Stone cement mold, forming method and temperature and humidity control creep testing system

Abstract

The invention discloses a set cement mold, a forming method and a temperature and humidity control creep test system, the mold comprises a first workpiece, a second workpiece, an upper cover, a lower cover and a core rod, the first workpiece and the second workpiece are both semicircular, the first workpiece is provided with a groove, the second workpiece is provided with a protrusion, and the upper cover is provided with a groove; the protrusion of the second workpiece is embedded in the groove of the first workpiece to form a hollow cylinder, the upper cover and the lower cover are connected to the upper end and the lower end of the hollow cylinder through threads, through holes are formed in the upper cover and the lower cover in a penetrating mode, the upper cover is provided with an opening used for injection, and the radius of the through holes is the same as that of the core rod. In order to accurately control the temperature and humidity of the environment where the test piece is located in the creep test, the creep test is carried out in the high-precision temperature and humidity control box, and in order to apply a creep load to the test piece in the test box, the small creep frame is designed; uniform and accurate control of the internal temperature and humidity process of the test piece in the macroscopic creep test process is realized.

Description

Technical Field

[0001] This invention relates to the field of cement testing, and in particular to a cement stone specimen mold, molding method, and temperature and humidity controlled creep testing system. Background Technology

[0002] Concrete has the advantages of abundant raw materials, low price, and good molding plasticity, and is widely used in the construction of buildings and bridge structures. Creep is an inherent time-varying behavior of concrete and an important part of concrete structure design and calculation. Concrete creep is mainly caused by the creep of cement paste. Compared with aggregate, cement paste cannot maintain dimensional stability under load.

[0003] Traditional cement stone creep tests involve significant temperature and humidity gradients within the specimen, making it difficult to reflect the creep development pattern of the cement stone material itself under the influence of temperature and humidity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing traditional cement stone creep test process, which is difficult to reflect the creep development law of cement stone material itself under the influence of temperature and humidity. The invention proposes to use thin-walled hollow cylindrical specimens to achieve rapid balance between the internal temperature and humidity of cement stone and the environment, and provides a cement stone mold, molding method and temperature and humidity controlled creep test system.

[0005] The technical solution adopted by the present invention to solve its technical problem is a mold for a thin-walled hollow cylindrical specimen of cement stone, comprising a first workpiece, a second workpiece, an upper cover, a lower cover, and a mandrel. The first workpiece and the second workpiece are both semi-circular rings. The first workpiece has a groove, and the second workpiece has a protrusion. The protrusion of the second workpiece is fitted into the groove of the first workpiece to form a hollow cylinder. The upper cover and the lower cover are connected to the upper and lower ends of the hollow cylinder by threads. Both the upper cover and the lower cover have through holes. The upper cover has an opening for injection. The radius of the through hole is the same as the radius of the mandrel. The mandrel passes through the through hole and is located inside the hollow cylinder.

[0006] Furthermore, the first workpiece, the second workpiece, the upper cover, and the lower cover are all made of brass, and the mandrel is made of polytetrafluoroethylene.

[0007] Furthermore, the length of the core rod is greater than the length of the upper and lower covers connected to the hollow cylinder.

[0008] A further solution to the technical problem of the present invention is a molding method using a cement stone mold, comprising the following steps:

[0009] 1) Assemble the mold: Align the first and second workpieces and engage them with each other. Then, thread the upper cover to one end of the hollow cylinder and thread the lower cover to the other end of the hollow cylinder. Insert the mandrel into the hollow cylinder through the through hole of the upper or lower cover.

[0010] 2) Injecting the grout: After thoroughly mixing the cement grout with a water-cement ratio of 0.40, inject it into the mold through one opening of the top cover. At the same time as injecting, place the mold on a vibrating table to compact it until cement grout oozes out from the opening of the top cover.

[0011] 3) Curing and demolding: Place the mold in the curing chamber marked with a curing label and cure for 24 hours. After that, loosen and remove the top and bottom covers and take out the thin-walled hollow cylindrical specimen.

[0012] 4) Soaking and curing: Wrap the thin-walled hollow cylindrical specimen with a damp cloth soaked in ice water and place it in lime water at 20℃ for 27 days.

[0013] Furthermore, in step 3), before removing the specimen, the specimen and the mold should be soaked together in ice water for 3 minutes to allow the ice water to cause a large contraction through the polytetrafluoroethylene mandrel. Pushing one end of the mandrel can remove the mandrel. Then, pry open the mold and gently remove the thin-walled hollow cylindrical specimen.

