a suspension kiln.

[0022] Specifically, in the composite expansion agent, the mass ratio of the magnesium oxide expansion agent to the modified calcium oxide expansion agent is 2-3:3-2.

[0023] Specifically, the material of the protein-modified starch coating layer is carboxymethyl starch modified with alcohol-soluble protein.

[0024] Further preferably, the protein-modified starch coating layer is a structural layer formed by self-assembly of carboxymethyl starch modified with alcohol-soluble protein on the surface of the composite swelling agent.

[0025] Specifically, the carbonized puffed rice husk is obtained by sequentially subjecting the rice husk to puffing and pyrolysis carbonization treatments.

[0026] Specifically, the material of the microgel coating layer is temperature-sensitive microgel.

[0027] Furthermore, the temperature-sensitive microgel can be any one of N-isopropylacrylamide microgel, N-isopropylacrylamide-acrylic acid copolymer microgel, N-isopropylacrylamide copolymer methacrylic acid microgel, isopropylmethacrylamide, or a mixture of at least two of them in any proportion.

[0028] The above-mentioned anti-cracking functional material provided by the present invention has a layered wrapping structural feature, thereby achieving a sequential slow-release effect. Specifically, in the above-mentioned anti-cracking functional material, first, by coating calcium carbonate on the surface of the calcium oxide expander, the purpose of regulating the hydration reaction rate of the calcium oxide expander is achieved, and it serves as an early expansion source; its composite magnesium oxide expander is used as a mid- and late-stage expansion source, providing a full-process expansion effect while also delaying the occurrence of early expansion. Secondly, the protein-modified starch coating layer is used as a hydration heat regulating layer. On the one hand, the protein-modified starch therein enhances the regulating effect of a single starch on the hydration heat of cement; on the other hand, it is coated on the outside of the composite expander, exerting a slow-release effect on the internal composite expander, slowing down the contact reaction time between the composite expander and the free water in the concrete, reducing the ineffective expansion of the composite expander in the plastic stage of the concrete, and enhancing the shrinkage compensation effect of the composite expander on the hardening stage of the concrete. Secondly, carbonized expanded rice husks were used as a biomass water-absorbing and releasing material. Leveraging their porous, high-volume, and high-surface-area water-absorbing properties, they were used to store and absorb excess free water in the early stages of concrete hydration. This water was then slowly released during the mid-to-late stages of concrete hydration and hardening, when the concrete was dehydrated due to the self-drying effect. This replenished the concrete's internal humidity and reduced its autogenous and drying shrinkage. Furthermore, their porous properties were utilized as a carrier for protein-modified starch / composite expansive agent core-shell spheres, physically regulating the hydration reaction rate of the spheres in concrete. Finally, a thermosensitive microgel was used as the outermost component of the anti-cracking functional material. By utilizing its inherent temperature-dependent phase-change heat absorption properties, the microgels reduced the temperature-rise aggregation effect of the roadbed slab concrete during the initial hydration phase, lowering its maximum temperature, improving the concrete's temperature-drop shrinkage stress, and suppressing the risk of thermal shrinkage cracking in the roadbed slab concrete.

[0029] Another object of the present invention is to provide a method for preparing the above-mentioned anti-cracking functional material for ballastless track slab concrete, comprising the following steps:

[0030] S1. Preparation of modified calcium oxide expansion agent: introducing CO2 into calcium oxide clinker powder to carry out gas phase suspension carbonation reaction to form a calcium carbonate coating layer on the surface of calcium oxide to obtain a modified calcium oxide expansion agent;

[0031] S2. Preparation of a composite expansion agent: fully mixing a magnesium oxide expansion agent and a modified calcium oxide expansion agent in a mass ratio of 2:3 to 3:2 to obtain a composite expansion agent;

[0032] S3. Preparation of core-shell structured spheres: using 60-75 parts by mass of a composite expansion agent as a nucleating seed, spray-drying a solution of alcohol-soluble protein-modified starch, and self-assembling on the surface of the composite expansion agent to form a 5-10 parts by mass protein-modified starch coating layer to obtain core-shell structured spheres;

[0033] S4. Preparation of loaded microspheres: Carbonized expanded rice husk powder and core-shell structured microspheres are uniformly mixed in a mass ratio of 15-20:65-85. After sufficient dispersion, the core-shell structured microspheres are loaded into the pores of the carbonized expanded rice husk powder to obtain loaded microspheres.

