Asphalt mixture hollow cylindrical specimen static pressure forming instrument and forming method thereof

Abstract

The present invention discloses a static pressure molding instrument for asphalt mixture hollow cylindrical specimens and a molding method thereof, and belongs to the technical field of road engineering material testing. The instrument comprises a load-bearing frame, a power device, a specimen mold, a control system and a demoulding device; the molding method of the instrument comprises three steps of test preparation, static pressure molding and specimen demoulding. The present invention can effectively overcome many shortcomings of the existing asphalt mixture hollow cylindrical specimen molding methods, ensure the quality of the specimens, prepare hollow cylindrical asphalt mixture specimens that meet the compaction requirements and road performance requirements, and are used for triaxial torsional shear tests or other mechanical performance tests, which greatly meets the actual needs.

Description

Technical Field

[0001] The invention belongs to the technical field of road engineering material testing, and relates to a static pressure molding instrument for a hollow cylindrical specimen of an asphalt mixture and a molding method thereof. Background Art

[0002] Asphalt mixture is one of the important pavement construction materials for road engineering. During the pavement structure design stage and the pavement engineering construction stage, laboratory mix design and road performance inspection are the key to ensuring its quality. Limited by the requirements of traditional asphalt mixture test and inspection instruments and equipment, conventional asphalt mixture specimens are solid, and most of them are solid cylinders. For example, in typical test methods such as Marshall stability test, splitting test, shear strength test (triaxial compression method), uniaxial compression dynamic modulus test, uniaxial compression test, etc., the specimen shape is a cylindrical specimen with a diameter of D = 101.6mm (or D = 152.4mm,) and a height of H = 63.5mm (or H = 95.3mm, H = 170mm, etc.) or a cylindrical specimen with a diameter of D = 152.4.6mm and a height of H = 95.3mm or a cylindrical specimen with a diameter of D = 100mm and a height of H = 150mm or a cylindrical specimen with a diameter of D = 100mm and a height of H = 100mm.

[0003] Traditional asphalt mixture test methods are difficult to effectively simulate the stress change characteristics of asphalt pavement structures, especially the complex stress state of the rotation change of the principal stress axis. The key problem is that the test device lacks controllable shear stress application conditions. The torsion-shear triaxial test instruments and test methods that are gradually being used and popularized can not only apply controllable torque, but also use controllable internal and external pressures, thereby realizing a true triaxial test environment and perfectly solving the above problems. However, the main difficulty of the torsion-shear triaxial test method is that if a solid cylindrical specimen is used, the true triaxial test environment cannot be simulated; at the same time, because the shear stress changes along the cross-sectional linear shape, this non-uniformity will have a serious impact on the accurate and effective control of the stress and strain of the specimen. In this regard, the use of hollow cylindrical specimens can ensure the axisymmetric uniformity of the stress of the cross-sectional area of ​​the cylindrical specimen as much as possible, and the torsion-shear triaxial test method can be effectively applied and developed.

[0004] At present, the relevant test procedures for pavement materials lack standard methods for forming hollow cylindrical specimens. The feasible ways to form hollow cylindrical specimens of asphalt mixtures are: 1. Forming solid cylindrical asphalt mixture specimens → forming hollow cylindrical specimens with inner diameters that meet the requirements by drilling once or forming hollow cylindrical specimens with inner and outer diameters that meet the requirements by drilling twice; 2. Forming plate-type asphalt mixture specimens → forming by drilling twice. Their common characteristics are: at least one drilling must be used. Since drilling inevitably involves cooling water spraying, the interior of the specimen is damaged, and it is especially difficult to ensure the integrity of the ends of the specimen. The hollow cylindrical specimens formed in this way all have major quality problems. Summary of the invention

[0005] The purpose of the present invention is to provide a static pressure molding instrument for asphalt mixture hollow cylindrical specimens and a molding method thereof, which can effectively overcome the many shortcomings of the existing asphalt mixture hollow cylindrical specimen molding methods and ensure the quality of the specimens.

[0006] The technical solution adopted by the present invention is:

[0007] The invention discloses a static pressure forming instrument for a hollow cylindrical specimen of an asphalt mixture, which comprises a load-bearing frame, a power device, a specimen mould, a control system and a demoulding device.

[0008] The bearing frame is placed on the platform and is composed of columns and partitions; the columns are composed of column rods and threaded rods; the partitions are composed of bottom partitions, lower bearing plates, middle partitions, upper bearing plates, demoulding holes, and reserved holes for hangers, wherein the bottom partitions, lower bearing plates, and middle partitions are all fixedly connected to the column rods, and the upper bearing plate is sleeved on the threaded rods through reserved holes, and the position can be adjusted up and down, and vertical positioning and fixation are achieved through positioning nuts and bearing nuts; the demoulding hole is located at the center of the upper bearing plate, and the hollow cylindrical specimen will be removed from the demoulding hole when the specimen is demoulded after static pressure molding; the reserved holes for the hangers are symmetrically arranged around the demoulding holes, and are used to install temporary brackets during demoulding;

[0009] The power device is composed of an electric motor, a transmission, a spiral push rod, a tray and a limit block; the transmission is connected to the control system and receives instructions from the control system to control the output speed of the electric motor; the spiral push rod is controlled by the electric motor and can move vertically; the tray is fixedly connected to the spiral push rod, and the limit block is fixed to the upper surface of the tray 12;

[0010] The test piece mold is composed of a lower pad annular base, a test mold outer cylinder, an outer cylinder liner, a test mold inner rod, an inner rod connecting plate, a connecting screw, an annular pressure head, an upper pad and three limit blocks, wherein the limit block and annular limit block I are respectively fixed to the lower surface and upper surface of the lower pad, and the annular limit block II is fixed to the lower surface of the upper pad; the upper end of the pressure sensor is located at the center of the limit block; the annular base is placed at the center of the annular limit block I, the test mold outer cylinder is placed in the annular groove of the annular base, the outer cylinder liner is composed of two symmetrical pieces, which are placed inside the test mold outer cylinder and the annular groove of the annular base, and are at the same height as the test mold outer cylinder, and are always in close contact with the test mold outer cylinder and maintain the same vertical position; the test mold inner rod is composed of two symmetrical pieces, inner rod connecting plates are respectively arranged at both ends, and are fixed to the test mold inner rod by connecting screws. Fixed connection, the inner rod connecting plate located at the bottom end of the inner rod of the test mold is fixedly connected to the annular base through connecting screws; the asphalt mixture is located in the annular, columnar space formed between the inner lining of the outer cylinder and the inner rod of the test mold; the bottom end of the annular pressure head is embedded in the inner lining of the outer cylinder, placed on the asphalt mixture, and passes through the inner rod of the test mold, and can slide up and down. Annular pressure heads of different numbers and thicknesses are used and are vertically limited and contacted by annular limit blocks II to ensure that the upper end surface of the annular pressure head and the lower end surface of the annular limit block III are both higher than the upper end surfaces of the outer cylinder of the test mold and the inner lining of the outer cylinder; the upper pad is placed on the annular pressure head, and the upper surface of the annular pressure head is located at the center of the annular limit block III; at the same time, the annular part of the upper end of the upper pad is tightly embedded in the demoulding hole to ensure that the center of the load-bearing frame, the spiral push rod of the power device, and the test piece mold are aligned;

