JP4436730B2 - Test method for estimating unit water content of concrete and test apparatus used in the method - Google Patents

Description

  The present invention relates to a unit water amount estimation test method for concrete, and is used in the test method and method for estimating the unit water amount of concrete easily in a short time by measuring the concentration of the collected suspension. It relates to a test apparatus.

  The change in unit water volume of fresh concrete has a large effect on the quality and durability of the finished concrete structure, such as strength. Confirmation of whether or not is secured has been regarded as important.

  Currently, various unit water amount measuring methods (apparatuses) have been put into practical use (Non-patent Document 1). Among the methods for measuring the unit water amount disclosed in Non-Patent Document 1, the air meter method (Non-Patent Document 2), the microwave method, and the capacitance method are known as relatively popular methods.

  In the air meter method disclosed in Non-Patent Document 2, by utilizing the relationship between the change in the unit volume mass of concrete and the change in the air volume due to the change in the unit water volume, the air volume and the unit volume mass are measured with high accuracy, A method for obtaining a unit water amount is disclosed. The microwave oven method is a method of estimating the unit water amount from the amount of evaporated water of a target sample by heat drying, and uses a microwave oven (high frequency heating device) as the heat drying means. The capacitance method is a method for obtaining an estimated unit water amount by utilizing the fact that the capacitance of a mortar obtained by wet screening varies depending on the amount of water.

Katahira Hiroshi, “Unit Water Volume of Fresh Concrete”, Concrete Engineering, published by Japan Concrete Institute, 2001.5. Vol. 39, p. 65-67 Nakamura Hiroyuki et al., “Inspecting unit water volume from measurement results of unit volume mass-Demonstration test with high-precision air meter”, published by Cement and Concrete, Cement Association, 2002.2. No. 659, p. 44-48

  By the way, it is known that each of the above-described measurement methods has a problem in any of the requirements of quickness, simplicity, and accuracy. Since the air meter method disclosed in Non-Patent Document 2 depends on the measurement accuracy of the air meter to be used, the unit water volume measurement accuracy requires a high-precision air meter, and it is necessary to obtain the aggregate density correctly in advance. Necessary for ensuring accuracy. It is known that even if the aggregate density is the same, the aggregate density varies slightly depending on the storage position in the stockyard. For this reason, it is cumbersome to perform a density test according to the state, and a problem is likely to occur in data consistency.

  In addition, since the microwave oven method generally uses wet-screened mortar as a sample, the composition of the mortar in the composition to be placed may not match the composition of the mortar after the wet screening in addition to the labor of the wet screening work. There is. In addition, the amount of water in the fine aggregate and the initial hydration amount of the cement must be determined in advance by testing. Furthermore, in the capacitance method, wet screening mortar is used, and in calculating the unit water amount, the unit amount (water, cement, fine aggregate, coarse aggregate) and surface dry density (cement, fine aggregate, coarse aggregate) are calculated in advance. Measurement items such as (aggregate), water absorption rate (each aggregate), sample mass, air volume, etc. are required, and the measurement is complicated.

  Furthermore, it has been pointed out that each measurement method described above still has many error factors. Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, and by adding a predetermined amount of water to the concrete and measuring the concentration of the suspension obtained by stirring, Another object of the present invention is to provide a test apparatus that can be used for the same method as the test method that can easily estimate the unit water amount of concrete.

  In order to achieve the above object, the present invention immediately after a concrete volume of a certain volume and the first dilution water are put into a stirring vessel, and the concrete sample and the dilution water are mixed and stirred by the stirring vessel. And collecting the first suspension in which the binder, the fine particles of the aggregate and the water contained in the concrete sample are uniformly suspended, and measuring the concentration of the first suspension. Subsequently, the second diluent is added to the stirring vessel, and the concentration of the second suspension obtained immediately after the same mixing and stirring is measured, and at least the first suspension and the first suspension are measured. Based on the concentration of the suspension of 2, the amount of the concrete sample is calculated from the relationship between the first dilution water, the second dilution water, and the volume of the concrete sample. Estimating the unit water volume of the concrete that is the basis of To.

