Compact force-feed testing apparatus and concrete fluidity evaluation system

Abstract

To provide a small-sized force feed testing device and a concrete fluidity evaluation system capable of making a force of the same degree as a shearing force generated by actual force feed act on concrete at a low cost and in a short time.SOLUTION: The small-sized force feed testing device 10 includes a short pipe 12, a pressure gauge 17 for measuring the pressure in the short pipe 12, and an energizing means 13 for reciprocating concrete 14 in the short pipe 12 while applying force feed pressure to the concrete 14, wherein the short pipe 12 is a different-diameter composite pipe formed by connecting a large-diameter pipe 15 and a small-diameter pipe 16.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a small pumping test device and a concrete fluidity evaluation system for estimating the fluidity of concrete after pumping. [Background technology]

[0002] The fluidity (slump and slump flow) of pumped concrete changes (mainly decreases). Changes in concrete quality due to pumping are evaluated by conducting full-scale pumping tests using concrete pumps and pumping piping. Other evaluation methods include those described in Patent Documents 1 and 2. The evaluation method in Patent Document 1 uses the results of a pressure bleeding test as one of the parameters, and determines whether pumping is possible by taking into account the pressure that the concrete receives when pumped. Specifically, the method compares the sum of the pressure load of the concrete pumping pipe, which is calculated from the pressure loss in the pipe during pumping through the concrete pumping pipe and the horizontal equivalent distance, and the pressure load, which is calculated by taking into account the elevation difference between the start and end points of the concrete pumping pipe, with the pumpable load of a selected concrete pump, and determines that pumping is possible if the sum of the pressure loads exceeds the pumpable load. The evaluation method in Patent Document 2 is a concrete pump pumping evaluation method that uses a pumping evaluation device to determine the pumping distance until clogging. In this evaluation method, the test device applies pressure to the concrete within the pipe at internal pressures of up to 5 MPa while moving the concrete back and forth within the pipe, and evaluates the pumpable distance by determining the time and number of piston movements until the concrete becomes clogged, taking into account the effect of shear force acting on the concrete due to pumping. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-213079 [Patent Document 2] Patent No. 6704245 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned conventional evaluation methods have the following problems. Full-scale piping tests require a great deal of effort and cost to prepare the piping, and the test specimens inside the piping would be wasted, making it difficult to conduct the tests at the construction site each time. The evaluation method in Patent Document 1 simulates the pressure applied to concrete by pumping, but does not reflect the movement of concrete inside the pumping pipe, and therefore cannot consider the effect of shear force acting on the concrete due to movement. Therefore, changes in concrete quality due to pumping are generally evaluated and examined by conducting full-scale pumping tests, which requires a great deal of effort and cost. In the evaluation method of Patent Document 2, the piping distance is short and the pumping speed (discharge rate) is low, so it takes a long time to apply a force to the concrete that is equivalent to the shear force generated by actual pumping. Because the fluidity of concrete changes over time, it becomes difficult to determine the effects of pumping alone after a long time has passed. From this perspective, an object of the present invention is to provide a small pumping test device and a concrete fluidity evaluation system that can apply a force to concrete equivalent to the shear force generated by actual pumping at low cost and in a short time. [Means for solving the problem]

[0005] The first invention for solving the above problems is a small-sized pumping test device comprising a short pipe, a pressure gauge for measuring the pressure in the short pipe, and a biasing means for applying a pumping pressure to the concrete in the short pipe and causing it to flow back and forth, wherein the short pipe is a composite pipe of different diameters made by connecting a large diameter pipe and a small diameter pipe. According to the compact pumping test device of the present invention, the short pipe into which the concrete is poured is a composite pipe with different diameters, so that when the concrete is pumped through the pipe, the pressure drops due to the friction with the pipe wall and the wall shape, and the pressure loss within the pipe increases, compared to when the concrete is pumped through a pipe with the same diameter. This makes it possible to reproduce the situation in which the fluidity of concrete changes due to actual pumping in a short period of time, and to estimate the fluidity of the concrete after pumping.

[0006] The second invention for solving the above-mentioned problems is a concrete fluidity evaluation system for estimating the fluidity of concrete after pumping, comprising: a short pipe which is a composite pipe of different diameters formed by connecting a large diameter pipe and a small diameter pipe; a pressure gauge which measures the pressure in the short pipe; a small-sized pumping test unit which includes a biasing means for applying a pumping pressure to the concrete in the short pipe and causing it to flow back and forth; a correction coefficient calculation unit which calculates a correction coefficient for correcting the difference between a test result using the short pipe and a test result using a full-size pipe; and a correction coefficient which is calculated based on a fluidity measurement value of the full-size concrete to be pumped before pumping or a concrete design strength of the full-size concrete to be pumped into the full-size pipe. and a fluidity estimation unit that estimates a full-scale post-pumping fluidity measurement value at the nozzle of the full-scale pipe by multiplying the fluidity measurement value by a correction coefficient, and the correction coefficient calculation unit calculates the correction coefficient by multiplying the change rate ratio of the fluidity measurement value calculated by dividing the small-scale post-pumping fluidity measurement value, which is an index correlating to the fluidity of the concrete after pumping that has been reciprocated for a predetermined pumping time under the application of a predetermined pumping pressure, by the small-scale pre-pumping fluidity measurement value, which is an index correlating to the fluidity of the concrete before pumping, by a test coefficient calculated by dividing the full-scale post-pumping fluidity measurement value in a full-scale pumping test that has been stored in advance in a data unit by the small-scale post-pumping fluidity measurement value. According to the concrete fluidity evaluation system of the present invention, by using a composite pipe with different diameters as the short pipe into which concrete is poured, the shear stress acting on the concrete in the short pipe can be increased, thereby reproducing the situation in which the fluidity of concrete changes due to actual pumping. This allows a force equivalent to the cumulative shear stress, calculated by multiplying the shear stress generated by actual pumping with the pumping time, to be applied to the concrete during a short reciprocating flow, thereby enabling accurate evaluation of changes in the fluidity of concrete. Furthermore, corrections are made using the results of past pumping tests stored in the data unit, thereby improving the accuracy of evaluation of changes in the fluidity of concrete.