[0011] The control system is composed of sensors and controllers; the sensors include pressure sensors, displacement sensors, temperature sensors, and contact sensors; the pressure sensor is placed on the upper part of the pallet and is limited at the center of the pallet by a limit block, and its upper end is located at the center of the limit block; the displacement sensor is fixed in the reserved hole of the auxiliary plate, the auxiliary plate is fixedly connected to the pallet, and the upper surface of the middle partition is the relative zero point of the displacement sensor; the temperature sensor is arranged on the outer surface of the outer cylinder of the test mold and inside the annular base; the contact sensor is sleeved on the column rod, fixedly connected to the auxiliary plate, and keeps the vertical displacement synchronous with the spiral top rod, the pallet, and the auxiliary plate; the lower limit The position block and the upper limit block are fixed on the column rod. When the contact piece of the contact sensor contacts the lower limit block or the upper limit block, the control system will instruct the electric motor to stop running and automatically reverse, thereby limiting the vertical movement range of the contact sensor and indirectly controlling the lowest and highest vertical positions of the pallet to ensure that the vertical movement of the spiral push rod is within a safe range; the controller is composed of a signal converter and a program control platform. The pressure sensor, displacement sensor, temperature sensor, contact sensor, and transmission data are all connected to the program control platform through the signal converter. The program control platform completes tasks such as process control, data transmission, processing and analysis, and information interaction;

[0012] The demoulding device is composed of a demoulding rack and a demoulding tool; the demoulding rack comprises a rack base plate, a rack base plate reserved hole, a rack upright rod, and a rack fixing screw, wherein the rack base plate is fixedly connected to the rack upright rod, the rack base plate reserved hole is located at the center of the rack base plate, the rack upright rod passes through the rack reserved hole on the upper bearing plate of the support frame, and is fixed to the upper bearing plate by the rack fixing screw; the demoulding tool is composed of a demoulding base, a demoulding top shaft, and a demoulding top cylinder, wherein the demoulding base is placed on the tray 12 and is located at the center position within the limit block, the demoulding top shaft is eccentrically arranged relative to the demoulding base, and is aligned with one of the two test mold inner rods in the specimen mold; the demoulding top cylinder is placed on the tray, located at the center position outside the limit block, and is aligned with the inner lining of the outer cylinder in the specimen mold.

[0013] The molding method of the above-mentioned static pressure molding instrument for the asphalt mixture hollow cylindrical specimen includes three steps: test preparation, static pressure molding and specimen demoulding. The specific steps are as follows:

[0014] S1 Experimental Preparation:

[0015] ①Prepare the experimental instruments and materials according to the relevant requirements of "Test Procedure for Asphalt and Asphalt Mixture in Highway Engineering JTG E20-2011" "T0704-2011 Asphalt Mixture Specimen Preparation Method (Static Pressure Method)";

[0016] ② The experimental instrument adopts the static pressure forming instrument for asphalt mixture hollow cylindrical specimen of the present invention, and the spiral jack, tray and auxiliary plate are adjusted to a reasonable lower position through the control system to ensure that there is enough operating space above the tray 12 for sensor installation, specimen mold installation, asphalt mixture pouring, etc.; the pressure sensor and the bottom pad are installed;

[0017] ③ The experimental materials mainly include asphalt mixtures, which can include hot mix, room temperature mix, sampling and other types; the asphalt mixture that meets the quantity and temperature requirements is determined according to the purpose of the specimen molding and the number of specimens;

[0018] ④ Place the annular base, outer cylinder, outer cylinder lining, inner rod, inner rod connecting plate and annular pressure head of the test mold in an oven at about 100℃ and heat for one hour for standby use. No heating is required when making the normal temperature asphalt mixture test piece. Among them, the two ends of the two inner rods of the test mold have been fixedly connected to the two inner rod connecting plates by connecting screws, and are fixedly connected to the annular base by connecting screws; the two outer cylinder liners have been placed inside the outer cylinder of the test mold;

[0019] S2 static pressure molding: including five steps: test mold assembly, mixed material pouring, initial pressure, front constant pressure, and back constant pressure:

[0020] ① Test mold assembly: Take out the connected annular base and the inner rod of the test mold, and place them in the center of the annular limit block I; take out the outer cylinder and the inner liner of the test mold, and place them in the annular groove of the annular base; apply a proper amount of lubricating oil on the inner surface of the inner liner of the outer cylinder, the inner rod of the test mold, and the inner surface of the outer surface annular base; install the temperature sensor around the annular base and the outer cylinder of the test mold;

[0021] ②Mixture pouring: Weigh the asphalt mixture that meets the quantity requirements and pour it into the cylindrical annular space between the outer tube lining and the inner rod of the test mold in batches. At the same time, use the insertion rod to insert and tamp along the inner periphery of the outer tube lining and the outer periphery of the inner rod of the test mold for multiple times. Finally, use a hot shovel or annular pressure head to manually level the upper surface of the asphalt mixture;

[0022] ③ Initial pressure: lay a piece of annular thin paper on the upper surface of the asphalt mixture, place the annular pressure head on the asphalt mixture, and then place the upper pad on the annular pressure head. The bottom end of the annular pressure head is embedded in the inner lining of the outer cylinder, placed on the asphalt mixture, and passes through the inner rod of the test mold, and can slide up and down; use annular pressure heads of different numbers and thicknesses and connect them through the vertical limit contact of the annular limit block II to ensure that the upper end surface of the annular pressure head and the lower end surface of the annular limit block III are higher than the upper end surface of the outer cylinder of the test mold and the inner lining of the outer cylinder during the molding of the specimen; start the control system to lift the spiral jack, and lower The pad and the specimen mold rise synchronously, and finally the upper pad is in close contact with the upper bearing plate to form a reaction force, and the reaction force is transmitted to the annular pressure head, thereby applying static pressure to the asphalt mixture; when the static pressure stress reaches the set initial pressure stress control value, the spiral jack stops rising and maintains it for the specified initial pressure time; during the initial pressure process, the control system will dynamically control the spiral jack to slowly rise or fall or stop at a certain rate according to the size relationship between the actual pressure stress value and the set initial pressure stress control value, and dynamically adjust the actual pressure stress value to maintain a stable initial pressure stress;

[0023] ④ Front constant pressure: After the initial pressure is completed, the control system automatically controls the spiral ram to rise at a certain rate, eventually reaching the target static pressure stress value, and maintaining the corresponding front constant pressure time; during this period, the control system will dynamically control the spiral ram to slowly rise or fall or stop at a certain rate based on the size relationship between the actual pressure stress value and the set front constant pressure target value, dynamically adjust the actual front constant pressure stress, and maintain the set front constant pressure time; during the static pressure forming stage of the specimen, the annular pressure head will gradually descend vertically, and there will be relative sliding between the asphalt mixture and the inner lining of the outer cylinder and the inner rod of the test mold; the maximum displacement occurs on the upper surface of the asphalt mixture, that is, the contact surface with the annular pressure head; the minimum displacement is located on the lower surface of the asphalt mixture, that is, the contact surface with the annular base; the control system will record the time and displacement data in real time, and the constant pressure creep curve can be obtained;

