A cement-based material shrinkage stress detection device and full-temperature detection method thereof

Abstract

A device for detecting shrinkage stress of cement-based materials and a full-temperature detection method thereof. Since the detection precision of shrinkage or expansion stress generated by concrete deformation is high, difficult, inefficient and poor in accuracy, there is a lack of test devices and methods for quickly evaluating concrete shrinkage or expansion stress before construction. The quality of civil engineering construction using high-performance cement-based materials is seriously affected and urgently needs to be solved. In the detection device of the present invention, the sleeve is detachably connected in the mold, and the two ends of the mold are respectively provided with a first connecting piece and a second connecting piece. A force sensor is provided in the second connecting piece. The disc end of the disc-type cylinder is detachably connected to the first connecting piece. The column end of the disc-type cylinder passes through the sleeve and is tightly attached to the detection end of the force sensor. A gap is set between the column end of the disc-type cylinder and the sleeve, and concrete is filled between the sleeve and the mold. The detection method of the present invention is implemented based on the detection device. The present invention is used for shrinkage stress detection of cement-based materials.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering, and in particular relates to a cement-based material shrinkage stress detection device and a full-temperature detection method thereof. Background Art

[0002] Cement-based materials will undergo volume changes, some of which are spontaneous and some are caused by external factors such as temperature, humidity and load. For example, the volume change caused by the self-drying effect of the hydration reaction and water evaporation during the development of concrete strength is called concrete shrinkage. It is a time-related deformation property that can reduce the volume of concrete without being affected by external forces. Volume change is one of the important factors affecting the long-term strength and durability of cement-based materials. Autogenous shrinkage is the reduction of macroscopic volume caused by capillary negative pressure and internal relative humidity caused by cement hydration reaction under the condition of concrete being isolated from external moisture, and the generation of shrinkage stress can be considered to be caused by a certain degree of restriction on volume shrinkage deformation. For actual engineering, when the shrinkage tensile stress on concrete is greater than the tensile strength at this moment, the concrete will crack. The early shrinkage stress of high-performance concrete mainly includes autogenous shrinkage stress, temperature stress and drying shrinkage stress, among which autogenous shrinkage stress is the most significant. Because the salient features of high-performance concrete mix are low water-cement ratio, more binder and a large amount of ultrafine mineral admixtures, the rapid self-drying effect leads to a greater volume change in high-performance concrete than in ordinary concrete. Early high-performance concrete was subject to constraints including internal and external constraints. The existence of constraints will cause autogenous shrinkage stress inside the concrete. In addition to being related to the autogenous shrinkage strain, the magnitude of the autogenous shrinkage stress is also affected by the mechanical properties of the concrete, such as tensile strength.

[0003] At present, the experimental evaluation methods of autogenous shrinkage stress include uniaxial constraint test, ring method, etc. In terms of constraint form, axial constraint test can be divided into two forms, one is end constraint and the other is continuous constraint inside the steel bar. The internal constraint shrinkage test of steel bar is used to simulate the restriction of steel bar on concrete shrinkage, which is an incomplete constraint. When the length of the specimen is much larger than the cross-sectional size, it can be approximately considered that only axial shrinkage occurs. If it is restricted, uniformly distributed tensile stress, i.e., shrinkage stress, will be generated in its cross section. The thinner the specimen, the easier it is to implement axial constraint, the more fully the cracks develop, and the better the experimental effect. One of the concrete shrinkage stress measuring instruments is based on the fact that after the slender shrinkage, the concrete specimen is pulled back to the initial position of the concrete specimen by the tension system. At this time, the tensile stress of the system is the shrinkage stress of the concrete. The test device is complex and requires high precision. The axial restrained shrinkage experiment used in teaching is to compare the concrete specimens with embedded steel bars with the free shrinkage experiment of the same size. Strain gauges are attached to the steel bars to monitor the restrained deformation, and then the restrained stress can be indirectly measured. The stress state of this component is similar to the actual structure and does not require special loading equipment and control systems. However, it only considers the restraining effect of the steel bars. The restraining effect of the steel bars will increase the tensile creep of the concrete specimen and reduce the measured shrinkage stress. This method is mainly used to study the effects of different reinforcement ratios, steel bar diameters, steel bar surface shapes, bonding lengths, etc. on concrete shrinkage restrictions, and can obtain a quantitative relationship between different reinforcement ratios and restraint rates.

