FRACTURE AND IMPACT RESISTANCE OF STEEL FIBER REINFORCED CONCRETE (SOFTENING CHARACTERISTICS, TENSILE FRACTURE, STRAIN-RATE EFFECTS)

An analytical and experimental investigation of the tensile fracture and impact resistance of steel fiber reinforced concrete (SFRC) has been carried out. The composite model takes into account phenomenological aspects of the failure mechanisms in such composites including the non-linear behavior of the fiber-matrix interface and the softening characteristics of the unreinforced matrix. It is realistically sensitive to the reinforcement parameters like fiber volume content and aspect ratio, and to the properties of the fiber, the matrix and fiber-matrix interface. A strain-controlled test method for conducting stable fracture tests of tension-weak brittle materials in direct tension has been developed. Using this scheme, uniaxial tension tests have been conducted for several concrete, mortar, paste and SFRC mixes. The characteristics of the unreinforced matrix have been investigated in depth, to study the local and macroscopic deformations of such composites undergoing softening. SFRC behavior in tension, it has been concluded, is influenced largely by the matrix softening behavior, the interfacial bond-slip response, and its composition parameters (fiber volume fraction and aspect ratio).; A modified instrumented Charpy test has been developed to conduct reliable impact tests on plain concrete and SFRC specimens. A spring-mass of the impact set-up has been used to propose guidelines for the selection of different test parameters. Tests conducted at five different strain rates (1 x 10('-6)/s to 0.3/s) show that the rate sensitivity exhibited by such composites is primarily due to changes in the micro-cracking process. Concrete, mortar and SFRC all exhibit increased strengths, corresponding deformations, and energy absorption capacities at the dynamic rates. Results from these tests have been compared with those from other instrumented tests as well as some conventional impact tests to evaluate the suitability of the different test methods for cementitious composites.