Underwater concrete test piece forming device and method for low-temperature sand-containing water flow

Abstract

The invention discloses a low-temperature sand-containing water flow underwater concrete test piece forming device which comprises a circulating constant-temperature water tank, a stirring device, a test water tank and a water pump, a water tank cover plate is arranged on the circulating constant-temperature water tank, a material opening is formed in the water tank cover plate, and the stirring device is arranged on the water tank cover plate. The circulating constant-temperature water tank is connected with the bottom of the test water tank through a water conveying pipe, the test water tank is provided with a tail water gate, and a tail water pool is arranged below the tail water gate. The forming method comprises the following steps of S1, experiment preparation; s2, refrigerating the materials; s3, mixing and stirring; s4, injecting water into the test water tank; s5, recording parameters; s6, test mold pouring; s7, trowelling and calendaring the test mold; s8, demolding and curing; and S9, detecting the test piece. The device is suitable for forming an underwater concrete test piece under the condition of low-temperature sand-containing water flow, the water temperature is pre-cooled through the circulating constant-temperature water tank, the sediment concentration is simulated through sand adding, uniform distribution of the sediment concentration is ensured through stirring, and the underwater cast-in-place environment can be truly simulated.

Description

Technical Field

[0001] This invention relates to the field of underwater concrete performance testing technology, specifically to a device and method for molding concrete specimens in low-temperature sandy water flow. Background Technology

[0002] Currently, the preparation of underwater-formed concrete specimens mainly refers to the "Test Procedure for Underwater Non-Dispersible Concrete" (DL / T 5117-2021). The specific test steps and requirements are as follows: First, place the mold with the opening facing upwards in the water tank and pour in an appropriate amount of water, ensuring the water level is 150mm from the top of the mold. Next, cover the small end of the inverted slump cone with a cover plate, and fill the inverted slump cone with the prepared concrete mixture to 2 / 3 of its height. Then, move the slump cone above the water surface, aligning the small end with the underwater mold. Open the cover plate to allow the concrete mixture to fill the upper part of the mold opening, forming a small mound shape. Each mold must be filled within 60 seconds. Afterward, slowly remove the mold filled with concrete mixture from the water and allow it to stand in the air for 10-15 minutes. Gently tap each of the four corners of the mold 6-8 times with a rubber mallet. To promote drainage, the surface of the mold is smoothed and polished. The smoothed mold is then placed in a standard curing chamber and demolded after 1 day. The demolded specimens must be placed in water for curing, maintaining a certain distance between them. Three specimens are used as a group for each curing age. If the underwater water temperature at the pouring site is below 10℃, it is advisable to use the same underwater temperature as the site conditions for curing. After the specimens reach the specified curing age, they are removed from the water for testing. The above underwater pouring method can be referenced. Figure 1 . In the relevant technical field, Chinese Patent Publication No. CN116973195A discloses an apparatus and method for molding underwater concrete specimens under dynamic water conditions. This apparatus and method can simulate the influence of water flow velocity on concrete performance to a certain extent. However, such apparatus and methods only focus on the effect of dynamic water factors on underwater concrete pouring and molding, without considering the influence of sand-containing water flow and low water temperature environment on the molding of underwater concrete specimens, and have obvious technical limitations. Meanwhile, traditional indoor underwater concrete specimen molding methods typically place the mold in a still water environment, considering only a single water pressure condition, which cannot match the complex environment of actual underwater concrete pouring. In real engineering scenarios, underwater concrete pouring is not only affected by dynamic water but also often faces the combined influence of multiple environmental factors such as low-temperature, sandy water flow. Low temperatures slow down the cement hydration process, thus affecting the normal development of concrete strength; while the sediment carried by the water flow can alter the composition and density of the concrete, causing its performance to deviate from design expectations. Therefore, concrete specimens molded solely under still water conditions or a single dynamic water factor have significant limitations in performance characterization, failing to accurately reflect the actual state of concrete in complex field environments and thus unable to provide accurate basis for engineering quality assessment. Furthermore, during underwater concrete construction, especially in complex environments with both low temperatures and sand content, concrete faces multiple adverse effects when poured into the casting surface via tremie pipe or drop pouring methods. Firstly, water erosion leads to the loss of cementitious materials from the concrete. Secondly, the low temperature environment delays concrete setting and hardening. Additionally, sandy water flow can damage the homogeneity of the concrete and the structure of the casting interface. These factors combined affect freshly mixed concrete, impacting not only its workability and initial structure formation but also its later mechanical properties and durability. Therefore, simulating low-temperature, sandy water flow conditions in indoor experiments for underwater concrete specimen molding is crucial for accurately evaluating the quality and long-term performance of underwater concrete in actual engineering projects. Currently, domestic research on the effects of low water temperature and sandy water flow on the performance of underwater concrete is insufficient, and there is a lack of indoor underwater concrete specimen molding devices and testing methods capable of simulating such environments. To systematically reveal the performance evolution laws of underwater concrete under the combined effects of multiple factors and to provide a reliable basis for its scientific application in practical engineering, it is urgent to develop an indoor underwater concrete specimen molding device and method capable of simulating low water temperature and sandy water flow conditions, thereby improving the realism and accuracy of experimental simulations and filling the existing technological gaps. Summary of the Invention

