High-crack-resistance concrete

Abstract

The invention discloses high-crack-resistance concrete, and relates to the technical field of building materials, and the high-crack-resistance concrete is prepared from the following raw materials in parts by mass: 350 to 450 parts of Portland cement, 80 to 120 parts of fly ash, 60 to 100 parts of granulated blast furnace slag powder, 650 to 750 parts of fine aggregate, 950 to 1100 parts of coarse aggregate, 140 to 165 parts of mixing water, 4.5 to 8.0 parts of high-performance polycarboxylate superplasticizer and 15 to 35 parts of anti-crack synergistic toughening modifier. The anti-cracking synergistic toughening modifier is prepared by mixing a first component, a second component and a third component, and through double bionic-chemical co-modification of dopamine and a silane coupling agent, the basalt fiber is endowed with extremely strong surface chemical reaction activity; the carbon fiber is directly and firmly riveted in a concrete gel network through chemical covalent bonds in a cement strong alkaline hydration process, and has more excellent and lasting pull-out resistance and tensile strain bearing capacity than conventional carbon fibers.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically high crack-resistant concrete. Background Technology

[0002] As modern construction engineering develops towards complex structures such as super high-rise buildings, large spans, ultra-deep underground spaces, large-volume structures, and harsh marine environments, increasingly stringent requirements are placed on the mechanical properties, volume stability, and long-term durability of concrete materials. In practical engineering applications, high-performance concrete or ultra-high-performance concrete typically requires extremely low water-cement ratios (usually below 0.30) and extremely high amounts of cementitious materials. However, this mix design inevitably leads to significant autogenous shrinkage, chemical shrinkage, and a dramatic increase in hydration heat during the concrete's hydration and hardening process. Autogenous shrinkage and temperature shrinkage are further exacerbated by the influence of reinforcing steel, formwork, or existing structures. When subjected to external constraints, enormous tensile stress is generated within the concrete. Once this tensile stress exceeds the early tensile strength of the concrete, it will cause micro-cracks to form and rapidly expand into macroscopic penetrating or non-penetrating cracks. The presence of these cracks not only severely weakens the overall mechanical load-bearing capacity and integrity of the building structure, but also provides a rapid intrusion channel for corrosive media such as moisture, chloride ions, sulfate ions, and carbon dioxide, greatly accelerating the corrosion of internal steel bars and the chemical deterioration of the matrix materials. This leads to a sharp reduction in the service life of the concrete structure, causing serious safety hazards and huge subsequent maintenance costs.

[0003] To address the severe cracking problem in concrete with high cementitious material systems, existing technologies often employ single-dimensional control methods such as adding physical crack-resistant fibers (e.g., steel fibers, polypropylene fibers, ordinary carbon fibers) or chemical expansion agents (e.g., calcium oxide, calcium sulfoaluminate expansion agents) and shrinkage-reducing agents.

[0004] For example, Chinese invention patent document CN115959870A discloses a crack-resistant low-carbon high-performance concrete and its preparation method. This prior art document discloses the following raw materials and their dosages: LC3 cementitious material 390-410 kg / m3, sand 640-660 kg / m3, stone 1000-1100 kg / m3, water 150-170 kg / m3, water-reducing agent 8.0-8.5 kg / m3, activated carbon fiber 0.1-0.3 kg / m3, and graphene oxide 0.1-0.3 kg / m3. The LC3 cementitious material is mainly composed of cement, calcined clay, limestone powder and gypsum; The water is composed of a mixture of wastewater from the mixing plant and clean water. This existing technology aims to improve the crack resistance of cement-based materials by introducing activated carbon fibers and graphene oxide, thereby leveraging the bridging and crack-resistant effect of carbon fibers and the micro-filling and hydration-promoting effect of graphene oxide.

[0005] However, a deeper analysis reveals the following significant technical shortcomings in the aforementioned existing literature: First, while carbon fiber possesses extremely high axial tensile strength and elastic modulus, its surface exhibits typical chemical inertness. Even after conventional acid electroactivation treatment as described in the comparative literature, the interfacial chemical bonding force between it and cement hydration products (such as calcium silicate hydrate gel, CSH) remains very limited in the highly alkaline cement hydration liquid environment. With increasing age, under the complex alternating effects of temperature fluctuations and humidity variations, the interface between carbon fiber and the matrix is ​​prone to microscopic slippage and debonding, leading to a significant reduction in long-term bridging and crack-resistant effects. Second, although graphene oxide has an extremely high specific surface area, in actual large-volume ready-mixed concrete mixing processes... During the process, due to strong van der Waals attraction, π-π stacking effect, and double-layer compression caused by high calcium ion concentration, graphene oxide is prone to irreversible and severe aggregation in strongly alkaline porous solutions. Such aggregates not only fail to exert the nano-effect of effectively filling micropores, but also form natural stress concentration weaknesses inside the concrete matrix. Under the action of shrinkage stress, they become the source of initiation of microcracks. Third, this scheme only starts from the perspective of physical crack prevention and micro-filling, and fails to fundamentally solve the problem of temperature difference shrinkage caused by the rapid temperature rise and subsequent temperature drop due to the hydration of a large amount of cementitious materials. It also fails to effectively compensate for the surge in capillary negative pressure and moisture loss caused by the self-drying effect under extremely low water-cement ratio. Therefore, its comprehensive crack resistance potential is greatly restricted.

[0006] A simultaneous search of existing technologies, in addition to the aforementioned uploaded literature, revealed that some studies have attempted to introduce superabsorbent polymer (SAP) for internal curing or to introduce phase change materials to control the heat of hydration. However, conventional SAP, after absorbing water and expanding and hardening and releasing water, leaves a large number of micron- or even millimeter-sized macroscopic pores inside the concrete. This not only significantly reduces the compressive strength and impermeability of the concrete, but these pores also easily become weak points for shrinkage stress concentration. In addition, if existing phase change materials are not effectively encapsulated or are only encapsulated with a simple polymer shell, they are very prone to breakage and leakage during the mechanical mixing of concrete with intense aggregate friction. The leaked organic phase change substances (such as paraffin) will severely coat the surface of unhydrated cement particles, completely blocking the cement hydration reaction, resulting in the concrete not setting or a precipitous drop in strength.

[0007] In summary, existing single-modification technologies or simple compounding technologies cannot adequately address the cracking problem of concrete under complex environments. Developing a high-crack-resistant concrete that can synergistically control the heat of hydration, effectively compensate for internal moisture loss, and possess a stable interfacial bridging effect to completely solve the technical challenge of concrete cracking under high cementitious material content is a bottleneck problem that urgently needs to be addressed in this field. Summary of the Invention

[0008] Addressing the shortcomings and deficiencies of existing technologies, such as weak interfacial bonding of fibers, easy agglomeration of nanomaterials, difficulty in controlling the heat of hydration and temperature rise, and the introduction of large pore defects by internal curing materials, the primary objective of this invention is to provide a high crack-resistant concrete. This invention creatively introduces a crack-resistant synergistic toughening modifier composed of dopamine / silane co-grafted modified basalt fibers, core-shell structured phase change microcapsules, and salt-resistant internal curing water-absorbing microspheres through a multi-dimensional synergistic regulation mechanism. This achieves closed-loop control of the entire process of autogenous shrinkage, temperature shrinkage, and plastic shrinkage, significantly improving the crack resistance, mechanical strength, and service durability of concrete.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high crack-resistant concrete is composed of raw materials comprising the following parts by weight: Silicate cement: 350-450 parts; Fly ash: 80-120 parts; Granulated blast furnace slag powder: 60-100 parts; Fine aggregate: 650-750 parts; Coarse aggregate: 950–1100 parts; Mixing water: 140-165 parts; High-performance polycarboxylate superplasticizer: 4.5–8.0 parts; Crack-resistant and toughening modifier: 15-35 parts.

