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This thesis investigated corrosion of a reinforcing steel bar embedded in concrete and the effect of corrosion coupling on the bar/concrete interface induced by the variation of corrosion potentials with concrete depth. Two separate numerical models were used to simulate the corrosion process which included: a two-dimensional finite element model for mass transport of oxygen and chloride to the bar/concrete interface; and, a one-dimensional model for the corrosion current flow through the electrolyte induced by corrosion potential differences on the bar/concrete interface. A novel approach to corrosion modeling in reinforced concrete that had not been identified in the literature was used. This new approach, incorporated: variable solution conductivity developed from concentrations within the pore solution; anodic and cathodic areas modified to maximize corrosion current through the electrolyte; and, kinetics of corrosion set by the pore solution chemistry. Various reinforcing configurations and moisture conditions were evaluated within the simulation to obtain insight into the effect these variables have on corrosion potentials measured on the concrete surface and the corresponding corrosion currents generated on the bar/concrete interface. Variables related to bar diameter, concrete cover, and bar spacing where all shown to affect corrosion potentials and current densities on the bar/concrete interface and the concrete surface where field measurements are obtained. Moisture conditions were found to have the largest impact on corrosion potentials and current density’s on the bar/concrete interface. When relative humidity’s of 90% or higher were used, simulated corrosion potentials on the concrete surface under high chloride conditions were found to reach values identified in ASTM C876 and Alberta Transportations Deck Testing Guidelines that indicate active corrosion. However, when moisture conditions were reduced to below 90% relative humidity, simulated corrosion potentials on the concrete surface for high chloride concentrations did not achieve values that indicate a high probability of corrosion. This result suggests a secondary mechanism must be present on the bar/concrete interface that changes the chemical composition within the pore solution to shift the kinetics of corrosion to an environment that will produce the negative corrosion potentials recognized as indicating a high probability of corrosion. Therefore, a new mechanism is proposed that outlines the process necessary for the pore solution on the bar/concrete interface to transition the kinetics of corrosion to an actively corroding state at low relative humidity. This mechanism requires local acidification of the pore solution along portions of the bar where anodic processes are increased due to the presence of chloride and reduced oxygen availability. Reaching this environment requires free OH- to be consumed without replenishment from the surrounding environment by either diffusion from high pH areas or dissolution of the hardened portions of the pore structure. The proposed mechanism begins with corrosion by-products formed when Fe2+ reacts with free OH-, precipitates from the pore solution onto the pore structure as Fe(OH)2. Once precipitated, the contact area between pore solution and hardened portions of the pore structure are reduced which restricts the dissolution process for restoring OH- removed from the electrolyte. Additionally, precipitation of Fe(OH)2 reduces the flow of OH- from the surrounding high pH zones as the pore structure is restricted. Both mechanisms result in a pH gradient being formed with acidified zones created on the bar/concrete interface in the anodic regions. These acidified zones cause the kinetics of corrosion to transition from a passivated state, towards an environment similar to carbonation.

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The excess molar volumes VEm and the excess molar enthalpies HEm have been determined for several binary systems at 298.15 K using an Anton Paar Digital Densitometer and a 2277 Thermal Activity Monitor, respectively. VEm and HEm have been determined over the whole composition range for three types of binary mixtures involving hydrogen bonded interactions. The three types are: (i) a short chain alkanol (methanol, ethanol, 1-propanol, 2-propanol) or (ii) a symmetrical secondary amine (di-n-ethylamine, di-n-propylamine) or (iii) 1-alkyne (l-hexyne, 1-heptyne, l-octyne) with a branched chain ether (diisopropyl ether, 1,1-dimethylethyl methyl ether, 1,1dimethylpropyl methyl ether) and a cyclic ether (tetrahydrofuran, tetrahydropyran, 1,4dioxane). For mixtures of (an alkanol + a branched chain ether or a cyclic ether) the results are explained in terms of the strong self association exhibited by the alkanol and the cross association of the OH:::::O specific interaction. In particular for mixtures of (an alkanol + a cyclic ether) the results show trends relating to the size of the cycloether ring and the number of carbon atoms in the alkanol molecule. For mixtures of a secondary amine + a branched chain ether or a cyclic ether the experimental results have been explained on the basis of the strong molecular interactions (NH·····O) between the weakly self associating secondary amine and the ether oxygen. For binary mixtures of 1-alkyne + a branched chain ether the results indicate a dominance of the π....π interaction over either the dissociation effects of the 1-alkyne (π..... π interactions) or the breakdown of the branched chain ether molecules self association. Thermophysical property data, density p, cubic expansion coefficient ex and isothermal compressibility KT have also been determined for several aliphatic ethers from 288.15 K to 328.15 K at pressures ranging from 0.1 to 8 MPa. The molar volumes derived from the densities have been fitted to a polynomial as a function of temperature and pressure and the second order thermodynamic functions, the cubic expansion coefficient ex and the isothermal compressibility KT determined. For all the ethers, the cubic expansion coefficients decrease with an increase in temperature or pressure while the isothermal compressibilities increase with an increase in temperature or pressure over the temperature and pressure ranges investigated. This work was carried out in the Thermodynamics laboratory of the Indian Institute of Technology in India. This data was required so that the experimental VEm and HEm data could be analyzed using modern theories of liquid mixtures. The VEm and HEm data presented here has been subjected to the following theoretical analysis: (i)The Extended Real Associated Solution (ERAS) model, (ii)The Modified Universal Functional Activity Coefficient (UNIFAC) group contribution model and (iii) The simple Flory and the Prigogine Flory Patterson theory (PFP). All the theories exhibited partial success when applied to the systems investigated here. Excess molar volumes and excess molar enthalpies, VEm and HEm have also been determined over the whole composition range for binary mixtures involving symmetrical (a straight chain ether or ketone + a pseudo straight chain ether or a pseudo straight chain ketone) to test the applicability of the congruency theory. Not all of the mixtures satisfied the null test of the congruency principle. / Thesis (Ph.D.)-University of Natal, 1996.

Iron is the most common impurity in hydrometallurgy which is usually removed by precipitation of insoluble iron compounds, such as hematite and jarosite. The knowledge of iron solubility in multicomponent solutions is important for design and optimization of the iron removal steps. The OLI Software package is a chemical modeling tool that incorporates the powerful mixed-solvent electrolyte (MSE) model capable of performing simulations of multicomponent electrolyte solutions from the freezing point up to the limit of fused salt and near the critical temperature of the solution. Literature or experimental solubility data was fitted on the OLI MSE model to improve the performance in simulating multicomponent Fe(II)/Fe(III) solutions. The particular focus of this work aimed at developing simulation capability for the FeCl3-MgCl2-HCl-H2O system through experimental solubility measurement and modeling, relevant to atmospheric processing of saprolites by HCl using MgCl2 brines.

Iron is the most common impurity in hydrometallurgy which is usually removed by precipitation of insoluble iron compounds, such as hematite and jarosite. The knowledge of iron solubility in multicomponent solutions is important for design and optimization of the iron removal steps. The OLI Software package is a chemical modeling tool that incorporates the powerful mixed-solvent electrolyte (MSE) model capable of performing simulations of multicomponent electrolyte solutions from the freezing point up to the limit of fused salt and near the critical temperature of the solution. Literature or experimental solubility data was fitted on the OLI MSE model to improve the performance in simulating multicomponent Fe(II)/Fe(III) solutions. The particular focus of this work aimed at developing simulation capability for the FeCl3-MgCl2-HCl-H2O system through experimental solubility measurement and modeling, relevant to atmospheric processing of saprolites by HCl using MgCl2 brines.

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