Asphalt Cement: Asphalt shall meet the specified requirements. For SM-4.75 mixes, a PG64-22 or similar is typically used. For bonded wearing courses or other specialty applications, a harder pen polymer modified asphalt may be specifed. Asphalt grade may very depending on environmental and traffic considerations.
Aggregate: Use high quality aggregates that meet the specified gradation and other testing requirements. The aggregate shall have a sand equivalency of 45 or greater and meet the required polish (skid) values.
RAP: Reclaimed Asphalt Pavement may be used in ultra thin lift applications. Limit use of RAP to no greater than 20% of the mix.
Tack Coat: Use tack coat from an approved source as specified. Tack coat may be a CRS, CSS or specialty formulation depending on the type of ultra thin lift application. Tack coat is typically applied at a rate of .1 to .15 gallons per Square Yard. Higher application rates are necessary for bonded wearing course.
Because the overlay is thin, the interface between the old and new pavement is in close proximity to the shear forces created by vehicles during braking and turning movements. As a result, the tack coat is extremely important to the long term success of ultra thin lift asphalt. The tack coat creates a bond between the new surface and the old pavement.