  A device for use in the estimation test described above, which can penetrate the rotary drive source installed on the base set at a predetermined tilt angle and the rotary shaft of the rotary drive source while maintaining watertightness. And an outer peripheral surface through which the binder, aggregate fines and water contained in the concrete sample can be permeated when a concrete sample is accommodated in the outer container. An internal container that can rotate in the external container by a rotational driving force transmitted by a rotary shaft that penetrates the bottom surface of the external container, and a stirring means that can stir the suspension stored in the external container; The suspension is circulated through the inner container, and the suspension is provided with a suspension circulation means having a liquid inlet / outlet capable of collecting the suspension in the path or capable of being hydrated in the inner container. .

  Further, in this estimation test method, the unit water amount of the concrete sample obtained by repeatedly performing the dilution water for diluting the concrete sample from the second dilution water to the higher-order dilution water is averaged, and the concrete It is preferable to determine the unit water amount of the sample.

  According to the present invention, regardless of the type of concrete, the type of aggregate used, and the composition, the amount of unit water in fresh concrete can be measured quickly and accurately with a simple device, for example, at the site. Play.

  Hereinafter, as the best mode for carrying out the concrete unit water amount estimation test method of the present invention, the following examples will be described with reference to the accompanying drawings.

Hereinafter, as Example 1, the measurement principle of the unit water amount of the present invention and the configuration of the test apparatus used for measuring the concentration of the suspension will be described.
[Measurement principle of unit water volume]
(Sample collection, concentration measurement)
The measurement principle of the unit water amount in the concrete unit water amount estimation test method of the present invention will be described with reference to FIG.

  A predetermined volume of fresh concrete sample obtained through a predetermined kneading step and a primary dilution water (hereinafter referred to as primary water) are put into a predetermined watertight container. A stirring operation is applied so that the concrete sample accommodated in a state where the watertight container is covered and the primary water are completely mixed. In general, the concrete material and the primary water are mixed by continuously shaking the watertight container or applying sufficient vertical vibration. Immediately after this agitation operation, coarse aggregate settles on the bottom of the container, and a suspension of uniform concentration in which water, cement, admixture and aggregate fine particles are sufficiently mixed on the top. A liquid is obtained. Since the suspension of the fine particles settles with time, a predetermined amount of the suspension (primary sample) is collected immediately after the stirring operation. And the mass of the solid content of this primary sample is measured by the measuring method mentioned later, and suspension concentration is measured.

  Thereafter, a predetermined amount of secondary dilution water (secondary water) is added to the watertight container after the primary sample is collected, and the same stirring operation as described above is performed, and the suspension immediately after stirring (secondary sample) Are collected again by the same method, and the concentration of the secondary sample is measured in the same manner.

  In the concentration measurement, it is important in terms of measurement efficiency that the sample container containing the suspension is heated, the sample is completely dried by heating, and the sample container in a high temperature state is efficiently cooled. In the present embodiment, a hermetically sealed stainless steel cylindrical container having a small hole for venting is formed in the center as the sample container, and heated by a heating device to completely evaporate the moisture in the sample. In this embodiment, a gas heater is used, but normal heating means such as an electric heater can be used.

  Immediately after the heating, the sample container itself is accommodated in the cooling apparatus, and the sample container is cooled so that the completely dry state of the sample is maintained. In the present embodiment, the cooler is equipped with an exhaust heat fan, and the stored sample container is cooled in a short time by the operation of the exhaust heat fan. At this time, it is preferable that the cooler is filled with a desiccant such as silica gel so that the sample in the cooler does not absorb moisture in the air. Mass measurement of the sample (solid content) obtained through the heating and cooling steps described above is performed by a known measuring means. This series of measurement steps can be performed in about 15 minutes.

(Calculation of unit water volume)
By using the mass value of the solid content in the suspension obtained from the above-mentioned primary sample and secondary sample, the unit water amount of fresh concrete at the time of kneading can be calculated by a series of the following equations. The calculation of the unit water amount is based on the mixing of cement and water in the suspension in the sample containing concrete mixed water and the primary water and secondary water added for the test. This is based on the assumption that the amount of fine particles of aggregates such as binders and aggregates is included.

