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Xiao, Tutumluer, Qian and Siekmeier 1 1 Gradation Effects Influencing Mechanical Properties of Aggregate Base/Granular Subbase 2 Materials in Minnesota 3 4 Yuanjie Xiao – Graduate Research Assistant 5 Erol Tutumluer – Professor, Paul F. Kent Endowed Faculty Scholar 6 Yu Qian – Graduate Research Assistant 7 University of Illinois at Urbana-Champaign 8 9 John A. Siekmeier – Office of Materials & Road Research, Mn/DOT 10 11 12 13 ABSTRACT 14 15 This paper presents findings from a recent research study aimed at investigating aggregate 16 gradation effects on strength and modulus characteristics of aggregate base/granular subbase 17 materials used in Minnesota. The importance of specifying proper aggregate grading or particle 18 size distribution has long been recognized for achieving satisfactory performance in pavement 19 applications. For constructing dense-graded unbound aggregate base/subbase layers, these are 20 often well-graded gradation bands, established many years ago based on experience of the state 21 transportation agency, which may not have a direct link with mechanical performance. To 22 continually improve specifications for superior performance targeted within the mechanistic-23 empirical pavement analysis and design framework, there is a need to better understand how 24 differences in aggregate gradations may impact unbound aggregate base/subbase behavior for 25 any site-specific design conditions. To accomplish this, aggregates with different gradations and 26 material properties were compiled in a statewide database established from a variety of sources 27 in Minnesota. Analysis results showed non-unique modulus and strength relationships for most 28 aggregate base and especially subbase materials. Further, laboratory resilient modulus and shear 29 strength results were analyzed for critical gradation parameters using common gradation 30 characterization methods. Based on statistical analyses, the most significant correlations were 31 found to exist between a Gravel-to-Sand (G/S) ratio (proposed based on ASTM D2487-11) and 32 aggregate shear strength properties. Aggregate compaction (AASHTO T99) and resilient 33 modulus characteristics could also be linked to G/S ratio identified and further verified using 34 other databases collected from literature. Findings illustrate that the G/S ratio can be used to 35 optimize aggregate gradations for improved base/subbase performances primarily influenced by 36 shear strength. 37 38 39 Key Words: Unbound Aggregate, Gradation, Aggregate Base, Granular Subbase, Flexible 40 Pavement, Gravel-to-Sand Ratio, Shear Strength, Resilient Response. 41 42 43 44 45 TRB 2012 Annual Meeting Paper revised from original submittal.
