Best Practices for Reclaimed Asphalt Pavement management

RAP Management
800,000,000+ Tons of Experience ...

• Has moved from Strategic Advantage …to a
Strategic Necessity for the producer
• The greater percentage your recycling
capability, the better your strategic positioning
• Need to be able to recycle effectively to the
highest RAP % the mix quality / mix
characteristics / plant equipment allows
Why Recycle? Why RAP?

What we will discuss …
• Stockpiling RAP
• Crushing and Sizing RAP
• What Kinds of Crushers Work Best
• The Need for Testing…
• Feeding RAP into the Plant
• “Limits to RAP”

Stockpiling RAP
Original Best Mgt. Practices
• Stockpile known RAP sources – process and
stockpile separately – ID - design JMF to pile
(Requires large stockpile area – But some sources do not yield
enough RAP to stockpile separately! – Although some states do
require state owned RAP in a separate pile …)

Processing RAP
Best Management Practices
• Crushing/screening, together with loader
blending, makes homogenous RAP product
from a pile of different RAP sources
(Unexpected originally,
but now time-proven)
(Really!)

Stockpiling RAP
• DO stockpile unprocessed RAP so there
aren’t “valleys” to accumulate moisture …

Stockpiling RAP
• RAP stockpiles don’t drain – it is there forever
– keep water from accumulating by how you
stockpile material

RAMPS allow more material in smaller footprint
AND seal the material from moisture accumulation

Processing RAP
• “Working the face” - loader or trackhoe
blending the feed stock - is typical for making
a homogenous product from “different source”
stockpiles

Processing RAP
• And reducing to 3/8”, 5/8” or 1/2” minus is
typical so RAP can be used in “all mixes”
… (and target size is locale specific)

Processing RAP
• Making two RAP products – splitting on 3/8”,
5/8” or 1/2” is typical
– Coarse product
– Fine product
– Helps control gradation
of fines in final mix
– Provides faster heat
transfer for higher
RAP %’s and more
effective drying

Processing RAP
• “Fractionating”
– Started with commercial
mixes to eliminate
“oversize” rock in mixes

Processing RAP
• “Fractionating”…
mixes to eliminate
– Now used to control the
–200 fraction and fine
aggregate (voids)
in the final mix

Processing RAP
• “Fractionating”…
mixes to eliminate
– Now used to control the
–200 fraction and fine
aggregate (voids)
in the final mix
– Can aid in the design
of produce-able mixes
(AC, gradation, heat xfr)

Processing RAP
“Fractionating”
3/8”(1/4) x 0”
High -200s
High AC%
Fast Heat XFR
5/8”(1/2) x 3/8”(1/4)
Lower -200s
Lower AC%
Ave Heat XFR
3/4”(5/8) +
No -200s?
Very Low AC%
Slow Heat XFR

Processing RAP
“Fractionating”
3/8”(1/4) x 0”
High -200s
High AC%
Fast Heat XFR
5/8”(1/2) x 3/8”(1/4)
Lower -200s
Lower AC%
Ave Heat XFR
3/4”(5/8) +
No -200s?
Very Low AC%
Slow Heat XFR
May Help You to Control
the Design, Quality,
and “Produce-Ability”
of Your Final Mix
for Higher RAP %

Processing RAP
Crushing and Screening RAP
• Impact crushers have highest reduction ratio
• Impact crushers break particle bonds easier
• Jaw/Roll combination crushers are second
most popular choice (getting harder to find used
plants once cheap + sometimes used to reduce fines)

Processing RAP
• Feed and primary/secondary breaking
curtains affect throughput and gradation
• “High” and “Low” bars help improve
throughput and produce uniform gradation

Processing RAP
• Remember to work face with loader or hoe
while feeding the crusher to help produce a
uniform final product (KEY)

Processing RAP
• OK to stack material – typically will not compact
(At least not too much! Depends on AC% and age…)
(Slight amount of moisture reduces dust and aids in
removal later, but too much reduces tph and raises
drying costs)

Processing RAP
• OK to stack material – typically will not compact
(At least not too much! Depends on AC% and age…)
(Proper stacking techniques minimize segregation!)
(This influences your final AC content and gradation)

Processing RAP
Stockpiling and Handling
• Stockpile finished RAP so that water drains
“off” stockpile … don’t create “valleys” where
moisture can accumulate in finished piles

Processing RAP
Stockpiling and Handling
• Covering at crushing can lower moisture %,
which lowers fuel cost and raises RAP %
(Many producers process as they use or cover
stockpile with a tarp or shed or both)

Stockpiling and Feeding RAP
Unique Characteristics to RAP:
• Does not drain - retains moisture
• Forms a “crust” on the surface from
absorbing radiant heat from sun
• Crust, however, easily broken with loader

