Loading method and loading device for restraining long-term deformation of light aggregate under compression condition

Abstract

The application provides a loading method and device for restraining long-term deformation of light aggregate under pressure condition, and the main process of the loading method is as follows: light aggregate is poured into a confining cylinder, a creep meter composed of a pressure plate, a nut, a screw rod and a spring is used to pressurize a pressure-bearing cylinder composed of the confining cylinder, a guide cylinder and a punch die to provide restraint, thereby long-term pressure is applied to the light aggregate particles to obtain long-term performance of the light aggregate under pressure. The loading device mainly comprises the confining cylinder, the guide cylinder, the punch die, a strain conduction iron rod and a dial gauge, the upper end of the confining cylinder is connected with the lower end of the guide cylinder and the punch die, a fixed plate is connected with the dial gauge and the first mounting end of the strain conduction iron rod, the second mounting end of the strain conduction iron rod is connected with a round hole threaded bolt, and the connecting hole of the upper pressure plate is connected with the screw rod and the base. The average value of the four dial gauges is used as the judgment of whether the pressure is balanced, so that the measured deformation data of the light aggregate has less interference and the measurement accuracy is ensured.

Description

Technical Field

[0001] This invention relates to the field of mechanical property testing of lightweight aggregates, and in particular to a loading method and apparatus for constraining long-term deformation of lightweight aggregates under compression. Background Technology

[0002] Lightweight aggregate concrete possesses advantages such as light weight, high strength, excellent frost resistance, and good fire resistance, making it promising for applications in long-span structures, marine engineering, and prefabricated buildings. Applying lightweight aggregate concrete to long-span bridge structures with a high proportion of dead load can effectively reduce cross-sectional dimensions, increase specific strength, and enhance span capacity. However, creep in lightweight aggregate concrete can cause time-varying defects such as excessive bridge deflection and severe cracking, adversely affecting structural performance and posing significant safety hazards.

[0003] Our understanding of the long-term performance of lightweight aggregate concrete remains insufficient. Aggregate is a crucial component of concrete, and its long-term deformation characteristics significantly influence the creep rate and trend of concrete. Existing creep theories suggest that aggregates in ordinary concrete lack viscoelastic properties and can constrain the deformation of surrounding cement paste. However, the deformation patterns of porous lightweight aggregates are unclear, and relevant testing methods are lacking, requiring further research.

[0004] The existing compression cylinder method uses the pressure when a stamping die is pressed in 20mm to obtain the cylinder compressive strength of lightweight aggregate particles, but it cannot obtain the deformation law of lightweight aggregate particles under long-term compression (180-360 days) under constrained conditions. Therefore, a dial indicator and a strain transmission rod are connected to the outer surfaces of the stamping die and the confining cylinder, respectively. Using this device to conduct cylinder compressive strength tests, the strain of lightweight aggregate particles under compression under constrained conditions can be obtained as a function of time. This allows for analysis of the long-term compressive performance of lightweight aggregate particles under constrained conditions, and the materials and dimensions of the device are also provided. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a loading method and apparatus for constraining the long-term deformation of lightweight aggregates under pressure. The method primarily utilizes a creep meter composed of a lower pressure plate, an upper pressure plate, a nut, a lead screw, and a spring to apply a long-term, constant constraint pressure to the lightweight aggregates located within the confining pressure cylinder, which is composed of a confining pressure cylinder, a guide cylinder, and a stamping die. A dial indicator on the outer wall of the confining pressure cylinder is used to measure the deformation corresponding to the accumulated lightweight aggregates, thereby obtaining the stress-strain relationship of the lightweight aggregates under long-term load and thus obtaining the long-term performance of the lightweight aggregate particles under pressure under constraint.

[0006] This invention provides a loading method for constraining the long-term deformation of lightweight aggregate under compression, comprising the following steps:

[0007] S1. Preparation of lightweight aggregate samples:

[0008] S2. After filling the confining cylinder with the lightweight aggregate obtained in step S1, connect it to the guide cylinder and the lower end of the stamping die in sequence, and evenly set four dial gauges and four strain transmission iron rods on the outer circumference of the confining cylinder to obtain a bearing device.

