Method for avoiding shrinkage cracking of uhpc structural members during hardening

Abstract

The application discloses a method for avoiding shrinkage cracking of UHPC structural members in the hardening process, and aims at solving the problems of grouting non-densification and poor concrete combination caused by the incompatibility of two groups of concrete in different construction stages.The method comprises the following steps: S1, performing concrete performance test on different gradation concrete samples, and determining the optimized aggregate gradation through the concrete performance test; S2, determining the concrete raw material ratio and the optimal water-binder ratio; S3, when installing the UHPC structural members, adopting the post-cast strip and prestress process for assistance, and increasing the tension force of the prestressed reinforcement according to the total prestress loss value F, so that the prestress can be effectively transmitted to the concrete structure; and S4, performing layered pouring on the installed UHPC structural members.The construction precision during the structure installation and pouring can be ensured through the selection and optimization of raw materials and the adjustment of the construction process, and the shrinkage cracking risk of the UHPC structural members in the hardening process is remarkably reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ultra-high performance concrete prefabricated component manufacturing, and particularly relates to a method for avoiding shrinkage cracking of UHPC structural components in the hardening process. BACKGROUND

[0002] UHPC (ultra-high performance concrete) has advantages of high strength and high durability, but is prone to shrinkage cracking in the hardening process, which not only affects the appearance and performance of the component, but also may reduce its service life.

[0003] For example, Chinese patent CN110027109A discloses a method for avoiding shrinkage cracking of UHPC structural components in the hardening process, which reserves a hole when pouring UHPC, and then configures stress reinforcement after the UHPC hardens, thereby reducing the incoordination deformation of concrete and internal steel caused by concrete shrinkage. According to needs, prestress is selected to be applied or not. Finally, the reserved hole is grouted and maintained, and the component is completed.

[0004] In the above method, although the problem of shrinkage cracking of UHPC structural components in the hardening process is solved by reserving a hole and stress reinforcement, two groups of ultra-high performance concrete are used, and the two groups of concrete are used in different construction stages. It is necessary to ensure that the performance of the two groups is mutually adapted, including fluidity, setting time, strength development, etc. If they are not adapted, problems such as grouting not being dense and poor concrete bonding will occur, affecting the integrity and durability of the structure. SUMMARY

[0005] The purpose of the present application is to solve the problem of using two groups of concrete in different construction stages, which requires that the performance of the two groups is mutually adapted, including fluidity, setting time, strength development, etc. If they are not adapted, problems such as grouting not being dense and poor concrete bonding will occur, affecting the integrity and durability of the structure, thereby providing a method for avoiding shrinkage cracking of UHPC structural components in the hardening process.

[0006] The method for avoiding shrinkage cracking of UHPC structural components in the hardening process according to the present application is implemented according to the following steps:

[0007] S1, raw material selection and optimization:

[0008] The cement and different continuously graded aggregates are mixed to prepare a plurality of concrete samples. The concrete performance of the different graded concrete samples is tested, and the optimized graded aggregate is determined through the concrete performance test. The cement, the optimized graded aggregate and the additive are mixed to obtain a mixed raw material.

[0009] S2, mix proportion improvement:

[0010] The mixed raw materials, water, silica ash and fly ash are stirred and mixed to prepare concrete test pieces with different water-binder ratios, the concrete compactness of the concrete test pieces is detected, the optimal water-binder ratio is determined, and the concrete raw material ratio and the optimal water-binder ratio are determined;

[0011] S3, optimizing the structure design:

[0012] In the installation of the UHPC structural member, the post-cast strip and the prestress process are adopted for assistance, the width of the post-cast strip is set to 850-1200mm, the prestress steel and the anchor are adopted in the prestress process, the total prestress loss is calculated according to the influence of the relaxation of the prestress steel, the shrinkage and the creep of the concrete on the prestress, and the calculation formula of the total prestress loss value is as follows:

[0013] F=F l1 +F l2 +F l3 +F l4 +F l5 ;

[0014] In the formula, F l1 is the prestress loss caused by the deformation of the anchor and the shrinkage of the prestress steel, F l2 is the prestress loss caused by the friction between the prestress steel and the hole wall, F l3 is the prestress loss caused by the temperature difference between the tensioned steel and the tension equipment during the heating and curing of the concrete, F l4 is the prestress loss caused by the stress relaxation of the prestress steel, and F l5 is the prestress loss caused by the shrinkage and the creep of the concrete.

