Yangtze estuary high-pile wharf surface layer crack control method

Abstract

The application relates to the technical field of port engineering construction, and discloses a Yangtze estuary high-pile wharf surface layer crack control method, which comprises the following steps: preparing a mixture: selecting medium-heat or low-heat portland cement to reduce hydration heat, and adding steel fibers to improve the toughness and tensile performance of the concrete; pouring and processing: implementing temperature control measures such as aggregate pre-cooling, mixing water with ice or night construction to reduce the mold temperature, carrying out secondary vibrating before the initial setting of the concrete to improve the compactness, and then carrying out at least twice surface finishing operations on the surface to repair plastic microcracks; curing: adopting a composite covering layer composed of geotextile and plastic film and the like to implement heat and moisture preservation curing on the concrete surface. The application systematically combines material optimization, process precision control and long-term curing, and inhibits hydration heat temperature difference and volume shrinkage in the whole process from the source to the terminal, so that the cracking risk of the wharf surface layer can be reduced, and the safety and durability of the structure can be improved.

Description

Technical Field

[0001] This invention relates to the field of port engineering construction technology, specifically a method for controlling cracks in the surface layer of a high-pile wharf in the Yangtze River Estuary. Background Technology

[0002] High-pile wharves are important port infrastructure in deep-water navigation areas such as the Yangtze River Estuary. The surface layer of these wharves, as a key structure directly bearing loads and environmental erosion, is of paramount importance in terms of durability. However, cracking of the concrete surface layer has been a long-standing engineering challenge. The Yangtze River Estuary region experiences large temperature differences and high humidity throughout the year, providing extremely unfavorable external conditions for the formation of concrete cracks.

[0003] In current construction practices, ordinary Portland cement is used to prepare concrete. This type of cement releases a large amount of heat during hydration. For large-volume, large-area surface structures like high-pile wharves, the huge accumulation of hydration heat will cause the internal temperature of the concrete to rise sharply, while the surface will dissipate heat more quickly due to contact with the environment. The resulting huge internal and external temperature gradient will generate strong tensile stress. When this stress exceeds the early tensile strength of the concrete, it will trigger penetrating temperature cracks.

[0004] Meanwhile, traditional concrete is inherently a brittle material with tensile strength far lower than compressive strength and is highly sensitive to volumetric deformation. During the evaporation of moisture, concrete inevitably undergoes drying shrinkage, which also induces internal tensile stress. Conventional concrete mix design, in pursuit of ease of construction, uses a higher water content, increasing the potential for later drying shrinkage. Furthermore, due to the lack of a microscopic toughening mechanism in the material itself, it is highly susceptible to crack initiation under shrinkage stress, which then propagates rapidly.

[0005] Furthermore, conventional construction techniques and curing methods also have shortcomings. The one-time vibration and finishing operations during construction are insufficient to completely eliminate micro-cracks and internal voids caused by bleeding and aggregate settlement in concrete before initial setting. During the curing stage, short-term water spraying with a single layer of covering cannot provide a stable temperature and humidity environment for the concrete, leading to premature and rapid moisture loss from the concrete surface. This also makes the concrete highly susceptible to surface plastic shrinkage cracking and drying shrinkage cracks due to direct fluctuations in ambient temperature, affecting the integrity and durability of the wharf surface layer. Therefore, this invention proposes a method for controlling cracks in the surface layer of high-pile wharves in the Yangtze River Estuary to address the deficiencies of existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for controlling surface cracks in high-pile wharves in the Yangtze River Estuary. This method solves the problem that existing technologies lack a systematic control mechanism covering the entire process from materials and processes to maintenance, which leads to the easy generation of temperature cracks and shrinkage cracks in concrete due to the combined effects of multiple factors such as hydration heat temperature difference, drying shrinkage, and plastic shrinkage, thus affecting the long-term safety and durability of the wharf structure.

[0007] To achieve the above objectives, the present invention provides a method for controlling cracks in the surface layer of a high-pile wharf in the Yangtze River Estuary, comprising the following steps: Step S1: Prepare concrete mixture: Mix medium-heat silicate cement or low-heat silicate cement, steel fibers, aggregates and water to prepare concrete mixture; Step S2, Pouring and Treatment: Implement temperature control measures before and during concrete pouring; after the concrete is poured and before it initially sets, perform secondary vibration on the poured concrete; after secondary vibration, perform at least two finishing operations on the concrete surface. Step S3, Curing: After the finishing work is completed, a composite covering layer consisting of at least two different materials is used to keep the concrete surface warm and moist.

