Performance evaluation of unsurfaced pavements using the UIUC Accelerated Transportation Loading Assembly

Over 1.6 million miles of roads in the United States (US) are unpaved. In under-developed and developing countries, unpaved roads or unsurfaced pavements account for an even larger share in the total number of road miles. The absence of bound surface layers in these pavements results in direct application of traffic loads to the aggregate layer. Most methods used for thickness design of unsurfaced pavements are based on subgrade strength as the primary design consideration without giving much consideration to aggregate material quality. This paper presents findings from a recently completed research study at the University of Illinois aimed at investigating the effects of aggregate type and quality on unsurfaced pavement performance. Five full-scale unsurfaced pavement test sections were constructed at different combinations of aggregate quality and subgrade strength, and were tested to failure using the University of Illinois AcceleratedTransportation Loading Assembly (ATLAS). Pavement performance was monitored through surface profile measurements as well as transverse scanning using Ground Penetrating Radar (GPR). The use of different field modulus measurement techniques was also pursued for identifying anomalies in construction conditions, and for justifying observed trends in test section performance. The performance of two different test "cells" constructed using uncrushed gravel with high fines and crushed limestone with low fines, respectively, were quite different.