Aggregates must be relatively clean when used in HMA or PCC. Vegetation, soft particles, clay lumps, excess dust and vegetable matter are not desirable because they generally affect performance by quickly degrading, which causes a loss of structural support and/or prevents binder-aggregate bonding.
To test for clay lumps or friable particles, a sample is first washed and dried to remove material passing the 0.075-mm (No. 200) sieve. The remaining sample is separated into different sizes and each size is weighed and soaked in water for 24 hours. Particles that can be broken down into fines with fingers are classified as clay lumps or friable material. The amount of this material is calculated by percentage of total sample weight. Specifications usually limit clay and friable particles to a maximum of one percent.
The standard test procedure is:
- AASHTO T 112 and ASTM C 142: Clay Lumps and Friable Particles in Aggregate