[0024] ⑤ Reverse side constant pressure: including three steps: instrument disassembly, specimen inversion and reverse side static pressure;

[0025] a. Instrument disassembly: After the positive constant pressure is completed, the control system automatically controls the spiral jack to descend to a suitable position, and the static pressure stress of the asphalt mixture is unloaded to zero; remove the upper pad, and remove the annular pressure head from the upper end of the asphalt mixture, the inner lining of the outer cylinder and the inner rod of the test mold;

[0026] b. Invert the test piece: Loosen the connection screws to release the connection between the annular base and the test mold inner rod and the inner rod connecting plate 22, separate the asphalt mixture and the test mold outer cylinder, outer cylinder lining, test mold inner rod, and inner rod connecting plate from the annular base as a whole, and invert the asphalt mixture and the test mold outer cylinder, outer cylinder lining, test mold inner rod, and inner rod connecting plate as a whole, and then place them on the annular base; finally, use the connection screws to fix the inner rod connecting plate on the annular base to complete the inversion of the asphalt mixture test piece. Place the annular pressure head on the asphalt mixture, and then place the upper pad on the annular pressure head;

[0027] c. Reverse side static pressure: Start the control system to control the spiral jack to rise, the lower pad and the specimen mold to rise synchronously, and finally the upper pad and the upper bearing plate are in close contact to form a reaction force, and the reaction force is transmitted to the annular pressure head, thereby applying constant pressure stress to the inverted asphalt mixture again; the control method of the reverse side constant pressure is the same as the positive side constant pressure. According to the set reverse side constant pressure stress target value, the spiral jack is dynamically controlled to rise or fall or stop at a certain rate, the actual reverse side constant pressure stress is dynamically adjusted, and the set reverse side constant pressure time is maintained; after the reverse side constant pressure time reaches the set value, the control system automatically controls the spiral jack to descend to a suitable position and stop, completing the unloading and the static pressure forming of the specimen;

[0028] S3 specimen demoulding: including four steps: connection release, rack installation, inner film demoulding and outer mold demoulding:

[0029] ① Connection release: After the compaction and unloading of the test piece, remove the upper pad and annular pressure head, take out the test mold and asphalt mixture test piece; loosen the connection screws to release the connection between the annular base and the inner rod of the test mold and the inner rod connecting plate, and remove the annular base; loosen the connection screws to release the connection between the inner rod of the test mold and the inner rod connecting plate;

[0030] ② Installation of the hanger: Pass the hanger pole through the hanger reserved hole on the upper bearing plate, adjust the clearance height between the hanger bottom plate and the upper bearing plate to a suitable value, and fix the hanger on the bearing plate with the hanger fixing screws; place the disconnected test piece as a whole at the center of the hanger bottom plate, and then place the annular pressure head and the upper pad on the asphalt mixture of the test piece; adjust the vertical position of the hanger bottom plate with the hanger fixing screws so that the upper end of the upper pad is embedded in the demoulding hole and in close contact with the upper bearing plate;

[0031] ③ Inner film demoulding: Start the control system, lower the spiral ejector and the tray to a reasonable lower position, and then place the demoulding base on the tray and place it in the center of the limit block; start the control system, gradually raise the spiral ejector and the tray until the demoulding ejector shaft is in close contact with one of the inner rods of the test mold; start the control system again, the spiral ejector and the tray rise at a certain rate, and the test mold outer cylinder, outer cylinder lining, and asphalt mixture of the test piece mold cannot move due to the restrictions of the annular pressure head, upper pad and upper bearing plate, and the inner rod of the test mold will be gradually ejected from the demoulding hole under the pushing action of the demoulding ejector shaft; because the connection between the two inner rods of the test mold is released, only the inner rod of the test mold that is under force is ejected; rotate or adjust the position of the demoulding base so that the demoulding ejector shaft is aligned with the remaining inner rods of the test mold, and remove the remaining inner rods of the test mold in the same way;

[0032] ④ Demolding of the outer mold: remove the annular upper pressure head and the upper pad, adjust the vertical position of the bottom plate of the hanger, so that the outer cylinder of the test piece mold is in close contact with the upper bearing plate and located at the center of the bearing plate, to ensure that the outer cylinder lining of the test piece mold can be ejected from the demoulding hole; start the control system, lower the spiral ejector and the tray to a reasonable lower position, and place the demoulding ejector in the center of the tray; start the control system again, gradually raise the spiral ejector and the tray until the demoulding ejector is in close contact with the outer cylinder lining of the test piece mold; finally, start the control system, the spiral ejector and the tray rise at a certain rate, because the upper end of the outer cylinder of the test piece mold is restricted by the upper bearing plate and will remain fixed, and the outer cylinder lining and the asphalt mixture test piece as a whole will be gradually ejected from the demoulding hole under the action of the demoulding ejector; there are still two separated outer cylinder liners around the ejected asphalt mixture test piece, and the two separated outer cylinder liners and the asphalt mixture test piece can be peeled off by knocking or other methods.

[0033] The present invention can effectively overcome many shortcomings of existing asphalt mixture hollow cylindrical specimen molding methods, ensure the quality of the specimens, and prepare hollow cylindrical asphalt mixture specimens that meet the compaction requirements and road performance requirements, which are used for triaxial torsional shear tests or other mechanical property tests, greatly meeting actual needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the present invention;

[0035] Figure 2 A schematic diagram of the molding instrument of the present invention for demoulding a specimen from an inner mold;

[0036] Figure 3 It is a schematic diagram of demoulding a specimen from an outer mold by the molding apparatus of the present invention.

[0037] In the figure: 1 column rod, 2 threaded rod, 3 bottom partition, 4 lower bearing plate, 5 middle partition, 6 upper bearing plate, 7 demoulding hole, 8 positioning nut, 9 bearing nut, 10 electric motor, 11 spiral ejector, 12 tray, 13 limit block, 14 pressure sensor, 15 lower pad, 16 limit block, 17 annular limit block I, 18 annular base, 19 test mold outer cylinder, 20 outer cylinder liner, 21 test mold inner rod, 22 inner rod connecting plate, 23 connecting screw, 24 connecting screw, 25 asphalt mixture, 26 Annular pressure head, 27 annular limit block II, 28 upper pad, 29 annular limit block III, 30 displacement sensor, 31 auxiliary plate, 32 contact sensor, 33 lower limit block, 34 upper limit block, 35 temperature sensor, 36 transmission, 37 signal converter, 38 programmable platform, 39 demoulding top shaft, 40 bracket reserved hole, 41 bracket bottom plate, 42 bracket bottom plate reserved hole, 43 bracket upright, 44 bracket fixing screw, 45 demoulding base, 46 demoulding top shaft, 47 demoulding top cylinder. DETAILED DESCRIPTION

[0038] like Figure 1 As shown, the present invention is a static pressure molding instrument for a hollow cylindrical specimen of asphalt mixture, which includes a load-bearing frame, a power device, a specimen mold, a control system and a demoulding device, wherein:

[0039] ① The bearing frame is placed on the platform and consists of columns and partitions; the columns are composed of column rods 1 and threaded rods 2; the partitions are composed of bottom partitions 3, lower bearing plates 4, middle partitions 5, upper bearing plates 6, demoulding holes 7, and reserved holes 40 for hangers, wherein the bottom partitions 3, lower bearing plates 4 and middle partitions 5 are all fixedly connected to the column rods 1, and the upper bearing plate 6 is sleeved on the threaded rods 2 through reserved holes, and its position can be adjusted up and down, and vertical positioning and fixation are achieved through positioning nuts 8 and bearing nuts 9; the demoulding hole 7 is located at the center of the upper bearing plate 6, and the hollow cylindrical specimen will be removed from the demoulding hole 7 when the specimen is demoulded after static pressure molding; the reserved holes 40 for hangers are symmetrically arranged around the demoulding holes 7, and are used to install temporary brackets during demoulding.