[0009] S3. Move the bearing device obtained in step S2 into the center of the lower pressure plate, and use nuts to bring the lower surface of the upper pressure plate into contact with the upper end of the stamping die. The thickness t1 of the bottom plate in the stamping die is in the range of t1>6mm, and the thickness t5 of the side wall of the stamping die should meet the following requirements:

[0010]

[0011] Where t5 is the thickness of the sidewall of the stamping die; E1 is the stability coefficient of the stamping die; D2 is the elastic modulus of the stamping die; f is the outer diameter of the stamping die. s The compressive strength of lightweight aggregate;

[0012] S4. Align the press with the center of the upper pressure plate, read the initial reading of the dial indicator, and apply a uniform load to the bearing device obtained in step S2 at a speed of 300N to 500N per second. When the pressure reaches 20% of the compressive strength of the lightweight aggregate cylinder, obtain the change in the dial indicator. The compressive strength is generated by the confining cylinder and the guide cylinder. The thickness t3 at the second end of the confining cylinder should satisfy the following expression:

[0013]

[0014] Where t3 is the thickness of the second end of the confining cylinder; P1 is the pressure value when the depth of the confining cylinder containing the sample pressed into the stamping die reaches 20mm; P2 is the weight of the stamping die; D1 is the outer diameter of the confining cylinder; σ is the allowable stress of the selected material at the design temperature; and S is the area of ​​the stamping die base plate.

[0015] The thickness t4 at the first end of the confining cylinder should satisfy the following expression:

[0016]

[0017] The thickness t2 of the bottom plate in the confining cylinder is in the range of t2>10mm;

[0018] If the change of each dial gauge is less than 10% of the average change of the four dial gauges, then continue loading and proceed to step S5; if the change of one or more dial gauges is greater than or equal to 10% of the average change of the four dial gauges, then unload the stress, adjust and repressurize.

[0019] S5. First, continue to pressurize the bearing device after loading in step S4 to 40% of the compressive strength of the lightweight aggregate cylinder, obtain the change of the dial gauge, and take the average of the changes of the four dial gauges at this time as the initial deformation value under the load of 40% of the cylinder compressive strength; then tighten the nut at the connection between the screw and the upper pressure plate to unload the stress, and record the readings of the four dial gauges. If the deformation of any dial gauge changes by more than 10%, repressurize to 40% of the compressive strength of the lightweight aggregate cylinder, and adjust the tightness of the nut until the deformation of each dial gauge is less than 10% after unloading.

[0020] S6. Record the reading of the dial indicator at the specified testing time, and calculate the strain ε of the lightweight aggregate. a The time to draw the lightweight aggregate - ε a The curve shows the long-term deformation law of lightweight aggregate under constrained compression, and the strain ε of the lightweight aggregate is obtained. a The expression is as follows:

[0021]

[0022] Where, x t The average deformation measured by four dial gauges is the test time when the pressure is increased to 40% of the compressive strength of the lightweight aggregate cylinder; t6 is the height of the confining cylinder; x1 is the initial deformation value under a load of 40% of the cylinder compressive strength.

[0023] Preferably, the specific implementation process of step S1 is as follows:

[0024] S11. Screen out a certain amount of lightweight aggregate with a nominal particle size of 10mm to 20mm and put it into a drying oven to dry to a constant weight.

[0025] S12. Pour the dried lightweight aggregate obtained in step S11 evenly from 50mm away from the top opening of the confining cylinder until the lightweight aggregate at the top opening of the confining cylinder forms a triangular cone shape. Stop pouring and scrape it flat.

[0026] S13. Place the confining cylinder filled with lightweight aggregate from step S12 on the concrete test vibration table and vibrate until the lightweight aggregate inside the confining cylinder is compacted.

[0027] Preferably, in step S1, the volume content of lightweight aggregate with a nominal particle size of 10mm to 15mm accounts for 50% to 70% of the total volume of lightweight aggregate.

[0028] Preferably, in steps S4 and S5, the measurement time from the application of the load to obtaining the initial deformation value is less than or equal to 30 minutes.

[0029] Preferably, in step S6, the detection duration is 360 days, and the specified detection times are 1, 3, 7, 14, 28, 45, 90, 120, 150, 180, 270 and 360 days respectively.