[0003] The purpose of this invention is to provide a device and method for molding concrete specimens in low-temperature sandy water flow, addressing the aforementioned problems.

[0004] The technical solution of this invention: An apparatus for molding concrete specimens underwater in low-temperature sandy water flow includes a circulating constant-temperature water tank, a mixing device, a test water tank, and a water pump. The circulating constant-temperature water tank is equipped with a water tank cover plate, and a material inlet is provided on the water tank cover plate. The mixing device is located on the water tank cover plate. The circulating constant-temperature water tank is connected to the bottom of the test water tank through a water supply pipe. The test water tank is equipped with a tailwater gate, and a tailwater pool is located below the tailwater gate. The bottom of the tailwater pool is connected to the circulating constant-temperature water tank through a return water pipe. A control switch is provided on the circulating constant-temperature water tank.

[0005] The stirring device includes a motor, a stirring shaft, stirring blades, and a motor bracket. The motor bracket is mounted on the water tank cover plate, the motor is mounted on the motor bracket, the stirring shaft is connected to the motor via a coupling, and the stirring blades are fixedly connected to the stirring shaft and positioned inside the water tank within the circulating constant temperature water bath via the stirring shaft.

[0006] The test water tank is equipped with an overflow weir, a flow guide grid, a flow velocity meter, a sediment content meter, a water temperature meter, a display, a slump cylinder, and a test mold. The overflow weir is located inside the test water tank near one end of the water supply pipe. The flow guide grid is located at the rear end of the overflow weir. The flow velocity meter, sediment content meter, and water temperature meter are located at the front end of the test mold and are coupled to the display. A slump cylinder is located directly above the test mold and is fixedly mounted on the test water tank by a fixing bracket.

[0007] The slump cone is used to hold underwater concrete. A draw plate is provided at the bottom of the slump cone. A fixed support is provided on the test water tank. The flow rate measuring instrument, sediment content measuring instrument and water temperature measuring instrument are installed inside the test water tank through the fixed support.

[0008] The tailrace gate is connected to the bottom of the test tank via a bottom pivot. An upper pivot is provided on the tailrace gate, and a steel wire rope is connected to the upper pivot. A fixing buckle is provided on the test tank to facilitate the fixing of the steel wire rope.

[0009] Both the water supply pipe and the return pipe are equipped with water pumps.

[0010] A method for molding concrete specimens underwater in low-temperature sandy water flow includes the following steps: S1: Experimental preparation. Based on the environment of the underwater concrete pouring point, determine the target water temperature, flow rate and sediment concentration for the experiment. Pour water into the circulating constant temperature water tank, calculate the initial sediment dosage based on the target sediment concentration, and add it to the water tank through the material outlet. S2: Material cooling, set the target temperature, start the operation of the circulating constant temperature water tank, and cool the water and sediment inside the circulating constant temperature water tank; S3: Mix and stir. After the water temperature drops to the target temperature, turn on the stirring device and stir for 4-6 minutes to mix the mud and water evenly. S4: Fill the test water tank with water, turn on the water pump on the water supply pipe to supply water to the test water tank, and adjust the height of the tailwater gate so that the water level in the test water tank reaches the working water level H1. S5: Record parameters, adjust the flow rate of the water supply pipe so that the flow velocity measured and displayed by the flow velocity meter reaches the simulated flow velocity and stabilizes for 0.8-1.2 minutes. Record the readings of the water temperature detector and the sediment content detector at this time. S6: Casting the test mold. Fix the test mold in the water tank. Cover the small end of the inverted slump cone with a pull plate. Fill the prepared concrete mixture into 2 / 3 of the height of the inverted slump cone. Then move the slump cone to the water surface, align the small end with the test mold, pull open the pull plate, and pour the concrete mixture into the upper part of the test mold opening to form a pointed cone shape. S7: Smooth and polish the test mold, take out the test mold filled with concrete mixture, let it stand in the air for 10 to 15 minutes, tap the four top corners of the test mold 6 to 8 times each, and smooth and polish the surface of the test mold. S8: Demolding and curing. Place the smoothed mold into the standard curing room and demold after 1 day. Then, place the demolded specimen in water for curing. S9: Specimen testing. Three specimens of the same age are grouped together and cured in water. When the specified age is reached, the specimens are taken out for testing.

