Optimizing Stability and Stiffness Through Aggregate Base Gradation

Pavement base layer quality is vital for long-term performance. Low stiffness and shear strength can result in a loss of support and increased tensile stresses under loads. To maintain uniform support under concrete pavements and ensure satisfactory performance, a stable, nonerodible, drainable base layer is necessary. The primary objective of this paper is to present the analysis and evaluations conducted as part of the associated research and to recommend improvements to base layer aggregate gradations for the Class 5 and permeable aggregate base specifications used by the Minnesota Department of Transportation. Improved aggregate classes are presented, considering gradation and aggregate shape properties. An analytical gradation analysis was introduced to establish an effective level of gravel-to-sand ratio of 1.4. Other analyses presented in this paper include the use of a revised resilient modulus model that was used in a Monte Carlo simulation to develop probabilities for resilient modulus values depending on gradation and season in Minnesota and the use of the Mechanistic–Empirical Pavement Design Guide for comparing gradation and gravel-to-sand ratio with expected pavement performance. The gravel-to-sand ratio of 1.4 was identified with the following analysis methods: a coordination number and packing analysis, a discrete element model for load-carrying capacity, and a pavement performance analysis using the Mechanistic–Empirical Pavement Design Guide software.