Field performance evaluations of large sized unconventional and recycled aggregates for subgrade improvement

Illinois Department of Transportation has recently introduced new gradation bands to accommodate large sized unconventional and recycled materials in subgrade remedial applications. Existing standardized test protocols cannot characterize these materials properly. To this end, an accelerated pavement testing study was undertaken to evaluate rutting performance trends of pavements constructed with such aggregate materials. An advanced field image segmentation technique was implemented for the in situ characterization of aggregate size and morphological properties, i.e. shape, texture and angularity, texture. Four pavement working platform test sections were constructed with railway ballast or riprap sized virgin aggregates as well as large-sized concrete demolition waste capped with densely graded dolomite and reclaimed asphalt pavement (RAP) materials. Construction quality control was achieved through nuclear gauge density checks and modulus measurements, the latter utilizing lightweight deflectometer and soil stiffness gauge. Next, the full scale test sections constructed over weak engineered subgrades were tested with unidirectional wheel loading in accelerated pavement testing. Periodic rut measurements were taken to quantify the rutting progression. Contributions of the subsurface layers to surface rut accumulation were assessed by the use of the following field equipment: Variable energy lightweight penetrometer, ground penetrating radar (GPR), and geo-endoscopic probe for visualization of layer compositions and interfaces. Despite higher modulus properties obtained, RAP capped sections typically accumulated higher permanent deformation. Geo-endoscopic imaging revealed that presence of shallow water table led to early failure in one of the test sections. According to the study results, current Illinois subgrade stability design framework was found to be adequate for utilizing large sized unconventional and recycled materials in subgrade remedial applications.