[0007] In the concrete fluidity evaluation system of the present invention, it is preferable that the specified pumping time is calculated by dividing the cumulative shear stress obtained by multiplying the pumping time in the full-scale pumping test stored in the data section by the shear stress acting on the inner wall of the pipe, by the specified pumping pressure applied in the small-scale pumping test section. With this configuration, the pumping time is set using past data stored in the data section, so that an integrated shear stress equivalent to the integrated shear stress obtained by multiplying the pumping time in a full-scale pumping test by the shear stress acting on the inner wall of the pipe can be applied to the concrete. [Effects of the Invention]

[0008] The compact pumping test device of the present invention can apply a force to concrete equivalent to the cumulative shear stress obtained by multiplying the shear stress generated by actual pumping by the pumping time, at low cost and in a short time. Furthermore, the concrete fluidity evaluation system uses the compact pumping test device to reproduce the changes in concrete fluidity caused by actual pumping over time, allowing for estimation of the fluidity of concrete after pumping. This allows for accurate evaluation of changes in concrete fluidity in a short time. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a configuration diagram showing a concrete fluidity evaluation system according to an embodiment. [Figure 2] FIG. 1 is a plan view showing a small-sized pressure-feeding test device according to an embodiment. [Figure 3] 1(a) and 1(b) are cross-sectional views showing a state in which concrete is reciprocated using a small-sized pumping test device of a concrete fluidity evaluation system according to an embodiment. [Figure 4] Graphs showing the relationship between mortar flow and concrete slump flow, where (a) is a graph showing the values ​​for lightweight type 1 concrete, and (b) is a graph showing the values ​​for high-strength concrete. [Figure 5] Graphs showing the changes in pipe pressure and pipe pressure loss during pumping tests, where (a) is a graph showing the values ​​for lightweight type 1 mortar, and (b) is a graph showing the values ​​for high-strength mortar. [Figure 6] The table shows the changes in fresh properties due to pumping tests. (a) is a table showing the values ​​for lightweight type 1 concrete, and (b) is a table showing the values ​​for high-strength concrete. [Figure 7] (a) is a model diagram showing the flow velocity distribution of concrete flowing inside a pipe, and (b) is a model diagram showing the apparent shear stress distribution of concrete flowing inside a pipe. [Figure 8] (a) is a diagram showing the flow of concrete in a sudden expansion pipe, and (b) is a diagram showing the flow of concrete in a sudden contraction pipe. [Figure 9] This is a table showing various measured and calculated values ​​for lightweight type 1 concrete and high-strength concrete in full-scale pumping tests and indoor pumping tests. [Figure 10] Graphs showing the relationship between pumping time and shear stress, where (a) is a graph showing the values ​​for lightweight type 1 concrete, and (b) is a graph showing the values ​​for high-strength concrete. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention is a small-scale pumping test device and concrete fluidity evaluation system for estimating the fluidity of concrete after pumping it into the nozzle of a full-scale pipe, and is intended for lightweight concrete and high-strength concrete. The small-scale pumping test device is equipped with a force-applying device that applies pumping pressure to the concrete in a composite pipe of different diameters, which is made up of alternatingly connected large-diameter and small-diameter pipes, causing it to flow back and forth, and a pressure gauge that measures the pressure in the composite pipe of different diameters, allowing the fluidity of the concrete to be estimated after pumping. In addition, this concrete fluidity estimation system does not use full-scale piping, but instead uses a small pumping test device to estimate the measurement value after full-scale pumping at the end of the full-scale pipe based on the measurement data of the concrete before and after pumping and the results of past concrete pumping tests. In detail, the fluidity of concrete after pumping in a full-scale pipe can be estimated by multiplying the fluidity measurement value at the time of unloading before pumping (before the back-and-forth movement) by the change ratio of the concrete fluidity measurement value before and after pumping using a small-diameter, short pipe, the slump flow ratio (= slump flow at the nozzle after pumping / slump flow at the time of unloading before pumping), and a correction coefficient that includes the influence of the test method using a short pipe and a full-scale pipe, which is stored in advance in the correction coefficient memory unit. The fluidity of concrete targeted in this embodiment is an index expressed by a slump value or a slump flow.

