JPH0521184B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the invention of a method and device for measuring the moisture content of fine aggregate, which is an indispensable material when mixed with hydraulic material powder such as cement or gypsum to prepare a kneaded material such as mortar or concrete. The present invention relates to a method for accurately measuring the moisture content of fine aggregate such as sand within a short period of time in order to determine a reasonable amount of water for mixing and kneading the fine aggregate. Adding and mixing fine aggregate (and coarse aggregate, fiber materials, and other auxiliaries or additives) and mixed water to hydraulic substance powder such as cement to prepare a ready-mixed material such as mortar or concrete. Although this has been widely practiced in the past, it is inevitable that there will be some variation in the quality characteristics of the green kneaded material prepared in this way or the various products obtained by molding and hardening the green kneaded material. As is well known. In particular, when using the shell kneading (divided kneading) method developed by the present inventors, the primary water amount (or the subsequent
It is necessary to accurately determine the amount of water used, and how it is determined will greatly affect the quality characteristics. This is due to the fact that the amount of water adsorbed to or attached to the fine aggregate cannot be accurately determined as described above, and in fact, the amount of water adsorbed to or attached to the sand piled outdoors varies widely. It is clear from a practical point of view that when sand with different amounts of water is used, the above-mentioned quality or characteristics inevitably vary greatly. By the way, regarding such fine aggregate,
JISA1109 “Specific gravity and water absorption test method of fine aggregate”
In other words, a sample is filled in a specified flow cone using a specified method, placed upside down on a table, and when the flow cone is pulled up, the time when the fine aggregate slumps for the first time is defined as surface drying. Saturated surface-dry
condition), and the moisture contained in the fine aggregate in this state is that the voids inside the fine aggregate are filled with water (saturated), and the surface is dry with no water. When preparing such a green kneaded product, the water content obtained in the above test is used as the ineffective water content of the fine aggregate itself, and the water content of such fine aggregate does not play a role in the blending. The standard value is that which is excluded when determining the blended water. However, as a result of the inventors' study of fine aggregate in a surface dry state as specified by JIS,
We have reached the conclusion that it is unreasonable to consider water as ineffective as described above. That is, the present inventors used C sand, E sand, and crushed sand from Oigawa River, and mixed them with water using a vacuum mixer under a reduced pressure of 730 mmHg so as not to leave any air on the sand surface, and then mixed them with water to a predetermined moisture content. A sample was prepared, filled into an acrylic container in the specified precise state, placed on a flow test table, and compacted by moving up and down 15 times. After measuring the weight, the moisture content and voids were determined. rate (in absolute dry condition)
Figure 1 summarizes these measurement results and also shows the moisture content in the surface dry saturated state (hereinafter referred to as surface dry state) for these fine aggregates according to JIS regulations. be. According to Fig. 1 of the cover, in each of the fine aggregates mentioned above, changes in bulking (porosity) are clearly shown due to changes in moisture content even if the condition is below the above-mentioned surface dry state. In addition, results similar to this have been found in the influence of particle size due to changes in water absorption of fine aggregates separated into sections, or in centrifugal force tests. In the water state Q, it must be said that the aggregate surface still has a certain limit surface adsorption water rate (SWlim) bound by the aggregate. That is, the surface dry water saturation state Q is the sum of the internal water saturation rate Q ₀ and the intrinsic surface adsorption water (SWlim) Q = Q ₀ +
It is SWlim, and it should be confirmed that the true non-effective water is only the Q ₀ mentioned above, and this should be used as the standard value for the non-effective water. By the way, the surface dry saturated state Q as mentioned above,
In order to obtain the internal water saturation rate Q ₀ and the specific surface adsorbed water SWlim, it is basic to measure them and find at least the Q value. For example, even if such a state could be created by storing the fine aggregate in a closed container and holding it for a long time (for example, about one month), it would be difficult to maintain the condition for such a long time. The demand conditions for fine aggregate (sand), which requires a period of months to obtain one measured value, is consumed in large quantities in mass production, and inevitably has to be produced in many different types. It is not possible to obtain measurement results that match the actual conditions. In addition, the present inventors have confirmed that for the above-mentioned fine aggregates, there is something that should be called the maximum surface adsorption water rate SWmax, in addition to the above-mentioned SWlim, and it is hoped that these relationships will be clarified within a relatively short period of time. is important. The present invention was devised after repeated studies in view of the above circumstances, and for this purpose, appropriately moistened fine aggregate stored in a closed container is processed by a centrifugal force mechanism. However, as for the separated water, it should be separated from the fine aggregate and should be properly managed to prevent it from being adsorbed or attached to the fine aggregate again, regardless of whether it is subjected to centrifugal force or stopped. It should be kept as such. The details of the water separation test device for fine aggregate using centrifugal force, which was designed and used by the inventors to specifically realize this idea based on this concept, are shown in Figure 2. 10 cm height with acrylic plate 11 attached to one end of 5 mmφ PVC pipe 10
A second cylindrical body 1 with the same dimensions as the first cylindrical body and a height of 5 mm.