[0008] By adopting the above technical solutions, this invention establishes a comprehensive crack control system from source to maintenance. Firstly, in the material preparation step, medium-heat or low-heat silicate cement is selected, which has a lower hydration heat release rate and total heat release, reducing the peak hydration heat inside the concrete and decreasing the temperature difference between the inside and outside of the concrete structure. This reduces thermal stress caused by temperature gradients and inhibits the formation of temperature cracks. Simultaneously, steel fibers are incorporated into the mixture. These randomly distributed fibers form a three-dimensional support network in the concrete matrix. When microcracks occur in the concrete due to shrinkage or tension, the steel fibers can act as a bridging agent, inhibiting crack formation. The method expands and distributes stress, improving the toughness and tensile properties of the concrete. Secondly, during the pouring and finishing stages, a series of technological measures, including temperature control, secondary vibration, and multiple finishing processes, further reduced the concrete's temperature upon placement, increased its density, and promptly repaired micro-cracks that appeared during the plastic stage. Finally, in the curing stage, a composite covering layer was used for heat and moisture insulation, which slowed the rate of heat loss from the concrete surface to the environment and effectively prevented premature moisture evaporation, maintaining a stable temperature and humidity field. This created conditions for full cement hydration, thereby reducing temperature shrinkage and drying shrinkage. This method combines material optimization with process control, working synergistically to solve the cracking problem of the wharf surface concrete.

[0009] Preferably, the concrete mixture prepared in step S1 is made from raw materials containing the following components per cubic meter: 255 kg-265 kg of medium-heat silicate cement or low-heat silicate cement; 740 kg-760 kg of fine aggregate; 1145 kg-1155 kg of coarse aggregate; and 62.8 kg-94.2 kg of steel fiber. Furthermore, the mass ratio of water to medium-heat silicate cement or low-heat silicate cement is 0.42-0.45. By adopting the above technical solution, with a lower cement content, precise control of the water-to-cement mass ratio, and optimization of aggregate gradation, the density of the concrete matrix is ​​ensured, the total amount of evaporable moisture and the porosity of the hardened cement paste are reduced, thereby lowering the long-term drying shrinkage potential of the concrete and enhancing its crack resistance.

[0010] Preferably, the slump of the concrete mixture prepared in step S1 is 100 mm-120 mm. By adopting the above technical solution, the concrete mixture is ensured to have good workability and pumpability, meeting the needs of large-area continuous pouring on site, while avoiding material segregation and bleeding caused by excessive fluidity, thus ensuring the uniformity and overall quality of the hardened concrete.

[0011] Preferably, the mixing process in step S1 further includes adding a polycarboxylate-based high-performance water-reducing agent, wherein the amount of the polycarboxylate-based high-performance water-reducing agent is 1.0%-1.1% of the mass of medium-heat silicate cement or low-heat silicate cement. By adopting the above technical solution, the introduction of the polycarboxylate-based high-performance water-reducing agent enables the ideal flowability of the mixture to be obtained while maintaining a low water-to-cement mass ratio. The water-reducing agent improves the workability of the mixture by dispersing cement particles and releasing the encapsulated moisture. This is a key technical means to achieve low shrinkage and high workability.

[0012] Preferably, in step S2, the temperature control measures implemented include at least one of the following: shading and spraying water to pre-cool the sand and stone aggregates used to prepare the concrete mixture; adding ice to the mixing water used to prepare the concrete mixture; and selecting a low-temperature period at night for concrete pouring. By adopting the above technical solutions, these measures can reduce the temperature of the concrete mixture upon placement, further reduce the absolute value of the hydration heat temperature rise, significantly reduce the maximum internal temperature of the concrete, thereby more effectively controlling the internal and external temperature difference and reducing thermal stress.

[0013] Preferably, before pouring concrete in step S2, the following steps are also included: tying the surface steel mesh according to the design drawings, and ensuring the thickness of the protective layer of the surface steel mesh by setting steel reinforcement supports. By adopting the above technical solution, controlling the position of the steel mesh and the thickness of the protective layer ensures that the steel reinforcement is in the correct design position in the hardened concrete, giving full play to the role of steel reinforcement in restraining shrinkage and controlling crack width, while avoiding structural durability problems caused by mesh sinking or an excessively thin protective layer.

[0014] Preferably, in step S2, the secondary vibration is performed using an immersion vibrator, with a vibration spacing of 45-50 cm. By adopting the above technical solution, secondary vibration before the initial setting of concrete can drain the voids and moisture formed under the coarse aggregate and horizontal reinforcing bars due to bleeding and aggregate settlement, repair plastic settlement cracks, make the concrete structure denser and more homogeneous, and improve the impermeability and strength of the concrete.

