JP3593376B2 - Method for measuring moisture content of fine aggregate for concrete - Google Patents

Description

[0001]
[Industrial applications]
TECHNICAL FIELD The present invention relates to a method for measuring the water content of fine aggregate for concrete, which enables the water content of fine aggregate for concrete to be quickly measured using microwaves.
[0002]
[Prior art]
In the production of ready-mixed concrete, it is desirable to adjust the water injection amount and the like according to the water content of the fine aggregate to produce a concrete of a constant quality. Therefore, it is necessary to measure the moisture content of the fine aggregate carried into a factory or the like. In the conventional measurement of the moisture content, a fine aggregate sample was dried to a completely dry state using a drying furnace at 100 to 110 ° C., and was calculated from the difference in mass between before and after drying. For drying to the absolutely dry state, it is necessary to dry the fine aggregate sample in a drying furnace for only 24 hours, which is disadvantageous in that the time required for measuring the water content is long.
[0003]
Therefore, the inventors have repeated research on a method of rapidly measuring the water content of fine aggregate for concrete using microwaves, and have reported in the collection of papers at the 48th Annual Meeting of the Japan Society of Civil Engineers, “High-frequency phase type simple Part of the research results was entitled "Prototype of Moisture Analyzer". A brief description of the technology presented here is as follows. First, since the propagation speed of microwaves is delayed when passing through a substance having a large dielectric constant, the microwave is transmitted through a substance containing moisture having a constant dielectric constant, and the time delay is measured as a phase delay. This is based on the principle that moisture contained in a substance can be measured. Then, a fine aggregate sample having a constant moisture content was filled in a glass container, and microwaves were transmitted at different filling ratios to measure the phase lag between the fine aggregate sample and the container. We have found that the phase lag is large. Further, it was found that the filling rate increased when the fine aggregate sample was filled in a container and this was vibrated by a vibrator, but when the vibration was applied for about 3 minutes, the increase in the filling rate was almost saturated. Therefore, a fine aggregate sample having a known moisture content is filled in the container without pressurizing, and a vibration is applied to the container for about 3 minutes to transmit microwaves, and the phase lag is measured. When this measurement was performed at various known moisture contents from a completely dry state to a wet state, a graph of the moisture content versus the phase lag characteristic as shown by a broken line in FIG. 5 was obtained. As a result, if the graph is measured in advance for a fine aggregate, the water content is measured immediately by referring to the graph by measuring the phase lag of the fine aggregate newly brought into a factory or the like. I can do it. In the drawing, the water content at the refraction point indicated by the polygonal line is substantially the same as the water content in the surface dry and saturated state (hereinafter referred to as the surface dry state) in JIS A119 (test method for specific gravity and water absorption of fine aggregate). Match.
[0004]
[Problems to be solved by the invention]
The technology presented in the above-mentioned collection of papers is different from the conventional method, in which the fine aggregate sample is dried to the absolutely dry state every time fine aggregate is brought into a factory or the like, and the moisture content is measured. Thus, the moisture content of the fine aggregate can be measured very quickly. However, variations were observed in the phase lag measured from fine aggregate having a known moisture content. Therefore, the inventors have further studied to further improve the measurement accuracy. As a factor of the variation in the measurement accuracy, the filling rate of the fine aggregate sample in the container is not constant, and also changes in the height direction in the container, and the width of the value is detected as a phase lag due to the change in the height direction. It was presumed to be wider, and for this reason, studies were made to improve the filling rate.
[0005]
The present invention is a further improvement of the technology disclosed in the above-mentioned collection of papers, in which a highly reproducible measurement is performed by improving the filling rate of the fine aggregate sample into the container, and the water content of the fine aggregate sample is measured. It is an object of the present invention to provide a method for measuring the water content of fine aggregate for concrete, which can quickly and accurately measure water content.
[0006]
[Means for Solving the Problems]
In order to achieve this object, the method for measuring the water content of fine aggregate for concrete according to the present invention is characterized in that a microwave is transmitted through an empty container made of a dielectric material and having an open top, and the microwave including the empty container is used. Correct the phase delay due to the wave propagation path, adjust the display of the phase meter to zero, fill the container with the fine aggregate sample, place a weight thereon, and vibrate the container with a vibrator. The fine aggregate sample has a predetermined filling rate, and the microwave is transmitted through the container and the fine aggregate sample except for the weight to measure the phase lag of the microwave with the phase meter. The water content of the fine aggregate sample is determined from the measured phase delay in light of the water content versus phase lag characteristic data actually measured with the fine aggregate sample having a known water content.