[0011] Hereinafter, a concrete fluidity evaluation system and a small-sized pumping test device according to an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a configuration diagram showing a concrete fluidity evaluation system according to an embodiment, Fig. 2 is a plan view showing a small-sized pumping test device according to an embodiment, and Fig. 3(a) and (b) are cross-sectional views showing a state in which concrete is reciprocated using the small-sized pumping test device. The concrete fluidity evaluation system 1 is for estimating the fluidity of concrete after pumping at the nozzle of a full-scale pipe, and as shown in Figures 1 and 2, it is equipped with a small pumping test section 2, a measuring section (not shown), and a fluidity estimation device 3 (see Figure 1). The test targets concrete, mortar, cement paste, etc., but the test in this embodiment targets concrete with a water-binder ratio of 24.9 to 52.0% and a slump flow of approximately 40 to 75 cm.

[0012] As shown in Figure 2, the small-scale pumping test section 2 includes a small-scale pumping test device 10 and a control device 11. A short pipe 12 is arranged in the small-scale pumping test device 10. The small-scale pumping test section 2 moves back and forth for a predetermined time while applying a predetermined pumping pressure to concrete 14 using biasing means 13 provided at both ends of the short pipe 12.

[0013] First, a description will be given of the configuration of the small-sized pumping test device 10. As shown in Figures 2 and 3, the small-sized pumping test device 10 includes a short pipe 12, a biasing means 13, and a pressure gauge 17. The short pipe 12 is a cylindrical member (sample pipe) that contains the concrete 14, and is a composite pipe of different diameters made by connecting a large-diameter pipe 15 and a small-diameter pipe 16. The large-diameter pipes 15 and small-diameter pipes 16 are arranged alternately, with their axes aligned in a straight line. The short pipe 11 has a diameter of 50 mm or less, smaller than the usual diameter (125 mm), to accommodate the high internal pressure of over 20 MPa (maximum of approximately 27 MPa is possible with this device) that occurs during high-altitude or long-distance pumping, while also achieving a compact chamber size. The large-diameter pipe 15 is 50 mm, and the small-diameter pipe 16 is 30 mm. In this embodiment, the large diameter pipes 15 and the small diameter pipes 16 are arranged in the following order from the end: large diameter pipe 15 (φ50×300 mm), small diameter pipe 16 (φ30×250 mm), large diameter pipe 15 (φ50×250 mm), small diameter pipe 16 (φ30×250 mm), and large diameter pipe 15 (φ50×300 mm). The type, number, and order of the connected pipes can be changed as needed, but the basic configuration is to alternately connect large diameter pipes 15 of φ50 mm and small diameter pipes 16 of φ30 mm. The overall length of the short pipes 12 is basically about 1300 mm, and is a pipe length sufficient to obtain the amount of sample required for the test (approximately 2 L) in order to perform a fresh test on the sample after the pressure test.

[0014] A pressure gauge 17 is attached to the short pipe 12. The pressure gauge 17 measures the pressure inside the short pipe 12 in real time during the test. The pressure gauge 17 is provided at the longitudinal middle of each of two pipes (large diameter pipe 15 and small diameter pipe 16) located near the center of the short pipe 12. Connection parts 19 are attached to both ends of the short pipe 12. The connection parts 19 are tubular members that connect the short pipe 12 and the biasing means 13, and each connection part 19 has a sample injection port 20 formed therein. The sample injection port 20 is the part through which concrete is injected into the short pipe 12, and is provided at the top of each connection part 19. Bolt holes 21 are formed on the periphery of the sample injection port 20, and the flange at the tip of a concrete injection pipe (not shown) is bolted to the periphery of the sample injection port 20.

[0015] The biasing means 13 reciprocates the concrete in the short pipe 12 and moves the concrete under a predetermined pressure (e.g., 0 to 27 MPa). The biasing means 13 is arranged to sandwich the short pipe 12 and includes an actuator 22 and a guide portion 23. The actuator 22 is, for example, a hydraulic cylinder and includes a cylinder tube 24 and a piston rod 25. The piston rod 25 is retractable from the cylinder tube 24. A pump 30 that sends oil to a hydraulic chamber in the cylinder tube 24 is connected to the actuator 22. The pump 30 is electrically connected to the control device 11 and operates in response to a signal from the control device 11. Note that the power source of the actuator 22 is not limited to hydraulic pressure. The movement of the piston rod 25 can be controlled manually or automatically. The movement distance (stroke length) of the piston rod 25 is, for example, approximately 300 mm. A pressure feed rod 26 is connected to the tip of the piston rod 25 via a load cell 18. The load cell 18 detects the load acting on the pressure feed rod 26. The number of times the measurement value of the load cell 18 exceeds a predetermined value is counted as the number of pressure feeds by the biasing means 13. The load cell 18 is electrically connected to the control device. The tip of the pressure feed rod 26 is inserted into the short pipe 12, and the tip surface presses against the concrete in the short pipe 12.

[0016] Guide portion 23 is a portion that guides the movement of piston rod 25 and pressure feed rod 26, and is provided at the inner end portion (the end portion on the short pipe 12 side) of actuator 22. Guide portion 23 includes a support portion 28 and a connecting rod 29. Support portion 28 is fixed to the outer end portion (the end portion on the biasing means 13 side) of the outer connecting portion of short pipe 12. Support portion 28 is configured to have a through hole in the center of a disk-shaped member, through which pressure feed rod 26 is inserted, and slidably supports pressure feed rod 26. The connecting rod 29 is a member that connects the support part 28 and the actuator 22. The connecting rod 29 extends from the actuator 22 toward the short pipe 12. Four connecting rods 29 are provided, and are attached parallel to each other and spaced apart at four locations on the top, bottom, left, and right of the support part 28. In the area surrounded by the four connecting rods 29, 29..., the piston rod 25, the load cell 27, and the pumping rod 26 move in a visible state.