[0011] In step S6, the concrete mix for each test mold is filled within 60 seconds.

[0012] In step S7, a rubber mallet is used to strike the object.

[0013] In step S8, when the underwater water temperature at the pouring site is below 10℃, the water is cured in water at the same underwater temperature as the site conditions.

[0014] The beneficial effects of this invention are: This invention is applicable to the molding of underwater concrete specimens under low-temperature sandy water flow conditions. It can realistically simulate the underwater on-site pouring environment and demonstrate the influence of multiple factors on the underwater concrete pouring process, workability, and quality.

[0015] This invention uses a circulating constant temperature water tank to pre-cool the water temperature, adds sand to simulate the concentration of silt, stirs to ensure uniform distribution of silt concentration, and uses a flow rate measuring instrument, a silt content measuring instrument, and a water temperature measuring instrument to read the data in real time, thus realistically simulating the underwater on-site pouring environment.

[0016] This invention determines the target value based on the working conditions, adds sand to a constant-temperature water tank and pre-cools it to the target temperature, starts stirring to ensure uniform mud and sand, adjusts the water flow and water level to a stable state, performs underwater pouring, and then carries out long-term curing under the same environmental conditions. This invention is simple and effective to operate, and provides experimental support for future research on underwater concrete. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of traditional underwater non-dispersible concrete pouring; Figure 2 This is a schematic diagram of the structure of the present invention. Figure 1 ; Figure 3 This is a schematic diagram of the structure of the present invention. Figure 2 ; Figure 4 This is an enlarged structural schematic diagram of the test water tank part of the present invention; Figure 5 This is an enlarged structural schematic diagram of the stirring device part of the present invention.

[0018] Attached reference numerals: 1-Circulating constant temperature water tank, 2-Control switch, 3-Material inlet, 4-Water tank, 5-Motor, 6-Agitator shaft, 7-Mixing blades, 8-Water tank cover, 9-Motor bracket, 10-Water pump, 11-Overflow weir, 12-Guide grid, 13-Flow velocity meter, 14-Sediment content meter, 15-Water temperature detector, 16-Fixed bracket one, 17-Display, 18-Fixed bracket two, 19-Slump cone, 20-Underwater concrete, 21-Draw-out plate, 22-Bottom rotating shaft, 23-Tailgate, 24-Upper rotating shaft, 25-Wire rope, 26-Fixing buckle, 27-Tailgate pool, 28-Return water pipe, 29-Test mold, 30-Test water tank. Detailed Implementation

[0019] refer to Figures 2-5 A device for molding concrete specimens underwater in low-temperature sandy water flow includes a circulating constant temperature water tank 1, a stirring device, a test water tank 30, and a water pump 10. The circulating constant temperature water tank 1 is equipped with a water tank cover plate 8, and a material inlet 3 is provided on the water tank cover plate 8. The stirring device is provided on the water tank cover plate 8. The circulating constant temperature water tank 1 is connected to the bottom of the test water tank 30 through a water supply pipe. The test water tank 30 is equipped with a tailwater gate 23. A tailwater pool 27 is provided below the tailwater gate 23. The bottom of the tailwater pool 27 is connected to the circulating constant temperature water tank 1 through a return water pipe 28. A control switch 2 is provided on the circulating constant temperature water tank 1.

[0020] In this application, the circulating constant temperature water tank 1 can be a constant temperature water tank produced by Changzhou Jintan Liangyou Instrument Co., Ltd., model HH-DW-525L, with a temperature control range of -5~99℃, microcomputer intelligent temperature control, constant temperature accuracy of ±0.1℃, and constant temperature fluctuation of ±0.1℃. The water tank cover 8 is made of high-strength metal cover plate, with a polyurethane insulation layer attached underneath, which helps to maintain constant temperature. The setting of the feed port 3 facilitates timely water replenishment and sand addition.