A wire mesh 12 made of a metal wire of 0.15 mm, a filter paper 13, and a perforated punched iron plate 14 of 1.6 mm in thickness are interposed between the first cylindrical body and the second cylindrical body. The cylindrical body 10 is filled with absorbent cotton 16 and placed facing each other as shown in FIG. 3, and is integrated and sealed by adhering vinyl tape 15 to the circumferential surface, and then a lid 21 is attached as shown in FIG. The shaft 2 is attached to the rotary plate 22 in the case 20, which is
A predetermined centrifugal force is applied by rotating the rotary plate 22 in this state, and a predetermined centrifugal force is applied to the first cylinder. Water separated and discharged from the body is absorbed by the absorbent cotton 16 of the second cylindrical body, and the water absorbed by the absorbent cotton 16 is prevented from flowing back when the rotary plate 22 stops rotating for testing. It is. Note that sealing the pipe bodies 10, 10 with vinyl tape 15 as described above is useful for determining the critical surface adsorption water rate SWlim and the internal water saturation rate Q ₀ in the surface dry saturated state as described above in the present invention. This is important, and when a centrifugal force is applied to a container filled with a test material with a lid, the air inside the container is released to the outside under the conditions of centrifugal force. is reduced in pressure and the conversion flow of air between the inside and outside of the container is repeated, and moisture is also diffused and discharged due to this conversion flow of air between the outside and outside of the container. This also results in increased moisture dissipation. It is necessary to appropriately prevent the vaporization and discharge of moisture associated with such air flow conversion and apply centrifugal force to obtain measurement results, and for this reason, the formation of the sealed state is important. However, as an example, E sand from Oigawa (FM = 3.23, porosity ε = 33.8%) was obtained using the above-mentioned device.
The Q value measured according to JISA1109 above is
The amount of water landing on this item is 1.39%.
Once dried at a temperature of 110℃ for 24 hours, its weight was measured, and then -730mm
In a Hg vacuum mixer, various samples with varying degrees of pressure ranging from 1Q to 10Q are prepared, and a centrifugal force of 453g (g is gravitational acceleration) is applied to these samples for 120 minutes to separate water. The results are summarized and shown in FIG. 5, with the horizontal axis (processing time) plotted on a logarithmic scale. That is, according to the results shown in Fig. 5, the water content of samples with a water content of 4Q or less decreases in an orderly manner in proportion to the centrifugal force action time, and the water content of samples with a moisture content of 1Q hardly decreases. On the other hand, in the case of water content higher than 4Q, the water content decreases rapidly within the first 5 minutes, but then it decreases slowly, and at least after 5 minutes, there is almost no difference between the moisture content and the water content of water content lower than 4Q. It shows no moisture content decreasing behavior. In other words, there is an inflection point on this horizontal logarithmic graph, which is recognized as the maximum surface adsorption water rate SWmax, and the water attached above this inflection point, which is the maximum surface adsorption water rate, is relatively easily separated. On the other hand, if it is less than that, it can be said that the separation becomes more relaxed. Incidentally, this phenomenon is observed in almost the same way in all other types of sand, even if the specific numerical values are different. So, porosity ε=33.0%
The Q value of Sagami River sand according to JISA1109 is 3.12%.