[0014] Furthermore, it also includes step 5) grinding the end faces: after curing for 27 days, the two ends of the specimen are ground to obtain parallel end planes, so as to reduce the bending effect during the creep test.

[0015] The solution to further solve the technical problem of the present invention is a cement stone temperature and humidity controlled creep testing system, including a temperature and humidity control box, a small creep frame, a pressure head, and a thin-walled hollow cylindrical specimen. The small creep frame includes connecting bolts, steel plates, pressure sensors, and springs. Two symmetrical pressure heads and steel plates are provided. The pressure head, pressure sensor, spring, and thin-walled hollow cylindrical specimen are all arranged between the two steel plates. The pressure head is located at both ends of the thin-walled hollow cylindrical specimen. The pressure sensor abuts against the lower pressure head. The spring abuts against the pressure sensor and the lower steel plate. The connecting bolts lock the two steel plates and the pressure is adjusted by tightening or loosening the bolts as needed. Strain gauges are attached to both sides of the surface of the thin-walled hollow cylindrical specimen, and the small creep frame and the thin-walled hollow cylindrical specimen are placed inside the temperature and humidity control box.

[0016] Furthermore, the pressure head has spherical grooves, and the spherical grooves on the pressure head are all opposite to the thin-walled hollow cylindrical specimen. The edge of the pressure head is slotted to connect the interior of the thin-walled hollow cylindrical specimen with the environment.

[0017] Furthermore, a sphere is provided between the upper pressure head and the upper steel plate, and the sphere is located in a spherical groove to transmit creep load.

[0018] In summary, the present invention has the following beneficial technical effects:

[0019] Thin-walled hollow cylindrical specimens were fabricated using a specimen mold and a specified molding method. Demolding was achieved without damage during cooling, even with different shrinkage deformations in brass and PTFE materials. Curing and polishing were necessary to minimize bending effects. To precisely control the temperature and humidity of the specimens during creep testing, the creep test was conducted in a high-precision temperature and humidity control chamber. A small creep frame was designed to apply creep loads to the specimens within the chamber, enabling uniform and precise control of the internal temperature and humidity history of the specimens during macroscopic creep testing. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the first workpiece according to an embodiment of a cement stone mold of the present invention;

[0021] Figure 2 This is a schematic diagram of the second workpiece of an embodiment of a cement stone mold according to the present invention;

[0022] Figure 3 This is a schematic diagram of the overall structure of an embodiment of a cement stone mold according to the present invention;

[0023] Figure 4 This is an assembly diagram of an embodiment of a cement stone mold according to the present invention;

[0024] Figure 5 This is a physical image of an embodiment of a cement stone mold according to the present invention;

[0025] Figure 6 This is a schematic diagram of a small creep frame according to an embodiment of a cement stone temperature and humidity control creep testing system of the present invention;

[0026] Figure 7 This is a schematic diagram of the pressure head of a cement stone temperature and humidity controlled creep testing system according to the present invention;

[0027] Figure 8 This is a physical image of the temperature and humidity control box of an embodiment of the cement stone temperature and humidity control creep testing system of the present invention;

[0028] Figure 9 This is an internal schematic diagram of an embodiment of a cement stone temperature and humidity control creep testing system according to the present invention.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1. First workpiece; 11. Groove; 2. Second workpiece; 21. Protrusion; 3. Top cover; 31. Opening; 4. Bottom cover; 5. Mandrel; 6. Connecting bolt; 7. Steel plate; 8. Pressure sensor; 9. Spring; 10. Indenter; 100. Thin-walled hollow cylindrical specimen. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0032] Reference Figures 1 to 5 This embodiment of a specimen mold for testing the creep of cement stone includes a first workpiece 1, a second workpiece 2, an upper cover 3, a lower cover 4, and a mandrel 5. Both the first workpiece 1 and the second workpiece 2 are semi-circular in shape and can be combined to form a ring. Specifically, the first workpiece 1 has a groove 11 on one side relative to the second workpiece 2, and the second workpiece 2 has a protrusion 21 on one side relative to the first workpiece 1. The protrusion 21 of the second workpiece 2 fits into the groove 11 of the first workpiece 1 to interlock and form a hollow cylinder. Simultaneously, both the upper and lower ends of the first workpiece 1 and the second workpiece 2 are threaded, and the upper cover 3 and the lower cover 4 are also threaded. The upper cover 3 and the lower cover 4 are connected to the upper and lower ends of the hollow cylinder via threads. Both the upper cover 3 and the lower cover 4 have through holes. In addition, the upper cover 3 has an opening 31 for injection, and the opening 31 is connected to the through hole. There are two symmetrical openings 31. The radius of the through hole is the same as the radius of the mandrel 5. At the same time, the length of the mandrel 5 is greater than the length of the upper cover 3 and the lower cover 4 connected to the hollow cylinder. The mandrel 5 passes through the through hole and is located inside the hollow cylinder.

