Corrosion-resistant prestressed concrete cylinder pipe and manufacturing method thereof

Abstract

The invention belongs to the technical field of prestressed concrete cylinder pipe production, and provides a corrosion-resistant prestressed concrete cylinder pipe and a manufacturing method thereof. The concrete pipe comprises a concrete pipe core and a protective layer which are sequentially arranged from inside to outside. The protective layer comprises a corrosion-resistant mortar material and fibers; the corrosion-resistant mortar material comprises cement, an active admixture, fine aggregate, an additive and water. The corrosion inhibitor has the capability of keeping good working performance for a long time in a medium-degree or even severe-degree corrosion environment. The manufacturing method comprises the following steps: (1) positioning a concrete pipe core wound with a prestressed reinforcement and enabling the concrete pipe core to be in a rotating state; uniformly stirring a corrosion-resistant mortar material and fibers to obtain mortar, and then pouring the mortar into a pumping station; (2) spraying mortar to the surface of the rotating concrete pipe core to form a protective layer; and (3) after spraying is completed, the concrete pipe core is cured. The manufacturing method has the advantages that the production cost is low, the production efficiency is high, and the production quality can be movably guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of prestressed steel cylinder concrete pipe production, and in particular relates to a corrosion-resistant prestressed steel cylinder concrete pipe and a manufacturing method thereof. Background Art

[0002] PCCP is the abbreviation of "prestressed steel cylinder concrete pipe". It is a prestressed concrete structure pressure water pipeline widely used in large, medium and long-distance water pipelines in my country. It has good engineering performance and economy.

[0003] The basic structure of PCCP pipe is to wrap prestressed steel bars in a circular direction on the outer surface of the concrete pipe core embedded with an impermeable steel cylinder, and use roller spraying technology to make a layer of dry hard cement mortar protective layer with a net thickness of not less than 25mm on the outer surface of the steel bar to form a finished pipe. In order to improve the corrosion resistance of the pipe, a layer of anti-corrosion paint is often sprayed on the outer surface of the protective layer.

[0004] However, in the prior art, even if the pipe body structure as described above is adopted, the corrosion resistance of PCCP is still insufficient in some corrosive environments. In existing projects, there have been many cases where corrosion caused the pipe steel to rust and break, thus causing engineering accidents.

[0005] The main reasons for the insufficient anti-corrosion performance of the PCCP protective layer include: (1) The protective layer is a dry hard cement mortar layer manufactured by the roller spraying process. The technical performance of the protective layer meets the requirements of an average water absorption rate of no more than 9%, a 28-day cubic compressive strength of no less than 45MPa, and a minimum thickness of no less than 25mm; there is no direct corrosion resistance performance index requirement, and such performance requirements and actual performance cannot meet the requirements of corrosive environments. (2) When an anti-corrosion coating is used, an epoxy coal tar coating is generally used, and the coating thickness is generally between 0.6-0.9mm; however, there are many instabilities in the coating materials, construction, and pipe production, transportation, and installation processes, which makes the coating quality prone to weak points, thereby causing defects in the overall anti-corrosion performance of the pipe. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the first object of the present invention is to provide a corrosion-resistant prestressed steel cylinder concrete pipe. The corrosion-resistant prestressed steel cylinder concrete pipe has a protective layer with a compressive strength of not less than 60MPa, a tensile strength of not less than 5.0MPa, a water absorption rate of not more than 3%, and a chloride ion permeability coefficient D RCM No more than 0.8×10 -12 m 2 / s, and the sulfate corrosion resistance level is not less than KS150. It has the ability to maintain good working performance for a long time in moderate or even severe corrosion environments, without relying on other anti-corrosion measures. The service life in the above corrosion environment can reach more than 50 years, or even 100 years.

[0007] In view of the above-mentioned deficiencies in the prior art, the second purpose of the present invention is to provide a method for manufacturing a corrosion-resistant prestressed steel cylinder concrete pipe, which effectively solves the problems of production cost, production efficiency, and production quality assurance of the PCCP corrosion-resistant protective layer. It has the advantages of low production cost, high production efficiency, and guaranteed production quality. It can not only replace the traditional dry hard cement mortar protective layer production process, but also has better cost and efficiency performance than the mold casting process, and is suitable for large-scale promotion and application.

