Asphalt surface seals are defined herein as slurry seals, micro-surfacings,and chip seals (seal coats). The objective of this study is toestimate, by laboratory testing, the relative aging abatementeffects of surface seals on the upper 13 mm of an asphalt pavement.

A surface seal can retard oxidative hardening of an underlyingasphalt concrete layer by 0 to 2 years, depending on the situation.However, most of the oxidative aging in the upper stratum of anasphalt concrete pavement occurs during the first 4 years afterconstruction. Therefore, in order for a surface seal to significantlydelay oxidative hardening of the underlying pavement, it mustbe placed during the first two years (approximately) of the pavement'slife. Ultraviolet (actinic) light penetrates asphalt cement onlya few microns and, therefore, does not contribute materially tohardening of the uppermost 13 mm of an asphalt concrete pavement.For practical purposes, these three surface seals will protectthe top 13 mm of an underlying pavement from oxidation as if theywere impermeable to air and water.