The first and second suspension concentration measurement values m ₁ (%) and m ₂ (%) can be expressed by (Expression 1) and (Expression 2), respectively.

m ₁ (%) = (b + p) / (w + w ₁ ) × 100 (Formula 1)

m ₂ (%) = (b + p) / (w + w ₁ + w ₂ ) × 100 (Expression 2)
Where, b: the mass of the binder in the concrete sample (kg), p: the mass of the fine particles in the fine aggregate suspended in the suspension and the mass of the solids attached to the coarse aggregate (kg), w: amount of water in concrete sample (kg), w ₁ , w ₂ : primary water, secondary water added water amount

When b + p is eliminated from (Expression 1) and (Expression 2), an expression (Expression 3) for obtaining the amount of water (w) in the sample is derived. Thus, the unit amount of water of the concrete 1 m ³ can be obtained from (Equation 4).

w = {w ₁ × (m ₁ −m ₂ ) −w ₂ × m ₂ } / (m ₂ −m ₁ )
... (Formula 3)

At this time, the unit water volume W (kg / m ³ ) per 1 m ^{3 of} concrete is
W = w / v × 1000 (Formula 4)
Where v: volume of the concrete sample (l)

  As is clear from the above development, the unit water amount of the concrete obtained at this time is characterized by not depending on the type and composition of the material used for the concrete. Moreover, since a calibration curve and a correction coefficient for estimating the unit water amount are unnecessary, there is an advantage that the unit water amount can be measured even in concrete whose composition and material type are unknown.

  In addition, when water is added to the primary water and the secondary water, the primary water is added so that the suspension concentration is about 60% when the primary water is added, and the suspension concentration is 50% when the secondary water is added. It is preferable to determine the amount of secondary water added. In addition, after the test is completed, the aggregate remaining in the inner container is washed and analyzed, so that the difference from the composition of the mortar content in the sampled concrete sample can be known, and the measurement accuracy of the unit water volume can be further improved. Can do.

[Unit water quantity estimation test equipment]

The above-mentioned concrete unit water amount estimation test can be performed efficiently, the suspension as the primary sample and secondary sample is automatically collected, the mass of the solid content at that time can be easily known, and the above calculation The configuration of a concrete unit water quantity estimation test apparatus (hereinafter simply referred to as a test apparatus) that can accurately estimate the unit water quantity of the target concrete by the method will be described.
As shown in FIG. 1, the test apparatus of the present embodiment is supported by a leg 3 whose front end can be adjusted to a predetermined height, and is installed on the fixed floor 2. A cylindrical outer container 10 fixedly supported on the apparatus base 4 installed at an inclination angle, and a wire mesh 22 having a predetermined mesh size is attached to an open window 21 which is accommodated in the outer container 10 and formed on the outer peripheral side surface. , And supported by a hollow drive shaft 11 formed in the lower half lid 12 of the outer container 10 and a rotary drive shaft 11 extending through the bottom central hole (not shown) of the outer container 10 and extending into the outer container 10. In this state, the inner container 20 that can be rotated in the outer container 10 by the rotation drive shaft 11 and the rotating shaft 13 protrude from the bottom surface of the outer container 10, and the suspension stirring is performed with the stirring blade 14 attached to the tip of the rotating shaft 13. Is attached to the bottom surface of the outer container 10 in the same manner as the device 15, A suspension inlet (not shown) is provided in the vicinity of the turbid liquid stirring device 15, and the suspension sucked from the inlet passes through the hollow bearing 16 formed in the lower half lid 12 of the outer container 10. A circulation pump 17 that circulates in the inner container 20 through a circulation pipe 30 that is piped to extend, and a drive motor 5 that extends in the outer container 10 and rotates the inner container 20. Consisting of

  The inclination angle of the apparatus base 4 affects the stirring efficiency of the concrete sample in the inner container 20. For example, as shown in FIG. 2, when the angle between the apparatus base 4 and the fixed bed 2 is set to about 30 °, it is confirmed that there is no adhesion of cement particles or moisture unevenness of the concrete sample in the inner container 20. Has been. If this angle is less than 25 °, there is a risk of liquid leakage of the suspension, and if it is greater than 35 °, the concrete in the inner container 20 cannot be sufficiently stirred, and aggregate cement particles are deposited on the inner surface of the container. There is a tendency for the concentration of the suspension to decrease due to the attached state.

