AAPA 2010 Study Tour – Recycled Asphalt Pavement Recycled Asphalt Pavement Trevor Distin | Rick...

AAPA 2010 Study Tour – Recycled Asphalt Pavement

Recycled Asphalt Pavement

Trevor Distin | Rick Hennig Robert Patience


Use of RAP in the USA

• USA produces @100Mt of RAP annuallyo average of 17% RAP is recycled in HMA o 23 States have experience with >25% RAPo aim is to increase RAP in all mixes >25%o still some perceptions that asphalt with RAP is inferior to

all virgin material

• Main driver for using RAP is economics and sustainability has become the new drivero NAPA reported that 25% RAP usage neutralises the carbon

foot print of a HMA plant

‘Trade in your old pavement for a new one’


U.S. Department of TransportationFederal Highway Administration

States that Permit More than 25% RAP in HMA Layers

CA

AZ

CO

NM

TX

OK AR

LA

MO KY

AL GA

FL

VA

OH

MI

VTAK

MT

NV

ME

WA

OR

UT

KS

IDWY

ND

SD

MN

NE

WI

IA

IL IN

MS

TN

SC

NC

WV

PA

NY

CTNJDEMD

DC

MA

NH

HI

RI

All layersBase and Intermediate Layers OnlyBase layer onlyDo not permit more than 25% RAP Jones 2009 survey


Obstacles to using > 20% RAP

• Concern over comingled binder propertieso Stiffening of binder could lead to early crackingo Use of high % RAP may negate the benefit of using PMB’s

i.e. dilution of the PMB• Durability of surface layers could lead to raveling• Variability/consistency of RAP

o Lack of QC by contractor• Meeting skid resistance requirements• Two biggest obstacles in mix design:

o Binder characteristics o Percent passing 75µm i.e. excessive fines


Benefits of using RAP

• RAP reduces potential of mix to rut• Adding RAP stiffens the binder to a higher

performance grade o Substituting RAP for PMB was found to render similar

deformation resistance i.e. rutting performance

• Monitoring on 18 test sections up to 17 years with RAP showed pavements using >30% RAP are performing well

• Up to 40% RAP does not increase CV of HMAo In some cases contractors found less variability in RAP than

virgin aggregates


Summary of t-Test Analysis

DistressParameter

Virgin Performed Better than

RAP

RAP Performed Better than

Virgin

Insignificant Difference Between RAP and

Virgin

RAP Performed

Equal or Better Than

Virgin

IRI 42 39 19 58

Rutting 33 29 38 67

Fatigue Cracking 29 10 61 71

Longtnl. Cracking 15 10 75 85

Transverse Cracking

32 15 53 68

Block Cracking 3 1 96 97

Raveling 7 15 78 93


AB

MN

MB

MEMT

COMD

MO

NJ

CA

GA

MS

NM OK

TX

AL

AZ

FL

Did not use softer binder in RAP mixes

LTPP – Cracking Assessment


Variability: RAP vs. Aggregate

Based on 74 RAP stockpiles in 14 states, and 60 Aggregate stockpiles in 6 states


Benefits of RAP to contractors

• Reduction in energy requirements to heat virgin agg & binders

• Hedge against rising bitumen prices & global uncertainty which can effect supply

• Reduces amount of virgin aggs & bitumen which reduces material costs


Differences by State• Caltrans

o Can use up to 15% in WC without additional testing otherwise can increase to 30%

o No RAP allowed in OGA & BRA• VDoT

o < 30% allowed in WC except SMA <20%o < 35% in base

• South Carolinao non fractionated RAP: <20% in WC & <30% in baseo Fractionated RAP: <25% in WC

• North Carolinao <50% baseo <30% in WC if RAP screened through 25 mm sieve


New Approach

• Base maximum % RAP on net effect that RAP binder has on the properties of new mix

• Limiting factor will be determined by:o recovered aged binder properties o% binder in RAP i.e. 4% vs 7% depending on

grading (fine or coarse)• This means that you can use double the

amount of coarse RAP vs fine RAP for same aged binder properties

• Typically 70% of binder must be virgin


Virgin binder class to use

• FHWA recommendations:o <15% RAP: no change in binder gradeo <15 < 25%: use one binder grade lower i.e. softero >25%: use blending charts