[0034] S5. Preparation of anti-cracking functional material: 80 to 105 parts by mass of loaded microspheres are dispersed in an alcohol solution of thermosensitive microgel, and the thermosensitive microgel is grown on the surface of the loaded microspheres by soap-free emulsion polymerization. After drying and calcination, a microgel coating layer of 5 to 10 parts by mass is formed on the surface of the loaded microspheres to obtain an anti-cracking functional material.

[0035] Preferably, in step S1, the preparation method of the modified calcium oxide expansion agent is: the high-temperature CO2 flue gas generated in the process of calcining magnesite in a suspension kiln to produce the magnesium oxide expansion agent is filtered, pressurized, and concentrated, and then introduced into a fluidized boiling furnace to undergo a gas-phase suspension carbonation reaction with the calcium oxide clinker powder to form a calcium carbonate coating layer on the surface of the calcium oxide to obtain the modified calcium oxide expansion agent.

[0036] Preferably, in step S2, the preparation method of the composite expansion agent is: mixing the magnesium oxide expansion agent and the modified calcium oxide expansion agent in a mass ratio of 2:3 to 3:2, and stirring at high speed in a single-shaft plowshare forced mixer for 100s to 120s to obtain the composite expansion agent.

[0037] Further preferably, in step S2, the magnesium oxide expansion agent is prepared by the following method: grinding magnesite powder into raw material powder, placing it in a suspension kiln, and calcining it in suspension at 900°C to 1000°C for 10min to 30min, and obtaining the magnesium oxide expansion agent after cooling.

[0038] Preferably, in step S3, the preparation method of the prolamin-modified starch solution is:

[0039] S31, fully dispersing the prolamin in an alcohol solvent to prepare a prolamin colloidal solution;

[0040] S32, adding carboxymethyl starch to the alcohol-soluble protein colloid solution and stirring evenly to obtain an alcohol-soluble protein modified starch solution.

[0041] Furthermore, the concentration of the alcohol-soluble protein colloid solution in step S31 is controlled to be 35 wt% to 50 wt%, and the mass ratio of carboxymethyl starch to alcohol-soluble protein in the alcohol-soluble protein colloid solution in step S32 is 88 to 93:7 to 12.

[0042] Preferably, in step S4, the carbonized and expanded rice husk powder and the core-shell structured balls are mixed and fully dispersed in a stirring and mixing device with ultrasonic vibration.

[0043] Furthermore, in step S4, the preparation method of carbonized puffed rice husk powder is:

[0044] S41, crushing the raw rice husk into coarse powder particles with a fineness of 10-20 mesh using a crusher, soaking the powder in water to moisten it, and then performing a puffing pretreatment in an extruder to obtain puffed rice husk;

[0045] S42, using a carbonization furnace to pyrolyze the carbonized puffed rice husk, and crushing and screening it into a fineness of 40 to 60 mesh to obtain carbonized puffed rice husk powder.

[0046] Furthermore, in step S42, the pyrolysis carbonization temperature is controlled to be 120°C to 150°C, and the time is controlled to be 20 minutes to 30 minutes.

[0047] Preferably, in step S5, the preparation method of the alcohol solution of the thermosensitive microgel is: dispersing the thermosensitive microgel in an alcohol solvent.

[0048] The main function of the alcohol solvent in step S5 is to effectively dilute and disperse the thermosensitive microgel, thereby facilitating the combination of the loaded microspheres with the thermosensitive microgel in the alcohol solvent. Generally, the concentration of the alcohol solution of the thermosensitive microgel is controlled to be 15 wt % to 25 wt %.

[0049] Generally, in step S5, the calcination is generally low-temperature calcination, with the temperature controlled at 120° C. to 150° C. and the time being 20 min to 30 min.

