Demonstration 2

Conducting an Organic Matter Test

Objective: The purpose of this demonstration is to determine the viability of an aggregate based on the amount of organic matter present.

Materials Needed:

• Sand
• A 50:50 mixture of sand and dirt
• Glass container (10 oz. juice jar or similar size) with lid
• A 3% solution of sodium hydroxide NaOH (made by dissolving 9 grams of sodium hydroxide, household lye, or caustic soda, in 300 mL of water, preferably distilled).

Procedure:

1. Fill container with sand to the 150 mL mark.
2. Add 120 ml of 3 % NaOH solution.
3. Shake thoroughly for 1 or 2 minutes and allow to stand for 24 hours.
4. Repeat the procedure using the sand-dirt mixture.
5. Indicate the color of the liquid remaining on the top of the aggregate.

Video Clip

The color of the liquid will indicate whether or not the aggregate contains too much organic matter. A colorless liquid indicates a clean aggregate, free from organic matter. A straw-colored solution, not darker than apple-cider vinegar, indicates some organic matter bur not enough to be seriously objectionable. Darker colors mean that it contains too much organic matter and should not be used unless it is washed and tested again.

Expected Results:

The sand leaves a colorless liquid. The sand-dirt mixture produces a yellow to orange liquid.