Internal Friction

The internal friction can be very roughly estimated from the angle of repose.  This value may increase with compaction forces, which are about 50 psi at the base of an average cement silo.

The 'angle of repose' of  ASTM Type "C" Flyash is ~ 60 to 85°
The angle formed on an air-slide by Type "C" is 16° (called the working angle)

Using PMT this working angle for Type "C" Flyash is reduced to 4.5°, (about a 72% reduction).
Hence, air-slide chutes using PMT will reach much further for the same vertical drop.