LONG-TERM DEFLECTION STUDY OF AN EXCEPTIONALLY MAINTENANCE- FREE PAVEMENT

REPORTED IS AN ANALYSIS OF PAVEMENT DEFLECTION MEASUREMENTS TAKEN OVER A TEN YEAR PERIOD ON AN EIGHTEEN YEAR OLD PAVEMENT. MEASUREMENTS WERE BEGUN IN 1955 AFTER EIGHT YEARS OF EXCEPTIONALLY MAINTENANCE FREE PAVEMENT SERVICE AND HAVE CONTINUED THROUGH 1965. THE PAVEMENT STUDIED IS A 16.8 MILE LENGTH OF A MAJOR EAST-WEST TWO LANE HIGHWAY THAT CROSSES THREE PHYSIOGRAPHIC PROVINCES IN MARYLAND. DEFLECTION MEASUREMENTS HAVE BEEN OBTAINED UTILIZING THE BENKELMAN BEAM TECHNIQUE AND AN 11.2 KIP WHEEL LOAD. SPRING AND FALL MEASUREMENTS WERE MADE AT 70 SITES. IN ADDITION, RESULTS OF A PHYSICAL SAMPLING INVESTIGATION OF PAVEMENT LAYERS, BASE AND SUBGRADE AT A NUMBER OF SITES ARE REPORTED AND ANALYZED. AN ANALYSIS OF DATA FOR THIS HIGHWAY REVEALS WITH REASONABLE ASSURANCE THAT PAVEMENT DEFLECTIONS ARE DEPENDENT UPON SUBGRADE SOIL TYPE WHERE PAVEMENT THICKNESS IS NOT A VARIABLE. OUTER WHEEL PATH DEFLECTIONS ARE HIGHER AND MORE DISPERSED THAN INNER WHEEL PATH DEFLECTIONS, AND SPRING DEFLECTIONS ARE HIGHER AND MORE DISPERSED THAN FALL DEFLECTIONS FOR THE SAME WHEEL PATH. ALSO, THE CONTINUOUS GOOD PERFORMANCE OF THE PAVEMENT HAS BEEN THE DIRECT RESULT OF AN ADEQUATE STRUCTURAL SECTION AND A PROTECTED SUBGRADE. IT IS NOTED THAT THE SUBGRADE HAS BEEN PROTECTED BY AN IMPERVIOUS BITUMINOUS CONCRETE PAVEMENT AND GOOD LONGITUDINAL DRAINAGE, AND THAT DISTRESS, WHERE IT HAS OCCURRED, HAS BEEN DUE TO WATER REACHING AND SOFTENING THE SUBGRADE. PHYSICAL TESTING OF PAVEMENT SAMPLES HAS REVEALED NON-AGING OF THE ASPHALT CEMENT AND CONTINUED VIABILITY OF THE BITUMINOUS CONCRETE. BOTH ARE ATTRIBUTED TO THE IMPERVIOUS LOW VOID MIXTURE. /AUTHOR/