Evaluating Thermal Characteristics of Foam Glass Aggregates as an Insulation Layer in Asphalt Pavements

Cold region pavements experience extreme weather conditions that lead to structural issues like soil freeze-thaw cycles and upheaval. Insulation materials such as extruded polystyrene boards (XPS), foam glass aggregate (FGA), and tire chips (TC) are used to prevent these issues by thermally isolating soil from upper pavement layers. Because of structural limitations of XPS, identifying sustainable alternatives with adequate thermal and mechanical performance is necessary. Effective compaction is critical as materials like TC and FGA are structurally weak and their thermal behavior can be significantly influenced by moisture content. This study examines the thermal characteristics of FGA under varying conditions of temperature, moisture, and compaction. Currently, the thin line source (TLS-100) method has limited laboratory protocols for characterizing FGA. To address this, a heat transfer-based finite element (FE) simulation was developed to estimate necessary sample dimensions and dwell time—the duration required to achieve thermal steady state. Results indicated an eightfold increase in FGA thermal conductivity with rising moisture content, while temperature decrease and compaction increase had minor effects. Sensitivity analysis using a one-at-a-time (OAT) approach highlighted moisture as the dominant factor affecting thermal conductivity, followed by temperature and compaction. A second-order response surface methodology-based model was developed to predict thermal conductivity for specific moisture content and temperature conditions. Statistical analysis indicated minimal interaction between temperature and moisture content above freezing temperatures. Partial substitution of FGA with TC provided more stable compaction compared to increasing moisture content alone.