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Call number: LD2668 .T4 1986 M34 / Master of Science / Civil Engineering

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This thesis reports a research of the corrosion mechanism and corrosion rate of steel reinforcement in concrete. Experimental results are presented to compare the corrosion behaviours of steel reinforcement in two blended-cement concretes in seawater. The experimental program included a study of the influence of crack width on macrocell corrosion, an investigation of the procedure for the determination of polarisation curves of steel in concrete and, an evaluation of the corrosion rate of steel in concrete and the influence of crack width as determined by a new polarisation curve analysis. A mechanism is proposed to interpret the different influences, in both the short and long term, of concrete crack width on the macrocell corrosion rate. This mechanism is based on the finding that the corrosion-spread phenomenon is caused by polarisation effects. An oxygen-depletion mechanism is also proposed to explain the much lower macrocell corrosion rate in the slag cement concrete than that in the flyash cement concrete. The procedure for polarisation testing of steel in concrete is found to be critical to obtaining correct polarisation curves. A twotest procedure is verified to be an appropriate procedure and used in this investigation. Experimental polarisation curves of steel in concrete are found to be very different to those expressed by the kinetic Butler-Volmer equation and, this is considered to be a result of the influence of the passive film on the steel surface in concrete. An empirical polarisation formula is developed and its interpretation is based on the postulation of two parallel kinetic processes occurring at the steel/passive-film/concrete interface; one is the active corrosion process and the other is the film growth/dissolution process. The formula is used to model experimental polarisation curves of steel in concrete through curvefitting analyses. Good curve-fitting results are obtained between the polarisation test curves and model curves. The results are used for evaluation of the corrosion rate and Tafel behaviours of steel in the two concretes and for assessment of the influence of crack width on the corrosion rate within the crack zone.

Environmental factors and physical properties of latex modified concrete (LMC) are hypothesized to contribute to early age cracking in bridge deck overlays. Cracking permits the ingress of moisture and aggressive solutions into the substrate and may contribute to other subsequent distresses. Understanding the material properties and mechanisms involved is necessary to minimize these distresses. This research consisted of a two part study: first, the development of LMC strength and fracture properties at ages ranging from 5 hours to 28 days was studied, and secondly, the effects of the environment on LMC distresses were modelled. Environmental conditions: temperature, solar energy, and wind speed were determined from weather records. A fracture mechanics based model, the Fictitious Crack Model (FCM), incorporating finite element analyses and superposition techniques was employed with material properties from the first part of study on LMC performance. Different bilinear strain softening diagrams were used to predict fracture performance at different ages. The predictions agreed well with the test data. The impacts of temperature differentials on crack development were studied. The shrinkage effect was also indirectly incorporated through the temperature analysis. The material properties study indicated significant changes in strength, deformability and fracture properties, particularly during the early age. The developments differ slightly from conventional concrete. Test results indicated a significant improvement in reducing and bridging microcracks, especially in the prepeak-load region. Fracture toughness and deformability increased significantly with time. Fracture energy varied from 2.3 to 133.1 N/m, depending on age, and to some degree, on notch depth ratio. In the second stage, the FCM provided a reasonable prediction for crack initiation and propagation when only temperature effects are of concern. Age, surface conditions and structural restraint strongly affect crack resistance of the overlays. Only slight effects were observed from the overlay thickness in the study range (51-76 mm). Shallow preexisting cracks possibly reduce the crack resistance of the overlay about 30 percent. A prolonged moist cure for 48 hours after placing is suggested to reduce the risk of cracking. With available environmental information, it is possible to develop guidelines for appropriate environmental conditions for LMC bridge deck construction to minimize the risk of early age cracking. / Graduation date: 1997