  In this embodiment, the outer container 10 is made of a metal cylindrical container having a diameter of 220 mm and a height of 180 mm, is fixed on the apparatus base 4, and is located at the center of the bottom at the end of the rotary drive shaft 11 of the drive motor 5. Is fixed through the seal bearing 19. On the other hand, a lower half lid 12 is detachably provided on the upper opening side so as to cover the lower half of the circular cross section. The lower half lid 12 is kept liquid-tight so that the concrete and suspension stored in the inner container 20 and the outer container 10 do not overflow or leak out of the container. Further, a hollow bearing 16 is formed on the central axis of the outer container 10 of the lower half lid 12, and cooperates with a bearing 25 provided at the central position of the cross section of the inner lid 24 of the inner container 20 on one side of the inner container 20. It functions as a rotation support shaft.

  In this embodiment, the inner container 20 is formed of a metal cylindrical container having a diameter of 210 mm and a height of 140 mm. As described above, the bottom side is provided by the rotary drive shaft 11 and the opening side is provided by the bearing provided on the inner lid. It is coaxial with the outer container 10 and is housed in the outer container 10 so as to be rotatable with a predetermined clearance around it. As shown in FIG. 2, opening windows 21 having predetermined dimensions are formed at predetermined intervals in the circumferential direction on the outer peripheral surface of the inner container 20, and each opening window 21 is covered with a wire mesh 22. . In this embodiment, the mesh of the wire mesh 22 is set to 150 μm, but the aggregate of the concrete sample is stored in the inner container 20, and the binder and the fine particles of the aggregate freely pass through the wire mesh 22 during the stirring. What is necessary is just to set it as the possible scale size. Further, the wire mesh 22 may have a wire diameter that can maintain rigidity sufficient to prevent deformation due to the collision of the aggregate when the concrete sample is stirred. The inner container 20 may be a bowl-shaped body in which a metal mesh 22 is stretched on a cylindrical frame as long as sufficient rigidity is secured during rotation.

  As shown in FIG. 2, the inner container 20 is rotated by a rotary drive shaft 11 that passes through a seal bearing 19 provided at the bottom of the outer container 10 and is connected to the bottom of the inner container 20. The rotary drive shaft 11 and the bearing 25 are made of a member having a rigidity that does not cause shaft shake even when the weight of the stored concrete sample is applied when the inner container 20 is in an inclined state. Further, the rotational speed can be switched to a predetermined rotational speed by a gear box 6 connected to the drive motor 5.

  In addition, a space 18 having a predetermined height is formed between the bottom of the outer container 10 and the bottom of the inner container 20, and as described later, the suspension that accumulates in the space 18 in a state where both containers are inclined. A stirring blade 14 serving as a suspension stirring device for stirring is provided from the device base 4 of the outer container 10. On the other hand, a suspension inlet (not shown) is provided in the vicinity of the stirring blade 14 so that the suspension can be sucked into the circulation pump 17 installed outside the container.

  As the circulation pump 17, a known electric pump having a performance capable of sucking a liquid material having a predetermined viscosity including a solid content such as a suspension and discharging the liquid at a predetermined pressure without clogging is used. In this embodiment, the circulation pump 17 is provided with a circulation pipe 30 that sucks the suspension in the outer container 10 and sends it again into the container from the upper opening side of the inner container 20. The suspension is circulated through the circulation pump 17 and the circulation pipe 30. A three-way valve 31 is provided at an intermediate position of the circulation pipe 30, and by switching the path of the three-way valve 31, a part of the circulating suspension is collected in an external sample container, or secondary water described later. Water can be supplied into the circulation pipe 30.

Here, the function of the apparatus described above will be briefly described with reference to FIG.
When a concrete sample in a predetermined kneaded state and primary water for dilution are put into the internal container 20 of the test apparatus 1 installed at a predetermined inclination, the concrete sample is accumulated in the internal container 20 and the primary water is It passes through the wire mesh 22 and accumulates in the outer container 10. In this state, the inner container 20 is rotated by the drive motor 5 to stir the internal concrete sample. The stirring and the centrifugal force accompanying the rotation of the inner container 20 act on the concrete, and fine particles such as cement and additives are dispersed and pass through the wire mesh 22 and are collected in the outer container 10 where the primary water is accumulated. In this state, the primary water accumulated in the outer container 10 and the components passing through the wire mesh 22 are stirred at high speed with the stirring blade provided at the bottom of the outer container 10. Further, the suspension is circulated into the inner container 20 via the circulation pump 17 and the circulation pipe 30 so that the concentration of the suspension in the inner container 20 does not decrease due to the action of the centrifugal force accompanying the rotation of the inner container 20. Is done.