Although this is considerably higher than the case in Figure 5,
The same test and measurement results for this product are summarized in FIG. 6. In other words, in the case of this Sagami River sand, the fifth
In the same horizontal axis logarithmic graph as shown in the figure, the moisture content decreases almost linearly up to 3Q, but above 4Q, a clear inflection is observed at the position of 5 minutes of centrifugal force action, and in this case, around 3Q. Said
It is recognized that SWmax exists. In addition, each of the above-mentioned fine aggregates and other representative 5
Figure 7 shows the results of a similar centrifugal force separation test on seed fine aggregates whose initial moisture content was adjusted to around 1Q, with some fluctuations observed. However, it was confirmed that all fine aggregates remained almost unchanged regardless of the length of the separation treatment time, and from this result, it can be said that the test results according to JISA1109 are stable in terms of moisture content. In addition, in the above-mentioned test measurements, it is important to add attached water under reduced pressure conditions as mentioned above after measuring the absolute dry weight. If the pressure is reduced to -730 mmHg, the air adhering to the surface of the fine aggregate can be effectively removed, and if water is added and mixed in this state, the added water will damage the structure of the fine aggregate. The water is effectively permeated into the inside, and the attached moisture becomes stable and constant. On the other hand, if the mixture is simply mixed with water in the atmosphere, there is a high possibility that the adhering water will be unevenly distributed on the surface of the fine aggregate, and therefore it will be unstable and the measurement results will fluctuate. For example, the results of the same centrifugal separation treatment of the Oigawa E sand, which was kept in an absolutely dry state and mixed with water under the reduced pressure conditions in a vacuum mixer, and with water added in the air, are shown in Figure 8. However, even if the treatment time is the same, the measurement results will vary, and those mixed with water in the atmosphere have a low moisture content and have considerable variation. Those using reduced pressure conditions are almost stable with almost no fluctuation even in the repeated test results, and similar results were obtained with any of the above-mentioned Sagami river sand, water slag sand, or standard sand. In order to obtain accurate measurement results, it is essential to add water and mix under reduced pressure conditions to obtain a specified Q value for substances that have been confirmed and kept in an absolutely dry state for purposes such as weight measurements. However, for items that have been immersed in water for a fairly long period of time, such as 24 hours, equally accurate results can be obtained by testing and measuring them as they are (after that, the weight is measured in an absolutely dry state). It is necessary to maintain a constant water encounter history in at least the fine aggregate. Furthermore, to explain the results of examining various types of fine aggregates for centrifugal force separation as described above, 11 types of fine aggregates shown in Table 1 below each contained moisture equivalent to 3Q. These fine aggregates were subjected to centrifugal separation treatment using the same gravitational acceleration of 453 g as described above.The results are also shown in the lower part of Table 1 in relation to the elapsed treatment time.

【table】

[Table] Figure 9 is a diagram that summarizes these results, and the value taken at the 0 minute position on the horizontal axis on the vertical axis is the value corresponding to 3Q for each fine aggregate. The moisture content of this material decreases with each treatment time, but Sagami River sand (×...
…x) and North American sand, there is a roughly parallel relationship in which the moisture content decreases due to treatment effects, and in all cases
After 120 minutes of treatment, the moisture content was approximately twice that of the surface dry saturated state Q, and the coarse particle ratio FM shown in Table 1 was reached.
It is recognized that it is hardly affected by the porosity or the porosity ε. However, Figure 10 shows the above results organized by the multiplier of Q, and it is clear that there is a linear correlation between the Q value and the processing time of 30 minutes. , 60 minutes and 120 minutes are arranged as shown in Figures 11 a to c. In other words, the slope of the linear relationship between the moisture content after centrifugal force and the Q value of the fine aggregate is 2.5 at 30 minutes, 2.3 at 60 minutes,
It is 2.0 at 120 minutes, which is approximately regular, and decreases as the processing time increases, but both are regular on the graph. However, if we consider the aforementioned Sagami River sand and sand from North America, which deviate to some extent from the straight line of Q = 2.5, 2.3, or 2.0 on the chart, the reason why values deviate from the standard line in this way is already explained. It is recognized that this is due to the Q ₀ (internal water saturation rate), and the relationship remains almost the same after centrifugation treatment for at least 30 minutes or more. Therefore, the time required for test measurements is shortened and is also preferable.
In order to obtain the SWmax or Q ₀ value, it is practical to set the time to 30 minutes in the case of separation treatment using centrifugal force as described above. According to the present invention, either or both of the limit surface adsorption water rate SWlin and the maximum surface adsorption water rate SWmax can be determined as described above, and the internal water saturation rate Q ₀ can be taken into consideration as appropriate. Expressing the relationship between them, the maximum surface adsorption water rate SWmax is the percentage of water adsorbed on the surface when the inside of the fine aggregate is saturated with water, and the limit surface adsorption water rate is It is a value obtained by multiplying the rate Swlim by an experimental coefficient A determined according to experimental conditions, and is expressed as the following equation. SWmax=A SWlim=A(Q-Q ₀ )......If SWg is the experimental value under certain conditions (for example, treating fine aggregate with 3Q of attached water at 730 mmHg for 30 minutes with a centrifugal force of 453 g), then This SWg is expressed as the following formula. SWg=A SWlim+Q ₀ ... Also, based on the relationship mentioned above, now A=2.5.
