Use of Expanded Polystyrene in Slab-on-Grade Concrete Foundation Systems for Thermal Insulation and Settlement Reduction

Integration of lightweight concrete in foundation design, coupled with advancements in energy efficiency, is gaining traction in the pursuit of net-zero homes. Approximately 55% of the annual energy bill of a US household is due to space heating and cooling purposes. While there have been significant studies on insulating the superstructure, limited studies have been done on insulating the foundation system. Expanded polystyrene (EPS) geofoams are lightweight, rigid foam materials with a closed-cell structure that exhibit low moisture absorption and high thermal insulation properties. Their high strength-to-weight ratio, along with features like impermeability, hydrophobicity, and insulation capabilities, make them a suitable option for providing structural support, i.e., foundations. Therefore, this study was conducted to explore the innovative use of EPS geofoam in concrete foundations, focusing on its potential to enhance thermal insulation and reduce settlement. Large-scale laboratory tests were conducted to evaluate the performance of two slabs (0.3 m × 0.3 m × 0.1 m), one controlled and one lightweight concrete where 50% of coarse aggregates by volume were replaced with EPS geofoam aggregates. The insulation tests were performed inside a temperature-controlled environmental chamber, and the temperature profile within the test setup was measured using thermocouple probes. Furthermore, the settlement tests were conducted using the large-scale box, where deformation sensors and LVDTs were used within the setup to study the load-deformation characteristics of the foundation system. The test results show that the inclusion of EPS aggregates in the foundation systems potentially reduces the heat transfer between the foundation and the soil/air interfaces and also the settlement of the soils underneath. These results show preliminary evidence that using EPS geofoam in a foundation system could contribute to an energy-efficient foundation with improved structural integrity. Utilizing EPS in the foundation system addresses settlement challenges while reducing the need for extensive ground improvement.