Thermal cracking of asphalt concrete pavements is responsible for millions of dollars in annual maintenance and rehabilitation costs in the United States and Canada. Thermal cracking is typically associated with low temperatures in northern climates and at high elevations. However, another form of thermal cracking, known as thermal fatigue cracking, has been proposed by several researchers as a potential mode of distress in regions with relatively moderate climates but significant differences in high and low daily temperatures. The primary purpose of the research reported herein was to evaluate the possibility of occurrence of the thermal fatigue cracking mode of distress. A secondary objective was to identify a suitable laboratory test procedure to facilitate a mechanistic analysis of the thermal fatigue mode of distress. In light of these objectives, several laboratory test procedures were evaluated in the bituminous materials laboratory at Oregon State University (OSU). The test procedures evaluated included the phenomenological Thermal Stress Restrained Specimen Test (TSRST), the Energy Rate Integral Test (ERIT), the Direct Tension Test under constant rate of extension (DTT), and the Direct Tensile Creep Test (DTCT). The TSRST results were used to evaluate the possibility of occurrence of the thermal fatigue mode of distress. The ERIT, DTT, and DTCT procedures were evaluated with respect to the identification of a suitable laboratory test procedure to facilitate a mechanistic analysis of thermal fatigue. The results from the laboratory test program indicate that thermal fatigue distress in asphalt concrete mixtures is not a viable mode of distress in the absence of environmental aging. Based on the data presented herein and the results of previous researchers, it is evident that distress often attributed to thermal fatigue cracking is more likely the result of low temperature cracking of environmentally aged mixtures, and/or subgrade-related distress; fatigue distress due to thermal loading of semi-restrained pavements does not occur. / Graduation date: 1993

A non-linear finite element computer program capable of predicting the complete response of two-dimensional reinforced concrete members was developed. This tool which accounts for the stress strain characteristics of cracked concrete was used to predict the responses of a number of members containing discontinuities. These members included corbels, dapped end beams, beams with web holes, and deep beams. The results of tests performed by the author as well as tests performed by other researchers were compared with the non-linear predictions. In addition, simple strut and tie models suitable for designing regions near discontinuities were developed. The predictions obtained by these models were compared with the non-linear finite element predictions and with the test results.

This thesis reports a research of the corrosion mechanism and corrosion rate of steel reinforcement in concrete. Experimental results are presented to compare the corrosion behaviours of steel reinforcement in two blended-cement concretes in seawater. The experimental program included a study of the influence of crack width on macrocell corrosion, an investigation of the procedure for the determination of polarisation curves of steel in concrete and, an evaluation of the corrosion rate of steel in concrete and the influence of crack width as determined by a new polarisation curve analysis. A mechanism is proposed to interpret the different influences, in both the short and long term, of concrete crack width on the macrocell corrosion rate. This mechanism is based on the finding that the corrosion-spread phenomenon is caused by polarisation effects. An oxygen-depletion mechanism is also proposed to explain the much lower macrocell corrosion rate in the slag cement concrete than that in the flyash cement concrete. The procedure for polarisation testing of steel in concrete is found to be critical to obtaining correct polarisation curves. A twotest procedure is verified to be an appropriate procedure and used in this investigation. Experimental polarisation curves of steel in concrete are found to be very different to those expressed by the kinetic Butler-Volmer equation and, this is considered to be a result of the influence of the passive film on the steel surface in concrete. An empirical polarisation formula is developed and its interpretation is based on the postulation of two parallel kinetic processes occurring at the steel/passive-film/concrete interface; one is the active corrosion process and the other is the film growth/dissolution process. The formula is used to model experimental polarisation curves of steel in concrete through curvefitting analyses. Good curve-fitting results are obtained between the polarisation test curves and model curves. The results are used for evaluation of the corrosion rate and Tafel behaviours of steel in the two concretes and for assessment of the influence of crack width on the corrosion rate within the crack zone.

This paper presents the comparison of shrinkage and corrosion characteristics of optimized hybrid Rice Husk Ash (RHA)/Fly Ash (FA)-modified Concrete, with those of normal concrete in the marine environment. Uses of both FA and RHA have numerous environmental benefits. Shrinkage performance was determined by subjecting the mixes to restrained shrinkage testing per ASTM C1581. The time to cracking of the specimens improved an average of 18% with the hybrid mixes. Corrosion testing of reinforced columns was performed in a simulated tidal cycle Marine Environment. Corrosion potential improved by as much as 35% for the mix with the highest FA/RHA replacement, and corrosion activity as measured with potentiostat equipment improved by an average of 34% . These results indicate a clear performance improvement of the modified concrete that is proportional to the percent replacement of cement. / by Diana Arboleda. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010 / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.