[0050] The preparation method of the above-mentioned anti-cracking functional material for ballastless track bed slab concrete provided by the present invention successively prepares the anti-cracking functional material for ballastless track bed slab concrete through carbonation coating of calcium oxide expansion agent, protein modified starch shell coating of composite expansion agent, carbonization and expansion of porous embedded coating (i.e. loading mode) of rice husk powder, and surface core-shell coating of temperature-sensitive microgel loaded microspheres, thereby finally preparing the anti-cracking functional material for ballastless track bed slab concrete, realizing layer-by-layer coating and sequential slow release of the anti-cracking functional material, accurately regulating various shrinkage stresses of the bed slab concrete such as temperature shrinkage, drying shrinkage, and self-drying shrinkage, effectively compensating and improving the limiting constraint stress of the prefabricated sleepers and base on the bed slab concrete itself, and fundamentally improving the anti-cracking performance of the ballastless track bed slab concrete. DETAILED DESCRIPTION

[0051] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention. Unless otherwise specified, the experimental methods used in the examples of the present invention are conventional methods. The materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources unless otherwise specified.

[0052] A crack-resistant functional material for ballastless track slab concrete comprises a microgel coating layer and loaded microspheres coated inside the microgel coating layer; wherein the microgel coating layer accounts for 5 to 10 parts by mass.

[0053] The loaded microspheres include carbonized puffed rice husks and core-shell structured microspheres loaded in the pores of the carbonized puffed rice husks; wherein the carbonized puffed rice husks account for 15 to 20 parts by mass.

[0054] The core-shell structured ball comprises a protein-modified starch coating layer and a composite swelling agent coated inside by the protein-modified starch coating layer; wherein the composite swelling agent is 60 to 75 parts by mass and the protein-modified starch coating layer is 5 to 10 parts by mass.

[0055] Furthermore, the composite expansion agent is obtained by fully and uniformly mixing a magnesium oxide expansion agent and a modified calcium oxide expansion agent in a mass ratio of 2-3:3-2.

[0056] In some embodiments, the formula of the above components can be: 60 parts of composite expander, 5 parts of protein-modified starch coating material, 15 parts of carbonized puffed rice husk, and 5 parts of microgel coating material.

[0057] Alternatively, the composition comprises: 70 parts of a composite expander, 10 parts of a protein-modified starch coating material, 15 parts of carbonized puffed rice husks, and 10 parts of a microgel coating material.

[0058] Alternatively, the composition may include: 75 parts of a composite expander, 10 parts of a protein-modified starch coating material, 20 parts of carbonized puffed rice husks, and 10 parts of a microgel coating material.

[0059] All of the above are parts by mass.

[0060] Preferably, the magnesium oxide expansion agent is light-burned MgO produced by calcining magnesite in a suspension kiln and having a hydration activity of about 100s to 150s.

[0061] Preferably, the preparation process of the calcium oxide expansion agent is as follows: the high-temperature CO2 flue gas generated during the production of light-burned MgO by calcining magnesite in a suspension kiln is filtered, pressurized, and concentrated, and then introduced into a fluidized boiling furnace to undergo a gas-phase suspension carbonation reaction with calcium oxide clinker powder to obtain a modified calcium oxide expansion agent with calcium carbonate generated on the surface.

[0062] Preferably, the amount of calcium carbonate wrapped on the surface of the modified calcium oxide expander is 5% to 10% of the mass of the calcium oxide expander.

[0063] Furthermore, the material of the protein-modified starch coating layer is alcohol-soluble protein-modified carboxymethyl starch.

[0064] Preferably, the preparation process of carbonized puffed rice husk is as follows: the raw rice husk is crushed into coarse powder particles with a fineness of 10 to 20 meshes by a crusher, soaked in water to moisten it, and then placed in an extruder for puffing pretreatment; then pyrolysis and carbonization are carried out in a carbonization furnace at 120° C. to 150° C. for 20 min to 30 min to prepare the carbonized puffed rice husk; finally, the carbonized puffed rice husk is crushed and sieved into carbonized puffed rice husk powder with a fineness of 40 to 60 meshes.

[0065] Furthermore, the material of the microgel coating layer is a temperature-sensitive microgel, which can be specifically selected from any one of N-isopropylacrylamide microgel, N-isopropylacrylamide-acrylic acid copolymer microgel, N-isopropylacrylamide copolymer methacrylic acid microgel, isopropylmethacrylamide, or a mixture of at least two of them in any proportion.

[0066] In the following examples, N-isopropylacrylamide microgel was selected.

