JP4020837B2 - Method for measuring moisture content of fresh concrete - Google Patents

Description

  The present invention relates to a method for measuring the moisture content of fresh concrete.

The goal of constructing high-quality concrete structures in the development of social capital through public works is the company's philosophy and the starting point for the on-site construction management. In addition, since concrete structures are generally required to have a long life on the order of several tens of years to a hundred years, in order to ensure their strength and durability, quality control of the fresh concrete to be placed is also required. Requires strictness.
On the other hand, since the quality of fresh concrete is greatly influenced by the amount of moisture contained therein, the management of the amount of moisture is regarded as important in the production of fresh concrete. And generally the measurement using a slump test or a neutron beam is known as a method of managing the unit water quantity contained in the manufactured fresh concrete. Japanese Patent Application Laid-Open No. 7-52143 discloses a concrete moisture content measuring apparatus using neutron rays and gamma rays.
Japanese Patent Laid-Open No. 7-52143

  However, the slump test is to know the degree of resistance (fluidity) expressed by the amount of fresh concrete lump that is essentially frustoconical and deformed by gravity, and is not able to directly measure the unit water volume. Indirectly, the amount of unit water was estimated. And considering that factors other than the unit water amount are related to the slump test result, the measurement of the water amount using this test was inferior in estimation accuracy and reliability.

  In addition, at present, there is “JISA 1112: 1997 Washing analysis test method for fresh concrete” as an officially specified unit water amount measuring method. However, when it is carried out based on this method, it takes about 1 hour to determine the measurement result, and this method has been standardized with the analytical work in the laboratory in mind. It was unfamiliar as a test to be conducted.

  On the other hand, in the method using neutron beam, in order to measure the unit water amount of the manufactured fresh concrete, first, it was necessary to obtain in advance a lot of material property values such as aggregate density by a skillful test. . For this reason, there is a problem that it requires a skillful technique for preparation work before the measurement can be performed, and it takes time. In addition, these material property values include those that fluctuate greatly depending on the properties of the aggregate. In actual measurement, blending data for reflecting these material property values in the calculation of unit water volume is used for blending fresh concrete. There was a problem that required a complicated work of replacing every time. Moreover, if there is a change in the blending ratio, etc., it is necessary to replace the blending data each time, and considering the effort required to carry out such data replacement work, it is also preferable as a method to be carried out at the work site. There wasn't.

  The concrete moisture measuring device measures the unit water amount of fresh concrete sent out from a concrete pump car and pumped through a temporarily installed pipe to a placement site at a predetermined point in the middle of the pipe. is there. In this case, although it is suitable for fluctuation management of the unit water volume, it is difficult to eliminate the inappropriate portion from the placement site even if it is determined that the concrete is inappropriate using this measuring device. As a result, there is a fear that the quality of the concrete cannot be ensured sufficiently.

  Therefore, the present invention can easily measure the unit water amount of fresh concrete which is an important target of quality control, and the measurement result is highly reliable and prevents improper placement of fresh concrete. An object of the present invention is to provide a method for measuring the moisture content of fresh concrete.

In the method for measuring the moisture content of fresh concrete according to the present invention, first, a plurality of test fresh concretes having different blending ratios are prepared prior to the production of fresh concrete. On the other hand, a plurality of test concretes are prepared, and one of the plurality of test concretes having the most preferable properties is defined as a reference concrete at a predetermined work site, and is set in advance when the fresh concrete is prepared. The determined unit water amount is determined as the reference unit water amount in the reference concrete. On the other hand, the plurality of test fresh concretes are collected in a container, gamma rays and neutron rays are irradiated from the outside of the container, and the attenuation rate and neutron rays of the gamma rays that have passed through the container and the test fresh concrete are collected. Is measured separately for each of the plurality of test fresh concretes. And the correction coefficient in the calibration formula used for the calculation of unit water quantity is calculated | required by the calculation using the attenuation factor of this neutron beam and a gamma ray. When the fresh concrete is manufactured, a sample of the fresh concrete is collected in the container before placing. Subsequently, gamma rays and neutron rays are irradiated from the outside of the vessel, and the measured gamma ray attenuation rate and neutron ray attenuation rate that passed through the sample are applied to the calibration formula, and the unit water amount of the sample is calculated. calculate. Then, the unit water amount of the sample is regarded as the unit water amount of the fresh concrete which is used as a unit water amount for comparison with the reference unit water amount necessary for determining the suitability for placing the fresh concrete. In the present invention, the unit water amount is a value obtained by subtracting the water absorption amount from the total water amount.