[0015] The tension force of the prestress steel is increased according to the total prestress loss value F to compensate for the prestress loss, after the tension of the prestress steel is completed, the anchor is anchored to ensure that the prestress is effectively transmitted to the concrete structure, and the installed UHPC structural member is obtained.

[0016] S4, adjusting the construction process:

[0017] According to the concrete raw material ratio and the optimal water-binder ratio determined in step S2, the concrete raw materials are configured, the installed UHPC structural member is layered and poured with the concrete raw materials, the lower layer of concrete is poured and vibrated first, when the lower layer of concrete is initially cured but not completely hardened, the surface of the lower layer of concrete is brushed and chiseled, and then the upper layer of concrete is poured and vibrated, after the pouring is completed, the moisture curing is carried out, the entire UHPC structure is protected by wrapping, and thus the method for avoiding the shrinkage cracking of the UHPC structural member during the hardening process is completed.

[0018] The application establishes a complete UHPC structural member shrinkage and cracking control system through material optimization, mix proportion regulation and construction process optimization of the concrete, and effectively solves the problems of poor adaptability and poor combination of two groups of concrete in the prior art.

[0019] Compared with the prior art, the method for avoiding shrinkage and cracking of the UHPC structural member in the hardening process has the following beneficial effects:

[0020] In the application, the raw materials and mix proportion of the concrete can be treated through selection and optimization of the raw materials and mix proportion improvement, so as to ensure the coordination and unity of the performances of the two groups of UHPC, reduce the interference of the adaptability, avoid the problems of poor grouting and poor combination of the concrete, and ensure the integrity and durability of the structure; through optimization of the structural design and adjustment of the construction process, the construction precision during the installation and pouring of the structure can be ensured, and then the construction precision control level is improved, the quality and safety of the structural member are ensured, the material cost is reduced, the shrinkage and cracking risk of the UHPC structural member in the hardening process is significantly reduced, the quality and durability of the member are improved, the maintenance and reinforcement cost is reduced, and the service life of the structure is prolonged. DETAILED DESCRIPTION

[0021] Specific implementation method one: the method for avoiding shrinkage and cracking of the UHPC structural member in the hardening process according to the embodiment is implemented according to the following steps:

[0022] S1, raw material selection and optimization:

[0023] The cement and the aggregate with different continuous gradations are mixed to prepare a plurality of groups of concrete samples, the concrete performance test is performed on the concrete samples with different gradations, the optimized gradation aggregate is determined through the concrete performance test, the cement, the optimized gradation aggregate and the additive are mixed to obtain the mixed raw materials;

[0024] S2, mix proportion improvement:

[0025] The mixed raw materials, water, silica fume and fly ash are stirred and mixed to prepare a plurality of groups of concrete test pieces with different water-binder ratios, the concrete density of the concrete test pieces is detected, the optimal water-binder ratio is determined, and the concrete raw material ratio and the optimal water-binder ratio are determined;

[0026] S3, optimization of structural design:

[0027] When the UHPC structural member is installed, the post-cast strip and the prestress process are used for assistance, the width of the post-cast strip is set to 850-1200mm, the prestressed reinforcement and the anchor are used in the prestress process, the total prestress loss is calculated according to the influence of the relaxation of the prestressed reinforcement, the shrinkage and creep of the concrete on the prestress, and the calculation formula of the total prestress loss value is as follows:

[0028] F=F l1 +Fl2 +F l3 +F l4 +F l5 ;

[0029] In the formula, F l1 is the loss of prestress caused by deformation of the anchorage device and shrinkage of the prestressed steel, F l2 is the loss of prestress caused by friction between the prestressed steel and the hole wall, F l3 is the loss of prestress caused by temperature difference between the tensioned steel and the tensioning equipment during concrete heating and curing, F l4 is the loss of prestress caused by stress relaxation of the prestressed steel, F l5 is the loss of prestress caused by shrinkage and creep of the concrete.