[0033] The first workpiece 1, the second workpiece 2, the upper cover 3, and the lower cover 4 are all made of brass, while the mandrel 5 is made of polytetrafluoroethylene (PTFE). Since the temperature shrinkage deformation of PTFE during cooling is about 15 times that of cement slurry and brass, the large volume shrinkage during the cooling process facilitates demolding.

[0034] A method for forming a specimen mold using the above-mentioned cement stone creep test includes the following steps:

[0035] 1) Assemble the mold: Align the first workpiece 1 and the second workpiece 2 and engage them with each other. Then, thread the upper cover 3 to one end of the hollow cylinder and thread the lower cover 4 to the other end of the hollow cylinder. Insert the core rod 5 into the hollow cylinder through the through hole of the upper cover 3 or the lower cover 4.

[0036] 2) Injecting grout: After thoroughly mixing the cement grout with a water-cement ratio of 0.40, inject it into the mold through an opening 31 of the top cover 3. At the same time as injecting, place the mold on a vibrating table to compact it until cement grout emerges from the opening 31 of the top cover 3.

[0037] 3) Curing and demolding: Place the mold in the curing chamber and cure for 24 hours. Then loosen and remove the upper cover 3 and the lower cover 4. Soak the specimen and the mold together in ice water for 3 minutes. Let the ice water cause a large contraction through the polytetrafluoroethylene core rod 5. Push one end of the core rod 5 to remove the core rod 5. Then pry open the mold and gently take out the thin-walled hollow cylindrical specimen 100.

[0038] 4) Soaking and curing: Wrap the thin-walled hollow cylindrical specimen 100 with a damp cloth soaked in ice water and place it in lime water at 20℃ for 27 days; all processes must be done carefully to prevent cracks from being caused by rough handling or sudden temperature changes.

[0039] 5) Grinding the end faces: After curing for 27 days, grind both ends of the specimen to obtain parallel end planes, so as to minimize the bending effect during uniaxial compression creep test.

[0040] Reference Figures 6 to 9 A cement stone creep testing system includes a temperature and humidity control box, a small creep frame, an indenter 10, and a thin-walled hollow cylindrical specimen 100 made by the above molding method. The indenter 10, the thin-walled hollow cylindrical specimen 100, and the small creep frame are assembled together and placed in the temperature and humidity control box for creep testing.

[0041] The small creep tester includes connecting bolts 6, steel plates 7, pressure sensors 8, and springs 9. Two symmetrical pressure heads 10 and steel plates 7 are provided, and the pressure heads 10, pressure sensors 8, springs 9, and thin-walled hollow cylindrical specimen 100 are all positioned between the two steel plates 7. Specifically, the pressure heads 10 are located at both ends of the thin-walled hollow cylindrical specimen 100. The pressure sensors 8 are positioned below the lower pressure head 10, continuously recording the stress on the sample. The springs 9 are positioned between the pressure sensors 8 and the lower steel plate 7. The connecting bolts 6 lock the two steel plates 7 together, and the pressure can be adjusted by tightening or loosening the bolts as needed. Furthermore, strain gauges are attached to both sides of the surface of the thin-walled hollow cylindrical specimen 100 to measure the axial deformation of the specimen, which is collected by a data acquisition device. In addition, the indenter 10 has spherical grooves 11, all of which are opposite to the thin-walled hollow cylindrical specimen 100. Four through slots are formed at the edge of the indenter and are evenly distributed around its axis. These through slots communicate with the spherical grooves 11, allowing the interior of the thin-walled hollow cylindrical specimen to be connected to the environment. A sphere is positioned between the upper indenter 10 and the upper steel plate 7, within the spherical grooves 11 to transfer creep loads and limit potential bending effects. Furthermore, the smoothing of both ends of the thin-walled hollow cylindrical specimen 100 also helps to limit bending effects. The lower indenter 10 and the pressure sensor 8 are connected via grooves 11.

