Performance evaluation device and method for improving macadam mixture by using micro-doped cement

Abstract

The invention discloses a device and a method for evaluating the performance of a macadam mixture improved by micro-doped cement, the device comprises a rigid container, a temperature and pressure distribution sensor is arranged in the rigid container, a cylindrical rigid cushion block is fixed at the bottom in the rigid container, and a cylindrical lifting cushion block is placed on the rigid cushion block; a cylindrical detection test piece is placed on the lifting cushion block, a circular opening vertically corresponding to the detection test piece is formed in the center of the top of the rigid container, a rigid sliding way extending into the rigid container is arranged in the circular opening, the bottom end face of the rigid sliding way is flush with the top end face of the detection test piece, and a cylindrical rigid bearing plate is placed on the upper portion of the detection test piece. And the rigid bearing plate can move downwards along the rigid slide way under external loading and applied pressure. According to the device, the change of the volume of the test piece is measured by detecting the change of the pressure, temperature and volume of air in the device, the test method is more advanced, more accurate and more sensitive, and meanwhile, the detection precision is further improved through various thermal insulation measures.

Description

Technical Field

[0001] The present invention belongs to the field of improving gravel mixtures with micro - dosage cement, and particularly relates to a performance evaluation device and method for improving gravel mixtures with micro - dosage cement. Background Art

[0002] Cement - stabilized gravel and graded gravel are commonly used base and sub - base materials in roads; cement - stabilized gravel is a semi - rigid material, mainly relying on the skeleton interlock of aggregates and the cementing effect of cement to provide strength, and has a plate - like property; graded gravel is a typical flexible material, mainly relying on skeleton interlock to provide strength; the strength and stiffness of graded gravel are weaker than those of cement - stabilized gravel materials, but the requirements for raw materials of graded gravel are usually higher than those of cement - stabilized gravel.

[0003] The micro - dosage cement - improved gravel mixture mainly has the following characteristics:

[0004] ① The cement dosage is lower than that of cement - stabilized gravel, generally 1 - 3%.

[0005] ② The formed structural layer has a certain plate - like property in details and still shows flexibility in large sizes.

[0006] ③ It overcomes the inherent characteristics of temperature shrinkage and dry shrinkage cracks of water - stable gravel.

[0007] ④ The strength and stiffness are between those of graded gravel and cement - stabilized gravel, and the requirements for raw materials are relatively low.

[0008] At present, there are few evaluation methods for improving gravel with micro - dosage cement. Generally, the CBR value or 7 - day unconfined compressive strength is used for evaluation, but there are the following problems:

[0009] ① The CBR test is mainly used to evaluate non - cemented materials. The micro - dosage cement - improved gravel uses cement as a cementing material, and the CBR value cannot directly reflect its performance.

[0010] ② The 7 - day unconfined compressive strength test is mainly used to evaluate cemented materials. The micro - dosage cement - improved gravel has a low cement dosage, uniformly distributed micro - cracks in the structural layer, low strength after forming, and the 7 - day unconfined compressive strength cannot characterize the flexible characteristics of the micro - dosage cement - improved gravel.

[0011] The present invention overcomes the above problems and provides a performance evaluation device and method for improving gravel mixtures with micro - dosage cement in view of the characteristics of the micro - dosage cement - improved gravel mixture. Summary of the Invention

[0012] The present invention aims at the deficiencies of the prior art and provides a performance evaluation device and method for improving gravel mixtures with micro - dosage cement.

[0013] To achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0014] A device for evaluating the performance of a gravel mixture improved by micro-amount cement, comprising a rigid container, a temperature and pressure distribution sensor is arranged inside the rigid container, a cylindrical rigid cushion block is fixed at the inner bottom of the rigid container, a cylindrical lifting cushion block is placed on the rigid cushion block, a cylindrical test specimen is placed on the lifting cushion block, a circular opening corresponding to the upper and lower parts of the test specimen is arranged at the center of the top of the rigid container, a rigid slideway extending into the rigid container is arranged in the circular opening, the bottom end face of the rigid slideway is flush with the top end face of the test specimen, a cylindrical rigid bearing plate is placed on the upper part of the test specimen, and the rigid bearing plate can move downward along the rigid slideway under the pressure applied by external loading.