[0007]
Further, the microwave is transmitted through an empty container made of a dielectric material and having an open top, and the display of the phase meter is adjusted to zero by correcting the phase delay due to the propagation path of the microwave including the empty container, The container is filled with a fine aggregate sample having a known moisture content in a wet state, a weight is placed thereon, and the container is vibrated by a vibrator to set the fine aggregate sample to a predetermined filling rate. Further, the microwave is transmitted through the container and the fine aggregate sample except for the weight, and the phase lag of the microwave is measured by the phase meter. The phase lag is measured at two different known moisture contents and a known moisture content in an air-dried state, and a line connecting the two measured values in the wet state in the moisture content vs. phase lag characteristic graph is obtained in the air-dried state. The moisture content at the point where the phase delay of the measured value It may be measured as the water content in Thailand.
[0008]
[Operation]
In the method for measuring the moisture content of fine aggregate for concrete according to claim 1, the weight is placed on the fine aggregate sample filled in the container and vibration is applied. Rises, and the filling rate becomes substantially constant in the height direction in the container. On the other hand, in the conventional apparatus which simply applies vibration, the filling rate is lower than that using a weight, and the filling rate tends to change in the height direction in the container. Therefore, in the method of the present invention, the change of the phase lag is large relative to the change of the water content in the wet state, and the width of the value detected as the phase lag is also narrow, so that the water content can be accurately measured. .
[0009]
Further, in the method for measuring the moisture content of fine aggregate for concrete according to claim 2, the filling rate of the fine aggregate sample in the container increases, and the change of the phase lag increases with the change of the moisture content. Therefore, the slope of the line connecting the two measured values in the wet state is so large that it becomes clear that this line becomes the phase lag of the measured value in the air-dry state, and the measurement of the moisture content in the surface-dry state is also accurate. Will be better.
[0010]
【Example】
An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram of an example of an apparatus used in the method for measuring the moisture content of fine aggregate for concrete according to the present invention. FIG. 2 is a flowchart for explaining the operation of obtaining the water content of the embodiment of the method for measuring the water content of fine aggregate for concrete using the apparatus shown in FIG. It is a flowchart which produces the graph of a delay characteristic, and (b) is a flowchart which calculates | requires the unknown moisture content of a fine aggregate sample. FIG. 3 is a flowchart for explaining the operation for obtaining the moisture content in the surface-dry state of another embodiment of the method for measuring the moisture content of fine aggregate for concrete using the apparatus shown in FIG. FIG. 4 is a graph showing that the filling rate and the phase delay change depending on the weight of the weight. FIG. 5 is a graph showing water content versus phase lag characteristics.
[0011]
First, the configuration of the apparatus used in the method for measuring the moisture content of fine aggregate for concrete according to the present invention will be described. As shown in FIG. 1, a hole into which the container 12 is inserted is provided in the center of the waveguide 10. The container 12 has a cylindrical shape with an open top, and is made of, for example, a dielectric material such as glass and has an inner diameter of 36.8 mm, a depth of 89.6 mm, and a volume of about 95 ml. One end of the waveguide 10 is connected to a microwave oscillator 16 via an isolator 14. A probe 18 is provided at the other end of the waveguide 10. A part of the microwave (for example, 2.45 GHz) oscillated by the microwave oscillator 16 propagates through the waveguide 10 via the isolator 14, further passes through the container 12, and is picked up by the probe 18 at the other end. The signal is supplied to the phase meter 20, and a part is supplied to the phase meter 20 from the isolator 14. The phase meter 20 includes a phase delay detector 20a for detecting a phase delay of two microwaves supplied from the isolator 14 and the probe 18, a memory 20b for recording the measured phase delay, and a memory 20b for storing the measured phase delay. And a display device 20d for calculating the difference between the phase delays stored in the storage device and a display device 20d for displaying the calculation result. Further, a vibrator 22 is provided to apply vibration to the container 12 inserted into the hole of the waveguide 10. Further, a weight 26 that is placed on the fine aggregate sample 24 filled in the container 12 and presses the fine aggregate sample 24 with a predetermined pressure is prepared. The weight 26 applies, for example, a surface pressure of about 10 g / cm ² to the fine aggregate sample 24.