[0067] The present invention also provides a method for preparing an anti-cracking functional material for ballastless track slab concrete, comprising the following steps:

[0068] The first step is to grind the magnesite powder into raw material powder, feed it into a suspension kiln for suspension calcination, control the calcination temperature at 900℃~1000℃, control the calcination time at 10min~30min, and obtain the magnesium oxide expansion agent after cooling.

[0069] In the second step, the high-temperature CO2 flue gas generated during the production of magnesium oxide expansion agent by calcining magnesite in a suspension kiln is filtered, pressurized, and concentrated, and then introduced into a fluidized boiling furnace to undergo a gas-phase suspension carbonation reaction with calcium oxide clinker powder to obtain a modified calcium oxide expansion agent with a calcium carbonate coating on the surface.

[0070] The third step is to automatically measure the magnesium oxide expansion agent and the modified calcium oxide expansion agent in a ratio of 2:3 to 3:2 using a metering scale, and then stir them at a high speed for 100s to 120s in a single-shaft plowshare forced mixer to obtain a composite expansion agent.

[0071] The fourth step is to add alcohol-soluble protein into an alcohol solvent (such as ethanol) to prepare a 35 wt% to 50 wt% alcohol-soluble protein colloidal solution, and then slowly add carboxymethyl starch into the alcohol-soluble protein colloidal solution and stir evenly to obtain an alcohol-soluble protein-modified carboxymethyl starch solution.

[0072] The mass ratio of carboxymethyl starch to the alcohol-soluble protein in the alcohol-soluble protein colloid solution can be controlled to be 88-93:7-12.

[0073] In the following examples, the carboxymethyl starch solution modified with prolamin was prepared according to a mass ratio of carboxymethyl starch to prolamin in the prolamin colloidal solution of 9:1.

[0074] In the fifth step, 60 to 75 parts by mass of the composite expansion agent prepared in the third step is used as a nucleating seed, and the alcohol-soluble protein-modified carboxymethyl starch solution prepared in the fourth step is spray-dried to self-assemble into a 5 to 10 parts by mass protein-modified starch coating layer on the surface of the composite expansion agent particles, forming a core-shell structured sphere with the protein-modified starch as the coating layer and the composite expansion agent as the core.

[0075] Step 6: The raw rice husk is crushed into coarse powder particles with a fineness of 10 to 20 meshes by a crusher, soaked in water to moisten it, and then placed in an extruder for extrusion pretreatment. Then, the raw rice husk is pyrolyzed and carbonized in a carbonization furnace at 120° C. to 150° C. for 20 min to 30 min to obtain carbonized extruded rice husk. Finally, the carbonized extruded rice husk is crushed and sieved into a fineness of 40 to 60 meshes to obtain carbonized extruded rice husk powder.

[0076] In the following embodiments, the carbonized and puffed rice husk powder used is derived from slightly fluctuating batches of preparation processes. The performance of the carbonized and puffed rice husk powder obtained based on the above preparation process is not much different and is relatively stable.

[0077] In the seventh step, the core-shell structured balls prepared in the fifth step and the carbonized puffed rice husk powder prepared in the sixth step are mixed in a ratio of 15-20:65-85, and then placed in a stirring and mixing equipment with ultrasonic vibration. Under the combined action of mechanical stirring force and ultrasonic vibration force, the loose porous structure of the carbonized puffed rice husk powder itself is used as a carrier, and the core-shell structured balls of the protein-modified starch / composite swelling agent are uniformly dispersed and filled in the loose structure pores of the carbonized puffed rice husk powder to obtain loaded microspheres.

[0078] In the eighth step, the thermosensitive microgel is dissolved in an alcohol solvent (such as methanol) to obtain a modified sol, and the loaded microspheres prepared in the seventh step are uniformly dispersed in the modified sol. The thermosensitive microgel is grown on the surface of the loaded microspheres by soap-free emulsion polymerization. After drying and calcining at 120°C to 150°C for 20min to 30min, a microgel coating layer with controllable thickness is formed, and finally an anti-cracking functional material with layer-by-layer wrapping and sequential sustained release is prepared.

[0079] Generally, the thickness of the microgel coating is controlled by adjusting the relative amounts of modified sol and loaded microspheres. For example, a higher amount of modified sol dispersed with fewer loaded microspheres results in a thicker microgel coating, while a lower amount of modified sol dispersed with more loaded microspheres results in a thinner microgel coating.

[0080] Based on the above formula and production process, the amounts of different components were adjusted to obtain Examples 1 to 3.

