Post-Crack Behavior of Macro-Fiber Reinforced Concrete

University of Minnesota M.S. thesis.January 2018. Major: Civil Engineering. Advisor: Manik Barman. 1 computer file (PDF); ix, 142 pages.Structural fibers are used in thin concrete overlays, pavements, and many other civil engineering structures for improving concretes long-term performance. These fibers improve the structural integrity of concrete by enhancing the post-crack performance and load transfer efficiency of concrete in un-dowelled thin concrete overlays. However, the pavement industry often encounters problem in selecting the appropriate type of fibers and their corresponding dosages. The primary objective of this study was to conduct a laboratory study to quantify the benefit of structural fibers in terms of pre-and post-crack behaviors in flexural specimens and to, as a goal, provide methods that characterize the behavior of fibers in fiber reinforced concrete (FRC). In this study, two new properties (post-crack toughness and post-crack performance (PCP) index) were proposed. Eleven different types of fibers were tested at three different dosages each for regular strength mixes (total 33 mixes). Also, four other low strength FRC mixes were considered. Hardened concrete properties of all these FRC mixes were compared with the control plain concrete mix. The following hardened concrete properties were considered: compressive strength, modulus of elasticity, modulus of rupture, residual strength, residual strength ratio, post-crack toughness, and PCP index. The study found good correlations between properties of fibers and FRC performance. It was found that fibers having a crimped, embossed, twisted or hooked-end geometry greatly outperform straight fibers. Post crack toughness was seen to produce stronger and more accurate correlations to cracked FRC, while the PCP index provided a tool for evaluating a fiber’s ability to add post crack performance with an increase in a fiber’s volume fraction. The mechanistic estimation method was developed to complete two tasks; estimate the fibers effective working stress (EWS) and to provide a tool for approximating a FRC’s flexural performance. As an auxiliary component to the core of this study, joint performance (as it pertains to concrete slabs -on -ground) was also evaluated. This separate study drew correlations between joint performance and fiber dosage and then compared joint performance to flexural performance