[0015] Preferably, in step S2, the finishing operation specifically includes: performing the first finishing operation within 1-2 hours after the concrete pouring is completed; and performing the second finishing operation 2-3 hours after the first finishing operation. By adopting the above technical solution, multiple finishing operations at different times can gradually eliminate micro-cracks on the surface caused by bleeding and plastic shrinkage, according to the setting and hardening process of the concrete. The first finishing operation mainly serves to smooth and raise the slurry, while the second finishing operation further compacts the surface after the concrete has reached a certain strength, closes the capillary channels, and forms a dense surface layer, improving the surface's crack resistance and wear resistance.

[0016] Preferably, in step S3, the composite covering layer is constructed by sequentially covering geotextile, plastic film, and another layer of geotextile from bottom to top. By adopting the above technical solution, this three-layer composite structure has the dual functions of heat preservation and moisture retention. The bottom layer of moist geotextile provides a continuously moist environment for the concrete surface; the middle plastic film is the main vapor barrier layer, which can prevent moisture evaporation to the maximum extent; and the top layer of geotextile plays the role of heat preservation and protection of the film, mitigating surface temperature fluctuations.

[0017] Preferably, in step S3, the duration of heat preservation and moisture retention curing is no less than 21 days. By adopting the above technical solution, a sufficiently long curing period ensures that the cement can undergo a full hydration reaction, allowing the strength and various properties of the concrete to develop steadily, the pore structure to become increasingly refined, and the tensile strength and resistance to shrinkage deformation of the concrete itself to be improved, which is crucial for controlling later cracks.

[0018] This invention provides a method for controlling cracks in the surface layer of a high-pile wharf in the Yangtze River Estuary. It has the following beneficial effects: 1. This invention achieves control over the internal temperature of concrete by selecting medium-heat or low-heat silicate cement at the source of materials and combining it with temperature control measures such as pre-cooling aggregates, adding ice to mixing water, or selecting low-temperature periods at night for pouring. This reduces the total heat release and peak value of cement hydration reaction, while also lowering the concrete's placement temperature and reducing the temperature gradient between the core and surface of the concrete structure, thereby suppressing temperature cracks caused by severe temperature difference shrinkage.

[0019] 2. This invention improves the crack resistance and volume stability of concrete materials by incorporating three-dimensionally randomly distributed steel fibers into the concrete mixture and adopting a low water-cement ratio mix design. The steel fibers act as a micro-skeleton and bridging agent in the matrix, which can inhibit the propagation of micro-cracks. The low water-cement ratio reduces the capillary porosity and total evaporable moisture of the hardened cement paste, thereby reducing the drying shrinkage potential of the concrete. The combination of these two factors gives the hardened concrete higher toughness and resistance to shrinkage deformation.

[0020] 3. This invention ensures the quality of concrete during its fragile plastic and early hardening stages by introducing refined measures such as secondary vibration, multiple finishing processes, and long-term composite curing layers into the construction process. Secondary vibration and multiple finishing processes can promptly repair early micro-cracks caused by bleeding settlement and plastic shrinkage, improving structural density. The composite curing layer, composed of geotextile and plastic film, provides a stable heat-insulating and moisture-retaining environment for concrete for more than 21 days, ensuring full hydration of cement and transforming the excellent performance potential of the material into the final engineering quality. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below through Examples 1-3. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Examples 1-3: Example 1: This example provides a method for controlling cracks in the surface layer of a high-pile wharf in the Yangtze River Estuary, including the following steps: Preparation of concrete mixture: Weigh 260 kg of medium-heat silicate cement, 750 kg of fine aggregate, 1150 kg of coarse aggregate, 62.8 kg of steel fiber (volume admixture of 0.8%), 117 kg of water (water-cement ratio of 0.45), and 1.0% of polycarboxylate-based high-performance water-reducing agent by mass of cement per cubic meter. Put the above raw materials into a mixer and mix them evenly to obtain a concrete mixture with a slump of 110 mm.

[0023] Preparations before construction: Shade the sand and stone aggregate stockpile and spray water for pre-cooling to ensure that the aggregate temperature does not exceed 50℃. Tie the surface steel mesh according to the design drawings and ensure the thickness of the steel protective layer is accurate by setting steel supports (stirrups) to prevent the mesh from sinking.