[0040] ② The power unit consists of an electric motor 10, a transmission 36, a spiral push rod 11, a tray 12 and a limit block 13; the transmission 36 is connected to the control system and receives instructions from the control system to control the output speed of the electric motor 10; the spiral push rod 11 is controlled by the electric motor 10 and can move vertically; the tray 12 is fixedly connected to the spiral push rod 11, and the limit block 13 is fixed to the upper surface of the tray 12.

[0041] ③ The test piece mold is composed of a lower pad 15, an annular base 18, a test mold outer cylinder 19, an outer cylinder liner 20, a test mold inner rod 21, an inner rod connecting plate 22, a connecting screw 23, an annular pressure head 26, an upper pad 28 and three limit blocks, wherein the limit block 16 and the annular limit block I17 are respectively fixed to the lower surface and the upper surface of the lower pad 15, and the annular limit block II27 is fixed to the lower surface of the upper pad 28; the upper end of the pressure sensor 14 is located at the center of the limit block 16; The annular base 18 is placed at the center of the annular limit block 117, the test mold outer cylinder 19 is placed in the annular groove of the annular base 18, the outer cylinder liner 20 is composed of two symmetrical pieces, placed inside the test mold outer cylinder 19 and the annular groove of the annular base 18, and is at the same height as the test mold outer cylinder 19, and is always in close contact with the test mold outer cylinder 19 and maintains the same vertical position; the test mold inner rod 21 is composed of two symmetrical pieces, and inner rod connecting plates 22 are respectively arranged at both ends, and are connected to the test mold by connecting screws 23. The inner rod 21 is fixedly connected, and the inner rod connecting plate 22 located at the bottom end of the inner rod 21 of the test mold is fixedly connected to the annular base 18 through the connecting screw 24; the asphalt mixture 25 is located in the annular and columnar space formed between the outer tube liner 20 and the inner rod 21 of the test mold; the bottom end of the annular pressure head 26 is embedded in the outer tube liner 20, placed on the asphalt mixture 25, and passes through the inner rod 21 of the test mold, and can slide up and down. Different numbers and thicknesses of annular pressure heads 26 are used and are vertically limited and contacted by annular limit blocks II27 to ensure that the upper end surface of the annular pressure head 26 and the lower end surface of the annular limit block III29 are both higher than the upper end surfaces of the outer tube 19 of the test mold and the outer tube liner 20; the upper pad 28 is placed on the annular pressure head 26, and the upper surface of the annular pressure head 26 is located at the center position within the annular limit block III29; at the same time, the annular part of the upper end of the upper pad 28 is tightly embedded in the demoulding hole 7 to ensure that the bearing frame, the spiral push rod 11 of the power device, and the center of the test piece mold are aligned.

[0042] During static pressure molding loading, as the spiral jack 11 rises, the lower pad 15 and the specimen mold rise synchronously, and finally the upper pad 28 is in close contact with the upper bearing plate 6 to form a reaction force, and transmits the reaction force to the annular pressure head 26, thereby applying static pressure to the asphalt mixture 25.

[0043] ④ The control system is composed of sensors and controllers; the sensors include pressure sensor 14, displacement sensor 30, temperature sensor 35, and contact sensor 32; the pressure sensor 14 is placed on the upper part of the tray 12 and is limited at the center of the tray 12 by the limit block 13, and its upper end is located at the center of the limit block 16; the displacement sensor 30 is fixed in the reserved hole of the auxiliary plate 31, the auxiliary plate 31 is fixedly connected to the tray 12, and the upper surface of the middle partition 5 is the relative zero point of the displacement sensor; the temperature sensor 35 is arranged on the outer surface of the test mold outer cylinder 19 and inside the annular base 18; the contact sensor 32 is sleeved on the column rod 1, fixedly connected to the auxiliary plate 31, and keeps the vertical displacement synchronous with the spiral top rod 11, the tray 12, and the auxiliary plate 31; The limit block 33 and the upper limit block 34 are fixed on the column rod 1. When the contact piece of the contact sensor 32 contacts the lower limit block 33 or the upper limit block 34, the control system will instruct the electric motor 10 to stop running and automatically reverse, thereby limiting the vertical movement range of the contact sensor 32, and indirectly controlling the lowest and highest vertical positions of the tray 12 to ensure that the vertical movement of the spiral push rod 11 is within a safe range; the controller is composed of a signal converter 37 and a program-controlled platform 38. The receiving and sending data of the pressure sensor 14, displacement sensor 30, temperature sensor 35, contact sensor 32, and transmission 36 are all connected to the program-controlled platform 38 through the signal converter 37. The program-controlled platform 38 completes tasks such as process control, data receiving and sending, processing and analysis, and information interaction.

[0044] During static pressure forming, the program-controlled platform 38 will monitor the pressure value of the pressure sensor 14 and the displacement value of the displacement sensor 30 in real time, and dynamically adjust the output operating frequency of the transmission 36 according to the deviation from the target control value to maintain a constant target static pressure stress; the program-controlled platform 38 automatically records real-time data such as time, pressure, displacement, temperature, etc., and gives warnings or other feedback information according to the target value or control value.

[0045] ⑤ The demoulding device consists of a demoulding rack and a demoulding tool; the demoulding rack includes a rack bottom plate 41, a rack bottom plate reserved hole 42, a rack upright rod 43, and a rack fixing screw 44, wherein the rack bottom plate 41 is fixedly connected to the rack upright rod 43, the rack bottom plate reserved hole 42 is located at the center of the rack bottom plate 41, the rack upright rod 43 passes through the rack reserved hole 40 on the upper bearing plate 6 of the support frame, and is fixed to the upper bearing plate 6 by the rack fixing screw 44; the demoulding tool consists of a demoulding base 45, a demoulding top shaft 46, and a demoulding top cylinder 47, wherein the demoulding base 45 is placed on the tray 12 and is located at the center position within the limit block 13, the demoulding top shaft 46 is eccentrically arranged relative to the demoulding base 45, and is aligned with one of the two test mold inner rods 21 in the specimen mold; the demoulding top cylinder 47 is placed on the tray 12, is located at the center position outside the limit block 13, and is aligned with the outer cylinder liner 20 in the specimen mold.

[0046] The present invention is a method for forming a static pressure forming instrument for a hollow cylindrical specimen of an asphalt mixture, comprising three steps of test preparation, static pressure forming and specimen demoulding, wherein:

[0047] S1 Experimental Preparation:

[0048] ①Prepare the experimental instruments and materials according to the relevant requirements of "Test Procedure for Asphalt and Asphalt Mixture in Highway Engineering JTG E20-2011" "T0704-2011 Asphalt Mixture Specimen Preparation Method (Static Pressure Method)";

[0049] ② The experimental instrument adopts the static pressure forming instrument for asphalt mixture hollow cylindrical specimen of the present invention, and the spiral push rod 11, the tray 12, and the auxiliary plate 31 are adjusted to a reasonable lower position through the control system to ensure that there is enough operating space above the tray 12 for sensor installation, specimen mold installation, asphalt mixture pouring, etc.; the pressure sensor 14 and the bottom pad 15 are installed;

[0050] ③ The experimental materials mainly include asphalt mixtures, which may include hot mix, room temperature mix, sampling and other types; the asphalt mixture that meets the quantity and temperature requirements is determined according to the purpose of the specimen molding and the number of specimens.

[0051] ④ Place the annular base 18, the outer cylinder 19, the outer cylinder lining 20, the inner rod 21, the inner rod connecting plate 22 and the annular pressure head 26 of the test piece mold in an oven at about 100°C and heat them for one hour for standby use. No heating is required when making the normal temperature asphalt mixture test piece; wherein, the two ends of the two inner rods 21 of the test mold are respectively fixedly connected to the two inner rod connecting plates 22 by connecting screws 23, and are fixedly connected to the annular base 18 by connecting screws 24; the two outer cylinder liners 20 are placed in the outer cylinder 19 of the test mold;

[0052] S2 static pressure molding: including five steps: test mold assembly, mixed material pouring, initial pressure, front constant pressure, and back constant pressure:

[0053] ① Test mold assembly: Take out the annular base 18 and the test mold inner rod 21 that have been connected as one, and place them in the center of the annular limit block I17; take out the test mold outer cylinder 19 and the outer cylinder liner 20, and place them in the annular groove of the annular base 18; apply a proper amount of lubricating oil on the inner surface of the outer cylinder liner 20, the test mold inner rod 21, and the inner surface of the outer surface annular base 18; install the temperature sensor 35 around the annular base 18 and the test mold outer cylinder 19;

[0054] ② Mixture pouring: Weigh the asphalt mixture that meets the quantity requirements, and pour it into the cylindrical annular space between the outer tube liner 20 and the test mold inner rod 21 in batches. At the same time, use the insertion rod to insert and tamp along the inner periphery of the outer tube liner 20 and the outer periphery of the test mold inner rod 21 for multiple times. Finally, use a hot shovel or annular pressure head 26 to manually level the upper surface of the asphalt mixture 25;

[0055] ③ Initial pressure: lay a piece of annular thin paper on the upper surface of the asphalt mixture 25, place the annular pressure head 26 on the asphalt mixture 25, and then place the upper pad 28 on the annular pressure head 26. The bottom end of the annular pressure head 26 is embedded in the outer tube liner 20, placed on the asphalt mixture 25, and passes through the test mold inner rod 21, and can slide up and down; different numbers and thicknesses of annular pressure heads 26 are used and connected by the annular limit block II27 to ensure that the upper end surface of the annular pressure head 26 and the lower end surface of the annular limit block III29 are higher than the upper end surfaces of the test mold outer tube 19 and the outer tube liner 20 during the molding of the test piece; start the control system to The spiral jack 11 is lifted, and the lower pad 15 and the specimen mold are lifted synchronously. Finally, the upper pad 28 is in close contact with the upper bearing plate 6 to form a reaction force, and the reaction force is transmitted to the annular pressure head 26, thereby applying static pressure to the asphalt mixture 25; when the static pressure stress reaches the set initial pressure stress control value, the spiral jack 11 stops rising and is maintained for the specified initial pressure time; during the initial pressure process, the control system will dynamically control the spiral jack 11 to slowly rise or fall or stop at a certain rate according to the size relationship between the actual pressure stress value and the set initial pressure stress control value, and dynamically adjust the actual pressure stress value to maintain a stable initial pressure stress;

[0056] ④ Front constant pressure: After the initial pressure is completed, the control system automatically controls the spiral ram 11 to rise at a certain rate, and finally reaches the target static pressure stress value, and maintains the corresponding front constant pressure time; during this period, the control system will dynamically control the spiral ram 11 to slowly rise or fall or stop at a certain rate according to the size relationship between the actual pressure stress value and the set front constant pressure target value, dynamically adjust the actual front constant pressure stress, and maintain the set front constant pressure time; in the static pressure forming stage of the specimen, the annular pressure head 26 will gradually descend vertically, and there will be relative sliding between the asphalt mixture 25 and the outer tube lining 20 and the test mold inner rod 21; the maximum displacement occurs on the upper surface of the asphalt mixture 25, that is, the contact surface with the annular pressure head 26; the minimum displacement is located on the lower surface of the asphalt mixture 25, that is, the contact surface with the annular base 18; the control system will record the time and displacement data in real time, and the constant pressure creep curve can be obtained;

[0057] ⑤ Reverse side constant pressure: including three steps: instrument disassembly, specimen inversion and reverse side static pressure;

[0058] a. Instrument disassembly: After the positive constant pressure is completed, the control system automatically controls the spiral jack 11 to descend to a suitable position, and the static pressure stress of the asphalt mixture 25 is unloaded to zero; remove the upper pad 28, and remove the annular pressure head 26 from the upper end of the asphalt mixture 25, the outer tube liner 20 and the test mold inner rod 21;

[0059] b. Invert the test piece: Loosen the connecting screws 24 to release the connection between the annular base 18 and the test mold inner rod 21 and the inner rod connecting plate 22, separate the asphalt mixture 25 and the test mold outer cylinder 19, the outer cylinder lining 20, the test mold inner rod 21, and the inner rod connecting plate 22 from the annular base 18 as a whole, and invert the asphalt mixture 25 and the test mold outer cylinder 19, the outer cylinder lining 20, the test mold inner rod 21, and the inner rod connecting plate 22 as a whole, and then place them on the annular base 18; finally, use the connecting screws 24 to fix the inner rod connecting plate 22 on the annular base 18 to complete the inversion of the asphalt mixture test piece. Place the annular pressure head 26 on the asphalt mixture 25, and then place the upper pad 28 on the annular pressure head 26;

[0060] c. Reverse side static pressure: Start the control system to control the spiral jack 11 to rise, the lower pad 15 and the specimen mold to rise synchronously, and finally the upper pad 28 is in close contact with the upper bearing plate 6 to form a reaction force, and transmits the reaction force to the annular pressure head 26, thereby applying constant pressure stress to the inverted asphalt mixture 25 again; the control method of the reverse side constant pressure is the same as the positive side constant pressure. According to the set reverse side constant pressure stress target value, the spiral jack 11 is dynamically controlled to rise or fall or stop at a certain rate, the actual reverse side constant pressure stress is dynamically adjusted, and the set reverse side constant pressure time is maintained; after the reverse side constant pressure time reaches the set value, the control system automatically controls the spiral jack 11 to descend to a suitable position and stop, completing the unloading and the static pressure forming of the specimen;

[0061] Generally, the inverted test mold outer cylinder 19 and outer cylinder lining 20 have not yet been embedded in the annular groove of the annular base 18, and the lower end surface of the asphalt mixture 25 has not yet contacted the annular base 18; but under the action of static pressure, the positions of the asphalt mixture 25 and the test mold outer cylinder 19 and outer cylinder lining 20 will gradually decrease, and finally the lower end surface of the asphalt mixture 25 will contact the annular base 18, and the test mold outer cylinder 19 and outer cylinder lining 20 are both embedded in the annular groove of the annular base 18.

