Comparative Physical and Mechanical Characterization of Lightweight Porous Materials: Bulk Density as Indicator of Mechanical Properties

Lightweight porous materials are widely used in construction due to their low density and favorable thermal insulation properties; however, their mechanical performance depends on factors extending beyond bulk density alone. The aim of this study was to perform a comprehensive physical and mechanical characterization of three representative lightweight porous materials belonging to different material classes: autoclaved aerated concrete (AAC), foamed concrete, and rigid polyurethane foam, within a common experimental and analytical framework. The investigation included the determination of particle density, bulk density, porosity, unconfined compressive strength (UCS), Young’s modulus, and shear strength parameters obtained from triaxial compression tests. In addition, correlations between bulk density and selected mechanical properties were analyzed for each material. The mean bulk density, porosity, and UCS values were 566 kg/m3, 73%, and 5.24 MPa for AAC; 518 kg/m3, 77%, and 0.88 MPa for foamed concrete; and 82 kg/m3, 93%, and 0.52 MPa for rigid polyurethane foam, respectively. Despite similar bulk densities, AAC and foamed concrete differed by approximately sixfold in UCS, eightfold in Young’s modulus, and sixfold in cohesion. Correlation analyses further showed that the density–property relationships were material-specific. The findings indicate that bulk density alone is not a universal predictor of the mechanical behavior of different classes of lightweight porous materials. A comprehensive characterization combining physical and mechanical properties is therefore required for reliable material evaluation and comparison.