Crack-resistant durable concrete suitable for arid regions and preparation method of crack-resistant durable concrete

Abstract

The invention relates to the technical field of concrete, and discloses anti-crack durable concrete suitable for arid regions and a preparation method thereof.The preparation method includes the steps that in a plastic stage time window after concrete pouring and leveling, a surface catalytic sealing agent containing an active silicate component and a pH sensitive indicator is applied, the sealing agent generates gel through an in-situ reaction of free alkali and moisture on the surface layer of the base material to block capillary pores, the pH sensitive indicator objectively feeds back the process of the pore sealing reaction through color development and color fading, closed-loop coupling is conducted on the material chemical reaction and the construction process, water loss cracking in the plastic stage is blocked from the mechanism, and the service life of the sealing agent is prolonged. And objective verification of maintenance-free and construction quality is realized.

Description

Technical Field

[0001] This invention relates to a crack-resistant and durable concrete suitable for arid regions and its preparation method, belonging to the field of concrete technology. Background Technology

[0002] The setting, hardening, and long-term durability of current materials are highly dependent on the full hydration reaction of cement. The core condition for ensuring the initiation and continuation of the hydration reaction is the continuous supply of water. Therefore, the industry-consensus curing methods, such as water spraying and mulching or spraying curing agents, focus on how to provide a long-term moist environment for concrete after it has reached a certain strength. However, the above-mentioned conventional processes that target later hydration have a common and unresolved technical defect in application scenarios facing harsh climatic conditions such as drought, high temperature, and strong wind. In the plastic stage after concrete has just been poured and leveled, its interior does not yet have effective tensile strength. At this time, the capillary network of the surface layer is completely open. Harsh climatic conditions cause the evaporation rate of surface free water and exudate to far exceed the migration rate of core water to the surface, thus forming a severe surface-core water loss gradient and triggering the generation of plastic shrinkage cracks.

[0003] Faced with this physical failure occurring in the early stages of setting and hardening, existing technical approaches are insufficient to effectively address it. Their limitations are mainly: 1. Traditional wet curing methods, whether watering or covering, are applied with a delayed timing. They focus on long-term hydration after the concrete's final setting, offering little protection against the instantaneous water loss and stress cracking during the plastic stage; 2. While other chemical materials exist, such as silicate hardeners for floor wear resistance, their application and mechanism are based on hardened, already strong concrete substrates. Their purpose is to improve density and wear resistance, not to address crack protection during the plastic stage. Applying such materials to substrates still in a fluid or semi-plastic state is inconsistent with conventional techniques in this field. To address this issue, while chemical curing agents for water retention have been developed, their technical approach generally remains at the level of physical film formation and barrier. This makes it difficult to match the timing of application and protective mechanism with the instantaneous physical state of the substrate during the plastic stage. For example, [the text abruptly ends here, likely due to an incomplete sentence or missing information]. Chinese invention patent CN102320860B discloses a concrete curing agent and its preparation method suitable for windy and arid regions. The core technology of this solution is the compounding of organosilicon / fluorine modified styrene-acrylic emulsion and modified sodium silicate solution. Its main mechanism still relies on the polymer emulsion to aggregate and form a film on the concrete surface to form a physical barrier layer. However, the application of such physical film-forming materials has an inherent contradiction with the state of the substrate during the plastic stage: on the one hand, its film-forming process, namely the demulsification and aggregation of polymer emulsion, depends on the evaporation of water, which is difficult to control in arid and windy environments; on the other hand, the concrete surface during the plastic stage is still wet or even oozing water, and the polymer emulsion is difficult to effectively adhere to the wet surface and form a uniform, dense, and continuous film. Therefore, this technical approach that relies on physical film formation in the later stage is essentially lagging. It cannot use the original environment of the substrate within the time window of the plastic stage to achieve immediate sealing of capillary pores from a mechanistic perspective, and thus it is difficult to truly block the source of plastic cracking.

[0004] Therefore, the technical problem to be solved by this invention is how to provide a new preparation method that, in the plastic stage after concrete pouring, can block the formation of the surface-core water loss gradient and utilize surface moisture to achieve self-generated internal curing, thereby solving the plastic cracking defect in arid regions. Summary of the Invention

[0005] This invention provides a crack-resistant and durable concrete suitable for arid regions and its preparation method. Its main purpose is to solve the problem of plastic cracking of concrete in arid regions and achieve self-curing by blocking the formation of the surface-core water loss gradient during the plastic stage of concrete.

[0006] To achieve the above objectives, the present invention provides a method for preparing crack-resistant and durable concrete suitable for arid regions, the method comprising: Step 101: Prepare the concrete mixture, and pour and level the surface of the concrete mixture; Step 102: After surface leveling is completed and within the time window when the concrete mixture is still in the plastic stage, a surface catalytic sealant is applied to the plastic surface of the concrete mixture. The time window of the plastic stage is defined as: the stage where surface bleeding of the concrete mixture has ended or is about to end, but surface water to be evaporated and free alkaline substances released by the early stage of cement hydration still exist in its surface capillary pores. The surface catalytic sealant is an aqueous solution containing an active silicate component and a pH-sensitive indicator. When the active silicate component comes into contact with surface water and free alkaline substances, an in-situ chemical reaction occurs to generate hydrated calcium silicate gel. The hydrated calcium silicate gel precipitates in the capillary pores of the plastic surface and seals the capillary pores. The pH-sensitive indicator shows color when the surface catalytic sealant comes into contact with free alkaline substances, and fades after the free alkaline substances are consumed by the in-situ chemical reaction of the active silicate component, resulting in a decrease in pH value. Fading is defined as a signal that the sealing is complete. Step 103: After the sealing completion signal is detected in step 102, the concrete is allowed to harden naturally without external wet curing.

