High durability cement stabilized macadam base material and preparation method thereof

Abstract

The application relates to the technical field of road engineering materials, and particularly discloses a high-durability cement-stabilized macadam base material and a preparation method thereof. The material is mainly composed of graded aggregate, composite cementitious material and mixing water, the aggregate adopts a multi-grade particle size compounding system, porous basalt is selected as skeleton coarse aggregate, a gradient release composite modified layer is constructed on the surface and internal pores of the aggregate, and the composite cementitious material is compounded by ordinary Portland cement and calcined coal gangue powder. The preparation method mainly comprises the following core working procedures: aggregate gradient modification, aggregate dry mixing, glue material coating, wet mixing and standard curing. Through the gradient modification structure of the aggregate interface, the application optimizes the weak interface area of the aggregate and the slurry, adapts to the whole-cycle service requirements of material hydration, deformation and damage repair, improves the material interface structure, and improves the overall structural stability and long-term durability of the base. The preparation process is suitable for conventional engineering equipment and is suitable for large-scale construction application of road base materials.

Description

Technical Field

[0001] This application relates to the field of road engineering materials technology, and more specifically, it relates to a high-durability cement-stabilized crushed stone base course material and its preparation method. Background Technology

[0002] Cement-stabilized crushed stone is a commonly used inorganic binder material in road base engineering. It relies primarily on the aggregate interlocking skeleton and cementitious hydration products to form an integral load-bearing structure, possessing excellent mechanical load-bearing capacity and engineering applicability. The overall service quality of this type of material largely depends on the interfacial bonding state between the aggregate and the cementitious paste. The stability of the interfacial structure directly affects the strength development, volume deformation, and long-term durability of the base material, and is crucial to ensuring the long-term stable service of the road base.

[0003] Existing conventional cement-stabilized crushed stone base materials mostly use ordinary dense crushed stone aggregates without functional modification and optimization of the aggregate-slurry interface. The interface transition zone generally suffers from loose pore structure and weak bonding performance. At the same time, conventional materials lack a full-cycle control mechanism to adapt to the hydration process, drying shrinkage deformation, and later crack damage. They are prone to interface failure, shrinkage cracking, and durability degradation during service. It is difficult to balance the early forming stability and long-term service durability of the material, which is a common technical problem in the current technology. Summary of the Invention

[0004] To address the problem of insufficient long-term durability caused by the temporal and spatial mismatch between the interface modification methods of cement-stabilized crushed stone base courses and the full-cycle performance requirements of the base courses in existing technologies, this application provides a high-durability cement-stabilized crushed stone base course material and its preparation method.

[0005] In a first aspect, this application provides a high-durability cement-stabilized crushed stone base course material, employing the following technical solution:

[0006] A high-durability cement-stabilized crushed stone base course material comprises the following raw materials in parts by weight: 100 parts graded aggregate, 4.5-6 parts composite cementitious material, and 5.0-6.5 parts mixing water;

[0007] The graded aggregate comprises coarse aggregate with a skeleton particle size of 9.5–31.5 mm, coarse aggregate with a filler particle size of 4.75–9.5 mm, and fine aggregate. The coarse aggregate with the skeleton particle size is entirely made of porous basalt aggregate. The internal pores of the porous basalt aggregate are impregnated with a nucleus-in-cell curing composite layer. The aggregate surface is coated with a temperature-sensitive controlled-release expansion layer and a stress-sensitive mineralization repair layer from the inside out. The three layers together constitute a gradient release composite modification layer. The total mass of the gradient release composite modification layer is 2.8%–3.8% of the mass of the porous basalt aggregate. The modification layer consists of the nucleus-in-cell curing composite layer, the temperature-sensitive controlled-release expansion layer, and the stress-sensitive mineralization repair layer from the inside out.

[0008] By adopting the above technical solution, and addressing the characteristics of high porosity and weak mechanical properties in the aggregate-slurry interface transition zone of cement-based materials, which is a major point of attack for cracking and erosion, functional modification is precisely anchored on the surface of the coarse aggregate skeleton that bears the load transfer. Based on the pore structure and surface morphology of porous aggregates, a gradient functional layer is constructed from the inner pores to the outer surface, allowing all functional components to concentrate their effects on the weak interfacial area. This overcomes the limitations of conventional admixtures, such as uneven component dispersion, low effective utilization, and easy induction of matrix side effects. The three-layer structure is distributed radially along the aggregate, with functional sequences corresponding to the different needs of early, middle, and late stages of cement hydration. Based on spatially directional strengthening, full-cycle performance regulation is achieved, resulting in a systematic improvement in durability performance at a relatively low modification cost.

[0009] Preferably, the coarse aggregate of the skeleton particle size accounts for 32% to 38% of the total mass of the graded aggregate, with a porosity of 18% to 25% and a crushing value ≤ 22%; the coarse aggregate of the filler particle size accounts for 20% to 25% of the total mass of the graded aggregate and is made of limestone crushed stone; the fine aggregate accounts for 37% to 48% of the total mass of the graded aggregate and is made of manufactured sand with a fineness modulus of 2.6 to 2.9; the composite cementitious material is composed of P·O 42.5 ordinary Portland cement and calcined coal gangue powder, wherein the calcined coal gangue powder accounts for 8% to 12% of the total mass of the composite cementitious material, has a loss on ignition ≤ 5%, and a 7-day activity index ≥ 75%.

[0010] By adopting the above technical solution, the parameter settings of the skeleton aggregate take into account both the load-bearing stability of the skeleton interlocking structure and the load capacity of the functional components, providing sufficient adhesion space for interface modification while ensuring the overall mechanical strength of the base layer. Conventional road materials are used for the filler and fine aggregates, ensuring gradation continuity while controlling overall costs. Calcined coal gangue powder is incorporated into the composite cementitious material, utilizing its pozzolanic activity to undergo a secondary reaction with cement hydration products, generating cementitious substances such as hydrated calcium silicate. This refines the internal pores of the slurry, improves the matrix density and interfacial bonding performance, and simultaneously disposes of industrial solid waste, reducing the environmental impact of the material. The limited quality parameters ensure stable strength development of the cementitious system, avoiding problems such as insufficient early strength or later performance fluctuations.

[0011] Preferably, the nucleus-in-the-core protective composite layer accounts for 29%–31% of the total mass of the modified layer and is composed of nano-calcium silicate seeds and nano-superabsorbent resin microspheres at a mass ratio of 4:(1–1.2); the temperature-sensitive controlled-release expansion layer accounts for 44%–46% of the total mass of the modified layer and is composed of a core composite powder and an outer temperature-sensitive composite coating. The core composite powder is composed of citric acid chelated calcium, anhydrite, and metakaolin micro powder at a mass ratio of 1:(2.5–3):(0.3–0.5); the stress-sensitive mineralization repair layer accounts for 23%–27% of the total mass of the modified layer and uses hydroxypropyl methylcellulose as the film-forming matrix. The film-forming matrix is ​​doped with nano-calcium carbonate whiskers and nano-active calcium carbonate micro powder.

[0012] By adopting the above technical solution, the inner layer penetrates into the pores of the aggregate, and the nano-calcium silicate seed crystals can serve as hydration heterogeneous nucleation sites, reducing the hydration reaction energy barrier, inducing the orderly growth of hydration gel products in the interface region, refining the grain size, and significantly reducing the porosity of the interface transition zone. Nano-superabsorbent resin microspheres are sealed in the pores and slowly release water with changes in the humidity of the slurry, continuously replenishing the water required for hydration in the interface region, promoting the later hydration of the cementitious material, and reserving an in-situ water source for the repair reaction at cracks during service life. The middle layer coats the outer side of the inner layer. Citric acid chelated calcium, anhydrite, and metakaolin together constitute an ettringite-type expansion source, which gradually reacts in an alkaline porous solution environment to generate ettringite, compensating for the drying shrinkage of cement stone through the volume expansion effect. The external temperature-sensitive coating has a dense structure at room temperature, which can significantly reduce the dissolution rate of the expansion components and avoid early rapid expansion causing internal micro-damage. The outermost layer, located on the outermost side of the modified layer, serves as a polymer film-forming matrix that supports functional fillers. Nano-calcium carbonate whiskers regulate the mechanical properties of the film, ensuring it remains intact and sealed under normal service stress and fractures directionally under stress concentration at the crack tip, guaranteeing the precise release of repair components. These three functional layers are interconnected, forming a complete regulatory chain of interface strengthening, shrinkage compensation, and crack repair.

