Experimental Study of Repaired Concrete via Epoxy
Tien, Rebecca L.
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During pre-stress transfer, the bottom portion of steel-reinforced concrete girders is subjected to an important compression induced by the relaxation of tension in the bars, which opens longitudinal cracks along the horizontal axis. Reactions at the supports induce shear stress, which sometimes translates into additional diagonal cracks at the ends of the girders. During the subsequent lifespan of the girder, a variety of crack patterns can occur, including longitudinal (along the beam axis), transverse (perpendicular to the beam axis), and diagonal cracks. At present, there is a need to assess the mechanical integrity and sustainability of pre-stressed concrete beams during the entire life cycle of the built infrastructure, which includes crack propagation, crack reparation, and repaired crack aging with possible re-opening. As such, a Georgia Institute of Technology research program, sponsored by the Georgia Department of Transportation, seeks to develop modeling strategies to predict the behavior of cracked concrete repaired by epoxy. In order to develop such strategies, experimental investigations are needed to provide calibration and validation data. This thesis describes the experimental characterization and analysis at both the materials and system level. Three main sets of experiments were conducted: (1) concrete and epoxy-repaired concrete cylinders, (2) mortar cylinders, and (3) concrete beams. The concrete and epoxy-repaired cylinder experiments consisted of both uniaxial and splitting tension tests and involved a newly developed protocol for including epoxy-repair into these material characterization tests. The mortar cylinder experiments also consisted of uniaxial and splitting tension characterization. Additionally, a study as to the effect of specimen size for computational efficiency was conducted. Both unreinforced and reinforced concrete beams were tested using a three-point bending procedure. In both cases, both “as-built” and epoxy-repaired specimens were tested for comparison and for model validation. The epoxy-repaired reinforced specimens were loaded to induce cracking of various levels, unloaded, repaired with epoxy, and reloaded to failure. In the cases where the cracks were very small (< 0.006 in), the epoxy did not have a significant effect on the ultimate capacity, but the beam behaved in a more brittle fashion. Interestingly, in the experiments where the cracks were larger (> 0.006 in), the beams exhibited a much higher capacity than the “as-built” and the failure mechanism and ductility of the beam was affected