[0007] Preferably, the active silicate component is selected from at least one of colloidal silica, lithium silicate, sodium silicate, and potassium silicate.

[0008] Preferably, the pH-sensitive indicator is selected from at least one of phenolphthalein and thymolphthalein.

[0009] Preferably, between steps 101 and 102, the method further includes: step 401, performing in-situ monitoring of the surface conductivity or surface resistance of the plastic surface of the concrete mixture, and calculating the rate of change of the surface conductivity or surface resistance over time; step 402, when the absolute value of the rate of change is detected to fall from a peak and stabilize in a preset low value range, determining that the time window of the plastic stage has been reached, and triggering the execution of step 102.

[0010] Preferably, in step 102, the surface catalytic sealing agent, in addition to containing an active silicate component and a pH-sensitive indicator, also contains a water-based polymer emulsion; while the active silicate component undergoes an in-situ chemical reaction to generate hydrated calcium silicate gel, the water-based polymer emulsion undergoes demulsification and aggregation on the plastic concrete surface, and forms a flexible film between the skeletons of the hydrated calcium silicate gel, thus forming an organic-inorganic hybrid sealing layer in situ on the plastic surface.

[0011] Preferably, the aqueous polymer emulsion is selected from at least one of styrene-acrylate emulsion, styrene-acrylic emulsion, and silicone-acrylic emulsion.

[0012] Preferably, in step 102, the surface catalytic sealant is pre-formulated as a shear-thinning thixotropic fluid; and the application of the surface catalytic sealant is performed through a high-shear atomizing nozzle; the shear-thinning thixotropic fluid undergoes viscosity reduction due to high shear force when passing through the high-shear atomizing nozzle to achieve atomization, and its viscosity recovers after leaving the high-shear atomizing nozzle due to the disappearance of shear force, forming droplets resistant to wind drift; the apparent viscosity of the shear-thinning thixotropic fluid... With shear rate In 25 The test temperature satisfies The relationship, among which Where n is the consistency coefficient and n is the fluid property index, and .

[0013] Preferably, the shear-thinning thixotropic fluid is prepared by adding a thixotropic agent to a surface catalytic blocking agent, the thixotropic agent being selected from at least one of xanthan gum, alginate and modified cellulose.

[0014] Preferably, step 102 specifically includes: step 901, applying an alkaline accelerator to the plastic surface of the concrete mixture by atomization, wherein the alkaline accelerator is an aqueous solution containing at least one of lithium hydroxide and potassium hydroxide; step 902, immediately after step 901 is completed and within the time interval during which the alkaline accelerator is absorbed but not dried, applying a surface catalytic sealant by atomization to the plastic surface to which the alkaline accelerator has been applied; wherein the active silicate component in the surface catalytic sealant undergoes an in-situ chemical reaction with the alkaline accelerator and the free alkaline substances in the concrete mixture, and in step 101, the step of preparing the concrete mixture further incorporates polypropylene microfibers or basalt fibers.

[0015] A crack-resistant and durable concrete suitable for arid regions is a product directly obtained from a method for preparing crack-resistant and durable concrete suitable for arid regions, the product comprising: A concrete substrate; A self-generated sealing layer formed on the surface of a concrete matrix; the self-generated sealing layer comprises: hydrated calcium silicate gel precipitated and sealing the capillary pores of the concrete matrix surface by in-situ chemical reaction in the method, and residues of a pH-sensitive indicator applied in the method.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The preparation method of the present invention couples the chemical reaction mechanism of the material with a specific physical stage in the concrete setting process. By applying a catalytic sealant during a specific time window after pouring and leveling, while the substrate is still in the plastic stage, the original alkaline environment of the substrate surface and the surface moisture that is about to evaporate are utilized to trigger the rapid formation of hydrated calcium silicate gel in situ in the capillary network. This process physically blocks the moisture evaporation gradient between the surface and the core, protecting the concrete from tearing damage by plastic shrinkage stress in the most vulnerable stage before it gains tensile strength. At the same time, it effectively seals the mixing water inside the concrete, providing conditions for long-term cement hydration without the need for external wet curing.

[0017] 2. By synergistically compounding water-based polymer emulsions in the catalytic sealant, the inorganic gelation reaction and the organic film-forming process occur simultaneously in situ on the surface of plastic concrete. The resulting rigid hydrated calcium silicate gel skeleton provides immediate capillary pore sealing efficiency, while the synchronously aggregated polymer forms a flexible filling film between the gel skeletons, ultimately forming an organic-inorganic hybrid sealing layer on the concrete surface. This hybrid layer not only solves the problem of water loss and cracking in the plastic stage, but its flexibility and toughness also enable it to adapt to thermal expansion and contraction deformation caused by extreme diurnal temperature differences in arid regions in the later stage, avoiding brittle cracking and failure of the sealing layer itself.

[0018] 3. By compounding a pH-sensitive indicator into the catalytic sealing agent, a closed-loop coupling is achieved between the microscopic chemical sealing reaction and the macroscopic construction quality control. The indicator utilizes the free alkaline substances abundant on the surface of plastic concrete to instantly develop color, providing immediate and complete visual confirmation of the coverage area for construction operations. This color will automatically fade as the pH value of the microenvironment decreases due to the continuous consumption of alkaline substances by the sealing reaction, providing objective process verification for the effective implementation of the sealing reaction. This transforms a construction step that relies on subjective experience into a standardized process with immediate feedback and quality self-inspection functions. Attached Figure Description

[0019] Figure 1 This is a closed-loop process flow diagram for the preparation of cured concrete according to the present invention; Figure 2 This is a comparison diagram of the impermeability of different sealing layers of the present invention before and after temperature cycling; Figure 3 This is a timing diagram of the synergistic reaction of the organic-inorganic hybrid blocking layer of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the scope of protection of the invention.