[0013] Preferably, the temperature-sensitive composite coating is composed of hydroxypropyl methylcellulose and stearic acid in a mass ratio of 7:(3-3.6), and the softening temperature is 32-38°C; in the stress-sensitive mineralization repair layer, the amount of nano-calcium carbonate whiskers is 15%-20% of the total mass of the stress-sensitive mineralization repair layer, the amount of nano-active calcium carbonate micropowder is 10%-15% of the total mass of the stress-sensitive mineralization repair layer, and the stress-sensitive mineralization repair layer also contains diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase, wherein the diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase accounts for 55%-60% of the total mass of the stress-sensitive mineralization repair layer.

[0014] By adopting the above technical solution, the temperature-sensitive composite coating regulates the softening temperature through the component ratio, so that it reaches the softening range under the combined effect of the normal construction environment temperature in summer and the heat release from cement hydration. When the local temperature at the interface reaches the threshold, the coating softens, resulting in an increase in porosity and a significant increase in the dissolution rate of the expansion component. This allows the occurrence time of the expansion effect to adaptively match the development process of cement drying shrinkage without the need for additional external triggering conditions, thus improving the accuracy of shrinkage compensation. In the outer repair system, the calcium alginate encapsulation structure creates a local protective microenvironment for carbonic anhydrase, blocking the strong alkaline erosion of the cement pore solution, extending the retention period of enzyme activity, and ensuring that it still has repair capabilities when cracks appear in the later stages of service. Diatomaceous earth, as a porous carrier for dispersing and encapsulating enzyme preparations, avoids component aggregation and also plays a buffering and protective role. Nano-active calcium carbonate powder, with its high specific surface area, adsorbs and enriches free calcium ions in the slurry pores, and at the same time serves as a heterogeneous nucleation site for mineralization deposition, providing an in-situ crystal nucleus template for calcium carbonate crystal growth. It combines with carbonate ions generated by carbonic anhydrase catalyzing carbon dioxide hydration, and in-situ deposits calcium carbonate to fill microcracks, blocking the intrusion channels of water and harmful ions, and achieving active repair of cracks.

[0015] Secondly, this application provides a method for preparing a high-durability cement-stabilized crushed stone base course material, employing the following technical solution:

[0016] A method for preparing a high-durability cement-stabilized crushed stone base course material includes the following steps:

[0017] S1. Negative pressure load inner layer: After the porous basalt aggregate is dried to constant weight, it is transferred to a negative pressure impregnation tank, injected with a composite suspension for forming a nucleus-in-the-mold composite layer, and after negative pressure treatment, it is taken out and dried at low temperature until the surface is dry to obtain the inner layer load aggregate.

[0018] S2, Middle Layer Fluidized Coating: The inner layer of loaded aggregate is fluidized and coated. The air inlet temperature is controlled. First, a temperature-sensitive binder is sprayed to wet the surface of the aggregate. Then, composite powder containing expansion components is sprayed in at a uniform speed. The powder is evenly coated by airflow tumbling. After low-temperature drying to form a film, a temperature-sensitive controlled-release expansion layer is formed, resulting in middle layer coated aggregate.

[0019] S3, outer fluidized coating: continue fluidized coating treatment, spray film-forming liquid containing brittle filler and mineralized crystal nucleus components, and simultaneously spray repair composite powder containing mineralizing enzyme at a uniform speed, so that the powder adheres evenly to the outside of the temperature-sensitive controlled release expansion layer, and after low-temperature drying to form a film, modified porous skeleton aggregate is obtained.

[0020] S4. Dry mixing of aggregates: Add the modified porous skeleton aggregate, filled particle size crushed stone and fine aggregate into the mixing tank according to the mix ratio and perform dry mixing.

[0021] S5. Dry mixing and coating of adhesive materials: Add premixed composite cementitious material into the mixing tank and continue dry mixing to make the cementitious powder evenly coat the surface of each grade of aggregate.

[0022] S6. Wet Mixing and Curing: Add metered mixing water and start the wet mixing mode. Stir until the mixture is uniform, then discharge and spread it. After rolling and molding, cover with a moisturizing material for curing.

[0023] By adopting the above technical solution, a process route of first impregnating and loading the pores, and then coating with a layered fluidized bed is used to construct a three-layer modified structure from the inside out. This ensures accurate spatial positioning and structural integrity of each functional layer, avoiding premature mixing and reaction of different functional components. The stepwise mixing process first completes the uniform mixing of aggregates at each level to form a stable gradation skeleton, and then uniformly coats the aggregate surface with cementitious powder. The buffering effect of the powder reduces the direct erosion of the modified layer by water flow during wet mixing, maximizing the preservation of the functional integrity of the interface modified structure. The entire preparation process can be realized by modifying existing aggregate processing and water-stabilized mixing equipment. The process is smoothly connected, the parameters are highly controllable, the batch stability is high, and it is suitable for the needs of large-scale applications in road engineering.

[0024] Preferably, in step S1, the drying temperature for drying to constant weight is 100-110°C, the mass concentration of the composite suspension is 9%-11%, the composite suspension is prepared by dispersing the components forming the crystal nucleus inner nucleation layer in water at a mass ratio of 4:(1-1.2), the relative negative pressure is 0.06-0.10 MPa, the processing time is 30-40 min, and the low-temperature drying temperature is 55-65°C.

[0025] By adopting the above technical solutions, the drying process can fully remove adsorbed water and free water from the pores of porous aggregates, and empty the pore space to provide conditions for the loading of functional components; the suspension of appropriate concentration ensures uniform dispersion of components and stable and controllable loading; the negative pressure treatment can displace the air in the pores, promote the suspension to penetrate into the microporous structure inside the aggregate, and improve the loading depth and distribution uniformity of the inner layer components; the low temperature drying conditions can remove excess free water from the surface of the aggregate and the pores, while avoiding structural damage to the superabsorbent resin microspheres due to excessive water loss at high temperature, thus ensuring the stability of its internal curing function.

[0026] Preferably, in step S2, the inlet air temperature is controlled at 26–30°C, the atomizing binder is a temperature-sensitive composite emulsion formulated from the components forming the temperature-sensitive composite film, and the softening temperature is 32–38°C; the expanding composite powder is the internal composite powder of the temperature-sensitive controlled-release expanding layer, which is composed of the powder components forming the layer; the powder injection rate corresponding to each 100 kg of inner layer loaded aggregate is controlled at 0.8–1.2 kg / min; the low-temperature drying film formation temperature is 26–30°C, and the drying time is 12–18 min.

[0027] By adopting the above technical solution, the inlet air temperature in this section is adapted to the film-forming conditions of the temperature-sensitive composite emulsion, ensuring that the binder forms a uniform and continuous film on the aggregate surface, while preventing premature softening failure of the temperature-sensitive coating; the atomized binder uniformly wets the aggregate surface, improving the adhesion and coating uniformity of the expanded composite powder; matching the powder injection rate according to the aggregate processing volume allows for precise control of the intermediate coating thickness, ensuring consistency of modification effects between batches; the low-temperature curing conditions allow the temperature-sensitive coating to fully form and cross-link, while preventing premature reaction of the internal expansion components, ensuring the timing accuracy of the expansion function. The coating microstructure formed under these low-temperature drying conditions is dense and uniform, with stearic acid uniformly dispersed in the hydroxypropyl methylcellulose matrix in microcrystalline form, enabling stable triggering of softening when the temperature is first raised to the softening temperature during subsequent service life.

[0028] Preferably, in step S3, the film-forming solution is a hydroxypropyl methylcellulose solution, in which nano-calcium carbonate whiskers and nano-active calcium carbonate micropowder are pre-dispersed; the mineralization repair composite powder is diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase; and the low-temperature drying film-forming temperature is 26–30°C, and the drying time is 18–22 min.

[0029] By adopting the above technical solution, the pre-dispersed functional filler in the film-forming solution can ensure that the nano-calcium carbonate whiskers and nano-active calcium carbonate micropowder are uniformly distributed in the film layer, avoiding local agglomeration that affects the mechanical properties and repair effect of the film layer; the simultaneous spraying of mineralized repair composite powder allows the functional components to be uniformly embedded in the film-forming matrix, ensuring that each component is released synchronously when the crack is triggered; the corresponding curing temperature and time can allow the outer film layer to dry and form fully, while maintaining the biological activity of carbonic anhydrase and avoiding the denaturation and inactivation of enzyme protein caused by high temperature.