[0017] The control device 11 is a device that controls the operation of the biasing means 13. The control device 11 is electrically connected to the actuators 22, and controls the pressure of the actuators 22 on both sides (the pressure of the pump 30) to move the concrete while maintaining the pressure inside the pipe at a desired pressure. Specifically, by making the pressing force of one actuator 22 greater than the pressing force of the other actuator 22, the pressure inside the pipe is increased and the concrete is moved toward the actuator 22 with the smaller pressing force (see Figures 3(a) and (b)). The control device 11 is also electrically connected to the pressure gauge 17 and the load cell 18, and monitors the pressure inside the pipe and manages the number of pumping operations.

[0018] The measurement unit is equipment for obtaining concrete fluidity measurements and is equipped with instruments for measuring indicators related to the fluidity of concrete. An operator obtains concrete fluidity measurements by performing slump tests, slump flow tests, etc. in the measurement unit. The measurement unit can obtain concrete fluidity measurements for concrete before pumping pressure is applied in the small-scale pumping test unit 2. The measurement unit can also obtain concrete fluidity measurements for concrete after the concrete has been moved back and forth for a predetermined time in the small-scale pumping test unit 2 while applying a predetermined pressure (a pressure simulating pumping pressure) to the concrete 14 using the biasing means 13, 13 provided at both ends of the short pipe 12. The measurement unit may be provided near the small-scale pumping test device 10 or in a test room provided separately from the small-scale pumping test unit 2. The measurement unit measures the fluidity of the concrete (pre-pumping measured value) before pumping pressure is applied in the small-sized pumping test device 10 (i.e., before reciprocating movement), and also measures the fluidity of the concrete after reciprocating movement in the small-sized pumping test device 10 (post-pumping measured value). Specifically, the measurement unit performs a slump flow test on the concrete before pumping pressure is applied, and obtains the slump flow before pressure. Furthermore, after the test in the small-sized pumping test device 10 (i.e., after applying pressure to the concrete in the short pipe 12 using the biasing means 13, and moving the concrete back and forth for the desired pumping time while gradually increasing the concrete pressure to the desired maximum pipe pressure), the measurement unit performs a slump flow test on concrete sampled from inside the short pipe 12, and obtains the slump flow after reciprocating movement.

[0019] 1, the fluidity estimation device 3 is a calculation device (computer) for approximately correcting a concrete fluidity measurement value (e.g., slump flow value) acquired by a measurement unit to a concrete fluidity measurement value (e.g., slump flow value) of a full-scale pipe. The fluidity estimation device 3 includes a correction coefficient calculation unit 4, a storage unit 5, and a fluidity estimation unit 6. The correction coefficient calculation unit 4 calculates a correction coefficient K to calibrate the difference between the test results using the short pipe 12 and the test results using the full-scale pipe, i.e., a correction coefficient K to be multiplied by the concrete fluidity measurement value obtained by the measurement unit. The correction coefficient calculation unit 4 calculates the correction coefficient K (= S × T) by multiplying the "change rate ratio S of the fluidity measurement value" by the "test coefficient T." The change rate ratio S of the fluidity measurement value is calculated by dividing the small-scale post-pumping fluidity measurement value Sa by the small-scale pre-pumping fluidity measurement value Sb (i.e., S = Sa / Sb). The small-scale post-pumping fluidity measurement value Sa is an index correlating with the fluidity of the concrete after pumping, which is pumped back and forth for a predetermined pumping time under a predetermined pumping pressure in the short pipe 12. The small-scale pre-pumping fluidity measurement value Sb is an index correlating with the fluidity of the concrete before pumping. The test coefficient T is calculated by dividing the full-scale post-pumping fluidity measurement value La in the full-scale pumping test stored in advance in the data section by the small-scale post-pumping fluidity measurement value Sa (i.e., T=La / Sa). Specifically, the correction coefficient calculation section 4 calculates the correction coefficient K from the concrete fluidity measurement value at the end of the pipe after pumping (full-scale post-pumping fluidity measurement value La), the concrete fluidity measurement value before reciprocating movement in the small-scale pumping test using the small-scale pumping test section 2 (small-scale pre-pumping fluidity measurement value Sb), and the concrete fluidity measurement value after reciprocating movement (small-scale post-pumping fluidity measurement value Sa).

[0020] The measured values ​​before full-scale pumping and the measured values ​​after full-scale pumping are values ​​measured in a full-scale pumping test in which full-scale piping is arranged, and are stored in advance in the memory unit 5. The full-scale pumping test is a test that is carried out in advance as a preliminary test. In the full-scale pumping test, changes in fluidity before and after pumping were confirmed for two types of concrete mixes: lightweight type 1 concrete and high-strength concrete. In the full-scale pumping test, slump, slump flow, air content, and concrete temperature were measured at the time of unloading and at the nozzle of the pipe. In the pumping experiment, the concrete was pumped after confirming that the fresh properties at the time of unloading were the same, and the fresh properties before and after pumping were compared. In order to collect concrete at the nozzle from the same agitator truck as the concrete collected at unloading, the timing of sample collection was adjusted taking into account the concrete volume in the pipe and the discharge rate. In addition, in order to confirm the effects of pumping and aging on fresh properties, some of the samples collected at unloading were stored in a stationary state and tested at the same time as the samples collected at the nozzle.

