ASTM C40 Standard Test Method for Organic Impurities in Fine Aggregates for Concrete 2024

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ASTM C40 Standard Test Method for Organic Impurities in Fine Aggregates for Concrete

The ASTM C40 test method is an essential procedure that aids in identifying the presence of potentially harmful organic impurities in fine aggregates destined for use in hydraulic cement mortar or concrete. It involves a comparison of the color of a liquid extract of the aggregates to a standard color, serving as an initial indication of the material’s quality.

Significance of the Test:

The test’s principal value lies in its ability to act as a preliminary warning signal. Should the tested sample exhibit a color that is darker than the reference standard, it is traditionally recommended to conduct Test Method C87 to assess the potential impact of these impurities on the strength of mortar.

Test Apparatus:

• Glass Bottles: Colorless, graduated, with oval cross section and watertight stoppers—350 to 470 mL capacity. Thickness measured for color comparison should not exceed 60 mm or be less than 40 mm.
• Graduations: Millimeters or U.S. fluid ounces with allowance for user calibration if unmarked.

Sample Collection:

• In line with Practice D75, samples must be representative of the bulk material.

Testing Sample:

• A sample weight of approximately 450 g (1 lb) should be obtained as per Practice C702.

Testing Procedure:

1. Fill the glass bottle to about 130 mL with the fine aggregate sample.
2. Add sodium hydroxide solution until the post-shake mixture totals approximately 200 mL.
3. Seal, shake vigorously, and let it stand for 24 hours.

Determination of Color:

• Standard Color Solution Procedure: Utilize a freshly prepared standard color solution to compare with the supernatant liquid after the standing period. The color intensity should be noted as lighter, darker, or equivalent to the standard.
• Glass Color Standard Procedure: Instead of the solution, five distinct glass color standards are applied, with the result matching one of the organic plate numbers.

Interpretation:

Aggregates that result in a color deeper than the Glass Color Standard No. 11 suggest the possible presence of deleterious organic impurities, and further testing is advised.

Precision and Bias:

Given that this test method does not produce quantitative measurements, the precision and bias cannot be determined.

Keywords:

• colorimetric test
• fine aggregate
• organic impurities

This standard sequence of operations helps ensure that the construction industry uses materials that adhere to safety guidelines, hence safeguarding structural integrity.

ASTM C40 Standard Test Method for Organic Impurities