  The capacity of the container may be 6-7 liters.

  When the container having the above capacity is adopted, the source of the gamma rays may be cesium 137.

  The unit water amount is measured within a predetermined range, the calibration formula is a linear function, and the attenuation rate of the neutron beam and gamma ray used to obtain the correction factor is measured separately for each of the plurality of test fresh concretes. It may be all that has been done.

  The unit water amount is measured within a predetermined range, the calibration formula is a linear function, and the attenuation rate of the neutron beam and gamma ray used to obtain the correction factor is measured separately for each of the plurality of test fresh concretes. Of these, those corresponding to the reference concrete may be used.

The predetermined range of the unit water amount may be 123 to 185 kg / m ³ .

An apparatus suitable for the moisture content measuring method according to the present invention has a container for storing a sample, and the container includes a neutron beam irradiation apparatus and a neutron beam calibration apparatus, and a gamma ray irradiation apparatus and a gamma ray calibration apparatus, respectively. It will be attached so as to face each other. Then, each of the neutron calibration apparatus and the gamma ray calibration device is connected to the calculating means, the capacity of the container is 6-7 liters source of the gamma ray irradiation apparatus if 137Cs, The water content measuring method according to the present invention can be carried out.

  According to the moisture content measuring method according to the present invention, the correction coefficient in the calibration formula used for the calculation of the unit water amount is applied to the test fresh concrete prepared in advance prior to the production of fresh concrete with neutrons and gamma rays. In addition, many of the material property values necessary for calculating the unit amount of water were determined by irradiating gamma rays to the fresh concrete to be measured. Therefore, the preparation work for actually measuring the fresh concrete is saved in labor, the time required for the preparation work is shortened, and the fresh concrete can be easily measured with high measurement accuracy. In addition, since the calculation of physical property values (surface water ratio) that fluctuate greatly depending on the properties of the aggregate is no longer necessary, there is no need to replace formulation data to reflect this physical property value in the calculation of unit water volume. Simplify on-site measurement. In particular, even if there is a change in the blending ratio or the like, additional work such as data exchange does not occur at the work site, and the target unit water amount can be measured very easily.

In addition, the correction factor is obtained using test fresh concrete corresponding to the reference concrete, which is the desired blending state of the fresh concrete to be measured, and the unit of fresh concrete is also calculated when calculating the correction factor. As in the case of measuring the amount of water, fresh concrete for testing is collected in a container , and the attenuation rate of neutrons and gamma rays is measured. Therefore, as long as the fresh concrete to be measured is blended in the same way as the reference concrete, the accuracy of the measured value will be high, and whether the fresh concrete is blended in the same way as the reference concrete will show high precision even by measuring the sample alone. Can be estimated. In addition, since the measurement is performed before placing, it is possible to prevent the placement of inappropriate fresh concrete by stopping the use of the fresh concrete according to the measurement result.

  Furthermore, by comparison with the reference concrete, it is possible to follow up when a property change is observed in the fresh concrete carried into the work site. For example, if the measured unit water amount is abnormal in the work site despite the proper blending, it is presumed that the properties of other aggregates other than moisture have changed.

  Furthermore, by setting the capacity of the container to 6 to 7 liters, it is possible to obtain sufficient measurement accuracy for determining that the workability is excellent and the unit water amount of the fresh concrete is appropriate.

  Furthermore, by using cesium 137 as a source of gamma rays, the amount of gamma rays radiated out of the apparatus is reduced compared to cobalt used as a normal source, and the safety of the operator can be improved. Moreover, sufficient gamma rays necessary for measurement can be obtained.

  Furthermore, by limiting the measurement range, sufficient measurement accuracy can be obtained even if a calibration equation that is normally an exponential function is approximated as a linear function. Then, by approximating the calibration equation as a simpler linear function, the suitability of the equation can be easily confirmed, and the measurement accuracy and the like can be easily grasped visually.

