Reddy, Dronnadula V.

This thesis addresses municipal ash-modified and fly ash-modified concrete utilization for the transportation infrastructure. The mix design included unmodified (control) concrete (Mix A), fly ash-modified concrete (Mix B), and municipal ash-modified concrete (Mix C). The laboratory investigation was carried out through compressive, tensile, testing of the cylinders and flexural testing of concrete slabs on grade comprised of varying proportions of coal fly ash and MSW bottom ash. The load-strain relationships for experimental pavements was obtained through slab testing, modeled as a two-way infinite slab on an elastic foundation. A finite element model using STAAD-III was used to predict the stresses and deflection of the slab. For comparison, a simplified analysis was also performed to obtain stresses and deflections variations of the slabs, following ACI Committee 436. Based on the results presented in this report, conclusions were drawn to evaluate the ideal mix design for municipal ash-modified and fly ash-modified concrete.

Durability of marine reinforced and unreinforced concretes was tested under accelerated environmental conditions. The specimens were subjected to alternate wet and dry cycles in specially constructed durability testing tanks. The specific objective was to evaluate the durability of different types of concretes with varying water-cementitious material ratios (0.3, 0.4, and 0.6), cement types (Types I and II), mineral admixtures (blast furnace slag, fly ash, microsilica), and steel types (black, galvinized and epoxy-coated rebars). The unreinforced cylindrical specimens were tested for compressive and splitting tensile strengths and the reinforced prismatic specimens for corrosion. The test results after 300 cycles of accelerated exposure indicated the adverse effects of the marine environment on the durability of concretes, resulting in loss of strength and corrosion resistance. The specimens with lower w/c ratios (0.3 and 0.4) showed good performance, whether or not they were admixture modified. However, mineral admixture inclusions improved the properties of strength and corrosion resistance of the specimens even with high w/c ratios (0.6). The specimens with regular rebars indicated least resistance to corrosion induced from the accelerated marine exposure compared to the ones with galvanized and epoxy-coated rebars.

This thesis presents an experimental and analytical investigation of concrete structural members strengthened with externally bonded composite laminates with varying configurations. Parameters, such as size, type of laminate, debond, etc., are evaluated from the viewpoint of stress patterns and their influence on interfacial debonds. Stress patterns in the structure and stress intensity factors around crack tips are determined using a finite element model developed for this purpose. The study also includes a precise description of cracking and the failure function of each parameter investigated. Besides the development of an innovative finite element program, which enables the study of interfacial cracks in structures with highly nonlinear behavior and multiple irregular cracking patterns, the significant contributions include the effect of laminate geometry, the inefficiency of laminate prestressing, the negative effect of end debond, and the insignificant effect of midspan debond on the cracking and the strength of a laminated concrete structural member.

Noise mitigation and enhancement of skid resistance on Bascule bridge decks, including bridges, pose a considerable challenge. Typically measured noise levels that vary from 60 to 70 dB(A) need to be reduced to eliminate public concern. The objective of this investigation was to find possible modifications to the structure of the open grid decking to reduce the radiated noise from the bridges and at the same time to improve the skid resistance. This study was complementary to the acoustic testing completed in September 1994 at Florida Atlantic University. Deck panels infilled with different types of lightweight infill material for noise mitigation, were tested for fatigue performance and abrasion characteristics. The computer software ANSYS was used to model the grid panel and analyzed for different depths of concrete infill to evaluate the composite action between the infill concrete and the grid panel. A typical case study on counterbalance dynamics of an infilled deck for the Sunrise Boulevard Bridge, included horsepower requirements, trunnion bearing and bending stresses, and flexural strength adequacies of the stringer and floor beams. Skid resistance values for twelve bridges from E-274 and G-analyst measurements were compared for dry and wet conditions, and accident statistics compiled for the period 1988-1992. The cost analysis of identified options was carried out.

