What is Reclaimed Asphalt Pavement (RAP)?
A reclaimed asphalt pavement (RAP) is removed asphalt pavement that contains aged binder and aggregate and is reused in new pavement.
What RAP contains
RAP is mostly aggregate. FHWA gives 93 to 97 percent aggregate by weight and typically 3 to 7 percent asphalt binder. The binder on the aggregate is harder than new binder, because it has aged in service.
How RAP is made
The old pavement is removed by milling or by full-depth removal. The material is then crushed, screened, conveyed and stacked. Properly processed RAP is well-graded aggregate coated with asphalt binder.
How RAP is reused
In new asphalt mixtures, RAP replaces part of the virgin aggregate and part of the virgin binder. FHWA states that a RAP content of 15 percent or less needs no change in binder grade or mix design. A content above 25 percent is high RAP. Such a mixture is stiffer, and the designer may use a lower binder grade or a blending chart.
RAP is also used in granular base and subbase. The FAA subbase specification (Item P-154) lists it as an option. Item P-207 covers in-place full depth reclamation, which produces a recycled asphalt aggregate base course.
RAP in FAA airport specifications
AC 150/5370-10H, dated 12/21/2018, treats RAP in hot mix asphalt as an option that the engineer can turn off. In Items P-401 and P-403, the rules are:
- RAP is for shoulder surface course mixes and for intermediate courses only.
- From 0 to 20 percent RAP, the virgin binder does not change. From more than 20 to 30 percent, the binder is one grade softer.
- RAP that contains coal tar is not allowed. Recycled asphalt shingles are not allowed.
- The maximum RAP size is 1 in (25 mm) in P-401 and 1-1/2 in (38 mm) in P-403.
The engineer’s note in P-401 says RAP should not be used for surface mixes, except on shoulders, and limits the amount to 30 percent.
Frequently Asked Questions
- Can RAP be used in an airport runway surface course?
- Not under the FAA standard specification. AC 150/5370-10H allows RAP in P-401 and P-403 only for shoulder surface course mixes and for intermediate courses. Both items also let the engineer prohibit RAP in a project.
- What is high-RAP asphalt?
- High RAP is a RAP content above 25 percent of the mixture, and it may exceed 50 percent. FHWA notes that such mixtures become stiffer and may need a lower binder grade or a blending chart.
- Does RAP change the binder grade of the new mixture?
- It can. For P-401 and P-403, the FAA specifies no change in the virgin binder from 0 to 20 percent RAP. From more than 20 up to 30 percent RAP, it specifies a binder one grade softer.
References
- faa-ac-150-5370-10h
- AC 150/5370-10H, Standard Specifications for Construction of Airports FAA
- fhwa-rd-97-148-rap
- User Guidelines for Waste and Byproduct Materials in Pavement Construction (FHWA-RD-97-148): Reclaimed Asphalt Pavement FHWA
- fhwa-rap-page
- Reclaimed Asphalt Pavement FHWA, Pavement Recycling
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