A MODIFICATION OF THE AASHO ROAD TEST SERVICEABILITY INDEX FORMULA

USE OF THE CHLOE PROFILOMETER IN TEXAS INDICATED THAT THIS DEVICE FOR MEASURING ROAD ROUGHNESS TENDS TO RANK PAVEMENTS HAVING A COARSE-TEXTURED SURFACE TOO LOW ON THE SERVICEABILITY SCALE. A HAND-OPERATED DEVICE FOR MEASURING COARSENESS OF TEXTURE WAS DEVELOPED, AND A TERM FOR TEXTURAL ROUGHNESS WAS ADDED TO THE AASHO ROAD TEST FORMULA FOR THE SERVICEABILITY INDEX. THE COEFFICIENT OF THE NEW TERM WAS EVALUATED BY ANALYSIS OF THE SUBJECTIVE RATINGS GIVEN 43 FLEXIBLE PAVEMENTS. THE NEW FORMULA FOR SERVICEABILITY INDEX PREDICTED THE ADJUSTED RATINGS WITH SATISFACTORY ACCURACY AND THE FOLLOWING CONCLUSIONS JUSTIFIED BY THE DATA AND ANALYSIS PRESENTED ARE' /1/ THE LOCAL RATING PANEL SEEMED TO RATE PAVEMENTS AT A SLIGHTLY LOWER LEVEL THAN THE AASHO ROAD TEST RATING PANEL, /2/ THE TEXTUREMETER OR A SIMILAR DEVICE IS A NECESSARY TOOL FOR USE WITH THE CHLOE PROFILOMETER ON COARSE-TEXTURED PAVEMENTS SUCH AS SURFACE TREATMENTS, /3/ THE MODIFIED FORMULA FOR THE SERVICEABILITY INDEX IS BELIEVED TO BE SATISFACTORY FOR THE PURPOSES OF THIS PROJECT AND SHOULD BE USED FOR CALCULATING THE SERVICEABILITY INDEX OF FLEXIBLE PAVEMENTS IN LIEU OF THE ORIGINAL AASHO ROAD TEST FORMULA INASMUCH AS ABOUT ONE-HALF OF THE FLEXIBLE PAVEMENT TEST SECTIONS HAVE A COARSE-TEXTURED SURFACE, AND /4/ THE CHLOE PROFILOMETER IN USE ON THIS PROJECT SHOULD AGAIN BE CORRELATED WITH THE AASHO ROAD TEST PROFILOMETER.