[0081] Example 1

[0082] According to the ratio of 60 parts of composite swelling agent, 5 parts of protein-modified starch coating material, 15 parts of carbonized puffed rice husk and 5 parts of microgel coating layer material, according to the above-mentioned stepwise layered wrapping preparation process, Example 1 of the present invention was prepared.

[0083] In this embodiment, the composite expansion agent is a mixture of a magnesium oxide expansion agent and a modified calcium oxide expansion agent in a mass ratio of 4:6; wherein the amount of calcium carbonate encapsulated in the modified calcium oxide expansion agent is 5% of the mass of the calcium oxide expansion agent.

[0084] Example 2

[0085] 70 parts of composite swelling agent, 10 parts of protein-modified starch coating material, 15 parts of carbonized puffed rice husks and 10 parts of microgel coating layer material were prepared according to the above-mentioned step-by-step layered wrapping preparation process to obtain Example 2 of the present invention.

[0086] In this embodiment, the composite expansion agent is a mixture of a magnesium oxide expansion agent and a modified calcium oxide expansion agent in a mass ratio of 5:5; wherein the amount of calcium carbonate encapsulated in the modified calcium oxide expansion agent is 10% of the mass of the calcium oxide expansion agent.

[0087] Example 3

[0088] 75 parts of composite swelling agent, 10 parts of protein-modified starch coating material, 20 parts of carbonized puffed rice husks and 10 parts of microgel coating layer material were prepared according to the above-mentioned step-by-step layered wrapping preparation process to obtain Example 3 of the present invention.

[0089] In this embodiment, the composite expansion agent is a mixture of a magnesium oxide expansion agent and a modified calcium oxide expansion agent in a mass ratio of 6:4; wherein the amount of calcium carbonate encapsulated in the modified calcium oxide expansion agent is 8% of the mass of the calcium oxide expansion agent.

[0090] In order to demonstrate the differences between the anti-cracking functional material of the present invention and the traditional anti-cracking functional material in terms of mechanical properties, shrinkage deformation properties, and thermal insulation temperature rise properties, the following comparative experiments were conducted. The specific proportions and preparation processes are as follows:

[0091] Comparative Example 1

[0092] Comparative Example 1 was prepared by directly mixing and compounding 70 parts of calcium oxide expansion agent, 10 parts of carboxymethyl starch, 15 parts of water-absorbing resin and 10 parts of polypropylene fiber.

[0093] In this comparative example, commercially available unmodified calcium oxide expander replaces the calcium-magnesium composite expander as the expansion material; unmodified carboxymethyl starch replaces alcohol-soluble protein-modified carboxymethyl starch as the material for the hydration heat regulation layer; water-absorbing resin replaces carbonized puffed rice husk powder as the water absorption and release material; and polypropylene fiber replaces the microgel coating material. The four raw material compounding ratios are exactly the same as in Example 2 of the present invention, and all are replaced in equal proportions. Comparative Example 1 differs from Example 2 in that the raw material composition is different and the production process is also directly mixed and compounded according to the specified proportions, rather than using the stepwise layered packaging / loading method described in Example 2 of the present invention.

[0094] Comparative Example 2

[0095] The similarities between this comparative example and Example 2 are not repeated here, and only the differences from Example 2 are described. This comparative example differs from Example 2 in that 70 parts of a composite expansion agent, 10 parts of a hydration heat regulating material, 15 parts of carbonized puffed rice hulls, and 10 parts of a microgel coating material are directly mixed and compounded according to the same component ratios as in Example 2 to prepare Comparative Example 2, rather than using the gradual layered encapsulation / loading method described in Example 2 of the present invention.

[0096] Comparative Example 3

[0097] The similarities between this comparative example and Example 2 are not repeated here, and only the differences from Example 2 are described. The difference between this comparative example and Example 2 is that the core-shell structured spheres are obtained according to the same component ratio and the same encapsulation process as in Example 2, and then directly mixed and compounded with carbonized puffed rice husk powder and microgel coating layer material (thermosensitive microgel) to prepare Comparative Example 3, while the "carbonized puffed rice husk powder loaded core-shell structured spheres to obtain loaded microspheres" and "thermosensitive microgel coated loaded microspheres" methods in Example 2 of the present invention are not adopted.