  The drive motor 5 can be controlled to a predetermined rotation speed by a transmission of the gear box 6 connected to the rotation drive shaft 11, but in this embodiment, the rotation speed is set to 30 rpm. If the rotational speed is too fast, the concrete material sticks to the inner peripheral surface of the inner container 20 and the wire mesh 22 due to centrifugal force, and sufficient stirring cannot be achieved, and a suspension with a uniform concentration cannot be obtained. On the other hand, if the rotation speed is too slow, it takes time to disperse and suspend fine particles such as cement.

  In the present embodiment shown in FIG. 2, a dilution water supply device capable of adding secondary water or higher-order dilution water to one path of a three-way valve 31 provided in a part of the circulation pipe 30. 35, a primary sample, a secondary sample are collected, and a suspension concentration measuring device 36 capable of measuring the suspension concentration of the collected sample automatically or manually is provided to be switchable. It is shown.

(Suspension concentration measuring device)
It is easy to measure the concentration of the suspension by the heating process, the heat dissipation process and the mass measurement of the solid content as described above. However, when the automation of the apparatus is taken into consideration, as shown in FIG. 2, a circulating water pipe and a concentration measuring apparatus such as microwaves, lasers, ultrasonic waves, and near infrared rays, which are known automatic measuring apparatuses, are connected to the circulation pipe. It is preferable to equip it on the path | route or the side switched by the three-way valve. Thereby, primary water, secondary water, or higher-order diluted water can be automatically weighed and added, or the concentration of the suspension immediately after stirring can be continuously measured in real time. In the measurement apparatus such as the above-described microwave, laser, ultrasonic wave, near infrared ray, etc., it is preferable to perform measurement using a calibration curve corresponding to the measurement object as necessary.

  The time required for the test is 15 minutes for the concentration measurement in the measurement using the heating and cooling apparatus after adding and stirring (5 minutes each) for the primary water and secondary water, and the test time is about 25 minutes. However, by using an automated device for concentration measurement, hydration, etc., the measurement time can be greatly shortened even if higher-order hydration of tertiary water or higher is performed.

  Hereinafter, as Example 2, the procedure of the experiment using the above-described test apparatus 1 and the result thereof will be described with reference to FIGS.

[Materials used for concrete samples]
The materials used for the concrete samples are as follows.
1) Cement: Ordinary Portland cement (JIS R 5210)
Density 3.16g / cm ³ , specific surface area 3,310cm ² / g
2) Coarse aggregate: Crushed stone from Taku (density 2.7g / cm ³ , water absorption 1.4%)
3) Fine aggregate: Chikugogawa river sand (density 2.56g / cm ³ , water absorption 2.5%)
4) AE water reducing agent; modified lignin sulfonic acid compound, polycarboxylic acid ether complex (trade name: Pozzolith 78H)
5) AE agent: alkylallyl sulfonic acid compound anionic surfactant
(Product name: Micro Air 303A)
6) Water; tap water

[Concrete mix]
Using the above-mentioned materials, an experiment was conducted using four types of concrete samples (weighed with 1 batch volume of 1 kneaded after kneading) based on the recipe shown in Table-1.

[Experiment / Measurement Procedure]
First, as shown in FIGS. 3A to 3B, with the apparatus base 4 of the test apparatus 1 set at an inclination angle of 30 °, the lower half lid 12 of the outer container 10 is attached, and the above-mentioned concrete sample is attached. The primary water is added at the same time. The amount of primary water W ₁ added at this time is determined so that the suspension concentration is about 60%. In this state, the inner container 20 is rotated at 30 rpm for 5 minutes, and at the same time, the stirring blade at the bottom of the outer container 10 is rotated at high speed to make the suspension concentration uniform. Further, the suspension M is circulated to the inner container 20 through the circulation pipe 30 by the operation of the circulation pump 17 to promote the suspension of the fine particles in the concrete sample C. After the elapse of a predetermined stirring time (5 minutes in this embodiment), a suspension as the primary sample M ₁ is collected from the three-way valve 31 provided in the circulation pipe 30 (FIG. 3 (c)). In this embodiment, the mass of the sample to be collected is 10 to 20 g, but it is preferable to collect an appropriate amount according to the suspension concentration measuring means. In the present Example, the mass measurement was performed in each step by the procedure such as the heating and cooling method described above, and the concentration measurement was performed.

