In early January of 1999, approximately 15 miles ofl-75 in Scott County began to rapidly deteriorate. The existing pavement exhibited several potholes and delaminations. The worst section of deterioration fell approximately between milepoints 125 and 133.

In the latter part of January, the condition of the highway had declined to the point thatcorrective action was necessary. The worst sections were milled and patched with hotmixasphalt (HMA). Despite this temporary improvement to the pavement condition, adesire developed within the Department to investigate the cause of the deterioration inorder to prevent a future similar occurrence.

Therefore, personnel from the Division of Materials and the Kentucky Transportation Center conducted an abbreviated investigation of the deteriorating pavement and theasphalt mixtures involved. The findings from this investigation, including analyses of thehistorical data for these mixtures and testing of the in-place pavement, revealed severalpossibilities for the premature pavement failure.

These possibilities included questionable quality of the aggregates in the mixtures, lowasphalt contents and high dust contents, poor volumetric properties of the mixtures, andlow in-place densities and high permeability of the existing pavement. It was concludedthat no single deficiency caused the failure, but rather, a combination of several factors.

A companion section of I-7 5 immediately south of the deteriorated Scott County portions,constructed about one year prior to the pavement presently in question, continues toperform well. Investigation of this pavement and the involved asphalt mixtures revealedhigher asphalt contents, better volumetric properties, higher in-place densities, and lowerpermeability.

It is believed that recent revisions to the applicable asphalt mixture specifications have allbut eliminated the possibility of the recurrence of this type of failure. Mixtures designedcurrently under the Superpave system undergo greater scrutiny and must satisfy tougherspecifications. Also, asphalt mixtures are accepted differently today than when thispavement was originally constructed. It is highly unlikely that the mixtures that arecurrently deteriorating on I-75 could satisfy today's specifications.

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The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, nor the Kentucky Transportation Cabinet. This report does not constitute a standard, specification, or regulation. The inclusion of manufacturer names and trade names are for identification purposes and are not to be considered as endorsements.