[0098] Using the benchmark cement specified in GB8076 and in accordance with the provisions of GB / T23439-2017 "Concrete Expansion Agent", the anti-cracking functional materials prepared in the examples and comparative examples were mixed with 10% cement to form a mortar limited expansion test. The limited expansion rate and expansion development clinker of the mortar specimens were tested under curing conditions in 20°C water. The results are shown in Table 1.

[0099] Table 1 Comparative analysis of the limited expansion rate and expansion development rate of the anti-cracking functional material mortar prepared in the embodiment and the comparative example

[0100]

[0101] It can be seen from the results in Table 1 that the anti-cracking functional material samples prepared in Examples 1 to 3 of the present invention have small early expansion within 1d to 3d, good expansion development sustainability, and an obvious growth effect in the mid-to-late expansion from 3d to 28d, and have a good compensation effect on the shrinkage stress and constraint stress of the roadbed slab concrete in the mid-to-late period.

[0102] In contrast, the anti-cracking functional material sample prepared in Comparative Example 1 exhibited significant expansion performance within 1 to 3 days, with essentially no increase in expansion in the mid- to late-stage from 3 to 28 days. The overall expansion performance was low, and the expansion rate was too rapid, resulting in no compensation for the shrinkage stress and constraint stress of the trackbed concrete in the mid- to late-stage. This is because the expansion component used in this comparative example was a commercially available conventional calcium oxide expansion agent. The essential characteristics of this expansion component are early expansion onset, rapid expansion development, and short expansion duration. Without encapsulation modification and the addition of a magnesium oxide expansion agent as a mid- to late-stage expansion component, the entire compounding production process lacked the necessary gradual layered encapsulation process to slow the expansion rate. The anti-cracking functional material prepared in this comparative example could only utilize the inherent properties of its expansion component, the calcium oxide expansion agent. Its expansion performance was fully exerted in the early stages, but no expansion performance was achieved in the mid- to late-stage, resulting in poor compensation for the shrinkage stress and constraint stress of the trackbed concrete in the mid- to late-stage.

[0103] The crack-resistant functional material samples prepared in Comparative Examples 2 and 3 showed some suppression of early expansion from 1 to 3 days, and also showed some sustained growth in mid-to-late expansion from 3 to 28 days. However, the overall expansion efficiency and expansion rate at 28 days were lower than those of the crack-resistant functional material samples prepared in the examples of the present invention, and their compensation for shrinkage stress and restraint stress in the track slab concrete was relatively weak. This is because, while the raw materials and compounding ratios used in Comparative Examples 2 and 3 were identical to those in the examples, they lacked the necessary layered encapsulation process during production, resulting in a poorer graded release process for the crack-resistant functional material samples. Comparative Example 2, due to its direct physical mixing and compounding process without any layered encapsulation, exhibited faster early expansion and less mid-to-late expansion efficiency. Comparative Example 3, due to its partial encapsulation process without full layered encapsulation, exhibited a suppressed early expansion rate, enhanced mid-to-late expansion efficiency, and a controlled expansion history. This suggests that the layered encapsulation process employed in the present invention can further optimize and control the expansion rate and final expansion efficiency of the crack-resistant functional material, enhancing its crack-resistant effectiveness in practical engineering applications. .

[0104] Taking the concrete mix ratio of a certain section of ballastless track slab as the application mix ratio, different types of slab concrete were prepared by adding equal amounts of the anti-cracking functional materials prepared in the examples and comparative examples to 8% of the cementitious material. The specific concrete mix ratios are shown in Table 2.

[0105] Table 2 Concrete mix ratio of a section of ballastless track slab

[0106] Ingredients cement fly ash Anti-crack functional materials sand gravel water water reducer <![CDATA[Weight (kg / m 3 )]]> 321 73 34 727 1091 154 4.3

[0107] The adiabatic temperature rise test for concrete was conducted in accordance with GB / T 50080-2016, "Standard for Test Methods of Ordinary Concrete Mixture Properties." The adiabatic temperature rise of concrete was measured using a BY-ATC / JR adiabatic temperature rise instrument from Zhoushan Boyuan Technology Development Co., Ltd. The initial temperature of the test was 20°C. The early-stage crack resistance test for concrete was conducted in accordance with GB / T 50082-2024, "Standard for Test Methods for Long-term Properties and Durability of Ordinary Concrete." The drying shrinkage test for concrete was conducted in accordance with GB / T 50082-2024, "Standard for Test Methods for Long-term Properties and Durability of Ordinary Concrete." The autogenous shrinkage test for concrete was conducted in accordance with GB / T 50082-2024, "Standard for Test Methods for Long-term Properties and Durability of Ordinary Concrete." The specific experimental results are shown in Tables 3 to 6.