[0004] At present, more and more high-performance concrete and ultra-high-performance cement-based materials are used in practical projects. They have low water-cement ratio and large amount of cementitious materials. Their autogenous shrinkage is 2 to 4 times that of ordinary concrete. The risk of cracking caused by shrinkage deformation is greatly increased. In order to quickly and easily determine the crack resistance of the above materials, accurate, reliable and fast autogenous shrinkage stress test devices and methods are needed. It is difficult to quantitatively detect the shrinkage (frost heave) stress of cement-based materials under high temperature, room temperature or negative temperature environment. In short, due to the high precision requirements of concrete volume deformation detection, the difficulty, low efficiency and poor accuracy of autogenous shrinkage stress detection, there is a lack of test devices and methods for quickly evaluating concrete shrinkage stress before construction. The quality of civil engineering construction using high-performance cement-based materials is seriously affected and urgently needs to be solved quickly. Summary of the invention

[0005] In view of the above problems, the present invention discloses a cement-based material shrinkage stress detection device and a full-temperature detection method thereof.

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

[0007] A device for detecting shrinkage stress of cement-based materials comprises a mould, a first connecting piece, a second connecting piece, a disc-type cylinder, a sleeve, a force sensor and two groups of positioning pins, wherein the sleeve is detachably connected in the mould, the first connecting piece and the second connecting piece are respectively arranged at two ends of the mould, the force sensor is arranged in the second connecting piece, the disc end of the disc-type cylinder is detachably connected to the first connecting piece, the column end of the disc-type cylinder passes through the sleeve and is tightly attached to the detection end of the force sensor, a gap is arranged between the column end of the disc-type cylinder and the sleeve, concrete is filled between the sleeve and the mould, the two groups of positioning pins are arranged in the concrete, one group of positioning pins in the two groups is inserted into the concrete through the disc-type cylinder, and the other group of positioning pins in the two groups is inserted into the concrete through the mould.

[0008] As a preferred solution: the disc-type column includes a disc body and a steel column, one end of the steel column is fixedly connected to the disc body, and the steel column and the disc body are coaxially arranged.

[0009] As a preferred solution: the mold includes an outer cylinder and a bottom plate, and annular bosses are respectively processed on the outer walls at both ends of the outer cylinder, one of the two annular bosses is detachably connected to the first connecting piece, and a bottom plate is provided at the other end of the outer cylinder, and the other of the two annular bosses is detachably connected to the second connecting piece through the bottom plate, the first connecting piece is a first flange, and the second connecting piece is a second flange.

[0010] As a preferred solution: the outer cylinder is formed by enclosing two semicircular arc pieces, and the two semicircular arc pieces are detachably connected.

[0011] As a preferred solution: one end of the sleeve is tightly attached to the end surface of the disc body through a first sealing ring, and the other end of the sleeve is tightly attached to the inner wall of the mold bottom plate through a second sealing ring.

[0012] As a preferred solution: a limit ring is sleeved outside the force sensor.

[0013] As a preferred solution: the force sensor is a disc-type pressure sensor.

[0014] As a preferred solution: an adjusting screw is arranged on the first connecting member, the adjusting screw is arranged at the central axis of the first connecting member, and a rocker is arranged outside the adjusting screw.

[0015] A testing method using a cement-based material shrinkage stress detection device, characterized in that the testing method includes the following contents:

[0016] Install the mold: insert a steel column into the sleeve, hold one end of the steel column and push it until the front end of the steel column abuts against the second flange and then stop pushing;

[0017] Put concrete into the mold and tamp it, vibrate it to make it dense, and then take out the steel column from the casing;

[0018] A limiting ring is arranged in the second flange, a force sensor is arranged in the limiting ring, and the force sensor is arranged in the second flange through the limiting ring to ensure that the central axis of the force sensor coincides with the central axis of the second flange, and then the cylindrical end of the disc-type cylinder is inserted into the sleeve until the cylindrical end of the disc-type cylinder is against the force sensor and the push is stopped, and then the first flange is installed on the mold;

[0019] A set of positioning pins is arranged on the disc-shaped column to adjust the initial position of the disc-shaped column in the concrete, and at the same time, the connection strength between the disc-shaped column and the concrete is enhanced, and the initial reading of the force sensor is recorded;

[0020] Record the readings of the force sensor at different ages and subtract the initial reading of the force sensor to obtain the autogenous shrinkage stress of concrete at room temperature or high temperature environment.