[0062] S3 specimen demoulding: including four steps: connection release, rack installation, inner film demoulding and outer mold demoulding:

[0063] ① Connection release: After the compaction and unloading of the test piece, remove the upper pad 28 and the annular pressure head 26, take out the test mold and the asphalt mixture test piece; loosen the connection screws 24 to release the connection between the annular base 18 and the test mold inner rod 21 and the inner rod connecting plate 22, and remove the annular base 18; loosen the connection screws 23 to release the connection between the test mold inner rod 21 and the inner rod connecting plate 22;

[0064] ② Installation of the rack: Pass the rack upright 43 through the rack reserved hole 40 on the upper bearing plate 6, adjust the clearance height between the rack bottom plate 41 and the upper bearing plate 6 to a suitable value, and fix the rack on the bearing plate 6 by the rack fixing screws 44; place the disconnected test piece as a whole at the center of the rack bottom plate 41, and then place the annular pressure head 26 and the upper pad 28 on the test piece asphalt mixture 25; adjust the vertical position of the rack bottom plate 41 by the rack fixing screws 44, so that the upper end of the upper pad 28 is embedded in the demoulding hole 7 and in close contact with the upper bearing plate 6;

[0065] ③ Inner film demoulding: Start the control system, lower the spiral ejector 11 and the tray 12 to a reasonable lower position, and then place the demoulding base 45 on the tray 12 and locate it in the center position within the limit block 13; start the control system, gradually raise the spiral ejector 11 and the tray 12 until the demoulding ejector shaft 46 is in close contact with one of the test mold inner rods 21; start the control system again, the spiral ejector 11 and the tray 12 rise at a certain rate, the test mold outer cylinder 19, the outer cylinder liner 20, and the asphalt mixture 25 of the test piece mold cannot move due to the restrictions of the annular pressure head 26, the upper pad 28 and the upper bearing plate 6, and the test mold inner rod 21 will be gradually ejected from the demoulding hole 7 under the pushing action of the demoulding ejector shaft 46; because the connection between the two test mold inner rods 21 is released, only the test mold inner rod 21 that is under force is ejected; rotate or adjust the position of the demoulding base 45 so that the demoulding ejector shaft 46 is aligned with the remaining test mold inner rods 21, and the remaining test mold inner rods 21 are removed in the same way, such as Figure 2 As shown;

[0066] ④ Demolding of the outer mold: remove the annular upper pressure head 26 and the upper pad 28, adjust the vertical position of the bottom plate 41 of the hanger, so that the outer cylinder 19 of the test piece mold is in close contact with the upper bearing plate 6 and is located at the center of the bearing plate 6, ensuring that the outer cylinder liner 20 of the test piece mold can be ejected from the demoulding hole 7; start the control system, lower the spiral ejector 11 and the tray 12 to a reasonable lower position, and place the demoulding ejector 47 at the center of the tray 12; start the control system again, gradually raise the spiral ejector 11 and the tray 12, until the demoulding ejector 47 is in close contact with the test piece mold. Finally, the control system is started, and the spiral push rod 11 and the tray 12 rise at a certain rate. Because the upper end of the test mold outer cylinder 19 of the test piece mold is restricted by the upper bearing plate 6, it will remain fixed, and the outer cylinder lining 20 and the asphalt mixture test piece 25 as a whole will be gradually ejected from the demoulding hole 7 under the action of the demoulding ejector 47; there are still two separated outer cylinder linings 20 around the ejected asphalt mixture test piece 25, and the two separated outer cylinder linings 20 and the asphalt mixture test piece 25 can be peeled off by knocking or other methods, such as Figure 2 , Figure 3 shown.

