For typical Type II Cement mix designs, drum chipping should only be required once a week and should be about a wheel barrel.  Daily washouts and rock-outs will also help reduce mixer maintenace.  If you are having more build-up, then I would suggest confirming the current Mixer Charging Sequence is correct; see below.  Some build up or material-on-material wear is needed to extend the life of the mixer blade legs.  Rebar is commonly welded to the pad of the mixer blade leg to increase build-up around high impact area's.

Mixer Charging Sequence -  Is based on when materials enter barrel.  Not based on when material leaves scale.
*Water enters mixer first.
*Aggregate enters drum 1 sec. after water.
*Cement enters drum 1 sec. after aggregate.
*Cement finishes first - (approximately 1-2 sec. before aggregate)
*Aggregate finishes (approximately 1-2 sec. before water)
*Water finishes last