[0030] According to the total prestress loss value F, the tensioning force of the prestressed steel is increased to compensate for the loss of prestress. After the tensioning of the prestressed steel is completed, the anchorage device is anchored to ensure that the prestress is effectively transmitted to the concrete structure, and the installed UHPC structural member is obtained.

[0031] S4, adjusting the construction process:

[0032] According to step S2, the concrete raw materials are prepared according to the determined concrete raw material ratio and optimal water-binder ratio. The installed UHPC structural member is layered and poured with the concrete raw materials. The lower layer of concrete is poured and vibrated first. When the lower layer of concrete is initially cured but not completely hardened, the surface of the lower layer of concrete is brushed and chiseled. Then the upper layer of concrete is poured and vibrated. After pouring, the UHPC structure is protected by wrapping method, thereby completing the method for avoiding shrinkage cracking of the UHPC structural member during hardening.

[0033] Specific implementation method two: The difference between this implementation method and the specific implementation method one is that the concrete performance test in step S1 includes shrinkage test and strength test.

[0034] Specific implementation method three: The difference between this implementation method and the specific implementation method one or two is that the surface treatment of the optimized graded aggregate is performed by isobutyl triethoxysilane immersion in step S1.

[0035] In this implementation method, the silane immersion method is used to modify the surface of the aggregate, so that the silane molecules form a dense molecular film on the surface of the aggregate. This molecular film not only forms a chemical bond with the surface of the aggregate, but also can produce good physical adsorption with the cement hydration products, thereby significantly enhancing the structure of the interface transition zone at the micro level and improving the overall performance of the concrete.

[0036] In this embodiment, isobutyl triethoxysilane is selected. The isobutyl triethoxysilane has good permeability and can penetrate into the pores of the aggregate. The chemical structure of the isobutyl triethoxysilane enables it to react with the hydroxyl groups on the surface of the aggregate after hydrolysis, forming a strong chemical bond, thereby effectively improving the performance of the aggregate. In the treatment of some high-performance concrete aggregates, the use of silane materials can enhance the adhesion between the aggregate and the cement paste.

[0037] Specific embodiment four: The difference between this embodiment and specific embodiment three is that the isobutyl triethoxysilane is used to impregnate the optimized graded aggregate at a temperature of 20-30°C for 2-4 hours.

[0038] Specific embodiment five: The difference between this embodiment and one of specific embodiments one to four is that the additive in step S1 is one or more of a water reducing agent, an expansive agent, and a shrinkage reducing agent.

[0039] Specific embodiment six: The difference between this embodiment and one of specific embodiments one to five is that the optimal water-binder ratio range of the concrete is determined to be 0.10-0.21 in step S2.

[0040] In this embodiment, the preferred water-binder ratio range of the concrete is determined to be 0.15-0.20 in step S2.

[0041] Specific embodiment seven: The difference between this embodiment and one of specific embodiments one to six is that the total amount of the gel material composed of cement, silica fume, and fly ash in the concrete raw materials is determined to be 800-1300 kg / m 3 .

[0042] In this embodiment, the total amount of the gel material is preferably 1000-1200 kg / m 3 .

[0043] In this embodiment, the initial water-binder ratio of the mixed raw materials (including cement, silica fume, fly ash, etc.) obtained in step S1 is determined, and these raw materials are divided into 5 groups. The water-binder ratio of each group is adjusted in turn, the compactness of the adjusted concrete is detected, the optimal water-binder ratio is determined according to the detection results, and the amount of gel material is adjusted according to the proportion.