[0030] In a second aspect, the present invention provides a loading device for the aforementioned loading method for long-term deformation of lightweight aggregate under constrained compression conditions, comprising a confining cylinder, a guide cylinder, a stamping die, a strain transmission rod, a dial indicator, a lower pressure plate, an upper pressure plate, a lead screw, a spring, and a base. A fixing plate is provided at the lower end of the outer wall of the confining cylinder, and a threaded pin with a circular hole is provided at the upper end of the outer wall of the stamping die. The upper end of the confining cylinder is connected to the lower end of the guide cylinder, and the upper end of the guide cylinder is connected to the lower end of the stamping die. A hole on the fixing plate is connected to the first mounting end of the dial indicator, and a second mounting end of the dial indicator is connected to the first mounting end of the strain transmission rod. The second mounting end of the strain transmission rod is connected to the threaded pin with a circular hole. The first mounting end of the lead screw is connected to the connecting hole of the upper pressure plate via a nut and a nut washer. The second mounting end of the lead screw passes sequentially through the connecting hole of the lower pressure plate and the spring and is connected to the base. The spring is located between the lower pressure plate and the base.

[0031] Preferably, the central axes of the confining cylinder, the guide cylinder, the stamping die, the upper pressure plate, the lower pressure plate, and the base are on the same straight line, and the central axes of the lead screw and the spring are on the same straight line.

[0032] Preferably, the diameter d2 of the lead screw should satisfy:

[0033]

[0034] Where d2 is the diameter of the lead screw; E2 is the elastic modulus of the lead screw.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. This invention provides the required dimensions of stamping die, spring, and lead screw for the long-term compressive performance of lightweight aggregate under constrained conditions. It utilizes a creep meter consisting of a lower pressure plate, an upper pressure plate, a nut, a lead screw, and a spring to apply pressure to a pressure-bearing cylinder consisting of a confining cylinder, a guide cylinder, and a stamping die to provide constrained conditions. By applying pressure to lightweight aggregate particles for 180-360 days, the long-term compressive performance of lightweight aggregate particles under constrained conditions can be obtained.

[0037] 2. To ensure the rigidity of the long-term loading device, this invention provides lower limit quantitative indicators for parameters such as the thickness of the bottom plate in the stamping die, the thickness of the bottom plate in the confining cylinder, the thickness of the second end of the confining cylinder, and the thickness of the side wall of the stamping die. The device size that is compatible with the lightweight aggregate to be tested can be designed by simple calculation, which effectively ensures the accuracy of the measurement.

[0038] 3. This invention uses four dial gauges installed on the outside of the pressure-bearing cylinder instead of using a universal testing machine or other instruments for displacement. The average value of the four dial gauges can be used to determine whether pressure balance has been applied, resulting in less interference and higher accuracy in the measured deformation data of the lightweight aggregate inside the cylinder. Attached Figure Description

[0039] Figure 1 This is a structural diagram of the loading device of the present invention for constraining the long-term deformation of lightweight aggregates under compression conditions;

[0040] Figure 2 This is a front view of the loading device of the present invention for constraining the long-term deformation of lightweight aggregates under compression.

[0041] Figures 3a-3c This is a structural diagram of the confining cylinder, guide cylinder, and stamping die in the loading device of the present invention for constraining long-term deformation of lightweight aggregates under compression conditions;

[0042] Figure 4 This is a flowchart of the loading method of the present invention for constraining the long-term deformation of lightweight aggregates under compression.

[0043] Key reference numerals:

[0044] 1. Confining cylinder; 2. Guide cylinder; 3. Stamping die; 4. Fixing plate; 5. Threaded pin with round hole; 6. Strain transmission rod; 7. Dial gauge; 8. Lower pressure plate; 9. Upper pressure plate; 10. Nut; 11. Lead screw; 12. Spring; 13. Base. Detailed Implementation

[0045] To fully describe the technical content, structural features, objectives, and effects of this invention, a detailed description will be provided below in conjunction with the accompanying drawings.

[0046] Loading devices used to constrain the long-term deformation of lightweight aggregates under compression, such as Figure 1 As shown, it includes a confining pressure cylinder 1, a guide cylinder 2, a stamping die 3, a strain transmission rod 6, a dial indicator 7, a lower pressure plate 8, an upper pressure plate 9, a lead screw 11, a spring 12, and a base 13, as follows. Figure 3b As shown, the lower end of the guide cylinder 2 is provided with an inner boss, such as... Figure 3c As shown, the upper end of the confining cylinder 1 is provided with an outer boss, and the inner boss and the outer boss are connected.

