Aggregate Properties Affecting Shear Strength and Permanent Deformation Characteristics of Unbound–Base Course Materials
Publication: Journal of Materials in Civil Engineering
Volume 32, Issue 1
Abstract
Resistance to permanent deformation is the primary performance indicator of unbound aggregate pavement layers. In relation to the applied wheel-load deviator stress, the shear strength property of a confined base/subbase controls the rate of permanent strain accumulation in that aggregate layer. The objective of this study was to quantify the impact of aggregate properties on the shear strength and permanent deformation characteristics of unbound aggregates. Sixteen different aggregates were studied in the laboratory for two different gradations: original quarry source and engineered midrange gradations. Aggregate specimens were prepared at these gradations to determine moisture-density relationships, and conduct monotonic and repeated load triaxial tests at the target maximum dry densities and optimal moisture contents. In addition, imaging-based aggregate particle shapes or morphological indices were obtained. The laboratory findings indicated that the particle size corresponded to 60% passing, and imaging-based angularity index contributed significantly to the increases in the shear strength properties of aggregates, which were also affected by density and moisture content. Permanent strain accumulations were primarily influenced by applied shear stress in relation to the shear strength of aggregates, and rutting model parameters obtained through regression analyses were influenced by applied stress, strength, and material properties. Further, an aggregate with plastic fines showed the highest permanent strain accumulation, hence clearly indicating the significant influence of plasticity of fines on the permanent strain accumulation.
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Acknowledgments
This research study was supported by the North Carolina Department of Transportation (NCDOT) and conducted at the Illinois Center for Transportation (ICT) at the University of Illinois at Urbana-Champaign. The authors would like to thank Judith Corley-Lay and Clark Morrison with the NCDOT for providing the research support and guidance, the ICT research engineers and graduate students for their laboratory assistance, and the NC aggregate producers for providing the aggregates used in the laboratory study. Finally, many thanks to Liang Chern Chow for conducting the laboratory tests on aggregates at the engineered gradation.
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Published In
Journal of Materials in Civil Engineering
Volume 32 • Issue 1 • January 2020
Copyright
©2019 American Society of Civil Engineers.
History
Received: Feb 5, 2019
Accepted: Jul 1, 2019
Published online: Oct 31, 2019
Published in print: Jan 1, 2020
Discussion open until: Mar 31, 2020
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