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Short answer
Recycled asphalt pavement, usually called reclaimed asphalt pavement (RAP), is old asphalt pavement that has been removed during resurfacing, rehabilitation or reconstruction and processed so its asphalt binder and aggregate can be used again. The Federal Highway Administration (FHWA) treats the share of RAP in a new mix as the key variable: at 15% or less, no change to binder grade or mixture design is required; above 25%, the mix needs closer laboratory attention.
Definition and scope
FHWA defines RAP as existing asphalt pavement that is removed and processed, and that contains valuable asphalt binder and aggregate (FHWA-HRT-11-021, Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice, April 2011). Both words appear in practice: FHWA documents say “reclaimed”, while industry and general-audience pages often say “recycled”. They refer to the same material when the topic is RAP.
How RAP is used in practice
According to FHWA, RAP is used as a substitute for aggregate and virgin binder in recycled asphalt paving, and also as granular base or subbase, stabilized base aggregate, and embankment or fill. For granular base, the FHWA user guidelines describe RAP as recovered, crushed, screened and blended with conventional aggregates. For hot mix asphalt, it must be processed into granular material first.
FHWA states that RAP is most economical in intermediate and surface layers, because the binder it carries replaces costly virgin binder. The same report notes that materials make up roughly 70% of hot mix asphalt production cost and that binder is the most expensive and most variable material, which is why binder replacement drives the interest in RAP.
The RAP content ladder: what changes as the percentage rises
The table below restates FHWA statements only. It is a reading aid, not a mix-design procedure.
| RAP share of mix | What FHWA says |
|---|---|
| Up to 15% | “No change is required in the binder PG or in the mixture design” (FHWA RAP page, updated 10/30/2020). Before the late 1990s, RAP was typically below 15%, with no binder grade change or extra tests needed (FHWA-HRT-11-021). |
| Above 15% to 25% | No threshold statement on the pages read here. This is the range where agencies and mix designers use their own specifications and the published guidance below. |
| 25% and above (“high RAP”) | FHWA’s RAP page defines high-RAP content as greater than 25% and possibly above 50%; the 2011 report defines high RAP as 25% or more by weight of total mix. Mixture stiffness increases, in some cases significantly; the virgin binder grade may need to be lowered or blending charts used; added stiffness may contribute to low-temperature cracking. |
Note the small difference in wording between the two FHWA sources (greater than 25% versus 25% or more); cite whichever your specification uses.
Why laboratory characterization matters
FHWA-HRT-11-021 explains the historical reason RAP use was limited. The Superpave mix design system of the late 1990s had no guidance for RAP, and high fines in RAP stockpiles affected voids in mineral aggregate (VMA) and the dust-to-effective-binder ratio, which limited how much RAP could be used. Interim guidelines from the FHWA Superpave Mixtures Expert Task Group were verified under NCHRP Project 9-12 (see NCHRP Research Results Digest 253 and the NCHRP technician’s manual). Later work on high-RAP mix design appears under NCHRP 9-46, and NAPA Quality Improvement Series 124 covers designing mixtures with high RAP content.
FHWA also flags an unresolved point: uncertainty about how virgin binder and RAP binder interact during plant mixing. Practically, this is why labs working with RAP look at the following, each traceable to the FHWA statements above:
- Stockpile fines: they affect VMA and the dust-to-effective-binder ratio.
- Binder grade: whether the virgin binder PG needs to be lowered, or blending charts applied, as RAP content rises.
- Stiffness and low-temperature cracking: the main performance concern raised for higher RAP content in cold climates.
- Binder blending: the degree to which RAP binder and virgin binder mix is not fully settled.
Test methods for aggregate gradation, such as sieve analysis under ASTM D6913, address soils rather than RAP specifically; use the ASTM or AASHTO method your agency specification names for RAP stockpiles. Standards can be searched through ASTM Compass.
Where it matters for labs and materials programs
For a materials laboratory, the practical question is whether a given RAP percentage stays within the “no change” zone or moves into high-RAP territory. FHWA’s guidance gives a clear split: at 15% or less the binder grade and mixture design stay as for virgin mixes, while above 25% the design must account for stiffer blended binder. The FHWA RAP User Guidelines (hot recycling, granular base, embankment or fill) and NAPA QIS 124 are the starting references named by FHWA. For an overview of the wider field, see what civil engineering is, and for lab habits that apply to any materials work, basics of laboratory work.
Common misunderstandings
- “RAP is just crushed old asphalt.” FHWA stresses that its value lies in the binder as well as the aggregate.
- “Any RAP percentage works the same.” FHWA separates the no-change range (15% or less) from high-RAP mixes, which behave differently.
- “RAP only goes back into asphalt.” FHWA lists granular base, subbase, stabilized base and embankment or fill as further uses.
- “Reclaimed and recycled are different materials.” In this context the terms are used interchangeably; FHWA prefers “reclaimed”.
FAQ
What is recycled asphalt pavement?
Asphalt pavement removed during resurfacing, rehabilitation or reconstruction and processed so its binder and aggregate can be reused (FHWA-HRT-11-021).
What counts as high-RAP content?
FHWA’s RAP page says greater than 25%, possibly above 50%; its 2011 report says 25% or more of total mix weight.
Does a low RAP percentage need a different binder?
At 15% RAP or less, FHWA states no change is required in the binder PG or the mixture design.
Sources
- FHWA, Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice, FHWA-HRT-11-021, April 2011: fhwa.dot.gov (read 2026-11-08).
- FHWA, Reclaimed Asphalt Pavement (page updated 10/30/2020): fhwa.dot.gov/pavement/recycling/rap (read 2026-11-08).
