A testing device and measuring method for yield stress of fresh concrete

Abstract

A kind of testing device and measurement method of fresh concrete yield stress, including pedestal, vertical support, transverse support, fine steel cable, first vertical plate, second vertical plate, container, tension sensor one, tension sensor two, motor one and motor two;Vertical support is fixedly connected with pedestal;Transverse support connects two vertical supports;Motor one, motor two are fixed below transverse support;Fine steel cable is connected with the cable rope wheel of motor one and motor two at both ends respectively;Container is fixed on pedestal, and is equipped with fixed pulley, fine steel cable is wound over fixed pulley;First vertical plate, second vertical plate are connected by fine steel cable on the two sides of fixed pulley, and alternately enter container;Tension sensor one and tension sensor two are all connected on fine steel cable, are used for measuring the tension of corresponding side fine steel cable respectively, and data acquisition is carried out by data acquisition instrument;The present application solves the problem that measurement result is inaccurate when aggregate migration, plug flow etc. occur during the measurement of concrete yield stress by rheometer.

Description

Technical Field

[0001] This invention relates to the field of concrete workability testing technology, and in particular to a testing device and measurement method for concrete yield stress. Background Technology

[0002] Concrete rheological parameters are key indicators for evaluating concrete workability, mainly including yield stress, plastic viscosity, and thixotropy. Rheological properties can assess the fluidity, pumpability, and self-compacting ability of concrete, which are crucial for the concrete construction process. Rheological properties directly affect the quality of concrete pouring, compaction, and final molding.

[0003] For self-compacting concrete, its rheological parameters mainly include yield stress and plastic viscosity. A lower yield stress is required to allow the concrete to better fill the formwork, and an appropriate plastic viscosity helps to maintain the stability and fluidity of the concrete.

[0004] For 3D printed concrete, the study of rheological properties is particularly important. 3D printed concrete needs to have appropriate yield stress to ensure interlayer bonding, and at the same time, it needs appropriate plastic viscosity to prevent collapse or insufficient flow during the printing process.

[0005] For shotcrete, yield stress affects its cohesiveness and anti-segregation properties during the spraying process. Appropriate yield stress ensures that the shotcrete maintains its shape during spraying while possessing sufficient fluidity for spraying and compaction.

[0006] Currently, coaxial cylindrical rheometers and plate rheometers are mainly used to measure the yield stress of concrete. However, the former is prone to aggregate migration or choking during measurement. Aggregate migration alters the homogeneity of the concrete sample, leading to inaccurate measurements. Choking results in an overestimation of the yield stress and affects the accuracy and repeatability of the data. The latter may experience edge effects during measurement, causing differences in flow behavior between the sample's edge and center, leading to inaccurate results.

[0007] The concrete penetration resistance method is a test used to measure the setting time of concrete mixtures, and it is directly related to the yield stress of concrete. However, when using a needle or cylinder for penetration, slippage is more likely to occur at the interface between the material and the measuring tool due to the small contact area. This slippage can lead to a lower measured shear stress than the actual value, thus affecting the accurate measurement of the yield stress.

[0008] Therefore, there is a need to develop a device and method that is both simple to operate and can accurately measure the yield stress of concrete. Summary of the Invention

[0009] To address the above problems, this invention proposes a testing device and measurement method for concrete yield stress, and the technical solution adopted is as follows:

[0010] A testing device for the yield stress of freshly mixed concrete, characterized in that it comprises a base, vertical supports, a horizontal support, thin steel cables, a first vertical plate, a second vertical plate, a container, a tension sensor one, a tension sensor two, a fixed pulley, a motor one, a motor two, and a data acquisition instrument; the vertical supports are fixedly connected to the base; the horizontal support connects the two vertical supports; the motor one and motor two are fixed below the horizontal support; the two ends of the thin steel cable are respectively connected to the cable pulleys of motor one and motor two; the container is fixed on the base, and the container contains a fixed pulley, with the thin steel cable passing over the fixed pulley; the first vertical plate and the second vertical plate are respectively connected to both sides of the fixed pulley by the thin steel cable, and alternately enter the container; the tension sensor one and tension sensor two are both connected and installed on the thin steel cable, respectively used to measure the tension of the corresponding side of the thin steel cable, and the data is acquired by the data acquisition instrument.

[0011] Furthermore, the first vertical plate is different in size from the second vertical plate, in order to eliminate the influence of the resistance between the thin steel cable and the fixed pulley and concrete on the test results during the test.

[0012] Furthermore, the measurement range of both the tension sensor one and the tension sensor two is 0.001-2kN, and the minimum accurate load is 0.001kN.