[0008] In order to achieve the above object, the solution adopted by the present invention is:

[0009] A corrosion-resistant prestressed steel cylinder concrete pipe comprises a concrete pipe core and a protective layer which are arranged in sequence from the inside to the outside; the protective layer comprises a corrosion-resistant mortar material and fibers; the corrosion-resistant mortar material comprises, by weight, 0.3-0.7 parts of cement, 0.2-0.5 parts of active admixtures, 0.7-1.4 parts of fine aggregates, 0.005-0.04 parts of admixtures and 0.15-0.3 parts of water; the volume ratio of the fibers to the corrosion-resistant mortar material is 0.007-0.025:1.

[0010] Furthermore, in a preferred embodiment of the present invention, the diameter of the fiber is less than 0.2 mm.

[0011] Furthermore, in a preferred embodiment of the present invention, the fiber includes at least one of metal fiber and non-metal fiber.

[0012] Furthermore, in a preferred embodiment of the present invention, the non-metallic fiber includes at least one of synthetic fiber, basalt fiber, ultrafine steel fiber and glass fiber.

[0013] Furthermore, in a preferred embodiment of the present invention, the active admixture includes at least two of fly ash, mineral powder, silica fume, microspheres and expansion agent.

[0014] Furthermore, in a preferred embodiment of the present invention, the fine aggregate includes at least one of quartz sand, natural sand and artificial sand.

[0015] Furthermore, in a preferred embodiment of the present invention, the admixture is an admixture that can reduce water and improve pumping effect.

[0016] Further, in a preferred embodiment of the present invention, the cement grade is higher than or equal to grade 42.5.

[0017] Furthermore, in a preferred embodiment of the present invention, the thickness of the protective layer is greater than or equal to 20 mm.

[0018] A method for manufacturing the above-mentioned corrosion-resistant prestressed steel tube concrete pipe comprises: (1) positioning a concrete pipe core wrapped with prestressed steel bars and placing it in a rotating state; mixing corrosion-resistant mortar material and fiber evenly until its fluidity index is an expansion degree of 500-650 mm to obtain mortar, and then pouring the mortar into a pumping station; (2) spraying the mortar onto the surface of the rotating concrete pipe core to form a protective layer; (3) after the spraying is completed, the concrete pipe core is subjected to natural moisturizing curing or accelerated curing.

[0019] The corrosion-resistant prestressed steel cylinder concrete pipe and the manufacturing method thereof provided by the present invention have the following beneficial effects:

[0020] (1) The corrosion-resistant prestressed steel tube concrete pipe provided by the present invention has a protective layer, and the protective layer is prepared by using a special mortar.

[0021] The mortar has excellent corrosion resistance, good fluidity and is easy to pump and produce. Due to the addition of extremely fine fiber materials, it can significantly improve the tensile and crack resistance of the protective layer, and further enhance the corrosion resistance of the protective layer.

[0022] The corrosion-resistant prestressed steel cylinder concrete pipe provided in the present application has a protective layer with high strength (28-day compressive strength is above 60MPa, and tensile strength is not less than 5.0MPa), high density (water absorption rate is not more than 3%), high corrosion resistance (anti-chloride ion permeability coefficient D RCM No more than 0.8×10 -12 m 2 / s, the sulfate corrosion resistance level is not less than KS150, the corrosion resistance can reach more than 100 times of the existing PCCP protective layer), and high crack resistance (the crack resistance is significantly better than the existing PCCP protective layer).

[0023] The corrosion-resistant prestressed steel cylinder concrete pipe provided by this application has the ability to maintain good working performance for a long time in a moderate or even severe corrosion environment without relying on other anti-corrosion measures. The service life in the above corrosion environment can reach more than 50 years, or even 100 years. It completely solves the shortcomings of insufficient durability of PCCP engineering and is conducive to the engineering application of PCCP products in a wider range.

[0024] (2) The corrosion-resistant prestressed steel cylinder concrete pipe provided by the present invention can meet the durability index of 100 years in a Class E corrosion environment without any additional anti-corrosion measures such as epoxy coal tar coating on the basis of reducing the thickness of the protective layer by 20% (D RCMNo more than 4×10 -12 m 2 / s), thus completely solving the problem of PCCP's shortcomings in corrosion resistance.

[0025] (3) Through the manufacturing method provided by the present invention, combined with the excellent plasticity and cohesiveness of the corrosion-resistant mortar material itself, the corrosion-resistant mortar material is sprayed out by a spraying process so that it adheres firmly to the surface of the PCCP prestressed steel wire. The spraying thickness of the protective layer is not less than 20 mm. After the mixture is hardened by natural curing or accelerated curing, a dense protective layer structure with excellent corrosion resistance and mechanical properties is formed. Moreover, its compactness is not mainly formed by external pressure, but by its own fluidity and viscosity. Therefore, the mixture on the surface of the tube core has a relatively stable structure. After reasonable curing, its various properties will steadily increase, forming a protective layer structure with stable quality.