[0047] like Figure 2As shown, a fixing plate 4 is provided at the lower end of the outer wall of the confining cylinder 1, and a threaded pin 5 with a round hole is provided at the upper end of the outer wall of the stamping die 3. The upper end of the confining cylinder 1 is connected to the lower end of the guide cylinder 2, and the upper end of the guide cylinder 2 is sleeved with the lower end of the stamping die 3. The hole on the fixing plate 4 is connected to the first mounting end of the dial indicator 7, the second mounting end of the dial indicator 7 is connected to the first mounting end of the strain transmission iron rod 6, and the second mounting end of the strain transmission iron rod 6 is connected to the threaded pin 5 with a round hole.

[0048] The first mounting end of the lead screw 11 is connected to the connecting hole of the upper pressure plate 9 through the nut 10 and the nut washer. The second mounting end of the lead screw 11 passes through the connecting hole of the lower pressure plate 8 and the spring 12 in sequence and is connected to the base 13. The spring 12 is located between the lower pressure plate 8 and the base 13. The spring 12 is a square formed by 2×2.

[0049] To ensure that the entire loading device provides long-term constraint loading for the lightweight aggregate, it is necessary to ensure that the central axes of the confining cylinder 1, guide cylinder 2, stamping die 3, upper pressure plate 9, lower pressure plate 8 and base 13 are on the same straight line, and the central axes of the lead screw 11 and spring 12 are on the same straight line.

[0050] Under the test load, the tensile stress of the lead screw 11 should not exceed 30% of the material's yield point, the working pressure of the spring 12 should not exceed 80% of the allowable ultimate load, and the compressive deformation of the spring 12 during operation should not be less than 20mm. The diameter d2 of the lead screw 11 should meet the following requirements:

[0051]

[0052] Where d2 is the diameter of lead screw 11; E2 is the elastic modulus of lead screw 11.

[0053] The dimensions of spring 12 should satisfy the following expression:

[0054]

[0055]

[0056]

[0057] Where C is the heave ratio of spring 12; d is the diameter of spring 12; f is the deformation of spring 12 under working load; τ is the shear stress; [τ] is the allowable shear stress; G is the shear modulus; n is the effective number of turns of spring 12; and D is the center diameter of spring 12.

[0058] In another aspect, the present invention provides a loading method for constraining the long-term deformation of lightweight aggregates under compression, such as... Figure 4As shown, the screened and dried lightweight aggregate is poured into the confining pressure cylinder 1 with a bottom. Then, the confining pressure cylinder 1 is assembled with other parts of the measuring device in sequence. Pressure is applied by a combination of a lower pressure plate 8, an upper pressure plate 9, a nut 10, a lead screw 11, and a spring 12. Data is then collected and analyzed. The specific implementation steps are as follows:

[0059] S1. Preparation of lightweight aggregate samples:

[0060] S11. Sift 5L of lightweight aggregate samples with a nominal particle size of 10mm to 20mm. In a preferred embodiment, fly ash ceramsite is allowed to be in a nominal particle size of 10mm to 15mm, and ultra-lightweight ceramsite is allowed to be in a nominal particle size of 5mm to 10mm or 5mm to 20mm. Dry the samples in a drying oven until constant weight. Specifically, the volume content of lightweight aggregate samples with a nominal particle size of 10mm to 15mm should account for 50% to 70% of the total.

[0061] S12. Using a sampling spoon or shovel, pour the dry lightweight aggregate sample obtained in step S11 evenly from 50mm away from the top opening of the confining cylinder 1 or using a standard funnel. Let the lightweight aggregate sample fall naturally without colliding with the confining cylinder 1. Continue pouring until the lightweight aggregate sample at the top opening of the confining cylinder 1 forms a triangular pyramid shape. Then stop pouring and use a ruler to scrape the surface level from the center to both sides along the edge of the confining cylinder 1. Fill any depressions on the surface with lightweight aggregate of smaller particle size.

[0062] S13. Place the confining cylinder 1 filled with lightweight aggregate samples from step S12 on the concrete test vibration table and vibrate until the lightweight aggregate samples inside the confining cylinder are compacted. Specifically, fill the confining cylinder 1 with lightweight aggregate samples until it is higher than the opening of the confining cylinder 1, place it on the concrete test vibration table and vibrate for 3 seconds, then fill the confining cylinder 1 with lightweight aggregate samples until it is higher than the opening of the confining cylinder 1, place it on the vibration table and vibrate for 5 seconds, and scrape or level the lightweight aggregate samples with the opening of the confining cylinder 1.

[0063] S2. Connect the confining cylinder 1, which is filled with the lightweight aggregate sample in step S13, to the guide cylinder 2 and the stamping die 3 in sequence, and evenly set four dial gauges 7 and four strain transmission iron rods 6 on the outer circumference of the confining cylinder 1 to obtain the bearing device.

