Rubber modified high strength-high ductility concrete: Effect of rubber replacement ratio and fiber length

[Display omitted] •Rubber-modified high strength-high ductility concrete was developed.•Tensile behavior was investigated at macro and micro levels.•Tensile behavior was strongly influenced by fiber length and rubber replacement ratio.•Longer fibers promoted multiple cracking behavior, improved ultimate tensile strain and strain energy.•Introduction of rubber enhanced tensile ductility by reducing matrix fracture toughness. High-strength high-ductility concrete (HSHDC) have gained significant attention due to its high compressive strength and tensile ductility. However, the high fracture toughness of HSHDC’s matrix can resist crack initiation, hindering the development of tensile ductility. To improve HSHDC’s tensile ductility, power rubber (PR) was introduced to develop a rubber modified HSHDC (R-HSHDC) in this study. Axial compressive, axial tensile, single-crack tensile, and matrix fracture toughness tests were conducted to investigate the effect of rubber replacement ratios (0 vol%, 10 vol%, 20 vol%, 35 vol%) and PE fiber lengths (6 mm, 12 mm, 18 mm) on compressive and tensile properties of R-HSHDC. Digital image correlation (DIC) technology was utilized to obtain crack parameters of R-HSHDC under tensile load. The results revealed that fiber length had minimal influence on compressive strength of R-HSHDC. However, introducing PR substantially reduced compressive strength due to increased bubbles, interface discontinuity between PR particles and matrix, and low strength and elastic modulus of PR. Still, unless rubber replacement surpasses 20 vol%, compressive strength could exceed 100 MPa. In axial tensile tests, specimens reinforced with 12 mm and 18 mm fibers exhibited multiple cracks, while specimens reinforced with 6 mm fibers displayed brittle failure. Longer fibers enhanced fiber-bridging strength, promoting tensile ductility. Introducing PR also enhanced tensile ductility, likely attributed to reduced matrix fracture toughness and slightly increased fiber-bridging strength. Excessive rubber replacement negatively affected tensile ductility. This study suggests the optimal combination of 12 mm or 18 mm PE fiber and 20 vol% rubber replacement for optimal tensile ductility and compressive strength.