| dc.description.abstract | Ultra-high-performance-concrete (UHPC) is a cementitious material with a high compressive strength, densely packed structure resulting in near zero permeability, small crack opening, and significant post-cracking tensile strength. UHPC has both mechanical properties and durability exceeding those of normal strength concrete. However, these properties come with a substantial material cost, with most of the cost associated with the fiber amounts. In this research, the effect of both fiber content (1, 2, 4 and 6% by volume) and type (0.5 in. straight microfibers and 1.2 in. hooked-end fibers) on UHPC properties has been studied in a non-proprietary UHPC mix developed at the University of Oklahoma (J3). Compression, flexure, direct tensile, and splitting tensile behaviors emphasizing strain responses of J3 concrete have been examined in this study to better understand the linear-elastic response, fiber bridging property and failure mode. Also, the study of flexure behavior of J3 concrete with hooked-end fibers subjected to freezing-thawing cycles in both pre-cracked and uncracked specimens was undertaken to better understand the effect of initial cracking on durability and actual damage of rapid freezing and thawing on the concrete matrix.
Furthermore, UHPC was used to retrofit a half-scale AASHTO Type-II prestressed girder which was failed using a point load positioned to induce bond shear failure. The beams were then repaired by encapsulating the failure zone using J3 mix with 2% straight microfibers. Though this process did not restore the prestress, it successfully restored original shear capacity and created an impermeable layer to prevent water ingress into the existing cracks. | en_US |
