Chloride diffusivity in high performance concrete is influenced by the exposure environment, aside from the concrete mixture properties like, water to cementitious ratio (w/cm) and presence of add-on pozzolans. In this study, a set of concrete specimens (eleven-different concrete mixtures) were cast and exposed to three different environmental conditions (Tidal, Splash and Barge) in which the solution was seawater or brackish water. These exposures simulated environmental field conditions. After the specimens had been wet cured for 32 days (on average), the specimens were exposed to three different field simulation conditions for up to 54 months. The specimens under the field simulated conditions were cored at 6, 10, 18, 30 and 54 months at four elevations and then the chloride profiles were obtained from the cores. The apparent diffusivity values for each profile were calculated based on Fick’s 2nd law. Then, the aging factor “m” was calculated by regression analysis of the diffusivity values vs. time (days) plotted in the log10-log10 scale. This was done for samples exposed to the three different exposure conditions and then the results were compared side-by-side. First, the “m” values were calculated using the exposure duration. Then, to study the effect of including the curing time on “m” value, the curing time was added to the exposure time and a new calculation and “m” value was obtained and compared with the previous results. Moreover, upon inspecting the chloride diffusivity values vs. time plots, it was observed that in some cases, a number of data points showed significantly higher or lower values in comparison with the rest of the data points. It was decided to recalculate the “m” values for these cases, and to only use selected data points instead of all data points (i.e., remove outlier data points). In terms of chloride diffusivity value, it was found that in most cases the specimens with higher water to cementitious (w/cm) ratio showed higher diffusivity, as expected. Further, the presence of pozzolans had a noticeable impact on the chloride diffusivity by decreasing the diffusion rate due to microstructure changes that occurred with time. In terms of “m” values, the result for the field simulated conditions showed a range of “m” values dependent on the specimen’s mixture composition and the elevation at which the specimens were cored. It was observed that the chloride diffusivity declined with time and after a certain amount of time (in this research, almost after 30 months) the diffusivity reduction became small and a transition in the slope of the diffusivity trend appeared in a number of cases. After the transition, the diffusivity trend reached either a plateau zone or continued with a significantly lower slope, depending on the time, composition and exposure. It was found that the specimens under tidal and splash field simulation conditions that had only fly ash in their mixtures showed higher “m” values when compared with samples that contained fly ash and silica fume or fifty percent slag. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Laboratory experiments were conducted to observe, document and evaluate the mechanical behavior of Fiber Reinforced Concrete after being submitted to five different environments for 8 months. The specimens were molded and reinforced with synthetic fibers with a composition similar to that used for dry-cast concrete. Four different types of fibers with different composition were used. The fibers were mixed with the concrete to create the samples and the samples were exposed to different environmental conditions. Some of these environments were meant to increase degradation of the interface fiber-concrete to simulate longevity and imitate harsh environments or marine conditions. The environments consisted of: a high humidity locker (laboratory conditions), submerged in the Intracoastal Waterway in a barge (SeaTech), a wet/dry cycle in seawater immersion simulating a splash/tidal zone, low pH wet/dry seawater immersion cycle and samples submerged in calcium hydroxide solution. The latter three were in an elevated temperature tank (87-95°F) to increase degradation process. The specimens were monitored weekly and the environments were controlled. Then, specimens were evaluated using different mechanical testing as the Indirect Tensile (IDT) test method, compressive strength according to ASTM standards. Results of testing were documented and observed in this study for further understanding of mechanical properties of Fiber Reinforced concrete. Forensic observation of fiber distribution after the IDT tests were also performed. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

In order to study the mechanical performance of dry-cast synthetic fiber reinforced concrete (SynFRC), samples of varying geometry, fiber content, and environmental exposure were developed and tested using the modified indirect tensile test. The samples created consisted of three different thicknesses (with two different geometries), and six different fiber contents that differed in either type, or quantity, of fibers. Throughout the duration of this research, procedures for inflicting detrimental materials into the concrete samples were employed at a number of different environments by implementing accelerated rates of deterioration using geometric adjustments, increased temperature exposure, wetting/drying cycles, and preparation techniques. The SynFRC samples studied were immersed in a wide range of environments including: the exposure of samples to high humidity and calcium hydroxide environments, which served at the control group, while the sea water, low pH, and barge conditioning environments were used to depict the real world environments similar to what would be experienced in the Florida ecosystem. As a result of this conditioning regime, the concrete was able to imitate the real-world effects that the environments would have inflicted if exposed for long durations after an exposure period of only 20-24 months. Having adequately conditioned the samples in their respective environments, they were then tested (and forensically investigated) using the modified indirect tensile testing method to gather data regarding each sample’s toughness and load handling capability. By analyzing the results from each sample, the toughness was calculated by taking the area under the force displacement curve. From these toughness readings it was found that possible degradation occurred between the fiber-matrix interface of some of the concrete samples conditioned in the Barge environment. From these specimens that were immersed in the barge environment, a handful of them exhibited multiple episodes of strain softening characteristics within their force displacement curves. In regard to the fibers used within the samples, the PVA fibers tended to pull off more while the Tuff Strand SF fibers had the highest tendency to break (despite some of the fibers showing similar pull off and breaking failure characteristics). When it comes to the overall thickness of the sample, there was clear correlation between the increase in size and the increase in sample toughness, however the degree to which it correlates varies from sample to sample. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection