This thesis evaluates the use of fibrous reinforced concrete as a viable structural repair alternative. An independent laboratory investigation was conducted to substantiate the validity of the marketed claims of Polypropylene Fiber Reinforced Concrete (PFRC) and of Steel Fiber Reinforced Concrete (SFRC) to improve the long-term performance of conventional portland cement concrete. The study found that SFRC significantly increases the compression strength, flexural behavior, and material toughness of PCC, whereas the test response for PFRC yielded minimal contributory strengths. The work examines the function of fibers; FRC's historical background, prevalent economic considerations, and modern repair applicational developments; remedies to overcome the negative aspects of SFRC; current research programs; and future trends. The author recommends trial field demonstration of Steel Fiber Reinforced Micro-Silica Dense Concrete (SFR-MSDC) as a cost-competitive material alternate in lieu of non-fibrous Latex-Modified Concrete (LMC) to more proficiently rehabilitate fatigue-distressed bridge decks.

No description available.

No description available.

Typescript, etc. / Digitized by Kansas Correctional Industries

This research was conducted to better understand the corrosion propagation stage on dry-cast reinforced concrete pipes (DCRCPs) while exposed to high moisture conditions and chlorides. Corrosion initiation and propagation were studied in instrumented specimens obtained from segments of dry-cast reinforced concrete pipes. All specimens were subjected to accelerated chloride transport by the application of an electric field. Corrosion of the steel wire mesh initiated after a few days to a few months rather than several years. The specimens were then transferred to high moisture environments (immersed in water, high humidity and/or covered with wet sand) during the corrosion propagation stage. Reinforcement potentials, linear polarization resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) measurements were carried out periodically. During the propagation stage in different exposures, reinforcement eventually reached negative potentials values (< –-0.55 Vsce), which suggest mass transfer limitations. These specimens showed no visual signs of corrosion such as cracks or corrosion products except the ones exposed to high humidity and laboratory environments; where some corrosion products have reached the concrete surface. Moreover, the apparent corrosion rate values obtained suggest high corrosion rates. No crack appearance on specimens exposed to other conditions could be explained by the porosity of the specimens; the corrosion products moved into saturated pores. It is speculated that although there might be mass transfer limitations present, the current demanded by the anode is being balanced by a larger cathode area due to macrocell effects since the high moisture conditions likely reduced the concrete resistivity and increased the throwing power. The corrected polarization resistance (Rc) was calculated by subtracting the solution resistance from the apparent polarization resistance measured. The Rc values measured over time were used to obtain the calculated mass loss (using Faraday’s Law). Most specimens were forensically analyzed and the measured mass loss compared to the calculated mass loss. The forensic examination includes the measurement of the actual corroding areas. The measured corroding areas were used to obtain corrosion current density (icorr) values. A comparison was made of the calculated corrosion current densities obtained using the linear polarization resistance method (LPR) and the extrapolation method from cyclic polarization tests. It was evident that most of the specimens’ corrosion rates were significantly high. The corrosion products filled the wet-pores inside the concrete and provide an explanation for no cracks or corrosion bleed outs being visually observed on the specimens. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

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The research reported in this thesis was carried out in two phases to investigate the behaviour of reactive powder concrete (RPC) columns. In the first phase of this study, six steel fibre reinforced RPC columns of 150 mm square cross section were tested to failure under various loading eccentricities. The RPC mix contained 2 percent (by volume) of straight steel fibres with a concrete strength of about 150 MPa. The columns contained either 4 or 7 percent of longitudinal reinforcement but no tie reinforcement in the test region. All the columns failed in a controlled manner and no buckling of the longitudinal steel or cover spalling was observed, even well beyond the peak load. The tests revealed that stirrups can be significantly reduced for steel fibre reinforced RPC columns, which could lead to an increase in the speed of construction with an associated potential reduction in construction costs. In the second phase, 17 RPC columns were tested with 16 confined using carbon fibre reinforced polymer (CFRP). The concrete mix contained either no fibres or 2 percent (by volume) of straight steel fibres with concrete strength of approximately 160 MPa. The columns contained no conventional steel reinforcement. For the concentrically loaded specimens, failure occurred at or close to the peak loading and the CFRP increased the strength by 19 percent compared with the unconfined specimen. The tests showed that the formulae developed to predict the peak strength of concentrically loaded FRP confined conventional strength concrete columns, in general, overestimate the load carrying capacity of FRP confined RPC specimens. The CFRP was shown to be effective in controlling the failure for the eccentrically loaded specimens. There was no evidence, however, that the use of CFRP in the hoop direction significantly increased the strength of the columns. Three dimensional nonlinear FE analyses of the test specimens were undertaken using the program DIANA. The FE analyses showed a reasonable comparison with the experimental results for the specimens tested under eccentric loading.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Chloride ion migration was studied under accelerated cathodic protection conditions using 6" x 6" x 6" mortar blocks of varying initial chloride content and water to cement ratios. An iron mesh embedded parallel to one face in the blocks acted as the cathode and zinc was thermally sprayed on the opposite face to form an anode. First, the potential response of two blocks was studied at a current density of 3 mA/ft��. One block was outfitted with a heat sink and moisture barrier while the other block was periodically wetted. Second, eight blocks were polarized at various current densities for a period of one year. In both sets of experiments, the blocks were maintained in controlled humidity and temperature. The potential across the blocks was recorded at periodic intervals and mortar samples were drilled to measure the chloride content as a function of aging. Based on observations of the first study a theoretical model was constructed which indicates that zinc based electrochemical products form at the zinc-concrete interface. The effect of the electrochemical product on raising the resistance across a cathodic protection set-up may be of consequence and should be further studied. Blocks polarized at 6 mA/ft�� exhibited similar behavior as the blocks polarized at 3 mA/ft��, but the response was twice as fast. This result indicates that studying cathodic protection under accelerated conditions is valid. The chloride content of samples obtained from one set of blocks over the course of the experiment was normalized against the initial chloride profile. The normalized profiles were calculated as a function of aging and they supported the hypothesis that chloride ions would move away from the rebar and towards the sprayed zinc anode under cathodic protection. / Graduation date: 2001

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 119-121). Also available in electronic version.