[0015] The further technology of the present invention:

[0016] Preferably, the inner wall of the rigid container is filled with heat-insulating material or is vacuum.

[0017] Preferably, the rigid cushion block, the lifting cushion block and the test specimen are coaxial and have the same diameter.

[0018] Preferably, lubricants are applied between the test specimen and the lifting cushion block and the rigid bearing plate.

[0019] Preferably, the outer parts of the rigid cushion block, the test specimen and the rigid slideway are wrapped with flexible sealing materials.

[0020] Preferably, an annular groove is arranged along the circumferential direction on the side wall of the rigid cushion block, and the bottom end of the sealing material is hermetically connected with the rigid cushion block through its annular groove.

[0021] Preferably, a water outlet with a switch is arranged at the bottom of the rigid container, and a water inlet with a switch and an exhaust port with a switch are arranged at the top.

[0022] Preferably, the evaluation method is as follows:

[0023] After putting the test specimen, before loading, close the water outlet, open the water inlet and the exhaust port, inject water until the rigid container is full of water, then stop injecting water, open the water outlet, drain the water in the rigid container, repeat 3 - 5 times, measure the volume of the drained water, and do not count the first value, calculate the average value, which is the air volume;

[0024] Close the water outlet, the water inlet and the exhaust port, apply pressure through external loading, and at the same time automatically count the displacement, pressure of the external loading, as well as the average temperature and average pressure of the temperature and pressure distribution sensor, and each value corresponds to time one by one; the pressure applied by the external loading gradually increases, and the test ends when the test specimen is damaged;

[0025] According to the ideal gas law, the lateral volume expansion rate of the test specimen can be calculated; record the pressure acting on the test specimen and the corresponding lateral volume expansion rate to draw a relationship graph;

[0026] The greater the pressure, the smaller the lateral volume expansion rate, and the better the skeleton performance.

[0027] Preferably, the calculation method of the lateral volume expansion rate η of the test specimen is as follows:

[0028]

[0029] In the formula: V 1 , T 1 , P 1 are the air volume, temperature and pressure before loading respectively; V 2 , T 2 , P 2 are the air volume, temperature and pressure during loading respectively; V 3 is the volume of the test specimen after forming.

[0030] Preferably, the calculation method of the pressure P acting on the test specimen is as follows:

[0031]

[0032] In the formula: S is the cross-sectional area of the rigid bearing plate, and F is the force applied by the external load.

[0033] The beneficial effects of the present invention are:

[0034] Compared with the existing CBR value and 7-day unconfined compressive strength and other indicators, this device and method can more directly and comprehensively characterize the performance of micro-dosed cement-improved gravel, and better guide the design and evaluation of micro-dosed cement-improved gravel mixtures. Among them, the lateral volume expansion rate index directly characterizes the large-size flexible characteristics of micro-dosed cement-improved gravel mixtures, filling the gap in existing research; this device uses large-size specimens, which can effectively reflect the large-size flexible characteristics of micro-dosed cement-improved gravel mixtures; this device measures the change in the volume of the specimen by detecting the changes in the air pressure, temperature and volume in the detection device, and the test method is more advanced, more accurate and more sensitive. At the same time, various heat insulation measures are adopted to further improve the detection accuracy. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0036] Figure 1 Overall view of the device

[0037] The symbols in the figure are: 1 - Rigid container, 2 - Rigid cushion block, 3 - Rigid slideway, 4 - Sealing material, 5 - Rigid bearing plate, 6 - Test specimen, 7 - Lifting cushion block, 8 - Water outlet, 9 - Water inlet, 10 - Exhaust port. Specific implementation manners

[0038] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] The present invention provides a device for evaluating the performance of a gravel mixture improved with micro - doped cement as shown in Figure 1 Figure, which includes a rigid container. The shape of the rigid container is not limited and can be cylindrical, cube - shaped or cuboid - shaped. In this embodiment, a cylindrical shape is selected.

