Free draining base materials properties.

PDFTech ReportFHWA-OR-RD-92-11HPR 5283DrainagePavement designOpen graded aggregatesModulus of resilienceAsphalt based materialsOregonOregon. Dept. of Transportation. Research UnitZhou, HaipingMoore, LucindaHuddleston, JimGower, JeffOregon. Dept. of Transportation. Research UnitOregon. Department of Transportation. Materials and Research SectionUS Transportation CollectionThe importance of providing a positive drainage system and removing free water from pavement structures has long been recognized. Inadequate drainage of the pavement structures has been identified as one of the primary causes of pavement distress. In the last few years, Oregon has started designing and constructing permeable bases in both flexible and rigid pavements. Two types of permeable bases have been used: one is asphalt treated permeable material (ATPM) base and the other is open-graded aggregate base. The desirable characteristics (permeability and resilient modulus) of both materials have not been determined. In addition, construction with the existing open-graded aggregate gradation revealed that the material was less stable and would ravel easily under construction traffic. Because of this ravelling, compaction was poor, the grade was difficult to control, and the open graded aggregate materials did not provide a suitable surface for paving. This project established the desirable materials properties (permeability and resilient modulus) for the two types of free-draining base materials and establishes a more stable gradation for the open-graded aggregate base. Appropriate layer and drainage coefficients for use in the AASHTO design of permeable base sections are also determined. For comparison, a dense-graded aggregate material is also investigated. This project consisted primarily of a laboratory investigation. Pavement cores of the asphalt treated permeable base and samples of aggregate materials were tested in the laboratory for permeability and resilient modulus. The permeability was determined using both constant and falling head test procedures. The laboratory study indicated that the current Oregon ATPM has a sufficient drainage capability and the resilient modulus of this material is typical of other states' findings. A modified open-graded aggregate gradation is proposed. The proposed aggregate gradation has a higher permeability and a higher resilient modulus than the existing gradation. Recommendations for implementation include selection of layer and drainage coefficients for pavement structural design and use of the proposed open-graded aggregate gradation in pavement construction