[0030] Preferably, in step S4, the mixing time for the dry mixing process is 80-100 seconds; in step S5, the duration of the continued dry mixing is 50-70 seconds.

[0031] By adopting the above technical solutions, the dry mixing stage of aggregates can ensure that aggregates of all sizes are mixed evenly, forming a continuous and stable dense gradation structure. After the addition of cementitious powder, dry mixing can be continued, so that the powder can be evenly coated on the surface of aggregates of all sizes, forming a continuous powder buffer layer. This reduces the direct scouring and wear of the modified layer on the surface of the aggregates by the water flow during subsequent wet mixing, and preserves the structural integrity and functional effectiveness of the gradient modified layer to the greatest extent.

[0032] Preferably, in step S6, the mixing time of the wet mixing mode is 110-130s, the curing time of the moisturizing material is not less than 7 days, and the time between the end of the rolling and the completion of the water mixing does not exceed 2 hours.

[0033] By adopting the above technical solutions, a suitable wet mixing time can ensure that the mixture is uniformly mixed without any white spots, while avoiding excessive mixing that could cause wear and detachment of the modified layer on the aggregate surface; the compaction operation is completed before the initial setting of the cement, which can ensure the structural density and overall mechanical strength of the base layer after compaction; sufficient moisture curing can provide enough moisture for the hydration reaction of cement and active admixtures, ensuring the stable development of early strength, while providing external replenishment for the moisture reserve of the inner curing components, ensuring the long-term effectiveness of the inner curing function.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. Since this application uses porous basalt aggregate as the skeleton coarse aggregate and constructs a three-layer gradient release composite modification layer on the surface and internal pores of the aggregate, it can accurately act on the weak area of ​​the interface between the aggregate and the cement paste. Relying on the layered functional structure to adapt to the full cycle change law of material hydration, deformation and damage repair, it effectively optimizes the material interface structure and overall service performance, and improves the comprehensive durability of cement-stabilized crushed stone base course.

[0036] 2. In this application, a multi-grade aggregate combined with a composite cementitious material system containing calcined coal gangue powder is preferred. By reasonably matching the aggregate skeleton parameters and the activity index of the cementitious material, the structure of the cementitious hydration products can be optimized by utilizing the pozzolanic activity of coal gangue powder, the internal pores of the matrix can be refined, the stability of the aggregate interlocking skeleton structure can be improved, and the overall mechanical properties and structural density of the material can be steadily improved.

[0037] 3. This application sets up a time-adaptive temperature-sensitive controlled-release expansion system and a stress-sensitive mineralization repair system. It relies on the temperature-sensitive coating to regulate the release rhythm of the expansion components under the synergistic conditions of the construction environment and cement hydration heat to match the material's drying shrinkage deformation process. It also relies on the embedded functional components to ensure long-term mineralization repair capability after damage, effectively improving the material's volume stability and microcrack self-repair capability.

[0038] 4. The preparation method of this application uses a process of negative pressure impregnation layered loading and fluidized bed gradient coating to prepare modified aggregates, combined with a step-by-step dry and wet mixing molding process. This method can completely preserve the independent structure and sequential function of each functional layer, reduce the loss of modified components, and ensure the performance uniformity and process stability of the batch-prepared materials. Attached Figure Description

[0039] Figure 1 This is a flowchart of a method for preparing a high-durability cement-stabilized crushed stone base course material provided in this application;

[0040] Figure 2 These are comparison diagrams of the unconfined compressive strength tests of the various embodiments provided in this application and the comparative examples;

[0041] Figure 3 These are comparative diagrams of the drying shrinkage performance tests of the various embodiments and comparative examples provided in this application;

[0042] Figure 4 These are comparative diagrams showing the crack self-healing performance tests of the various embodiments and comparative examples provided in this application. Detailed Implementation

[0043] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0044] Technical concept: The existing methods for improving the durability of cement-stabilized crushed stone base courses mainly involve the uniform addition of admixtures. This approach has problems such as low utilization rate of functional components, misalignment between expansion compensation and shrinkage development, and difficulty in the repair components taking effect at the crack initiation site. The root cause is that the uniform addition method cannot accurately apply the modified function to the mechanically weak link and crack origination site of the aggregate-slurry interface transition zone.

[0045] This application shifts the modification target from the entire matrix to the interface of the aggregate skeleton. Utilizing porous basalt aggregate as a carrier, a three-layer gradient release composite modification layer is constructed sequentially on its surface and within its internal pores. This achieves a spatiotemporal synergistic configuration of three functions: nucleus-induced hydration enhancement, temperature-sensitive controlled-release expansion compensation, and stress-sensitive mineralization repair. The inner layer strengthens interfacial bonding and stores internal curing water in the early stages. The middle layer utilizes the synergistic effect of ambient temperature and cement hydration exothermics to trigger the directional release of expansion components during the shrinkage development period. The outer layer activates mineralization repair through tip stress rupture during service life when cracks propagate along the interface, forming a full-cycle durability assurance system encompassing early enhancement, mid-term compensation, and long-term repair.

[0046] Preparation Example 1: The preparation method of diatomaceous earth micropowder loaded with calcium alginate-encapsulated carbonic anhydrase is as follows: Take 5 parts of refined diatomaceous earth with a particle size of 20-50 μm, completely immerse it in 5% hydrochloric acid solution for 12 h for acidification treatment, wash with deionized water until the pH of the washing solution is 7.0, and dry at 120℃ to constant weight to obtain pretreated diatomaceous earth. Dissolve 1 part of carbonic anhydrase in 100 parts of pH 7.0 phosphate buffer, add the pretreated diatomaceous earth under 35℃ water bath conditions, and slowly stir at a rate of 80-120 r / min for 4 h to adsorb, to obtain an enzyme-carrier complex suspension.

[0047] Take another 200 parts of deionized water, heat it to 45℃, add 5 parts of sodium alginate and stir to dissolve, to prepare a 2.5% sodium alginate solution. Transfer the entire enzyme-carrier complex suspension into it and stir at a high speed of 1500-2000 r / min for 30 min to form a uniform slurry. Under continuous stirring at 60 r / min, the slurry is dripped into 500 parts of a 3% calcium chloride solution at a rate of 5 mL / min through an injection needle with an inner diameter of 0.5 mm. After dripping, allow it to stand for cross-linking and solidification for 2 h, filter out the microspheres, wash them 3 times with deionized water, spread them evenly in a freeze dryer at -50℃ and a vacuum degree of 10 Pa and dry for 24 h to obtain diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase.

[0048] Example 1: This example provides a high-durability cement-stabilized crushed stone base material, comprising the following raw materials in parts by weight: 100 parts graded aggregate, 5.25 parts composite cementitious material, and 5.75 parts mixing water.

[0049] The graded aggregate includes coarse aggregate with a skeleton size of 9.5–31.5 mm, coarse aggregate with a filler size of 4.75–9.5 mm, and fine aggregate. The skeleton coarse aggregate is made entirely of porous basalt aggregate, accounting for 35% of the total mass of the graded aggregate, with a porosity of 21.5% and a crushing value of 21%. The filler coarse aggregate accounts for 22.5% of the total mass of the graded aggregate and is made of limestone crushed stone. The fine aggregate accounts for 42.5% of the total mass of the graded aggregate and is made of manufactured sand with a fineness modulus of 2.75.

[0050] The composite cementitious material is composed of P·O 42.5 ordinary Portland cement and calcined coal gangue powder, wherein the calcined coal gangue powder accounts for 10% of the total mass of the composite cementitious material, the loss on ignition is 4.2%, and the 7-day activity index is 78%. The 7-day activity index is determined according to the activity index test method in GB / T1596-2017 "Fly Ash for Cement and Concrete".

[0051] The porous basalt aggregate has an internal nucleus curing composite layer impregnated in its pores. The aggregate surface is covered with a temperature-sensitive controlled-release expansion layer and a stress-sensitive mineralization repair layer from the inside out. The three layers together constitute a gradient release composite modification layer. The total mass of the gradient release composite modification layer is 3.3% of the mass of the porous basalt aggregate. The modification layer consists of the internal nucleus curing composite layer, the temperature-sensitive controlled-release expansion layer, and the stress-sensitive mineralization repair layer from the inside out.