[0026] (4) The manufacturing method provided by the present invention can be applied to PCCP pipes with an inner diameter ranging from 600 mm to 4000 mm, and can also be applied to pipes with larger diameters, and is suitable for pipe sections of various lengths.

[0027] (5) The manufacturing method provided by the present invention effectively solves the problems of production cost, production efficiency, production quality assurance, etc. of PCCP corrosion-resistant protective layer, and has the advantages of low production cost, high production efficiency, and guaranteed production quality. It can not only replace the traditional dry hard cement mortar protective layer production process, but also has better cost and efficiency performance than the mold casting process, and is suitable for large-scale promotion and application.

[0028] (6) The manufacturing method provided by the present invention adopts a high-fluidity mixture and a pressure injection method. The material is ejected through a pipe without obvious noise. Since the mixture has good viscosity and does not ooze water, there will be no obvious site hygiene and dust problems. The production site can maintain good working hygiene conditions. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0030] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0031] Example 1

[0032] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer includes a corrosion-resistant mortar material and basalt fiber. Among them, the corrosion-resistant mortar material includes, by weight: 0.3 parts of cement, 0.5 parts of active admixture (ash fly ash: mineral powder = 1:1), 0.7 parts of quartz sand, 0.04 parts of lignin sulfonate and 0.15 parts of water. The volume ratio of basalt fiber to corrosion-resistant mortar material is: 0.025:1.

[0033] The present embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe, comprising: (1) positioning a concrete pipe core wrapped with prestressed steel bars and rotating it; mixing corrosion-resistant mortar material and fiber evenly until its fluidity index is an expansion of 600 mm to obtain mortar, and then pouring the mortar into a pumping station; (2) spraying the mortar onto the surface of the rotating concrete pipe core to form a protective layer with a thickness of 25 mm; (3) after the spraying is completed, the concrete pipe core is naturally sprinkled with water for moisture maintenance.

[0034] Example 2

[0035] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer includes a corrosion-resistant mortar material and basalt fiber. Among them, the corrosion-resistant mortar material includes, by weight: 0.7 parts of cement, 0.2 parts of active admixture (ash fly ash: mineral powder = 1:1), 1.4 parts of quartz sand, 0.005 parts of polycarboxylate and 0.3 parts of water. The volume ratio of basalt fiber to corrosion-resistant mortar material is: 0.007:1.

[0036] This embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe, please refer to Example 1.

[0037] Example 3

[0038] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer includes a corrosion-resistant mortar material and basalt fiber. Among them, the corrosion-resistant mortar material includes, by weight: 0.5 parts of cement, 0.5 parts of active admixture (ash fly ash: mineral powder = 1:1), 1 part of quartz sand, 0.008 parts of polycarboxylate and 0.2 parts of water. The volume ratio of basalt fiber to corrosion-resistant mortar material is: 0.012:1.

[0039] This embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe, please refer to Example 1.

[0040] Example 4

[0041] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, comprising a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer comprises a corrosion-resistant mortar material and ultrafine steel fibers. Among them, the corrosion-resistant mortar material comprises, by weight: 0.7 parts of cement, 0.5 parts of active admixture (silica fume: microspheres = 1:1), 0.8 parts of quartz sand, 0.02 parts of polycarboxylate and 0.18 parts of water. The volume ratio of ultrafine steel fibers to corrosion-resistant mortar materials is: 0.015:1.

[0042] This embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe. Please refer to Example 1. The difference from Example 1 is that the fluidity index of the mortar is an expansion of 650 mm.

[0043] Example 5

[0044] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer includes a corrosion-resistant mortar material and polyvinyl alcohol fiber. Among them, the corrosion-resistant mortar material includes, by weight: 0.5 parts of cement, 0.35 parts of active admixture (silica fume: mineral powder = 1:1), 1.1 parts of natural sand, 0.02 parts of polycarboxylate and 0.17 parts of water. The volume ratio of polyvinyl alcohol fiber to corrosion-resistant mortar material is: 0.018:1.

[0045] This embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe. Please refer to Example 1. The difference from Example 1 is that the fluidity index of the mortar is an expansion of 650 mm.

[0046] Example 6

[0047] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer includes a corrosion-resistant mortar material and polypropylene fiber. Among them, the corrosion-resistant mortar material includes, by weight: 0.35 parts of cement, 0.3 parts of active admixture (silica fume: microbeads = 1:1), 1.4 parts of natural sand, 0.008 parts of polycarboxylate and 0.16 parts of water. The volume ratio of polypropylene fiber to corrosion-resistant mortar material is: 0.022:1.

