RAP and RASAt DelDOT

Karl Zipf, Chief ChemistDelDOT

2014

Status Check

Asphalt Concrete Pavements are like Goldilocks and the Three Bears

It Can’t be too Hot

It Can’t be too Cold

It has to be Just Right

Too Soft (Hot) it Ruts• Problem generally with new pavements.• Wrong binder grade• Poor aggregate gradation.• Poor substructure.

Too Stiff (Cold) it Cracks• Problem generally

with older pavements.

• Thermal cracking (rare in Delaware)

• Fatigue cracking typical.

• Substructure- reflective cracking

Pavement End of Life• The pavement distress is evaluated.• Selected pavements milled off the top

approximate 2”.• This becomes RAP and being a small state and

processing the RAP gives a uniform product.• From 1997-2013 average grade is PG 88-16.• Low temperature has been -18 to -19C which

would indicate average pavement distress and binder properties are linked.

How does the RAP Affect the Mix

• The FHWA states that under 20% one does not need to change grade.

• Over 25% one should use a blending chart.• Blending chart is based on Percent Binder

Replacement.• It is based on the True Grade of the asphalt.• Typical RAP high temperature TG at 89C while

for PG 64-22/28 it is 66C.

How Much RAP?• The amounts are based on binder replacement.• HMA Plants prefer as a percent of the mix.• The RAP Calculator converts from binder

replacement to percent of mix.• Assumes 100% contribution of AC from RAP• There are three DelDOT absolutes.– PG 70/76-22, maximum is 10% replacement.– PG 64-22, maximum is 20% replacement.– PG 58/64-28, maximum is 40% replacement.

Asphalt Binder Grading

• Whether it is PG grading (M-320) or MSCR grading (M-322) the grading ASSUMES that all pavements are made with 100% virgin asphalt.

• The suppliers are only required to meet M-320 or M-322. They do not need to meet any RAP/RAS requirements.

• Any supplier can buy asphalt on the open market and rebrand it.

What Happened Here?• Rt 13 South of Smyrna• Crack sealed after 1 year.

Black Rock or Asphalt?

• FHWA starts to get vague here.• A number of states discount the binder

contribution from the RAP.• By experience, New York allows an 80%

contribution.• By testing, Georgia has determined 75% of the

RAP binder contributes to the effective asphalt in the mix.

Our Problem Pavement• Rt 13 SB Smyrna-Dover, Paved 2012, PG 76-22

and 10% RAP, Crack Sealed 2013• Compare to Rt 13 Dover, Paved 1997, PG 70-

22 SMA. Milled 2012. Not crack sealed.

Best Guess

• Winter 2012-13 not very severe.• Seeing similar problems in recent pavements.• Probably some of RAP acting like black rock.• DelDOT will probably discount asphalt

contribution from RAP by 10-20% (to be determined) in the new RAP calculator.

Shingles (RAS)

• Shingles are rich in asphalt (20%)• Shingles, new or old, are far stiffer than RAP.• RAP PG: 88-16• New Shingle Waste: PG 115-16• RAS since 2012: PG 142-10• Post Consumer RAS: PG 160-10• DelDOT will adjust the RAP Calculator to

reflect the 2012-13 RAS properties.

Asphalt Contribution• Again the FHWA is vague on the asphalt

contribution from RAS. All they say is the finer it is ground, the more asphalt is released.

• DelDOT will probably discount RAS 10-20%.

RAP and RAS can Make Good Hot Mix• Blending and processing RAP produces a more

uniform product.• The plant operation might need to be re-

optimized for RAP or RAS.• Stockpiles might have to be covered.

DelDOT is Committed

• DelDOT is committed to the use of RAP and RAS in its pavements.

• DelDOT has one of the most liberal use policies for RAP and RAS.

• However, DelDOT is committed to quality and durable pavements and will keep that as its primary goal.

Closing Thoughts“Infrastructures are buildings, but also roads, bridges, domestic water, sanitary sewer, transmission lines for electricity, digital media or telephones, all which materially support markets, transportation, or networks. These artifacts have a non-energized function – they do not significantly utilize energy – and are not informational – they do not significantly use the information that they eventually transport. Their usage is essentially collective. These structures merit the prefix “infra” because they are placed below the functioning of other artifacts, for they support the functionality of them. By definition, the infrastructures are the means and not the ends in themselves. The intermingled and interconnected networks of the infrastructures constitute the support of the functioning of our technological civilization.”

– M. Puech

Thank You

• Any Questions?

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