An innovative concept of the Centrally Prestressed, Unreinforced Concrete (CPUC) column with modified Freyssinet hinges formulated by Paul Csagoly, to prevent rebar corrosion and additionally mitigate seismic damage, was investigated. The first phase of this work emphasized the mode of failure, ultimate strength, and ductility characteristics of the CPUC columns. As expected, CPUC columns showed adequate axial and flexural resistance as well as ductility. The ultimate strengths of most of the CPUC columns were about 10 to 20% higher than those of conventional ones. The second phase dealt with an energy absorbing device compatible with CPUC column to meet the occasional high ductility demand of the CPUC columns in earthquake conditions. Hinges were tested for compressive strength and moment-rotation capability. Parametric studies of the hinges were conducted for different filler materials, and width-to-height ratios. The confined filler material in the Freyssinet type hinge was found to have excellent compressive strength and moment-rotation capability. The parameters, width-to-height ratios and different filler material, had significant effect on hinge's performance.

Landfilling, by all indications, will continue to be the predominant method of solid waste disposal. Traditional civil engineering drainage medium (i.e. sand or gravel) are being replaced by geosynthetics which are much thinner in an effort to create more usable volume for waste. This study examines the effect of compressive creep of geonets as used in leachate collection and detection systems, and how it affects in-plane drainage. HDPE geonet was subjected to a compressive load of 110 psi. The in plane flow rate of municipal solid waste leachate was measured, as well as the change in thickness, for 120 days. In addition, geonet samples were placed between two pieces of HDPE geomembrane. These samples were subjected to a normal load of 140 psi for 120 days. The samples were then inspected for sign of geonet imprint into the geonet, or for strand layover.

Many modern landfills are constructed with double liner systems. Leachate leakage rates through double liner systems are calculated using recently developed formulations which are theoretically correct for leakage detection system (LDS) materials that have unrestricted lateral flow properties. But their applicability to geonets, the most commonly used LDS material, has yet to be determined. In double liner systems, the leakage through the primary liner, the properties of the LDS material, and the slope of the LDS determine the flow patterns in the LDS. These flow patterns are then used to determine the amount of leachate, if any, which leaks through the bottom liner into the ground. This thesis describes the experimental determination of the flow patterns in the geonets and their relationships to established design formulations.

This thesis addresses the evaluation of the durability of reinforced concrete marine structures subjected to fatigue loading. The laboratory investigation was carried out on full and half size reinforced concrete specimens with three different water cement ratios (0.3, 0.4, and 0.56), static and fatigue loading conditions, and epoxy-coated and regular black steel reinforcements; a mineral admixture (silica fume), and a corrosion inhibitor (calcium nitrite) were used for specimens made with water/cement ratio 0.4 concrete. The marine tidal zone was simulated by alternate filling and draining of the tank (wet and dry cycles), and a galvanostatic corrosion technique to accelerate corrosion of rebar was introduced. Half-cell potentials and changes of crack width were measured periodically during the exposure and followed by ultimate strength testing. The significant findings include adverse effect of fatigue loading, existence of an explicit size effect, poor performance of epoxy coated steel, and negative effect of the increasing water/cement ratio.

The effect of corrosion on the fatigue life of reinforced concrete beams is studied. Two analytical models are developed to study the chloride diffusion in concrete and the percent reduction in fatigue lives in seawater as compared to air. An initial stress equivalent to the tensile strength of concrete is induced in the rebar to simulate the corrosive nature of marine environment. The analytical values are compared with the available experimental data.

Temperature and thermal stress variations in a segmental box girder bridge arc studied. A finite element model using the general finite element software MARC is used to predict temperature and thermal stress variation, for segmental box girder bridges. The predictions are compared with actual measured temperature data of two segmental box girder bridges, instrumented with thermocouples and vibrating wire strain gages, in Davie, Florida. Continuous monitoring was carried out for two months in July-August, 1991, and for one month in January-February, 1992. Comparison are also made with the NCHRP suggested profiles. A Monte Carlo analysis is performed to accommodate the probabilistic variation of ambient temperature conditions.