  Furthermore, by approximating the calibration equation as a linear function, the slope can be regarded as constant even if the mixing ratio is slightly changed. Therefore, even if only the attenuation rate relative to the reference concrete is measured, the correction coefficient is calculated. Can be sought. In addition, when the attenuation rate is obtained also about the other fresh concrete for a test, the precision of a calibration type | formula can be improved by using them for an error correction.

Furthermore, by setting the predetermined range in which the unit water amount is measured to be 123 to 185 kg / m ³ , the unit water amount of fresh concrete to be used can be suitably measured in general civil engineering work. The upper limit in a general civil engineering work is sufficient if 175 kg / ^{m 3,} and 180 kg / ^{m 3} the upper limit value when the road construction, the case of the construction work the upper limit be 185 kg / ^{m 3} preferable.

In addition, according to the measuring device in which the neutron beam irradiation device and the neutron beam calibration device, and the gamma ray irradiation device and the gamma ray calibration device are mounted so as to face each other in the container in which the sample is put, , Neutrons pass through the container and the sample stored therein, and the attenuation rate can be measured with a neutron beam calibration apparatus. Similarly, when gamma rays are irradiated from a gamma ray irradiation apparatus, the attenuation rate can be measured by the gamma ray calibration apparatus. Further, if each of the neutron beam calibration device and the gamma ray calibration device is connected to the calculation means, the calculation of the correction coefficient and the unit water amount can also be performed by the calculation means. By obtaining Bei proper dose containers and gamma ray source of (6-7 l) (Cesium 137), can be suitably used in the water content measurement method of fresh concrete according to the present invention.

  A specific example of the fresh concrete moisture measuring method according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a work flow in the moisture measuring method.

In this moisture measuring method, prior to the production of fresh concrete (step 7), in order to set the blending ratio of water, cement, and aggregate used in the manufacturing of the fresh concrete 7, first, a plurality of blending ratios were changed. to create a fresh concrete for the test (step 1). The process after creating the test fresh concrete is divided into two, one of which is process 11 of curing the test fresh concrete to create a plurality of test concretes. And the property of the test concrete produced here is test | inspected (process 12), and if it is appropriate, the test concrete will be prescribed | regulated to the reference | standard concrete in a predetermined work site (process 2). Further, the unit water amount of the test concrete (the unit water amount set in advance in the production 7 of fresh concrete) is determined as the reference unit water amount in the reference concrete (step 3). As a result of the inspection, if all the test concrete is incompatible, another test fresh concrete is prepared by changing the blending ratio.

  In the other process after preparing the test fresh concrete, a plurality of the test fresh concretes prepared were collected in a container (process 4), and gamma rays and neutrons were irradiated from the outside of the container and collected. The attenuation rate of gamma rays and the attenuation rate of neutron rays that have passed through the test fresh concrete and the container are measured separately for each of the plurality of test fresh concretes (step 5). Then, the correction coefficient in the calibration formula used for the calculation of the unit water amount is obtained by calculation using the measured neutron beam and gamma ray attenuation rates (step 6). Here, if the correction coefficient can be obtained, the calibration formula used when measuring the actual water content is determined (step 61).

In preparing fresh test concrete, the blending ratio is determined based on a certain degree of property prediction. Therefore, in most cases, any of the test concretes prepared therefrom is appropriate. Therefore, when the properties of the test concrete are found (usually after about 4 weeks from the creation of the test fresh concrete), a calibration formula is obtained using the already measured attenuation rate to produce the fresh concrete for placement. 7 can be moved. However, if all the test concrete is incompatible, another test fresh concrete is prepared by changing the blending, and in that case, the attenuation rate is measured again (step 51).
This is the preparation work for measurement.

  When the reference concrete is defined, the fresh concrete is manufactured at a work site where the fresh concrete is actually handled (step 7). Then, after the fresh concrete production 7 and before the placing step 92, a sample of the produced fresh concrete is first collected in a container (step 8). Next, gamma rays and neutron rays are irradiated from the outside of the container, and the attenuation rate of the gamma rays and the neutron rays that have passed through the container and the sample, which are measured in step 81, are applied to the calibration formula, and the unit water amount of the sample Is calculated (step 9). Then, the calculated unit water amount of the sample is regarded as the unit water amount of the fresh concrete, and the on-site measurement work is completed.

