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Microstructural refinements of concrete due to fiber reinforcement and its influence on corrosion initiation of reinforcing steel Sappakittipakorn, Manote

Abstract

Permeability plays an important role in governing the durability of concrete in deleterious environments. Earlier studies indicated that the addition of cellulose fiber is effective in reducing water permeability and thereby making concrete more durable. In this thesis, microstructural refinement and corrosion resistivity performance of fiber reinforced concrete (FRC) were studied. Two fiber types, cellulose and polypropylene, at various dosages, were examined. Microstructural refinement was studied using thermoporometry (TP) and mercury intrusion porosimetry (MIP) methods. After that, a two-part experiment was performed to investigate corrosion of steel in concrete in the presence of fiber reinforcement. First, diffusion of chloride in concrete was investigated using the bulk diffusion test as well as a silver nitrate spray test. A rapid chloride permeability test was also performed. Secondly, FRC beams were subjected to flexural stress while exposed to a simulated tidal zone of marine environment. Corrosion activity in reinforcing steels was monitored for 56 weeks using three electrochemical methods: half-cell potential, galvanic current and linear polarization resistance. Results demonstrated that fibers did bring about a refinement in the pore structure by converting part of the permeable porosity to non-permeability porosity. Diffusion results clearly show that while the presence of fibers increased the coefficient of chloride diffusion based on total chlorides, there was a decrease in the coefficient related to free chlorides. Fibers therefore appear to bind the chlorides and inhibit their transport. Corrosion tests indicated that fibers delayed corrosion in specimens with no load or a lighter load, but were not as effective in specimens carrying a heavier load. Finally, a long-time performance of fiber reinforcement was illustrated through a service life modeling. Corrosion initiation period was analyzed using a model called LIGHTCON. Empirically based on the test results, it was modified to take the effects of fiber reinforcement and load intensity into consideration. The modified model was then verified in two case studies. In each of the cases, a critical impact of load induced cracks on a service life of structures was emphasized and a promising benefit of fiber reinforcement was demonstrated.

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