[0021] As a preferred solution: the first flange and the second flange are removed from the mold respectively, and the disc-shaped column, the sleeve and the concrete are taken out in turn, and the force sensor is removed from the second flange and installed at the adjustment screw of the first flange, and the second flange is reinstalled on one end of the mold, and the disc-shaped column is re-placed on the mold, ensuring that the column of the disc-shaped column passes through the bottom plate and is pressed against the second flange, and concrete is filled into the mold and inserted and tamped, and after vibrating and compacting, the force sensor is installed on the other end of the mold;

[0022] The mold with the first flange, the second flange, the force sensor and the disc-shaped cylinder is placed in a low temperature environment for testing, a set of positioning pins is set on the disc-shaped cylinder to adjust the initial position of the disc-shaped cylinder in the concrete and enhance the connection strength between the disc-shaped cylinder and the concrete, and the initial reading of the force sensor is recorded at the same time;

[0023] Record the readings of the force sensor at different ages and subtract the initial reading of the force sensor to obtain the frost heave stress of concrete in a negative temperature environment.

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention realizes quantitative detection of the autogenous shrinkage stress of cement-based materials through the cooperation between the mold, the first connecting member, the second connecting member, the disc-shaped cylinder, the sleeve, the force sensor and the two groups of positioning pins. The acquisition method is simple and direct, eliminating the tedious calculation process. The data of the autogenous shrinkage stress of the cement-based material is more accurate, which is conducive to a comprehensive evaluation of the crack resistance of the cement-based material.

[0026] 2. The device of the present invention can realize the shrinkage (frost heave) stress detection of cement-based materials under high temperature, room temperature or negative temperature environment, realize the full temperature detection process of internal stress of cement-based materials, effectively realize the detection effect of one device with multiple uses, and the detection results are accurate and reliable.

[0027] 3. The detection method of the present invention has the characteristics of high efficiency, simple operation steps, low operation difficulty, and time and labor saving.

[0028] Fourth, the present invention can be applied to engineering laboratory testing and provide basic data for the design of concrete mix ratio.

[0029] 5. The present invention is particularly suitable for simulating the shrinkage stress detection of concrete at the construction site. According to the actual temperature of the concrete at the construction site, a laboratory simulation test is carried out to obtain a more realistic and reliable shrinkage stress value of the concrete, which has important application value in preventing early cracking of concrete, improving project quality and service life.

[0030] 6. The present invention has a simple structural design, is easy to assemble, has a low manufacturing cost, a reliable detection structure, and is easy to promote and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] For ease of explanation, the present invention is described in detail with reference to the following specific implementations and the accompanying drawings.

[0032] Figure 1 It is a main structural cross-sectional view of the testing device in the present invention when it is in a horizontal setting. The testing device in the figure is used for concrete shrinkage stress detection under high temperature and normal temperature environments;

[0033] Figure 2 It is a front structural cross-sectional view of the test device of the present invention when it is in a vertical setting;

[0034] Figure 3 It is a main structural cross-sectional view of the test device in the present invention when it is in a horizontal setting. The test device in the figure is used for concrete shrinkage stress detection in a negative temperature environment;

[0035] Figure 4 This is the main structural diagram of the steel column;

[0036] Figure 5 This is a trend diagram of the shrinkage stress change of room temperature concrete during the test process of the present invention.