[0021] The concrete pumping time performed using the short pipe 12 of the small-scale pumping test device 10 is calculated by dividing the cumulative shear stress obtained by multiplying the pumping time in the full-scale pumping test by the shear stress acting on the inner wall of the pipe, by the specified pressure (shear stress acting on the inner wall of the pipe with a different diameter) applied in the small-scale pumping test section 2. This makes the cumulative shear stress in the full-scale pumping experiment and the cumulative shear stress in the small-scale pumping test equivalent.

[0022] The fluidity estimation unit 6 is a part that estimates the actual-size post-pumping fluidity measurement value at the nozzle of the actual-size pipe by multiplying the actual-size pre-pumping fluidity measurement value of the actual-size concrete to be pumped into the actual-size pipe or the concrete design strength by the correction coefficient calculated by the correction coefficient calculation unit 4. Specifically, the slump flow ratio calculated by dividing the concrete fluidity measurement value after reciprocating movement (small-scale post-pumping measurement value) acquired by the measurement unit by the concrete fluidity measurement value before reciprocating movement (before pumping pressure is applied) (small-scale pre-pumping measurement value) is multiplied by the actual-size pre-pumping measurement value and the correction coefficient to estimate the actual-size post-pumping measurement value.

[0023] Next, the procedure for a small-sized pumping test performed using the small-sized pumping test device 10 will be described. First, the concrete, mortar, or cement paste to be examined for pumpability is mixed to form a sample (concrete). Measurements of the resulting concrete are obtained in the measuring section using a slump flow test or similar method before small-scale pumping (before reciprocating movement), and it is confirmed that the target fresh properties have been achieved. At this point, a portion of the sample (approximately 2 liters) is set aside to be poured into the small-scale pumping test device, and the remainder is stored stationary. Approximately 2 liters of sample are then poured into the short pipe 12 through the sample inlet 20 on one side of the small-scale pumping test device 10. During the pouring process, the actuator 22 on one side is pushed out, and as much air as possible is expelled from the short pipe 12 through the sample inlet 20 on the other side. The short pipe 12 is then filled with the sample, and the inlet is closed. By pushing and pulling the actuators 22 of the biasing means 13 on both sides, the sample in the short pipe 12 is moved left and right while applying pressure. 2 ) is reached. In addition to a test method in which the pressure inside the pipe is maintained at a constant pressure while moving, a test method can also be used in which a pressure history is given by increasing and decreasing the pressure inside the pipe over time. After pressurizing and moving the sample for a predetermined time, the small pumping test device 10 is stopped and the sample is removed from the short pipe 12. Then, in the measurement section, various tests such as a slump flow test are performed and compared on the sample removed from the short pipe 12 and the sample that was left stationary, and the effects of pumping on the fluidity of the concrete, etc. are examined.

[0024] Next, we will explain a test example that examined the effect on concrete fluidity (slump flow) of differences in the piping shape of the short pipe 12 of the small-sized pumping test device 10. First, we will explain the materials used and the mix of concrete. The mixes examined were two types: lightweight type 1 concrete and high-strength concrete, and the mortar was mixed by removing coarse aggregate from the mix of each concrete. The materials used for lightweight type 1 concrete and mortar are as follows: W1: Groundwater C1: Ordinary Portland cement, density 3.15g / cm3 S1: Land sand Surface dry density 2.55g / cm3, coarse grain ratio 2.40 S2: Crushed limestone sand Surface dry density 2.62g / cm3, coarse grain ratio 3.20 G1: Artificial lightweight coarse aggregate, absolute dry density 1.30g / cm3, actual area ratio 64.0%, water absorption rate 28%, The mix proportions for lightweight type 1 concrete are shown in Table 1, and those for lightweight mortar in Table 2. The unit amount of artificial lightweight coarse aggregate G1 is shown as the value in an absolute dry state. A high-performance air-entraining water-reducing agent was added as an admixture. The amount of high-performance air-entraining water-reducing agent added was 0.92% of the unit cement amount.

[0025] [Table 1]

[0026] [Table 2]

[0027] The materials used for high-strength concrete and mortar are as follows: W2: Tap water C2: Moderate heat Portland cement, density 3.21 g / cm 3 S3: Mountain sand Surface dry density 2.60g / cm 3 , coarse grain ratio 2.65 G2: Hard crushed sandstone, surface dry density 2.60g / cm 3 , coarse grain ratio 2.65 The mix proportions for high-strength concrete are shown in Table 3, and for high-strength mortar in Table 4. A high-range water-reducing agent was added as an admixture. The amount of high-range water-reducing agent added was 1.2% of the unit cement amount.

[0028] [Table 3]

[0029] [Table 4]

[0030] Figure 4 shows the relationship between mortar flow and concrete slump flow. (a) shows the values ​​for lightweight, Class 1 concrete, and (b) shows the values ​​for high-strength concrete. To convert the concrete slump flow values ​​from the mortar flow test results, test mixes were conducted in advance to determine the relationship between the two test values. The test results are shown in Figure 4. In the mortar flow test, multiple batches containing different amounts of high-range water-reducing agent were mixed to determine the correlation between multiple mortar flows and slump flows. The amounts of high-range water-reducing agent used were 0.05%, 0.2%, 0.35%, 0.5%, and 0.92% of the unit cement weight for lightweight, Class 1 concrete, and 0.7%, 0.85%, 0.92%, 1.0%, 1.1%, 1.2%, 1.33%, and 1.5% for high-strength concrete. For lightweight type 1 concrete, a high correlation was found between the 15-ply flow value of mortar and the slump flow value of concrete. For high-strength concrete, a high correlation was found between the 0-ply flow value of mortar and the slump flow value of concrete. Therefore, we decided to convert the slump flow value of concrete using the regression equations shown in Figure 4 (a) and (b).