[0040] The inside of the wall of the rigid container is filled with heat - insulating material or is vacuum, which is used to delay the rapid transfer of external heat to the inside of the device.

[0041] A temperature - pressure distribution sensor is arranged inside the rigid container to measure the temperature and pressure values inside the rigid container 1; a water outlet 8 with a switch is arranged at the bottom of the rigid container, and a water inlet 9 with a switch and an exhaust port 10 with a switch are arranged at the top of the rigid container.

[0042] A cylindrical rigid cushion block 2 is fixed at the inner bottom of the rigid container. A cylindrical lifting cushion block 7 is placed on the rigid cushion block 2, and a cylindrical test specimen 6 is placed on the lifting cushion block 7. A circular opening corresponding to the test specimen 6 up and down is provided at the center of the top of the rigid container. A rigid slideway 3 extending into the rigid container is arranged inside the circular opening. The bottom end surface of the rigid slideway 3 is flush with the top end surface of the test specimen 6. A cylindrical rigid bearing plate 5 is placed on the upper part of the test specimen 6. The rigid bearing plate 5 can move downward along the rigid slideway 3 under the external loading and applying pressure. When the test specimen 6 bears the load, it is in an approximately unconstrained lateral state.

[0043] It should be noted that the external loading in this embodiment can be any device that can apply pressure downward, as long as it is equipped with pressure data and movement data.

[0044] The rigid cushion block 2, the test specimen 6 and the rigid slideway 3 are wrapped with a flexible sealing material 4.

[0045] An annular groove is provided along the circumferential direction of the side wall of the rigid spacer block 2, and the bottom end of the sealing material 4 is sealingly connected to the rigid spacer block 2 through its annular groove. The annular groove of the rigid spacer block 2 is for better connection with the flexible sealing material 4 to achieve sealing performance.

[0046] It should be noted that the thickness of the rigid bearing plate 5 should be greater than the vertical displacement of the rigid bearing plate 5. If it is less, when the air pressure inside the container is greater than the outside and the rigid bearing plate 5 is completely pressed down, the internal air pressure will dissipate through the upper sealing material 4.

[0047] In this embodiment, the rigid spacer block 2, the lifting spacer block 7, and the test specimen 6 are coaxial and have the same diameter. Lubricant is applied between the test specimen 6 and the lifting spacer block 7 and the rigid bearing plate 5 to reduce the hoop effect during the loading process.

[0048] At the same time, pulleys can also be installed on the side of the rigid bearing plate 5 to reduce friction. The rigid slideway 3 is circular, and its annular wall is filled with heat-insulating material to prevent the external loading heat from being quickly transferred to the inside of the testing device.

[0049] The evaluation method is as follows:

[0050] After placing the test specimen, before loading, close the water outlet, open the water inlet and the exhaust port, inject water until the rigid container is full of water, then stop injecting water, open the water outlet, drain the water in the rigid container, repeat 3 - 5 times, measure the volume of the drained water, where the first value is not counted, and calculate the average value, which is the air volume;

[0051] Close the water outlet, the water inlet and the exhaust port, apply pressure through external loading, and at the same time automatically count the displacement, pressure of the external loading, as well as the average temperature and average pressure of the temperature - pressure distribution sensor, and each value corresponds one - to - one with time; the pressure applied by the external loading gradually increases, and the test ends when the test specimen is damaged;

[0052] According to the ideal gas state equation, the lateral volume expansion rate of the test specimen can be calculated; record the pressure acting on the test specimen and the corresponding lateral volume expansion rate and draw a relationship graph;

[0053] When the pressure is greater and the lateral volume expansion rate is smaller, the framework performance is better.