• Do not dig into “new crust” or dry area of RAP
pile after rain to reduce moisture!
(Remove “wet part” of open face
and set aside to dry)
(Keeps RAP % up, drying
costs down, and ensures
adequate drying and heating
of RAP)

• “Breaker” or “Scalping Screen” helps keep
“crust” or re-agglomerated particles from mix

• Can also install impact crusher into feed bin
and scalping screen circuit – downsize in
route to plant
(couple different
ways to do this)

• “Trickle feed” RAP bin when charging bin with
loader
(RAP more prone to bridge
than even fine aggregates)
(Ensures uniform and
consistent feed of RAP)

• Unload RAP bin each night … and after 1-2
hours of down time?
(Helps keep feed uniform,
especially in humid
climates – depends
on RAP moisture)

• Key for mix success = keep RAP feed uniform
(ensures consistency of final mix, especially with
drum-mix style plants)
(affects scale signal &
“hunting / seeking” blend)
(affects temp of final mix)

Personally not a fan …
• Installing impact crushers into feed bin and
scalping screen circuit – downsize in route to
plant
– (can negatively consistency of mix, especially with
drum-mix style plants)
– (affects scale signal &
“hunting / seeking” blend)
– (affects temp of final mix)

The 3 “Limits” to High RAP Mixes…

1. Heat Transfer Capability of the Machine

2. Managing “Dust” in the Final Mix

2. Managing “Dust” in the Final Mix
3. Binder Characteristics in the Final Mix

• Not all plants are created equal

• Length is your friend (length = time)

• Longer heat transfer times = higher RAP
capability

Recycling with a Drum-
Mixer
Parallel-flow drum-mixers heat RAP
convectively with hot gases (50% possible)
Counter-flow drum-mixers heat RAP
conductively with super-heated virgin
aggregate (25-50% based on style/conditions)
RAP Enters
Here,
or Here

Counter-Flow Drum- Mixer
RAP
Entry

Counter-Flow Drum-Mixer with RAP
Introduced in Mixing Area / Zone
RAP

Introduced in Combustion Zone
RAP

Counter-Flow Dryer-Mixer with RAP
Introduced in Mixing Zone
RAP

capability
• High RAP plants are now often a two
step process

capability
• High RAP plants are now often a two
step process
• Drying and heating in one device
• Mixing AC in another

in Drying Drum and Outside Mixer for AC
RAP

Recycling with a Batch Plant
RAP is heated conductively with super-heated
virgin aggregate … and managing the steam
is key to successful high RAP ratio production

Using RAP in a Batch Plant
Two methods typical:
• Weigh Hopper / Weigh Batcher
• Bucket Elevator
(both rely on conductive heat transfer)

“Weigh Box” Batch Facility
Recycling Technique
RAP Bin Batch Steam
Release to
Emission
Control
Equipment

“Weigh Box” Batch Facility
Recycling Technique

“Pugmill” Recycling Technique with
Separate Weigh Hopper
RAP Bin
Batch Steam
Release to
Emission
Control
Equipment

Bucket Elevator Recycling
Technique
Continuous
Steam Release
to APC
Equipment

Conveyor Feeding RAP to
Bucket Elevator

Bucket Elevator Recycling
Technique
Screen By-Pass =
Gradation Control
at the Cold Feed

“Bucket Elevator” Recycling
Technique w/ Heat Transfer
RAP
RAP Steam
Release in
Dryer

Heat Transfer Chamber for
RAP on Dryer

2. Managing Dust in the Final Mix

• Maintaining a proper dust/binder ratio

• Dust in the RAP/RAS is “bound” and
can’t be “liberated”

• Can manage the dust removed from
the virgin material (partial dust removal)

• Can manage the dust removed from
the virgin material (partial dust removal)
• Several ways to do this …

Returned Dust
Wasted Dust
Variable Speed
Rotary Valve

Variable Speed Airlock at Transfer Screw
(excess fines wasted to ground or truck for disposal)

Baghouse Dust
Return Silo
Mineral Filler
Additive Silo

Weigh-pod on Silo for Fines Return

97
Return Pod
on Load Cells
Collection Pod
on Load Cells

3. Managing Final Binder Characteristics

• Rheology of the asphalt cement

• Use of softer binders OR rejuvenating
agents (choices affected by local market
conditions + preferences)

Rejuvenating
Agent Tank
AC Tanks

3 Way
Valve
V.S. Pump
Digital
Meter

Sampling
Port
In-Line Static
Mixer

• Use of softer binders or rejuvenating
• Measuring recovered Performance Grade

• Measuring Delta Tc

• Measuring Delta Tc
• Measuring with “mix performance tests”

Best Practices for Reclaimed Asphalt Pavement management

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