No description available.

This PhD dissertation addresses a number of issues pertaining to the use and application of surface treatments using asphalt emulsions. The work conducted as part of this research study shows in detail the problems associated with the state-of-practice and how these issues can be addressed using a scientific and rational approach as opposed to the experience-based approach which is prevailing currently. The first objective of this research study focuses on developing a methodology to determine the total amount of evaporative water loss of an emulsion before the aggregates are placed. An algorithm is presented that can be used by field inspectors and practitioners for the optimal timing of chip placement. The second objective focuses on another key aspect associated with the constructability of surface treatments, i.e., the optimal time to open a new surface treatment to traffic. Laboratory tests were conducted on the emulsion and aggregates to measure the rate of moisture loss and the evolution of the rheological properties as function of time. This was related to the field measured evaporation rates to determine the minimum stiffness required for optimal performance of the chip seal towards adequate resistance to raveling. The final objective of this dissertation focuses on developing a theoretical understanding of the current flowing through a circuit when an emulsion separates into its constituent phases when placed in an electric field. The measured current depends on a set of material properties that include the emulsion’s viscosity, surface potential, and dielectric of the medium and the strength of the electric field. A theoretical formulation was developed that relates the current flowing through the circuit with the mobility of the charged particles and the bulk charge density. The proposed theory was further utilized in developing a test procedure to quantify the breaking characteristics of asphalt emulsions. Results demonstrated that the parameters obtained from these tests were repeatable and different for different types of asphalt emulsions. It was also noticed that for a given type of emulsion the test method is sensitive to factors such as water content and partial breaking due to mechanical agitation. / text

This work is a contribution to the study of the curing of silicone prepolymers (hydroxyfunctional polydimethyl siloxanes) and the physical properties of the resulting networks. The kinetics of curing of one of the prepolymers has been studied with a simple new inexpensive piece of equipment i.e the Vibrating Needle Curemet~r (VNC). The order of reaction with respect to crosslinker and catalyst concentration has been determined to be unity and 0.24 respectively while an attempt has been made to determine the order of reaction with respect to silanol group concentration in the prepolymer. The effect of. crosslinker and catalyst concentration was observed to check the validity of the Lake and Thomas theory; namely that tear strength at a particular condition is proportional to the square root of the molecular weight between crosslinks. It has been found that varying crosslinker concentration is a better way to test this theory. Surprisingly the detailed physical properties such as tear and tensile of the supposedly different prepolymer networks showed little relationship to the molecular weight. The effect' of blending short and long chain polymers i.e bimodality, and that of the concentration of the crosslinker on the physical propert; es has been investigated. It became apparent that in addition to bimodality, the physical properties are dependent upon the amount of cross1inker used for curing This is a factor which has not previously been reported. It has also been shown that unfortunately, contrary to expectation bimodality has adverse effects on the physical properties of the highly filled networks. In the case of the tensile properties, the stress strain curves were analysed in light of tne phenomenological Mooney - Rivlin (MRL) and Martin, Roath and Stiehler (MRS) equations. Apart from successfully applying these theories to stress-strain curves, the structure factors of networks have been' obtained. These theories have been used in parallel to check and compare the results of one technique with the other. However, in the case of the filled HOPDMS networks it is evident that only the MRS equation can successfully describe the stress-strain data. The stress-strain data for the various HOPDMS filled networks have been compared with one another in terms of Young's modulus from their practical point of view.

No description available.

This thesis is concerned primarily with the curing of epoxy resin and the effect of gamma-irradiation on the electrical properties of epoxy resin systems. The particular systems examined were a diglycidyl ether of bisphenol A (DGEBA, Ciba Geigy MY750) epoxy resin cured using one of two hardeners. These were a hydroxyalkylated polyamine (Ciba Geigy HY956) and a dodecenyl-succinicanhydride (DDSA) with an accelerator of benzyldimethylamine. Different methods of examining the curing of the epoxy resin system have been carried out including differential scanning calorimetry (DSC), infrared spectroscopy (I.R.), dielectric measurements, volume resistivity measurements and thermally stimulated discharge current. The results of dielectric relaxation measurements obtained during the curing of the epoxy resin system were interpreted on the basis of a model considering the growing polymer molecules to be in solution, the solvent being the unreacted monomer and hardener. The investigation of the effect of gammairradiation on the electrical properties (conduction mechanism and dielectric behaviour) of the epoxy resin system was achieved by examining the electrical properties of the fully cured epoxy resin system before and after irradiation and the results compared. To establish the electrical properties of the fully cured epoxy resin system before and after irradiation, a series of experiments which provide information about the conduction mechanism, the dielectric properties, the infrared spectra (I.R.) and the glass transition temperature (Tg) obtained from (DSC) measurements were carried out. For the epoxy resin system MY750/HYS56, it was found that the D.C. conductivity, dissipation factor and capacitance values increase, whereas the glass transition temperature (Tg) and the activation energy, E, obtained from D.C. measurements decreased for the irradiated samples. Furthermore, a modification in the I.R. spectrum in the 1600 to 1800 cm⁻¹ range due to the formation of carbonyl groups (C = O) in the irradiated sample has been observed. However in the case of epoxy resin system MY750/DDSA, it was found that the dissipation factor and capacitance values decrease, whilst the glass transition temperature (Tg) and the activation energy obtained from dielectric measurements increased for the irradiated samples.

No description available.

Thesis--Wisconsin. / Includes bibliographical references (leaves 175-189).

The process of curing epoxides with amines has been for many years a route to obtain many useful materials, from everyday substances such as adhesives right through to thermoset resins used in advanced composite manufacture. This work will try to highlight how a combination of chemical and numerical techniques come together to aid the further understanding, of what is an extremely complex reaction. Chapter 1(a) is a general review of epoxy resin curing chemistry, paying particular attention as to how our understanding of the process has developed over several decades, and highlights the various techniques used to study the reaction. Chapter 1(b) describes the experimental approach taken in this work, namely that of using model reactants in combination with radiochemical techniques in order to gain kinetic information about cure reactions. In Chapter 2 the development of the various kinetic models is discussed. It is first described how, and on what basis, various aspects of the cure chemistry are incorporated into the model. One then goes on to describe the numerical analysis applied to the rate equations, and how this is incorporated within the model. The results of the two major aspects of the work are divided into two distinct areas. The first (Chapter 3) deals with the modelling of those reactions using a low initial concentration of primary amine (usually < 0.6M). These systems are devoid of many of the complicating features of cure reactions, and are shown to be modelled to a high degree of accuracy. In essence they are ideal systems, and ones which the initial model (KINET31) used in this study is able to describe. Chapter 3 also describes some studies carried using aromatic diamines, and the modelling performed of these reactions. Chapter 4 on the other hand deals with those reactions which used high initial amine concentrations. By contrast the standard of modelling shown here with KINET31 was much poorer. It is then described how various physical aspects of the cure reaction are investigated in an attempt to highlight the model's inadequacy. It is eventually shown how H-bonding of species, and the formation of pre-complexes, can play a very significant role in cure reactions. When the model is adapted to take these interactions into account a significant improvement is noted (KINET31H). Finally Chapter 5 deals with another interesting aspect of cure reactions, namely that of accelerators. With the model now taking into account the formation of the most are. significant pre-complexes, the reactivities of various -OH type accelerators are investigated.

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