[0054] Furthermore: The specific calculation method of the lateral volume expansion rate η of the test specimen is as follows:

[0055]

[0056] In the formula: V 1 、T 1 、P 1are the air volume, temperature, and pressure before loading; V 2 , T 2 , P 2 are the air volume, temperature, and pressure during loading; V 3 is the volume after the test specimen is formed.

[0057] Furthermore: The calculation method of the pressure P acting on the test specimen is as follows:

[0058]

[0059] In the formula: S is the cross-sectional area of the rigid bearing plate, and F is the force applied by the external load.

[0060] Example 1:

[0061] Take granite aggregates from a certain project. To reduce the variability caused by different synthetic gradations, grading screening is carried out, and graded blending is carried out. The blending is divided into three synthetic gradations: coarse, medium, and fine (Gradation 1, Gradation 2, and Gradation 3. Coarse, medium, and fine are relative to the relative passing rate of the 4.75 mm sieve hole. The smaller the passing rate, the coarser). The synthetic gradation range requirements and the three blended synthetic gradations are shown in the following table.

[0062] Aggregate gradation passing rate table / %

[0063]

[0064] Use P.O42.5 cement for blending tests. The cement dosage is 2.5%. Use the vibration molding method to form specimens. 3 specimens are formed for each gradation, a total of 9 specimens. The specimen size is 30 cm in diameter and 30 cm in height; cure for 10 d in a curing room with a relative humidity of 95% and a curing temperature of 25 ± 2 °C. After curing, measure the volume of each specimen by the volume method. Conduct the test at room temperature of 20 °C and evaluate according to the above evaluation method. The test results are shown in the following table.

[0065] Summary of test results (I)

[0066]

[0067]

[0068] Note: In the above calculations, ν is uniformly taken as 0.3.

[0069] From the above test results, the average values of the lateral volume expansion rate and strength of the three gradations are as shown in the following table:

[0070] Summary of sorted test results (I)

[0071] Item Strength / MPa Lateral volume expansion rate Remarks Gradation 1 2.01 0.152 Gradation 2 2.64 0.118 Gradation 3 1.12 0.071

[0072] It can be seen from sorting out the data in the above table that at a cement dosage of 3%, although the lateral volume expansion rate of gradation three is small, its strength is small. By comparison, it can be known that gradation two has high strength and a moderate lateral volume expansion rate, so gradation two is a better gradation.

[0073] Example 2:

[0074] Limestone aggregates were taken from a certain project for grading and blending, and the synthetic gradation is shown in the following table.

[0075] Passing rate table of mineral aggregate gradation (two) / %

[0076] Sieve pore size / mm 26.5 19 9.5 4.75 2.36 0.6 0.075 Passing rate 100 95 60 40 30 10 5

[0077] P.O42.5 cement was used for blending tests. The cement dosages were 1%, 2% and 3% respectively. Specimens were formed by the vibration molding method. There were 3 specimens for each cement dosage, a total of 9 specimens. The specimen size was 30 cm in diameter and 30 cm in height; they were cured in a curing room with a relative humidity of 95% and a curing temperature of 25±2°C for 10 d. After curing, the volume of each specimen was measured by the volume method. The test was carried out at room temperature of 20°, and evaluated according to the above evaluation method. The test results are shown in the following table.

[0078] Summary table of test results (two)

[0079]

[0080] It can be obtained from sorting out the above test results that the average values of the lateral volume expansion rate and strength of the three cement dosages are as shown in the following table:

[0081] Summary table of sorted test results (two)

[0082] Cement content / % Strength / MPa Lateral volume expansion rate Remarks 1% Cement 0.94 0.160 2% Cement 2.21 0.134 3% Cement 3.28 0.086

[0083] It can be seen from sorting out the data in the above table that the higher the cement dosage, the greater the strength and the smaller the lateral volume expansion rate.

