AASHTO T 71:2012 Standard Method of Test for Effect of Organic Impurities in Fine Aggregate on Strength of Mortar

AASHTO T 71:2012 Standard Method of Test for Effect of Organic Impurities in Fine Aggregate on Strength of Mortar.
3. SIGNIFICANCE AND USE
3.1. This test method is of significance in making a final determination of the acceptability of fine aggregates with respect to the requirements of M 6 concerning organic impurities.
3.2. This test method is oniy applicable to those samples which, when tested in accordance with T 21, have produced a supcrnatant liquid with a color darker than that of the reference standard color Plate No. 3 or color solution.
4. BASIS FOR COMPARISON
4.1. The line aggregate that produced a color darker than the standard in T 21 shall be compared in mortar, as described in this test method, with a sample of the same aggregate that has been washed in a solution of sodium hydroxide followed by thorough rinsing in water. The washing shall be repeated a sufficient number of times until the supernatant liquid obtained in T 21 has a color lighter than standard (Note 1).
4.2. Unless otherwise specified or permitted, strength comparisons shall be made at seven days in accordance with the following conditions:
4.2.1. Mix three batches of mortar with the aggregate washed in sodium hydroxide and three batches with the unwashed aggregate on the same day. All batches shall have the same quantity of fine aggregate. Mix the batches for the two conditions alternately.
4.2.2. Mold three 50-mm or 2-in, cubes from each batch.
4.2.3. Test the three cubes from each batch at the age specified.
Note 1—T 21 describes a standard procedure and an alternative procedure for the determination of color value. In the standard procedure, there is a single reference standard color. In the alternative procedure, five glass color standards are used. The reference standard color is equivalent to color Plate No. 3.
5. SAMPLING AND SAMPLE PREPARATION
5.1. Sample portions of fine aggregate for this test shall be obtained from the same sample used for
T 21. Needed reduction of samples to obtain test portions shall be in accordance with T 248.
5.2. Secure an additional field sample if needed from the aggregate supply in accordance with T 2.
5.3. In the event that the fine aggregate being used includes particles so large that the adjustment bracket (as described in T 162) cannot provide adequate clearance, the oversized particles shall be removed by sieving on the 4.75-mm (No. 4) or 2.36-mm (No. 8) sieve. If this procedure is employed, the report shall so state and shall indicate the percentage of material so removed. Note 2 —Caution: The clearances between the paddle and the bowl specified in T 162 are suitable when using the standard mortar made with graded sand. To permit the mixer to operate freely and to avoid serious damage to the paddle and bowl when coarser aggregates are used, it may be necessary to set the clearance adjustment bracket to provide greater clearances than specified. A clearance of approximately 4.0 mm is required in T 162; a clearance of approximately 5.0 mm has been found to be satisfactory for this method when used with fine aggregate from which the material retained on the 4.75-mm (No. 4) sieve has been removed.AASHTO T 71 pdf download.