[0012]
Here, the operation of the weight 26 will be described. In the method described in the above-mentioned collection of papers, it is intended to obtain a stable filling by applying a vibration to the fine aggregate sample 24 filled in the container 12, but it is not necessarily required. Was not obtained. This is because the filling state is exerted by the weight of the fine aggregate sample 24 itself, and the fine aggregate sample 24 near the surface may fly upward due to vibration, and a large filling rate is obtained at least near the surface. Because there is no. Therefore, in the present invention, a predetermined weight is applied to the fine aggregate sample 24 near the surface by placing the weight 26 on the fine aggregate sample 24 and applying vibration, and Improvements were made to obtain a substantially constant filling rate in the height direction. The graph shown in FIG. 4 shows the characteristics of the sample density and the phase lag when the weights 26 having different weights are placed on the fine aggregate sample 24 having the same moisture content and the vibration is applied to measure the phase lag. The water content was measured while changing it to (a), (b), (c), and (d). In all cases, the use of the heavier weight 26 increased the sample density, and the phase lag was clearly increased. ing.
[0013]
Next, a method for measuring the water content of the fine aggregate sample 24 using the apparatus shown in FIG. 1 will be described. First, the phase delay of the microwave at both ends of the microwave propagation path of the waveguide 10 including the empty container 12 is measured by the phase delay detector 20a, and the measured value is stored in the memory 20b (FIG. 2 ( a) Step 1). Next, the fine aggregate sample 24 having a known moisture content is filled in the container 12 (step 2 in FIG. 2 (a)), and a weight 26 is placed thereon to apply vibration (step 3 in FIG. 2 (a)). The vibrator 22 is stopped, and the phase delay at both ends of the waveguide 10 is measured by the phase delay detector 20a except for the weight 26, and an empty container stored in the memory 20b is obtained from the measured phase delay. The phase delay due to 12 or the like is subtracted by the calculator 20c, and the calculated value is displayed on the display 20d (FIG. 2A, step 4). The phase delay displayed on the display 20d is obtained by correcting the phase delay due to the propagation path including the empty container 12, and is caused only by the fine aggregate sample 24 filled in the container 12. That is, the phase delay caused by the propagation path including the empty container 12 is corrected, the display of the phase meter 20 is adjusted to zero, and the phase delay caused by the fine aggregate sample 24 is displayed as it is. Then, the measurement of the phase lag using each fine aggregate sample 24 with various known moisture contents is repeated until a predetermined number of measured values enough to create a graph are obtained (step 5 in FIG. 2A). Once a predetermined number of measured values have been obtained, a graph of the water content versus the phase lag characteristic is created from these data, as shown by the solid line in FIG. 5 (step 6 in FIG. 2 (a)). Here, by using the weight 26, the change in the phase delay with respect to the change in the water content is larger than that in the case where the weight 26 is not used (shown by a broken line in FIG. 5). In this way, the graph of FIG. 5 is created in advance for each type of fine aggregate sample 24. The known moisture content may be obtained, for example, by setting the fine aggregate sample 24 in a completely dry state and injecting water into the fine aggregate sample 24 at a predetermined rate.
[0014]
Next, the measurement of the water content of the fine aggregate sample 24 whose water content is unknown will be described using the graph of the water content versus the phase lag characteristic created as described above. First, the phase delay at both ends of the propagation path including the empty container 12 is measured (step 1 in FIG. 2B), and data for adjusting the display of the phase meter 20 to zero is obtained. Then, the fine aggregate sample 24 having an unknown moisture content is filled into the container 12 (step 2 in FIG. 2B), and the weight 26 is placed thereon, and the vibrator 22 is operated to apply vibration to the fine aggregate sample 24. The filling rate is set to a predetermined value (step 3 in FIG. 2B). Further, the vibrator 22 is stopped, the weight 26 is removed, the microwave oscillator 16 is operated, the microwave is transmitted into the container 12, and the phase delay at both ends of the waveguide 10 is measured. The measured values are subjected to arithmetic processing, and the phase delay caused by the fine aggregate sample 24 is displayed on the display 20d (step 4 in FIG. 2B). The phase lag measured from the fine aggregate sample 24 whose water content is unknown is compared with a graph of the water content versus the phase lag characteristic of the fine aggregate sample 24 prepared in advance in the process of FIG. And the water content is determined (step 5 in FIG. 2 (b)).
[0015]
In this manner, by previously creating a graph of the moisture content versus the phase lag characteristic as shown in FIG. 5 for each fine aggregate sample 24, the fine aggregate sample 24 having an unknown moisture content to be carried into a factory or the like can be obtained. On the other hand, the moisture content can be measured quickly. Moreover, the measurement accuracy is improved as compared with the one published in the previous paper.
