Construction Directive
The Material Properties of Stone Dust
Recently we had a customer who was building a new ProBounce surface over an old asphalt pavement which was cracked and uneven. He milled the asphalt instead of pulverizing it which left him with some rather large pieces. He then graded the milled materials to try and achieve planarity adding some crushed stone to blend in. When grading the milled materials, he was left with a very uneven and bumpy finish due to these large millings. Options would have been removal and/or blending with new stone. He instead chose to level the area with stone dust screenings. In some areas the screenings were 12” deep.
There’s no argument that stone dust has some extremely useful properties. Unfortunately, none of them are well suited to deep applications such as this. As a rule of thumb, I find a 2” depth is a safe application because stone dust poses some well-understood threats to the physical integrity of pavement projects. Water retention is a major one.
Stone dust is a fine material that will absorb moisture readily and will then releases it very slowly. The moisture in deeper applications of stone dust can wreak havoc on underneath pavements, causing effervescence and allowing them to settle or shift easily under a load. In extreme frost-thaw cycles, water-soaked stone dust can actually pump and lift up, shifting the pavement in the process.