Do not mix RAP in what?

Do not mix RAP in what?

• A. The uppermost 12 inches
• B. The top 6 inches
• C. The subgrade layer
• D. The middle 6 inches

Answer: (A)

RAP (reclaimed asphalt pavement) contains aged, stiff binder. Mixing it into the surface layer—the uppermost portion of the pavement that bears the load and is exposed to weather—can make the wearing surface harder to compact, less flexible, and more prone to cracking, stripping, and reduced ride quality. The surface needs a fresh, properly graded mix with adequate bonding and workability, so we avoid adding RAP into the top 12 inches where performance is most sensitive. In contrast, RAP can be used in other layers where its properties are less likely to compromise surface performance, such as in lower structural courses, but it’s not appropriate for the uppermost 12 inches. The subgrade layer isn’t a place for asphalt mixes at all, so mixing RAP there doesn’t fit the intended use of RAP in pavement construction.

RAP (reclaimed asphalt pavement) contains aged, stiff binder. Mixing it into the surface layer—the uppermost portion of the pavement that bears the load and is exposed to weather—can make the wearing surface harder to compact, less flexible, and more prone to cracking, stripping, and reduced ride quality. The surface needs a fresh, properly graded mix with adequate bonding and workability, so we avoid adding RAP into the top 12 inches where performance is most sensitive.

In contrast, RAP can be used in other layers where its properties are less likely to compromise surface performance, such as in lower structural courses, but it’s not appropriate for the uppermost 12 inches. The subgrade layer isn’t a place for asphalt mixes at all, so mixing RAP there doesn’t fit the intended use of RAP in pavement construction.