Counterflow drum-mix plant

Because of the separation of the mixing zone, fume emission is minimised. The bitumen, the filler and the reclaimed asphalt (if added) are all fed into the mixing zone. As a consequence, the drying zone can be used only as a dryer/heater of the aggregate if needed. 

All the other production stages are exactly the same as those in the parallel-flow drum-mix plant. 

The basic advantages of a counterflow plant over a parallel-flow drum-mix plant are that it is more environment friendly, fuel efficiency increases and higher percentages of reclaimed asphalt can be used. 

The desire to improve production efficiency, reduce hydrocarbon emissions, increase fuel efficiency, reduce operating cost and increase the percentage of reclaimed asphalt blend with virgin material led to the development of alternative counterflow drum dryer/mixer techniques. 

When recycling is predominant, the hot aggregate, fines and reclaimed asphalt pass through the double-barrel and mixing takes place in a twin-shaft pugmill or rotary mixer. Hence, the double-barrel dryer/mixer is called double RAP dryer (ASTEC Industries Inc. 2014). With the addition of the Green Pac, an option offered by the same company, the double RAP dryer produces warm mix asphalt. 

---