Experimental Study on the Dynamic and Static Mechanical Properties of Polyurea-Coated Foam Concrete

• Polyurea can compensate for the insufficient strength of foam concrete, and enhance its energy absorption capacity. • Under dynamic compression, foam concrete exhibits a plateau stage with plastic-like behavior; however, a "stress rebound" response is observed after polyurea coating. • Polyurea can inhibit crack propagation, increase the deformation resistance of foam concrete, and improve toughness and energy absorption performance. To investigate the influence of polyurea coating thickness and application location on the impact resistance of foam concrete, polyurea was applied to the surface of foam concrete specimens. Quasi-static uniaxial compression tests and Split Hopkinson Pressure Bar (SHPB) impact tests were conducted on the coated specimens, and the deformation field was measured using Digital Image Correlation (DIC). The results indicate that under static compression, both plain foam concrete and its polyurea-coated counterparts exhibit four distinct stages: elastic, plastic, post-yield failure, and densification. Under dynamic compression, a stress plateau stage is observed in plain foam concrete; however, the plateau changes to a "stress rebound" phenomenon after polyurea coating. Dynamic impact toughness analysis reveals that polyurea significantly enhances the toughness of foam concrete, with the most pronounced improvement observed in double-sided specimens coating with 3 mm polyurea. Polyurea improves the deformation resistance of foam concrete and delays the time to reach peak stress, and the delay is proportional to the coating thickness. DIC observations demonstrate that the polyurea coating alters the failure mode of foam concrete and effectively suppresses crack propagation. Energy dissipation analysis indicates that the polyurea coating increases the energy dissipation coefficient, which is positively correlated with the coating thickness. Double-sided coating demonstrates superior energy absorption performance compared to single-sided coating. In summary, polyurea shows strong potential for improving the toughness and energy absorption capacity of foam concrete, while also providing effective protection. These findings offer valuable insights for the further development and optimization of sustainable construction materials. The experimental program was structured as follows. A cement paste was first prepared by mixing cement and water. Subsequently, stable, pre-formed foam generated by mechanical foaming of the foaming agent was incorporated into the paste and was mixed thoroughly at a low speed to ensure homogeneity. The fresh mixture was cast into molds and then was demolded after setting. All specimens were subsequently cured under standard ambient conditions for 28 days. After curing, the specimens were cut and machined to the required dimensions for testing. Following specimen preparation, polyurea was mechanically sprayed onto the surfaces of the designated specimens according to the experimental design parameters, thereby forming the final composite test pieces. The prepared specimens, both plain and coated, were then subjected to a systematic testing regime comprising static loading and dynamic impact tests conducted in conjunction with Digital Image Correlation (DIC) for deformation measurement. The resultant data were analyzed to elucidate the mechanical characteristics and failure behavior under load. The specific experimental sequence and analytical methodology are detailed in the accompanying flowchart 1.