National Concrete Pavement Technology Center

Project description

For years, geosynthetics have been placed at the interface between the granular base course and the weak subgrade of pavement sections to provide stabilization. Geosynthetics may provide physical stabilization (i.e., separation), mechanical stabilization (lateral restraint), and reinforcement (tensioned membrane effect). For pavement design, allowable deformation is typically limited to 13 mm or less, so only separation and lateral restraint are mobilized in the pavement section. Although geosynthetics provide marked improvements in soil stabilization and pavement performance, a single approach to account for these improvements by separation and lateral restraint has not been well established. Various geosynthetics allow for different design considerations in varying climatic and load-intensity situations. This study focuses on geogrids but uses non-stabilized sections as control sections. Products were selected from a state department of transportation pre-approved materials list in order to remove bias in selection and to mimic the potential selection process in practice. Geosynthetics were installed at the interface of 250 mm of vibratory-compacted granular base course and weak subgrade in large-scale box tests. Cyclic loading was applied at eleven load intensities or until 25 mm maximum deformation was achieved. Permanent displacement at the surface of the base course and interface pressure beneath the geosynthetic (at the top of the subgrade) were recorded. Stress distribution angle and stress patterns at the bottom of the base course were observed. This paper discusses the effects of geogrid as a means of stabilization in terms of interface stress reduction as well as the ratio of permanent to resilient deformation. In this study, replacement of virgin aggregate with recycled concrete aggregate reduced the interface stress by 55%; addition of geogrid to both sections further reduced measured interface stresses. Addition of geogrid effected greater permanent deformation but a smaller incremental deformation in both VGB and RCA. The implications for pavement performance are also discussed.