[0048] This embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe. Please refer to Example 1. The difference from Example 1 is that the fluidity index of the mortar is an expansion of 500 mm.

[0049] Example 7

[0050] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer includes a corrosion-resistant mortar material and basalt fiber. Among them, the corrosion-resistant mortar material includes, by weight: 0.35 parts of cement, 0.3 parts of active admixture (ash fly ash: mineral powder = 1:1), 1.4 parts of quartz sand, 0.008 parts of polycarboxylate and 0.16 parts of water. The volume ratio of basalt fiber to corrosion-resistant mortar material is: 0.022:1.

[0051] This embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe. Please refer to Example 1. The difference from Example 1 is that the fluidity index of the mortar is an expansion of 560 mm.

[0052] Example 8

[0053] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer includes a corrosion-resistant mortar material and basalt fiber. Among them, the corrosion-resistant mortar material includes, by weight: 0.5 parts of cement, 0.35 parts of active admixture (ash fly ash: mineral powder = 1:1), 1.1 parts of quartz sand, 0.02 parts of polycarboxylate and 0.17 parts of water. The volume ratio of basalt fiber to corrosion-resistant mortar material is: 0.018:1.

[0054] This embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe. Please refer to Example 1. The difference from Example 1 is that the fluidity index of the mortar is an expansion of 650 mm.

[0055] Example 9

[0056] The present embodiment provides a corrosion-resistant prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer includes a corrosion-resistant mortar material and basalt fiber. Among them, the corrosion-resistant mortar material includes, by weight: 0.7 parts of cement, 0.5 parts of active admixture (ash fly ash: mineral powder = 1:1), 0.8 parts of quartz sand, 0.004 parts of polycarboxylate and 0.18 parts of water. The volume ratio of basalt fiber to corrosion-resistant mortar material is: 0.015:1.

[0057] This embodiment also provides a method for manufacturing a corrosion-resistant prestressed steel tube concrete pipe. Please refer to Example 1. The difference from Example 1 is that the fluidity index of the mortar is an expansion of 650 mm.

[0058] Comparative Example 1

[0059] This comparative example provides a common prestressed steel cylinder concrete pipe, including a concrete pipe core and a protective layer arranged from the inside to the outside. The protective layer includes a dry hard cement mortar material. The dry hard cement mortar material includes, by weight, 0.33 parts of cement, 1.0 parts of natural sand and 0.24 parts of water.

[0060] The comparative example also provides a method for manufacturing a common prestressed steel tube concrete pipe, comprising: (1) positioning a concrete pipe core wrapped with prestressed steel bars and rotating it; mixing dry hard mortar raw materials evenly to obtain mortar, and then pouring the mortar into a roller spraying device; (2) roller spraying the mortar onto the surface of the rotating concrete pipe core to form a protective layer with a thickness of 25 mm; (3) after roller spraying, naturally sprinkling water on the concrete pipe core to maintain moisture retention.

[0061] Comparative Example 2

[0062] The comparative example provides a common prestressed steel cylinder concrete pipe, comprising a concrete pipe core and a protective layer arranged in sequence from the inside to the outside. The protective layer comprises a dry hard cement mortar material. The dry hard cement mortar material comprises, by weight, 0.4 parts of cement, 1 part of artificial sand, and 0.22 parts of water.

[0063] This comparative example also provides a method for manufacturing a common prestressed steel tube concrete pipe, please refer to comparative example 1.

[0064] Experimental Example 1

[0065] Experimental method: The corrosion-resistant prestressed steel cylinder concrete pipes manufactured by the manufacturing methods provided in the test examples 1-9 and the comparative examples 1-2 were tested for compressive strength at 28 days (tested according to the method provided in "GB / T50081 (current version)"), water absorption (tested according to the method provided in "GB / T50081 (current version)"), chloride ion permeability resistance (tested according to the method provided in "GB / T50082 (current version)") (RCM method)), sulfate erosion resistance (tested according to the method provided in "GB / T50082 (current version)"), and tensile strength (tested according to the method provided in "GB / T50081 (current version)"), and the test results are shown in Table 1:

[0066] Table 1

[0067]

[0068] It can be seen from the data in Table 1 that the corrosion-resistant prestressed steel cylinder concrete pipe and the manufacturing method thereof provided by Examples 1-9 of the present invention have a compressive strength of not less than 60 MPa, a tensile strength of not less than 5.0 MPa, a water absorption rate of not more than 3%, and a chloride ion permeability coefficient of not more than 0.8×10 -12 m 2 / s, and the sulfate corrosion resistance grade is not less than KS150. Compared with the dry hard cement mortar layer (water absorption rate is not more than 9%, 28-day cubic compressive strength is not less than 45MPa) manufactured by the roller spraying process currently used, the corrosion-resistant prestressed steel cylinder concrete pipe provided by the embodiment of the present invention has very excellent corrosion resistance and crack resistance, and can maintain good working performance for a long time in a moderate or even severe corrosion environment without relying on other anti-corrosion measures.