[0021] This invention provides a crack-resistant and durable concrete suitable for arid regions and its preparation method. It focuses on the plastic stage of concrete after pouring and leveling but before hardening. By applying a surface catalytic sealant within this specific time window, the existing chemical environment and moisture on the concrete substrate surface are utilized to trigger an in-situ gel reaction to seal capillary pores, thereby preventing water loss cracking during the plastic stage and achieving self-hardening without curing. The complete process path of this preparation method includes: Step 101, preparing a concrete mixture and pouring and leveling the surface of the concrete mixture; Step 102, after surface leveling is completed and within the time window when the concrete mixture is still in the plastic stage, applying a surface catalytic sealant to the plastic surface of the concrete mixture; Step 103, after detecting the completion signal of pore sealing in Step 102, allowing the concrete to harden naturally without external wet curing; In Step 101, the preparation of the concrete mixture can be carried out using methods in the art. To further enhance the concrete matrix's resistance to plastic shrinkage, conventional admixtures such as cement, sand, aggregate, water, and water-reducing agents can be incorporated into the concrete mix preparation process. Polypropylene microfibers or basalt fibers can be added during this step. These fibers form a three-dimensional randomized support network within the matrix, helping to bear early plastic shrinkage stress. Step 102 defines the time window for the plastic stage, defined as the point where surface bleeding of the concrete mix has ended or is about to end, but the surface capillary pores still contain surface moisture awaiting evaporation and free alkaline substances released from early cement hydration. Applying the sealant too early, before surface bleeding has ended, excessive bleeding will dilute the sealant, preventing it from reacting effectively. Applying it too late, after a large amount of surface moisture has evaporated, not only lacks a reaction medium but plastic cracking may also have already occurred. In actual construction, this window can be judged empirically: the surface still retains a moist sheen but there is essentially no longer any free water film.

[0022] In one embodiment, to achieve objective determination of the time window, an in-situ monitoring procedure may be further included between steps 101 and 102: Step 401, in-situ monitoring of the surface conductivity or surface resistance of the plastic surface of the concrete mixture is performed, and the rate of change of surface conductivity or surface resistance over time is calculated; during the bleeding stage, a continuous ionized water film exists on the surface, with high conductivity and low resistance; when bleeding ends and the water film disappears, turning into discontinuous capillary pore water, the conductive path decreases sharply, and the conductivity will decrease once, its change The absolute value of the rate of change will show a peak; in step 402, when the absolute value of the rate of change is detected to fall from a peak and stabilize in a preset low range, it is determined that the time window of the plastic stage has been reached, and step 102 is triggered; the surface catalytic sealing agent is an aqueous solution containing an active silicate component and a pH-sensitive indicator; the active silicate component is used to provide a reactive silicon source, which can be selected from at least one of colloidal silica, lithium silicate, sodium silicate and potassium silicate; when the active silicate component reacts with surface moisture and free alkaline substances The main process involves the release of calcium hydroxide during the early hydration of cement, which, upon contact with water, undergoes an in-situ chemical reaction to form water-insoluble calcium silicate hydrate gel. This gel precipitates in the capillary pores of the plastic surface, sealing them and physically blocking the evaporation pathways of moisture. A pH-sensitive indicator is used to provide a visual feedback mechanism for construction quality and reaction progress; it can be selected from at least one of phenolphthalein and thymolphthalein. Given that the surface of plastic concrete is rich in free alkaline substances, its microenvironment pH value is usually higher than 12. The pH-sensitive indicator... When the surface catalytic sealing agent comes into contact with free alkaline substances, it will instantly change color due to the high pH environment, such as phenolphthalein turning purple-red. This color development process provides immediate and complete visual confirmation of the coverage area for the construction operation. As the in-situ chemical reaction of the active silicate component continues to consume the free alkaline substances, the pH value of the microenvironment gradually decreases. When the pH value drops below the color change point of the indicator, the indicator automatically fades. Fading is defined as a sealing completion signal, objectively indicating that the sealing reaction has occurred effectively. At this time, the application can be stopped or the process can proceed to step 103.

[0023] In one embodiment, to address the thermal expansion and contraction caused by extreme diurnal temperature variations in arid regions, a water-based polymer emulsion can be synergistically formulated into the surface catalytic sealing agent, in addition to containing active silicate components and a pH-sensitive indicator. The water-based polymer emulsion can be selected from at least one of styrene-acrylate emulsion, styrene-acrylic emulsion, and silicone-acrylic emulsion. Its mechanism of action is that, upon application of the formulated sealing agent, the active silicate components undergo an in-situ chemical reaction to generate hydrated calcium silicate gel, while the water-based polymer emulsion, under the dual effects of water evaporation and chemical demulsification, undergoes demulsification and aggregation on the plastic concrete surface, forming a flexible film between the rigid framework of the hydrated calcium silicate gel. Ultimately, an organic-inorganic hybrid sealing layer with both rigid sealing and flexible deformation capabilities is formed in situ on the plastic surface. This hybrid layer can better adapt to the thermal deformation of the substrate and maintain its own integrity. To ensure the integrity of the sealant and prevent it from being blown away and drifting before reaching the concrete surface, the surface catalytic sealant can be pre-formulated as a shear-thinning thixotropic fluid in response to the prevalent strong winds during construction in arid regions. This can be achieved by adding a thixotropic agent to the surface catalytic sealant, which can be selected from at least one of xanthan gum, alginate, and modified cellulose. This shear-thinning thixotropic fluid maintains a high viscosity when at rest, but its viscosity decreases dramatically and instantaneously under high shear force. Accordingly, the surface catalytic sealant is applied through a high-shear atomizing nozzle. The shear-thinning thixotropic fluid atomizes due to the high shear force as it passes through the high-shear atomizing nozzle, and its viscosity recovers as the shear force disappears after leaving the nozzle, forming large, wind-drift resistant droplets that are not easily blown away by the wind. The rheological properties of this fluid contribute to its apparent viscosity. With shear rate In 25 The test temperature satisfies The relationship, among which This is the consistency coefficient. The fluid property index and .