[0010] The crack-resistant synergistic toughening modifier is composed of a first component, a second component, and a third component. The first component is dopamine / silane co-grafted modified basalt fiber, the second component is core-shell structured phase change microcapsules, and the third component is salt-resistant internally maintained water-absorbing microspheres. Furthermore, the mass ratio of the first component, the second component, and the third component in the crack-resistant synergistic toughening modifier is (2-5):(8-15):(5-15).

[0011] In a preferred embodiment of the present invention, the preparation method of the first component, dopamine / silane co-grafted modified basalt fiber, includes the following detailed steps: (1) Cut the basalt coarse fibers with surface impregnation agent to a length of 12-18 mm, put them into an ethanol aqueous solution with a volume concentration of 70%-80%, clean them for 30-45 minutes under ultrasonic action at a frequency of 40-50 kHz, filter them out, rinse them with deionized water until neutral, and then dry them in a vacuum drying oven at 60-80℃ for 12-24 hours to obtain pretreated basalt fibers; (2) The pretreated basalt fiber is immersed in a hydrochloric acid solution with a concentration of 2-3 mol / L, and refluxed in a water bath at 60-70°C for 2-3 hours. After etching, the fiber is repeatedly filtered and washed with deionized water until the filtrate is neutral, and then dried again to obtain basalt fiber with surface hydroxyl activated. (3) Weigh the Tris-HCl buffer reagent and dissolve it in deionized water. Adjust the pH of the solution to 8.4-8.6 and prepare a Tris buffer solution with a concentration of 10-20 mmol / L. Add dopamine hydrochloride to the buffer solution and stir to dissolve it so that the concentration reaches 2-4 g / L. Obtain the dopamine polymerization solution. Put the basalt fiber with surface hydroxyl activated in step (2) into the dopamine polymerization solution and react mechanically for 18-24 hours under the conditions of avoiding light and constant temperature at 25°C. During this period, dopamine undergoes self-oxidation under the action of weak alkalinity and dissolved oxygen and polymerizes in situ into polydopamine (PDA) network that firmly coats the fiber surface. After the reaction is completed, wash with deionized water and vacuum dry to obtain PDA-coated basalt fiber. (4) Disperse the PDA-coated basalt fiber obtained in step (3) in anhydrous ethanol, and slowly add an ethanol hydrolysate containing 3-aminopropyltriethoxysilane (APTES) (the volume concentration of APTES is 5% to 10%, and hydrolysis is performed 2 hours in advance). Stir and reflux at 50 to 60°C for 6 to 8 hours. During this process, the phenolic hydroxyl and quinone structures remaining on the surface of the polydopamine coating undergo Michael addition and Schiff base reactions with APTES, firmly grafting the molecular chains with silanol groups onto the PDA modified layer. After the reaction is completed, wash with anhydrous ethanol 3 times and dry thoroughly in an 80°C drying oven to finally obtain the first component, dopamine / silane co-grafted modified basalt fiber.

[0012] In a preferred embodiment of the present invention, the second component core-shell structured phase change microcapsule is a microcapsule with n-octadecane as the core and silicon dioxide (SiO2) as the inorganic hard outer shell. Its preparation method employs a sol-gel in-situ encapsulation method, specifically including the following steps: (1) Weigh a certain amount of emulsifier cetyltrimethylammonium bromide (CTAB) and octylphenyl polyoxyethylene ether (Triton X-100) in a molar ratio of 1:1, mix them, dissolve them in deionized water, and prepare a composite surfactant aqueous solution with a mass concentration of 1.5% to 2.5%; (2) Heat the above-mentioned composite surfactant aqueous solution to 45-50°C (higher than the melting point of n-octadecane), slowly add molten n-octadecane to it, start a high-shear homogenizer, and homogenize and emulsify at an extremely high speed of 10,000-15,000 rpm for 20-30 minutes to form a stable and uniform liquid-in-liquid (O / W) type phase change core material microemulsion, wherein the n-octadecane droplet size is controlled between 1 and 3 micrometers; (3) Reduce the stirring speed to 400-600 rpm, adjust and stabilize the temperature of the reaction system to 35-40℃, add 5% ammonia solution dropwise to the above microemulsion, and precisely adjust the pH value of the system to 9.5-10.5. Then, use a high-precision micro-injection pump to add a mixture of tetraethyl orthosilicate (TEOS) precursor and anhydrous ethanol (volume ratio of 1:1) to the system at a very slow speed of 0.5-1.0 mL / min. After the addition is complete, continue to stir the reaction at a constant temperature for 12-16 hours. Under alkaline catalytic conditions, TEOS undergoes hydrolysis at the interface between n-octadecane micro-droplets and water to generate silanol, and rapidly condenses to form a dense inorganic SiO2 network cross-linked shell. (4) After the reaction is completed, the product is centrifuged (8000 rpm, centrifugation for 15 minutes), and the lower precipitate is collected. The precipitate is washed three times alternately with deionized water and anhydrous ethanol to remove unreacted precursors and surfactants. Finally, the precipitate is placed in a vacuum freeze dryer at 40°C and dried for 24 hours. It is then ground through a 200-mesh sieve to obtain the second component core-shell structure phase change microcapsules. The peak phase change temperature is 27.5-28.5°C, and the latent heat of phase change is 120-140 J / g. It has excellent crush resistance.

[0013] In a preferred embodiment of the present invention, the preparation method of the third component, salt-tolerant internal maintenance water-absorbing microspheres, employs a reverse suspension polymerization method, and the specific steps include: (1) Preparation of aqueous phase: Acrylic acid (AA) was placed in a reaction vessel cooled by an ice-water bath, and a 30% sodium hydroxide (NaOH) aqueous solution was slowly added dropwise to partially neutralize it. The degree of neutralization was strictly controlled at 65% to 75%. Then, 20% to 30% of the mass of acrylic acid nonionic monomer acrylamide (AM) and 10% to 15% of the mass of acrylic acid hydroxyethyl methacrylate (HEMA) were added to the reaction vessel in sequence. The mixture was stirred until completely dissolved. Then, 0.2% to 0.4% of the total mass of monomers N,N'-methylenebisacrylamide (MBA) crosslinking agent and 0.5% to 1.0% of the total mass of monomers potassium persulfate (KPS) water-soluble initiator were added. The mixture was continuously ultrasonically vented for 10 minutes to obtain a uniform and transparent aqueous phase solution. (2) Preparation of oil phase: Cyclohexane is used as the continuous phase solvent. 2% to 4% of the mass of cyclohexane is added as the dispersant sorbitan monostearate (Span-60). The mixture is stirred and dissolved in a water bath at 50°C. Then, high-purity nitrogen is bubbled for 30 minutes to remove dissolved oxygen from the system to obtain the oil phase solution. (3) Polymerization reaction: Under continuous nitrogen protection and mechanical stirring at 300-400 rpm, the aqueous phase solution prepared in step (1) is slowly added dropwise to the oil phase solution in step (2). After the addition is completed, the temperature of the reaction system is increased to 65-70℃ at a rate of 2℃ / min and the reaction is kept at a constant temperature for 4-6 hours. Due to the introduction of nonionic monomers AM and HEMA, the steric hindrance and hydrophilic group types in the copolymer network increase, which greatly weakens the charge shielding effect of cations (such as Ca2+, Na+, K+) on carboxyl groups in the strongly alkaline pore solution, giving the microspheres a strong ability to resist high concentration of ion interference. (4) After the reaction is completed, the reaction system is transferred to an azeotropic distillation apparatus equipped with a water separator, heated to 75-85°C for azeotropic dehydration and solvent removal, the polymer microsphere precipitate is collected, and thoroughly extracted and washed with excess acetone to remove the residual Span-60 on the surface. Finally, it is dried to constant weight under vacuum at 60°C, pulverized and screened to obtain powder with a particle size between 100 and 200 micrometers, thus obtaining the third component salt-resistant internal curing water-absorbing microspheres. The liquid absorption ratio of these microspheres in cement simulated pore solution can reach 35-50 times.