[0037] The following are marked in the figure:

[0038] 1-mold; 1-1-outer cylinder; 1-2-bottom plate; 1-3-annular boss; 2-first connecting piece; 3-second connecting piece; 4-disc-type column; 4-1-disc body; 4-2-column; 5-sleeve; 6-force sensor; 7-positioning pin; 8-concrete; 9-first sealing ring; 10-second sealing ring; 11-steel column; 12-limiting ring; 13-adjusting screw; 14-rocker. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described below by the specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0040] Specific implementation method 1: Combination Figure 1 The present embodiment is described, and the present embodiment includes a mold 1, a first connecting member 2, a second connecting member 3, a disc-type cylinder 4, a sleeve 5, a force sensor 6 and two groups of positioning pins 7. The disc-type cylinder 4 is horizontally arranged in the mold 1, and the first connecting member 2 and the second connecting member 3 are respectively arranged at both ends of the mold 1. The force sensor 6 is arranged in the second connecting member 3. The disc end of the disc-type cylinder 4 is detachably connected to the first connecting member 2, and the cylinder end of the disc-type cylinder 4 passes through the sleeve 5 and is tightly attached to the detection end of the force sensor 6. There is a gap between the cylinder end of the disc-type cylinder 4 and the sleeve 5, and concrete 8 is filled between the sleeve 5 and the mold 1. The two groups of positioning pins 7 are both arranged in the concrete 8, and the two groups of positioning pins 7 are respectively arranged on the disc-type cylinder 4 and the bottom plate 1-2 of the mold 1.

[0041] Furthermore, the mold 1 is a special mold for concrete.

[0042] Furthermore, the mold 1 is arranged horizontally, and a first connecting member 2 and a second connecting member 3 are vertically arranged at two ends thereof.

[0043] Further, each group of positioning pins 7 includes a plurality of anchor pins. Each group of positioning pins is designed to have 4 to 6 anchor pins, which are evenly arranged at an angle interval of 90° or 60°, and the anchor pins are used to position the disc-shaped cylinder 4 and the mold 1 respectively.

[0044] Further, the anchors are replaced with screws.

[0045] Furthermore, the force sensor 6 is preferably a pressure sensor.

[0046] Further, when the force sensor 6 is a pressure sensor, the force sensor 6 is preferably a disc-type pressure sensor.

[0047] Furthermore, a limiting ring 12 is provided in the second flange, and the limiting ring 12 assists in fixing the force sensor 6 at the end of the second flange so that the central axis of the disk-shaped force sensor 6 coincides with the central axis of the end of the second flange.

[0048] The working principle of the detection device in this embodiment is as follows:

[0049] When the concrete 8 undergoes self-shrinkage deformation, the disc-shaped column 4 and the mold 1 will undergo relative displacement, and the disc-shaped column 4 will move toward the second connecting member 3 along the length direction of the sleeve 5. The column end of the disc-shaped column 4 cooperates with the force sensor 6, and the change in the reading displayed on the force sensor 6 is the self-shrinkage stress of the concrete 8.

[0050] Specific embodiment 2: This embodiment is a further limitation of specific embodiment 1. The disc-shaped cylinder 4 includes a disc 4-1 and a cylinder 4-2. One end of the cylinder 4-2 is fixedly connected to the disc 4-1. The cylinder 4-2 and the disc 4-1 are coaxially arranged. The outer diameter of the disc 4-1 is 4 to 6 times the outer diameter of the cylinder 4-2. The outer diameter end of the disc 4-1 is gap-matched with the mold 1.

[0051] Furthermore, the disc body 4-1 is a disc body made of a lightweight high-strength alloy.

[0052] Furthermore, the column 4-2 is a column made of a solid lightweight high-strength alloy.

[0053] Specific embodiment three: This embodiment is a further limitation of specific embodiment one or two, the mold 1 includes an outer cylinder 1-1 and a bottom plate 1-2, two annular bosses 1-3 are integrally arranged on the outer walls at both ends of the outer cylinder 1-1, and annular bosses 1-3 are respectively processed on the outer walls at both ends of the outer cylinder 1-1, one of the two annular bosses 1-3 is detachably connected to the first connecting member 2, the other end of the outer cylinder 1-1 is matched with a bottom plate 1-2, and the other of the two annular bosses 1-3 is detachably connected to the second connecting member 3 through the bottom plate 1-2. The first connecting member 2 is a first flange, and the second connecting member 3 is a second flange.