[0024] In one specific implementation, the amount of xanthan gum, a thixotropic additive, added is not a fixed value, but is determined based on on-site construction conditions, particularly wind speed and the type of nozzle used, through a standardized engineering commissioning procedure. This procedure includes: under actual wind speed conditions at the construction site, using the same type of high-shear atomizing nozzle as in the formal construction, test spraying small samples of surface catalytic sealant with different mass fractions of 0.05%, 0.1%, 0.15%, and 0.2% thixotropic additive added. The determination criteria for this commissioning procedure are based on visual observation to select the lowest addition amount that simultaneously meets the following two conditions: Condition 1, the sprayed droplets possess sufficient viscosity and mass to resist wind drift at the current wind speed before reaching the plastic surface of the concrete; Condition 2, the fluid of this viscosity can still be effectively atomized into uniform droplets when passing through the high-shear atomizing nozzle, rather than forming a liquid flow or uneven, coarse droplets. Those skilled in the art can use this commissioning procedure to determine the fluid characteristic index... The value is controlled within an optimal range. If wind drift is observed, the amount of thixotropic agent added should be increased; if poor atomization is observed, the amount added should be appropriately reduced until the above-mentioned equilibrium state is reached. In another embodiment, for certain specific concrete substrates, such as those with slow early hydration and insufficient concentration of free alkaline substances on the surface due to the addition of a large amount of fly ash or slag, a two-liquid sequential activating method can be adopted. In this case, step 102 specifically includes: step 901, atomizing an alkaline activator onto the plastic surface of the concrete mixture. The alkaline activator is an aqueous solution containing at least one of lithium hydroxide and potassium hydroxide. The function of this activator is to artificially and instantaneously increase the pH value and cation concentration of the surface capillary pore liquid; step 902, immediately after step 901 is completed and within the time interval during which the alkaline activator is absorbed but not dried, the alkaline activator is applied to the plastic surface on which it has been applied. A surface catalytic sealant is applied via atomization. At this time, the active silicate component in the surface catalytic sealant undergoes an in-situ chemical reaction with the alkaline accelerator and free alkaline substances in the concrete mixture, ensuring a rapid and efficient gel sealing reaction even on low-activity substrates. The final product obtained through any of the above-described methods is a crack-resistant and durable concrete suitable for arid regions. The product comprises: a concrete matrix and a self-generated sealing layer formed on the surface of the concrete matrix. The self-generated sealing layer comprises: hydrated calcium silicate gel precipitated and sealing the capillary pores on the surface of the concrete matrix through the in-situ chemical reaction in the method, and residues of the pH-sensitive indicator applied in the method. If a composite aqueous polymer emulsion is used, the self-generated sealing layer also comprises a flexible film formed after the polymer emulsion demulsifies and coalesces.

[0025] Example 1: A large airport runway pavement was being poured. The on-site environmental conditions were: ambient temperature 42°C. The relative humidity is below 15%, and there is persistent strong wind with wind speeds exceeding 10 m / s. Under these conditions, after the large-area concrete mixture has been poured and leveled in step 101, the rate of moisture evaporation from its plastic surface is prone to cause instantaneous plastic cracking. At this time, step 102 is performed to apply a surface catalytic sealant to the plastic surface of the concrete mixture, which is still within the plastic stage time window. This surface catalytic sealant contains colloidal silica as an active silicate component and phenolphthalein as a pH-sensitive indicator, and is applied through... By adding xanthan gum, a shear-thinning thixotropic fluid is prepared. In strong wind environments, droplets from conventional low-pressure atomized spraying are easily blown away and drift, resulting in uneven coverage. In this method, the shear-thinning thixotropic fluid is applied through a high-shear atomizing nozzle. The fluid's viscosity decreases due to the high shear force as it passes through the nozzle, allowing it to be atomized uniformly. After the droplets leave the nozzle, the shear force disappears, and the viscosity immediately recovers, forming larger, wind-drift resistant droplets. These droplets are less affected by wind force, can settle stably, and adhere uniformly to the surface of plastic concrete.

[0026] During application, the pH-sensitive indicator comes into contact with the free alkaline substances abundant in the plastic surface, causing the sprayed pavement area to instantly turn purplish-red. Based on this color boundary, workers identify any uncolored gray areas—those missed in the spraying—and re-spray until the entire target surface appears purplish-red, thus achieving uniform coverage of the sealant. Subsequently, the active silicate component utilizes surface moisture and the visually confirmed free alkaline substances to undergo an in-situ chemical reaction, generating hydrated calcium silicate gel. This reaction continuously consumes alkaline substances, leading to surface... The pH value of the microenvironment of the layer decreases; about 3 to 5 minutes after the application is completed, the purplish-red color of the pavement surface begins to fade gradually, revealing the original color of the concrete. This is the signal that the sealing is complete, indicating that the capillary pores have been sealed by hydrated calcium silicate gel; finally, the concrete pavement enters the natural hardening stage of step 103 without any watering or covering; the mixing water inside has been locked by the self-generated sealing layer generated in situ during the plastic stage, preventing plastic shrinkage cracking caused by the surface-core water loss gradient, and providing internal moisture conditions for the subsequent long-term hydration of the concrete.

