Most dry concrete batch plants have a typical material charge sequence into a concrete mixer truck.  Usually this sequence looks like the following;
80% Water > 65% aggregate > release cement > after aggregate and cement > release final 20% water.
However, some times this sequence will create cement balling or packing on the mixer truck fins. Why?

Typically the cause is using the same ribbon charge sequence for all mix designs regardless of the cement sack content. Higher sack mix designs will have the cement sequence seeing more water then aggregate/sand. When the cement is being charged into the mixer truck, it should be feeding with the aggregate material and not water. By charging the mixer truck with 80% water, the aggregate in the mixer truck is below water level, and the incoming dry cement will skip across the water rolling and packing to the mixer blades. Reducing the amount of head water down to 70% will have the cement seeing aggregate instead of water.  Automatic Batch Controls are capable of having several discharge sequences available.  Sequences can then be matched to the applicable mix design group, allowing the correct discharge rates to be applied to the mixer truck charging sequence.

Reducing the cement balls in a load, will allow the plant operator to increase the overall plant production.