[0052] The modified layer comprises 30% of the total mass of the nucleus-in-the-core composite layer, which is composed of nano-calcium silicate seeds and nano-superabsorbent resin microspheres in a mass ratio of 4:1.1; the thermosensitive controlled-release expansion layer comprises 45% of the total mass of the modified layer, which consists of a core composite powder and an outer thermosensitive composite coating. The core composite powder is composed of citric acid chelated calcium, anhydrite, and metakaolin micro powder in a mass ratio of 1:2.75:0.4; and the stress-sensitive mineralization repair layer comprises 25% of the total mass of the modified layer, which uses hydroxypropyl methylcellulose as the film-forming matrix and incorporates nano-calcium carbonate whiskers and nano-active calcium carbonate micro powder.

[0053] The temperature-sensitive composite coating is composed of hydroxypropyl methylcellulose and stearic acid in a mass ratio of 7:3.3, with a softening temperature of 35℃. In the stress-sensitive mineralization repair layer, the amount of nano-calcium carbonate whiskers is 17.5% of the total mass of the stress-sensitive mineralization repair layer, the amount of nano-active calcium carbonate micropowder is 12.5% ​​of the total mass of the stress-sensitive mineralization repair layer, the amount of diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase is 57% of the total mass of the stress-sensitive mineralization repair layer, and the remainder is the hydroxypropyl methylcellulose film-forming matrix, with the total mass ratio of the four components being 100%. The diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase is prepared using the method of Preparation Example 1.

[0054] The preparation method of the above-mentioned high-durability cement-stabilized crushed stone base course material includes the following steps:

[0055] S1. Negative pressure load inner layer: After the porous basalt aggregate is dried to constant weight, it is transferred to a negative pressure impregnation tank, injected with a composite suspension for forming a nucleus-in-the-mold composite layer, and after negative pressure treatment, it is taken out and dried at low temperature until the surface is dry to obtain the inner layer load aggregate.

[0056] The drying temperature for constant weight was 105℃; the mass concentration of the composite suspension was 10%, and the composite suspension was prepared by dispersing the components that form the composite layer within the crystal nucleus in water at a mass ratio of 4:1.1. During preparation, a magnetic stirrer with a speed of 300 r / min was used to stir for 20 min until the dispersion was uniform; the relative negative pressure was 0.08 MPa, the treatment time was 35 min, and the liquid-solid mass ratio during the impregnation process was 1.5:1 to ensure that the aggregate was completely submerged; the low-temperature drying temperature was 60℃, the drying time was 2 h, and the material was turned over every 30 min during the drying process to ensure uniform drying.

[0057] S2. Middle layer fluidized bed coating: The inner layer loaded aggregate is transferred into the fluidized bed coating equipment. The inlet air temperature is controlled. First, a temperature-sensitive binder is sprayed to wet the surface of the aggregate. Then, composite powder containing expansion components is sprayed in at a uniform speed. The powder is uniformly coated by airflow tumbling. After low-temperature drying to form a film, a temperature-sensitive controlled-release expansion layer is formed, resulting in the middle layer coated aggregate.

[0058] The inlet air temperature is controlled at 28℃, and the apparent air velocity of the fluidized bed is controlled at 1.2~1.5m / s to ensure that the aggregate is in a fully fluidized state. The atomizing binder is a temperature-sensitive composite emulsion formulated from the components that form the temperature-sensitive composite film, with a softening temperature of 35℃, an emulsion solid content of 8%, and a spray pressure of 0.2MPa. The expanded composite powder is the internal composite powder of the temperature-sensitive controlled-release expanded layer, which is composed of the powder components that form this layer. The powder injection rate corresponding to each 100kg of inner layer loaded aggregate is controlled at 1.0kg / min. The low-temperature drying film formation temperature is 28℃, and the drying time is 15min.

[0059] S3. Outer fluidized bed coating: Maintain the operation of the fluidized bed coating equipment, spray the film-forming liquid containing brittle filler and mineralized crystal nucleus components, and simultaneously and uniformly spray the repair composite powder containing mineralizing enzymes, so that the powder adheres evenly to the outside of the temperature-sensitive controlled-release expansion layer, and after low-temperature drying to form a film, the modified porous skeleton aggregate is obtained.

[0060] The film-forming solution is a hydroxypropyl methylcellulose solution with a mass concentration of 6%. Nano-calcium carbonate whiskers and nano-active calcium carbonate micropowder are pre-dispersed in the solution. The dispersion process is carried out by a high-speed shearing machine at 2000 r / min for 15 min. The mineralization repair composite powder is diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase. The low-temperature drying film-forming temperature is 28℃, the drying time is 20 min, and after drying, it is sieved through a 10-mesh sieve to remove surface floating powder.

[0061] S4. Dry mixing of aggregates: Add the modified porous skeleton aggregate, filled crushed stone and fine aggregate into the mixing tank according to the mix proportion and perform dry mixing.

[0062] The dry mixing process lasts for 90 seconds and uses a twin-shaft forced mixer with a mixing shaft speed of 60 r / min.

[0063] S5. Dry mixing and coating of adhesive materials: Add premixed composite cementitious material into the mixing tank and continue dry mixing to make the cementitious powder evenly coat the surface of each grade of aggregate.

[0064] The dry mixing time is 60 seconds, the stirring speed is maintained at 60 r / min, and the composite cementitious material is premixed from P·O 42.5 ordinary Portland cement and calcined coal gangue powder. The calcined coal gangue powder accounts for 10% of the total mass of the composite cementitious material, and the premixing time is 5 minutes.

[0065] S6. Wet Mixing and Curing: Add metered mixing water and start the wet mixing mode. Stir until the mixture is uniform, then discharge and spread it. After rolling and molding, cover with a moisturizing material for curing.

[0066] The wet-mixing mode has a mixing time of 120 seconds and a mixing speed of 65 r / min; the paving uses a base course paver with a loose paving coefficient of 1.30 and a paving speed of 1.5 m / min; the compaction procedure is as follows: first, a double-drum static compaction for one pass, then a single-drum low-frequency high-amplitude vibratory compaction for two passes, and finally, a rubber-tired roller for one pass of rubbing compaction to finish the surface; the curing time of the moisture-retaining material is 7 days, during which water is sprayed 3 times a day to keep the surface moist; the time between the completion of compaction and the completion of water mixing is 1.5 hours.

[0067] Example 2: This example provides a high-durability cement-stabilized crushed stone base material, comprising the following raw materials in parts by weight: 100 parts graded aggregate, 4.5 parts composite cementitious material, and 5.0 parts mixing water.

[0068] The graded aggregate includes coarse aggregate with a skeleton size of 9.5–31.5 mm, coarse aggregate with a filler size of 4.75–9.5 mm, and fine aggregate. The skeleton coarse aggregate is made entirely of porous basalt aggregate, accounting for 32% of the total mass of the graded aggregate, with a porosity of 18% and a crushing value of 22%. The filler coarse aggregate accounts for 20% of the total mass of the graded aggregate and is made of limestone crushed stone. The fine aggregate accounts for 48% of the total mass of the graded aggregate and is made of manufactured sand with a fineness modulus of 2.6.

[0069] The composite cementitious material is composed of P·O 42.5 ordinary Portland cement and calcined coal gangue powder, wherein the calcined coal gangue powder accounts for 8% of the total mass of the composite cementitious material, the loss on ignition is 5%, and the 7-day activity index is 75%. The 7-day activity index is determined according to the activity index test method in GB / T1596-2017 "Fly Ash for Cement and Concrete".

[0070] The porous basalt aggregate has an internal nucleus curing composite layer impregnated in its pores. The aggregate surface is covered with a temperature-sensitive controlled-release expansion layer and a stress-sensitive mineralization repair layer from the inside out. The three layers together constitute a gradient release composite modification layer. The total mass of the gradient release composite modification layer is 2.8% of the mass of the porous basalt aggregate. The modification layer consists of the internal nucleus curing composite layer, the temperature-sensitive controlled-release expansion layer, and the stress-sensitive mineralization repair layer from the inside out.

[0071] The modified layer comprises 29% of the total mass of the nucleus-in-the-core composite layer, which is composed of nano-calcium silicate seeds and nano-superabsorbent resin microspheres in a mass ratio of 4:1; the thermosensitive controlled-release expansion layer comprises 44% of the total mass of the modified layer, which consists of a core composite powder and an outer thermosensitive composite coating. The core composite powder is composed of citric acid chelated calcium, anhydrite, and metakaolin micro powder in a mass ratio of 1:2.5:0.3; and the stress-sensitive mineralization repair layer comprises 27% of the total mass of the modified layer, which uses hydroxypropyl methylcellulose as the film-forming matrix and incorporates nano-calcium carbonate whiskers and nano-active calcium carbonate micro powder.