[0064] S3. Move the bearing device obtained in step S2 into the center of the lower pressure plate 8, and use the nut 10 to bring the lower surface of the upper pressure plate 9 into contact with the upper end of the stamping die 3, as follows. Figure 3a As shown, the thickness t1 of the base plate in stamping die 3 has a range of t1>6mm, and the thickness t5 of the sidewall of stamping die 3 should satisfy:

[0065]

[0066] Where t5 is the thickness of the sidewall of stamping die 3; E1 is the stability coefficient of stamping die 3; D2 is the elastic modulus of stamping die 3; f is the outer diameter of stamping die 3; s The compressive strength of lightweight aggregate.

[0067] S4. Align the press with the center of the upper pressure plate 9, read the initial reading of dial gauge 7, and apply a uniform load to the bearing device obtained in step S2 at a speed of 300N to 500N per second. When the pressure reaches 20% of the compressive strength of the lightweight aggregate, read the reading of dial gauge 7 and subtract it from the initial reading of dial gauge 7 to obtain the change in dial gauge 7. The compressive strength is generated by the confining cylinder and the guide cylinder. The compressive strength is one of the structures that generate the constraint conditions in the device of this invention. The thickness t3 at the second end of the confining cylinder 1 should satisfy the following expression:

[0068]

[0069] Where t3 is the thickness of the second end of the confining cylinder 1; P1 is the pressure value when the stamping die 3 presses into the confining cylinder 1 containing the sample to a depth of 20mm; P2 is the gravity of the stamping die 3; D1 is the outer diameter of the confining cylinder 1; σ is the allowable stress of the selected material at the design temperature; and S is the area of ​​the bottom plate of the stamping die 3.

[0070] The thickness t4 at the first end of the confining cylinder 1 should satisfy the following expression:

[0071]

[0072] like Figure 3c As shown, the thickness t2 of the bottom plate in the confining cylinder 1 ranges from t2>10mm.

[0073] If the change in reading of each dial gauge 7 is less than 10% of the average change of the four dial gauge 7, then continue loading and proceed to step S5; if the change in reading of one or more dial gauge 7 is greater than or equal to 10% of the average change of the four dial gauge 7, then unload the stress, readjust and then apply pressure.

[0074] S5. First, continue to pressurize the bearing device after loading in step S4 to 40% of the compressive strength of the lightweight aggregate cylinder. Read the readings of the four dial gauges 7 and subtract them from the initial readings of the dial gauges 7 to obtain the change in the value of the dial gauges 7. Take the average value of the changes in the four dial gauges 7 at this time as the initial deformation value under a load of 40% of the compressive strength of the cylinder. Then, tighten the nut 10 at the connection between the screw 11 and the upper pressure plate 9 to unload the stress and record the readings of the four dial gauges 7. If the deformation of any dial gauge 7 changes by more than 10%, repressurize to 40% of the compressive strength of the lightweight aggregate cylinder and adjust the tightness of the nut 10 until the deformation of each dial gauge 7 is less than 10% after unloading.

[0075] Specifically, in the loading method of the present invention, the measurement time from the application of load to obtaining the initial deformation value is less than or equal to 30 minutes.

[0076] S6. Record the readings of dial gauge 7 on days 1, 3, 7, 14, 28, 45, 90, 120, 150, 180, 270, and 360, and calculate the strain ε of the lightweight aggregate sample. a Plot the time ε of the lightweight aggregate sample. a The curves show the long-term deformation characteristics of lightweight aggregate samples under constrained compression, and the strain ε. a The expression is as follows:

[0077]

[0078] Where, x t The average deformation measured by four dial gauges 7 is the test time when the pressure is increased to 40% of the compressive strength of the lightweight aggregate cylinder; t6 is the cylinder height of the confining cylinder 1; x1 is the initial deformation value under a load of 40% of the cylinder compressive strength.

[0079] Furthermore, the testing period is 360 days.