  In step 91, whether or not the calculated unit water amount of fresh concrete is appropriate is determined. This suitability is judged by whether or not it is within the range of an allowable value (step 31) set based on the reference unit water amount. For example, a difference within a certain range in mass with respect to the reference unit water amount can be set as an allowable value. If it is within the allowable range, the manufactured fresh concrete is placed as it is, and if it is outside the allowable range, it is disposed without being placed (step 92).

  According to this moisture content measuring method, the correction coefficient in the calibration formula used for the calculation of the unit water content is the work of irradiating the test fresh concrete created prior to the production of fresh concrete 7 with neutrons and gamma rays (step 5). ) Only, and many of the material property values necessary for calculating the unit water volume are determined by irradiating gamma rays to the fresh concrete to be measured. Therefore, the preparation work for actually measuring the fresh concrete is saved in labor, the time required for the preparation work is shortened, and the fresh concrete can be easily measured with high measurement accuracy. In addition, since the calculation of physical property values (surface water ratio) that fluctuate greatly depending on the properties of the aggregate is no longer necessary, there is no need to replace formulation data to reflect this physical property value in the calculation of unit water volume. Simplify on-site measurement. In particular, even if there is a change in the blending ratio or the like, additional work such as data exchange does not occur at the work site, and the target unit water amount can be measured very easily.

  In addition, the correction factor is obtained using test fresh concrete corresponding to the reference concrete, which is the desired blending state of the fresh concrete to be measured, and the unit of fresh concrete is also calculated when calculating the correction factor. Similar to step 8 when measuring the amount of water, fresh concrete for test is collected in a container (step 4), and the attenuation rates of neutron rays and gamma rays are measured. Therefore, as long as the fresh concrete to be measured is blended in the same way as the reference concrete, the accuracy of the measured value will be high, and whether the fresh concrete is blended in the same way as the reference concrete will show high precision even by measuring the sample alone. Can be estimated. In addition, since the measurement is performed before the placement 92, it is possible to prevent the placement of inappropriate fresh concrete by stopping the use of the fresh concrete according to the measurement result.

  Furthermore, the comparison with the reference concrete (step 94) enables a follow-up investigation in the case where a property change is observed in the fresh concrete carried into the work site.

The capacity | capacitance of the container which extract | collects the sample of the fresh concrete for a test and the fresh concrete which is a measuring object is 6-7 liters.
If it carries out like this, it is excellent in workability | operativity and sufficient measurement accuracy for determining that the unit water quantity of fresh concrete is appropriate can be obtained.

Cesium 137 is used as a gamma ray source.
In this way, the amount of gamma rays emitted outside the apparatus is small and the safety of the measurer can be ensured. Moreover, sufficient gamma rays necessary for measurement can be obtained.

この校正式において、Ｃ及びＤは校正定数、αは補正係数である。Ｒｎは中性子線のカウント比で、上記容器が配置される場所に標準体を配置した状態で中性子線の減衰率を求め、それを分母とし、実際の計測で求めた減衰率を分子としたものである。中性子線の時間あたりの照射量が時間とともに減衰する影響を補正するために、中性子線の減衰率そのものではなく、このカウント比Ｒｎを採用している。
また、ρｍは全水量、ρｄは乾燥密度で、次の関係（数式２）がある。

この関係式（数式２）においてρｔは湿潤密度で、ガンマ線の減衰率と次の関係（数式３）にある。

この関係式（数式３）において、Ａ及びＢは校正定数である。また、Ｒγはガンマ線のカウント比であり、Ｒｎと同様に、ガンマ線の時間あたりの照射量が時間とともに減衰する影響を補正するために採用している。 The unit water amount is measured within a predetermined range, and the following calibration formula (Formula 1) is used.

In this calibration equation, C and D are calibration constants, and α is a correction coefficient. Rn is the neutron beam count ratio, and the attenuation rate of the neutron beam is obtained with the standard placed in the place where the vessel is placed, and this is used as the denominator, and the attenuation rate obtained by actual measurement is used as the numerator. It is. This count ratio Rn is used instead of the neutron beam attenuation rate itself in order to correct the influence of the neutron beam irradiation dose decaying with time.
Further, ρm is the total amount of water, ρd is the dry density, and has the following relationship (Formula 2).

