Strength-Deformation Characteristics of Two Different Foamed Glass Aggregates under a Static Design Load

Foamed glass aggregates (FGAs) are an emerging material in the US for use as a lightweight structural backfill. Manufactured from recycled glass powder mixed with a foaming agent, FGAs are considered a sustainable solution with advantageous engineering properties noted throughout the literature. For load-bearing applications, their long-term deformation behavior under typical, in-service static design loads is not as well understood, nor is its impact on shear strength. To address this gap in knowledge, the Federal Highway Administration conducted long-term (28-day) compression and direct shear tests on two different FGAs: one manufactured through a wet foaming process (FGA-1) and the other through a dry process (FGA-2). The compression tests were performed on both compacted and uncompacted specimens under 82.7 kPa of applied pressure in a large-scale direct shear (LSDS) device used as a consolidometer; both dry and submerged conditions were evaluated for the compacted specimens. LSDS tests were then conducted immediately after the 28-day compression, as well as after a short consolidation phase. The experimental program also included sieve analysis, relative density, absorption, and aggregate imaging. To serve as a basis for comparison, a conventional backfill, classified as a No. 8 stone, was similarly tested. The findings showed that the physical properties and deformation characteristics of the two FGAs were not the same, with FGA-1 experiencing significantly more vertical strain than FGA-2, which behaved similarly to the No. 8 backfill. All materials exhibited comparable peak shear strengths; however, the FGAs exhibited more ductile behavior. In addition, the changes in the gradation and shape characteristics after each test are presented. The particle size and brittleness of FGAs presented challenges when strictly applying and interpreting standard test procedures developed for soils, which are discussed as well. The overall results suggest that FGAs are a unique but viable substitute for sustainable geotechnical applications.