[0069] At the same time, the data of comparative examples 1 and 2 further illustrate that the corrosion-resistant prestressed steel tube concrete pipe prepared within the components of the corrosion-resistant mortar material and its ratio range, the ratio range of the corrosion-resistant mortar material and the fiber, and the fluidity extension range provided in Examples 1-9 of the present invention has more excellent corrosion resistance and crack resistance.

[0070] In summary, the corrosion-resistant prestressed steel cylinder concrete pipe provided by the present invention has a protective layer with a compressive strength of not less than 60MPa, a tensile strength of not less than 5.0MPa, a water absorption rate of not more than 3%, and a chloride ion permeability coefficient D RCM No more than 0.8×10 -12 m 2 / s, and the sulfate corrosion resistance level is not less than KS150. It has the ability to maintain good working performance for a long time in moderate or even severe corrosion environments, without relying on other anti-corrosion measures, and the service life in the above corrosion environment can reach more than 50 years, or even 100 years. The manufacturing method of the corrosion-resistant prestressed steel tube concrete pipe provided by the present invention effectively solves the problems of production cost, production efficiency, production quality assurance, etc. of the PCCP corrosion-resistant protective layer, and has the advantages of low production cost, high production efficiency, and guaranteed production quality. It can not only replace the traditional dry hard cement mortar protective layer production process, but also has better cost and efficiency performance than the mold casting process, and is suitable for large-scale promotion and application.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A corrosion-resistant prestressed steel cylinder concrete pipe, characterized in that: It includes a concrete pipe core and a protective layer arranged in sequence from the inside to the outside; The protective layer includes corrosion-resistant mortar material and fibers; The corrosion-resistant mortar material comprises, by weight, 0.3-0.7 parts of cement, 0.2-0.5 parts of active admixture, 0.7-1.4 parts of fine aggregate, 0.005-0.04 parts of admixture and 0.15-0.3 parts of water; the volume ratio of the fiber to the corrosion-resistant mortar material is 0.007-0.025:

1.

2. The corrosion-resistant prestressed steel cylinder concrete pipe according to claim 1, characterized in that: The diameter of the fibers is less than 0.2 mm.

3. The corrosion-resistant prestressed steel cylinder concrete pipe according to claim 2, characterized in that: The fibers include at least one of metal fibers and non-metal fibers.

4. The corrosion-resistant prestressed steel cylinder concrete pipe according to claim 3, characterized in that: The non-metallic fiber includes at least one of synthetic fiber, basalt fiber and glass fiber.

5. The corrosion-resistant prestressed steel cylinder concrete pipe according to claim 1, characterized in that: The active admixture includes at least two of fly ash, mineral powder, silica fume, microspheres and expansion agent.

6. The corrosion-resistant prestressed steel cylinder concrete pipe according to claim 1, characterized in that: The fine aggregate includes at least one of quartz sand, natural sand and artificial sand.

7. The corrosion-resistant prestressed steel cylinder concrete pipe according to claim 1, characterized in that: The admixture is an admixture that has the effect of reducing water and improving pumping effect.

8. The corrosion-resistant prestressed steel cylinder concrete pipe according to claim 1, characterized in that: The cement grade is higher than or equal to grade 42.

5.

9. The corrosion-resistant prestressed steel cylinder concrete pipe according to claim 1, characterized in that: The thickness of the protective layer is greater than or equal to 20 mm.

10. A method for manufacturing the corrosion-resistant prestressed steel cylinder concrete pipe according to claims 1 to 9, characterized in that: include: (1) positioning the concrete pipe core wrapped with prestressed steel bars and placing it in a rotating state; The corrosion-resistant mortar material and the fiber are uniformly mixed until the fluidity index thereof is an expansion degree of 500-650 mm to obtain mortar, and then the mortar is poured into a pumping station; (2) spraying the mortar onto the surface of the rotating concrete pipe core to form the protective layer; (3) After the spraying is completed, the concrete pipe core is subjected to natural moisturizing curing or accelerated curing.

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