Determination of the optimum base characteristics for pavements
In recent years, it has become apparent that the design and maintenance of pavement drainage extends the service life of pavements. Most pavement structures now incorporate subsurface layers, part of whose function is to drain away excess water, which can be extremely deleterious to the life of the pavement. However, aggregate materials for pavement bases must be carefully selected and properly constructed to provide adequate permeability and stability as well. To assure the effectiveness of such drainage layers after they have been spread and compacted, simple, rapid, in-situ permeability and stability testing and end-result specification are needed. This report includes conclusions and recommendations related to four main study objectives: (1) Determine the optimal range for in-place stability and in-place permeability based on Iowa aggregate sources; (2) Evaluate the feasibility of an air permeameter for determining the permeability of open and well-graded drainage layers in-situ; (3) Develop reliable end-result quality control/quality assurance specifications for stability and permeability; (4) Refine aggregate placement and construction methods to optimize uniformity. An Air Permeameter Test (APT) device was developed during this study for rapid measurement of in place permeability of pavement bases. Dynamic Cone Penetrometer (DCP), Clegg Hammer, and GeoGauge vibration tests were performed for in-place stability measurements. Significant spatial variation of most parameters is observed over the final compacted base layer. To achieve the PCC pavement design assumptions and by considering the spatial variability occurring in field, a target CBR of 15% and target permeability of 4 cm/sec and 0.84 cm/sec to achieve 90% and 50% drainage, respectively, is recommended for QC/QA. A strong influence of fines content and aggregate type on strength, stiffness, and permeability is observed. Construction operations are found to contribute to spatial variability in field. Alternate construction procedures and equipment are recommended to minimize this variation.