[0044] Specific embodiment eight: The difference between this embodiment and one of specific embodiments one to seven is that the spacing of the post-cast strip is controlled to be 20-45 m in step S3, and the retention time of the post-cast strip is controlled to be 50-65 days.

[0045] Specific embodiment nine: The difference between this embodiment and one of specific embodiments one to eight is that the pouring temperature of the upper layer of concrete and the lower layer of concrete is controlled to be between 10-25°C in step S4, and the pouring speed is 3-5 cubic meters per hour.

[0046] Specific implementation ten: the difference between this embodiment and one of the specific implementation one to nine is that the whole UHPC structure is protected by wrapping method in step S4, and the wrapping material is selected from plastic film, geotextile or insulation board.

[0047] In this embodiment, the wrapping material such as plastic film, geotextile or insulation board is selected according to the requirements of the component and the environment, and tools such as scissors, adhesive tape and rope are selected. The surface of the component is cleaned, the material is cut according to the size and shape, and the wrapping operation is carried out. When the plastic film is wrapped, the component is placed in the middle and the edge is sealed in turn. The geotextile is wrapped and reinforced with a rope. If multiple layers of wrapping are required, they are performed in order. After the wrapping is completed, the effect is checked, and the damaged wrapping material is repaired or replaced in time to ensure that the UHPC structure component is effectively protected.

[0048] Example one: the method for avoiding shrinkage cracking of UHPC structure component in the hardening process is implemented according to the following steps:

[0049] S1, raw material selection and optimization:

[0050] The cement and different continuously graded aggregates are mixed, the selection standard of the coarse aggregate during grading is high strength and good particle shape, the fine aggregate is natural sand and machine-made sand, a plurality of concrete samples are prepared, the concrete performance test is performed on the concrete samples with different gradings, the concrete performance test includes shrinkage test and strength test, the experimental data is analyzed, the particle distribution is focused on, if the particle content in a certain particle size range is unreasonable, it needs to be adjusted; attention is paid to the void ratio data, if the void ratio is high, the particle matching needs to be optimized to reduce it; the performance test results are referred to, if the strength is not up to standard, the grading needs to be improved, the optimized graded aggregate is determined through the concrete performance test, the cement (P·O 52.5 grade Portland cement is selected in this embodiment), the optimized graded aggregate and the additive (water reducing agent, expansive agent and shrinkage reducing agent) are mixed to obtain the mixed raw material; wherein, the mass ratio of the coarse aggregate and the fine aggregate is 3:7, the coarse aggregate is composed of gravel with particle size of 1.18-2.36mm, 2.36-4.75mm and 4.75-9.5mm in a mass ratio of 4:3:3, and the fine aggregate is composed of quartz sand with particle size of 0.15-0.3mm, 0.3-0.6mm and 0.6-1.18mm in a mass ratio of 1:1:1;

[0051] The grading and ratio of the coarse aggregate and the fine aggregate in this embodiment are determined by the concrete performance test;

[0052] In this embodiment, the coarse aggregate and the fine aggregate are treated by immersion with isobutyl triethoxysilane for 2.5 hours at a temperature of 25°C;

[0053] S2, mix proportion improvement:

[0054] The mixed raw materials, water, silica ash and fly ash are stirred and mixed to prepare 5 groups of concrete test pieces with different water-binder ratios, the concrete compactness of the concrete test pieces is detected, the optimal water-binder ratio is determined according to the detection result, and then the amount of gel material is adjusted according to the proportion, so as to determine the raw material ratio of the concrete and the optimal water-binder ratio, and the water-binder ratio of the UHPC in the embodiment is 0.10, the gel material includes cement, silica ash and fly ash, and the total amount of the gel material is 800 kg / m 3 ;

[0055] S3, optimizing the structure design:

[0056] When installing the UHPC structure member, the post-cast strip and the prestress process are used for assistance, the width of the post-cast strip is set to 850 mm, the interval is 20 m, the retention time of the post-cast strip is 50 days, the prestress steel and the anchor are used in the prestress process, the total prestress loss is calculated according to the influence of the relaxation of the prestress steel, the shrinkage and creep of the concrete on the prestress, and the calculation formula of the total prestress loss value is as follows:

[0057] F = F l1 + F l2 + F l3 + F l4 + F l5 ;

[0058] In the formula, F l1 is the prestress loss caused by the deformation of the anchor and the shrinkage of the prestress steel, F l2 is the prestress loss caused by the friction between the prestress steel and the hole wall, F l3 is the prestress loss caused by the temperature difference between the tensioned steel and the equipment bearing the tension during the heating and maintenance of the concrete, F l4 is the prestress loss caused by the stress relaxation of the prestress steel, and F l5 is the prestress loss caused by the shrinkage and creep of the concrete.

[0059] After the prestress loss is calculated, the following processing needs to be performed:

[0060] (1) According to the total prestress loss value obtained by calculation, the initial tensioning force is correspondingly increased to compensate for the expected prestress loss;

[0061] (2) The prestress steel is tensioned in stages, and each stage tensioning force is not more than 25% of the design tensioning force;

[0062] (3) After reaching the design tensioning force, the tensioning force is kept stable for a certain period of time (15-20 minutes), and whether the elongation value of the prestress steel is stable is observed;

[0063] (4) The actual tensioning force and the elongation value are recorded and compared with the theoretical calculation value to ensure that the deviation is within the allowable range (not more than ±6%).

[0064] (5) If the deviation exceeds the allowable range, analyze the reasons and take appropriate measures, if necessary, re-tensioning;

[0065] (6) After tensioning, anchor the prestressed steel in time to ensure that the prestress is effectively transmitted to the concrete structure to obtain the installed UHPC structural member;

[0066] S4, adjust the construction process:

[0067] According to step S2, the concrete raw materials are prepared according to the optimal water-binder ratio, and the installed UHPC structural member is layered and poured with the concrete raw materials. The lower layer of concrete (half of the total thickness) is poured and vibrated, and when the lower layer of concrete is initially cured and not completely hardened, the surface of the lower layer of concrete is brushed and chiseled. Then pour and vibrate the upper layer of concrete, and after pouring, perform moisture curing. The entire UHPC structure is protected using a wrapping method, thereby completing the method of avoiding shrinkage cracking of the UHPC structural member during hardening.

[0068] In this example, the water-binder ratio of the UHPC is low, the total amount of gel material is small, the compactness of the concrete after testing is low, the porosity in the cement stone is high, and the workability of the concrete is poor, which affects the construction quality.

[0069] Example Two: The difference between this example and Example One is that the water-binder ratio of the UHPC in step S2 is 0.15, and the gel material includes cement, silica fume and fly ash, and the total amount of gel material is 1100 kg / m 3 ;

[0070] In step S3, when installing the UHPC structural member, auxiliary post-cast strips and prestressing techniques are used. The width of the post-cast strip is set to 1100 mm, the spacing is 30 m, the retention time of the post-cast strip is 58 days, and the prestressing technique uses prestressed steel and anchorage. According to the influence of prestressed steel relaxation, concrete shrinkage and creep on prestress, total prestress loss is calculated.

[0071] In this example, the water-binder ratio of the UHPC is 0.15, the total amount of gel material is moderate, the compactness of the concrete is high, and the porosity in the cement stone is low, thereby reducing the space for water evaporation and shrinkage, and ensuring the workability and construction quality of the concrete.

[0072] Example Three: The difference between this example and Example One is that the water-binder ratio of the UHPC in step S2 is 0.21, and the gel material includes cement, silica fume and fly ash, and the total amount of gel material is 1300 kg / m 3 ;

[0073] In step S3, when installing the UHPC structural member, a post-cast strip and a prestress process are used for assistance, the width of the post-cast strip is set to 1200mm, the interval is 45m, the retention time of the post-cast strip is 65 days, and in the prestress process, prestressed steel bars and anchorage devices are used, and according to the influence of the relaxation of the prestressed steel bars, the shrinkage and creep of the concrete on the prestress, total prestress loss calculation is carried out.