[0024] Concrete pouring and vibration: The prepared concrete mixture is pumped and continuously poured during the low-temperature period at night. The pouring is carried out using the inclined layering method, with the natural flow slope controlled at 1:8. An immersion vibrator is used for vibration, with quick insertion and slow withdrawal during operation. The vibration interval is 50cm, and the vibrator is inserted 5cm deep into the lower layer of concrete. A second vibration is performed before the concrete initially sets.

[0025] Surface treatment: One hour after the concrete is poured, first use a long scraper to level it according to the elevation, then roll it twice with an iron roller, and then grind it flat with a wooden wedge. Two hours after the first finishing, carry out the second finishing operation to ensure that the concrete surface is flat and dense.

[0026] Curing: Immediately after the surface treatment process is completed, cover the concrete surface with a layer of geotextile, then cover it with a layer of plastic film, and finally cover it with another layer of geotextile for heat preservation and moisture retention. The curing process lasts for 21 days. During this period, keep the geotextile moist and prohibit heavy vehicles from driving on the surface.

[0027] Example 2: This embodiment provides a method for controlling surface cracks at a high-pile wharf in the Yangtze River Estuary, including the following steps: Preparation of concrete mixture: Weigh out 255 kg of low-heat silicate cement, 760 kg of fine aggregate, 1155 kg of coarse aggregate, 78.5 kg of steel fiber (volume admixture of 1.0%), and 1.0% of polycarboxylate-based high-performance water-reducing agent by mass of cement per cubic meter. Add ice to the mixing water to control the water temperature. Finally, weigh out 109.7 kg of water (water-cement ratio of 0.43). Put the above raw materials into the mixer and mix them evenly to obtain a concrete mixture with a slump of 100 mm.

[0028] Preparations before construction: Shade the sand and stone aggregate stockpile and spray water for pre-cooling. Tie the surface steel mesh according to the design drawings and ensure the thickness of the steel protective layer by setting up steel supports.

[0029] Concrete pouring and vibration: The prepared concrete mixture is continuously poured during the low-temperature period at night. The pouring adopts the sloping layer method with a natural flow slope of 1:10. An immersion vibrator is used for vibration, with a vibration time of 25 seconds per point and a vibration spacing of 45cm. The vibrator is inserted 5cm deep into the lower layer of concrete. A second vibration is performed before the concrete initially sets.

[0030] Surface treatment: 1.5 hours after the concrete is poured, use a long scraper to level it, then roll it three times with an iron roller, and then grind it flat with a wooden roller. 2.5 hours after the first finishing, carry out the second finishing operation.

[0031] Curing: Immediately after the surface treatment process is completed, cover the concrete surface with geotextile, plastic film and geotextile in sequence for curing. The curing process lasts for 28 days. During this period, keep the covering layer moist. Heavy vehicles are prohibited from driving on the surface layer for 14 days before the curing period.

[0032] Example 3: This embodiment provides a method for controlling surface cracks at a high-pile wharf in the Yangtze River Estuary, including the following steps: Preparation of concrete mixture: Weigh 265 kg of medium-heat silicate cement, 740 kg of fine aggregate, 1145 kg of coarse aggregate, 94.2 kg of steel fiber (volume admixture of 1.2%), 111.3 kg of water (water-cement ratio of 0.42), and 1.1% of polycarboxylate-based high-performance water-reducing agent by mass of cement per cubic meter. Put the above raw materials into a mixer and mix them evenly to obtain a concrete mixture with a slump of 120 mm.

[0033] Pre-construction preparations: Shade the sand and stone aggregate stockpile and spray water for pre-cooling. Tie the surface steel mesh according to the design drawings, and ensure the thickness of the steel protective layer by setting up steel supports. In the area around the reserved holes, increase the density of the steel reinforcement.

[0034] Concrete pouring and vibration: The prepared concrete mixture is continuously poured during the low-temperature period at night. The pouring adopts the sloping layer method with a natural flow slope of 1:6. An immersion vibrator is used for vibration. Vibration is performed until no more air bubbles appear on the concrete surface and mortar rises. A second vibration is performed before the concrete initially sets.

[0035] Surface treatment: Two hours after the concrete is poured, use a long scraper to level it, then roll it three times with an iron roller, and then grind it flat with a wooden wedge. Three hours after the first finishing, perform the second finishing operation. If there are still small cracks on the surface, perform the third finishing operation.

[0036] Curing: After the surface treatment process is completed, immediately cover the concrete surface with geotextile, plastic film and geotextile in sequence. According to the on-site temperature monitoring, add another layer of geotextile on the top layer to enhance the heat preservation effect. The curing process lasts for 28 days. During this period, keep the covering layer moist. Heavy vehicles are prohibited from driving on the surface layer for 14 days before the curing period.

