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Functionalities
4 main methods :
1) up to 10-15% - no screening
2) up to 25% - with screening
3) up to 35% - no screening
4) up to 50% - with screening
1) RAP to the foot of hot elevator Maximum 10-15%
Advantages
Low investment required.
Disadvantages
> Overheating of virgin aggregates; plant hourly output
reduced when feeding RAP
> No screening
> Low RAP %
> Emission of vapour at hot elevator and mixer level difficult to exhaust
2) RAP feeding into the virgin aggregates
weigh hopper or into the mixer Maximum % of RAP used up to 25%
Advantages
Virgin aggregates could be screened
It allows a very precise metering by weight of RAP
Disadvantages
> Necessity of overheating virgin aggregates, plant outputis drastically reduced due to increase of mixing cycle
> Low RAP %; RAP moisture evaporation during mixing operation, to be exhausted to bag filter
> Problems rising from a contact between bitumen over high temperature aggregates
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3) RAP feeding into the dryer via a recycling ring. It permits to reach up to 35% of RAP in the final mix
Advantages
High RAP %; heating starting in the dryer by irradiation from the flame; low capital investment; plant output unchanged when recycling up to 35% ; moisture exhausted through same main fan. Possibility of upgrading and retrofitting existing batch plants.
Emission well within the limits (same emission as when batch plant working with no RAP).
Disadvantages
Virgin aggregates cannot be screened.
4) RAP 50%, preheated and dried using a special parallel flow dryer drum
Advantages
Process and equipment permits to screen virgin aggregates; very accurate metering of RAP by weight; smooth and controlled heating of RAP; very high RAP percentage.
Plant output unchanged when recycling up to 50%; emission comfortably within the most strict limits.
Disadvantages
High capital investments.
To maximize the RAP % in any formula, the following special applications are also available:
a) when RAP% is lower than 15-20%, RAP can go through surge hopper, aggregate weighing hopper and mixer
b) vhen RAP is up to 35%, RAP can go through recycling ring
c) two separate lines of RAP feeding: recycling ring plus mixer to reach up to 40% total RAP in the mix |
