Experimental study on the fracture performance of rubberized high strength-high ductility concrete with J-integral method

Rubberized high strength-high ductility concrete (R-HSHDC) exhibits a ductile fracture mode which is different from the quasi-brittle fracture of traditional concrete. Therefore, the study on R-HSHDC's fracture is a non-trivial issue that still needs to be addressed in greater depth. The fracture performance of R-HSHDC with various polyethylene (PE) fiber lengths and rubber replacement ratios was investigated. The fracture process, double-K parameters, fracture energy, and ductility index were analyzed. Results showed that R-HSHDC had a considerably high damage tolerance before macrocrack formation. Both PE fibers and rubber particles presented toughening effects, delaying the fractural failure. Longer fibers could offer higher fiber-bridging strength, and the bridging effect was most pronounced when fiber length increased from 6 mm to 12 mm. The toughening effect of rubber particles was not as significant as that of PE fibers. Since the ductile fracture of R-HSHDC reinforced with long fibers gives rise to the inapplicability of the linear asymptotic superposition assumption of the double-K fracture model, a J-integral-based method was proposed to evaluate the fracture performance. The results indicated R-HSHDC with 12 mm PE fiber and 20% rubber replacement ratio had a large fracture process zone and a composite fracture energy Jc of 30.9 kJ/m2. Moreover, excessively long fibers could not further improve the fracture ductility and may reduce mechanical properties. Thus, a combination of 12 mm PE fiber and 20% rubber replacement ratio was recommended, which could guarantee high compressive strength and tensile ductility, while significantly delay the fracture.