[0037] Comparative Examples 1-7: Comparative Example 1: Compared with Example 1, the difference is that: conventional high-strength concrete formula and conventional construction process are used, the composition is 380kg of ordinary Portland cement and 171kg of water per cubic meter, without the addition of steel fiber; construction is carried out at normal daytime temperature, without pre-cooling of aggregates, using a single vibration process, and the surface is smoothed once. It is covered with a single layer of straw bags and watered for 7 days for curing, and the rest are the same.

[0038] Comparative Example 2: Compared with Example 1, the difference is that the medium-heat silicate cement in the components is replaced with an equal amount of ordinary silicate cement, while the rest are the same.

[0039] Comparative Example 3: Compared with Example 1, the difference is that steel fibers are not added to the components, and they are replaced with equal volumes of fine and coarse aggregates, while the rest are the same.

[0040] Comparative Example 4: Compared with Example 1, the difference is that a single layer of moist geotextile is used for curing, and the curing time is 7 days, while the rest are the same.

[0041] For example 5: Compared with Example 1, the difference is that the construction is carried out during the high-temperature period of the day and no pre-cooling treatment is performed on the aggregate and mixing water, otherwise they are the same.

[0042] Comparative Example 6: Compared with Example 1, the difference is that the concrete vibration is performed only once, and the surface treatment is performed only once; all other aspects are the same.

[0043] Comparative Example 7: Compared with Example 1, the difference is that: no steel reinforcement was used to strengthen the steel mesh before construction, and only conventional binding was used for fixation, while the rest are the same.

[0044] Test Examples 1-6: Test Example 1: Performance Test To verify the construction performance of the concrete mixtures in the embodiments and comparative examples of the present invention, the slump of each component was measured in accordance with GB / T:50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures".

[0045] The experimental steps are as follows: Wet the slump cone and the inner wall of the base plate, and place the base plate horizontally on a solid ground. Place the slump cone in the center of the base plate. The operator steps on the foot pedals on both sides to fix the position of the base plate. The prepared concrete mixture is evenly filled into the cone in three layers, with the height of each layer being about one-third of the cone height. After each layer is filled, use a tamping rod with a diameter of 16mm, a length of 600mm, and a hemispherical end to tamp the mixture evenly from the outside to the center along a spiral line 25 times. When tamping the bottom layer, the tamping rod should penetrate the entire depth. When tamping the second and top layers, the tamping rod should be inserted to the surface of the next layer. After the top layer is filled and tamped, scrape off the excess concrete mixture and smooth the cone opening. Then, lift the slump cone vertically and steadily within 3 to 7 seconds. After the concrete mixture stops slumping, measure the height difference between the cone height and the highest point of the slumped concrete specimen. This difference is the slump value.

[0046] Experimental data: Table 1. Slump test data of concrete mixtures for each component Test data shows that the concrete mixtures prepared in Examples 1, 2, and 3 all have slump values ​​within the target range of 100mm-120mm. This result confirms that the present invention, through the technical combination of selecting low-heat cement, optimized graded aggregates, incorporating steel fibers, and matching with polycarboxylate-based high-performance water-reducing agents, can achieve good workability of the mixture at a relatively low water-cement ratio. The mixture possesses sufficient fluidity and pumpability to meet the needs of modern large-volume casting, while avoiding material segregation and bleeding problems that may be caused by excessive slump. Comparative Example 1, due to its higher cement and water content, has excessively high slump, which may lead to quality problems. Comparative Example 3, due to the absence of steel fibers, has reduced cohesiveness and a relatively high slump. The other comparative examples, with similar mixture components to Example 1, also exhibit similar initial workability. In summary, the formulation design of the present invention, while ensuring the effective introduction of crack-resistant components, can stably obtain the workability of the mixture that meets construction requirements, verifying the technological feasibility of this solution in engineering applications.

[0047] Test Example 2: Setting Time Test To determine the time characteristics of the concrete mixtures in the embodiments and comparative examples of the present invention during the setting process, the setting time of each component was measured in accordance with the provisions of the penetration resistance method in GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures".

[0048] The experimental steps are as follows: The prepared concrete mixture was wet-sieved through a 4.75mm standard sieve to obtain mortar samples for testing. The mortar was then placed in two layers into a special mold, each layer approximately 100mm thick. After tamping with a tamping rod, the surface was leveled. The filled mold was placed in an environment with a temperature of (20±2)℃. Timing began when the cement came into contact with water. The penetration resistance of the mortar was periodically measured using a penetration resistance meter. During the test, the tip of the probe was brought into contact with the mortar surface, and a uniform load was applied within 10 seconds, allowing the probe to penetrate 25mm into the mortar. The penetration resistance at this point was recorded. When the penetration resistance reached 3.5MPa, the corresponding time was recorded as the initial setting time; when the penetration resistance reached 28.0MPa, the corresponding time was recorded as the final setting time.