[0042] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Identical components are represented by the same reference numerals. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, while the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component. Therefore, all equivalent changes made to the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A specimen mold for testing the creep of cement stone, characterized in that, The assembly includes a first workpiece (1), a second workpiece (2), an upper cover (3), a lower cover (4), and a mandrel (5). Both the first workpiece (1) and the second workpiece (2) are semi-circular rings. The first workpiece (1) has a groove (11), and the second workpiece (2) has a protrusion (21). The protrusion (21) of the second workpiece (2) is fitted into the groove (11) of the first workpiece (1) to form a hollow cylinder. The upper cover (3) and the lower cover (4) are connected to the upper and lower ends of the hollow cylinder by threads. Both the upper cover (3) and the lower cover (4) have through holes. The upper cover (3) has an opening (31) for injection. The radius of the through hole is the same as the radius of the mandrel (5). The mandrel (5) passes through the through hole and is located inside the hollow cylinder.

2. The specimen mold for testing the creep of cement stone according to claim 1, characterized in that, The first workpiece (1), the second workpiece (2), the upper cover (3), and the lower cover (4) are all made of brass, and the core rod (5) is made of polytetrafluoroethylene.

3. The specimen mold for testing the creep of cement stone according to claim 1, characterized in that, The length of the core rod (5) is greater than the length of the upper cover (3) and lower cover (4) connected to the hollow cylinder.

4. A molding method using a specimen mold for cement stone creep testing as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) Assemble the mold: Align the first workpiece (1) and the second workpiece (2) and engage them with each other. Then, thread the upper cover (3) to one end of the hollow cylinder and thread the lower cover (4) to the other end of the hollow cylinder. Insert the mandrel (5) into the hollow cylinder through the through hole of the upper cover (3) or the lower cover (4). 2) Injecting grout: After thoroughly mixing the cement grout with a water-cement ratio of 0.40, inject it into the mold through an opening (31) of the top cover (3). At the same time as injecting, place the mold on a vibrating table to compact it until cement grout emerges from the opening (31) of the top cover (3). 3) Curing and demolding: Place the mold in the curing chamber and cure for 24 hours. Then loosen and remove the top cover (3) and the bottom cover (4) and take out the thin-walled hollow cylindrical specimen (100). 4) Soaking and curing: Wrap the thin-walled hollow cylindrical specimen (100) with a damp cloth soaked in ice water and place it in lime water at 20℃ for 27 days.

5. The molding method for a specimen mold for testing the creep of cement stone according to claim 4, characterized in that, In step 3), before removing the specimen, the specimen and the mold should be soaked together in ice water for 3 minutes to allow the ice water to cause a large contraction through the polytetrafluoroethylene mandrel (5). Pushing one end of the mandrel (5) will remove the mandrel (5). Then pry open the mold and gently remove the thin-walled hollow cylindrical specimen (100).

6. The molding method for a specimen mold for cement stone creep testing according to claim 4, characterized in that, It also includes step 5) grinding the end faces: after curing for 27 days, the two ends of the specimen are ground to obtain parallel end planes to reduce the bending effect during the creep test.

7. A cement stone creep testing system, characterized in that, The test includes a temperature and humidity control box, a small creep frame, an indenter (10), and a thin-walled hollow cylindrical specimen (100) made using the molding method of the specimen mold for cement stone creep testing as described in claims 4-6. The small creep frame includes connecting bolts (6), steel plates (7), pressure sensors (8), and springs (9). Two symmetrical indenters (10) and steel plates (7) are provided. The indenter (10), pressure sensors (8), springs (9), and thin-walled hollow cylindrical specimen (100) are all located on two steel plates. Between the plates (7), the pressure head (10) is set at both ends of the thin-walled hollow cylindrical specimen (100), the pressure sensor (8) is abutted below the lower pressure head (10), the spring (9) is abutted between the pressure sensor (8) and the lower steel plate (7), the connecting bolt (6) locks the two steel plates (7) and the pressure is adjusted by tightening or loosening the bolt as needed. Strain gauges are attached to both sides of the surface of the thin-walled hollow cylindrical specimen (100), and the small creep frame and the thin-walled hollow cylindrical specimen (100) are placed in a temperature and humidity control box.

8. The cement stone creep testing system according to claim 7, characterized in that, The pressure head (10) has a spherical groove (11), and the spherical groove (11) on the pressure head (10) is opposite to the thin-walled hollow cylindrical specimen (100).

9. A cement stone creep testing system according to claim 7, characterized in that, A sphere is provided between the upper pressure head (10) and the upper steel plate (7), and the sphere is located in the spherical groove (11) to transmit creep load.

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