[0021] The stirring device includes a motor 5, a stirring shaft 6, stirring blades 7, and a motor bracket 9. The motor bracket 9 is mounted on the water tank cover plate 8, the motor 5 is mounted on the motor bracket 9, the stirring shaft 6 is connected to the motor 5 via a coupling, and the stirring blades 7 are fixedly connected to the stirring shaft 6 and are disposed in the water tank 4 inside the circulating constant temperature water tank 1 via the stirring shaft 6.

[0022] In this application, the motor 5 can be equipped as needed to provide the power required for stirring. The stirring shaft 6 is made of metal and supports the stirring blades 7 to realize the stirring function. The stirring shaft 6 and the motor 5 are connected by a coupling to transmit power. The motor bracket 9 is welded from steel plates to support the entire stirring device.

[0023] The test water tank 30 is equipped with an overflow weir 11, a flow guide grid 12, a flow velocity meter 13, a sediment content meter 14, a water temperature detector 15, a display 17, a slump cylinder 19, and a test mold 29. The overflow weir 11 is located inside the test water tank 30 near one end of the water supply pipe. The flow guide grid 12 is located at the rear end of the overflow weir 11. The flow velocity meter 13, the sediment content meter 14, and the water temperature detector 15 are located at the front end of the test mold 29 and are coupled to the display 17. The slump cylinder 19 is located directly above the test mold 29 and is fixedly mounted on the test water tank 30 by a fixing bracket 2 18.

[0024] The guide grid 12 installed at the rear end of the overflow weir 11 is made of small squares of polyethylene material, which can make the water flow at the outlet smooth and fully dissipate energy, ensuring stable flow velocity.

[0025] The slump cone 19 is used to hold underwater concrete 20. A draw plate 21 is provided at the bottom of the slump cone 19. A fixed bracket 16 is provided on the test water tank 30. The flow rate measuring instrument 13, the sediment content measuring instrument 14 and the water temperature measuring instrument 15 are installed inside the test water tank 30 through the fixed bracket 16.

[0026] The flow velocity meter 13, sediment content meter 14, water temperature meter 15, and display 17 in this application can directly measure the water temperature, flow velocity, and sediment content during underwater concrete forming, simulating the actual on-site construction environment. The flow velocity meter 13 can be an LS3000A portable flow meter, the water temperature meter 15 can be a Teens TA612C thermometer, the sediment content meter 14 can be a LianCe MLSS sludge concentration meter, and the display 17 is used to display the water temperature, flow velocity, and sediment concentration in real time. The fixed bracket 16 is made of stainless steel and is fixed to the upper end of the water tank, providing a fixed support point for the flow velocity meter 13, sediment content meter 14, and water temperature meter 15.

[0027] In this application, the slump cone 19 is the slump cone specified in the "Test Procedure for Underwater Non-Dispersible Concrete" DL / T 5117-2021, with a lower diameter of 100mm and an upper diameter of 200mm, and is a truncated conical cylinder made of thick sheet metal. The slump cone 19 is spot-welded to a stainless steel fixing bracket 18. A removable iron pull plate 21 with a circular cross-section is provided at the bottom of the discharge port of the slump cone 19 to control the concrete discharge. The test mold 29 is placed upright at the lower part of the discharge port of the slump cone 19 to form underwater concrete specimens.

[0028] The tailrace gate 23 is connected to the bottom of the test tank 30 via a bottom pivot 22. An upper pivot 24 is provided on the tailrace gate 23, and a steel wire rope 25 is connected to the upper pivot 24. A fixing buckle 26 is provided on the test tank 30 to facilitate the fixing of the steel wire rope 25.

[0029] In this application, the tailrace gate 23 is made of a wooden baffle plate. The wooden baffle plate is used to block water. The bottom rotating shaft is rotated by the release and retraction of the steel wire rope 25, which is used to flip the tailrace gate 23 and adjust and control the water level of the test water tank 30.

[0030] In this application, the test mold 29 is made of cast iron, and different molding test molds can be selected according to the requirements, such as compression test molds, freeze-thaw test molds, impact and abrasion test molds, etc.

[0031] Both the water supply pipe and the return pipe 28 are equipped with water pumps 10. The water pumps 10 are used for circulating water to ensure a stable water flow, and the water pumps 10 are variable frequency pumps, which can control the flow rate.

[0032] In this application, the test water tank 30 adopts a tempered glass structure and is covered with a polyurethane insulation layer. The PVC water pipe connected to the water inlet of the test water tank 30 and the overflow weir 11 set at the front end of the water tank can work with the variable frequency water pump 10 to precisely control the inlet flow rate and adjust the flow velocity of the water inside the test water tank 30.

