ASPHALT OVERLAY DESIGN

A PREDICTED $120 MILLION ANNUAL COST FOR HIGHWAY PAVEMENT AND SHOULDER MAINTENANCE IN THE U.S. BY 1975 POINTS OUT THE NEED FOR ASPHALT CONCRETE OVERLAYS TO BE STRUCTURALLY DESIGNED WITH AS MUCH PRECISION AS POSSIBLE IN ORDER TO MAKE THE MOST EFFICIENT USE OF THE TAX DOLLAR. FOR THIS PURPOSE, THE ASPHALT INSTITUTE HAS PREPARED A DESIGN MANUAL ENTITLED ASPHALT, OVERLAYS, AND PAVEMENT REHABILITATION. THE MANUAL DESCRIBES TWO METHODS FOR DETERMINING THE THICKNESS REQUIREMENTS OF AN ASPHALT CONCRETE OVERLAY. THE COMPONENT ANALYSIS METHOD REQUIRES AN EVALUATION OF THE EXISTING PAVEMENT TO COMPARE WITH A NEW FULL-DEPTH ASPHALT PAVEMENT DESIGN. THE SECOND METHOD REQUIRES AN ANALYSIS OF PAVEMENT DEFLECTION AND IS PARTIALLY BASED ON ELASTIC-LAYERED THEORY. BOTH METHODS PROVIDE THICKNESSES OF ASPHALT CONCRETE DIRECTLY AND ARE BASED ON FIELD OBSERVATIONS AND ENGINEERING EXPERIENCE. THIS REPORT DESCRIBES THE NEW TECHNOLOGY RELATED TO EACH METHOD. /AUTHOR/