If Q ₀ ≒ 0, then SWlim=Q, and SWg is
2.5SWlim+0=2.5Q (SWmax=2.5Q),
Therefore, SWg/A=Q (SWg/2.5≈Q), and SWg in this case can be treated as SWmax. Furthermore, in cases where the internal water saturation rate Q ₀ cannot be ignored, such as the Sagami River sand and the North American sand in Figures 10 and 11 mentioned above, SWg/A≠0 and SWg/2.5≠Q, and the above formula From this, SWlim=Q−Q ₀ can be derived,
By substituting this into the above equation and rearranging it, the following equation is derived and the internal water saturation rate can be determined, and surface adsorption water relationships such as SWlim can also be determined. Q ₀ =AQ-SWg/A-1... According to the present invention as explained above, it is possible to measure and clarify the moisture content of this type of fine aggregate within a short time, thereby reducing surface dryness saturation. Not only the water state but also the internal water saturation rate Q ₀ and the specific surface adsorption water rate
Appropriately determine water percentages that have not been elucidated in conventional technology, such as SWlim and maximum surface adsorption water rate SWmax, and use this effectively to adjust mortar or concrete mixes as described above to find rational and optimal mixing conditions. It is an invention that has great industrial effects because it can accurately obtain the following.

[Brief explanation of the drawing]

The drawings show the technical content of the present invention, and Figure 1 is a chart showing the relationship between the surface dry saturated state and the porosity according to JIS regulations for various fine aggregates.
Fig. 2 is an explanatory diagram showing the disassembled state of the sealed container used in the method of the present invention in cross section and plan view, Fig. 3 is a sectional view of the assembled state, and Fig. 4 is a sectional view of the entire test device using this. , Figure 5 is a diagram summarizing the relationship between centrifugal force action time and water content when measurements are made according to the present invention on fine aggregates with various amounts of adhering water; Diagrams and charts showing the results of similar measurements on fine aggregates different from those shown in the figure.
Figure 7 is a graph showing similar centrifugal force separation test results for various fine aggregates whose initial moisture content was adjusted to around 1Q, and Figure 8 is a graph showing the results of a similar centrifugal force separation test for various fine aggregates with the initial moisture content adjusted to around 1Q. Diagrams and charts of the results of similar centrifugal force separation treatment for water-added materials, No. 9
The figure is a graph summarizing the results of centrifugal separation treatment of various fine aggregates, Figure 10 is a graph showing the results of the initial moisture content of Figure 9 organized by Q value magnification, and Figure 11 is Furthermore, the processing time for this is 30
This is a chart showing the results organized for minutes, 60 minutes, and 120 minutes. In these drawings, 10 is a synthetic resin pipe, 11 is an acrylic plate, 12 is a wire mesh, 13 is a filter paper, 14 is a perforated iron plate, 15 is an adhesive tape, and 16
20 is absorbent cotton, 20 is a case, 21 is a lid, 22 is a rotating plate, 23 is a rotating shaft, 24 is a receiver, and 25 is a shaft.

Claims (1)

[Scope of Claims] 1. Moisturized fine aggregate is placed in a closed container, centrifugal force is applied to the closed container for a predetermined period of time to separate water adhering to the fine aggregate, and moisture adhering to the fine aggregate is separated. 1. A method for measuring the moisture content of fine aggregate for blending hydraulic substances, characterized by measuring the moisture remaining attached to the fine aggregate after separation treatment, and determining the surface adsorbed water and internal water saturation rate of the fine aggregate. 2. A method for measuring the water content of fine aggregate according to claim 1, in which the water removed by centrifugal force separation is adsorbed onto an absorbent material so that it is not absorbed into the fine aggregate even during stoppage. . 3. A filter medium and a suitable support member are set in the middle part of a closed tubular container, and the middle part of the closed tubular container, which contains wet fine aggregate on one side and moisture absorbing material on the other side, is placed on a rotating plate. An apparatus for measuring moisture content of fine aggregate, which is rotatably supported on a shaft, and is configured to apply a centrifugal force to the fine aggregate in the sealed tubular container by rotation of the rotary plate.