[0080] The following describes in further detail a loading method and apparatus for constraining long-term deformation of lightweight aggregate under compression conditions, based on specific embodiments:

[0081] In this specific embodiment, as shown in Figure 3, the specific dimensions of each component in the loading device are as follows: the base of the confining cylinder 1 has an inner diameter of 135mm, an inner diameter height of 8mm, an outer diameter of 160mm, and an outer diameter height of 20mm, and is made of Q235 steel; the confining cylinder 1 has an inner diameter of 115mm, an outer diameter of 135mm, and a height of 100mm, and is made of Q235 seamless steel pipe; the guide cylinder 2 has an inner diameter of 115mm, an outer diameter of 135mm, and a height of 100mm, and is made of Q235 seamless steel pipe; the stamping die 3 has an inner diameter of 93mm, an inner diameter height of 128mm, an outer diameter of 113mm, and an outer diameter height of 140mm, and is made of Q345 steel; and a fixing plate with a dial indicator screw hole. 4 is a steel block made of Q235 steel, with a length of 55mm, a width of 30mm, and a height of 5mm; the threaded pin 5 is a cross-head screw with a length of 15mm and a diameter of 4mm, with a small steel ring welded to its top; the strain transmission rod 6 is 80mm long and 10mm in diameter; the dial indicator 7 is 130mm high and 57mm wide; the lead screw 11 is 700mm high and made of ordinary HRB335 threaded steel with a cross-sectional diameter of 25mm; the nut 10 is the nut that matches the lead screw 11; the spring 12 is made of 60CrMnA spring steel, with a center diameter D of 120mm, a free height H0 of 275mm, a total number of coils n1 = 6, and a support number of coils n z=1.5, effective number of turns n=4.5; upper pressure plate 9, lower pressure plate 8 and base 13 are made of Q235 steel with a side length of 250mm and a thickness of 15mm.

[0082] The loading method in this specific embodiment is implemented as follows:

[0083] S1. Preparation of lightweight aggregate samples:

[0084] S11. Take 5L of lightweight aggregate samples with a nominal particle size of 10mm to 20mm. Fly ash ceramsite is allowed to be in a nominal particle size of 10mm to 15mm, and ultra-lightweight ceramsite is in a nominal particle size of 5mm to 10mm or 5mm to 20mm. Dry the samples in a drying oven to constant weight. The volume content of the lightweight aggregate sample with a nominal particle size of 10mm to 15mm should account for 50% to 70% of the total.

[0085] S12. Using a sampling spoon, pour the dry lightweight aggregate sample obtained in step S11 evenly from 50mm away from the top opening of the confining cylinder 1, allowing the lightweight aggregate sample to fall naturally without colliding with the confining cylinder 1, until the lightweight aggregate sample at the top opening of the confining cylinder 1 forms a triangular cone shape. Stop pouring and use a ruler to scrape the surface level from the center to both sides along the edge of the confining cylinder 1. Fill the surface depressions with lightweight aggregate with smaller particle size.

[0086] S13. Fill the lightweight aggregate sample with confining cylinder 1 until it is higher than the opening of confining cylinder 1, place it on the concrete test vibration table and vibrate for 3 seconds, then fill the lightweight aggregate sample with it until it is higher than the opening of confining cylinder 1, place it on the vibration table and vibrate for 5 seconds, and scrape or level the lightweight aggregate sample with the opening of confining cylinder 1.

[0087] S2. Connect the confining cylinder 1, which is filled with the lightweight aggregate sample in step S13, to the guide cylinder 2 and the stamping die 3 in sequence, and evenly set four pairs of dial gauges 7 and strain transmission iron rods 6 on the outer circumference of the confining cylinder 1 to obtain the bearing device.

[0088] Connect the upper end of the confining pressure cylinder 1 to the lower end of the guide cylinder 2. Connect the confining pressure cylinder 1 and the strain transmission iron rod 6 to the transmission iron rod screw hole of the confining pressure cylinder 1 through the threaded pin 5 with a round hole. Fix the dial indicator 7 to the stamping die 3 through the dial indicator screw hole of the stamping die 3 and the fixing plate 4. Embed the stamping die 3 into the guide cylinder 2 along the inner surface of the loading device, so that the scale line of the stamping die 3 is aligned with the upper edge of the guide cylinder 2, and connect the lower end of the dial indicator 7 to the first end of the strain transmission iron rod 6. Install the lower pressure plate 8 on the upper end of the base 13 with 4 lead rods 11 and 25 springs 12 through the hole corresponding to the lead rod. Place the upper pressure plate 9 on the upper end of the loading device through the hole corresponding to the lead rod 11. The upper end of the upper pressure plate 9 with the hole corresponding to the lead rod 11 has a spring washer with an inner diameter slightly larger than the hole. The spring washer has a nut 10 corresponding to the thread of the lead rod 11.

