Smart Coating: Explosion Protection for Wall Panels

The "Smart Coating" project investigates an innovative explosion protection coating. In the event of explosions, not only immediate dangers arise from the shock wave itself, but also secondary hazards from ejected debris and fragments. In particular, wall panels made of concrete or masonry exhibit significant fragmentation under high explosive pressure, which can pose a considerable risk to individuals in the vicinity.

To counter these risks, a special coating based on polyurea is being experimentally and numerically analyzed to increase the resilience of the structural elements and reduce fragmentation. The application of these coatings aims to ensure that load-bearing elements, such as exterior walls, can withstand explosive loads, thus enhancing the structural integrity of the building and ensuring the safety of the surrounding area.

Building on material tests regarding the strain-rate-dependent strength behavior of polyurea, the bonding of polyurea with the substrate material (e.g., concrete), as well as component tests using the shock tube at Fraunhofer EMI to study explosive behavior, a numerical simulation model has been developed and validated, which serves as the foundation for comprehensive parameter studies.

These studies examine the influence of the polyurea coating on various parameters of concrete wall elements, including the maximum deflection of the concrete slab and the plastic deformations in the reinforcement. The results show that concrete wall panels can be effectively reinforced with a polyurea coating. The effectiveness of the measure increases with the thickness of the coating. However, thicknesses greater than 6 mm are practically difficult to implement, and the increasing positive effect compared to a 6 mm coating is relatively negligible in relation to the effort involved.

In slender, flexurally stressed structures, such as those made of normal concrete (C35) with a typical reinforcement ratio (0.5%), the application of the coating results in a reduction of bending deformation and a corresponding reduction in reinforcement plasticization, leading to higher residual load-bearing capacity after an event. For constructions that exhibit more brittle failure or failure with spalling and chipping, the polyurea coating reduces fragment ejection and spalling on the protected side. The thicker the coating, the more pronounced the spall-liner effect, which prevents fragmentation and splintering.

For compact, massive components, the polyurea coating shows a reduction of plasticization in the reinforcement to zero in the analyzed configurations. Further analyses could indicate that the repair effort after an event is limited to the concrete, while the reinforcement retains full load-bearing capacity.

The project aims to quantify and qualify the effectiveness of the PUA coating, allowing builders and engineers to rely on effective solutions for enhancing structural protection against explosion-related hazards in the future. The easy application in flexible forms also allows for retrofitting of existing structures.