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Deleterious Materials and Organic Impurities in Aggregates as per IS: 2386 Part-2 (1963)

This method of test i.e. IS: 2386 Part-2 (1963) covers an approximate method of estimating the organic impurities and deleterious materials, whether organic compounds are present in natural sand in sufficient quantities to be harmful, and hence is intended to show whether further tests are necessary or desirable.

Why the Test for Estimation of Deleterious Materials in Aggregates is Important?

Organic compounds are present in natural sand in sufficient quantities, that will be harmful, and hence is intended to show whether further tests are necessary or desirable.

Harmless organic materials may cause colouration and certain naturally occurring organic compounds do not cause colouration.

This standard IS: 2386 Part-2 (1963) covers the following tests for aggregates for concrete:

1. Determination of clay lumps, (read here)
2. Determination of clay, fine silt and fine dust (sedimentation method), (read here)
3. Determination of light-weight pieces (coal and lignite), (read here)
4. Determination of soft particles, and (read here)
5. Estimation of organic impurities. (read here)

Example of Organic Impurities in Aggregates:

Organic substances in fine aggregate or sand: If sand is extracted from the river bed; it may contain humus, organic soil, decayed vegetation, decayed animal material, etc. These organic materials interfere with the cement setting and ultimately affect the strength of concrete. It shows that the presentence of organic materials excess of a limit in aggregates may be harmful.

Deleterious Materials in Aggregates:

The deleterious materials in aggregates are defined as below:-

1. The harmful and injurious substances including various types of weak or low quality particles or coatings naturally found on the surface of aggregates.
2. The substances, who affect the bond between cement and aggregates and break easily, are considered to be deleterious.
3. The substances, who affect harmful physically or chemically on the aggregates, are considered to be deleterious.
4. Commonly deleterious materials are organic matters, dust (materials passing through 75 micron sieve), clay lumps, shale, coal iron pyrites, friable particles, chert (weak in terms of freezing and thawing), etc. which are weak, soft and fine.
5. They affect the properties of concrete in fresh as well as in hardened state and are undesirable.
6. They may be classified as those interfering with the process of hydration i.e. organic matters, coatings such as clay, etc. affecting the development of bond between aggregate and cement paste.
7. The surface coating impurities in aggregate can be removed by adequate washing.

Note: The test determination of effect of organic impurities on mortar strength is covered by IS: 2386 (Part 4)-1963 (Method of test for aggregates for concrete; Part-4: Measuring mortar making properties or fine aggregates).

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