The results generated in the first GRK 2250 cohort demonstrated the necessity of using hybrid-fiber reinforcement in strengthening layers on the rear side of impacted reinforced concrete (RC) elements. The materials which showed an adequate performance under such loading conditions consist of strain-hardening cement-based composites (SHCC) reinforced additionally with continuous textiles made of carbon or ultra-high molecular weight polyethylene (UHMWPE) yarns. On the back side of an impacted RC element the strengthening layers are mainly subjected to tensile stresses, whereas shear and compression play a secondary role. On the front side, however, the strengthening layers are subjected to local punching shear and compressive actions. Furthermore, shear stresses are also dominant in lateral strengthening layers on vertically impacted beams. Thus, the strengthening performance of mineral-bonded composites should be also investigated under in-plane and out-of-plane shear loading.
Penetration of a steel projectile in a RC plate on the impacted side after an impact experiment in the drop tower facility (left). Damage representation across the thickness of an impacted RC plate strengthened on the rear side – cut plane through the location of projectile impact, i.e. middle of the plate (right).
The image indicates that on the back side of an impacted element mainly tensile stresses occur in the strengthening layer, while on the front side punching shear type of loading may dominate.
The goal of the project is to develop and optimize testing methodologies for a reliable characterization of the shear behavior of mineral-bonded composites with short-dispersed and continuous fiber reinforcement at the composite and constituents scales, i.e., matrix, fibers and fiber-matrix bond. For this purpose dedicated testing setups shall be developed. The influence of various reinforcement configurations, geometries and materials in medium-strength and high-strength matrices shall be investigated experimentally and numerically. The findings from this research should serve as basis for the formulation and validation of material design concepts with respect to impact shear loading.