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The Effect Of Fiber Corrosion On Shear Capacity Of Steel Fiber Reinforced Concrete Beams And An Initial Investigation On Alkali-silica Reaction In Steel Fiber Reinforced Concrete

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The Effect Of Fiber Corrosion On Shear Capacity Of Steel Fiber Reinforced Concrete Beams And An Initial Investigation On Alkali-silica Reaction In Steel Fiber Reinforced Concrete

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Title: The Effect Of Fiber Corrosion On Shear Capacity Of Steel Fiber Reinforced Concrete Beams And An Initial Investigation On Alkali-silica Reaction In Steel Fiber Reinforced Concrete
Author: Waweru, Regina Nyambura
Abstract: The first part of this research aims to investigate the effect of fiber corrosion on the shear capacity of Steel Fiber Reinforced Concrete beams. It will also strive to determine at what reduction in minimum diameter of the fiber does the effect of corrosion become most severe on the shear capacity of the beam. Four simply-supported beams with a shear span to depth ratio of 3.3 were subjected to a monotonically increasing load. The targeted concrete compressive strength for all beams was 6000 psi. This however differed from the measured strength due to a number of factors as will be discussed in the paper. The fixed parameters for the experiment were the beam size, shear span-to-effective depth ratio, and concrete compressive strength, while the varied parameters were the fiber content and the extent of corrosion of the steel fibers. Pre-corroded fibers were used in this research to give the worst case scenario because in real life situations, only the fibers closest to the surface of the concrete (0.10 in. from surface) or those close to a crack will be corroded. Hooked steel fibers were used at a volume fraction of 0.75% with an aspect ratio of 125 and a length of 1 in.. Small specimen tests were also conducted to determine the change in the mechanical properties of SFRC at different levels of corrosion. The tests conducted were: the three point loading test, the compression test and the fiber pullout tests.Test results revealed that a 12.5% reduction in the minimum fiber diameter, has almost no effect on the shear capacity of beams. Results from the fiber pullout tests showed a slight increase in the pullout load which seems to indicate an increase in the bond between the fiber and cementitious matrix. However, for beams with a 50% reduction in the minimum fiber diameter a 24% reduction in the shear strength of the beam was witnessed. These observations indicated that the type of failure for these beams was through fiber breakage before pullout. The results from the fiber pullout specimens also seemed to support this failure mode as 80% of the fibers broke before pullout. Finally recommendations are made for more future research on the topic.The second part of the thesis covers the initial investigation on alkali-silica reaction (ASR) in SFRC. Most importantly, it tries to determine whether the addition of fibers to concrete can actually arrest cracks due to ASR in concrete and thus counteract its effect on the durability of the structure. Four beams with dimensions of 20 x 6 x 6 in. were cast using reactive aggregates, in accordance to ASTM C1260 and C1293 and subjected to an accelerated ASR test. Two beams were reinforced with 1% fibers while the control specimens had no fibers. From the preliminary observations on the beams by measuring their elongation, the SFRC beams showed less expansion compared to the plain concrete beams. Based on these these initial findings, a more intense research was recommended on the effect of steel fibers on ASR. This is an ongoing research that will take a couple of years as the specimens with reactive aggregates will be cast and put in the natural environment for cracking to occur due to ASR. The specimens will then be compared with their counterparts with no fibers to reach a conclusion.
URI: http://hdl.handle.net/10106/6156
Date: 2011-10-11

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