[0014] Working mechanism and inventive theory analysis of this invention: 1. Interface chemical resonance anchoring enhancement mechanism: The first component of this invention abandons the traditional non-activated fiber or fiber modification route of only surface roughening treatment, and innovatively adopts a dual chemical modification system of "dopamine biomimetic self-assembly-silane grafting". The polydopamine (PDA) layer formed by the self-polymerization of dopamine under weak alkalinity is like a layer of highly adhesive "double-sided tape". On the one hand, it tightly wraps the basalt fiber through hydrogen bonds and van der Waals forces, and forms a strong bond by using the hydroxyl groups generated by etching; On the other hand, the abundant catechol groups on the PDA surface undergo a chemical cross-linking reaction with the amino groups of APTES, successfully grafting silane groups. When this modified fiber is incorporated into fresh concrete, the silanol groups (-Si-OH) exposed on the outermost layer can undergo in-situ pozzolanic condensation reaction with the active calcium hydroxide or hydrated calcium silicate (CSH) gel precipitated from silicate cement hydration at the molecular scale, forming a robust Si-O-Ca and Si-O-Si covalent bond network. This "chemical anchoring" mechanism completely changes the disadvantage of traditional fibers being easily pulled out under tensile stress, enabling them to provide extremely large interfacial shear resistance in the early stage of microcrack initiation, and significantly improving the peak strain and fracture toughness of the matrix.

[0015] 2. Mechanism for Precise Peak Shaving and Valley Filling of Hydration Heat Pulse: To address the problem of rapid core heating and subsequent rapid temperature drop and contraction caused by the large hydration heat unique to high-cementation systems, this invention introduces a second component, a core-shell structured SiO2 phase change microcapsule. The core of this microcapsule is n-octadecane, and the phase change temperature precisely matches the temperature range in which the peak of hydration heat release occurs from the initial setting to the final setting of cement (starting from approximately 28°C). When the internal temperature of the concrete rises and crosses this critical point, the n-octadecane inside the microcapsule changes from solid to liquid, absorbing a large amount of the high-energy latent heat generated by hydration heat release, thus "smoothing out" the temperature peak like a sponge absorbing water. When the cement hydration rate slows down and the concrete structure begins to dissipate heat to the environment, causing the temperature to drop, n-octadecane recrystallizes from the liquid phase to the solid phase, slowly releasing the stored heat to "fill" the temperature trough. More importantly, this invention uses dense inorganic SiO2 as the microcapsule shell, which not only has extremely high mechanical strength to withstand the strong physical shear and aggregate collision during concrete mixing, but also completely eliminates the leakage and pollution of phase change substances. Moreover, the surface of the SiO2 shell is active and can react synergistically with cement hydration products, perfectly integrating into the three-dimensional network of the cement matrix. This makes the microcapsule itself no longer a pore defect in the matrix, but a robust microscopic support unit.

[0016] 3. Multi-component network internal stress buffering and compensation mechanism: Another fatal flaw of high-performance concrete with extremely low water-cement ratio is the self-shrinkage cracking caused by the rapid self-drying and the surge in capillary negative pressure in the early stages. The third component of this invention, salt-resistant internal curing water-absorbing microspheres, can quickly absorb an appropriate amount of water to form a gel-like water reservoir in the early stages of mixing. As hardening progresses, when external hydration consumes water and causes a decrease in internal relative humidity, the free water stored inside the microspheres is continuously and stably released due to the osmotic pressure difference. This provides a deep internal curing water source for the surrounding unhydrated cement particles, which not only greatly promotes the degree of hydration in the later stages and significantly refines the capillary size distribution, but also completely eliminates the extreme negative pressure caused by the gas-liquid meniscus contraction in the capillary, thus addressing the problem from its source. The head eliminates the self-shrinkage driving force. The disadvantage of traditional water-absorbing resins is that they leave large voids after water loss. However, this invention introduces modified fibers and SiO2 phase change capsules into the system simultaneously. The dense spatial network formed by the fibers and the support of the SiO2 capsules as a rigid skeleton can effectively share and redistribute the local stress concentration caused by matrix deformation in the surrounding cement paste during the water release and shrinkage of the microspheres. In addition, the microspheres are made of a network modified by HEMA copolymer with large volume steric hindrance and non-dissociated AM. Their volume shrinkage rate after water release is controlled within a very small range. At the same time, the newly formed gel produced by subsequent hydration will spontaneously penetrate and fill this part of the micro-nano scale shrinkage space, ensuring the high impermeability and extreme density of the concrete.

[0017] To quantify and analyze the technical effects of this invention, the following multiple variables are defined to guide the proportioning and mechanism calculations: (1) Formula 1: Formula for evaluating the fiber equivalent crack resistance factor In this invention, a fiber-equivalent crack-resistant factor is introduced to quantify the theoretical crack resistance provided by the first component (modified fiber) in the concrete matrix. This factor not only considers the physical dimensions of the fiber, but also introduces interfacial strengthening correction, as shown in the following formula: ; The variables are disclosed as follows: The fiber equivalent crack resistance factor is dimensionless; the larger the value, the stronger the crack resistance. The value represents the chemical grafting effectiveness coefficient, which is related to the grafting density of silanol groups on the fiber surface. For the dopamine / silane co-grafted fibers of this invention, the value is 1.85, while for the unmodified fibers, the value is 1.0. It represents the overall volume fraction of fibers in the concrete mixture, that is, the volume percentage of the first component; The average cut length of the fiber is represented by millimeters (mm). The equivalent diameter of a single basalt fiber is expressed in millimeters (mm), and ( / This is the aspect ratio; Represents the ultimate interfacial shear stress between the fiber and the cement matrix, in megapascals (MPa). The standard shear stress constant is taken as an empirically fixed value of 1.0 MPa for normalization. function Represented by the natural constant An exponential function with base α represents the microscopic dynamic characteristics of interfacial bonding forces that amplify exponentially with the formation of covalent bonds.

[0018] (2) Formula 2: Formula for temperature control coefficient of composite phase change microcapsules To accurately reflect the temperature suppression capability of the second component during the peak of hydration exothermic period, a phase change microcapsule temperature control coefficient is proposed. : ; The variables are disclosed as follows: The phase change microcapsule temperature control coefficient represents the ratio of heat absorbed by the phase change material to the heat stored by the temperature rise of the matrix. The effective admixture mass of the second component (phase change microcapsules) in each cubic meter of concrete is expressed in kilograms (kg). The average latent heat of phase transition of the synthesized microcapsules is represented by joules per gram (J / g). The apparent specific heat capacity of pure cement concrete is expressed in joules per kilogram of Kelvin (J / (kg·K)). This represents the total mass of concrete per cubic meter, expressed in kilograms (kg). This represents the highest peak temperature of the theoretical adiabatic temperature rise at the center of concrete without the addition of phase change materials, expressed in degrees Celsius (°C). This represents the initial temperature of the external environment during pouring, expressed in degrees Celsius (°C). This represents the correction function for microcapsule particle size distribution, when the average particle size of the microcapsules... When the value falls within the 1-3 micrometer range, this correction function is set to 0.95 to ensure the optimal balance between thermal conductivity area and anti-breakage performance.