[0031] Next, for each mortar mixture, a pumping test was carried out using two types of piping combinations. One was a same-diameter piping (comparison example) in which all φ50 mm transport pipes (2 x 300 mm + 2 x 250 mm) were connected together to form a total length of 1100 mm, and the other was a different-diameter piping (short piping 12) in which φ50 mm large-diameter pipes 15 (2 x 300 mm + 1 x 250 mm) and φ30 mm small-diameter pipes 16 (2 x 250 mm) were alternately connected to form a total length of 1350 mm. Figure 5 is a graph showing the changes in pipe pressure and pipe pressure loss during a pumping test, with (a) showing the values ​​for lightweight Class 1 mortar and (b) showing the values ​​for high-strength mortar. For the pumping test, after mixing each mortar mix and confirming that the required mortar flow had been obtained, some of the samples were placed into a small pumping test device. After the samples were placed, the pumping test was performed by flowing the samples from side to side while maintaining a pipe pressure of approximately 20 MPa. An example of the changes in pipe pressure and pipe pressure loss during a pumping test is shown in Figure 5.

[0032] The pressure loss inside the pipe was calculated by dividing the difference in the measured values ​​of the pressure gauges installed in the two pipes by the distance between them (250 mm). The pressure inside the pipes during pumping tests of lightweight Class 1 concrete and high-strength concrete remained at the same level (approximately 20 MPa) for both same-diameter and different-diameter pipes, but the pressure loss inside the pipes was greater for different-diameter pipes than for same-diameter pipes. The greater the pressure loss inside the pipes, the greater the apparent shear stress generated in the mortar (details will be given later), so it was confirmed that by combining different-diameter pipes, a greater shear force could be applied.

[0033] Figure 6 is a table showing the changes in fresh properties due to pumping tests, with (a) showing the values ​​for lightweight class 1 concrete and (b) showing the values ​​for high-strength concrete. Here, we will show an example of the changes in fresh properties due to laboratory testing. Mortar samples from lightweight class 1 concrete and high-strength concrete, from which the coarse aggregate had been removed, were subjected to mortar flow tests on samples that had undergone pumping tests and samples that had been left to stand without undergoing pumping tests, and the concrete's slump flow equivalent was calculated using the regression equation mentioned above (see Figure 4). Figure 6 shows the changes in fresh properties due to pumping tests. For lightweight type 1 concrete mortar, the change in slump flow equivalent value in the pumping test was -121 mm for the same diameter pipe and -155 mm for the combination of different diameter pipes. In other words, the change was greater for different diameter pipes than for the same diameter pipes. For high-strength concrete mortar, the change in slump flow equivalent value in the pumping test was -11 mm for the same diameter pipe and -66 mm for the combination of different diameter pipes. In other words, the change was greater for different diameter pipes than for the same diameter pipes.

[0034] From the above results, it was confirmed that the fluidity of concrete can be significantly changed by using the small pumping test device 10 equipped with different diameter pipes. It was also found that by combining different diameter pipes, the amount of change in the fluidity of concrete is greater than when only same diameter pipes are used. This is thought to be because, as mentioned above, a greater shear force is generated in the concrete sample inside the pipe.

[0035] Below, we will consider why the shear force increases when different diameter pipes are combined. First, we will explain the shear force generated by pumping. In response to the pressure that the sample inside the pipe is subjected to in the direction of travel, the sliding resistance force acting on the pipe wall due to the flow inside the pipe acts as a counter force, resulting in a shear force acting between the sample and the pipe wall. This shear force generates shear stress in the sample inside the pipe. The shear stress generated in the sample inside the pipe can be calculated using the following formula (1).

[0036]

number

[0037] where τ R : apparent shear stress of the sample in contact with the pipe wall (MPa), R: pipe radius (m), ΔP / l: pressure loss inside the pipe (MPa / m). In formula (1), it is assumed that concrete and mortar are Bingham fluids with a yield value, and the apparent shear stress of concrete and mortar flowing inside the pipe is distributed in a linearly increasing manner in the radial direction from the center of the pipe cross section. From formula (1), it can be seen that shear stress increases in proportion to the pressure loss inside the pipe.

[0038] A model of the flow velocity distribution and apparent shear stress distribution of concrete flowing inside a pipe is shown in Figure 7. Figure 7(a) is a model diagram showing the flow velocity distribution of concrete flowing inside a pipe, and (b) is a model diagram showing the apparent shear stress distribution of concrete flowing inside a pipe. As shown in Figure 7, when a fluid flows inside a pipe, the flow is resisted by friction with the pipe wall and the wall shape, causing a drop in pressure (pressure loss). There are two factors that cause pressure loss: Factor 1. Friction loss: Loss caused by friction (viscous force) between a solid wall and a fluid Factor 2. Form loss: Loss caused by form resistance If there is a change in pipe cross-sectional area or change in flow direction midway through the piping, not only friction loss but also geometric loss occurs. The loss coefficient ζ is used to evaluate the magnitude of loss due to geometry. Below, we will explain pressure loss due to changes in pipe cross-sectional area. Figure 8 (a) shows the flow of concrete in a sudden expansion pipe, and (b) shows the flow of concrete in a sudden contraction pipe.

