Recycled expanded polystyrene foam utilization in 3D-Printed fiber-reinforced concrete

The construction industry is increasingly exploring lightweight materials to reduce structural load and improve sustainability. Expanded polystyrene (EPS) foams have gained attention for their lightweight properties, while their application in 3D-printed concrete remains underexplored. The evaluation of how EPS affects the mechanical performance of 3D-printed concrete is essential since it could lead to innovative lower-density materials that balance weight reduction with structural integrity. This study investigates the mechanical behavior of 3D-printed concrete incorporating EPS foams, focusing on optimizing EPS content for performance. Specimens with EPS substitution ratios of 0%, 10%, 20%, and 30% were prepared for both cast and 3D-printed formats, with densities ranging from 2138 to 2080 kg/m 3 . Mechanical testing revealed that EPS-printed samples exhibited significant improvements in flexural strength, increasing from 0.1 MPa to 2.48 MPa, while experiencing a reduction in compressive strength by 8.58% to 36.52%. A 20% EPS substitution ratio provided a favorable balance, maintaining comparable compressive strength to mold-cast specimens and achieving minimal anisotropy (0.038). Microstructural analysis using scanning electron microscopy (SEM) and computed tomography (CT) were conducted to assess the internal microstructure and foam distribution. This highlighted the refined cellular structures and localized cement infiltration as key contributors to the observed mechanical properties. In addition, environmental impact indicators such as acidification potential (AP) and global warming potential (GWP) demonstrated a 6-8% reduction in comprehensive environmental impact at 20 wt% EPS foam incorporation. These findings demonstrate that incorporating EPS foams into 3D-printed concrete yields lower-density, mechanically sound materials, which could promote sustainable construction and enhance efficiency and versatility in modern building practices.