[0019] (3) Formula 3: Prediction formula for self-shrinkage compensation degree A comprehensive evaluation of the volume stabilization effect brought about by the third component (internal maintenance microspheres) was conducted, and the self-shrinkage compensation degree was defined. : ; The variables are disclosed as follows: This represents the degree of self-contraction compensation, with a value between 0 and 1. The closer it is to 1, the more completely the contraction is offset. The micro-strain shrinkage rate of concrete at 28 days of age is represented by the addition of the anti-cracking and synergistic toughening modifier of this invention. The baseline microstrain shrinkage rate of standard ordinary concrete under the same conditions at 28 days; The damping coefficient representing the internal curing release kinetics reflects the lag effect of the third component in the dense matrix on the release of moisture. In this system, the empirical constant is taken as 0.15. function Represents the natural logarithm function; The total mass of water actively released into the matrix pores by the third component microspheres within 28 days of cement hydration; This represents the theoretical water demand compensation amount corresponding to the chemical shrinkage produced by the cement hydration reaction.

[0020] Through the deep coupling of these three major mechanisms and guiding formulas, this invention is the first in the field of concrete materials science to realize a cross-scale, multi-phase joint defense system from nano-atomic covalent bonds, micron thermal energy storage capsules to millimeter water-releasing microspheres, fundamentally solving the problem of cracking in high-strength concrete.

[0021] In this invention, the high-performance polycarboxylate superplasticizer is a commercially available, mature product, requiring a solid content of not less than 40% and a water reduction rate of more than 25%. The silicate cement is recommended to be ordinary silicate cement of P·O 42.5 or P·O 52.5 grade, and the fly ash is recommended to be Class I fly ash conforming to the national standard GB / T 1596-2017. Granulated blast furnace slag powder is recommended to be S95 grade or above slag powder. The fine aggregate is preferably hard river sand or manufactured sand with a fineness modulus of 2.6 to 3.0, and the mud content is strictly controlled to be within 1.0%. The coarse aggregate should preferably be high-quality crushed stone with a continuous gradation of 5-20mm, with a crushing index value not exceeding 8%, and should have a multi-faceted, irregular, polyhedral shape to enhance mechanical interlocking. Tap water that meets engineering standards is recommended for mixing. Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows: 1. Completely solves the problem of interface peeling and achieves ultimate crack resistance: Through the dual biomimetic-chemical co-modification of dopamine and silane coupling agent, basalt fiber is endowed with extremely strong surface chemical reactivity, which allows it to be firmly anchored to the concrete gel network directly through chemical covalent bonds during the strong alkaline hydration process of cement. It has superior and more durable pull-out resistance and tensile strain bearing capacity compared with conventional carbon fiber.

[0022] 2. Peak shaving and valley filling, completely blocking temperature difference contraction: Innovatively introducing SiO2 hard-shell phase change microcapsules, which can intelligently absorb and store latent heat during the high hydration heat release period of concrete, greatly reducing the internal surface temperature difference; at the same time, the inorganic silicon shell is not only resistant to mechanical abrasion without damage or leakage, but also has good compatibility and integration with the hydration system, avoiding the problem of structural strength degradation.

[0023] 3. Dynamic full life cycle water retention and anti-drying shrinkage: The specially synthesized salt-resistant internal curing microspheres are not afraid of being surrounded and poisoned by ultra-high concentrations of alkaline cations (such as calcium ions) inside the concrete. They fully absorb liquid in the early stage and intelligently pump out deep water as the relative humidity decreases in the later stage, filling the negative pressure gap in the capillary pores. This controls the self-shrinkage of concrete to an extremely low level from the source, greatly avoiding the initiation of internal micro-cracks in the early and later stages. The multi-component three-dimensional mesh restricts the water-absorbing resin from shrinking and becoming porous, ensuring extremely high ultimate compressive strength and flexural strength peak values. Attached Figure Description

[0024] Figure 1 Flowchart of the preparation process for crack-resistant synergistic toughening modifier. Detailed Implementation

[0025] To make the objectives, core technologies, complex microscopic mechanisms, and superior engineering performance advantages of this invention clearer, the following will be discussed in conjunction with the appendix. Figure 1 The present invention will be described in more detail, comprehensively and deeply through numerous specific embodiments. It should be understood that the detailed embodiments described herein are merely for explaining and illustrating the present invention, and are not intended to limit the technical solutions and protection scope of the present invention in any way. After reading and understanding the principles of this specification, conventional changes or equivalent substitutions made to the specific parameters of materials, substitute materials or process fine-tuning without departing from the innovative concept and essential core of the present invention shall naturally fall within the patent protection scope of this application.

[0026] Unless otherwise specified, all raw materials (including cement, fly ash, mineral powder, aggregates, etc.) used in the examples and comparative examples are commercially available ordinary building materials that meet the relevant national inspection standards; All chemical reagents used (such as CTAB, TEOS, dopamine, APTES, etc.) are analytical grade reagents and are used directly without special pretreatment.

[0027] Preparation of Crack-Resistant Synergistic Toughening Modifier Before preparing the concrete examples, it is necessary to first prepare the "crack-resistant synergistic toughening modifier", which is the core element of this invention. The modifier is composed of a mixture of a first component, a second component and a third component. The process of preparing a single batch is described in detail below for reference in the examples and comparative examples.

[0028] (I) First Component: Preparation of Dopamine / Silane Co-grafted Modified Basalt Fiber Weigh 1000 grams of continuous basalt fiber bundles that have been cut (average length approximately 15 mm) and immerse them completely in a large ultrasonic cleaning tank containing 15 liters of 75% ethanol aqueous solution. Set the ultrasonic frequency to 45 kHz and ultrasonically vibrate and wash at room temperature for 40 minutes. The vibration removes most of the industrial wetting agent and organic impurities coated on the fiber surface at the factory. Filter out the fibers and rinse them with high-pressure deionized water until the washing solution is neutral. Place the cleaned fibers in a 70°C vacuum drying oven with a vacuum degree set to -0.09 MPa and continue drying for 16 hours.

[0029] Subsequently, the dried pretreated fibers were immersed in 20 liters of 2.5 mol / L dilute hydrochloric acid solution and placed in a three-necked flask reaction apparatus equipped with a reflux condenser. The water bath temperature was precisely controlled at 65°C, and the etching process was carried out at a constant temperature for 2.5 hours. This step dissolved some metal cations on the fiber surface and exposed a large number of highly active microscopic hydroxyl structure sites. After etching, the fiber was filtered out and rinsed with deionized water until the filtrate was measured to be 7.0 by a precision pH meter. Then, the fiber was thoroughly dried at 60°C.

[0030] Next, dopamine biomimetic coating was performed. An appropriate amount of Tris-HCl buffer powder was dissolved in 30 liters of deionized water to prepare a 15 mmol / L Tris buffer solution. A very small amount of dilute hydrochloric acid or sodium hydroxide was added dropwise to finely adjust the pH to an absolute 8.5. 90 grams of dopamine hydrochloride powder (ensuring a concentration of 3 g / L) was slowly added to the buffer solution, and mechanical stirring was continued until the solution became clear and transparent (subsequently turning light brown to dark black due to oxidation). All the hydroxyl-activated basalt fibers were then immersed in the solution. In the polymerization solution, the reaction system was kept in a strictly dark environment at 25°C and mechanically stirred at a gentle speed of 150 rpm for 20 hours. During this period, dopamine molecules spontaneously oxidized, cyclized and condensed, depositing and growing a dense and tough polydopamine (PDA) biomimetic interface coating on the fiber surface. After the reaction was completed, the fiber was taken out and washed with a large amount of deionized water to remove free non-grafted dopamine oligomers. It was then vacuum dried at 60°C to obtain PDA-coated basalt fiber with a uniform dark brown color.