[0089] S3. Move the bearing device obtained in step S2 into the center of the lower pressure plate 8 using the handle, and make the lower surface of the upper pressure plate 9 and the upper end of the stamping die 3 contact using the nut 10.

[0090] S4. Align the press with the center of the upper pressure plate 9, read the initial reading of dial gauge 7, and apply a uniform load to the bearing device obtained in step S2 at a speed of 300N to 500N per second. When the pressure reaches 20% of the compressive strength of the lightweight aggregate, read the reading of dial gauge 7 and subtract it from the initial reading of dial gauge 7. If the change of each dial gauge 7 is less than 10% of the average change of the four dial gauge 7, continue loading and proceed to step S5. If the change of one or more dial gauge 7 is greater than or equal to 10% of the average change of the four dial gauge 7, unload the stress, readjust, and then apply pressure again.

[0091] S5. First, continue to pressurize the loaded bearing device obtained in step S4 to 40% of the compressive strength of the lightweight aggregate cylinder. Read the readings of four dial gauges 7 and subtract them from the initial readings of dial gauges 7 to obtain the change in dial gauge 7. Take the average of the changes in the four dial gauges 7 as the initial deformation value under a load of 40% of the cylinder compressive strength. Then, tighten the nut 10 at the connection between the screw 11 and the upper pressure plate 9 to unload the stress and record the readings of the four dial gauges 7. If the change in deformation of any dial gauge 7 exceeds 10%, repressurize to 40% of the compressive strength of the lightweight aggregate cylinder and adjust the tightness of the nut 10 until the change in deformation of each dial gauge 7 after unloading is less than 10%.

[0092] Specifically, in this embodiment, the measurement time from applying the load to obtaining the initial deformation value is less than or equal to 30 minutes.

[0093] S6. In this specific embodiment, the testing period is 360 days. Therefore, the readings of the dial gauge 7 are recorded on days 1, 3, 7, 14, 28, 45, 90, 120, 150, 180, 270, and 360, respectively, and the strain ε of the lightweight aggregate sample is calculated. a Plot the time-strain ε of the lightweight aggregate sample. a The curves were used to derive the long-term deformation law of lightweight aggregate samples under constrained compression conditions.

[0094] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A loading method for constraining the long-term deformation of lightweight aggregate under compression, characterized in that, It includes the following steps: S1. Preparation of lightweight aggregate samples: S2. After filling the confining cylinder with the lightweight aggregate obtained in step S1, connect it sequentially to the guide cylinder and the lower end of the stamping die. Four dial indicators and four strain transmission iron rods are evenly arranged on the outer circumference of the confining cylinder to obtain a bearing device. The upper outer boss of the confining cylinder is connected to the lower inner boss of the guide cylinder, and the upper end of the guide cylinder is sleeved with the lower end of the stamping die. S3. Move the bearing device obtained in step S2 into the center of the lower pressure plate. The first mounting end of the lead screw is connected to the connecting hole of the upper pressure plate through a nut and a nut washer. The second mounting end of the lead screw passes through the connecting hole of the lower pressure plate and the spring and is connected to the base. The spring is located between the lower pressure plate and the base, and the lower surface of the upper pressure plate is in contact with the upper end of the stamping die through a nut. The thickness t1 of the bottom plate in the stamping die is in the range of t1>6 mm, and the thickness t5 of the side wall of the stamping die should meet the following requirements: ； in, This refers to the thickness of the sidewall of the stamping die; This is the stability coefficient of the stamping die; The elastic modulus of the stamping die; The outer diameter of the stamping die; S is the compressive strength of the lightweight aggregate; S is the area of ​​the stamping die base plate. S4. Align the press with the center of the upper pressure plate, read the initial reading of the dial indicator, and apply a uniform load to the bearing device obtained in step S2 at a speed of 300N~500N per second. When the pressure reaches 20% of the compressive strength of the lightweight aggregate cylinder, obtain the change in the dial indicator. The compressive strength is generated by the confining cylinder and the guide cylinder, wherein the thickness t3 at the second end of the confining cylinder should satisfy the following expression: ； Where t3 is the thickness of the second end of the confining cylinder; P1 is the pressure value when the stamping die presses the confining cylinder containing the sample to a depth of 20mm; P2 is the gravity of the stamping die; and D1 is the outer diameter of the confining cylinder. The allowable stress of the selected material at the design temperature; S is the area of ​​the stamping die base plate; the second end of the confining cylinder refers to the side wall of the confining cylinder; The thickness t4 at the first end of the confining cylinder should satisfy the following expression: ； The first end of the confining cylinder refers to the outer protrusion at the upper end of the confining cylinder; the thickness t2 of the bottom plate in the confining cylinder is in the range of t2>10mm; If the change of each dial gauge is less than 10% of the average change of the four dial gauges, then continue loading and proceed to step S5; if the change of one or more dial gauges is greater than or equal to 10% of the average change of the four dial gauges, then unload the stress, adjust and repressurize. S5. First, continue to pressurize the bearing device after loading in step S4 to 40% of the compressive strength of the lightweight aggregate cylinder, obtain the change in the dial gauge readings, and take the average of the changes in the four dial gauge readings at this time as the initial deformation value under a load of 40% of the cylinder compressive strength; then tighten the nut at the connection between the screw and the upper pressure plate to unload the stress, and record the readings of the four dial gauges. If the deformation change of any dial gauge exceeds 10%, repressurize to 40% of the compressive strength of the lightweight aggregate cylinder, and adjust the tightness of the nut until the deformation change of each dial gauge is less than 10% after unloading. S6. Record the reading of the dial indicator at the specified testing time, and calculate the strain ε of the lightweight aggregate. a Plot the time-strain ε of lightweight aggregate. a The curve shows the long-term deformation law of lightweight aggregate under constrained compression, and the strain ε of the lightweight aggregate is obtained. a The expression is as follows: ； Where, x t The average deformation measured by four dial gauges is the test time when the pressure is increased to 40% of the compressive strength of the lightweight aggregate cylinder; t6 is the height of the confining cylinder; x1 is the initial deformation value under a load of 40% of the cylinder compressive strength.