[0072] The temperature-sensitive composite coating is composed of hydroxypropyl methylcellulose and stearic acid in a mass ratio of 7:3, and the softening temperature is 32℃. In the stress-sensitive mineralization repair layer, the amount of nano-calcium carbonate whiskers is 15% of the total mass of the stress-sensitive mineralization repair layer, the amount of nano-active calcium carbonate micropowder is 10% of the total mass of the stress-sensitive mineralization repair layer, the amount of diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase accounts for 55% of the total mass of the stress-sensitive mineralization repair layer, and the remainder is the hydroxypropyl methylcellulose film-forming matrix, with the total mass ratio of the four components being 100%. The diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase is prepared using the method of Preparation Example 1.

[0073] The preparation method of the above-mentioned high-durability cement-stabilized crushed stone base course material includes the following steps:

[0074] S1. Negative pressure load inner layer: After the porous basalt aggregate is dried to constant weight, it is transferred to a negative pressure impregnation tank, injected with a composite suspension for forming a nucleus-in-the-mold composite layer, and after negative pressure treatment, it is taken out and dried at low temperature until the surface is dry to obtain the inner layer load aggregate.

[0075] The drying temperature for constant weight is 100℃; the mass concentration of the composite suspension is 9%, and the composite suspension is prepared by dispersing the components that form the protective composite layer in the crystal nucleus in water at a mass ratio of 4:1. During preparation, a magnetic stirrer with a speed of 280r / min is used to stir for 18min until the dispersion is uniform; the relative negative pressure is 0.06MPa, the treatment time is 30min, and the liquid-solid mass ratio during the impregnation process is 1.4:1 to ensure that the aggregate is completely submerged; the low-temperature drying temperature is 55℃, the drying time is 1.8h, and the material is turned over every 30min during the drying process to ensure uniform drying.

[0076] S2. Middle layer fluidized bed coating: The inner layer loaded aggregate is transferred into the fluidized bed coating equipment. The inlet air temperature is controlled. First, a temperature-sensitive binder is sprayed to wet the surface of the aggregate. Then, composite powder containing expansion components is sprayed in at a uniform speed. The powder is uniformly coated by airflow tumbling. After low-temperature drying to form a film, a temperature-sensitive controlled-release expansion layer is formed, resulting in the middle layer coated aggregate.

[0077] The inlet air temperature is controlled at 26℃, and the apparent air velocity of the fluidized bed is controlled at 1.1~1.4m / s to ensure that the aggregate is in a fully fluidized state. The atomizing binder is a temperature-sensitive composite emulsion formulated from the components that form the temperature-sensitive composite film, with a softening temperature of 32℃, an emulsion solid content of 7%, and a spray pressure of 0.18MPa. The expanded composite powder is the internal composite powder of the temperature-sensitive controlled-release expanded layer, which is composed of the powder components that form this layer. The powder injection rate corresponding to each 100kg of inner layer loaded aggregate is controlled at 0.8kg / min. The low-temperature drying film formation temperature is 26℃, and the drying time is 12min.

[0078] S3. Outer fluidized bed coating: Maintain the operation of the fluidized bed coating equipment, spray the film-forming liquid containing brittle filler and mineralized crystal nucleus components, and simultaneously and uniformly spray the repair composite powder containing mineralizing enzymes, so that the powder adheres evenly to the outside of the temperature-sensitive controlled-release expansion layer, and after low-temperature drying to form a film, the modified porous skeleton aggregate is obtained.

[0079] The film-forming solution is a hydroxypropyl methylcellulose solution with a mass concentration of 5%. Nano-calcium carbonate whiskers and nano-active calcium carbonate micropowder are pre-dispersed in the solution. The dispersion process is carried out by a high-speed shearing machine at 1800 r / min for 12 min. The mineralization repair composite powder is diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase. The low-temperature drying film-forming temperature is 26℃, the drying time is 18 min, and after drying, it is sieved through a 10-mesh sieve to remove surface floating powder.

[0080] S4. Dry mixing of aggregates: Add the modified porous skeleton aggregate, filled crushed stone and fine aggregate into the mixing tank according to the mix proportion and perform dry mixing.

[0081] The dry mixing process lasted for 80 seconds and used a twin-shaft forced mixer with a mixing shaft speed of 55 r / min.

[0082] S5. Dry mixing and coating of adhesive materials: Add premixed composite cementitious material into the mixing tank and continue dry mixing to make the cementitious powder evenly coat the surface of each grade of aggregate.

[0083] The dry mixing time is 50 seconds, the stirring speed is maintained at 55 r / min, and the composite cementitious material is premixed with P·O 42.5 ordinary Portland cement and calcined coal gangue powder. The calcined coal gangue powder accounts for 8% of the total mass of the composite cementitious material, and the premixing time is 4 minutes.

[0084] S6. Wet Mixing and Curing: Add metered mixing water and start the wet mixing mode. Stir until the mixture is uniform, then discharge and spread it. After rolling and molding, cover with a moisturizing material for curing.

[0085] The wet-mixing mode has a mixing time of 110 seconds and a mixing speed of 60 r / min; the paving uses a base course paver with a loose paving coefficient of 1.28 and a paving speed of 1.6 m / min; the compaction procedure is as follows: first, a double-drum static compaction once; then, a single-drum low-frequency high-amplitude vibratory compaction twice; and finally, a rubber-tired roller for rubbing and compaction once to finish the surface; the curing time of the moisture-retaining material is 7 days, during which water is sprayed twice a day to keep the surface moist; the time between the completion of compaction and the completion of water mixing is 2 hours.

[0086] Example 3: This example provides a high-durability cement-stabilized crushed stone base material, comprising the following raw materials in parts by weight: 100 parts graded aggregate, 6 parts composite cementitious material, and 6.5 parts mixing water.

[0087] The graded aggregate includes coarse aggregate with a skeleton size of 9.5–31.5 mm, coarse aggregate with a filler size of 4.75–9.5 mm, and fine aggregate. The skeleton coarse aggregate is made entirely of porous basalt aggregate, accounting for 38% of the total mass of the graded aggregate, with a porosity of 25% and a crushing value of 20%. The filler coarse aggregate accounts for 25% of the total mass of the graded aggregate and is made of limestone crushed stone. The fine aggregate accounts for 37% of the total mass of the graded aggregate and is made of manufactured sand with a fineness modulus of 2.9.

[0088] The composite cementitious material is composed of P·O 42.5 ordinary Portland cement and calcined coal gangue powder, wherein the calcined coal gangue powder accounts for 12% of the total mass of the composite cementitious material, the loss on ignition is 3.5%, and the 7-day activity index is 82%. The 7-day activity index is determined according to the activity index test method in GB / T1596-2017 "Fly Ash for Cement and Concrete".

[0089] The porous basalt aggregate has an internal nucleus curing composite layer impregnated in its pores. The aggregate surface is covered with a temperature-sensitive controlled-release expansion layer and a stress-sensitive mineralization repair layer from the inside out. The three layers together constitute a gradient release composite modification layer. The total mass of the gradient release composite modification layer is 3.8% of the mass of the porous basalt aggregate. The modification layer consists of the internal nucleus curing composite layer, the temperature-sensitive controlled-release expansion layer, and the stress-sensitive mineralization repair layer from the inside out.

[0090] The modified layer comprises 31% of the total mass of the nucleus-in-the-core composite layer, which is composed of nano-calcium silicate seeds and nano-superabsorbent resin microspheres in a mass ratio of 4:1.2; the thermosensitive controlled-release expansion layer comprises 46% of the total mass of the modified layer, which consists of a core composite powder and an outer thermosensitive composite coating. The core composite powder is composed of citric acid chelated calcium, anhydrite, and metakaolin micro powder in a mass ratio of 1:3:0.5; and the stress-sensitive mineralization repair layer comprises 23% of the total mass of the modified layer, which uses hydroxypropyl methylcellulose as the film-forming matrix and incorporates nano-calcium carbonate whiskers and nano-active calcium carbonate micro powder.