[0031] Finally, the silane grafting step was carried out. 10 liters of anhydrous ethanol was placed in a sealed reaction vessel, and 750 ml of 3-aminopropyltriethoxysilane (APTES) was slowly added dropwise. An appropriate amount of deionized water was added to promote pre-hydrolysis and activation for 2 hours. Then, the aforementioned dark brown PDA-coated basalt fibers were dispersed into the APTES hydrolysate system. The temperature was raised to 55°C, and the circulating reflux condenser was turned on. The reaction was maintained at a medium speed for 7 hours. In a constant temperature environment, the amino groups and the groups of the PDA layer covalently bonded. After the reaction was completed, the fibers were filtered out and ultrasonically washed three times for 15 minutes each in anhydrous ethanol to remove unbonded silane molecules. The fibers were then placed in an 80°C drying oven for deep desolventizing and drying to obtain the perfectly prepared first component - dopamine / silane co-grafted modified basalt fiber. This fiber has both a strong alkali-resistant coating on its surface and extended chemical "tentacles" (silanol groups), which enable it to deeply bond with cement.

[0032] (II) Second Component: Preparation of Core-Shell Phase Change Microcapsules The component was prepared using the sol-gel method. 5000 mL of deionized water was placed in an emulsification reactor equipped with a jacketed heating and temperature control system. CTAB (hexadecyltrimethylammonium bromide) and Triton X-100 (octylphenyl polyoxyethylene ether) were weighed to ensure that the molar ratio of the two was accurately maintained at 1:1. The total mass was 2.0% of the mass of the deionized water in the reactor (i.e., about 100 g of composite emulsifier). The emulsifier was added to the water and heated to 48 °C and stirred until it was completely clear and dissolved.

[0033] In another clean glass beaker, 2000 grams of n-octadecane (phase change material) was weighed and placed in a water bath and heated to 48°C to completely melt it into a liquid oil phase. The molten n-octadecane was then slowly poured into the above-mentioned composite emulsifier aqueous solution under the extremely high shear force of a high-intensity shear homogenizer (speed set to 12000 rpm). The ultra-high-speed shear emulsification was continued for 25 minutes. Due to the synergistic reduction of the oil-water interfacial tension by the composite emulsifier, an extremely stable O / W type n-octadecane microemulsion system with a particle size of about 1.5 micrometers was formed.

[0034] The emulsified system was transferred to a conventional low-speed mechanically stirred reactor, and the stirring speed was reduced to a steady-state 500 rpm. The system temperature was precisely reduced to 38°C by circulating water cooling. A 5% ammonia solution (NH3·H2O) was added dropwise to the emulsion using a constant flow burette. With the help of an online pH meter, the pH of the entire system was precisely locked at 10.0.

[0035] In addition, the shell precursor solution was prepared: 1500 mL of tetraethyl orthosilicate (TEOS) and 1500 mL of anhydrous analytical grade ethanol were measured and mixed rapidly in a beaker. Using a high-precision dual-channel micro-injection pump, the precursor mixture was added dropwise at a very slow and uniform rate of 0.8 mL / min to the above microemulsion system which was kept at a constant temperature of 38°C. The dropwise addition of the precursor solution took a long time. After the dropwise addition was completed, the stirring was maintained at 500 rpm and the constant temperature of 38°C to allow the system to fully mature for 14 hours. During this long coating process, the TEOS molecules on the surface of the n-octadecane oil droplets hydrolyzed and condensed under the catalysis of alkaline ammonia water to form a tightly packed silica shell.

[0036] After the reaction was completely terminated, the suspension was introduced into a large-capacity centrifuge and centrifuged at 8000 rpm for 15 minutes. The supernatant was discarded, and the lower white paste-like precipitate was resuspended and dispersed with deionized water and centrifuged again (repeated twice). Finally, the precipitate was washed and centrifuged once with anhydrous ethanol to quickly remove residual water and emulsifier. The purified wet material was then freeze-dried for 24 hours in a large vacuum freeze dryer with a temperature set at -40°C and a cold trap vacuum degree of less than 10 Pa to prevent capillary shrinkage and cracking of the microcapsule shell. The freeze-dried product was lightly ground and dispersed using a planetary ball mill and passed through a 200-mesh standard test sieve to obtain the second component—core-shell structured phase change microcapsules—which appeared as a white, fine, flowing powder. Differential scanning calorimetry (DSC) tests showed that the melting phase change peak was concentrated at 28.1°C, and the phase change enthalpy was as high as 132.5 J / g.

[0037] (III) Third Component: Preparation of Salt-Tolerant Internal Maintenance Water-Absorbing Microspheres The polymerization reactor was constructed using the reverse suspension polymerization method and was equipped with an electric anchor-type agitator, a high-purity nitrogen inlet pipe, a condensate reflux separator, and an automatic programmed heating jacket.

[0038] Preparation of the polymerization aqueous phase: Accurately weigh 100 g of analytical grade acrylic acid (AA) into a 500 mL clean beaker pre-cooled to approximately 5 °C. Place the beaker in an ice-water bath for further cooling. Turn on a strong magnetic stirrer and use a micro-constant flow pump to very slowly add a 30 wt% sodium hydroxide aqueous solution. The adding rate should be such that the system temperature does not exceed 15 °C. The calculated amount of addition ensures that the acrylic acid neutralization degree strictly reaches 70% (i.e., 70% of the AA is converted to sodium acrylate), resulting in a viscous pre-neutralized monomer solution. Immediately afterwards, add 25 g of acrylamide (AM) powder and 1... 2 grams of hydroxyethyl methacrylate (HEMA) liquid monomer were stirred for 20 minutes to ensure complete amorphous dissolution and no particle residue. Then, 0.41 grams (0.3% of the total monomer mass) of N,N'-methylenebisacrylamide (MBA) was added as a network crosslinking backbone material, and 1.02 grams (0.75% of the total monomer mass) of potassium persulfate (KPS) was added as a thermally decomposable free radical initiator. After the aqueous phase was mixed evenly, it was transferred to a high-power ultrasonic cleaner and subjected to ice bath ultrasonic degassing and degassing for 10 minutes to obtain a bubble-free and clear aqueous mixed solution for later use.

[0039] Preparation of continuous oil phase: In a 2000 mL three-necked polymerization flask, pour in 800 mL of cyclohexane solvent, add 24 g (approximately 3.8% of the oil phase mass) of dispersant Span-60 (sorbitan monostearate), start the heating mantle to raise the temperature to 50 °C, turn on the anchor stirrer (speed set to 350 rpm), until Span-60 is completely melted and uniformly dispersed in the cyclohexane, turn off the heating mantle to stop heating, and introduce high-purity nitrogen gas at a flow rate of 200 mL / min into the bottom of the flask, continuously bubbling to replace the dissolved oxygen in the flask for 30 minutes.

[0040] Polymerization and crosslinking reaction process: Under the premise of maintaining a nitrogen positive pressure protective microenvironment and maintaining a uniform shearing and stirring state of 350 rpm, the above-mentioned ultrasonically degassed cold aqueous phase solution was uniformly dropped into the oil phase filled with protective agent within 40 minutes using a dropping funnel. Due to the surface active barrier of Span-60, the aqueous phase was dispersed and cut into countless tiny droplets suspended in cyclohexane. After the dropping was completed, the system temperature was gradually increased to 68°C at a strictly set ramp rate of 2°C / min using an automatic temperature controller, and the polymerization reaction was maintained at this constant temperature for 5 hours. During this period, KPS was heated and bonded to generate primary free radicals, which initiated a strong copolymerization reaction of the AA, AM and HEMA ternary monomers, forming an intricate three-dimensional network of crosslinked macromolecules containing multiple salt-resistant functional groups inside the tiny droplets.