[0033] A method for molding concrete specimens underwater in low-temperature sandy water flow includes the following steps: S1: Experimental preparation. Based on the environment of the underwater concrete pouring point, determine the target water temperature, flow rate and sediment concentration for the experiment. Add water to the circulating constant temperature water tank 1. Calculate the initial sediment dosage based on the target sediment concentration and add it to the water tank 4 through the material outlet 3. S2: Material cooling, set the target temperature, start the operation of the circulating constant temperature water tank 1 to cool the water and sediment inside the circulating constant temperature water tank 1; S3: Mix and stir. After the water temperature drops to the target temperature, turn on the stirring device and stir for 4-6 minutes to mix the mud and water evenly. In this application, the stirring time is preferably 5 minutes.

[0034] S4: Fill the test water tank with water, turn on the water pump 10 on the water supply pipe to supply water to the test water tank 30, so that water enters the test water tank 30, adjust the height of the tailwater gate 23 so that the water level in the test water tank 30 reaches the working water level H1; In this application, the working water level H1 is calculated from the height of the test mold plus the height of the concrete poured into the formwork.

[0035] S5: Record parameters, adjust the flow rate of the water supply pipe so that the flow velocity value measured and displayed by the flow velocity meter 13 reaches the simulated flow velocity and stabilizes for 0.8-1.2 minutes. Record the readings of the water temperature meter 15 and the sediment content meter 14 at this time. In this application, the simulated flow velocity stabilization time is preferably 1 minute, and the flow velocity variation during this period shall not exceed 1%. The readings of the water temperature detector and sediment content analyzer at this time shall be recorded, and the difference from the test target shall not exceed 5%.

[0036] S6: Casting the test mold. Fix the test mold in the water tank. Cover the small end of the inverted slump cone 19 with the pull plate 21. Fill the prepared concrete mixture into 2 / 3 of the height of the inverted slump cone 19. Then move the slump cone 19 to the water surface, align the small end with the test mold 29, and pull open the pull plate 21 to pour the concrete mixture into the upper part of the test mold 29 to form a pointed cone shape. S7: Smooth and polish the test mold, take out the test mold 29 filled with concrete mixture, let it stand in the air for 10 to 15 minutes, tap the four top corners of the test mold 29 6 to 8 times each, and smooth and polish the surface of the test mold 29. S8: Demolding and curing. Place the smoothed mold 29 into the standard curing room. Demold after 1 day. Place the demolded specimen in water for curing. S9: Specimen testing. Three specimens of the same age are grouped together and cured in water. Upon reaching the specified age, the specimens are removed and tested. (Reference) Figure 1 .

[0037] In step S6, the concrete mix for each test mold 29 is filled within 60 seconds.

[0038] In step S7, a rubber mallet is used to strike the object.

[0039] In step S8, when the underwater water temperature at the pouring site is below 10℃, the water is cured in water at the same underwater temperature as the site conditions.

Claims

1. A device for molding concrete specimens underwater in low-temperature sandy water, characterized in that: The system includes a circulating constant temperature water tank (1), a stirring device, a test water tank (30), and a water pump (10). The circulating constant temperature water tank (1) is equipped with a water tank cover plate (8), and the water tank cover plate (8) is provided with a material inlet (3). The stirring device is located on the water tank cover plate (8). The circulating constant temperature water tank (1) is connected to the bottom of the test water tank (30) through a water supply pipe. The test water tank (30) is equipped with a tailwater gate (23). A tailwater pool (27) is located below the tailwater gate (23). The bottom of the tailwater pool (27) is connected to the circulating constant temperature water tank (1) through a return water pipe (28). A control switch (2) is provided on the circulating constant temperature water tank (1).

2. The apparatus for molding concrete specimens underwater in low-temperature sandy water as described in claim 1, characterized in that: The stirring device includes a motor (5), a stirring shaft (6), stirring blades (7) and a motor bracket (9). The motor bracket (9) is installed on the water tank cover (8), the motor (5) is installed on the motor bracket (9), the stirring shaft (6) is connected to the motor (5) through a coupling, the stirring blades (7) are fixedly connected to the stirring shaft (6), and are set in the water tank (4) inside the circulating constant temperature water tank (1) through the stirring shaft (6).

