Fatigue cracking is one of the fundamental distresses that occur in the life of a Hot Mix Asphalt Concrete (HMAC) pavement. This load induced distress leads to structural collapse of the entire pavement ultimately and can only be remedied by rehabilitation. There is the need, therefore, for a total understanding of the phenomenon to be able to counter its occurrence. The fatigue resistance of hot mix asphalt concrete (HMAC) has been estimated using approaches ranging from empirical methods to mechanistic-empirical methods to purely mechanistic methods. A continuum mechanics based approach called the Calibrated Mechanistic with Surface Energy (CMSE) measurements was developed at Texas A&M University and recommended after comparison with other approaches in predicting fatigue lives of two Texas HMAC mixtures. The CMSE approach which includes fundamental material properties such as fracture, aging, healing, and anisotropy has been shown to effectively model the parameters that affect the performance of HMAC pavements exposed to repetitive traffic loads. Polymer modified asphalt (PMA) improves pavement performance by providing additional resistance to the primary distresses in flexible pavements, including permanent deformation or rutting, thermal cracking, and fatigue cracking. In this research, the CMSE approach was utilized to estimate the fatigue resistance of HMAC fabricated with asphalts modified with Styrene-butadiene-Styrene (SBS) co-block polymer. These HMAC mixtures were fabricated from materials used on three different road sections in Texas and one test pavement in Minnesota. The CMSE approach was validated as an effective approach for estimating the fatigue resistance of HMAC mixtures with PMA. The effect of oxidative aging on the fatigue resistance of the HMAC mixtures was also verified. Oxidative aging of the mixtures resulted in a corresponding decrease in mixture fatigue resistance. In addition, for two HMAC mixtures with the same binder content and aggregate gradation, the mixture with the softer of the two Performance Grade (PG) binders exhibited greater fatigue resistance. The use of the Utility Theory revealed the possible effects of aggregate geometric properties on the HMAC mixture properties and consequently on their fatigue resistance.

In recent years an increased use of polymers has occurred to modify asphalt binders, mainly to decrease pavement rutting but also to improve binder failure strain in direct tension. Whereas all of these effects positively impact the durability of polymermodified pavements, a need exists to quantify these improvements and the duration in the presence of oxidative aging. This research evaluated the durability of polymer modified asphalt (PMA) through a number of determinations that included the characterization of the original binder property and pavement-aged binder for modified and unmodified binders. Changes in styrene-butadiene-styrene (SBS) polymer modified binder properties from oxidation were analyzed using dynamic shear rheometry, ductility, and force ductility. Previous literature reports using size exclusion chromatography showed that degradation of the molecular weight profile of SBS accompanied the loss of PMA ductility. Yet base binder embrittlement also occurred, as evidenced by ductility and force ductility. Testing aged PMA binders at higher temperatures to soften the base binder restored the polymer modulus to the force ductility measurements as did blending with a softer deasphalted oil. These measurements indicate that the more significant cause of PMA degradation with aging is base binder embrittlement rather than polymer degradation. Sixteen pavements in 11 Texas Districts, plus four MnRoad pavements were evaluated in order to obtain a more detailed profile of binder oxidation in pavements. Slices of each core provided detail on binder oxidation and air voids. The data confirm that binders can oxidize at least several inches into the pavement. However, oxidation also can be significantly slowed, apparently by very low accessible air voids. Interestingly, the data indicate that the air voids that are relevant to the binder at a specific depth of the pavement are those in the immediate vicinity of the binder; low air voids above or below the binder do not seem to significantly affect the binder oxidation rate. Furthermore, that binders oxidize inches below the surface shows that temperature conducts well into the pavement, consistent with a heat conduction model that is used to calculate ground temperatures as a function of depth.

Fatigue cracking is one of the fundamental distresses that occur in the life of a Hot Mix Asphalt Concrete (HMAC) pavement. This load induced distress leads to structural collapse of the entire pavement ultimately and can only be remedied by rehabilitation. There is the need, therefore, for a total understanding of the phenomenon to be able to counter its occurrence. The fatigue resistance of hot mix asphalt concrete (HMAC) has been estimated using approaches ranging from empirical methods to mechanistic-empirical methods to purely mechanistic methods. A continuum mechanics based approach called the Calibrated Mechanistic with Surface Energy (CMSE) measurements was developed at Texas A&M University and recommended after comparison with other approaches in predicting fatigue lives of two Texas HMAC mixtures. The CMSE approach which includes fundamental material properties such as fracture, aging, healing, and anisotropy has been shown to effectively model the parameters that affect the performance of HMAC pavements exposed to repetitive traffic loads. Polymer modified asphalt (PMA) improves pavement performance by providing additional resistance to the primary distresses in flexible pavements, including permanent deformation or rutting, thermal cracking, and fatigue cracking. In this research, the CMSE approach was utilized to estimate the fatigue resistance of HMAC fabricated with asphalts modified with Styrene-butadiene-Styrene (SBS) co-block polymer. These HMAC mixtures were fabricated from materials used on three different road sections in Texas and one test pavement in Minnesota. The CMSE approach was validated as an effective approach for estimating the fatigue resistance of HMAC mixtures with PMA. The effect of oxidative aging on the fatigue resistance of the HMAC mixtures was also verified. Oxidative aging of the mixtures resulted in a corresponding decrease in mixture fatigue resistance. In addition, for two HMAC mixtures with the same binder content and aggregate gradation, the mixture with the softer of the two Performance Grade (PG) binders exhibited greater fatigue resistance. The use of the Utility Theory revealed the possible effects of aggregate geometric properties on the HMAC mixture properties and consequently on their fatigue resistance.