In this relational expression (Formula 2), ρt is the wet density, and is in the following relation (Formula 3) with the attenuation rate of gamma rays.

In this relational expression (Formula 3), A and B are calibration constants. Also, Rγ is a gamma ray count ratio, and is used to correct the influence of the amount of gamma ray irradiation per hour decaying with time, similar to Rn.

  In the calibration formula (Formula 1) and the relational formulas (Formulas 2 and 3), the total water amount ρm and the wet density ρt can be measured by trial kneading. Using the calibration constants A, B, C, D, and the correction coefficient α, all of the neutron and gamma ray attenuation rates measured separately for multiple test fresh concretes for use in unit water volume measurements. Looking for. That is, for each test fresh concrete, the calibration constants A, B, C, by linear regression using a plurality of combinations of neutron beam count ratio Rn and total water amount ρm and gamma ray count ratio Rγ and wet density ρt obtained by measurement. D and the correction coefficient α are obtained.

  In this way, by approximating the calibration equation as a simpler linear function, the suitability of the equation can be easily confirmed, and the measurement accuracy and the like can be easily ascertained visually.

この関係式（数式４）において、ρｗが単位水量である。なお、ρｑは吸水量で、乾燥密度ρｄと次の関係（数式５）がある。

従って、この関係式（数式５）と上記数式４を連立することにより、全水量ρｍから単位水量ρｗを求めることができる。なお、数式５において、Ｑは吸水率で、この水分量測定方法では単位水量の算出に必要な材料物性値として試験により唯一算出する必要のある値である。しかしながら、この値は大きく変動するものではなく、試験の頻度は少なくても良い。 After determining the calibration formula, if the attenuation rate of neutron rays and gamma rays is measured for fresh concrete at the work site, the total amount of water ρm is obtained from the calibration formula. However, the unit water amount that is the target value of the measurement can be obtained from the following relational expression (Formula 4).

In this relational expression (Formula 4), ρw is a unit water amount. In addition, ρq is the amount of water absorption and has the following relationship (Formula 5) with the dry density ρd.

Therefore, the unit water volume ρw can be obtained from the total water volume ρm by combining the relational expression (Formula 5) and the above Expression 4. In Equation 5, Q is a water absorption rate, and in this moisture content measurement method, it is a value that must be calculated only by a test as a material property value necessary for calculating the unit water content. However, this value does not fluctuate greatly, and the frequency of testing may be small.

The correction coefficient α in the calibration equation is a value that varies when the elemental composition, the amount of crystal water (water contained in the aggregate), and the like differ depending on the type of aggregate. On the other hand, the calibration constants A, B, C, and D in the calibration formula and Formula 3 are constant when the unit water amount is within a predetermined range, and the slope of the calibration formula can be regarded as substantially constant. Therefore, when the calibration constants A, B, C, and D become known by repeating this moisture content measurement method, the reference concrete among the attenuation factors of neutron rays and gamma rays measured separately for each of a plurality of test concretes It is also possible to obtain the correction coefficient α using the one corresponding to. FIG. 2 shows a work flow when the correction coefficient is obtained using only the attenuation rate corresponding to the reference concrete. 2 that are substantially the same as those in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted.
In this way, the correction coefficient can be obtained even if only the attenuation rate with respect to the reference concrete is measured. In addition, when the attenuation factor is obtained also about the other concrete for a test, the precision of a calibration type | formula can be improved by using them for an error correction.

The predetermined range of the unit water amount is 123 to 185 kg / m ³ .
If it carries out like this, the unit water quantity of the fresh concrete to be used can be suitably measured in the civil engineering work in general.

In FIG. 3, the specific example of an apparatus suitable for the moisture content measuring method concerning this invention is shown. This moisture content measuring apparatus has a container 101 for containing a sample. A neutron beam irradiation device 102 and a neutron beam calibration device 103, and a gamma ray irradiation device 104 and a gamma ray calibration device 105 are attached to the container 101 so as to face each other. Further, each of the neutron beam calibration device 103 and the gamma ray calibration device 105 is connected to a microcomputer 106 which is a calculation means, and a correction coefficient and a unit water amount are calculated. Furthermore, the capacity of the container 101 is 6 to 7 liters, and cesium 137 is adopted as the radiation source of the gamma ray irradiation apparatus 104.