[0041] Post-processing and purification separation: After the polymerization stage is completed, the reaction system is configured in azeotropic dehydration mode, and the reactor temperature is gradually raised to approximately 82°C (the azeotropic point of cyclohexane and water). As the azeotropic vapor is condensed and separated in the water separator, water is continuously removed from the system. With increasing dehydration, the soft, gel-like polymer particles gradually transform into hard, discrete solid microspheres due to water loss and settle at the bottom. Heating is stopped and the mixture is cooled to room temperature when no more water droplets precipitate in the water separator. The solid-liquid mixture is then poured out, filtered, and the microspheres are collected. A large amount of high-purity acetone was poured into a beaker to soak and magnetically stir the microspheres to thoroughly extract and wash away the cyclohexane residue and Span-60 organic layer adhering to the surface (repeated washing 3 times). Finally, the particles were placed in a constant temperature vacuum negative pressure drying oven at 60°C and dried for 24 hours until constant weight. They were then removed and pulverized (for slightly agglomerated parts). They were then strictly sieved using a standard analytical sieve to collect the fine microsphere powder with a particle size between 100 and 200 micrometers. This yielded the third component of the final product – salt-resistant internally nourishing and water-absorbing microspheres.

[0042] (iv) Formulation of crack-resistant and toughening modifiers The first, second, and third components prepared independently above are poured into a zero-gravity biaxial paddle mixer according to the specific mass ratio values ​​specified in the following embodiments. They are then dry-mixed at a medium speed (60 rpm) for 3 minutes to achieve a highly uniform dispersion of the three powders / chopped fibers on a macroscopic scale. The mixture is then placed in a sealed bag for later use.

[0043] The following details various concrete implementation examples and comparative mix proportions.

[0044]

Example 1

[0045] In this embodiment, the crack-resistant synergistic toughening modifier is composed of the first component, the second component and the third component prepared above, which are precisely mixed in a mass ratio of 3:10:8.

[0046] The specific concrete mixing process steps are as follows: (1) Material premixing: The accurately weighed fine aggregate and coarse aggregate, together with the crack-resistant synergistic toughening modifier dry powder prepared in the above proportion, are all put into the forced twin-shaft concrete mixer. The equipment is turned on and dry-mixed for 60 seconds. The purpose of this step is to use the mechanical friction between the aggregates to completely break up the modifier agglomeration that may exist due to static electricity or van der Waals forces, so that it is initially evenly distributed in the skeleton gaps.

[0047] (2) Addition and coating of cementitious materials: Add precisely weighed cement, fly ash and mineral powder to the mixer and continue to dry mix for 60 seconds. The addition of powder further fills the gaps between aggregates and forms a dense gradation and packing state.

[0048] (3) Wet forced mixing intensification: The polycarboxylate superplasticizer is completely dissolved in the mixing water beforehand. The superplasticizer aqueous solution is poured into the mixer at one time, the wet mixing process is started, and the continuous forced mixing is carried out for 180 seconds. Under the intense high shear mixing action, the superplasticizer molecules cause the cement particles to disintegrate and disperse rapidly through steric hindrance and electrostatic repulsion, forming a slurry with excellent fluidity. Meanwhile, the third component of water-absorbing microspheres begins to swell moderately in the slurry and adsorb some free water and water-reducing agent ions (due to its salt-resistant modification, it maintains excellent stable expansion volume under high calcium ion conditions, rather than suddenly collapsing and shrinking). The second component, phase change microcapsules, fills the micropores along with the slurry. The first component fibers are perfectly dispersed and initially overlapped into a network on the surface of cement particles by the help of polydopamine and improved water wettability.

[0049] (4) Discharge and casting: After mixing, the material is discharged immediately. At this time, the slump of the mixture is measured to be 240 mm and the expansion is 620 mm, showing excellent self-compacting performance. No segregation or oil bleeding caused by microcapsule rupture occurs. The mixture is then poured into standard compressive strength and flexural strength molds, shrinkage deformation test prism molds and standard circular ring crack resistance molds. The mixture is then lightly vibrated on a micro high-frequency vibration table for 15 seconds to remove large air bubbles. The surface is smoothed and immediately covered with a waterproof plastic film. The mixture is then placed in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for curing until the specified age for subsequent precision performance testing.

[0050]

Example 2

[0051] In the modifier, the mass ratio of the first component, the second component, and the third component is adjusted to 5:8:15, which significantly increases the proportion of dopamine / silane modified fibers and internally cured microspheres, so as to provide more abundant internal moisture feedback and stronger interfacial overlap effect during the large-volume casting of high fly ash.

[0052] The preparation, mixing, and curing processes were the same as those described in Example 1. After discharge, the slump was tested to be 255 mm and the expansion was 645 mm.

[0053]

Example 3

[0054] In response to the characteristics of high heat generation and high shrinkage, the anti-cracking and toughening modifier in this embodiment is composed of the first component, the second component and the third component in a special mass ratio of 2:15:5. The amount of the second component (core-shell structure phase change microcapsules) is greatly increased in order to maximize the absorption and suppress the heat release in the early stage of hydration.

[0055] The preparation, mixing, pouring and curing process is the same as in Example 1, with a slump of 220 mm and a spread of 580 mm.

[0056]

Example 4

[0057] The mass ratio of the first component, the second component, and the third component in the modifier is 4:12:10.

[0058] The preparation, mixing, pouring, and curing processes are the same as in Example 1, and the workability is excellent.

[0059]

Example 5

[0060] The mass ratio of the first, second, and third components in the modifier is 3:10:10.

[0061] The preparation and maintenance details remain unchanged.

[0062] The following series of comparative examples lacking synergy are set up to demonstrate the substantial creativity of this invention and its irreplaceable, groundbreaking technological leap.

[0063]

Comparative Example 1

[0064] The preparation steps were performed exactly as described in Example 1.

[0065]

Comparative Example 2

[0066] The preparation and maintenance conditions are the same as above.

[0067]

Comparative Example 3

[0068]

Comparative Example 4

[0069] The specimens were prepared and standardized using the ultrasonic dispersion and mixing ball milling processes taught in the patent document.

[0070] In-depth analysis of concrete precision performance evaluation tests and comparative data. In order to reveal the extraordinary breakthrough of this invention in a rigorous scientific manner, we conducted extremely stringent multiple service performance tests on all concrete specimens prepared in Examples 1-5 and Comparative Examples 1-4, based on national core standards and cutting-edge academic research methods.

[0071] 1. Basic physical and mechanical load-bearing capacity test According to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" GB / T 50081-2019, 150×150×150mm cubic specimens were prepared to determine the compressive strength at 3 days and 28 days (representing early strength and final compressive strength, respectively). A 100×100×400 mm prism specimen was prepared, and its flexural strength after 28 days was determined by the four-point bending method, reflecting the toughness potential of the matrix material in response to bending tensile force.

[0072] 2. Semi-adiabatic temperature rise curve capture test (for phase transition peak reduction verification) Using a large-volume concrete semi-insulated temperature rise tester, freshly mixed concrete was placed into a 100-liter cylindrical test barrel wrapped with a thick polyurethane insulation layer. Pt100 high-sensitivity armored platinum resistance temperature sensors were embedded in the center and surface of the specimen, respectively, and the core peak temperature caused by the heat of hydration in the center of the concrete was recorded from the time of sealing to 120 hours. This serves as a direct and hard indicator for measuring the control of hydration heat and its ability to avoid excessive internal and external temperature differences that could lead to temperature stress cracking.