[0049] Experimental data: Table 2. Test data on setting time of concrete mortar for each component Test results show that the initial setting time of Examples 1, 2, and 3 is concentrated between 7 and 8 hours, and the final setting time is between 10 and 11 hours. In contrast, Comparative Examples 1 and 2, which use ordinary Portland cement, have significantly earlier initial and final setting times. This phenomenon is due to the fact that the medium-heat or low-heat Portland cement used in this invention has a lower content of tricalcium aluminate and tricalcium silicate in its clinker, resulting in a relatively slow early hydration reaction rate, which prolongs the setting time. This characteristic is not a defect, but rather an advantageous condition for realizing the crack-resistant process of this invention. The longer setting time provides sufficient construction window for the pouring of large-area surface concrete, secondary vibration, and multiple surface finishing treatments, ensuring that these key crack-resistant process steps can be effectively implemented. The setting times of Comparative Examples 3 to 7 are basically the same as those of Example 1, indicating that the incorporation of steel fibers and the change in the later construction and curing methods have no significant impact on the internal chemical process of cement hydration. This test verifies that the formulation of this invention can obtain a controllable and suitable setting process, laying the foundation for the implementation of a series of subsequent physical crack-resistant measures.

[0050] Test Example 3: Mechanical Property Test (Compressive Strength) To verify the load-bearing capacity of the concrete prepared in the embodiments and comparative examples of the present invention, the cubic compressive strength of each component was determined in accordance with GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0051] The experimental steps are as follows: The concrete mixtures prepared from each component were cast into cubic specimens with dimensions of 150mm × 150mm × 150mm, three specimens per group. The specimens were demolded within 24 hours of molding and immediately placed in a standard curing room for curing. The curing environment temperature was (20±2)℃, and the relative humidity was not less than 95%. After curing for 28 days, the specimens were removed and subjected to compressive strength testing using a pressure testing machine with a suitable range. The bearing surface of the specimen was wiped clean and placed centered on the lower pressure plate of the testing machine. The testing machine was started, and a continuous and uniform loading rate of 0.5MPa / s to 0.8MPa / s was applied until the specimen failed. The failure load of the specimen was recorded, and its compressive strength value was calculated. The arithmetic mean of the three specimens in each group was taken as the measured compressive strength value of that group of concrete.

[0052] Experimental data: Table 3. 28-day compressive strength test data of concrete components Test data show that the 28-day compressive strength of Examples 1, 2, and 3 all exceed 45 MPa, meeting the design strength requirements for C40 grade concrete in the pavement layer of high-pile wharves. This invention achieves this by using a relatively low amount of cementitious material (255 kg / m³). 3 -265kg / m 3 Under the conditions of low heat of hydration cement, by optimizing aggregate gradation, controlling the water-cement ratio, and supplementing with high-performance water-reducing agents, sufficient density and late-stage strength development of the concrete matrix are ensured. Although Comparative Example 2 achieved a higher 28-day strength due to the use of ordinary Portland cement, its technical approach contradicts the goal of this invention to suppress early heat of hydration. The strength of Comparative Examples 4 and 6 was significantly reduced, reflecting the damage to the final mechanical properties of concrete caused by insufficient curing and non-standard vibration processes. This, in turn, confirms the necessity of the construction process steps of this invention. Overall, the results of the mechanical performance test confirm the structural feasibility of the technical solution of this invention. That is, while effectively integrating multiple anti-cracking measures, the hardened body formed at the end can provide the load-bearing capacity that meets the safety requirements of the engineering structure. This proves that while solving the cracking problem, this invention does not sacrifice the basic physical and mechanical properties necessary for the material as a structural component.

[0053] Test Example 4: Flexural Strength Test To evaluate the ability of the concrete prepared in the embodiments and comparative examples of the present invention to resist flexural failure, that is, to directly reflect its tensile strength and crack resistance, the flexural strength of each component was determined in accordance with GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0054] The experimental steps are as follows: The concrete mixtures prepared from each component were cast into beam specimens with dimensions of 150mm×150mm×550mm. Three specimens were made in each group. After the specimens were formed, they were cured under standard conditions for 28 days and then tested using the four-point bending test method. The span of the support points of the testing machine was 450mm, and the two loading points were located at the three equal division points of the span with a spacing of 150mm. The loading was carried out continuously and uniformly at a loading rate of 0.05MPa / s to 0.08MPa / s until the specimen broke. The failure load was recorded, and the flexural strength of the specimen was calculated according to the standard formula. The arithmetic mean of the three specimens in each group was taken as the final measured value.