[0054] Specific embodiment 4: This embodiment is a further limitation of specific embodiments 1, 2 or 3. The outer cylinder 1-1 is formed by enclosing two semicircular arc pieces, and the two semicircular arc pieces are detachably connected. The detachable structure of the outer cylinder 1-1 in this embodiment is convenient for demoulding. In the specific operation process, since the outer walls at both ends of the outer cylinder 1-1 are integrally provided with annular bosses 1-3, the semicircular arc pieces are two semicircular arc-shaped pieces made of steel and with bosses. The two semicircular arc pieces are assembled into a hollow cylinder by tightening screws, namely the outer cylinder 1-1. One end of the mold 1 is the disc end of the disc-type column 4, and the other end is the bottom plate 1-2. The outer cylinder 1-1 is detachably connected to the bottom plate 1-2. Such a configuration facilitates the removal of the concrete 8 after the test is completed.

[0055] Specific embodiment five: This embodiment is a further limitation of specific embodiments one, two, three or four. One end of the sleeve 5 is tightly attached to the end face of the disc body 4-1 through the first sealing ring 9, and the other end of the sleeve 5 is tightly attached to the inner wall of the bottom plate 1-2 of the mold 1 through the second sealing ring 10. The first sealing ring 9 and the second sealing ring 10 are respectively bonded to the two ends of the sleeve 5.

[0056] Specific embodiment 6: This embodiment is a further limitation of specific embodiments 1, 2, 3, 4 or 5, and a limit ring 12 is provided outside the force sensor 6. The limit ring 12 is used to limit the string movement of the force sensor 6 and ensure the stable installation position of the force sensor 6.

[0057] Specific embodiment 7: This embodiment is a further limitation of specific embodiments 1, 2, 3, 4, 5 or 6. An adjusting screw 13 is provided on the first connecting member 2. The adjusting screw 13 is provided at the central axis of the first connecting member 2. A rocker 14 is provided outside the adjusting screw 13. The adjusting screw 13 is used to adjust the initial position of the disc-type cylinder 4. The adjusting screw 13 is provided with a rocker 14 to adjust the screwing-in and screwing-out position of the screw 13 at the first flange.

[0058] Specific implementation method eight: Combination Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 The present embodiment is described. The testing method in the present embodiment includes the following contents:

[0059] Installing the mold 1: Place the mold 1 vertically, insert a steel column 11 into the sleeve 5, hold one end of the steel column 11 and push the steel column 11 until the front end of the steel column 11 abuts against the second flange and then stop pushing; the steel column 11 plays a pre-supporting role, providing conditions for effectively filling the concrete 8. The steel column 11 provides a preset position for the column 4-2 in the disc-shaped column 4.

[0060] Concrete 8 is placed in the mold 1 and tamped. After compaction by vibration, the steel column 11 is removed from the sleeve 5.

[0061] Install the force sensor 6 in the limiting ring 12 of the second flange, insert the cylindrical end of the disc-shaped cylinder 4 into the sleeve 5 until the cylindrical end of the disc-shaped cylinder 4 abuts against the force sensor 6, and then stop pushing, and then install the first flange on the mold 1;

[0062] The screws 12 provided on the first flange are used to adjust the initial position of the disc-shaped column 4 in the concrete 8 and to enhance the connection strength between the disc-shaped column 4 and the concrete;

[0063] Place the mold 1 filled with concrete 8 horizontally and record the initial reading of the load cell 6;

[0064] The readings of the force sensor 6 at different ages are recorded, and the initial reading of the force sensor 6 is subtracted and divided by the cross-sectional area of ​​the concrete 8 to obtain the autogenous shrinkage stress of the concrete 8 .

