Reddy, Dronnadula V.

The purpose of this research project is to compare the strength and durability
characteristics of rice husk ash-modified concrete with those of normal concrete in
the marine environment. Specimens prepared from concrete mixes with watercementitious
ratios of 0.40 and 0.55, and rice husk ash content of 0%, 10%, and 20%
were tested. The rice husk ash used was obtained from Agrilectric, power plant
located in Lake Charles, Louisiana. The grinding of the ash to particle size of 7-J..tm
to 45-J..tm was done by Process Research ORTECH Inc., Ontario, Canada. Strength
and durability tests were performed, following ASTM (American Society for Testing
and Materials) Standards. The significant fmdings are that the properties and quality
of the rice husk ash-modified concrete are as good, if not better than normal concrete.

Corrosion damage is the mam cause of deterioration for reinforced concrete
marine structures. Given the current economic downturn, it has become increasingly
important to repair existing structures with techniques that prolong their life-cycle. The
process to identify suitable repairs is affected by the lack of a consistent methodology to
predict the outcome of the repairs. This investigation intends to compare the
performance of seven different repairs, in terms of corrosion resistance, structural
integrity, and cost-effectiveness. Following initial exposure to corrosion, the specimens
were repaired using the proposed techniques. They were then tested for durability under
simulated tidal conditions with periodic corrosion monitoring. The structural integrity
was evaluated by crack scoring and ultimate load testing, and a comprehensive evaluation
matrix was prepared, to determine which repairs were most adequate for corrosion
damage. The results of this investigation substantiate that the repairs including carbon
wrapping, HDPE jacketing, and MMFX steel, outperformed the rest of the repairs.

The durability of Reinforced Concrete (RC) structures in the Marine environment is
causing serious concern in the structural infrastructure. Reinforced concrete structures,
exposed to aggressive environments, are expected to last with little or no maintenance for
long periods of time. However, one of the most serious environmental exposures that
causes degradation is Chloride Diffusion, due to shrinkage, atmospheric corrosion, and
tide-induced wet and dry conditions at the air-water interfaces of coastal structures.
Therefore, chloride diffusivity, which correlates with the electrical resistivity, has a
significant impact on the durability of concrete. Concrete chloride diffusivity has been
experimented by multiple agencies and researchers on sound concrete, but there is a
considerable need for investigation of the durability of cracked concrete in the marine
environment. The two test methods carried out are presented: Standardized American Society for Testing
and Materials (ASTM) C1202 for Rapid Chloride Permeability (RCP) and ASTM D257
for Surface Resistivity (SR), and Nordtest (NT) Build 492 for Rapid Chloride Migration
(RCM) and Bulk Resistivity (BR) for both sound (uncracked) and cracked (micro and
macro) concrete. The limitations of the ASTM method, due to measurements before the
steady-state migration is reached, does not account for leakage in cracked concrete, and the
heating of the specimen due to higher current that increase the conductivity are indicated.
The Rapid Chloride Migration test provides for the non-steady state of diffusion. Again,
Bulk Resistivity, in contradistinction to Surface Resistivity is more accurate for cracked
concrete. The correlation betweeen RCM-BR are plotted. Chloride Permeability/Migration
is an important parameter that governs the Durability of Concrete.
The principal contribution is the highlighting of the inadequacy of the current widely used
standard ASTM C1202 for diffusivity testing, and the need for revision with further
investigation.

The Durability of Reinforced Concrete (RC) structures in the Marine environment is causing increasingly serious concern in the structural infrastructures. RC structures, exposed to aggressive environments, are expected to last with little or no maintenance for long periods of time. However, one of the most serious environmental exposures that cause degradation is Chloride Diffusion, with tide-simulated wet and dry conditions at the air-water interface.

This investigation, jointly project with Cemex (a cement mixing company), will address the change of chloride diffusion current resistivity due to macro and micro cracking, which is inevitable in all concrete structures. The correlation of Chloride Diffusivity with Electrical Current Resistivity of Sound and Cracked Concrete is studied experimentally, and the results compared with Analytically Determined values.

The principal benefit of the research is the formulation of models to predict time-dependent Chloride Penetration into Sound and Cracked Concrete in the Marine environment.

This research is aimed at investigating and analyzing the rain-windinduced cable vibration phenomena experienced in cables of cable-stayed bridges and also the countermeasures employed by engineers to mitigate the large-amplitude vibration problem reported by various researchers around the world. In order to investigate the problem of the water rivulet creation at the top of the cable surface, a single-degree-of-freedom (SDOF) analytical model was developed and analyzed. This thesis studies the aerodynamic instability of cables in cable-stayed bridges by doing literature review of a typical in-situ test, developing a single degree-of-freedom (SDOF) analytical model, and an ANSYS finite element model. Furthermore, a linear viscous damper that acts as a
countermeasure to the large amplitudes of vibration is reported and analyzed. The suppression characteristics and damper effectiveness of such countermeasure are summarized.