[0091] The temperature-sensitive composite coating is composed of hydroxypropyl methylcellulose and stearic acid in a mass ratio of 7:3.6, with a softening temperature of 38℃. In the stress-sensitive mineralization repair layer, the amount of nano-calcium carbonate whiskers is 20% of the total mass of the stress-sensitive mineralization repair layer, the amount of nano-active calcium carbonate micropowder is 15% of the total mass of the stress-sensitive mineralization repair layer, the diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase accounts for 60% of the total mass of the stress-sensitive mineralization repair layer, and the remainder is the hydroxypropyl methylcellulose film-forming matrix, with the total mass ratio of the four components being 100%. The diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase is prepared using the method of Preparation Example 1.

[0092] The preparation method of the above-mentioned high-durability cement-stabilized crushed stone base course material includes the following steps:

[0093] S1. Negative pressure load inner layer: After the porous basalt aggregate is dried to constant weight, it is transferred to a negative pressure impregnation tank, injected with a composite suspension for forming a nucleus-in-the-mold composite layer, and after negative pressure treatment, it is taken out and dried at low temperature until the surface is dry to obtain the inner layer load aggregate.

[0094] The drying temperature for achieving constant weight was 110℃; the mass concentration of the composite suspension was 11%, and the composite suspension was prepared by dispersing the components forming the crystal nucleus-in-the-core protective composite layer in water at a mass ratio of 4:1.2. During preparation, a magnetic stirrer with a speed of 320 r / min was used to stir for 22 min until the dispersion was uniform; the relative negative pressure was 0.10 MPa, the treatment time was 40 min, and the liquid-to-solid mass ratio during the impregnation process was 1.6:1 to ensure that the aggregate was completely submerged; the low-temperature drying temperature was 65℃, the drying time was 2.2 h, and the material was turned over every 30 min during the drying process to ensure uniform drying.

[0095] S2. Middle layer fluidized bed coating: The inner layer loaded aggregate is transferred into the fluidized bed coating equipment. The inlet air temperature is controlled. First, a temperature-sensitive binder is sprayed to wet the surface of the aggregate. Then, composite powder containing expansion components is sprayed in at a uniform speed. The powder is uniformly coated by airflow tumbling. After low-temperature drying to form a film, a temperature-sensitive controlled-release expansion layer is formed, resulting in the middle layer coated aggregate.

[0096] The inlet air temperature is controlled at 30℃, and the apparent air velocity of the fluidized bed is controlled at 1.3~1.6m / s to ensure that the aggregate is in a fully fluidized state. The atomizing binder is a temperature-sensitive composite emulsion formulated from the components that form the temperature-sensitive composite film, with a softening temperature of 38℃, an emulsion solid content of 9%, and a spray pressure of 0.22MPa. The expanded composite powder is the internal composite powder of the temperature-sensitive controlled-release expanded layer, which is composed of the powder components that form this layer. The powder injection rate corresponding to each 100kg of inner layer loaded aggregate is controlled at 1.2kg / min. The low-temperature drying film formation temperature is 30℃, and the drying time is 18min.

[0097] S3. Outer fluidized bed coating: Maintain the operation of the fluidized bed coating equipment, spray the film-forming liquid containing brittle filler and mineralized crystal nucleus components, and simultaneously and uniformly spray the repair composite powder containing mineralizing enzymes, so that the powder adheres evenly to the outside of the temperature-sensitive controlled-release expansion layer, and after low-temperature drying to form a film, the modified porous skeleton aggregate is obtained.

[0098] The film-forming solution is a hydroxypropyl methylcellulose solution with a mass concentration of 7%. Nano-calcium carbonate whiskers and nano-active calcium carbonate micropowder are pre-dispersed in the solution. The dispersion process is carried out by a high-speed shearing machine at 2200 r / min for 18 min. The mineralization repair composite powder is diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase. The low-temperature drying film-forming temperature is 30℃, the drying time is 22 min, and after drying, it is sieved through a 10-mesh sieve to remove surface floating powder.

[0099] S4. Dry mixing of aggregates: Add the modified porous skeleton aggregate, filled crushed stone and fine aggregate into the mixing tank according to the mix proportion and perform dry mixing.

[0100] The dry mixing process lasts for 100 seconds and uses a twin-shaft forced mixer with a mixing shaft speed of 65 r / min.

[0101] S5. Dry mixing and coating of adhesive materials: Add premixed composite cementitious material into the mixing tank and continue dry mixing to make the cementitious powder evenly coat the surface of each grade of aggregate.

[0102] The dry mixing time is 70 seconds, the stirring speed is maintained at 65 r / min, and the composite cementitious material is premixed from P·O 42.5 ordinary Portland cement and calcined coal gangue powder. The calcined coal gangue powder accounts for 12% of the total mass of the composite cementitious material, and the premixing time is 6 minutes.

[0103] S6. Wet Mixing and Curing: Add metered mixing water and start the wet mixing mode. Stir until the mixture is uniform, then discharge and spread it. After rolling and molding, cover with a moisturizing material for curing.

[0104] The wet-mixing mode has a mixing time of 130 seconds and a mixing speed of 70 r / min; the paving uses a base course paver with a loose paving coefficient of 1.32 and a paving speed of 1.4 m / min; the compaction procedure is as follows: first, one pass of static compaction with double steel wheels; then, three passes of low-frequency high-amplitude vibratory compaction with a single steel wheel; and finally, two passes of rubbing compaction with a rubber-tired roller to finish the surface; the curing time of the moisture-retaining material is 7 days, during which water is sprayed 4 times a day to keep the surface moist; and the time between the completion of compaction and the completion of water mixing is 1.8 hours.

[0105] Comparative Example 1: The only difference between this comparative example and Example 1 is that: all gradient release composite modified layers and corresponding modification processes are cancelled; the coarse aggregate of the skeleton particle size is replaced with ordinary limestone crushed stone; pure P·O 42.5 ordinary Portland cement is used as the composite cementing material, and calcined coal gangue powder is not added; the amount of mixing water is adjusted to the corresponding optimal moisture content; and all other construction parameters are exactly the same as in Example 1.

[0106] Comparative Example 2: The only difference between this comparative example and Example 1 is that the gradient release composite modification layer and corresponding coating process of porous basalt aggregate are cancelled. All functional components are uniformly added to the composite cementitious material with the same total mass as the modification layer in Example 1. The conventional one-time mixing process is used for feeding. The other raw material ratios and construction parameters are exactly the same as those in Example 1.

[0107] Comparative Example 3: The only difference between this comparative example and Example 1 is that the three-layer coating structure of inner, middle and outer layers is cancelled. All components of the nucleus inner curing composite layer, temperature-sensitive controlled-release expansion layer and stress-sensitive mineralization repair layer are mixed evenly and then loaded onto the surface of porous basalt aggregate through a single fluidized bed coating. The total mass of the modified layer remains unchanged. The preparation process is adjusted to a single fluidized bed coating. The other raw material ratios and other process parameters are exactly the same as in Example 1.

[0108] Comparative Example 4: The only difference between this comparative example and Example 1 is that the external temperature-sensitive composite coating of the temperature-sensitive controlled-release expansion layer is removed, and the composite powder of citric acid chelated calcium, anhydrite and metakaolin micro powder is directly coated on the outer side of the inner layer. The total mass ratio of the middle layer remains unchanged, and the other raw material ratios and preparation processes are exactly the same as those in Example 1.

[0109] Comparative Example 5: The only difference between this comparative example and Example 1 is that the nano-superabsorbent resin microspheres are removed from the nucleus curing composite layer and replaced with an equal amount of nano-calcium silicate seeds. The proportion of the total mass of the nucleus curing composite layer to the modified layer remains unchanged. The other raw material ratios and preparation processes are exactly the same as in Example 1.

[0110] Comparative Example 6: The only difference between this comparative example and Example 1 is that in the stress-sensitive mineralization repair layer, the diatomaceous earth micropowder loaded with calcium alginate-encapsulated carbonic anhydrase is replaced with an equal amount of diatomaceous earth micropowder loaded with free carbonic anhydrase. The total mass ratio of the stress-sensitive mineralization repair layer remains unchanged, and the remaining raw material ratios and preparation processes are exactly the same as in Example 1.

