This paper explores the effect of bonding size on the shear performance of ultra-high-performance concrete (UHPC) and normal concrete (NC). The study includes two sets of direct shear tests on a total of 16 Z-shaped UHPC-NC bonded specimens. The first set consists of eight direct shear tests on the chiseled UHPC-NC interface with an average roughness of 4 mm (referred to as series C), from the authors’ previous study. The second set involves eight direct shear tests on the chiseled UHPC-NC interface with additional short shear steel rebars (referred to as series CS) that possess identical roughness to the first set of tests. The study discusses the failure modes, shear stress–slip behavior, and strain histories of the UHPC-NC interfaces with varying bonding sizes and shear mechanisms. A finite element model incorporating the cohesive zone model for the UHPC-NC interface was developed to gain insights into the shear bond evolutions. Our experimental results show that the two sets of direct shear specimens exhibit similar size effects in the shear stiffness, bonding strength, and interfacial slippage of the UHPC-NC interface. The use of shear steel rebars mitigated the impact of interfacial size on the bond shear behavior, thereby enhancing shear stiffness and reducing susceptibility to brittle damage. Numerical simulations indicate that the shear stress inhomogeneity coefficients for the CS specimens with bonding heights of 100 mm, 200 mm, 330 mm, and 440 mm were 1.2%, 1.8%, 11.9%, and 17.4%, respectively. The findings of this study provide valuable insights for optimizing UHPC applications in the repair and strengthening of concrete structures.

This paper examines the splitting tensile properties of rubberized polyethylene-engineered cementitious composites (RPECC) through static and dynamic experimental tests, highlighting the effects of thermal cycles, impact strain rates, and rubber powder substitution rates for fine aggregates. Damage patterns, ultimate tensile strength, time-dependent stress curves, dynamic failure strain, and the dynamic increase factor of the RPECC are presented. The microstructure of the material is analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Experimental results reveal that incorporating rubber powders significantly enhances the deformability and ductility of RPECC in splitting tension. However, a high content of rubber powders, such as a substitution percentage of 30%, significantly reduces static and the dynamic ultimate tensile strength of the RPECC by 16.8% and 34.2%, respectively. Microstructural examinations indicate that thermal cycling weakens the internal adhesion between the rubber particles, polyethylene fibers, and the ECC matrix, resulting in the frequent withdrawal of fibers and the formation of calcium hydroxide, which diminishes the material tensile strength by up to 20.6% in static tests and 45.1% in dynamic tests. Despite these challenges, the RPECC with 20% rubber achieves a favorable balance between splitting the tensile properties and thermal resistance, even after undergoing 270 heat-cool cycles, suggesting its potential applicability in harsh environments.

This study explores the impact of thermal cycling and rubber particle content on the static and dynamic compressive properties of rubber–polyethylene fiber-reinforced engineered cementitious composites (RPECC). Through static and dynamic compression tests, supplemented by scanning electron microscopy and energy-dispersive X-ray spectroscopy, the mechanical behavior and microstructural evolution of RPECC under thermal cycling were analyzed. Results indicate that increasing rubber content from 10% to 30% enhances toughness and strain capacity but reduces the static compressive strength of ECC by up to 17.9% at 30%. Thermal cycling reduced strength: static and dynamic compressive strengths decreased by 18.0% and 41.2%, respectively, after 270 cycles. Dynamic tests demonstrated that RPECC is sensitive to strain rate. For example, C-20 specimens exhibited increases in dynamic strength of 6.9% and 9.9% as strain rate rose from 60.2 s⁻¹ to 77.4 s⁻¹ and 110.8 s⁻¹, respectively, and the dynamic increase factor correlated linearly with strain rate. By contrast, excessive rubber content (30%) diminishes dynamic strengthening, indicating that 20% rubber is optimal for enhancing strain rate sensitivity. Thermal cycling facilitates the formation of hydration products, such as calcium hydroxide, and creates interfacial defects, further deteriorating mechanical performance. These findings provide a reliable foundation for optimizing RPECC mix design and ductility in environments subject to temperature fluctuations and dynamic loading.