3. The apparatus for molding concrete specimens underwater in low-temperature sandy water as described in claim 1, characterized in that: The test tank (30) is equipped with an overflow weir (11), a flow guide grid (12), a flow velocity meter (13), a sediment content meter (14), a water temperature meter (15), a display (17), a slump cylinder (19), and a test mold (29). The overflow weir (11) is located inside the test tank (30) near the end of the water supply pipe. The flow guide grid (12) is located at the rear end of the overflow weir (11). The flow velocity meter (13), the sediment content meter (14), and the water temperature meter (15) are located at the front end of the test mold (29) and are coupled to the display (17). The slump cylinder (19) is located directly above the test mold (29). The slump cylinder (19) is fixedly mounted on the test tank (30) by a fixed bracket (18).

4. The apparatus for molding concrete specimens underwater in low-temperature sandy water as described in claim 3, characterized in that: The slump cone (19) is used to hold underwater concrete (20). A draw plate (21) is provided at the bottom of the slump cone (19). A fixed bracket (16) is provided on the test water tank (30). The flow rate measuring instrument (13), the sediment content measuring instrument (14) and the water temperature measuring instrument (15) are installed inside the test water tank (30) through the fixed bracket (16).

5. The apparatus for molding concrete specimens underwater in low-temperature sandy water as described in claim 1, characterized in that: The tailrace gate (23) is connected to the bottom of the test tank (30) via a bottom pivot (22). An upper pivot (24) is provided on the tailrace gate (23), and a steel wire rope (25) is connected to the upper pivot (24). A fixing buckle (26) is provided on the test tank (30) to facilitate the fixing of the steel wire rope (25).

6. The apparatus for molding concrete specimens underwater in low-temperature sandy water flow according to claim 1, characterized in that: Water pumps (10) are installed on both the water supply pipe and the return pipe (28).

7. The method for molding concrete specimens underwater in low-temperature sandy water flow according to claims 1-6, characterized in that: Includes the following steps: S1: Experimental preparation: Based on the environment of the underwater concrete pouring point, determine the target water temperature, flow rate and sediment concentration for the experiment, inject water into the circulating constant temperature water tank (1), calculate the initial sediment dosage based on the target sediment concentration, and add it into the water tank (4) through the material outlet (3). S2: Material cooling, set the target temperature, start the operation of the circulating constant temperature water tank (1) to cool the water and mud inside the circulating constant temperature water tank (1); S3: Mix and stir. After the water temperature drops to the target temperature, turn on the stirring device and stir for 4-6 minutes to mix the mud and water evenly. S4: Fill the test water tank with water, turn on the water pump (10) on the water supply pipe to supply water to the test water tank (30) so that water enters the test water tank (30), adjust the height of the tailwater gate (23) so that the water level in the test water tank (30) reaches the working water level H1; S5: Record the parameters, adjust the flow rate of the water supply pipe so that the flow velocity value measured and displayed by the flow velocity meter (13) reaches the simulated flow velocity and stabilizes for 0.8-1.2 min. Record the readings of the water temperature meter (15) and the sediment content meter (14) at this time. S6: Casting the test mold. Fix the test mold in the water tank. Cover the small end of the inverted slump cone (19) with the pull plate (21). Fill the prepared concrete mixture into the inverted slump cone (19) to 2 / 3 of its height. Then move the slump cone (19) to the water surface, align the small end with the test mold (29), and pull open the pull plate (21) to pour the concrete mixture into the upper part of the test mold (29) to form a pointed cone shape. S7: Smooth and polish the test mold, take out the test mold (29) filled with concrete mixture, let it stand in the air for 10 min to 15 min, tap the four top corners of the test mold (29) 6 to 8 times each, smooth and polish the surface of the test mold (29); S8: Demolding and curing. Place the smoothed mold (29) into the standard curing room. Demold after 1 day. Place the demolded specimen in water for curing. S9: Specimen testing. Three specimens of the same age are grouped together and cured in water. When the specified age is reached, the specimens are taken out for testing.

8. The method for molding concrete specimens underwater in low-temperature sandy water flow according to claim 7, characterized in that: In step S6, the concrete mix for each test mold (29) is filled within 60 seconds.

9. The method for molding concrete specimens underwater in low-temperature sandy water flow according to claim 7, characterized in that: In step S7, a rubber mallet is used to strike the object.

10. The method for molding concrete specimens underwater in low-temperature sandy water flow according to claim 7, characterized in that: In step S8, when the underwater water temperature at the pouring site is below 10℃, the water is cured in water at the same underwater temperature as the site conditions.

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