[0065] Specific implementation method 9: This implementation method is a further limitation of specific implementation method 8. Figure 3 As shown, the first flange and the second flange are removed from the mold 1 respectively, and after the disc-shaped column 4, the sleeve 5 and the concrete 8 are taken out, the force sensor 6 is removed from the second flange and installed at the adjustment screw 13 of the first flange, and the second flange is reinstalled on one end of the mold 1, and the disc-shaped column 4 is re-placed on the mold 1, ensuring that the column 4-2 of the disc-shaped column 4 passes through the bottom plate 1-2 and is pressed against the second flange, and concrete 8 is loaded into the mold 1 and inserted and tamped, and after vibrating and compacting, the force sensor 6 is installed on the other end of the mold 1;

[0066] The mold 1 with the first flange, the second flange, the force sensor 6 and the disc-shaped cylinder 4 is placed in a low temperature environment for testing, a set of positioning pins 7 is set on the disc-shaped cylinder 4 to adjust the initial position of the disc-shaped cylinder 4 in the concrete 8, and the initial reading of the force sensor 6 is recorded at the same time;

[0067] The readings of the force sensor 6 at different ages are recorded, the initial reading of the force sensor 6 is subtracted, and the result is divided by the cross-sectional area of ​​the concrete 8 to obtain the frost heave stress of the concrete 8 in a negative temperature environment.

[0068] Specific implementation method ten: Combination Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5To illustrate this embodiment, the sleeve 5 in this embodiment is a hard tube body with a smooth surface. A release agent is applied inside and outside the tube to reduce the friction between the sleeve and the concrete 8. The material selected is a lightweight smooth aluminum alloy material, which is adjusted according to the properties of the concrete 8 and the length and diameter of the sleeve 5.

[0069] Furthermore, the length of the sleeve 5 ranges from 30 to 60 cm, which can ensure that the detection is carried out stably and smoothly and avoid waste of materials.

[0070] Furthermore, the outer diameter of the sleeve 5 ranges from 4 to 5 cm.

[0071] Furthermore, the force sensor 6 is fixedly mounted on the inner wall of the second flange, and the second flange is provided with a lead outlet for a power supply.

[0072] Furthermore, the first sealing ring 9 and the second sealing ring 10 are respectively arranged at the two ends of the sleeve 5, and the first sealing ring 9 and the second sealing ring 10 are both made of elastic polymer materials, preferably rubber materials, that is, the first rubber sealing ring and the second rubber sealing ring. The first sealing ring 9 and the second sealing ring 10 both play the role of sealing and positioning.

[0073] Furthermore, the positioning pin 7 is fixedly connected to the bottom plate 1 - 2 , and the positioning pin 7 is fixedly connected to the disc body 4 - 1 .

[0074] Furthermore, the column 4 - 2 is inserted into the sleeve 5 , and there is a clearance fit between the two.

[0075] Furthermore, the mold 1 is cylindrical, which is convenient for inserting and filling the concrete 8, and a release agent is brushed inside to reduce the friction between it and the concrete 8.

[0076] Furthermore, the outer cylinder 1-1 in the mold 1 preferably has a cylindrical shape, an outer diameter of the outer cylinder 1-1 ranging from 10 to 20 cm, and a length of 40 to 80 cm. The material used for the outer cylinder 1-1 is a lightweight and high-strength aluminum alloy material.

[0077] Specific implementation method eleven: Combination Figure 2 In this embodiment, when the detection device is in a vertical state, the operation of vibrating the concrete 8 during detection is easier, and the vertical setting can also reduce the friction between the shrinkage of the concrete 8 and the mold 1, which is more conducive to ensuring the accuracy of the data obtained by the detection device. Other structures and connection relationships not mentioned are the same as those in the specific embodiments one, two, three, four, five, six or seven.

[0078] The following embodiments are described in conjunction with the beneficial effects of the detection device of the present invention:

[0079] Embodiment 1:

[0080] The concrete mix ratio of this embodiment is C50, and the cement dosage is 380kg / m 3 , fly ash is 70kg / m 3 , sand is 712kg / m 3 , coarse aggregate 1112kg / m 3 , water consumption is 166kg / m 3 , the slump is 180mm, the inner diameter of the outer cylinder 1-1 in the mold 1 is 100mm, the outer diameter is 110mm, the outer diameter of the sleeve 5 is 50mm, the inner diameter is 40mm, the thickness of the bottom plate 1-1 and the disc 4-1 is 10mm, the length of the anchor is 80mm, and 4 anchors are evenly arranged on the disc 4-1 and the bottom plate 1-1. The column 4-2 is a steel column, the outer diameter of the column 4-2 is 35mm, the length is 375mm, the outer diameter of the first sealing ring 9 and the second sealing ring 10 is 50mm, the inner diameter is 35mm, and the height is 12.5mm, the height of the concrete 8 is 400mm, and the cross-sectional area of ​​the concrete 8 is 5887.5mm 2 , volume is 235500mm 3 , weight is 5.6kg;