2. The loading method for constraining long-term deformation of lightweight aggregate under compression as described in claim 1, characterized in that, The specific sub-steps of step S1 are as follows: S11. Screen out a certain amount of lightweight aggregate with a nominal particle size of 10mm~20mm and put it into a drying oven to dry to a constant weight; S12. Pour the dried lightweight aggregate obtained in step S11 evenly from 50mm away from the top opening of the confining cylinder until the lightweight aggregate at the top opening of the confining cylinder forms a triangular cone shape. Stop pouring and scrape the surface flat. S13. Place the confining cylinder filled with lightweight aggregate from step S12 on the concrete test vibration table and vibrate until the lightweight aggregate inside the confining cylinder is compacted.

3. The loading method for constraining long-term deformation of lightweight aggregate under compression as described in claim 1 or 2, characterized in that, In step S1, the volume content of lightweight aggregate with a nominal particle size of 10mm to 15mm accounts for 50% to 70% of the total volume of lightweight aggregate.

4. The loading method for constraining long-term deformation of lightweight aggregate under compression as described in claim 1, characterized in that, In steps S4 and S5, the measurement time from the application of the load to obtaining the initial deformation value is less than or equal to 30 minutes.

5. The loading method for constraining long-term deformation of lightweight aggregate under compression as described in claim 1, characterized in that, In step S6, the detection period is 360 days, and the specified detection times are 1 day, 3 days, 7 days, 14 days, 28 days, 45 days, 90 days, 120 days, 150 days, 180 days, 270 days and 360 days respectively.

6. The loading method for constraining long-term deformation of lightweight aggregate under compression as described in claim 1, characterized in that, It includes a confining cylinder, a guide cylinder, a stamping die, a strain transmission rod, a dial indicator, a lower pressure plate, an upper pressure plate, a lead screw, a spring, and a base. The confining cylinder has a fixed plate at its lower outer wall, and the stamping die has a threaded pin with a round hole at its upper outer wall. A hole on the fixed plate connects to the first mounting end of the dial indicator, and the second mounting end of the dial indicator connects to the first mounting end of the strain transmission rod. The second mounting end of the strain transmission rod connects to the threaded pin with the round hole.

7. The loading method for constraining long-term deformation of lightweight aggregate under compression as described in claim 6, characterized in that, The central axes of the confining cylinder, the guide cylinder, the stamping die, the upper pressure plate, the lower pressure plate, and the base are on the same straight line, and the central axes of the lead screw and the spring are on the same straight line.

8. The loading method for constraining long-term deformation of lightweight aggregate under compression according to claim 6, characterized in that, The diameter of the lead screw It should meet the following requirements: ； in, The diameter of the lead screw; Let be the elastic modulus of the lead screw.

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