[0039] As shown in Figure 7(a), in a flow in a pipe where the cross-sectional area suddenly expands from A1 to A2, when the fluid (concrete 14) enters from the small diameter pipe 16 into the large diameter pipe 15, it draws in the surrounding fluid and creates a vortex, resulting in loss. The loss coefficient ζ in this case is expressed by the following equation (2).

[0040]

number

[0041] On the other hand, as shown in Figure 7(b), in the flow in an abrupt contraction pipe where the cross-sectional area suddenly contracts from A1 to A2, vortices are generated at the corners, causing losses. C After contracting to A C The loss coefficient ζ due to sudden contraction is expanded from A1 to A2. C The loss factor is small, approximately 0.04, up to A CThe loss coefficient from A to A2 is expressed by the same formula (2) as for the flow in a sudden expansion pipe. In this case, the loss coefficient ζ is expressed by the following formula (3). Also, the area ratio A C / A2 is expressed by the following formula (4).

[0042]

number

[0043]

number

[0044] From the above explanation, the reason why the shear force increases when different diameter pipes are combined can be considered as follows. Combining pipes of different diameters causes not only friction loss but also geometric loss, increasing the pressure loss inside the pipe. As a result, the shear stress generated in the sample inside the pipe increases in proportion to the pressure loss inside the pipe. In other words, the shear force acting on the sample inside the pipe increases. Furthermore, pressure and shear force act on the concrete during pumping. The pressure reaches a maximum immediately after pumping begins (at the base of the pump barrel), decreases almost linearly as the concrete advances through the pipe, and reaches zero when it is discharged from the tip of the barrel. Regarding shear force, when considering it as shear stress generated within the concrete, the shear stress is proportional to the pressure loss within the pipe, as described above (see Figure 7). When pressure decreases linearly from the base of the pump barrel to the tip of the barrel, the pressure loss within the pipe, which corresponds to the gradient, is constant, and therefore the shear stress generated in the concrete during pumping is also constant. These pressures and shear stresses resulting from pumping are thought to affect the fluidity of the concrete after pumping. In the laboratory testing method of this embodiment, the total amount of pressure or shear stress generated during pumping is set to be approximately the same as the total amount generated during full-scale pumping, thereby evaluating the change in the fluidity of the concrete after pumping.

[0045] Pressure can be controlled relatively easily by changing the hydraulic pressure of the test equipment, but shear stress depends on the discharge rate of the sample in the pipe (flow speed when pumped), and it is difficult to achieve a large discharge rate in a laboratory-scale test equipment, so the range of control is limited. Therefore, by changing the pipe shape without changing the discharge rate, it was possible to increase the shear stress. The various measured and calculated values ​​from the full-scale pumping test and the laboratory pumping test are shown in the table in Figure 9. Figure 9 is a table showing the various measured and calculated values ​​for lightweight class 1 concrete and high-strength concrete from the full-scale pumping test and the laboratory pumping test. The table in Figure 9 lists the results of the full-scale pumping test, which serves as a model for the total amount of pressure and shear stress generated during pumping for lightweight class 1 concrete and high-strength concrete, respectively.

[0046] In a full-scale pumping test of lightweight type 1 concrete, a 125 mm diameter, 735 mm long pipe was pumped from base to tip in 590 seconds. The maximum internal pressure at the pump base was 20 MPa, and the internal pressure loss was 0.064 MPa / m. The shear stress calculated from these results was 0.004 MPa, and the integrated shear stress calculated over the time required for pumping was 2.36 MPa·s. In laboratory tests of lightweight type 1 concrete, as mentioned above, the internal pressure loss differs depending on whether the pipes are of the same or different diameters. The internal pressure loss for each pipe is the average value of the internal pressure loss over a 30-second period shown in Figure 5(a). For the different-diameter pipes, the diameter of the pipe was calculated using the following formula, taking into account the ratio of the 30 mm and 50 mm diameter pipe lengths to the total pipe length. {30mm×(500mm / 1350mm)+φ50mm×(850mm / 1350mm)}=φ0.043mm When the pumping time required to reach the cumulative shear stress of full-scale pumping was calculated from the pressure loss in the pipes in the laboratory test and the shear stress calculated from the diameter of the transport pipe, it was calculated to be 199 seconds for same-diameter pipes and 94 seconds for different-diameter pipes. In other words, when generating a cumulative shear stress equivalent to full-scale pumping, it is clear that the time required for pumping tests with different-diameter pipes can be shorter than with same-diameter pipes.

[0047] Similarly, when calculating the time required to generate the cumulative shear stress generated by full-scale pumping for high-strength concrete, it is calculated to be 145 seconds for same-diameter pipes and 68 seconds for different-diameter pipes. In other words, in the case of high-strength concrete, just like lightweight Class 1 concrete, it is clear that the time required for pumping tests can be shortened using different-diameter pipes compared to same-diameter pipes.

[0048] Next, the relationship between pumping time and shear stress is shown in Figure 10. Figure 10 is a graph showing the relationship between pumping time and shear stress, with (a) showing the values ​​for lightweight type 1 concrete and (b) showing the values ​​for high-strength concrete. In Figure 10, the area of ​​the rectangle enclosed by the plots of pumping time and shear stress corresponds to the cumulative shear stress. It can be seen that by using different diameter pipes, the shear stress generated in the concrete is larger than with same diameter pipes, and the pumping test time required to reach the cumulative shear stress generated by full-scale pumping can be shortened.