Further, it is possible to by the system of quality control inspection posture site that makes full use of the characteristics of the water content measurement how according to the present invention, failure to (bad) prevention of concreting (exclusion). This ripple effect is large and contributes to the construction of high-quality concrete structures with high durability, and can greatly contribute to securing and improving the durability of concrete structures required by all social capital.

  Further, by systematizing the on-site quality control inspection system utilizing the features of the water content measuring method or the water content measuring device according to the present invention, it is possible to prevent (exclude) defective (poor) concrete placement beforehand. it can. This ripple effect is large and contributes to the construction of high-quality concrete structures with high durability, and can greatly contribute to securing and improving the durability of concrete structures required by all social capital.

At the work site using fresh concrete with a unit water amount set value of 155 kg / m ³ , the unit water amount was measured for four lots of fresh concrete, and the following results were obtained.
Lot 1 153kg / m ³
Lot 2 158kg / m ³
Lot 3 152kg / m ³
Lot 4 154kg / m ³

Each lot is formulated so that the unit water amount is 155 kg / m ³ , but it is within a range of about 2% difference from the set value of the unit water amount, and when appropriate preparation is performed In addition, it was confirmed that the measured value is almost the set value of the unit quantity.

It is a figure which shows the flow of the operation | work in the specific example of the moisture measuring method of the fresh concrete concerning this invention. It is a figure which shows the flow of the operation | work in the other specific example of the moisture measuring method of the fresh concrete concerning this invention. It is the schematic which shows the specific example of the moisture content measuring apparatus concerning this invention.

Explanation of symbols

1 Step of preparing test fresh concrete 2 Step of defining reference concrete 3 Step of setting reference unit water amount 4 Step of collecting part of test concrete 5 Step of measuring attenuation factor 6 Step of calculating correction coefficient 7 Step 8 for producing fresh concrete Step 9 for collecting fresh concrete sample 9 Step for calculating unit water amount 11 Step for preparing concrete for test 101 Container 102 Neutron beam irradiation device 103 Neutron beam calibration device 104 Gamma ray irradiation device 105 Gamma ray calibration device 106 Calculation means

Claims (4)

Prior to the production of fresh concrete (7), create several test fresh concretes with different blending ratios (1),
On the other hand, a plurality of test concretes are prepared, and one of the plurality of test concretes having the most preferable properties is defined as the reference concrete at the work site (2)
, A unit water amount set in advance for the production of the fresh concrete is defined as a reference unit water amount in the reference concrete (3),
On the other hand, the plurality of test fresh concretes are collected in a container (4), gamma rays and neutron rays are irradiated from the outside of the container, and the attenuation rate and neutrons of the gamma rays that have passed through the container and the test fresh concrete are collected. The attenuation factor of each line is measured separately for each of the plurality of test fresh concretes (5), and the correction coefficient in the calibration formula used for calculating the unit water amount is calculated by the calculation using the attenuation factors of the neutron and gamma rays. Seeking (6),
After the production of the fresh concrete (7), before placing, take a sample of the fresh concrete in the container (8),
Gamma rays and neutron rays are irradiated from the outside of the vessel, and the gamma ray attenuation rate and neutron ray attenuation rate that have passed through the measured vessel and the sample are applied to the calibration formula to calculate the unit water amount of the sample (9 ),
A method for measuring the amount of water in fresh concrete , wherein the unit water amount of the sample is used as a unit water amount for comparison with the reference unit water amount necessary for determining the suitability of placing the fresh concrete. The unit water amount is measured within a predetermined range, the calibration formula is a linear function, and the attenuation rate of the neutron beam and gamma ray used to obtain the correction factor is measured separately for each of the plurality of test fresh concretes. The method for measuring a moisture content of fresh concrete according to claim 1, wherein all of the measured amounts are the same. The unit water amount is measured within a predetermined range, the calibration formula is a linear function, and the attenuation rate of the neutron beam and gamma ray used to obtain the correction factor is measured separately for each of the plurality of test fresh concretes. The method for measuring the moisture content of fresh concrete according to claim 1, wherein the moisture content corresponds to the reference concrete. The method for measuring the moisture content of fresh concrete according to claim 2 or 3 , wherein the predetermined range of the unit water amount is 123 to 185 kg / m3.

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