[0013] Furthermore, the controllable speed range of both motor one and motor two is 0.5-100mm / s, and the minimum precision speed is 0.5mm / s.

[0014] Furthermore, both the first and second vertical plates are made of corrosion-resistant, high-weight materials; the thin steel cable is made of corrosion-resistant, low-weight materials.

[0015] Furthermore, the fixed pulley is made of corrosion-resistant material.

[0016] A method for measuring the yield stress of freshly mixed concrete, characterized by the following steps:

[0017] Step 1: Before adding concrete, loosen the thin steel cable to keep the first and second vertical plates slack, and read the readings G1 and G2 of tension sensor 1 and tension sensor 2 respectively using a data acquisition instrument.

[0018] Step 2: Fill the container with concrete, so that the first vertical plate is completely submerged and raised a certain distance above it, and read the reading B1 of the tension sensor 1 through the data acquisition instrument;

[0019] Step 3: Start motor one and pull the first vertical plate at a constant speed of 0.5-2 mm / s. After moving the set distance, turn off the motor and record the reading of tension sensor one through the data acquisition instrument, and take the average value F1.

[0020] Step 4: Pull the first vertical plate out of the concrete and clean its surface;

[0021] Step 5: Start motor 1 to make the second vertical plate fully immerse itself in the concrete at a speed of 1-5 mm / s and move downward a set distance. At this time, the height of the second vertical plate is the same as that of the first vertical plate in step 2. Then motor 1 reverses a certain angle and stops working, so that the second vertical plate is in a natural suspension state. Read the reading B2 of tension sensor 2 through the data acquisition instrument.

[0022] Step 6: Control the speed of motor 2 to 0.5-2 mm / s, so that the second vertical plate moves upward at a constant speed for a set distance and then stops. Record the reading of tension sensor 2 through the data acquisition instrument and take the average value F2.

[0023] Calculate the concrete yield stress using the following formula:

[0024]

[0025] Where τ is the yield stress of concrete; G1 and G2 are the self-weight values ​​of the first and second vertical plates, respectively, and the weight of the thin steel cable is negligible; F1 and F2 are the average load values ​​of tension sensor one and tension sensor two after the first and second vertical plates stop moving at a constant speed; B1 and B2 are the buoyancy forces on the first and second vertical plates in the concrete; H1 and H2 are the heights of the first and second vertical plates, respectively; and P1 = 2(L1 + E1), where L1 is the width of the first vertical plate and E1 is the thickness of the first vertical plate; P2 = 2(L2 + E2), where L2 is the width of the second vertical plate and E2 is the thickness of the second vertical plate.

[0026] Step 7: Control motor 1 and motor 2 to pull the first vertical plate and the second vertical plate upward at different set speeds to repeat the experiment. Take the average value of the yield stress values ​​obtained multiple times to obtain the final yield stress value.

[0027] Because the present invention adopts the above-described technical solution, the present invention has the following advantages:

[0028] 1. This invention solves the problems of inaccurate measurement results caused by aggregate migration and blockage during the testing process of rheometers, complex instrument structure, high cost, inability to be portable on site, and easy wall slippage when using needles or cylinders to measure concrete yield stress, which leads to lower measurement results.

[0029] 2. In each measurement and calculation, the present invention determines the concrete yield stress by using the difference between the corresponding data measured by tension sensor one and tension sensor two. This effectively eliminates the influence of the resistance between the thin steel cable and the fixed pulley and the concrete on the test results during the test, making the measurement results more accurate.

[0030] 3. The device of the present invention has a simple and reliable structure and is easy to operate. Attached Figure Description

[0031] Figure 1 This is an overall structural diagram of the present invention.

[0032] Figure 2 This is a front sectional view of the present invention.

[0033] Icon labels:

[0034] 1-Base, 2-Vertical support, 3-Horizontal support, 4-Thin steel cable, 5-First vertical plate, 6-Second vertical plate, 7-Container, 8a-Tension sensor one, 8b-Tension sensor two, 9-Fixed pulley, 10a-Motor one, 10b-Motor two, 11-Data acquisition instrument. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] In the description of this invention, it should be noted that the terms "upper", "lower", "in", "out", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0037] Example:

[0038] like Figure 1-2As shown, a testing device for the yield stress of freshly mixed concrete includes a base 1, vertical support columns 2, horizontal support 3, thin steel cable 4, first vertical plate 5, second vertical plate 6, container 7, tension sensor 1 8a, tension sensor 2 8b, fixed pulley 9, motor 1 10a, motor 2 10b, and data acquisition instrument 11; the vertical support columns 2 are fixedly connected to the base 1; the horizontal support 3 connects the two vertical support columns 2; the controllable speed motors 1 10a and 2 10b are fixed below the horizontal support 3; the two ends of the thin steel cable 4 are respectively connected to the cable pulleys of motor 1 10a and motor 2 10b; the container 7 is fixed to the base 1. In the container 7, a fixed pulley 9 is installed. A thin steel cable 4 passes around the fixed pulley 9. The first vertical plate 5 and the second vertical plate 6 are respectively connected to both sides of the fixed pulley 9 by the thin steel cable 4 and alternately enter the container 7. Tension sensor 1 8a and tension sensor 2 8b are both connected and installed on the thin steel cable 4, respectively, to measure the tension of the thin steel cable 4 on the corresponding side, and the data is collected by the data acquisition instrument 11 installed on the horizontal support 3. In this embodiment, the fixed pulley 9 is made of ceramic material, the first vertical plate 5 and the second vertical plate 6 are both made of high-weight stainless steel material, and the thin steel cable 4 is made of lightweight ultra-high molecular weight polyethylene material.

[0039] As a specific implementation of this embodiment, the base 1 has dimensions of 600mm × 500mm × 60mm (length × width × thickness); the vertical support 2 has dimensions of 70mm × 40mm × 600mm (length × width × height); the horizontal support 3 has dimensions of 70mm × 40mm × 600mm (length × width × height); the first vertical plate 5 has a height H1 of 100mm, a width L1 of 70mm, and a thickness E1 of 2mm; the second vertical plate 6 has a height H2 of 80mm, a width L2 of 45mm, and a thickness E2 of 2mm; the container 7 has a height of 450mm, an outer diameter of 300mm, and a wall thickness of 4mm; the tension sensor 8a and tension sensor 8b both have a measurement range of 0.001-2kN and a minimum accurate load of 0.001kN; the fixed pulley 9 has a radius of 50mm; the motors 10a and 10b both have a controllable speed range of 0.5-100mm / s and a minimum accurate speed of 0.5mm / s. It should be explained here that by designing the first vertical plate 5 to be larger than the second vertical plate 6, the difference between the measured values ​​of the two plates can be used to eliminate the influence of the resistance between the thin steel cable 4 and the fixed pulley 9 and the concrete on the test results during the test calculation process.

[0040] The specific steps of the measurement method in this embodiment are as follows:

[0041] Step 1: Before adding concrete, loosen the thin steel cable 4 to keep the first vertical plate 5 and the second vertical plate 6 slack. Use the data acquisition instrument 11 to read the readings G1 and G2 of the tension sensor 8a and tension sensor 8b respectively.

[0042] Step 2: Fill the container 7 with concrete so that the first vertical plate 5 is completely submerged and 70mm above it. Read the reading B1 of the tension sensor 8a through the data acquisition instrument 11.

[0043] Step 3: Start motor 10a and pull the first vertical plate 5 at a constant speed of 1mm / s. After moving 30mm, turn off the motor and record the reading of tension sensor 8a through data acquisition instrument 11, and take the average value F1.

[0044] Step 4: Pull the first vertical plate 5 out of the concrete and clean its surface to remove the concrete from its side and bottom surfaces.

[0045] Step 5: Start motor 10a to make the second vertical plate 6 fully immersed in the concrete at a speed of 2mm / s and continue to move downwards by 70mm. At this time, the second vertical plate 6 is at the same height as the first vertical plate 5 in step 2. Then motor 10a reverses 1° to 5° and stops working, so that the second vertical plate 6 is in a natural suspension state. Read the reading B2 of tension sensor 8b through data acquisition instrument 11.

[0046] Step 6: Control the speed of motor 10b to 1 mm / s, so that the second vertical plate 6 moves upward at a constant speed of 30 mm, and then stops. Record the reading of tension sensor 8b through data acquisition instrument 11 and take the average value F2.

[0047] Calculate the concrete yield stress using the following formula:

[0048]

[0049] Where τ is the yield stress of concrete; G1 and G2 are the self-weight values ​​of the first vertical plate 5 and the second vertical plate 6, respectively, and the weight of the thin steel cable 4 is negligible; F1 and F2 are the average load values ​​of the tension sensor 8a and tension sensor 8b after the first vertical plate 5 and the second vertical plate 6 stop moving at a constant speed; B1 and B2 are the buoyancy forces on the first vertical plate 5 and the second vertical plate 6 in the concrete; H1 and H2 are the heights of the first vertical plate 5 and the second vertical plate 6, respectively; and P1 = 2(L1 + E1), where L1 is the width of the first vertical plate 5 and E1 is the thickness of the first vertical plate 5; P2 = 2(L2 + E2), where L2 is the width of the second vertical plate 6 and E2 is the thickness of the second vertical plate 6.