[0027] Example 2: This example objectively verifies the inhibitory effect of the preparation method of the present invention on cracking during the plastic stage of concrete under simulated harsh environmental conditions in arid regions, as well as its support capacity for subsequent curing-free hardening. The test was conducted in an environmental control room, where the internal conditions were set as follows: constant temperature 40°C. The relative humidity was 15%, and a continuous unidirectional airflow with a wind speed of 8 m / s was applied to simulate strong wind evaporation conditions. The test materials included: a C30 concrete mixture prepared using P.O42.5 cement, medium sand, 5 mm to 20 mm continuously graded crushed stone, and polycarboxylate superplasticizer, with a water-cement ratio of 0.45; and a surface catalytic sealing agent prepared by mixing and dissolving 15% by mass of colloidal silica aqueous solution with 0.1% by mass of phenolphthalein indicator in water.

[0028] The experiment consisted of four test groups: a control group, an inventive sample group, and two comparative examples (Example 1 and Example 2) for verifying the application timing boundary. Four concrete slabs measuring 1 m × 1 m × 0.15 m were prepared, poured, leveled, and immediately placed in an environmental control room. Visual observation and surface conductivity monitoring determined that surface bleeding of the concrete mixture ended approximately 30 minutes after pouring and leveling, at which point the time window for the plastic stage was reached, and the surface began to show visually identifiable dryness after approximately 75 minutes. The processing of each group of test slabs was as follows: Control group: After step 101, no material was applied, and the slabs were left to harden naturally in the environment. Inventive sample group: Following the method of this invention, the surface was uniformly applied via low-pressure atomization immediately after the surface bleeding ended (T=30 minutes). Catalytic sealing agent was applied until the surface showed uniform color. Comparative Example 1 (applied too early): The surface catalytic sealing agent was applied at 10 minutes during the bleeding stage. Comparative Example 2 (applied too late): The surface catalytic sealing agent was applied after the surface had dried for 90 minutes. During the application process, it was observed that the surface of the sample group of the present invention quickly showed a uniform purplish-red color after contact with the sealing agent, and faded after about 4 minutes, indicating that the sealing reaction occurred effectively. The surface color of Comparative Example 1 was uneven and light, and some areas did not show color due to continuous bleeding. The surface of Comparative Example 2 showed almost no color, indicating that the surface layer lacked the moisture and sufficient free alkaline substances required for the reaction. The plastic cracks were checked after each test plate was exposed for 6 hours, and the cores of each test plate were taken after 28 days to test their compressive strength. The test data are shown in Table 1.

[0029] Table 1: Comparison of Plastic Cracking and Later Strength Test Data Table 1 shows that under simulated drought and strong wind conditions, the control group exhibited severe plastic cracking and insufficient hydration due to early water loss, resulting in the lowest 28-day strength. The sample group of this invention, by applying a surface catalytic sealant within the time window of the plastic stage, did not exhibit plastic cracks. Simultaneously, it achieved self-curing by effectively sealing internal moisture, resulting in the highest 28-day compressive strength, meeting the design requirements of C30 concrete. Comparative Example 1 (applied too early) and Comparative Example 2 (applied too late) failed to effectively suppress cracking, and their later strength was far lower than that of the sample group of this invention. This confirms that applying a surface catalytic sealant within the time window of the plastic stage is a necessary process condition for achieving crack resistance and curing-free operation.

[0030] Example 3: The test environment and initial materials in this example are the same as in Example 2, that is, the environmental control room conditions are 40°C. The relative humidity was 15%, the wind speed was 8 m / s, the concrete mixture was C30, and the water-cement ratio was 0.45. This embodiment sets up three test groups: control group, whose process is the same as in embodiment 2; the present invention sample group, whose process is the same as in embodiment 2, with the surface catalytic sealing agent of embodiment 2 applied within the plastic stage time window of T=30 minutes; and comparative sample group 3. Comparative Example 3, within the same plastic stage time window (T=30 minutes) as the present invention sample group, had its surface catalytic sealant replaced with a known physical film-forming material for later curing, specifically a Type I paraffin-based emulsion curing agent conforming to ASTM C309. During the experiment, the phenomenon observed in the present invention sample group was the same as in Example 2: surface coloring followed by fading, indicating a chemical reaction. In Comparative Example 3, when the paraffin-based emulsion curing agent was applied, the concrete surface was still in a wet plastic state, preventing the emulsion from effectively adhering and coalescing into a film. Under a wind speed of 8 m / s, the emulsion unevenly aggregated and flowed on the surface, forming white spots, failing to form a continuous and effective physical barrier layer. Plastic cracks were examined after each test panel was exposed for 6 hours, and core samples were taken from each panel after 28 days to test their compressive strength. The test data are shown in Table 2.

[0031] Table 2: Comparison of Test Results of Different Surface Treatment Materials Table 2 shows that, compared with the control group, the comparative sample group 3, which was treated with a conventional physical film-forming curing agent within the plastic stage time window, showed no improvement in crack resistance and later strength performance under harsh conditions, and a large number of plastic cracks appeared. This indicates that the design mechanism of conventional curing agents makes it impossible for them to form an effective physical barrier layer on the surface of plastic and wet substrates. The experimental data confirms that the method of the present invention must apply a surface catalytic sealing agent within the plastic stage time window, and utilize its unique sealing mechanism of reacting with the substrate in situ to generate hydrated calcium silicate gel. This is the necessary technical means to effectively block the water loss gradient, inhibit plastic cracking, and achieve self-curing.

