Correlation among fresh state behavior, fiber dispersion, and toughness properties of SFRCs

Effective structural use of steel fiber-reinforced concrete (SFRC) relies on the assumption of uniform dispersion of fibers within the elements. Fiber dispersion related issues hence stand as a cutting edge research and technology development topic. The use of self-consolidating concrete (SCC), thanks to its rheological stability and self-placability, which leads to the elimination of compaction by vibration, may be helpful in guaranteeing a uniform dispersion of fibers. With reference to the latter, several techniques [e.g., based on alternate current impedance spectroscopy (AC-IS), microwave reflectometry etc.] have been developed in the last few years for its nondestructive monitoring. Investigation into the connections between fiber dispersion and the performance of the composite in the fresh and hardened state stand as the natural completion for a thorough assessment of the FRC properties, aimed at promoting its wider use for full load bearing structural applications. This paper presents the results of a research project aimed at the above said purpose. Based on a previously calibrated mix-design methodology, suitable specimens were cast with SFRC characterized by different performance in the fresh state (vibration-, self-, and segregation consolidating) and tested in four-point bending, in order to assess the connections among fresh state behavior and fiber dispersion, herein investigated by means of AC-IS, and the performance in the hardened state. The results, highlighting this correlation, point out their importance for a design of the material composition tailored to the anticipated mechanical performance and to the specific structural application.