[0055] Experimental data: Table 4. 28-day flexural strength test data of concrete components The data clearly show that the flexural strength of Embodiments 1, 2, and 3 of the present invention is significantly higher than that of all comparative examples. The core mechanism of this performance improvement lies in the introduction of steel fibers. When the concrete matrix is ​​subjected to tensile stress, the three-dimensionally randomly distributed steel fibers can effectively cross the microcracks, inhibit the expansion of the cracks and share the stress through their own tensile action until they are pulled out or broken. This process consumes a lot of energy, which constitutes the key to improving toughness and crack resistance from the material constitutive level.

[0056] The direct comparison between Example 1 and Comparative Example 3 is crucial. Under identical conditions, the removal of steel fibers alone led to a significant decrease in flexural strength. This directly quantifies the contribution of steel fibers to improving the tensile properties of the material. Comparative Example 1, as conventional concrete, has the lowest flexural strength and serves as the benchmark for this invention. The results of Comparative Examples 4, 5, and 6 show that insufficient curing and non-standard construction techniques, even with a basically correct formula, can still weaken the density and integrity of the cement matrix, thereby reducing the final flexural performance. This demonstrates the necessity of the process control steps in this invention. Therefore, the flexural strength test systematically proves the effectiveness of the technical solution of this invention: through the reinforcing and toughening effect of steel fibers, coupled with a formula and process that ensures high-quality matrix, the tensile properties of the material are ultimately improved, thus providing a reliable physical and mechanical guarantee for suppressing the generation of structural cracks.

[0057] Test Example 5: Drying Shrinkage Rate Test To quantitatively evaluate the volume stability of the concrete prepared in the embodiments and comparative examples of the present invention, the drying shrinkage rate of each component was determined in accordance with GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete".

[0058] The experimental steps are as follows: The concrete mixtures prepared from each component were cast into prism specimens with dimensions of 100mm×100mm×515mm. Measurement nails were pre-embedded at both ends of the specimens. Three specimens were made in each group. The specimens were demolded after curing in a standard curing room for 3 days. The initial length was immediately measured using a horizontal concrete shrinkage meter. Subsequently, the specimens were quickly moved into a constant temperature and humidity chamber with a temperature of (20±2)℃ and a relative humidity of (60±5)%. The length change of the specimens was measured periodically at the specified time intervals. The length readings were recorded up to 56 days of age, and the drying shrinkage rate was calculated. The arithmetic mean of the three specimens in each group was taken as the final measured value.

[0059] Experimental data: Table 5. Test data of 56-day drying shrinkage rate of concrete components The above test data intuitively reflects the volumetric deformation characteristics of each component of concrete. The drying shrinkage rates of Examples 1, 2, and 3 are significantly lower than those of all comparative examples. The underlying mechanism of this result is the synergistic effect of multiple technical measures in this invention. First, from the perspective of material composition, the lower cement content and water-cement ratio reduce the total amount of evaporable water and the volume of capillary pores in the hardened cement paste, which is the basis for controlling shrinkage. Second, the three-dimensional constraint network formed by steel fibers in the cement matrix plays a physical inhibitory role in the shrinkage deformation of cement paste during the drying and water loss process. This is verified by the data difference between Example 1 and Comparative Example 3. Finally, the sufficient and effective curing process specified in this invention, as shown in Comparative Example 4, ensures that the cement hydration is fully carried out and a dense gel structure is formed, thereby reducing the potential for later water loss and shrinkage.

[0060] Drying shrinkage is one of the main driving forces causing non-load-bearing cracks in concrete surface layers. This test verifies the effectiveness of the technical solution of the present invention from the source of material deformation. That is, by combining material composition optimization with construction process control, the volume shrinkage deformation of hardened concrete can be reduced, thereby reducing shrinkage stress and reducing the inherent risk of structural cracking.

[0061] Test Example 6: Adiabatic Temperature Rise Test To quantitatively evaluate the heat of hydration release characteristics of concrete in the embodiments and comparative examples of the present invention, the components were tested using a large-capacity concrete adiabatic temperature rise tester, in accordance with the relevant provisions of DL / T5150-2017 "Test Procedure for Hydraulic Concrete".