No description available.

Current mathematical models, developed on straight asphalt binders, are inadequate to characterize the frequency dependence of response of polymer-modified asphalt binders. In an earlier study at Virginia Tech, mathematical models were developed to predict the storage and loss shear moduli of polymer-modified binders. However the model developed for the loss shear moduli is limited at high frequency (G" less than or equal to 10^7.5 Pa). This thesis presents a statistical modeling of loss shear modulus of polymer (random copolymers and thermoplastic block copolymers) modified binder. Data from dynamic mechanical analysis on modified binders, at temperatures between 5 and 75°C and frequencies ranging from 0.06 to 0188.5 rad/s, were reduced to dynamic master curves of moduli, and used to develop the model. Twenty-one polymer-binder blends prepared and tested earlier at Virginia Tech where included in the study. Realistic characterization of loss shear moduli values was obtained using the Gompertz statistical model. The model was validated by using mean square error of prediction (MSEP) in which a second set of frequency data was input in the model to obtain the moduli values, which were compared to the measured data of the second set. Although this model was successfully tested for shear loss modulus prediction of polymer-modified binders, caution should be exercised when it is applied, as such a model should be able to predict the storage modulus for a known phase angle. / Master of Science

No description available.

The increase and change in traffic loading in recent years has resulted in the introduction of a new range of high performance asphalt binders. These new binders known as modified asphalt binders, have a more complex behavior than traditional binders. A review of the current mathematical models shows that most of them suffer from different drawbacks that make them inadequate for their intended application. To describe the behavior of straight and modified binders in the thermorheologically simple linear viscoelastic region, two models are proposed. Models to characterize the absolute value of the complex shear modulus (|G*|) and the phase angle (d) were developed using the matching function approach and validated by an experimental program. The dynamic mechanical properties of two typical paving grade binders and three modified binders were tested at intermediate and high service temperatures. Short-term and long-term aging were simulated by the rolling thin film oven test and the pressure aging vessel test, respectively. A dynamic shear rheometer with parallel plate configuration was used to conduct the dynamic mechanical tests at frequencies between 0.06 to 188.5 rad/sec and temperatures ranging from 5 to 75°C. Prior to the frequency sweeps, strain sweeps were performed to establish the linear viscoelastic region. Results indicated a strong susceptibility to the defined strain at intermediate temperatures; however, strain susceptibility was less pronounced at high temperatures. Frequency sweeps were then conducted at a constant strain corresponding to greater than 95% of the initial complex shear modulus as established by AASHTO TP5 for straight asphalts. The Time-Temperature Superposition Principle was used to construct the master curves. The shift factors were determined based on the complex shear modulus master curves and verified for the phase angle, storage shear modulus and loss shear modulus. After construction of the master curves, non-linear regression was used to fit the proposed models to the experimental data. Comparison between the measured and predicted values indicated a good agreement for frequencies higher than 10⁵ rad/sec. The phase angle model was found to adequately describe unmodified binder with a small percentage of errors (less than 6%). On the other hand, the phase angle model was found unable to simulate the plateau region observed for polymer-modified binders. However, the error in this case was found to be relatively small (from zero to 10%). The ability of the models to estimate other viscoelastic functions, e.g. storage shear modulus (G'), loss shear modulus (G"), and relaxation spectrum (H(t)), was found to be adequate. / Master of Science

