Research Article Transportation Research Record 1–10 Ó National Academy of Sciences: Transportation Research Board 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0361198119848408 journals.sagepub.com/home/trr New Procedure to Evaluate the Post-Crack Behavior of Fiber-Reinforced Concrete Bryce Hansen 1 and Manik Barman 1 Abstract This study attempted to identify the challenges in testing and characterization of the post-crack behavior of structural fiber- reinforced concrete (FRC) for use in pavements. The benefits and challenges associated with three different FRC testing methods, ASTM C1550, C1399, and C1609 were discussed and compared. Two new parameters, post-crack toughness, and post-crack performance (PCP) index were proposed to characterize the post-crack behavior of FRC. These parameters are a function of the fibers’ contribution and are minimally influenced by the properties of the non-fiber ingredients of concrete such as aggregates, cement, and water. A laboratory study conducted on 10 different types of FRCs validated the applicability of the two proposed new parameters. Transportation agencies can use the PCP index to shortlist effective fibers and post- crack toughness to determine fiber dosage. The study found that fibers with irregular cross-section or geometry and high lat- eral stiffness provide a high post-crack contribution. Structural fibers extend the service life of thin concrete pavements and overlays. These fibers improve the post- crack performance (PCP) of concrete (1–4) by keeping cracks tight, which helps to reduce the propagation of fatigue cracks. These fibers increase the joint load trans- fer (5) and decrease the slab deflection at joints or cracks (6), which eventually can decrease joint faulting or other joint deteriorations. In the last few decades, transporta- tion agencies have used varieties of structural fibers vary- ing in length, geometry, aspect ratio (ratio of length to effective diameter), and parent materials. Among the various types of structural fibers, synthetic fibers have become predominant owing to their ease of handling, better dispersion, and resistance to corrosion. Many transportation agencies have used structural synthetic fibers in concrete overlays for decades: several combina- tions of fiber types, lengths, and dosages have been uti- lized. The performance of many of those concrete overlays provides evidence about the qualitative benefit of structural fibers (6); however, those evidences do not provide a comprehensive quantification of the benefits. In current practice, fiber-reinforced concrete (FRC) is usually characterized using the modulus of rupture (MOR), equivalent flexural strength ratio or residual strength ratio (RSR), flexural toughness, average resi- dual strength (ARS), and so forth. Some of the existing concrete overlay design procedures use MOR and RSR; the magnitude of MOR is artificially increased to account for the contribution of fibers based on the RSR value (7–9). However, several previous studies have found that the commonly used structural synthetic fibers do not significantly influence MOR (5, 6, 10, 11); there- fore, to suggest an increase in the MOR accounts for the fibers’ contribution is arguable. Moreover, as the RSR also depends on the MOR, it actually cannot discrimi- nate concrete mixes based on the contribution of the fibers alone. The complexities in FRC testing and the lack of relevant research studies, especially on the influ- ence of fiber to FRC post-crack behavior, are the prob- able reasons for the use of the MOR and RSR as the structural design inputs, as opposed to using the post- crack behavior parameters of FRC that are purely a function of the fibers’ contribution. This study focused on recognizing the challenges in testing and analyzing the post-crack behavior of FRC. Relevant literature was reviewed to identify the benefits and limitations associated with three FRC test methods. Two new parameters, namely post-crack toughness and the PCP index, were introduced to characterize the post- 1 University of Minnesota Duluth, Duluth, MN Corresponding Author: Address correspondence to Manik Barman: mbarman@d.umn.edu