[0073] 3. Monitoring of the entire process of micro-strain self-shrinkage (quantification of internal maintenance water compensation) A non-contact corrugated pipe self-shrinkage measuring device or a high-precision laser displacement sensor (operated according to ASTM C1698 standard) was used. The initial setting time of the concrete was taken as the zero point of the test. The sample was wrapped in tin foil to absolutely prevent any moisture exchange with the outside environment. The axial self-shrinkage deformation was continuously measured for up to 28 days in a completely sealed state. The unit is extremely fine micro-strain (10⁻¹⁰). -6 ), and contraction is recorded as a negative value.

[0074] 4. Severe resistance test to ring cracking in constrained environment (ultimate test of comprehensive crack resistance) Referring to the circular shrinkage cracking method in GB / T 50082-2009, "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", a concrete ring specimen rigidly constrained by an external steel ring was placed in an artificial climate chamber at 20°C with extremely low ambient humidity (relative humidity strictly controlled at 50%). This dry environment forces severe water loss shrinkage and auto-shrinkage, while the central rigid steel ring completely constrains this shrinkage, causing the internal circumferential maximum tensile stress to accumulate rapidly. A high-magnification industrial camera microscope system was used to continuously record and monitor the cracks for 24 hours to capture the true time of the initiation of the first visible or microscopic crack on the surface (initial crack age, in days (d)). The maximum width of the main crack (micrometers, μm) was also recorded on the 28th day after cracking. The longer the initial crack age and the smaller the width, the higher the comprehensive ultimate crack resistance level.

[0075] All test results have undergone rigorous data verification, and detailed in-depth analysis is shown in the table below.

[0076] [Summary Table of Mechanical and Durability Crack Resistance Characteristics] [In-depth scientific demonstration and microscopic mechanism analysis of data phenomena] 1. Leap in mechanical properties and breakthroughs in interface microstructure As can be seen from the table, all embodiments of the present invention (especially embodiments 1, 3, and 4) exhibit extremely superior compressive and flexural strengths (approaching or exceeding 80 MPa and 10 MPa, respectively), far exceeding the baseline sample Comparative Example 1. This proves that the addition of dopamine / silane co-grafted fibers not only does not weaken the matrix density, but also, due to the strong covalent bond bond on its surface (following the mechanism described in Formula 1 of the present invention), the fibers exert a high-strength anchoring effect similar to micro-reinforcing bars on the microscopic shear surface. The pull-out process is transformed into a difficult covalent bond strong tearing process, which greatly consumes the fracture energy (manifested as a surge in flexural strength).

[0077] In contrast, Comparative Example 2, using ordinary ungrafted basalt fibers and ordinary SAP which is highly susceptible to water loss due to high calcium content, resulted in a sharp drop in compressive strength to 58.4 MPa after 28 days due to a significant increase in porosity and a physical sliding state at the interface. Although the carbon fiber / graphene oxide system (CN115959870A) reproduced in Comparative Example 4 achieved a compressive strength of 69.5 MPa, it lagged far behind the present invention in the core toughness index of flexural strength (8.5 MPa). This confirms its inherent weakness of poor interfacial stability in the later stages of a strongly alkaline environment and the difficulty in eradicating the internal damage caused by graphene oxide agglomeration.

[0078] 2. The Miracle Barrier of Heat Buffering and Phase Change Microcapsules In extremely stringent tests for adiabatic temperature rise, the matrix of Comparative Example 1 exhibited a catastrophic high temperature of 68.4°C. Such a massive heat wave would inevitably lead to irreversible, severe, deep-penetrating temperature drop cracks in real large-volume construction. However, in Example 3 (which incorporates a large amount of microcapsules with a core of n-octadecane and a shell of silica), the core temperature peak was miraculously contained at 51.3°C, with a temperature drop of nearly 20°C (following the phase change microcapsule temperature control coefficient of this invention). (Thermodynamic conversion mechanism) octadecane perfectly executes the solid-liquid latent heat injection mechanism, and the outer nanoscale SiO2 shell not only withstood the extremely violent impact of the stirred gravel without any damage or oil leakage, but also provided active volcanic ash colloid crystal seeds in the later stage of hydration.

[0079] This remarkable performance can be directly corroborated by the disastrous results of Comparative Example 3: Comparative Example 3 blindly poured in the phase change n-octadecane emulsion without adding a hard inorganic shell. As a result, the droplets were violently crushed by the coarse aggregate during the instant of stirring. The n-octadecane completely covered the surface of the cement particles, blocking the contact between water and clinker, which led to a catastrophic drop in its strength. Its compressive strength was only 32.1 MPa, making it almost a waste engineering material.

[0080] 3. Self-shrinkage limit inhibition and all-weather crack resistance myth Under the cruel torment of circular ring cracking in a constrained environment, which even ordinary high-performance materials cannot withstand for more than two weeks, Comparative Example 1 only resisted for a short period of 5.2 days before emitting a crisp cracking sound, with a crack width as high as a terrifying 850μm. Comparative Example 4 (existing technology) lasted for 12.4 days before cracking, with a crack width reaching 310μm.

[0081] In contrast, Examples 1 to 4 of this invention, after enduring high-intensity drying and shrinkage for 28 days or even longer, showed, upon examination with an optical microscope, that their surfaces remained smooth and new, without any visible or even micron-level initial cracks (recorded as no cracks, initial cracking time > 28 days). This remarkable crack resistance achievement is attributed to the application of the self-shrinkage compensation prediction formula (Formula 3) for the salt-resistant microspheres of the third component of this invention. This formula, through the slow and controlled release of bound reservoir water, continuously supplies the constantly drying deep capillaries, smoothing out the extreme negative pressure caused by liquid surface tension, and greatly inhibiting its own intrinsic shrinkage (from 450 × 10⁻⁶). -6 Compress to 100×10 -6 (near the extremely low range), while the shrinkage strain process is smoothly passed at the microscale due to the anti-dissociation properties of the nonionic network of the cross-linked polymer. These three material components not only maintain their respective properties independently, but also undergo deep multiphase "synergistic symbiosis" in the same cement-based giant system, and the microcapsules dissolve thermal stress fluctuations; Salt-tolerant internal curing releases internal pressure water to eliminate intrinsic shrinkage sources; Biomimetic anchoring fibers act as an inescapable last line of defense against force on a network framework ranging from nanoscale to microscale. Any force deviation that occurs in any direction is firmly wrapped and dissolved by this rigid-flexible three-dimensional network.

[0082] Clearly, the significant leap forward made by this invention in the in-depth analysis of the system and the multi-dimensional collaborative technical approach is by no means a simple mechanical patchwork or imitation of existing technologies. Rather, it is an original leap based on cutting-edge achievements in molecular-level interface engineering and thermodynamic phase change regulation. The high crack-resistant concrete prepared by this invention, while ensuring super compressive strength, truly achieves an excellent engineering balance of resistance to temperature cracking, resistance to drying self-shrinkage cracking, and high flexibility and ductility. This lays an impeccable material foundation and cutting-edge solution for high-grade civil engineering projects and the construction of giant foundations under extremely complex hydrological conditions.

[0083] The above description merely illustrates preferred embodiments of the present invention and is not intended to limit or narrow the inventive concept and scope of the invention. For those skilled in the art with common knowledge, any equivalent substitutions, adjustments to proportions within a reasonable micro-range, or additions, deletions, or modifications of non-core components based on the technical content and core principles disclosed in this invention, all such extensions based on the teachings of this invention, unconditionally and indisputably fall within the scope of protection of this invention. The final and core protection boundary of this invention must be determined by the strict legal definition of the claims to be asserted in the future.

