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Gardner Color Standard: is a one-dimensional scale used to measure the shade of the color yellow.

Supernatant: liquid, floating

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Impurities : Impureza
Darker: Mas oscuro
sodium hydroxide: Hidróxido de sodio
organic impurity: Impureza organica
Reagents: Chemical solutions for mixtures
Calibrate: Instrument or measurement procedure

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Organic Impurities in Fine Aggregate (Sand) for Concrete | ASTM - C40 | All About Civil Engineer

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Colorimetric test; fine aggregate; organic impurities

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Since this test produces no numerical values, determination
of the precision and bias is not possible.

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When a sample subjected to this procedure produces a
color darker than the standard color, or Organic Plate No. 3
(Gardner Color Standard No. 11), the fine aggregate under test
shall be considered to possibly contain injurious organic
impurities. It is advisable to perform further tests before
approving the fine aggregate for use in concrete.

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9.1 Standard Color Solution Procedure:

* At the end of the 24-h standing period, fill a glass bottle to the approximately 75-mL (21⁄2-fluid oz) level with the fresh standard color solution, prepared not longer than 2 h previously.

*  Hold the bottle with the test sample and the bottle with the standard color solution side-by-side, and compare the color of light transmitted through the supernatant liquid above the sample with the color of light transmitted through the standard color solution.

* Record whether the color of the supernatant liquid is lighter, darker, or equal to the color of the standard color solution.

9.2 Glass Color Standard Procedure:
To define more precisely the color of the supernatant liquid of the test sample, five glass standard colors shall be used using the following colors:

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Fill the glass bottle to the level of approximately 130 mL (4 and 1/2 fluid ounces), with the total aggregate sample to be tested, then add the sodium hydroxide solution to the volume of aggregate and liquid, and then we shake, it is approximately 200 mL (7 - fluid ounces); to finish we cover the bottle, shake vigorously and let it rest for 24 hours. After all this procedure we will know how much organic impurity there is in the tested soil.

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The test sample will have a mass of approximately 450 g (1 lb), for each test required to be performed.

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3.1 This test method is used in making a preliminary determination of the acceptability of fine aggregates with respect to the requirements of Specification C 33 that relate to organic impurities.

3.2 The principal value of this test method is to furnish a warning that injurious amounts of organic impurities may be present. When a sample subjected to this test produces a color darker than the standard color it is advisable to perform the test for the effect of organic impurities on the strength of mortar in accordance with Test Method C 87.

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C 33 Specification for Concrete Aggregates.
C 87 Test Method for Effect of Organic Impurities in Fine Aggregate on Strength of Mortar .
C 125 Terminology Relating to Concrete and Concrete Aggregates .
C 702 Practice for Reducing Samples of Aggregate to Testing Size .
D 75 Practice for Sampling Aggregates .
D 1544 Test Method for Color of Transparent Liquids (Gardner Color Scale) .

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Sampling corresponding to ASTM D75 should be considered for the sampling of aggregates in situ, for fine and coarse aggregate linked to the maximum size of each aggregate and for the amount of mass that is necessary.

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Is required
1.- Reactive Sodium Hydroxide Solution (NaOH) (3%)
2.- Potassium dichromate (K2Cr2O7)
3.- Sulfuric Acid (H2SO4)
4.- Water (H2O)

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1.- Glass bottle.- This bottle must be graduated for each dosage of water, fine aggregate and solution, it must also be transparent with a capacity of 470mL with a lid.
2.- Standard test color table.- Contains 5 standard colors mounted on a plastic table that serves to classify the level of impurities.

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This test method covers two procedures for an approximate determination of the presence of injurious organic impurities in fine aggregates that are to be used in hydraulic cement mortar or concrete. One procedure uses a standard color solution and the other uses a glass color standard.