Lightweight and Alternative Backfills for Highway Applications: State-of-the-Art Practice in the USA

The use of lightweight and alternative materials in geotechnical applications may be advantageous when compared with more conventional structural backfills. This paper focuses on using seven lightweight and alternative backfill materials in highway applications: controlled low-strength materials (CLSM); expanded shale, clay, and slate (ESCS); foamed glass aggregates (FGA); lightweight cellular concrete (LCC); polystyrene geofoams; recycled glass aggregates; and tire-derived aggregates (TDA). The current knowledge and the state-of-the-art practice for using these materials in highway geotechnical applications of interest, that is, retaining walls, bridge abutments, pipes/culverts, embankments, and slope stabilization, were evaluated. The paper first introduces the materials, including the unit weight ranges for each lightweight and alternative fill material, and their applications. Then, the key aspects and advantages of each material for highway geotechnical applications are listed and evaluated. Further, for each material, the physical, chemical, and mechanical material properties are discussed, as well as the design requirements and guidelines, construction and placement guidelines, and the environmental considerations. Finally, the technology-ready aspects of each material studied with regard to its application to highway geotechnical problems, and the identified barriers to the deployment of each one were summarized and discussed. Based on the current knowledge, some lightweight and alternative materials (e.g., ESCS, CLSM, TDA) have been more widely used in the U.S.A. for geotechnical applications, whereas others are still emerging technologies. Further, certain materials (e.g., LCC, TDA, geofoam) have well-developed design guidelines, whereas others (e.g., CLSM, FGA) require more research.