• However studies have shown that:o 20% RAP can be used without changing binder

gradeo NCAT test sections indicate that the performance

of up to 45% RAP there is no evidence to adopt a lower grade


Determining blended binder grade


4.1

8.5

4

1.20.5

1

5.3

0

2

4

6

8

10

12

20% RAP PG 76-22

20% RAP PG 67-22

45% RAP PG 52-28

45% RAP PG 67-22

45% RAP PG 76-22

45% RAP PG 76-22 +

Sasobit

Virgin PG 67-22

Ru

t D

ep

th (

mm

)

Rutting performance @ 10 M ESALs


Milled RAP

•Keep millings from different projects in separate stockpiles

•Milled RAP can typically be used “as is” in HMA

without further crushing to save costs


Multi-Source RAP Stockpiles

•Avoid contamination from the beginning•Mix it up while feeding the screen or crusher•Don’t over crush•Fractionation helps for design of high RAP mixes•Watch the weather when processing•Blend again when moving stockpiles

AAPA 2010 Study Tour – Recycled Asphalt Pavement17

-4.75mm RAP +19mm RAP

19 – 4.75mm RAP

• Screening RAP into two or more sizes• Allows RAP to be used in practically any mix type• Do not crush RAP to avoid producing fines. Only crush

oversize RAP


Fractionating vs non fractionating


Stockpiling RAP

Building steep sided stockpiles will create segregation

Testing helps control binder content & air voids in mix


Minimise moisture

o Cover stockpileso Sloped pavement

underneatho Free moisture in the

RAP can cause caking of RAP in crushers and blinding of screens


Effect of moisture on heating


Testing of RAP• Take samples daily from RAP stockpile

o 1 set of samples for 1000 tonnes of RAP

• Binder Content: ignition method is preferredo Faster and more accurateo For dolomitic aggregates use solvent extraction

• Grading especially % passing:o 75µm sieveo Median sieve

• Bulk SGo Potential errors when calculating BSG

22


Effect of RAP Gsb on VMA

Gsb Virgin = 2.6700

12.4

12.6

12.8

13.0

13.2

13.4

13.6

0 10 20 30 40 50 60 70

RAP Aggregate %

VM

A%

2.644

2.624


Other issues

• Where skid resistance is a concern use small sized RAP < 7mm

• Reduced mix temperature allows more RAP to be used

• Using higher % RAP in WMA helped increase temperature of bag house

• Aged binder on RAP works as an “anti-stripping” agent & improves TSR values


Other issues cont…

• Consensus was that you could increase the FHWA recommended addition rates of RAP for WMA (by 10%) before changing the binder grade:o < 25%: no changeo >25 < 35%: bump to softer gradeo > 35%: use blending charts

• Lower mixing temperature resulted in less oxidation & light oil remaining in virgin bitumen

• Steam produced from drying RAP creates inert atmosphere• Recovered binder from WMA with 25% RAP has the same

rheological properties as recovered binder from HMA with virgin bitumen


Recommendations

• Optimise the use of RAP in asphalt mixes without compromising mix performanceo Valuable resourceo Engineered producto Reduce demand for non-renewable raw materials


Recommendations

• Develop guidelines for the inclusion of various % RAP into different application i.e. mixes and layerso Procedures for processing & stockpiling RAP

• Developed simplified procedures for evaluating RAP and binder properties for >30% RAP o Determine effect of the properties of the aged

binder and binder content of RAP on performance of mix specifications e.g. blending charts


Proposal

Dense graded wearing courses• < 15% RAP

oMust fractionate RAP <NMAS• >15%<30%

o Only if aged binder content <30% of new mix• > 30%

o Only if binder viscosity of new mix < max RTFOT• Subject to stringent process control &

monitoring


Proposal

Intermediate & base courses• < 15% RAP

oMust screened but not necessary to fractionate into different sizes

• >15%<30%oMust fractionate into different sizes

• > 30%o Aged binder must be < 30% of new mix

• Subject to stringent process control & monitoring


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AAPA 2010 Study Tour – Recycled Asphalt Pavement Recycled Asphalt Pavement Trevor Distin | Rick...

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