[0111] Comparative Example 7: This comparative example adopts the conventional scheme of overall admixture addition in the prior art. The only difference from Example 1 is that all coarse aggregate is ordinary limestone crushed stone without any surface modification treatment; all functional components of the gradient release composite modified layer in Example 1 are added to the mixing tank together with the composite cementitious material in the S5 dry mixing and coating step according to the same total mass. The remaining raw material dosage, process steps and construction parameters are exactly the same as those in Example 1.

[0112] I. Unconfined compressive strength test: The test shall be conducted in accordance with the test method for unconfined compressive strength of inorganic binder stabilized materials in standard JTGE51-2009 "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering".

[0113] The mixtures of Examples 1 to 3 and Comparative Examples 1 to 7 were respectively loaded into the corresponding molds and formed into cylindrical specimens with a diameter of 150 mm and a height of 150 mm by static pressing. After demolding, they were transferred to a standard curing room for curing. The curing environment temperature was 20℃ and the relative humidity was not less than 95%. After curing for 7 days and 28 days respectively, the specimens were taken out, the surface moisture was wiped off, and they were placed in the center of the bearing platform of the universal testing machine. Axial compression test was performed at a constant loading rate of 1 mm / min. The maximum load when the specimen failed was recorded and the unconfined compressive strength was calculated. Six parallel specimens were prepared for each group, and the final test result was the arithmetic mean of the parallel specimens.

[0114] II. Drying shrinkage test: The test shall be conducted in accordance with the drying shrinkage test method for inorganic binder stabilized materials in standard JTGE51-2009 "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering".

[0115] The mixtures from Examples 1 to 3 and Comparative Examples 1 to 7 were molded into prism specimens with a cross-sectional size of 100mm × 100mm and a length of 400mm. After standard curing for 7 days, the specimens were removed, their surface moisture was wiped dry, and they were placed horizontally on a shrinkage test rack. The test environment was kept constant at 20℃ and relative humidity at 60%. The deformation along the length of the specimens was monitored periodically using a dial indicator, and the mass change of the specimens was weighed using an electronic balance with an accuracy of 0.01g. The continuous test period was 28 days. The shrinkage strain and shrinkage coefficient of each group of specimens were calculated based on the test data. Three parallel specimens were prepared for each group, and the final test result was the arithmetic mean of the parallel specimens.

[0116] III. Crack self-healing performance test: The test shall be conducted in accordance with the evaluation method of crack repair effect in standard T / CECS787-2020 "Technical Standard for Application of Self-Healing Concrete";

[0117] The mixtures from Examples 1 to 3 and Comparative Examples 1 to 7 were molded into cylindrical specimens consistent with the specifications for the unconfined compressive strength test. After standard curing for 28 days, longitudinal microcracks with a width of 0.2 mm to 0.3 mm were pre-fabricated in the middle of the specimens using the splitting loading method. During the loading process, a crack width gauge was used to monitor the crack width in real time. The crack width was measured at the middle section along the height direction of the specimen, and three measuring points were taken at equal intervals along the crack length direction. The average value of the three points was used as the representative value of the crack width. After the preset width was reached, the load was slowly unloaded to complete the crack pre-fabrication. The initial permeability coefficient and initial residual compressive strength of the specimens were tested and recorded. Subsequently, the cracked specimens were placed in a curing environment with a temperature of 20°C, a relative humidity of 95%, and periodic carbon dioxide introduction for repair curing. The repair period was 28 days. After curing, the permeability coefficient and residual compressive strength of the specimens were tested again. The self-healing effect of each group of specimens was evaluated by calculating the permeability coefficient recovery rate and strength recovery rate. Three parallel specimens were prepared for each group, and the final test result was the arithmetic mean of the parallel specimens.

[0118] Table 1: Test Results of Unconfined Compressive Strength Test and Drying Shrinkage Test

[0119] Group 7d unconfined compressive strength / MPa 28-day unconfined compressive strength / MPa <![CDATA[28-day drying shrinkage coefficient / ×10 -6 > Example 1 4.1 5.6 242 Example 2 3.7 5.1 268 Example 3 4.0 5.4 253 Comparative Example 1 3.1 3.9 392 Comparative Example 2 3.4 4.4 336 Comparative Example 3 3.6 4.7 312 Comparative Example 4 3.5 4.6 345 Comparative Example 5 3.8 4.9 301 Comparative Example 6 4.0 5.5 246 Comparative Example 7 3.3 4.2 351

[0120] Table 2: Complete Test Results of Crack Self-Healing Performance Test

[0121] Group Initial crack width / mm <![CDATA[Initial water permeability coefficient / (mL・min -1 )]]> Initial residual compressive strength / MPa <![CDATA[Water permeability coefficient after 28 days of repair / (mL・min -1 )]]> Residual compressive strength after 28 days of repair / MPa Permeability coefficient recovery rate / % Strength recovery rate / % Example 1 0.25 1.82 2.12 0.40 4.03 78.0 72.0 Example 2 0.24 1.95 1.94 0.59 3.65 70.0 64.0 Example 3 0.26 1.89 2.05 0.49 3.89 74.0 68.0 Comparative Example 1 0.25 3.15 1.48 2.84 1.59 10.0 7.0 Comparative Example 2 0.25 2.68 1.67 1.85 2.20 31.0 25.0 Comparative Example 3 0.26 2.42 1.79 1.36 2.47 44.0 37.0 Comparative Example 4 0.25 1.85 1.74 0.44 3.92 76.0 70.0 Comparative Example 5 0.24 2.21 1.86 1.08 2.80 51.0 46.0 Comparative Example 6 0.25 1.83 2.09 1.10 2.64 40.0 34.0 Comparative Example 7 0.26 2.87 1.60 2.10 2.09 27.0 21.0

[0122] Note: The formula for calculating the permeability coefficient recovery rate is: (initial permeability coefficient - permeability coefficient after repair) / initial permeability coefficient × 100%; the formula for calculating the strength recovery rate is: residual compressive strength after repair / initial unconfined compressive strength of the sample × 100%. The higher the values ​​of the two indicators, the better the self-healing effect of the crack.

[0123] Based on Examples 1-3 and Comparative Example 1, and in conjunction with Tables 1 and 2, it can be seen that constructing a gradient release composite modified layer on the surface of the skeleton aggregate, and combining it with a composite cementitious system containing active admixtures, can act on cement-stabilized crushed stone materials from multiple levels, including interfacial bonding strengthening, volume deformation regulation, and damage self-repair. This has a positive regulatory effect on the mechanical properties and durability of the materials. Conventional base materials without functional modification have relatively weaker overall performance.

[0124] Based on Examples 1-3 and Comparative Example 2, and in conjunction with Tables 1 and 2, it can be seen that the interface modification method of directionally loading functional components onto the surface of the skeleton aggregate, compared with the conventional approach of uniformly adding functional components, allows the effective components to concentrate on the weak link of the interface transition zone between the aggregate and the slurry, thereby improving the utilization efficiency of the functional components and having a more significant effect on improving the material's resistance to drying shrinkage and its self-healing effect.

[0125] Based on Examples 1-3 and Comparative Example 3, and in conjunction with Tables 1 and 2, it can be seen that the gradient structure design with three layers of inner, middle and outer coating allows different functional components to be released in an orderly manner according to the hydration process and damage development law, achieving temporal synergy in performance regulation at each stage. The method of mixing all functional components and then coating them with a single layer will disrupt the functional release rhythm and weaken the synergistic gain effect between the components.

[0126] Based on Examples 1-3 and Comparative Example 4, and in conjunction with Tables 1 and 2, it can be seen that the temperature-sensitive composite coating can regulate the release rate of the internal expansion components. By relying on the exothermic reaction of cement hydration to trigger the softening of the coating, the timing of the expansion effect is matched with the drying shrinkage process. After the temperature-sensitive coating is removed, the expansion components are released rapidly in the early stage, and the drying shrinkage compensation effect is greatly reduced in the middle and late stages, which has an adverse effect on the volume stability of the material. However, the outer mineralization repair system is not affected by this variable.

[0127] Based on Examples 1-3 and Comparative Example 5, and in conjunction with Tables 1 and 2, it can be seen that the nano-superabsorbent resin microspheres and nano-calcium silicate seeds in the nucleus-in-nucleus curing composite layer have a synergistic effect. The internal curing components can slowly release water to continuously promote the hydration reaction in the interface region, and at the same time reserve in-situ water source for the later crack repair reaction. After removing the internal curing components, the interface hydration enhancement effect and the later self-repair ability will be affected to varying degrees.