[0074] In the embodiment, the water-binder ratio of the UHPC is 0.21, the total amount of the gel material is moderate, the compactness of the concrete is slightly lower than that in the second embodiment, and the porosity in the cement stone is higher than that in the second embodiment, which increases the space for water evaporation and shrinkage, reduces the workability and construction quality of the concrete compared with the second embodiment.

[0075] In the application, the raw materials and the mixing proportion of the concrete can be treated by selection and optimization of raw materials and improvement of the mixing proportion, the water-binder ratio is optimized, the coordination and unity of the two groups of UHPC in performance are ensured, the interference of adaptability is reduced, the problems of non-dense grouting and poor concrete combination are avoided, the integrity and durability of the structure are ensured, the structure design is optimized, the UHPC structural member is assisted by using the post-cast strip and the prestress technology, the post-cast strip can allow the concrete to freely shrink in the early stage and reduce the restraint stress, and by applying prestress to the structural member, the tensile stress generated in the hardening process of the concrete can be offset, so that the shrinkage cracking is prevented.

[0076] The layered pouring can reduce the one-time pouring amount of the concrete and reduce the shrinkage stress, the pouring speed and pouring sequence are strictly controlled during the pouring process, the uniformity and compactness of the concrete are ensured, the vibration control is strengthened, appropriate vibration equipment and vibration methods are used to ensure that the concrete is fully compacted, and over-vibration or missed vibration should be avoided during the vibration process to prevent quality problems such as segregation or honeycomb of the concrete, the construction precision during the installation and pouring of the structure can be ensured, and the construction precision control level is improved, so that the quality and safety of the structural member are ensured, the material cost is reduced, the shrinkage cracking risk of the UHPC structural member in the hardening process is significantly reduced, the quality and durability of the member are improved, the maintenance and reinforcement cost is reduced, and the service life of the structure is prolonged.

[0077] The application provides a systematic mixing proportion optimization method. The raw materials are divided into five groups for parallel test, a relationship curve between the water-binder ratio and the compactness of the concrete is established, and the accurate determination of the optimal mixing proportion is realized. The optimal distribution of the hydration product is realized in the microstructure, the workability of the concrete is ensured, and the shrinkage deformation is effectively controlled.

[0078] The application realizes integration in construction process. By controlling the thickness of each layer in layered pouring to be half of the total thickness, the optimal ratio is determined based on the liquidity and shrinkage characteristics of UHPC material. At the same time, the composite processing method of brush and chisel is adopted to form a transition layer with specific roughness in microcosm, which significantly improves the interlayer bonding strength. In the curing aspect, the combination of moisture curing and wrapping method is adopted, which not only controls the water evaporation rate, but also ensures the uniformity of curing.

[0079] The application establishes a complete prestress loss calculation and compensation system. By comprehensively considering various factors such as anchor deformation, prestressed steel shrinkage and friction loss, and providing specific compensation scheme, the durability of prestress effect is ensured. This systematic compensation method, combined with construction process control, significantly improves the application effect of prestress technology in UHPC structural members.