[0084] In this article, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0085] In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "arranged", "installed", "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0086] The above content is only an example and explanation of the structure of the present invention. Those skilled in the art of the present technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the structure of the invention or exceed the scope defined by the claims of the present invention, they should fall within the protection scope of the present invention.

Claims

1. A performance evaluation device for improving crushed stone mixture with a small amount of cement, characterized in that: It includes a rigid container, in which a temperature and pressure distribution sensor is arranged, a cylindrical rigid pad is fixed at the bottom of the rigid container, a cylindrical lifting pad is placed on the rigid pad, a cylindrical test piece is placed on the lifting pad, a circular opening corresponding to the upper and lower parts of the test piece is arranged at the top center of the rigid container, a rigid slide extending into the rigid container is arranged in the circular opening, the bottom end surface of the rigid slide is flush with the top end surface of the test piece, a cylindrical rigid bearing plate is placed on the upper part of the test piece, and the rigid bearing plate can move downward along the rigid slide under the pressure applied by external loading.

2. A performance evaluation device for improving crushed stone mixture with a small amount of cement added according to claim 1, characterized in that: The interior of the wall of the rigid container is filled with a heat insulating material or is a vacuum.

3. A performance evaluation device for improving crushed stone mixture with a small amount of cement as claimed in claim 1, characterized in that: The rigid pad, the lifting pad and the testing piece are coaxial and have the same diameter.

4. A performance evaluation device for improving crushed stone mixture with a small amount of cement as claimed in claim 1, characterized in that: Lubricant is applied between the test piece, the lifting pad and the rigid bearing plate.

5. A performance evaluation device for improving crushed stone mixture with a small amount of cement added according to claim 1, characterized in that: The rigid pad, the test piece and the rigid slideway are wrapped with a flexible sealing material.

6. A performance evaluation device for improving crushed stone mixture with a small amount of cement as claimed in claim 5, characterized in that: The side wall of the rigid pad is provided with an annular groove along the circumferential direction, and the bottom end of the sealing material is sealed and connected with the rigid pad through the annular groove.

7. A performance evaluation device for improving crushed stone mixture with a small amount of cement as claimed in claim 1, characterized in that: The bottom of the rigid container is provided with a water outlet with a switch, and the top is provided with a water inlet with a switch and an exhaust port with a switch.

8. A performance evaluation device for improving crushed stone mixture with a small amount of cement added according to claim 7, characterized in that: The evaluation method is: After placing the test piece, before loading, close the water outlet, open the water inlet and the exhaust port, and add water until the rigid container is full of water. Then stop adding water, open the water outlet, and drain the water in the rigid container. Repeat 3 to 5 times and measure the volume of the discharged water. The first value is not counted, and the average value is calculated, which is the air volume. Close the water outlet, water inlet and exhaust port, apply pressure through external loading, and automatically calculate the displacement and pressure of external loading, as well as the average temperature and average pressure of the temperature and pressure distribution sensor. Each value corresponds to each other over time. The pressure applied by external loading gradually increases, and the test ends when the test piece is destroyed. The lateral volume expansion rate of the test piece can be calculated according to the ideal gas state equation; the pressure acting on the test piece and the corresponding lateral volume expansion rate are recorded and a relationship diagram is drawn; The greater the pressure, the smaller the lateral volume expansion rate, and the better the skeleton performance.

9. A performance evaluation device for improving crushed stone mixture with a small amount of cement added according to claim 8, characterized in that: The calculation method of the lateral volume expansion rate η of the test piece is as follows: Where: V1, T1, P1 are the air volume, temperature and pressure before loading, respectively; V2, T2, P2 are the air volume, temperature and pressure during loading, respectively; V3 is the volume of the test piece after molding.

10. A performance evaluation device for improving crushed stone mixture with a small amount of cement as claimed in claim 8, characterized in that: The calculation method of the pressure P acting on the test piece is as follows: Where: S is the cross-sectional area of ​​the rigid load-bearing plate, and F is the force applied by the external load.

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