Claims

1. A static pressure forming instrument for a hollow cylindrical specimen of asphalt mixture, characterized by: The static pressure forming instrument for the asphalt mixture hollow cylindrical specimen comprises a load-bearing frame, a power device, a specimen mold, a control system and a demoulding device; The supporting frame is placed on the platform and is composed of columns and partitions; the columns are composed of column rods (1) and threaded rods (2); the partitions are composed of bottom partitions (3), lower bearing plates (4), middle partitions (5), upper bearing plates (6), demoulding holes (7), and reserved holes for hangers (40), wherein the bottom partitions (3), lower bearing plates (4) and middle partitions (5) are all fixedly connected to the column rods (1); the upper bearing plate (6) is sleeved on the threaded rods (2) through the reserved holes, and its position can be adjusted up and down, and vertical positioning and fixing are achieved through positioning nuts (8) and bearing nuts (9); the demoulding hole (7) is located at the center of the upper bearing plate (6), and when the test piece is demoulded after static pressure molding, the hollow cylindrical test piece will be removed from the demoulding hole (7); the reserved holes for hangers (40) are symmetrically arranged around the demoulding hole (7) and are used to install temporary brackets during demoulding; The power device is composed of an electric motor (10), a transmission (36), a spiral push rod (11), a tray (12) and a limit block (13); the transmission (36) is connected to a control system and receives instructions from the control system to control the output speed of the electric motor (10); the spiral push rod (11) is controlled by the electric motor (10) and can move vertically; the tray (12) is fixedly connected to the spiral push rod (11), and the limit block (13) is fixed to the upper surface of the tray (12); The test piece mold is composed of a lower pad (15), an annular base (18), a test mold outer cylinder (19), an outer cylinder liner (20), a test mold inner rod (21), an inner rod connecting plate (22), a connecting screw (23), an annular pressure head (26), an upper pad (28) and three limit blocks, wherein the limit block (16) and the annular limit block I (17) are respectively fixed to the lower surface and the upper surface of the lower pad (15), and the annular limit block II (27) is fixed to the lower surface of the upper pad (28); the upper end of the pressure sensor (14) is located at the limit block (16) ); the annular base (18) is placed at the center of the annular limit block I (17); the test mold outer cylinder (19) is placed in the annular groove of the annular base (18); the outer cylinder liner (20) is composed of two symmetrical pieces, which are placed inside the test mold outer cylinder (19) and in the annular groove of the annular base (18), and are at the same height as the test mold outer cylinder (19), and are always in close contact with the test mold outer cylinder (19) and maintain the same vertical position; the test mold inner rod (21) is composed of two symmetrical pieces, and inner rod connecting plates (22) are respectively provided at both ends thereof, and are connected by connecting screws (23 ) is fixedly connected to the inner rod (21) of the test mold; the inner rod connecting plate (22) located at the bottom end of the inner rod (21) of the test mold is fixedly connected to the annular base (18) through a connecting screw (24); the asphalt mixture (25) is located in the annular, columnar space formed between the outer cylinder liner (20) and the inner rod (21) of the test mold; the bottom end of the annular pressure head (26) is embedded in the inner liner (20) of the outer cylinder, placed on the asphalt mixture (25), and passes through the inner rod (21) of the test mold, and can slide up and down. Different numbers and thicknesses of the annular pressure heads (26) are used and the annular limit is used. The ring-shaped pressure head (26) and the ring-shaped limit block (27) are connected in a vertical limiting manner to ensure that the upper end surface of the annular pressure head (26) and the lower end surface of the annular limit block III (29) are both higher than the upper end surfaces of the outer cylinder (19) and the inner liner (20) of the outer cylinder of the test mold; the upper pad (28) is placed on the annular pressure head (26), and the upper surface of the annular pressure head (26) is located at the center position inside the annular limit block III (29); at the same time, the annular portion of the upper end of the upper pad (28) is tightly embedded in the demoulding hole (7) to ensure that the bearing frame, the spiral push rod (11) of the power device, and the center of the test piece mold are aligned; The control system is composed of sensors and a controller; the sensors include a pressure sensor (14), a displacement sensor (30), a temperature sensor (35), and a contact sensor (32); the pressure sensor (14) is placed on the upper part of the tray (12), and is limited at the center of the tray (12) by a limit block (13), and its upper end is located at the center of the limit block (16); the displacement sensor (30) is fixed in a reserved hole of the auxiliary plate (31), the auxiliary plate (31) is fixedly connected to the tray (12), and the upper surface of the middle partition (5) is the relative zero point of the displacement sensor; the temperature sensor (35) is arranged on the outer surface of the test mold outer cylinder (19) and inside the annular base (18); the contact sensor (32) is sleeved on the column rod (1), is fixedly connected to the auxiliary plate (31), and maintains a vertical position with the spiral top rod (11), the tray (12), and the auxiliary plate (31). The lower limit block (33) and the upper limit block (34) are fixed on the column rod (1). When the contact piece of the contact sensor (32) contacts the lower limit block (33) or the upper limit block (34), the control system will instruct the electric motor (10) to stop running and automatically reverse, thereby limiting the vertical movement range of the contact sensor (32) and indirectly controlling the lowest and highest vertical positions of the tray (12) to ensure that the vertical movement of the spiral push rod (11) is within a safe range. The controller is composed of a signal converter (37) and a program control platform (38). The receiving and sending data of the pressure sensor (14), the displacement sensor (30), the temperature sensor (35), the contact sensor (32), and the transmission (36) are connected to the program control platform (38) through the signal converter (37). The program control platform (38) completes the tasks of process control, data receiving and sending, processing and analysis, and information interaction. The demoulding device is composed of a demoulding rack and a demoulding tool; the demoulding rack comprises a rack bottom plate (41), a rack bottom plate reserved hole (42), a rack upright rod (43), and a rack fixing screw (44), wherein the rack bottom plate (41) is fixedly connected to the rack upright rod (43), the rack bottom plate reserved hole (42) is located at the center of the rack bottom plate (41), and the rack upright rod (43) passes through the rack reserved hole (40) on the upper bearing plate (6) of the support frame and is fixed to the upper bearing plate (6) by the rack fixing screw (44). The demoulding tool is composed of a demoulding base (45), a demoulding top shaft (46), and a demoulding top cylinder (47), wherein the demoulding base (45) is placed on the tray (12) and is located at the center position inside the limit block (13), and the demoulding top shaft (46) is eccentrically arranged relative to the demoulding base (45) and is aligned with one of the two test mold inner rods (21) in the test piece mold; the demoulding top cylinder (47) is placed on the tray (12) and is located at the center position outside the limit block (13), and is aligned with the outer cylinder liner (20) in the test piece mold.