[0080] Although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art can modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements to part of the technical features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. Method for avoiding shrinkage cracking of UHPC structural elements during hardening, characterized in that The method for avoiding shrinkage cracking of the UHPC structural member in the hardening process is realized according to the following steps: S1, raw material selection and optimization: The cement and different continuously graded aggregates are mixed to prepare a plurality of concrete samples, the concrete performance test is performed on the different graded concrete samples, the optimized graded aggregate is determined through the concrete performance test, the cement, the optimized graded aggregate and the additive are mixed to obtain the mixed raw material; S2, mix proportion improvement: The mixed raw material, water, silica fume and fly ash are stirred and mixed to prepare a plurality of concrete test pieces with different water-binder ratios, the concrete density of the concrete test piece is detected, the optimal water-binder ratio is determined, and the concrete raw material ratio and the optimal water-binder ratio are determined; S3, optimized structure design: When the UHPC structural member is installed, the post-cast strip and the prestress process are used for assistance, the width of the post-cast strip is set to 850-1200mm, the prestress steel and the anchor are used in the prestress process, the total prestress loss is calculated according to the influence of the relaxation of the prestress steel, the shrinkage and the creep of the concrete on the prestress, and the calculation formula of the total prestress loss value is as follows: F = F l1 + F l2 + F l3 + F l4 + F l5 ; In the formula, F l1 is the loss of prestress caused by deformation of the anchorage and shrinkage of the prestressed steel, F l2 is the loss of prestress caused by friction between the prestressed steel and the hole wall, F l3 is the loss of prestress caused by the temperature difference between the stretched steel and the tension equipment during the concrete heating and curing, F l4 is the loss of prestress caused by stress relaxation of the prestressed steel, F l5 is the loss of prestress caused by shrinkage and creep of the concrete; The prestress steel tension force is increased according to the total prestress loss value F to compensate for the prestress loss, after the tension of the prestress steel is completed, the anchor is used for anchoring to ensure that the prestress is effectively transmitted to the concrete structure, and the installed UHPC structural member is obtained; S4, adjusting construction process: According to the concrete raw material ratio and the optimal water-binder ratio determined in step S2, the concrete raw material is configured, the installed UHPC structural member is layered and poured, the lower layer concrete is poured and vibrated first, when the lower layer concrete is initially cured and not completely hardened, the surface of the lower layer concrete is brushed and chiseled, then the upper layer concrete is poured and vibrated, and after the pouring is completed, the moisture curing is performed, the whole UHPC structure is protected by using the wrapping method, so that the method for avoiding shrinkage cracking of the UHPC structural member in the hardening process is completed.

2. The method of avoiding shrinkage cracking of UHPC structural members during hardening according to claim 1, characterized in that The concrete performance test in step S1 includes the shrinkage test and the strength test.

3. The method of avoiding shrinkage cracking in UHPC structural members during hardening according to claim 1, characterized in that In step S1, the optimized graded aggregate is surface treated by using isobutyl triethoxysilane immersion.

4. The method of avoiding shrinkage cracking of a UHPC structural member during hardening according to claim 3, characterized in that The time for immersing the optimized graded aggregate by using isobutyl triethoxysilane is 2-4 hours at a temperature of 20-30℃.

5. The method of avoiding shrinkage cracking in UHPC structural members during hardening according to claim 1, characterized in that The additive in step S1 is one or more of a water reducing agent, an expansive agent and a shrinkage reducing agent.

6. The method of avoiding shrinkage cracking in UHPC structural members during hardening according to claim 1, characterized in that The optimal water-binder ratio range of the concrete is 0.15-0.20 in step S2.

7. The method of avoiding shrinkage cracking in UHPC structural members during hardening according to claim 1, characterized in that The total amount of the gel material composed of cement, silica fume and fly ash in the concrete raw material is determined to be 800-1300 kg / m3 in step S2 3 .

8. The method of avoiding shrinkage cracking in UHPC structural members during hardening according to claim 1, characterized in that The interval of the post-cast strip is controlled to be 20-45m in step S3, and the retention time of the post-cast strip is controlled to be 50-65 days.

9. The method of avoiding shrinkage cracking in UHPC structural members during hardening according to claim 1, characterized in that The pouring temperature of the upper layer concrete and the lower layer concrete is controlled to be 10-25℃, and the pouring speed is controlled to be 3-5 cubic meters per hour in step S4.

10. The method of avoiding shrinkage cracking in UHPC structural members during hardening according to claim 1, characterized in that The whole UHPC structure is protected by using the wrapping method in step S4, and the wrapping material is selected from plastic film, geotextile or insulation board.