[0108] Table 3 Test results of thermal insulation temperature rise of roadbed slab concrete with different anti-cracking functional materials (℃)

[0109] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 1d adiabatic temperature rise 1.9 1.6 1.4 16.5 12.6 11.2 3D adiabatic temperature rise 21.5 20.1 19.2 40.9 29.8 28.5 7d adiabatic temperature rise 34.5 33.8 32.7 46.1 42.9 41.6

[0110] Table 4 Experimental results of early crack resistance of roadbed slab concrete with different anti-cracking functional materials

[0111]

[0112] Table 5 Experimental results of drying shrinkage performance of roadbed slab concrete with different anti-cracking functional materials

[0113]

[0114] Table 6 Experimental results of autogenous shrinkage performance of roadbed slab concrete with different anti-cracking functional materials

[0115]

[0116]

[0117] It can be seen from the concrete adiabatic temperature rise test in Table 3 that, compared with the comparative example of anti-cracking functional materials prepared by the traditional scheme and process, the early adiabatic temperature rise of the roadbed slab concrete prepared by the embodiment of the present invention using the layer-by-layer wrapping and sequential slow-release scheme is significantly lower than that of the comparative example before 3 days, and the adiabatic temperature rise at 7 days is also lower than the corresponding value of the comparative example, indicating that the adoption of this method can significantly reduce the adiabatic temperature rise of the roadbed slab concrete, and correspondingly reduce the temperature drop amplitude and temperature drop shrinkage stress of the roadbed slab concrete, thereby improving the anti-cracking performance of the roadbed slab concrete.

[0118] It can be seen from the early crack resistance test of concrete in Table 4 that, compared with the comparative examples of anti-cracking functional materials prepared by traditional schemes and processes, the roadbed slab concrete prepared by the embodiment of the present invention using the layer-by-layer wrapping and sequential slow-release scheme can effectively reduce the occurrence of early cracks and even eliminate the risk of early cracking. Even if early cracks occur, their crack width, crack length and crack area are significantly suppressed.

[0119] The concrete drying shrinkage performance tests in Table 5 show that, compared to the comparative example of anti-cracking functional materials prepared using traditional methods and processes, the roadbed slab concrete prepared using the layer-by-layer coating and sequential slow-release method according to the present invention still exhibits a certain dry-curing expansion effect during the 14-28 days of curing. Drying shrinkage begins to appear in the concrete specimens after 28 days, and the final drying shrinkage value at 90 days is significantly lower than that of the comparative example. This shows that the present invention has a better shrinkage compensation effect on the drying shrinkage stress of the roadbed slab concrete and higher crack resistance.

[0120] The concrete drying shrinkage performance tests in Table 6 show that, compared to the comparative example of anti-cracking functional materials prepared using traditional methods and processes, the roadbed slab concrete prepared using the layer-by-layer wrapping and sequential slow-release method exhibited a sustained self-expansion effect over the 90-day sealed, insulated curing period. While the roadbed slab concrete prepared using the comparative example also exhibited some self-expansion early on, it exhibited significant shrinkage deformation later on. This indicates that the embodiments of the present invention can fully compensate for the self-shrinkage of the roadbed slab concrete under sealed, insulated curing conditions, generating self-expansion. This eliminates the self-shrinkage stress of the roadbed slab concrete while reducing the restraining stresses of the precast sleepers and baseplates through the self-expansion effect, significantly improving the roadbed slab concrete's crack resistance.

[0121] The embodiments used above are only for illustrating and explaining the contents of the present invention and do not constitute any special limitation to the present invention. Any form of modification made without departing from the basic concept of the present invention, as well as obvious modifications derived therefrom, fall within the scope of protection of the present invention.