Claims

1. High crack-resistant concrete, characterized in that, It is composed of raw materials comprising the following parts by weight: Silicate cement: 350-450 parts; Fly ash: 80-120 parts; Granulated blast furnace slag powder: 60-100 parts; Fine aggregate: 650-750 parts; Coarse aggregate: 950–1100 parts; Mixing water: 140-165 parts; High-performance polycarboxylate superplasticizer: 4.5–8.0 parts; Crack-resistant and toughening modifier: 15-35 parts; The crack-resistant synergistic toughening modifier is composed of a first component, a second component, and a third component; The first component is dopamine / silane co-grafted modified basalt fiber, the second component is a core-shell structured phase change microcapsule with n-octadecane as the core and silica as the shell, and the third component is a salt-resistant internally maintained water-absorbing microsphere prepared by ternary copolymerization of acrylic acid, acrylamide and hydroxyethyl methacrylate. The mass ratio of the first component, the second component and the third component in the crack-resistant synergistic toughening modifier is (2-5):(8-15):(5-15).

2. The high crack-resistant concrete according to claim 1, characterized in that, The preparation method of the first component includes the following steps: The coarse basalt fibers were cut and ultrasonically cleaned to remove the surface wetting agent, and then dried to obtain pretreated basalt fibers. The pretreated basalt fibers were immersed in hydrochloric acid solution for water bath reflux etching, and after washing and drying, basalt fibers with surface hydroxyl activated were obtained. The basalt fibers with surface hydroxyl activated were placed in Tris buffer containing dopamine hydrochloride and stirred under light-proof and constant temperature conditions. The dopamine self-oxidatively polymerized to form a polydopamine coating on the fiber surface. After washing and drying, polydopamine-coated basalt fibers were obtained. The polydopamine-coated basalt fibers were dispersed in anhydrous ethanol containing 3-aminopropyltriethoxysilane hydrolysate, and the mixture was stirred and refluxed at a constant temperature. The phenolic hydroxyl and quinone groups on the surface of the polydopamine coating underwent Michael addition and Schiff base reactions with 3-aminopropyltriethoxysilane, grafting silanol groups onto the polydopamine-modified layer. After washing and drying, the first component was obtained.

3. The high crack-resistant concrete according to claim 2, characterized in that, The cut length of the basalt coarse fibers is 12–18 mm; The ultrasonic cleaning uses an ethanol aqueous solution with a volume concentration of 70% to 80%, an ultrasonic frequency of 40 to 50 kHz, and a cleaning time of 30 to 45 minutes. The concentration of the hydrochloric acid solution is 2-3 mol / L, the etching temperature is 60-70℃, and the etching time is 2-3 hours; The concentration of the Tris buffer solution is 10–20 mmol / L, the pH value is 8.4–8.6, the concentration of dopamine hydrochloride in the Tris buffer solution is 2–4 g / L, the reaction temperature is 25°C, and the reaction time is 18–24 hours. The volume concentration of 3-aminopropyltriethoxysilane in the hydrolysate is 5%–10%, the reflux reaction temperature is 50–60°C, and the reaction time is 6–8 hours.

4. The high crack-resistant concrete according to claim 1, characterized in that, The second component was prepared using a sol-gel in-situ coating method, which included the following steps: Hexadecyltrimethylammonium bromide and octylphenyl polyoxyethylene ether were mixed in a molar ratio of 1:1 and dissolved in deionized water to prepare a composite surfactant aqueous solution with a mass concentration of 1.5% to 2.5%. The aqueous solution of the composite surfactant is heated to 45-50°C, and molten n-octadecane is added. The mixture is then subjected to high-shear homogenization emulsification at a speed of 10,000-15,000 rpm for 20-30 minutes to form an oil-in-water phase change core material microemulsion. The n-octadecane droplet size is controlled to be 1-3 micrometers. Reduce the stirring speed to 400-600 rpm, adjust the reaction system temperature to 35-40°C, add 5% ammonia solution to adjust the pH to 9.5-10.5, and add a mixture of tetraethyl orthosilicate and anhydrous ethanol dropwise to the system at a rate of 0.5-1.0 mL / min, wherein the volume ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:

1. After the addition is complete, continue stirring at a constant temperature for 12-16 hours. Tetraethyl orthosilicate hydrolyzes and condenses at the interface between n-octadecane micro-droplets and water to form a silica shell. The product was centrifuged, washed, freeze-dried under vacuum, and then ground through a 200-mesh sieve to obtain the second component.

5. The high crack-resistant concrete according to claim 1, characterized in that, The third component is prepared by reverse suspension polymerization, and the preparation method includes the following steps: Preparation of the aqueous phase: Acrylic acid was placed in an ice-water bath, and a 30% sodium hydroxide aqueous solution was added dropwise for partial neutralization, with the degree of neutralization controlled at 65%–75%. Acrylamide (20%–30% by mass of acrylic acid) and hydroxyethyl methacrylate (10%–15% by mass of acrylic acid) were added. After dissolution, N,N'-methylenebisacrylamide (0.2%–0.4% by mass of total monomers) was added as a crosslinking agent and potassium persulfate (0.5%–1.0% by mass of total monomers) was added as an initiator. After ultrasonic degassing, an aqueous solution was obtained. Preparation of the oil phase: Cyclohexane is used as the continuous phase solvent, and 2% to 4% of dehydrated sorbitan monostearate is added as a dispersant. After heating and dissolving, nitrogen gas is introduced to remove dissolved oxygen, and an oil phase solution is obtained. Under continuous nitrogen protection and mechanical stirring at 300-400 rpm, the aqueous phase solution was added dropwise to the oil phase solution, and the temperature was increased to 65-70°C at a rate of 2°C / min, and the reaction was carried out at a constant temperature for 4-6 hours. After the reaction is complete, the temperature is raised to 75-85℃ for azeotropic dehydration and solvent removal. The polymer microspheres are collected, extracted and washed with acetone, and dried to constant weight under vacuum at 60℃. Powder with a particle size of 100-200 micrometers is screened out to obtain the third component.

6. The high crack-resistant concrete according to claim 1, characterized in that, The core-shell structured phase change microcapsules have a peak phase change temperature of 27.5–28.5 °C and a latent heat of phase change of 120–140 J / g.

7. The high crack-resistant concrete according to claim 1, characterized in that, The salt-resistant internal curing water-absorbing microspheres have a liquid absorption ratio of 35 to 50 times in the cement simulated pore solution.

8. The high crack-resistant concrete according to claim 1, characterized in that, The silicate cement is ordinary silicate cement of grade P·O 42.5 or above; The fly ash is Class I fly ash conforming to GB / T 1596-2017; The granulated blast furnace slag powder is S95 grade or higher slag powder; The fineness modulus of the fine aggregate is 2.6 to 3.0, and the mud content is controlled within 1.0%. The coarse aggregate is continuously graded crushed stone with a particle size of 5-20mm and a crushing index value of no more than 8%; The high-performance polycarboxylate superplasticizer has a solid content of not less than 40% and a water reduction rate of more than 25%.

9. The high crack-resistant concrete according to any one of claims 1-8, characterized in that, The method for preparing the high crack-resistant concrete includes the following steps: Fine aggregate, coarse aggregate, and the aforementioned crack-resistant synergistic toughening modifier are put into a mixer for dry mixing; Add silicate cement, fly ash and granulated blast furnace slag powder to the mixer and continue dry mixing; High-performance polycarboxylate superplasticizer is dissolved in mixing water and added to a mixer for wet forced mixing to obtain a high crack-resistant concrete mixture.

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