Aggregate Stockpiles: How to Prevent Segregation and Contamination

Material carefully crushed, screened and washed can lose its quality in a stockpile. Segregation and contamination are the two main risks at this stage, and both are controlled by the right working method.

Why segregation happens

When material drops from height onto the tip of a cone, coarse particles roll to the toe of the slope and fine particles stay near the top. Material loaded from different parts of this pile does not have the same grading. The effect is stronger in materials with a wide size range.

Ways of building a stockpile

• In layers: material is placed in thin horizontal layers. This gives the best uniformity.
• Many small piles: dumping loads side by side is better than one tall cone.
• Radial stacker or stone ladder: reduces drop height and segregation.

Loading from a stockpile

A loader should work across the whole face of the stockpile, not only its toe. Taking from one spot raises the share of coarse particles. Blending several buckets before loading also improves uniformity.

Preventing contamination

• Stabilize the base and give it a slope so it drains.
• Separate size classes with walls or sufficient distance.
• Do not load the bottom layer that touches the soil.
• Cover sand and filler to control dust.

Sampling from a stockpile

A representative sample comes from several points and depths; the method is in ASTM D75. On moisture in stockpiles, read Moisture and absorption.