[0049] From the above, the time (pumping time) for the concrete to move back and forth using the short pipe 12 can be calculated by dividing the cumulative shear stress obtained by multiplying the pumping time in the full-scale pumping test by the shear stress acting on the inner wall of the pipe by the specified pressure applied in the small-scale pumping test section 2 (shear stress in the case of different diameter pipes).

[0050] As described above, according to the small-sized pumping test device 10 of this embodiment, by using the short pipe 12 as a composite pipe of different diameters, in which the large diameter pipe 15 and the small diameter pipe 16 are connected, it is possible to increase the shear stress acting on the concrete in the short pipe 12 and reproduce the situation in which the fluidity of concrete changes due to actual pumping. This makes it possible to reproduce the situation in which the fluidity of concrete changes due to actual pumping with a short period of back and forth flow and estimate the fluidity of the concrete after pumping, so that changes in the fluidity of concrete can be evaluated accurately in a short period of time.

[0051] Furthermore, according to the concrete fluidity evaluation system of this embodiment, a force equivalent to the shear force generated by actual pumping can be applied to the concrete in a short period of reciprocating flow, thereby shortening the time required for evaluation and enabling accurate evaluation of changes in concrete fluidity. Furthermore, corrections are made using the results of past pumping tests stored in the data section, thereby improving the accuracy of evaluation of changes in concrete fluidity. Furthermore, the concrete pumping time (predetermined pumping time) performed using the short pipe 12 of the small-scale pumping test device 10 is calculated by dividing the cumulative shear stress obtained by multiplying the pumping time in the full-scale pumping test stored in the data section by the shear stress acting on the inner wall of the pipe by the predetermined pumping pressure applied to the short pipe 12, so that an cumulative shear stress equivalent to the cumulative shear stress obtained by multiplying the pumping time in the full-scale pumping test by the shear stress acting on the inner wall of the pipe can be applied to the concrete.

[0052] Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to the above-described embodiments, and design changes can be made as appropriate without departing from the spirit of the present invention. For example, in the above-described embodiment, the short pipe 12 is configured by alternately connecting large-diameter pipes 15 each having a diameter of 50 mm and small-diameter pipes 16 each having a diameter of 30 mm, but the present invention is not limited to this. The diameter, length, and number of pipes can be changed as appropriate.

[0053] In the above embodiment, the concrete fluidity was measured in the full-scale pumping test for two types of concrete: lightweight type 1 concrete and high-strength concrete. However, the present invention is not limited to these. For other frequently used concrete mixes, if full-scale pumping tests are conducted in advance and the concrete fluidity is acquired and stored, the measurement can be applied to concrete mixes of various types. [Explanation of symbols]

[0054] 1. Concrete fluidity evaluation system 2. Small-sized pressure test section 4. Correction coefficient calculation section 5 Storage section 6 Liquidity Estimation Department 10. Small pumping test equipment 12 Short piping 13. Actuation means 14 Concrete 15 Large diameter pipe 16 Small diameter tube 17 Pressure gauge

Claims

1. A small-sized pumping test device comprising a short pipe, a pressure gauge for measuring the pressure in the short pipe, and a biasing means for applying a pumping pressure to the concrete in the short pipe and causing it to flow back and forth, The short pipe is a composite pipe of different diameters formed by connecting a large diameter pipe and a small diameter pipe. A compact pumping test device characterized by:

2. A concrete fluidity evaluation system for estimating the fluidity of concrete after pumping, a short pipe that is a composite pipe of different diameters formed by connecting a large diameter pipe and a small diameter pipe; a pressure gauge that measures the pressure in the short pipe; and a compact pressure test unit that includes a biasing means that applies pressure to the concrete in the short pipe and causes it to flow back and forth while a pressure is applied to the concrete in the short pipe. a correction coefficient calculation unit that calculates a correction coefficient for correcting a difference between a test result using the short-length pipe and a test result using the full-size pipe; a fluidity estimation unit that estimates a fluidity measurement value after full-scale pumping at the nozzle of the full-scale pipe by multiplying a full-scale pre-pumping fluidity measurement value of the full-scale concrete to be pumped into the full-scale pipe or a concrete design strength by the correction coefficient; The correction coefficient calculation unit calculates the correction coefficient by multiplying the change rate ratio of the fluidity measurement value calculated by dividing the small-scale post-pumping fluidity measurement value, which is an index correlating with the fluidity of the concrete after pumping that has been reciprocated for a predetermined pumping time under a predetermined pumping pressure, by the small-scale pre-pumping fluidity measurement value, which is an index correlating with the fluidity of the concrete before pumping, by a test coefficient calculated by dividing the full-scale post-pumping fluidity measurement value in a full-scale pumping test that has been stored in advance in a data unit by the small-scale post-pumping fluidity measurement value. A concrete fluidity evaluation system characterized by:

3. The predetermined pumping time is calculated by multiplying the pumping time in the full-scale pumping test stored in the data section by the shear stress acting on the inner wall of the pipe, and dividing the result by the predetermined pumping pressure applied in the small-scale pumping test section.

3. The concrete fluidity evaluation system according to claim 2.

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