Claims

1. A crack-resistant functional material for ballastless track slab concrete, characterized in that: The invention comprises a microgel coating layer and loaded microspheres coated inside by the microgel coating layer; the loaded microspheres comprise carbonized puffed rice husks and core-shell structured microspheres loaded in the pores of the carbonized puffed rice husks; the core-shell structured microspheres comprise a protein-modified starch coating layer and a composite expander coated inside by the protein-modified starch coating layer; the composite expander is obtained by thoroughly mixing a magnesium oxide expander and a modified calcium oxide expander; Among them, the mass of the composite expander is 60 to 75 parts; the mass of the protein-modified starch coating layer is 5 to 10 parts; the mass of the carbonized puffed rice husk is 15 to 20 parts; the mass of the microgel coating layer is 5 to 10 parts; the above are all mass parts; the modified calcium oxide expander is a calcium oxide expander with calcium carbonate coated on the surface.

2. The anti-crack functional material according to claim 1, characterized in that: In the modified calcium oxide expansion agent, the encapsulation amount of calcium carbonate is 5% to 10% of the mass of the calcium oxide expansion agent.

3. The anti-crack functional material according to claim 1 or 2, characterized in that: In the composite expansion agent, the mass ratio of the magnesium oxide expansion agent to the modified calcium oxide expansion agent is 2-3:3-2.

4. The anti-crack functional material according to claim 3, characterized in that: The material of the protein-modified starch coating layer is carboxymethyl starch modified by alcohol-soluble protein.

5. The anti-crack functional material according to claim 3, characterized in that: The carbonized puffed rice husk is obtained by sequentially subjecting the rice husk to puffing and pyrolysis carbonization treatments.

6. The anti-crack functional material according to claim 3, characterized in that: The material of the microgel coating layer is temperature-sensitive microgel.

7. The method for preparing the anti-cracking functional material according to any one of claims 1 to 6, characterized in that: Including steps: S1. Preparation of modified calcium oxide expansion agent: introducing CO2 into calcium oxide clinker powder to carry out gas phase suspension carbonation reaction to form a calcium carbonate coating layer on the surface of calcium oxide to obtain the modified calcium oxide expansion agent; S2. Preparation of a composite expansion agent: fully mixing the magnesium oxide expansion agent and the modified calcium oxide expansion agent to obtain the composite expansion agent; S3. Preparation of core-shell structured spheres: using 60-75 parts by mass of the composite swelling agent as nucleating seeds, spray-drying a solution of alcohol-soluble protein-modified starch, and self-assembling on the surface of the composite swelling agent to form a 5-10 parts by mass protein-modified starch coating layer to obtain the core-shell structured spheres; S4. Preparation of loaded microspheres: uniformly mixing the carbonized expanded rice husk powder and the core-shell structured spheres in a mass ratio of 15-20:65-85, and fully dispersing the core-shell structured spheres so as to load the pores of the carbonized expanded rice husk powder to obtain the loaded microspheres; S5. Preparation of anti-cracking functional material: 80 to 105 parts by mass of the loaded microspheres are dispersed in an alcohol solution of the thermosensitive microgel, and the thermosensitive microgel is grown on the surface of the loaded microspheres by soap-free emulsion polymerization. After drying and calcination, a microgel coating layer of 5 to 10 parts by mass is formed on the surface of the loaded microspheres to obtain the anti-cracking functional material.

8. The preparation method according to claim 7, characterized in that In step S2, the mass ratio of the magnesium oxide expansion agent to the modified calcium oxide expansion agent is 2-3:3-2.

9. The preparation method according to claim 7, characterized in that In step S3, the preparation method of the prolamin-modified starch solution is as follows: S31, fully dispersing the prolamin in an alcohol solvent to prepare a prolamin colloidal solution; S32, adding carboxymethyl starch to the alcohol-soluble protein colloid solution and stirring evenly to obtain the alcohol-soluble protein modified starch solution.

10. The preparation method according to claim 7, characterized in that In step S4, the method for preparing the carbonized and expanded rice husk powder is as follows: S41, crushing the raw rice husk into coarse powder particles with a fineness of 10-20 mesh using a crusher, soaking the powder in water to moisten it, and then performing a puffing pretreatment in an extruder to obtain puffed rice husk; S42, using a carbonization furnace to pyrolyze and carbonize the puffed rice husk, and crushing and screening it into a fineness of 40-60 mesh to obtain the carbonized puffed rice husk powder.

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