Plasticity Requirements of Aggregates Used in Pavement Base and Subbase Courses

In pavement unbound aggregate layers, fines content (passing No. 200 sieve size or finer than 0.075 mm) characteristics influence the aggregate matrix strength and the modulus and deformation behavior. A laboratory investigation was conducted to identify the effects of fines content, plasticity index, dust ratio (percent passing No. 200 to No. 40 sieve size), and gradations on the strength and the modulus and deformation characteristics of crushed gravel and limestone aggregates. A series of moisture-density and California Bearing Ratio (CBR) tests were conducted on considered configurations. Furthermore, triaxial strength and resilient modulus tests were conducted on selected samples. A series of guide charts are presented to show the effects of various fines content characteristics on the strength and the modulus and deformation behavior of aggregates. Some of the configurations that are in compliance with existing IDOT specifications provided unacceptable strength values. For example, the use of aggregates with low dust ratio and high fines content resulted in a weak aggregate matrix. In general, the detrimental effect of a high plasticity index is more pronounced on crushed gravels. The findings of this study relates to the IDOT SSRBC Article 1004.04 specification. For any modification to be applied to this specification, it is recommended that these laboratory results be further validated using field or full-scale tests.IDOT-R27-157Ope