Evaluating Constructed Aggregate Layers of Working Platforms and Flexible Pavements: Adequacy of In-Place Quality Control and Quality Assurance Techniques

Quality assurance is extremely important for satisfactory end performance of a constructed pavement. Traditional quality control and quality assurance (QC/QA) procedures based on volumetric and surface property checks are becoming outdated when used for constructing pavement foundation layers and ensuring pavement longevity. Recent emphasis in QC/QA procedures has shifted from a density-based approach to stiffness- and strength-based approaches with newly adopted advanced technologies. However, the need for QC/QA is often overlooked in the construction of low-volume roads with unbound aggregate layers, which may be built with recycled or out-of-specification materials of marginal quality: both are currently common sustainable practices. This paper summarizes key findings from QC/QA tests performed on full-scale pavement test sections in a recent research study conducted by the Illinois Center for Transportation. The focus of the tests was the validation of material specifications that the Illinois Department of Transportation has recently adopted for large-size unconventional aggregates, known as aggregate subgrade, through accelerated pavement testing. Seven representative aggregate types were used to construct test sections with aggregate subgrade and virgin and recycled capping and subbase layers. Density measurements from a nuclear gauge were collected and routinely contrasted with modulus results from the lightweight deflectometer and soil stiffness gauge (GeoGauge) from the constructed layers. Further, forensic strength assessment was carried out by dynamic cone penetrometer and a variable energy PANDA penetration device. Geoendoscopic imaging, coring, and trenching were also conducted to identify the depth of the water table and the thickness of the as-constructed layer. The PANDA penetrometer results, in conjunction with geoendoscopy, proved to be effective in correlating rutting performances to QC/QA test results.