2. A molding method using the static pressure molding instrument for asphalt mixture hollow cylindrical specimens according to claim 1, comprising three steps of test preparation, static pressure molding and specimen demoulding, characterized in that Here are the steps: S1 Experimental Preparation: ① The experimental instrument adopts the static pressure molding instrument for the asphalt mixture hollow cylindrical specimen as claimed in claim 1, and adjusts the spiral jack (11), the tray (12), and the auxiliary plate (31) through the control system to ensure that there is sufficient space above the tray (12) for sensor installation, specimen mold installation, and asphalt mixture pouring operation; install the pressure sensor (14) and the bottom pad (15); ② The experimental materials mainly include asphalt mixtures, including hot mix, room temperature mix and sampling types; the asphalt mixture that meets the quantity and temperature requirements is determined according to the purpose of the specimen molding and the number of specimens; ③ Place the annular base (18), the outer cylinder (19), the outer cylinder lining (20), the inner rod (21), the inner rod connecting plate (22), and the annular pressure head (26) of the test piece mold in a 100°C oven for heating for one hour for standby use. No heating is required when making the normal temperature asphalt mixture test piece; wherein, the two ends of the two inner rods (21) of the test mold are respectively fixedly connected to the two inner rod connecting plates (22) by connecting screws (23), and are fixedly connected to the annular base (18) by connecting screws (24); the two outer cylinder linings (20) are placed in the outer cylinder (19) of the test mold; S2 static pressure molding: including five steps of test mold assembly, mixture pouring, initial pressure, front constant pressure, and back constant pressure: ① Assembling the test mold: Take out the annular base (18) and the test mold inner rod (21) that have been connected as one, and place them in the center of the annular limit block I (17); take out the test mold outer cylinder (19) and the outer cylinder liner (20), and place them in the annular groove of the annular base (18); apply a proper amount of lubricating oil on the inner surface of the outer cylinder liner (20), the test mold inner rod (21), and the inner surface of the outer surface annular base (18); install the temperature sensor (35) around the annular base (18) and the test mold outer cylinder (19); ② Mixture pouring: Weigh the asphalt mixture that meets the quantity requirement and pour it into the cylindrical annular space between the outer tube lining (20) and the inner rod (21) of the test mold in batches. At the same time, use a plunger to tamp along the inner periphery of the outer tube lining (20) and the outer periphery of the inner rod (21) of the test mold for multiple times. Finally, use a hot shovel or an annular pressure head (26) to manually level the upper surface of the asphalt mixture (25); ③ Initial pressure: a piece of annular thin paper is laid on the upper surface of the asphalt mixture (25), an annular pressure head (26) is placed on the asphalt mixture (25), and then an upper pad (28) is placed on the annular pressure head (26). The bottom end of the annular pressure head (26) is embedded in the inner lining (20) of the outer cylinder, placed on the asphalt mixture (25), and passes through the inner rod (21) of the test mold, and can slide up and down; different numbers and thicknesses of annular pressure heads (26) are used and are vertically limited and contacted by annular limit blocks II (27) to ensure that during the molding of the test piece, the upper end surface of the annular pressure head (26) and the lower end surface of the annular limit block III (29) are both higher than the upper end surfaces of the outer cylinder (19) of the test mold and the inner lining (20) of the outer cylinder; The control system is started to lift the spiral jack (11), and the lower pad (15) and the specimen mold are lifted synchronously. Finally, the upper pad (28) and the upper bearing plate (6) are in close contact to form a reaction force, and the reaction force is transmitted to the annular pressure head (26), thereby applying static pressure to the asphalt mixture (25); when the static pressure stress reaches the set initial pressure stress control value, the spiral jack (11) stops rising and is maintained for a specified initial pressure time; during the initial pressure process, the control system will dynamically control the spiral jack (11) to slowly rise or fall or stop at a certain rate according to the size relationship between the actual pressure stress value and the set initial pressure stress control value, and dynamically adjust the actual pressure stress value to maintain a stable initial pressure stress; ④ Front constant pressure: After the initial pressure is completed, the control system automatically controls the spiral push rod (11) to rise at a certain rate, finally reaching the target static pressure stress value, and maintaining the corresponding front constant pressure time; during this period, the control system will dynamically control the spiral push rod (11) to slowly rise or fall or stop at a certain rate according to the size relationship between the actual pressure stress value and the set front constant pressure target value, dynamically adjust the actual front constant pressure stress, and maintain the set front constant pressure time; during the static pressure molding stage of the specimen, the annular pressure head (26) will gradually descend vertically, and there will be relative sliding between the asphalt mixture (25) and the outer tube lining (20) and the test mold inner rod (21); the maximum displacement occurs on the upper surface of the asphalt mixture (25), that is, the contact surface with the annular pressure head (26); the minimum displacement is located on the lower surface of the asphalt mixture (25), that is, the contact surface with the annular base (18); the control system will record the time and displacement data in real time, and the constant pressure creep curve can be obtained; ⑤ Reverse side constant pressure: including three steps: instrument disassembly, specimen inversion and reverse side static pressure; a. Instrument disassembly: After the front constant pressure is completed, the control system automatically controls the spiral jack (11) to descend, and the static pressure stress of the asphalt mixture (25) is unloaded to zero; the upper pad (28) is removed, and the annular pressure head (26) is removed from the upper end of the asphalt mixture (25), the outer cylinder lining (20) and the test mold inner rod (21); b. Inverting the test piece: loosen the connecting screws (24), release the connection between the annular base (18) and the test mold inner rod (21) and the inner rod connecting plate (22), separate the asphalt mixture (25) and the test mold outer cylinder (19), the outer cylinder lining (20), the test mold inner rod (21), and the inner rod connecting plate (22) from the annular base (18), and invert the asphalt mixture (25) and the test mold outer cylinder (19), the outer cylinder lining (20), the test mold inner rod (21), and the inner rod connecting plate (22) as a whole, and then place them on the annular base (18); finally, use the connecting screws (24) to fix the inner rod connecting plate (22) on the annular base (18), and complete the inversion of the asphalt mixture test piece; place the annular pressure head (26) on the asphalt mixture (25), and then place the upper pad (28) on the annular pressure head (26); c. Reverse side static pressure: start the control system to control the spiral jack (11) to rise, the lower pad (15) and the specimen mold to rise synchronously, and finally the upper pad (28) and the upper bearing plate (6) to form a reaction force, and transmit the reaction force to the annular pressure head (26), thereby applying constant pressure stress to the inverted asphalt mixture (25) again; the control method of the reverse side constant pressure is the same as that of the positive side constant pressure, according to the set reverse side constant pressure stress target value, the spiral jack (11) is dynamically controlled to rise or fall or stop at a certain rate, dynamically adjust the actual reverse side constant pressure stress, and maintain the set reverse side constant pressure time; after the reverse side constant pressure time reaches the set value, the control system automatically controls the spiral jack (11) to descend, complete unloading and specimen static pressure molding; S3 specimen demoulding: including connection release, hanger installation, inner film demoulding and outer mold demoulding: ① Connection release: After the compaction and unloading of the test piece, remove the upper pad (28) and the annular pressure head (26), and take out the test mold and the asphalt mixture test piece; loosen the connection screw (24) to release the connection between the annular base (18) and the test mold inner rod (21) and the inner rod connecting plate (22), and remove the annular base (18); loosen the connection screw (23) to release the connection between the test mold inner rod (21) and the inner rod connecting plate (22); ② Installation of the hanger: Pass the hanger upright (43) through the hanger reserved hole (40) on the upper bearing plate (6), adjust the clearance between the hanger bottom plate (41) and the upper bearing plate (6) to a suitable value, and fix the hanger on the bearing plate (6) by the hanger fixing screws (44); place the test piece after disconnection as a whole at the center of the hanger bottom plate (41), and then place the annular pressure head (26) and the upper pad (28) on the test piece asphalt mixture (25); adjust the vertical position of the hanger bottom plate (41) by the hanger fixing screws (44) so ​​that the upper end of the upper pad (28) is embedded in the demoulding hole (7) and is in close contact with the upper bearing plate (6); ③ Inner film demoulding: Start the control system, lower the spiral push rod (11) and the tray (12), and then place the demoulding base (45) on the tray (12) and place it in the center of the limit block (13); start the control system, gradually raise the spiral push rod (11) and the tray (12) until the demoulding push rod (46) is in close contact with one of the inner rods (21) of the test mold; start the control system again, the spiral push rod (11) and the tray (12) rise at a certain rate, and the test mold outer cylinder (19), the outer cylinder liner (20), and the asphalt The green mixed material (25) cannot move due to the restriction of the annular pressure head (26), the upper pad (28) and the upper bearing plate (6), while the inner rod (21) of the trial mold is gradually pushed out from the demoulding hole (7) under the pushing action of the demoulding top shaft (46); since the connection between the two inner rods (21) of the trial mold is released, only the inner rod (21) of the trial mold that is subjected to force is pushed out; the position of the demoulding base (45) is rotated or adjusted so that the demoulding top shaft (46) is aligned with the remaining inner rod (21) of the trial mold, and the remaining inner rod (21) of the trial mold is removed in the same way; ④ Demolding the outer mold: remove the annular upper pressure head (26) and the upper pad (28), and adjust the vertical position of the hanger bottom plate (41) so that the outer cylinder (19) of the test piece mold is in close contact with the upper bearing plate (6) and is located at the center of the bearing plate (6), ensuring that the outer cylinder lining (20) of the test piece mold can be ejected from the demoulding hole (7); start the control system, lower the spiral ejector (11) and the tray (12), and place the demoulding ejector cylinder (47) at the center of the tray (12); start the control system again, gradually raise the spiral ejector cylinder (11) and the tray (12) until the demoulding ejector cylinder (47) and the test piece are in close contact. The outer cylinder lining (20) of the mold is in close contact; finally, the control system is started, and the spiral ejector (11) and the tray (12) rise at a certain rate. Since the upper end of the outer cylinder (19) of the specimen mold is restricted by the upper bearing plate (6), it will remain fixed, and the outer cylinder lining (20) and the asphalt mixture specimen (25) as a whole will be gradually ejected from the demoulding hole (7) under the action of the demoulding ejector (47); there are still two separated outer cylinder linings (20) around the ejected asphalt mixture specimen (25), and the two separated outer cylinder linings (20) and the asphalt mixture specimen (25) can be peeled off by knocking.

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