One of the major causes of structural repairs worldwide is the corrosion of reinforced
concrete structures, such as residential buildings and piers, which are exposed to harsh
marine environments. This investigation aims to provide experimental evidence of the
fire resistance of corroded high strength reinforced concrete. For this, 14 reinforced
concrete beams of three different concrete mix designs (different strengths) were
prepared along with concrete cylinders for compression strength testing (ASTM C39).
After proper moist curing, all beams were corroded, in two phases, with impressed
current, then “crack scored ”for corrosion evaluation, after which half were exposed to
fire, also in two phases, following the ASTM E-119-12 time-temperature curve, using a
gas kiln. The fire damage was evaluated and compared between phases by using
Ultrasonic Pulse Velocity technology. Finally, all specimens were tested for flexural strength by using the third-point loading method (ASTM C78) and the effects of fire on the corroded beams were analyzed according to the level of corrosion.

Three vital factors, namely environmental protection, savings in energy, and technical benefits, make it advantageous to incorporate fly ash of controlled quality and composition in all concrete construction. The specific objective of this research was to compare the performance characteristics of fly ash-modified concrete with that of normal concrete in the coastal environment. To make this comparison, a series of tests using appropriate ASTM standards were conducted. First, the compressive strength development of five mixes was studied. Reinforced beam specimens were then subjected to varying periods of accelerated corrosion with sea water as electrolyte. These were tested under flexure and impact. An attempt was made to predict remaining life. Finally, permeability tests were carried out. Results indicate that fly ash increases compressive strength, improves both moment carrying capacity and impact resistance, and increases watertightness.

An overview of the current issues of HDPE pipe-soil systems is followed by a comprehensive literature review addressing current specifications, design methods, and relevant research projects. The following experimental tasks are described: (i) environmental stress cracking resistance (modified AASHTO M294), (ii) creep (10,000 hour parallel plate loading at super ambient temperatures), (iii) performance of buried pipes, subjected to live loading in a soil chamber, and (iv) field monitoring. The findings include (i) satisfactory short-term environmental stress cracking resistance, (ii) temperature-dependency of the flexural modulus, (iii) the evidence of transition between slow crack growth and rapid crack propagation due to imperfect installation, and (iv) high load carrying capacity for the properly installed pipe in uniform backfill, showing an over-deflection failure mode with top flattening. The analytical investigations are as follows: (i) Bidirectional shift-constructed master curve, based on accelerated creep test values for long-term modulus prediction that showed good agreement with the Arrhenius equation-based analysis, (ii) Development of a seven-degree Voigt-Kelvin viscoelastic model based on the bidirectional shift-constructed master curve for analytical prediction of the long-term modulus, (iii) Comparison of two-dimensional and three-dimensional harmonic FEM analyses with the measured response of pipe-soil interaction, that demonstrated the analytical predictability of the pattern of deformation and stress distribution, and (iv) Determination of axial stress distribution along the pipe in non-uniform backfill condition, evaluated by approximate analysis based on finite differencing the deflection profile obtained from the assembly of individual finite segments/sections. This overcomes the limitation of the harmonic FEM analysis for pipe-soil interaction involving non-uniform soil conditions longitudinally and/or varying soil thickness circumferentially. The findings include (i) importance of axial stress contribution at failure, (ii) top flattening failure mode due to over-deflection preceding buckling or yielding, and (iii) critical adverse effect of the non-uniform backfill condition that can lead to joint opening, localized buckling, liner tearing/debonding, or cracking. The work has "spin off" applications to the coastal and offshore environments for sewage outfalls, marine pipelines etc.

The primary goal of this study was to evaluate the service life of HDPE (High Density PolyEthylene) pipes. The following experimental tasks were carried out: (i) procurement of materials, and fabrication of test setups; (ii) creep evaluation: the performance of buried pipes (notched/unnotched), subjected to live loading, was studied in soil chambers for three levels of loading (service, 2/3 and 1/3 of service). The long-term behavior was accelerated with super-ambient temperatures; (iii) field monitoring: strains and diametral changes were measured for 10,000 hours. The analytical investigations were as follows: (i) extrapolation of the long-term performance at ambient temperature, based on the Bi-directional and the Arrhenius methods and (ii) 2-D Finite Element Analysis, using the software CANDE. The findings include: (i) the deflection threshold (7.5% vertical change of diameter) as the governing failure condition, (ii) similar life predictions, for Bi-directional and Arrhenius methods, with service lives of about 80 and 30 years at ambient temperature, for unnotched and notched specimens, respectively, subjected to maximum loading, and (iii) a reasonable agreement between analytical and experimental values.

An experimental and analytical investigation is presented for two types of geogrids: HDPE (High Density Polyethylene) and PET (Polyester). Sand and limerock were used for the backfill material, which meet the FDOT (Florida Department of Transportation) Material Specifications, with simulation of unsaturated and saturated condition. Eight pullout test boxes were designed and constructed, each with a specially designed stainless steel clamp. The measured strain-time relations for unsaturated and saturated soils for various levels of the pullout force until the peak value (up to 10,000 hours of exposure), and varying distances from the loading end were plotted. The normal and principal stresses in the soil, and the strains along the geogrid were determined from the finite element analysis for the unsaturated soil condition for various pullout force levels. The results were analyzed and a generalized method proposed for practical design using sliding resistance factors.