[0081] The detection method using this detection device is as follows:

[0082] Step 1: Install the concrete forming mold: Remove the first flange, and without pre-installing the pressure sensor in the second flange, insert a column 4-2 into the sleeve 5, place the column 4-2 in the second flange and make the bottom of the column 4-2 contact with the upper surface of the second flange to play a positioning role;

[0083] Step 2: Add concrete 8 and tamp it; after compacting it with vibration, take out the column 4-2; install a pressure sensor in the second flange;

[0084] Step 3: insert the disc-shaped column 4 into the sleeve 5, insert the positioning pins 7 on the disc-shaped column 4 into the concrete, so that the upper surface of the concrete is tightly combined with the disc body 4-1 in the disc-shaped column 4; install the first flange, and adjust the initial position of the disc-shaped column 4 with the adjusting screw 13;

[0085] Step 4: Record the initial reading of the pressure sensor N0 = 8.2 kg;

[0086] Step 5: After 11 hours, concrete 8 finally sets, concrete 8 begins to shrink, and the pressure sensor reading begins to increase. Record the reading N of the pressure sensor at different ages, subtract the initial reading of the pressure sensor, and divide it by the cross-sectional area of ​​the concrete to get the shrinkage stress of concrete 8. After 72 hours, the reading of the pressure sensor tends to the maximum value of 166kg, and the increase is not large in the later period. The force generated by the shrinkage of concrete 8 is ΔN=166-8.2=157.8kg, which is divided by the cross-sectional area of ​​concrete 8 to get the stress generated by the shrinkage of concrete 8 σ=ΔN / S=0.26MPa.

[0087] Because the greater the shrinkage stress of concrete 8, the more likely concrete 8 will crack under the constraints in actual engineering. Finally, by comparing the shrinkage stress of concrete 8 with different mix ratios, the crack resistance of concrete 8 can be quickly and easily obtained in the laboratory. At the same time, since the detection device can monitor the autogenous shrinkage stress of concrete 8 in real time, the time when the autogenous shrinkage stress of different concretes reaches the maximum value can be known. This provides basic data for avoiding cracking caused by drying shrinkage in actual engineering and optimizing the design of maintenance plans. The above process can draw an image to more clearly express the evolution process of concrete autogenous shrinkage stress.

[0088] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A device for detecting shrinkage stress of cement-based materials, characterized in that: The invention comprises a mold (1), a first connecting member (2), a second connecting member (3), a disc-shaped column (4), a sleeve (5), a force sensor (6) and two sets of positioning pins (7), wherein the sleeve (5) is detachably connected to the mold (1), the first connecting member (2) and the second connecting member (3) are respectively arranged at two ends of the mold (1), the force sensor (6) is arranged in the second connecting member (3), the disc end of the disc-shaped column (4) is detachably connected to the first connecting member (2), and the disc end of the disc-shaped column (4) is detachably connected to the first connecting member (2). The column end passes through the sleeve (5) and is closely attached to the detection end of the force sensor (6); a gap is set between the column end of the disc-shaped column (4) and the sleeve (5); concrete (8) is filled between the sleeve (5) and the mold (1); two groups of positioning pins (7) are both set in the concrete (8); one group of positioning pins (7) of the two groups of positioning pins (7) is inserted into the concrete (8) through the disc-shaped column (4); and the other group of positioning pins (7) of the two groups of positioning pins (7) is inserted into the concrete (8) through the mold (1); The disc-type column (4) comprises a disc body (4-1) and a steel column (4-2), one end of the steel column (4-2) is fixedly connected to the disc body (4-1), and the steel column (4-2) and the disc body (4-1) are coaxially arranged; The mold (1) comprises an outer cylinder (1-1) and a bottom plate (1-2); annular bosses (1-3) are respectively processed on the outer walls at both ends of the outer cylinder (1-1); one of the two annular bosses (1-3) is detachably connected to a first connecting member (2); the other end of the outer cylinder (1-1) is matched with a bottom plate (1-2); the other of the two annular bosses (1-3) is detachably connected to a second connecting member (3) via the bottom plate (1-2); the first connecting member (2) is a first flange; and the second connecting member (3) is a second flange.

