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Pavement base layer quality is vital for long term performance. Low stiffness and shear strength can result in loss of support and increased tensile stresses under loads. To maintain uniform support under concrete pavements and ensure satisfactory performance, a stable, non-erodible, drainable base layer is necessary. The primary objective of this report is to quantify the aggregate base properties required for concrete pavement foundations in accordance with currently established layer thickness requirements. The effects of properties of different base layers on concrete pavement performance were evaluated, based on an the mechanical and hydraulic properties of typical base materials collected from previous MnDOT studies and relevant literature. Field measured environmental data from the MnROAD test facility was collected and used for calibration purposes. The effects of environmental conditions on long-term concrete pavement performance were evaluated accordingly. Data from the LTPP SPS-2 study and MnROAD test cells were analyzed to evaluate the effects of design and site factors on performance. Improved aggregate classes were established, considering gradation, aggregate shape properties and drainage characteristics. Field test data were analyzed to assess the effectiveness of open-graded aggregate bases in providing structural stability. The analytical gradation analysis and the discrete element modeling approach for engineering aggregate shape and gradation were used to predict field performance. The findings from the study were synthesized to recommend revisions for performance-related specifications for aggregate bases supporting concrete pavements. The results would ideally help design cost effective base types and thicknesses suitable for both concrete and asphalt pavements.

Aggregate base materials are becoming increasingly expensive in many parts of Minnesota because gravel mines and rock quarries are being lost to other land uses. These aggregate materials are classified for use and placed in quantities based on design procedures and testing techniques that are several decades old. To optimize material use and reduce waste, new mechanistic-based design procedures and testing techniques need to be implemented to achieve better value during road construction. This research study is aimed at evaluating pavement base/subbase performances of locally available aggregate materials (with gradations still falling within the MnDOT specified gradation bands) in Minnesota through mechanistic pavement analysis and design. The main objective of this study is to demonstrate that locally available aggregate materials can be economically efficient in the implementation of the available mechanisticbased design procedures in Minnesota through the MnPAVE mechanistic-empirical flexible pavement design method. The goal is to develop the components of a new granular material best value software module to be added to the MnPAVE program. This report summarizes the detailed research findings from which the following conclusions can be drawn: (1) locally available aggregate materials with varying levels of quality can still properly serve traffic-level and environment-related loading from a mechanistic-empirical pavement design perspective provided that important aggregate properties, such as gradation and particle shape, are optimized; (2) potential shear failure in base and especially subbase need to be properly addressed as non-unique modulus-strength relationships were observed; and (3) the proper use of local materials can be quite cost-effective.