United States Department of Transportation
i
Field performance evaluations of Illinois aggregates for subgrade replacement and subbase : phase II.
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2013-04-01
[PDF-9.11 MB]
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Abstract:The project objective was to validate the results from ICT Project R27-1, which characterized in the
laboratory the strength, stiffness, and deformation behaviors of three different aggregate types
commonly used in Illinois for subgrade replacement and subbase applications, through accelerated
loading of full-scale pavement working platform test sections. Six different test “cells” were constructed at
different combinations of aggregate material quality and subgrade strength, and were tested to failure
using the University of Illinois Accelerated Transportation Loading Assembly (ATLAS). Each cell was
tested along two different wheel paths representing two different aggregate layer moisture contents
(Cells 1-5), or geotextile reinforcement conditions (Cell 6). Performances under loading were monitored
through surface profile measurements as well as transverse scanning with ground-penetrating radar
(GPR). Field and laboratory test results highlighted the importance of considering aggregate quality in
the thickness design of aggregate layers for construction platforms. Thick layers of uncrushed gravel
placed over a weak subgrade mainly underwent internal shear failure due to excessive movement of the
aggregate particles. Crushed aggregate layers constructed with high relative compaction, on the other
hand, showed significantly higher resistance to internal shear deformation and permanent deformation
accumulations. Prolonged exposure to moisture and freeze-thaw effects was found to be beneficial for a
crushed dolomite material with high amounts of nonplastic fines probably due to carbonate cementation
within the fine fraction. Failure of test sections under flooded conditions was primarily caused by
excessive deformation in the subgrade layer. Recommendations were made based on the study findings
for improved material selection and thickness designs of aggregate working platforms.
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