Then, from the state taken primary samples M _1, subsequently, hydro secondary water W ₂ through the inlet of the three-way valve 31 as shown in FIG. 4 (d). At the time of secondary water addition, the addition amount of the secondary water W ₂ is determined so that the concentration of the suspension M becomes 50%. Then, after rotating the inner container 20 under the same conditions as when collecting the primary sample M ₁ , stirring the suspension, and refluxing, the suspension as the secondary sample M ₂ is collected (FIG. 4 (e)). ) Determine the suspension concentration by the same measurement method.

  Thereafter, the estimated unit water amount of the concrete is obtained based on the above calculation formula (Formula 4). FIG. 5 shows a correlation with the calculated unit water amount estimated value with the unit water amount in the same composition as the vertical axis. As shown in the figure, according to the concrete unit water amount estimation test according to the present invention, it was confirmed that the unit water amount of the target fresh concrete can be estimated with high correlation.

  In the above description, the estimated value calculation by the primary sample and the secondary sample has been described as an example. However, the combined use of the automatic hydration device and the automatic concentration measurement device for the suspension allows higher order higher than tertiary water. It is also possible to measure the concentration of a higher-order suspension of the third sample or higher due to water. As a result, it is possible to improve the accuracy of measurement values by averaging multiple data.

Schematic explanatory drawing explaining the measurement principle of the estimation test of concrete unit water quantity. The apparatus block diagram which showed one Example of the concrete unit water quantity estimation test apparatus of this invention. FIG. 3 is a flow chart showing a unit water amount estimation test procedure using the test apparatus shown in FIG. 2 (part 1). FIG. 3 is a flowchart (part 2) showing a unit water amount estimation test procedure using the test apparatus shown in FIG. The graph which showed the experimental result of the concrete unit water quantity estimation test by a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Unit water quantity estimation test apparatus 4 Fixed base 5 Drive motor 10 External container 11 Rotation drive shaft 14 Stirrer blade 15 Suspension stirrer 17 Circulation pump 20 Inner container 21 Open window 22 Wire mesh 30 Circulation pipe 31 Three-way valve

Claims (3)

  A concrete sample and a first diluted water are poured into a stirring vessel, and a bond contained in the concrete sample is obtained immediately after mixing and stirring the concrete sample and the diluted water by the stirring vessel. The first suspension in which the fine particles of aggregate, aggregate and water are uniformly suspended is collected, the concentration of the first suspension is measured, and then the second suspension is placed in the stirring vessel. The concentration of the second suspension obtained immediately after adding the diluted solution and carrying out the same mixing and stirring is measured. Based on the concentration of at least the first suspension and the second suspension, From the relationship between the first dilution water, the second dilution water, and the volume of the concrete sample, the water amount of the concrete sample is calculated to estimate the unit water amount of the concrete that is the basis of the concrete sample. For estimating the unit water volume of concrete, Method.   A rotational drive source installed on a base set at a predetermined inclination, an external container capable of penetrating the rotational shaft of the rotational drive source while maintaining watertightness, and housed in the external container; When a concrete sample is housed inside, an outer peripheral surface is formed through which the binder, fine particles of aggregate, and water contained in the concrete sample can be transmitted, and is transmitted by a rotating shaft that penetrates the bottom surface of the outer container. An internal container that can be rotated in the external container, a stirring means that can stir the suspension stored in the external container, and the suspension is circulated through the internal container, A concrete unit water quantity estimation test apparatus for use in the estimation test method according to claim 1, further comprising a suspension circulation means having a liquid inlet / outlet capable of collecting the suspension in the path or capable of adding water in the internal container.   The estimation test method according to claim 1, wherein the unit water amount of the concrete sample obtained by repeating dilution water for diluting the concrete sample up to dilution water of higher order than the second dilution water is averaged, A unit water quantity estimation test method for concrete, characterized in that the unit water quantity of a concrete sample is obtained.

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