[0032] Example 4: This example combines Figures 1 to 3 This paper describes a crack-resistant and durable concrete suitable for arid regions and its preparation method. Figure 1 As shown, the process starts from the beginning and proceeds to step 101: preparation, pouring, and leveling of the concrete mixture. After preparation, pouring, and surface leveling are completed, a judgment node is reached, namely, the plastic stage time window is determined. This judgment monitors the bleeding status. If it is negative, the monitoring continues cyclically. If it is positive, that is, surface bleeding has ended or is about to end, then proceed to the next step. This judgment node can be supported by a key control module such as Claim4. This module monitors the surface conductivity or surface resistance of the plastic surface in situ and calculates its rate of change over time. When the absolute value of the rate of change falls from the peak and stabilizes in the preset low value range, the objective judgment window is reached. After the window is reached, step 102 is executed: application of a surface catalytic sealant, that is, application of a sealant containing... The solution of active silicate component and pH-sensitive indicator can be synergistically formulated with a performance enhancement module such as Claim5. A water-based polymer emulsion is co-formulated in the sealant. During the gelation reaction, the emulsion demulsifies and aggregates, forming an organic-inorganic hybrid sealing layer in situ on the plastic surface to accommodate subsequent thermal expansion and contraction deformation. After application, the process proceeds to the second judgment node. Judgment: If a sealing completion signal is detected, if not, the reaction is in progress and color is developed, then return to step 102. If yes, the indicator fades, indicating that sealing is complete, and proceed to step 103: natural hardening. Natural hardening occurs under conditions without external wet curing, achieving self-curing and ultimately obtaining crack-resistant and durable concrete with a self-generated sealing layer on its surface.

[0033] like Figure 2 As shown in the figure, the electrical flux (C) is used as the vertical axis to compare the performance changes of pure inorganic blocking layers and hybrid blocking layers before and after temperature cycling. The figure shows that for pure inorganic blocking layers, the electrical flux is low before cycling, but increases after cycling. In contrast, the electrical flux of the hybrid blocking layer sample group before cycling is close to that of the pure inorganic blocking layer, but the increase in electrical flux after cycling is much smaller than that of the pure inorganic blocking layer, indicating that the hybrid blocking layer still maintains good integrity after temperature cycling.

[0034] like Figure 3 As shown, when the compound sealant is applied to the concrete surface, its active silicate component initiates an inorganic reaction pathway: it contacts surface moisture and free alkali and obtains reaction conditions from the concrete surface to generate hydrated calcium silicate gel and form a rigid gel skeleton. At the same time, its aqueous polymer emulsion initiates an organic reaction pathway: it is affected by moisture evaporation and chemical demulsification, undergoes demulsification and aggregation, and forms a flexible film. Finally, the flexible film fills the spaces between the gel skeletons, together forming an organic-inorganic hybrid sealing layer. This sealing layer can adapt to the thermal expansion and contraction caused by diurnal temperature differences, as indicated by the arrow pointing from the concrete surface in the figure, and feeds back information about its combination of rigid sealing and flexible deformation capabilities to the construction personnel.

[0035] Example 5: This example is used to calibrate the suitable concentration range of the active silicate component in the surface catalytic sealant and to verify the effect of the synergistic compounded waterborne polymer emulsion corresponding to the scheme of claim 5 under extreme temperature cycling conditions; the test scenario simulates the construction and service conditions of bridge decks in arid regions; the first stage of the test (concentration calibration): using the same C30 concrete mixture and environmental control room conditions as in Example 2, 40 15%RH, 8 m / s wind speed; five groups of test plates were prepared, numbered A-1 to A-5, and a surface catalytic sealing agent was applied to all of them within the plastic stage time window of T=30 minutes; the sealing agent was the same except for the mass fraction of colloidal silica, which was different in active silicate component. All other components were the same, did not contain polymer emulsion, and contained 0.1% phenolphthalein; the concentration settings and test results of each group are shown in Table 3.

[0036] Table 3: Effect of Concentration of Active Silicate Component (Colloidal Silica) Table 3 shows that when the concentration of colloidal silica is 5% (Group A-1), the generated CSH gel is insufficient to completely seal the capillary pores, resulting in poor crack resistance and water retention. When the concentration is increased to 10% (Group A-2), the crack resistance and water retention properties improve. At concentrations of 15% and 20% (Groups A-3 and A-4), the sealing effect is good. Further increasing the concentration to 25% (Group A-5) does not significantly improve performance, and slight white silicate residue appears on the surface. Considering both sealing performance and material application, the suitable concentration range for the active silicate component can be determined to be 1%. 0% to 20%; Second stage of the test to verify the synergistic effect: To verify the weather resistance of the organic-inorganic hybrid sealing layer, two additional test plates were set up; Group B-1 pure inorganic sealing layer: using 15% concentration colloidal silica sealant (without emulsion); Group B-2 hybrid sealing layer sample group: using a synergistically compounded sealant, its composition being 15% colloidal silica and 5% styrene-acrylate emulsion with a solid content of 45%; Both groups were applied at T=30 minutes and, after 28 days of standard curing, were placed in a high and low temperature alternating test chamber for 100 temperature cycle tests +60. to -20 Each cycle lasted 4 hours. Before and after the temperature cycling test, the chloride ion penetration resistance (electric flux method) of the two groups of test plates was tested according to GB / T50082-2009 standard. The results are shown in Table 4.

