Fracture toughness of fiber reinforced concrete

Fracture and impact resistance are among the improved attributes of fiber reinforced concrete (FRC). Toughness, which is a measure of energy absorption capacity, is used to characterize FRC's ability to resist fracture when subjected to static, dynamic, and impact loads. There is still debate on how toughness should be measured, interpreted, and used. Results from the first phase of a six-university study funded by the Concrete Materials Research Council-American Concrete Institute (CMRC-ACI) and the National Science Foundation (NSF) are presented in this article. This first phase includes specimen size, fiber volume content, fiber type, and the effect of a notch as the primary parameters of investigation. Results from the tests, including toughness, and other important properties such as stress at first-crack, ultimate strength, and the elastic modulus as influenced by the specified parameters, are presented and discussed. The importance of making accurate deflection measurements and the influence of these measurements on the toughness and other flexural characteristics are discussed. Conclusions are made with regard to lessons learned from the inter-university testing program, drawbacks of some currently used measures of toughness, observed material property trends, and a possible alternate measure of toughness.