[0062] The experimental steps are as follows: Immediately load the freshly prepared concrete mixtures of each component into the sample bucket of the adiabatic temperature rise tester, insert a temperature sensor at the center of the sample, start the equipment, and the system will automatically track and control the ambient temperature to keep it synchronized with the temperature at the center of the sample, creating adiabatic conditions. The temperature-time curve from the time the cement is added to the time the temperature stops rising and begins to fall will be continuously recorded, and the highest temperature rise value, i.e. the difference between the peak temperature reached by the sample and the initial temperature, will be read from it.

[0063] Experimental data: Table 6. Peak temperature rise test data of each component of concrete in adiabatic conditions The data clearly reveal the core effect of the present invention in controlling the heat of hydration. The peak adiabatic temperature rise of Examples 1, 2, and 3 is significantly lower than that of Comparative Examples 1 and 2, which use ordinary silicate cement. This is because the present invention uses medium- or low-heat silicate cement with lower heat of hydration. By controlling the content of tricalcium aluminate and tricalcium silicate in the clinker, this type of cement slows down the exothermic rate and total heat release of the early hydration reaction.

[0064] The temperature rise data of Comparative Examples 3 to 7 are basically at the same level as those of Example 1. This result clearly shows that the incorporation of steel fibers and the changes in construction and curing processes have no direct impact on the hydration heat release characteristics of the concrete material itself. This test separates and verifies one of the key technical points of the present invention from the material source: reducing the heat release of concrete by selecting the best cementitious materials is an important reason for controlling the internal temperature rise. A lower adiabatic temperature rise means that the highest temperature that can be reached inside the large-volume concrete after pouring is lower. This directly reduces the temperature gradient between the concrete core and the surface, thereby reducing the internal tensile stress caused by the temperature difference and providing material-level protection for suppressing temperature cracks in large-volume concrete.

Claims

1. A method for controlling cracks in the surface layer of a high-pile wharf in the Yangtze River Estuary, characterized in that, Includes the following steps: S1. Preparation of concrete mixture: Mix medium-heat silicate cement or low-heat silicate cement, steel fibers, aggregates and water to prepare concrete mixture; S2. Pouring and Treatment: Temperature control measures shall be implemented before and during the pouring of the concrete mixture; after the concrete mixture is poured and before the initial setting of the concrete, the poured concrete mixture shall be vibrated a second time; after the second vibration, the surface of the concrete mixture shall be finished at least twice. S3. Curing: After the finishing work is completed, a composite covering layer consisting of at least two different materials is used to keep the concrete mixture surface warm and moist.

2. The method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, The concrete mixture prepared in step S1 is made from raw materials containing the following components per cubic meter: medium-heat silicate cement or low-heat silicate cement: 255kg-265kg. Fine aggregate: 740kg-760kg; Coarse aggregate: 1145kg-1155kg; Steel fiber: 62.8kg-94.2kg; The ratio of the mass of water to the mass of medium-heat silicate cement or low-heat silicate cement is 0.42-0.

45.

3. The method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, The slump of the concrete mixture prepared in step S1 is controlled to be 100mm-120mm.

4. The method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, In step S1, the mixing process also includes adding a polycarboxylate-based high-performance water-reducing agent, wherein the amount of the polycarboxylate-based high-performance water-reducing agent is 1.0%-1.1% of the mass of medium-heat silicate cement or low-heat silicate cement.

5. The method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, In step S2, the temperature control measures implemented include at least one of the following: Shade and spray water to pre-cool the sand and stone aggregates used to prepare the concrete mixture; Add ice cubes to the mixing water used to prepare the concrete mixture; Concrete pouring was carried out during the low-temperature period at night.

6. The method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, Before the concrete pouring in step S2, the following steps are also included: binding the surface steel mesh according to the design drawings, and ensuring the protective layer thickness of the surface steel mesh by setting steel reinforcement supports.

7. The method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, In step S2, the secondary vibration is performed using an immersion vibrator, and the interval between the secondary vibrations is 45cm-50cm.

8. The method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, In step S2, the finishing operation specifically includes: performing the first finishing operation within 1-2 hours after the concrete pouring is completed; and performing the second finishing operation 2-3 hours after the first finishing operation is completed.

9. A method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, In step S3, the composite covering layer is constructed by sequentially covering geotextile, plastic film and another layer of geotextile from bottom to top.

10. A method for controlling surface cracks at a high-pile wharf in the Yangtze River estuary according to claim 1, characterized in that, In step S3, the duration of the heat preservation and moisturizing maintenance shall not be less than 21 days.

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