[0037] Table 4: Effects of Extreme Temperature Cycling on the Impermeability of Different Blocking Layers Table 4 shows that both groups had low electrical flux (low permeability) before the first cycle, indicating that they had formed an effective sealing layer. However, after 100 temperature cycles, the electrical flux of group B-1 (pure inorganic layer) increased by 103.2%, indicating that its brittle CSH gel layer developed microcracks due to the mismatch between thermal deformation and the matrix, leading to sealing failure. Group B-2 (hybrid layer sample group) formed a flexible film between the gel skeleton due to the compounded aqueous polymer emulsion, which enabled its sealing layer to resist thermal expansion and contraction deformation. Its electrical flux increased by only 18.5%, maintaining the physical integrity and durability of the sealing layer.

[0038] Example 6: This example is used to verify the application effect of the two-liquid time-sequential activating scheme of the present invention on a specific substrate, namely a low-activity substrate with insufficient early free alkaline substance concentration; the test environment is the same as in Example 240. The test was conducted under conditions of 15% RH and a wind speed of 8 m / s. The test substrate was a C30 concrete mix with a high mineral admixture content and a water-cement ratio of 0.45. The cementitious material consisted of 50% (mass fraction) P.O42.5 cement and 50% S95 grade ground blast furnace slag. This mix proportion resulted in a lower surface free alkali concentration than ordinary cement concrete at the plastic stage (T=30 minutes). Three test groups were set up: control group 4 (no material applied); comparative sample group 4 (using a single-liquid scheme), which applied 15% colloidal silica + 0.1% phenolphthalein as the surface catalytic sealant of Example 2 within the plastic stage time window of T=30 minutes; and sample group 5 of this invention (using a two-liquid scheme), which strictly followed the steps of claim 9, applying an alkaline accelerator by atomization at T=30 minutes. A 1% (w / w) lithium hydroxide aqueous solution was applied, followed by the atomization of the surface catalytic sealing agent of Example 2 after a 30-second interval. During the application process, it was observed that on the surface of Comparative Sample Group 4 (single-liquid scheme), the phenolphthalein indicator only showed an uneven, light red color, which did not fade after 15 minutes, indicating that the in-situ chemical reaction rate was slow due to insufficient substrate alkalinity and could not be effectively initiated. In Sample Group 5 of the present invention (two-liquid scheme), when the surface catalytic sealing agent was applied after the alkaline accelerator, the phenolphthalein immediately showed a uniform, deep purple-red color, which faded rapidly after about 4 minutes, indicating that the introduction of the alkaline accelerator forcibly and immediately triggered the gel sealing reaction. The plastic cracks were checked after each test plate was exposed for 6 hours, and the compressive strength was tested after 28 days. The test data are shown in Table 5.

[0039] Table 5: Validation of the effectiveness of the two-liquid sequential activation scheme on low-activity substrates Table 5 shows that when facing low-activity substrates, the conventional single-liquid application method (comparative sample group 4) has poor crack resistance and strength retention due to the lack of sufficient reaction driving force (free alkali), and the improvement is limited compared with control group 4. The present invention sample group 5, by adopting a two-liquid sequential activating scheme, that is, applying an alkaline activator first and then applying a surface catalytic sealant, effectively solves the problem of insufficient reaction rate of low-activity substrates, almost completely suppresses plastic cracks, and improves its 28-day strength due to effective self-curing. This confirms the necessity of this scheme for expanding the applicability of the method of the present invention and ensuring its effectiveness on low-activity substrates.

[0040] Example 7: This example illustrates a standardized engineering procedure for objectively calibrating the time window of the plastic stage, eliminating the black box of the preset low-value range. The test subject is the C30 concrete mixture from Example 2, and the environmental conditions are the same as 40°C. The test conditions were: 15%RH, wind speed 8 m / s; the test equipment was a portable four-probe surface resistivity meter with a measurement range of 1 kΩ·m to 1000 kΩ·m and a measurement accuracy of 1%, used for in-situ monitoring of surface resistivity. The calibration procedure was as follows: immediately after the concrete was poured and leveled (T=0), continuous monitoring of the plastic concrete surface was started, and a surface resistivity data point was recorded every 1 minute. And calculate the rate of change of surface resistivity over time in real time. (in =1 minute); Under these experimental conditions, the following electrical response characteristic curves were observed and recorded: From T=0 to T=28 minutes (the bleeding stage), a continuous conductive water film existed on the surface, and the surface resistivity was... It remained at a low level of 1.5 kΩ·m to 2.0 kΩ·m, with its rate of change The surface resistivity approaches 0; during the water film rupture phase from T=29 minutes to T=32 minutes, surface bleeding ends, the continuous water film rapidly disappears and transforms into discontinuous capillary water, drastically reducing the conductive path and leading to a decrease in surface resistivity. It rapidly jumps from 2.1 kΩ·m to 14.8 kΩ·m; during this period, the rate of change The absolute value shows a sharp peak, reaching 12.7 kΩ·m / min; during the plastic evaporation stage from T=33 min to T=70 min, the resistivity... It continued to rise slowly from 15.5 kΩ·m to 38.0 kΩ·m, but its rate of increase had decreased, and the rate of change... The absolute value of the value drops from its peak and stabilizes in a lower plateau region. This plateau region is the preset low-value range, which, after calibration, is [value missing]. <0.8kΩ·m / min; during the surface drying stage after T=70 minutes, the surface moisture is gradually depleted, and the resistivity decreases. The rapid increase resumed; through the above calibration tests, the objective triggering condition for the time window of the plastic stage under this specific mix ratio and environmental conditions was determined to be: when the rate of change was monitored. After experiencing a peak value greater than 5 kΩ·m / min, the absolute value of the signal first falls back and stabilizes at a certain level. When the value is in the low range of <0.8kΩ·m / min, the judgment window is reached. To verify the effectiveness of the procedure, a surface catalytic sealant was applied according to the process of Example 2 at T=33 minutes, which is when the low range is just entered. The anti-crack effect (0 cracks) is consistent with the result of empirical judgment in Example 2, thus confirming the reproducibility and reliability of the conductivity monitoring method.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing crack-resistant and durable concrete suitable for arid regions, characterized in that, The method includes: Step 101: Prepare the concrete mixture, and pour and level the surface of the concrete mixture; Step 102: After surface leveling is completed and within the time window when the concrete mixture is still in the plastic stage, a surface catalytic sealant is applied to the plastic surface of the concrete mixture. The time window of the plastic stage is defined as: the stage where surface bleeding of the concrete mixture has ended or is about to end, but surface water to be evaporated and free alkaline substances released by the early stage of cement hydration still exist in its surface capillary pores. The surface catalytic sealant is an aqueous solution containing an active silicate component and a pH-sensitive indicator. When the active silicate component comes into contact with surface water and free alkaline substances, an in-situ chemical reaction occurs to generate hydrated calcium silicate gel. The hydrated calcium silicate gel precipitates in the capillary pores of the plastic surface and seals the capillary pores. The pH-sensitive indicator shows color when the surface catalytic sealant comes into contact with free alkaline substances, and fades after the free alkaline substances are consumed by the in-situ chemical reaction of the active silicate component, resulting in a decrease in pH value. Fading is defined as a signal that the sealing is complete. Step 103: After the sealing completion signal is detected in step 102, the concrete is allowed to harden naturally without external wet curing.

