In this study, the performance of reinforced concrete slabs strengthened using four methods was investigated under impact loads transferred from the top side to bottom side. The top and bottom sides of test slabs were strengthened by no-slump high-strength, high-ductility concrete (NSHSDC), fiber-reinforced-polymer (FRP) sheet, and sprayed FRP, respectively. The test results indicated that the test specimens strengthened with FRP series showed a 4% increase in reaction force and a decrease in deflection by more than 20% compared to the non-strengthened specimens. However, the specimen enhanced by the NSHSDC jacket at both the top and bottom sides exhibited the highest reaction force and energy dissipation as well as the above measurements because it contains two types of fibers in the NSHSDC. In addition, the weight loss rate was improved by approximately 0.12% for the NSHSDC specimen, which was the lowest among the specimens when measuring the weight before and after the impact load. Therefore, a linear relationship between the top and bottom strengthening of the NSHSDC and the impact resistance was confirmed, concluding that the NSHSDC is effective for impact resistance when the top and bottom sides are strengthened. The results of the analysis of the existing research show that the NSHSDC is considered to have high impact resistance, even though it has lower resistance than the steel fiber reinforced concrete and ultra-high-performance-concrete, it can be expected to further studies on strengthening of NSHSDC.

Despite extensive research on blast-resistant concrete structures, a clear scientific deficiency remains in the quantitative understanding of how fiber-reinforced concrete slabs behave under blast loading, particularly when experimental and numerical investigations are not conducted together under identical loading conditions. Existing studies often focus on either conventional reinforced concrete or isolated material systems, providing limited validation of comparative blast performance across different fiber-reinforced concretes. This study addresses this gap by investigating the blast resistance performance of four types of reinforced concrete slabs: normal concrete (NC), ultra-high-performance fiber-reinforced concrete (UHPFRC), organic fiber-reinforced high-performance concrete (O-HPC), and basalt FRP-sheet-strengthened slurry-infiltrated fiber concrete (F-SIFCON), using full-scale blast experiments and validated numerical simulations conducted with ANSYS Explicit Dynamics. Blast tests were performed to obtain time histories of reflected pressure, displacement, acceleration, reaction force, and internal energy. The influence of different fiber systems and FRP strengthening on dynamic response and failure mechanisms was systematically analyzed. The numerical models showed good agreement with experimental measurements, confirming their reliability. The results indicate that the normal concrete slab exhibited brittle failure and poor blast resistance, whereas the F-SIFCON slab demonstrated the best overall performance. Compared with the normal concrete slab, the F-SIFCON slab achieved approximately a 47% reduction in maximum displacement, a 56% increase in peak reaction force, and the highest internal energy absorption of 236 kJ. The UHPFRC and O-HPC slabs also showed improved blast resistance, although with different post-peak response characteristics. These findings demonstrate that hybrid fiber reinforcement combined with FRP strengthening can significantly enhance the blast resistance of concrete slabs and that coupled experimental–numerical approaches provide a robust framework for evaluating structural performance under extreme dynamic loading.

CaO-based alkali-activated high-strength cementless concrete is considered an environmentally friendly and cost-effective material for sustainable structures; however, to enable its structural application, the bond behavior between steel bars and cementless concrete must be properly assessed. This study experimentally investigates the local bond performance and bond–slip behavior of cementless concrete in comparison with existing design guidelines. For this purpose, steel bars were embedded in cube specimens with dimensions of 150 × 150 × 150 mm³, and direct pull-out tests were conducted. The test variables included embedded length (2d, 4d, and 6d), bar diameter (D10 and D13), and concrete cover thickness (1.5d, 2.5d, and 7d). The results indicate that increasing the bar diameter did not lead to a significant change in bond strength; instead, the bond strength increased by approximately 4.8%, and yielding of the steel bar at the loading end was observed for specimens with an embedded length of 6d. When the cover thickness exceeded 2.5d, its influence on bond strength enhancement became negligible, with similar bond strengths ranging from 23 to 25 MPa. A comparison of the ultimate bond strength revealed that the predicted values based on ACI 318-25 showed the best agreement with the experimental results, with the lowest mean absolute relative deviation (MARD) of 22.14%. Furthermore, in terms of bond–slip behavior, the CMR model demonstrated better agreement with the experimental results than the modified BPE model, exhibiting a coefficient of determination ($R^2$) of 97%.