2. A cement-based material shrinkage stress detection device according to claim 1, characterized in that: The outer cylinder (1-1) is formed by enclosing two semicircular arc pieces, and the two semicircular arc pieces are detachably connected.

3. A cement-based material shrinkage stress detection device according to claim 1, characterized in that: One end of the sleeve (5) is tightly attached to the end surface of the disc body (4-1) via a first sealing ring (9), and the other end of the sleeve (5) is tightly attached to the inner wall of the mold bottom plate (1-2) via a second sealing ring (10).

4. A cement-based material shrinkage stress detection device according to claim 1, 2 or 3, characterized in that: A limit ring (12) is sleeved outside the force sensor (6).

5. A cement-based material shrinkage stress detection device according to claim 4, characterized in that: The force sensor (6) is a disc-type pressure sensor.

6. A cement-based material shrinkage stress detection device according to claim 5, characterized in that: An adjustment screw (13) is provided on the first connecting member (2), the adjustment screw (13) is arranged at the central axis of the first connecting member (2), and a rocker (14) is provided outside the adjustment screw (13) in cooperation with the adjustment screw (13).

7. A testing method using a cement-based material shrinkage stress detection device according to claim 6, characterized in that: The test method includes the following: Installing the mold (1): inserting a steel column (11) into the sleeve (5), holding one end of the steel column (11) and pushing the steel column (11) until the front end of the steel column (11) abuts against the second flange and then stopping the pushing; Concrete (8) is placed in the mold (1) and rammed and vibrated to make it dense, and then the steel column (11) is removed from the sleeve (5); A limiting ring (12) is arranged in the second flange, a force sensor (6) is arranged in the limiting ring (12), and the force sensor (6) is arranged in the second flange through the limiting ring (12), ensuring that the central axis of the force sensor (6) coincides with the central axis of the second flange, and then the column end of the disc-shaped column (4) is inserted into the sleeve (5) until the column end of the disc-shaped column (4) abuts against the force sensor (6) and the pushing is stopped, and then the first flange is mounted on the mold (1); A set of positioning pins (7) are arranged on the disc-shaped column (4) to adjust the initial position of the disc-shaped column (4) in the concrete (8), and at the same time enhance the connection strength between the disc-shaped column (4) and the concrete (8), and record the initial reading of the force sensor (6); The readings of the force sensor (6) at different ages are recorded, and the initial reading of the force sensor (6) is subtracted to obtain the autogenous shrinkage stress of the concrete (8) at room temperature or high temperature.

8. The testing method according to claim 7, characterized in that: The first flange and the second flange are removed from the mold (1) respectively, and the disc-shaped column (4), the sleeve (5) and the concrete (8) are taken out in turn. The force sensor (6) is removed from the second flange and installed at the adjustment screw (13) of the first flange. The second flange is reinstalled on one end of the mold (1). The disc-shaped column (4) is placed back on the mold (1), ensuring that the column (4-2) of the disc-shaped column (4) passes through the bottom plate (1-2) and is pressed against the second flange. Concrete (8) is placed in the mold (1) and inserted and tamped. After compaction, the force sensor (6) is installed on the other end of the mold (1); The mold (1) with the first flange, the second flange, the force sensor (6) and the disc-shaped column (4) is placed in a low-temperature environment for testing, a set of positioning pins (7) is arranged on the disc-shaped column (4) to adjust the initial position of the disc-shaped column (4) in the concrete (8) and to enhance the connection strength between the disc-shaped column (4) and the concrete (8), and the initial reading of the force sensor (6) is recorded at the same time; The readings of the force sensor (6) at different ages are recorded, and the initial reading of the force sensor (6) is subtracted to obtain the frost heave stress of the concrete (8) in a negative temperature environment.

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