Nephropathic cystinosis is a rare autosomal recessive disease characterised by raised lysosomal levels of cystine in the cells of almost all organs. It is treated by regular oral and topical administration of the aminothiol, cysteamine(Cystagon™), which possesses an offensive taste and smell. The oral form frequently causes emesis,and should be administered every six hours to be maximally effective. The topical eye drop treatment requires hourly application to be most effective.In an attempt to reduce this frequency and improve the treatment, the preparation and evaluation of three alternative cysteamine containing formulations (suppositories, long-acting ophthalmic gels and an inhaler) was undertaken. The physiochemical properties, stability and release profiles of the active (cysteamine or phe conjugate) from the formulations were evaluated. The suppositories released cysteamine over a 20-40 minute period with a T75= 10-13minutes. They were most stable at 4°C. The analysis of the ophthalmic gels demonstrated that a weak gel network was formed at low shear stress, the bioadhesion of the gel was increased with inclusion of a cysteamine derivative (e.g.mean force of 0.067N compared to 0.107N with compound included) and eight-hour, first order release from the gel was observed. There was significant adhesion observed between the ophthalmic gels and bovine corneal tissue. The pulmonary microspheres were spherical and within the optimum size range for deep lung delivery (1-5μm). However, Andersen Cascade Impactor analysis revealed poor deep lung penetration. In conclusion, these results demonstrated that more development work was required to produce a useful pulmonary formulation of cysteamine, however, formulation of an ocular applicable gel or suppository was readily achievable. The suppository preparations may be particularly beneficial for the treatment of infants, whilst the ophthalmic gel preparations could be developed for daily or overnight use. With respect to pulmonary delivery, microspheres in the optimum size range were produced. However, deep lung targeting was prevented by static agglomeration, which requires further investigation.

Este trabalho teve como objetivo avaliar o comportamento de duas misturas asfálticas preparadas com asfaltos diferentes, uma com asfalto convencional (CAP 20) e outra com asfalto modificado pela adição de polímeros (BETUFLEX B 80/60), à luz dos resultados de dois ensaios distintos, o ensaio Marshall e o ensaio de fluência por compressão uniaxial estática. O ensaio de fluência uniaxial estática consiste, numa forma indireta, para avaliar a resistência da mistura asfáltica à formação de trilha de roda ou à deformação permanente. Os resultados dos ensaios Marshall não permitiram concluir se houve melhora no desempenho das misturas asfálticas em função da adição de polímeros, com exceção de uma única propriedade, a estabilidade, que apresentou-se sempre maior para a mistura feita com asfalto convencional, independente do teor utilizado. Já com relação aos resultados dos ensaios de fluência por compressão uniaxial estática, pode-se concluir que há uma tendência de melhora no comportamento das misturas preparadas com asfalto modificado com polímero. / The aim of this work is to evaluate the behaviour of two asphaltic mixtures prepared with different kinds of asphalts, one with conventional asphalt (CAP 20) and the other one with modified asphalt by addition of polymers (BETUFLEX B 80/60), from the results of the two different tests, the Marshall test and the static creep test. The latter test allows to estimate the asphaltic mixture resistance against the formation of the rut depth or the permanent deformation. The results of the Marshall did not allow to conclude if there was improvement in the performance of the asphaltic mixtures due to the addition of polymers, excluding only one feature, the stability, that showed always greater to the mixture made with the conventional asphalt, independently of the content used. As far as the results from the static creep test are concerned, it is possible to conclude that there is a tendency of improvement in the behaviour of the mixtures prepared with asphalt modified with polymer.

O presente trabalho avalia as alterações de propriedades dos asfaltos pela modificação por polímero do tipo RET (Reactive Elastomeric Terpolymer) e de comportamento de misturas asfálticas densas usinadas com estes asfaltos modificados. Para atingir este objetivo, são apresentados os resultados do monitoramento realizado no trecho experimental executado na SP-330, Rodovia Anhanguera, que empregou este tipo de asfalto modificado e estudo que compreende a modificação de ligantes do tipo CAP20 e CAP40 com 1,0%, 1,5% e 2%, de polímero RET, com posterior dosagem de uma mistura na Faixa III do DERSA no teor considerado como o mais adequado. Para verificação das propriedades mecânicas desta mistura, foram realizados ensaios de Módulo se Resiliência, Resistência à Tração por Compressão Diametral e Resistência à Deformação Permanente em simulador do tipo LPC. / The present document presents the alterations of the properties of the polymer modified asphalts using the polymer RET (Reactive Elastomeric Terpolymer) and the behavior of dense asphaltic mixtures using these modified asphalts. To reach this objective, the monitoring results accomplished in the experimental tram executed in SP-330, Rodovia Anhanguera, that used this type of modified asphalt are presented. The study comprehends the modification of the CAP20 and CAP40 asphalts with 1,0%, 1,5% and 2,0% of RET polymer, with subsequent dosage of a mixture in the Grade III of DERSA applying the RET polymeric proportion considered more appropriate. For the verification of the mechanical properties of this mixtures, Resilience Module, Traction Resistance for Diametrical Compression and Permanent Deformation Resistance in a LPC type simulator were accomplished.