[0016]
Further, a method for measuring the moisture content of the fine aggregate sample 24 in the surface dry state using the apparatus shown in FIG. 1 will be described. First, the phase delay at both ends of the propagation path including the empty container 12 is measured (Step 1 in FIG. 3). Then, in the same manner as in steps 2 to 4 of FIG. 2A, the phase lag is measured at at least two known water contents in a wet state (a state where the water content is higher than the surface-dry state). The phase lag is measured with at least one known moisture content (in a condition where the moisture content is between the absolutely dry state and the surface dry state) (steps 2, 3, and 4 in FIG. 3). When the measurement is completed in the wet state and the air-dry state (Step 5 in FIG. 3), a graph of the water content versus the phase lag characteristic is created from these measured values (Step 6 in FIG. 3). Here, in the wet state, there are at least two measured values, and a straight line connecting the two measured values is uniquely determined. Then, in the air-dry state, even if the moisture content changes, the phase lag is substantially constant, so that a straight line is uniquely determined from one measured value.
[0017]
The graph created in this manner is a polygonal line composed of two straight lines, and the refraction point is in a surface-dry state. Therefore, the moisture content in the surface-dry state can be easily obtained from the refraction point of the polygonal line (Step 7 in FIG. 3).
[0018]
In the above-described embodiment, the description has been made such that a graph of the water content versus the phase lag characteristic is created with the measured values obtained from the fine aggregate sample 24 having a known water content. However, the present invention is not limited to this. The value may be stored as data in a computer or the like, and the water content may be appropriately calculated from the value of the phase lag measured from the fine aggregate sample 24 having an unknown water content without actually creating a graph. .
[0019]
【The invention's effect】
The method for measuring the moisture content of fine aggregate for concrete according to the present invention has the following special effects.
[0020]
In the method for measuring the water content of fine aggregate for concrete according to claim 1, the weight is placed on the fine aggregate sample and vibration is applied to the fine aggregate sample so that the fine aggregate sample has a high filling rate and uniformity in the container. Accordingly, the change in the phase lag becomes large with respect to the change in the water content, and the water content can be measured with high accuracy.
[0021]
In the method for measuring the water content of fine aggregate for concrete according to the second aspect, the water content in a surface-dry state can be easily and accurately measured. According to the method of the present invention, the measurement of the water content is not affected by the shape of the fine aggregate and the like.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an example of an apparatus used in the method for measuring the moisture content of fine aggregate for concrete according to the present invention.
FIG. 2 is a flowchart for explaining the operation of obtaining the water content of an embodiment of the method for measuring the water content of fine aggregate for concrete according to the present invention using the apparatus shown in FIG. 1; It is a flowchart which produces the graph of a delay characteristic, and (b) is a flowchart which calculates | requires the unknown moisture content of a fine aggregate sample.
FIG. 3 is a flowchart illustrating an operation of obtaining a moisture content in a surface-dry state of another embodiment of the method for measuring the moisture content of fine aggregate for concrete using the apparatus shown in FIG. 1;
FIG. 4 is a graph showing that a filling factor and a phase delay change depending on the weight of a weight.
FIG. 5 is a graph showing water content versus phase lag characteristics.
[Explanation of symbols]
REFERENCE SIGNS LIST 10 waveguide 12 container 14 isolator 16 microwave oscillator 18 probe 20 phase meter 20 a phase delay detector 20 b memory 20 c calculator 20 d display 22 vibrator 24 fine aggregate sample 26 weight

Claims (2)

The microwave is transmitted through an empty container made of a dielectric material and having an open top, the phase delay due to the propagation path of the microwave including the empty container is corrected, the display of the phase meter is adjusted to zero, and the The container is filled with a fine aggregate sample, a weight is placed thereon, and the container is vibrated by a vibrator to make the fine aggregate sample a predetermined filling rate, and the container is further removed except for the weight. And the microwave is transmitted through the fine aggregate sample, the phase lag of the microwave is measured by the phase meter, and the water content versus phase lag characteristic data actually measured by a known fine aggregate sample of the water content in advance. A method for measuring the water content of the fine aggregate for concrete, wherein the water content of the fine aggregate sample is obtained from the measured phase lag. The microwave is transmitted through an empty container made of a dielectric material and having an open top, the phase delay due to the propagation path of the microwave including the empty container is corrected, the display of the phase meter is adjusted to zero, and the The container is filled with a fine aggregate sample having a known moisture content in a wet state, a weight is placed thereon, and the container is vibrated by a vibrator to make the fine aggregate sample have a predetermined filling rate, and Except for the weight, the microwave is transmitted through the container and the fine aggregate sample, and the phase lag of the microwave is measured by the phase meter. The phase lag is measured with a known moisture content and a known moisture content in an air-dried state, and a line connecting the two measured values in the wet state in the moisture content-phase lag characteristic graph is a measurement in the air-dried state. The moisture content at the point where the phase delay of the value Moisture content measuring method fine aggregate for concrete, which was characterized by measuring the water content in the state.

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