[0050] Step 7: Control motor 10a and motor 2 10b to pull the first vertical plate 5 and the second vertical plate 6 upward at speeds of 1.5 mm / s and 2 mm / s respectively. Repeat the experiment twice and take the average of the yield stress values ​​obtained in the three experiments to obtain the final yield stress value.

Claims

1. A method for measuring the yield stress of freshly mixed concrete using a testing device, characterized in that, The fresh concrete yield stress testing device includes a base (1), vertical support column (2), horizontal support (3), thin steel cable (4), first vertical plate (5), second vertical plate (6), container (7), tension sensor one (8a), tension sensor two (8b), fixed pulley (9), motor one (10a), motor two (10b), and data acquisition instrument (11); the vertical support column (2) is fixedly connected to the base (1); the horizontal support (3) connects the two vertical support columns (2); the motor one (10a) and motor two (10b) are fixed below the horizontal support (3); the thin steel cable ( 4) The two ends are connected to the cable pulleys of motor one (10a) and motor two (10b) respectively; the container (7) is fixed on the base (1), and the container (7) is equipped with a fixed pulley (9), and the thin steel cable (4) passes around the fixed pulley (9); the first vertical plate (5) and the second vertical plate (6) are respectively connected to both sides of the fixed pulley (9) by the thin steel cable (4), and alternately enter the container (7); the tension sensor one (8a) and the tension sensor two (8b) are both connected and installed on the thin steel cable (4), respectively used to measure the tension of the corresponding side thin steel cable (4), and data is collected by the data acquisition instrument (11); The measurement method of the fresh concrete yield stress testing device includes the following steps: Step 1: Before adding concrete, loosen the thin steel cable (4) to keep the first vertical plate (5) and the second vertical plate (6) relaxed. Read the readings G1 and G2 of the tension sensor 1 (8a) and tension sensor 2 (8b) respectively through the data acquisition instrument (11). Step 2: Fill the container (7) with concrete so that it completely submerges the first vertical plate (5) and is higher than the first vertical plate (5). Read the reading B1 of the tension sensor (8a) through the data acquisition instrument (11). Step 3: Start motor 1 (10a) and pull the first vertical plate (5) at a speed of 0.5 to 2 mm / s. After moving the set distance, turn off the motor and record the reading of the tension sensor 1 (8a) through the data acquisition instrument (11), and take the average value F1. Step 4: Pull the first vertical plate (5) out of the concrete and clean its surface; Step 5: Start motor 1 (10a) to make the second vertical plate (6) fully immerse itself in the concrete at a speed of 1-5 mm / s and move downward a set distance. At this time, the second vertical plate (6) is at the same height as the first vertical plate (5) in step 2. Then motor 1 (10a) reverses and makes the second vertical plate (6) in a natural suspension state before stopping. Read the reading B2 of tension sensor 2 (8b) through data acquisition instrument (11). Step 6: Control the speed of motor 2 (10b) to 0.5-2 mm / s, so that the second vertical plate (6) moves upward at a constant speed for a set distance and then stops. Record the reading of tension sensor 2 (8b) through data acquisition instrument (11) and take the average value F2. Calculate the concrete yield stress using the following formula: Where τ is the yield stress of concrete; H1 and H2 are the heights of the first vertical plate (5) and the second vertical plate (6) respectively; and P1 = 2(L1 + E1), where L1 is the width of the first vertical plate (5) and E1 is the thickness of the first vertical plate (5); P2 = 2(L2 + E2), where L2 is the width of the second vertical plate (6) and E2 is the thickness of the second vertical plate (6); Step 7: Control motor 1 (10a) and motor 2 (10b) to pull the first vertical plate (5) and the second vertical plate (6) upward at different set speeds to repeat the experiment. Take the average value of the yield stress values ​​obtained multiple times to obtain the final yield stress value.

2. The measurement method of the yield stress testing device for freshly mixed concrete according to claim 1, characterized in that, The first vertical plate (5) is different in size from the second vertical plate (6) to eliminate the influence of the resistance between the thin steel cable (4) and the fixed pulley (9) and the concrete on the test results during the test.

3. The measurement method of the yield stress testing device for freshly mixed concrete according to claim 1, characterized in that, The measurement range of both the tension sensor one (8a) and the tension sensor two (8b) is 0.001-2kN, and the minimum accurate load is 0.001kN.

4. The measurement method of the yield stress testing device for freshly mixed concrete according to claim 1, characterized in that, The controllable speed range of both motor one (10a) and motor two (10b) is 0.5-100mm / s, and the minimum precision speed is 0.5mm / s.

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