[0128] Based on Examples 1-3 and Comparative Example 6, and in conjunction with Tables 1 and 2, it can be seen that the calcium alginate encapsulation structure can provide a local protective microenvironment for carbonic anhydrase, resisting the high alkalinity erosion of cement pore solutions and extending the retention period of enzyme activity. In the system using free carbonic anhydrase, enzyme activity will rapidly decay under high alkalinity, leading to a decrease in the self-healing effect of cracks in the later stage. This variable has no significant impact on the early strength and drying shrinkage properties of the material.

[0129] As can be seen from Examples 1-3 and Comparative Example 7, and Tables 1 and 2, the directional gradient modification technology path of skeleton aggregate proposed in this application, compared with the conventional scheme of adding ordinary aggregates and admixtures as a whole in the prior art, can more accurately act on the weak areas of material performance. Under the premise of the same total amount of functional components, it has a better control effect on mechanical properties and durability, and has higher technical application value.

[0130] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high durability cement stabilized aggregate base material, characterized by: The raw materials include the following parts by weight: 100 parts graded aggregate, 4.5 to 6 parts composite cementitious material, and 5.0 to 6.5 parts mixing water; The graded aggregate comprises coarse aggregate with a skeleton particle size of 9.5–31.5 mm, coarse aggregate with a filler particle size of 4.75–9.5 mm, and fine aggregate. The coarse aggregate with the skeleton particle size is entirely made of porous basalt aggregate. The internal pores of the porous basalt aggregate are impregnated with a nucleus-in-cell curing composite layer. The aggregate surface is coated with a temperature-sensitive controlled-release expansion layer and a stress-sensitive mineralization repair layer from the inside out. The three layers together constitute a gradient release composite modification layer. The total mass of the gradient release composite modification layer is 2.8%–3.8% of the mass of the porous basalt aggregate. The modification layer consists of the nucleus-in-cell curing composite layer, the temperature-sensitive controlled-release expansion layer, and the stress-sensitive mineralization repair layer from the inside out.

2. The high-durability cement-stabilized crushed stone base course material according to claim 1, characterized in that: The skeleton coarse aggregate accounts for 32%–38% of the total mass of the graded aggregate, with a porosity of 18%–25% and a crushing value ≤22%; the filler coarse aggregate accounts for 20%–25% of the total mass of the graded aggregate and is made of limestone crushed stone; the fine aggregate accounts for 37%–48% of the total mass of the graded aggregate and is made of manufactured sand with a fineness modulus of 2.6–2.9; the composite cementitious material is composed of P·O 42.5 ordinary Portland cement and calcined coal gangue powder, wherein the calcined coal gangue powder accounts for 8%–12% of the total mass of the composite cementitious material, has a loss on ignition ≤5%, and a 7-day activity index ≥75%.

3. The high-durability cement-stabilized crushed stone base course material according to claim 1, characterized in that: The nucleus-in-the-core protective composite layer accounts for 29%–31% of the total mass of the modified layer and is composed of nano-calcium silicate seeds and nano-superabsorbent resin microspheres at a mass ratio of 4:(1–1.2). The temperature-sensitive controlled-release expansion layer accounts for 44%–46% of the total mass of the modified layer and is composed of a core composite powder and an outer temperature-sensitive composite coating. The core composite powder is composed of citric acid chelated calcium, anhydrite, and metakaolin micropowder at a mass ratio of 1:(2.5–3):(0.3–0.5). The stress-sensitive mineralization repair layer accounts for 23%–27% of the total mass of the modified layer and uses hydroxypropyl methylcellulose as the film-forming matrix. The film-forming matrix is ​​doped with nano-calcium carbonate whiskers and nano-active calcium carbonate micropowder.

4. The high-durability cement-stabilized crushed stone base course material according to claim 3, characterized in that: The temperature-sensitive composite coating is composed of hydroxypropyl methylcellulose and stearic acid in a mass ratio of 7:(3-3.6), and has a softening temperature of 32-38℃. In the stress-sensitive mineralization repair layer, the amount of nano-calcium carbonate whiskers is 15%-20% of the total mass of the stress-sensitive mineralization repair layer, and the amount of nano-active calcium carbonate micropowder is 10%-15% of the total mass of the stress-sensitive mineralization repair layer. The stress-sensitive mineralization repair layer also contains diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase, and the diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase accounts for 55%-60% of the total mass of the stress-sensitive mineralization repair layer.

5. A method for preparing a high-durability cement-stabilized crushed stone base course material, characterized in that, The high-durability cement-stabilized crushed stone base course material according to any one of claims 1-4 comprises the following steps: S1. Negative pressure load inner layer: After the porous basalt aggregate is dried to constant weight, it is transferred to a negative pressure impregnation tank, injected with a composite suspension for forming a nucleus-in-the-mold composite layer, and after negative pressure treatment, it is taken out and dried at low temperature until the surface is dry to obtain the inner layer load aggregate. S2, Middle Layer Fluidized Coating: The inner layer of loaded aggregate is fluidized and coated. The air inlet temperature is controlled. First, a temperature-sensitive binder is sprayed to wet the surface of the aggregate. Then, composite powder containing expansion components is sprayed in at a uniform speed. The powder is evenly coated by airflow tumbling. After low-temperature drying to form a film, a temperature-sensitive controlled-release expansion layer is formed, resulting in middle layer coated aggregate. S3, outer fluidized coating: continue fluidized coating treatment, spray film-forming liquid containing brittle filler and mineralized crystal nucleus components, and simultaneously spray repair composite powder containing mineralizing enzyme at a uniform speed, so that the powder adheres evenly to the outside of the temperature-sensitive controlled release expansion layer, and after low-temperature drying to form a film, modified porous skeleton aggregate is obtained. S4. Dry mixing of aggregates: Add the modified porous skeleton aggregate, filled particle size crushed stone and fine aggregate into the mixing tank according to the mix ratio and perform dry mixing. S5. Dry mixing and coating of adhesive materials: Add premixed composite cementitious material into the mixing tank and continue dry mixing to make the cementitious powder evenly coat the surface of each grade of aggregate. S6. Wet Mixing and Curing: Add metered mixing water and start the wet mixing mode. Stir until the mixture is uniform, then discharge and spread it. After rolling and molding, cover with a moisturizing material for curing.

6. The method for preparing a high-durability cement-stabilized crushed stone base course material according to claim 5, characterized in that: In step S1, the drying temperature for drying to constant weight is 100-110°C, the mass concentration of the composite suspension is 9%-11%, the composite suspension is prepared by dispersing the components forming the crystal nucleus inner nucleation layer in water at a mass ratio of 4:(1-1.2), the relative negative pressure is 0.06-0.10 MPa, the processing time is 30-40 min, and the low-temperature drying temperature is 55-65°C.

7. The method for preparing a high-durability cement-stabilized crushed stone base course material according to claim 5, characterized in that: In step S2, the air inlet temperature is controlled at 26–30°C, the atomizing binder is a temperature-sensitive composite emulsion formulated from the components forming the temperature-sensitive composite film, and the softening temperature is 32–38°C; the expanding composite powder is the internal composite powder of the temperature-sensitive controlled-release expanding layer, which is composed of the powder components forming the layer; the powder injection rate corresponding to each 100 kg of inner layer loaded aggregate is controlled at 0.8–1.2 kg / min; the low-temperature drying film formation temperature is 26–30°C, and the drying time is 12–18 min.

8. The method for preparing a high-durability cement-stabilized crushed stone base course material according to claim 5, characterized in that: In step S3, the film-forming solution is a hydroxypropyl methylcellulose solution, in which nano-calcium carbonate whiskers and nano-active calcium carbonate micropowder are pre-dispersed. The mineralization repair composite powder is diatomaceous earth micropowder loaded with calcium alginate-embedded carbonic anhydrase. The low-temperature drying film-forming temperature is 26-30°C, and the drying time is 18-22 min.

9. The method for preparing a high-durability cement-stabilized crushed stone base course material according to claim 5, characterized in that: In step S4, the mixing time for the dry mixing process is 80-100 seconds; in step S5, the duration of the continued dry mixing is 50-70 seconds.

10. The method for preparing a high-durability cement-stabilized crushed stone base course material according to claim 5, characterized in that: In step S6, the mixing time of the wet mixing mode is 110-130 seconds, the curing time of the moisturizing material is not less than 7 days, and the time between the end of the rolling and the completion of the water mixing is not more than 2 hours.

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