2. The method for preparing crack-resistant and durable concrete suitable for arid regions according to claim 1, characterized in that, The active silicate component is selected from at least one of colloidal silica, lithium silicate, sodium silicate, and potassium silicate.

3. The method for preparing crack-resistant and durable concrete suitable for arid regions according to claim 1, characterized in that, pH-sensitive indicators are selected from at least one of phenolphthalein and thymolphthalein.

4. The method for preparing crack-resistant and durable concrete suitable for arid regions according to claim 1, characterized in that, Between steps 101 and 102, the method further includes: step 401, performing in-situ monitoring of the surface conductivity or surface resistance of the plastic surface of the concrete mixture, and calculating the rate of change of the surface conductivity or surface resistance over time; step 402, when the absolute value of the rate of change is detected to fall from a peak and stabilize in a preset low value range, determining that the time window of the plastic stage has been reached, and triggering the execution of step 102.

5. The method for preparing crack-resistant and durable concrete suitable for arid regions according to claim 1, characterized in that, In step 102, the surface catalytic sealing agent, in addition to containing active silicate components and pH-sensitive indicators, also contains a water-based polymer emulsion. While the active silicate components undergo an in-situ chemical reaction to generate hydrated calcium silicate gel, the water-based polymer emulsion undergoes demulsification and aggregation on the plastic concrete surface, forming a flexible film between the skeletons of the hydrated calcium silicate gel, thus forming an organic-inorganic hybrid sealing layer in situ on the plastic surface.

6. The method for preparing crack-resistant and durable concrete suitable for arid regions according to claim 5, characterized in that, The aqueous polymer emulsion is selected from at least one of styrene-acrylate emulsion, styrene-acrylic emulsion, and silicone-acrylic emulsion.

7. The method for preparing crack-resistant and durable concrete suitable for arid regions according to claim 1, characterized in that, In step 102, the surface catalytic sealant is pre-formulated as a shear-thinning thixotropic fluid; and the application of the surface catalytic sealant is performed through a high-shear atomizing nozzle; the shear-thinning thixotropic fluid undergoes viscosity reduction due to high shear force when passing through the high-shear atomizing nozzle to achieve atomization, and recovers viscosity due to the disappearance of shear force after leaving the high-shear atomizing nozzle, forming wind-drift resistant droplets; the apparent viscosity of the shear-thinning thixotropic fluid is... With shear rate In 25 The test temperature satisfies The relationship, among which Where is the consistency coefficient, and n is the fluid property index. .

8. The method for preparing crack-resistant and durable concrete suitable for arid regions according to claim 7, characterized in that, Shear-thinning thixotropic fluids are prepared by adding a thixotropic agent to a surface catalytic blocking agent, the thixotropic agent being selected from at least one of xanthan gum, alginate and modified cellulose.

9. The method for preparing crack-resistant and durable concrete suitable for arid regions according to claim 1, characterized in that, Step 102 specifically includes: Step 901, applying an alkaline accelerator to the plastic surface of the concrete mixture by atomization, wherein the alkaline accelerator is an aqueous solution containing at least one of lithium hydroxide and potassium hydroxide; Step 902, immediately after Step 901 is completed and within the time interval during which the alkaline accelerator is absorbed but not dried, applying a surface catalytic sealant by atomization to the plastic surface to which the alkaline accelerator has been applied; wherein the active silicate component in the surface catalytic sealant undergoes an in-situ chemical reaction with the alkaline accelerator and the free alkaline substances in the concrete mixture; and in Step 101, in the step of preparing the concrete mixture, polypropylene microfibers or basalt fibers are further incorporated.

10. A crack-resistant and durable concrete suitable for arid regions, characterized in that, It is a product directly obtained from the method for preparing crack-resistant and durable concrete suitable for arid regions as described in claim 1, and the product comprises: A concrete substrate; A self-generated sealing layer formed on the surface of a concrete matrix; the self-generated sealing layer comprises: hydrated calcium silicate gel precipitated and sealing the capillary pores of the concrete matrix surface by in-situ chemical reaction in the method, and residues of a pH-sensitive indicator applied in the method.

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