Test for Clay Lumps and Friable Particles

Purpose

Clay and friable particles may be present in the form of lumps in natural aggregates. If they are near the surface, these lumps can cause pitting under the influence of traffic. Specifications frequently limit these particles to a maximum of 1%.

Equipment and Materials

• Weighing device accurate to 0.1%
• Flat pans for spreading the test specimens in a thin layer
• Sieves as called for in the Testing Procedure
• Drying oven capable of maintaining a free circulating air temperature of 110°±5°C (230°±9°F)
• Required amount of Test samples

Test Procedure

1. Test samples shall be prepared in accordance with ASTM Designation: C 117, and after oven drying at 110°±5°C (230°±9°F), shall consist of the following quantities: Fine aggregates shall consist of particles retained on a 1.18-mm (No. 16) sieve and weigh at least 25 grams. Coarse aggregate sizes and minimum quantities per sample are as follows:

where the test sample consists of both fine and coarse aggregates, the material is separated on a 4.75-mm (No. 4) sieve. The fine and coarse fractions are then handled as above.

2. The weighed specimens are spread in a thin layer on the bottom of a container and covered with distilled water for about 24 hours.
3. Roll and squeeze the individual particles between the thumb and forefinger. Try to break down the particles but only with the thumb and forefinger. Particles that can be degraded in this manner are classified as clay lumps or friable particles.
4. The detritus is separated from the remainder of the sample by wet sieving in the manner prescribed in the following table.

Agitate the sieve during the wet sieving operation to assure removal of all undersized particles.

5. Remove the retained particles and dry to a constant weight in the oven at a temperature of 110°±5°C (230°±9°F). Allow the aggregates to cool and weigh to nearest 0.1%.

Calculations

P = [(W − R)/W] × 100

P = % of clay lumps and friable particles

W = weight of the test sample

R = weight of particles retained on the designated sieve in wet sieving

For coarse aggregates, P shall be based upon the weighted average of the clay lumps and friable particles in each sieve size fraction. Any coarse aggregate fraction that is less than 5% of the total gradation shall not be tested separately. That coarse aggregate fraction shall be assumed to contain the same percent of clay lumps and friable particles as that found in the next larger or smaller coarse aggregate fraction.