As misturas asfálticas do tipo SMA apresentam granulometria descontínua, composta por uma maior fração de agregados graúdos, uma rica massa de ligante/fíler (mastique) e aproximadamente 4% de volume de vazios. Possuem um esqueleto pétreo de alta estabilidade devido ao contato pedra-pedra, que proporciona uma maior resistência à deformação permanente. Geralmente o teor de ligante asfáltico é superior a 6%, formando uma película asfáltica mais espessa. São utilizadas fibras para evitar o escorrimento do ligante durante as etapas de produção e lançamento e, geralmente, são usados asfaltos modificados por polímero. Esta pesquisa tem por objetivo avaliar se o ligante asfalto-borracha possibilita misturas asfálticas SMA capazes de atender aos valores limites de aceitação e, por meio de ensaios de laboratório (resistência à tração, módulo de resiliência, fadiga e deformação permanente em simulador de tráfego), comparar o comportamento de misturas SMA com diferentes tipos de ligante (asfalto convencional CAP 20, modificado por polímero e asfalto-borracha) com um concreto asfáltico convencional de granulometria contínua (Faixa C do DNER). Os resultados obtidos apresentam o comportamento de uma mistura SMA com asfalto-borracha muito mais próximo de misturas SMA produzidas com um ligante modificado por polímero do que com um asfalto convencional. / SMA is a gap-graded asphalt mixture with a large proportion of high quality coarse aggregate, a high content of mastic (binder/filler), and approximately 4% of air voids. The larger proportion of coarse aggregate provides a greater stone-to-stone contact, which results in a mixture more resistant to permanent deformation than the conventional Hot Mix Asphalt (HMA). The asphalt content is typically greater than 6.0 percent, which increases the film thickness. Fibers are used to prevent drainage of the asphalt binder during the HMA production and placement, and polymer-modified asphalt cements are usually used. This research aims to evaluate if an asphalt-rubber binder produces SMA mixtures able to meet the technical requirements. The behavior of SMA mixtures produced with different binders (conventional AC-20, polymermodified, and asphalt-rubber) is analyzed based on laboratory tests (tensile strength, resilient modulus, fatigue, and permanent deformation in a traffic simulator) and compared to the behavior of a conventional dense-graded HMA The results show that the behavior of SMA mixtures produced with asphalt-rubber is much closer to SMA mixtures produced with polymer-modified binder than conventional asphalts.

As misturas asfálticas do tipo SMA apresentam granulometria descontínua, composta por uma maior fração de agregados graúdos, uma rica massa de ligante/fíler (mastique) e aproximadamente 4% de volume de vazios. Possuem um esqueleto pétreo de alta estabilidade devido ao contato pedra-pedra, que proporciona uma maior resistência à deformação permanente. Geralmente o teor de ligante asfáltico é superior a 6%, formando uma película asfáltica mais espessa. São utilizadas fibras para evitar o escorrimento do ligante durante as etapas de produção e lançamento e, geralmente, são usados asfaltos modificados por polímero. Esta pesquisa tem por objetivo avaliar se o ligante asfalto-borracha possibilita misturas asfálticas SMA capazes de atender aos valores limites de aceitação e, por meio de ensaios de laboratório (resistência à tração, módulo de resiliência, fadiga e deformação permanente em simulador de tráfego), comparar o comportamento de misturas SMA com diferentes tipos de ligante (asfalto convencional CAP 20, modificado por polímero e asfalto-borracha) com um concreto asfáltico convencional de granulometria contínua (Faixa C do DNER). Os resultados obtidos apresentam o comportamento de uma mistura SMA com asfalto-borracha muito mais próximo de misturas SMA produzidas com um ligante modificado por polímero do que com um asfalto convencional. / SMA is a gap-graded asphalt mixture with a large proportion of high quality coarse aggregate, a high content of mastic (binder/filler), and approximately 4% of air voids. The larger proportion of coarse aggregate provides a greater stone-to-stone contact, which results in a mixture more resistant to permanent deformation than the conventional Hot Mix Asphalt (HMA). The asphalt content is typically greater than 6.0 percent, which increases the film thickness. Fibers are used to prevent drainage of the asphalt binder during the HMA production and placement, and polymer-modified asphalt cements are usually used. This research aims to evaluate if an asphalt-rubber binder produces SMA mixtures able to meet the technical requirements. The behavior of SMA mixtures produced with different binders (conventional AC-20, polymermodified, and asphalt-rubber) is analyzed based on laboratory tests (tensile strength, resilient modulus, fatigue, and permanent deformation in a traffic simulator) and compared to the behavior of a conventional dense-graded HMA The results show that the behavior of SMA mixtures produced with asphalt-rubber is much closer to SMA mixtures produced with polymer-modified binder than conventional asphalts.

Hot mix asphalt (HMA) is a composite material that exhibits a nonlinear response that is dependent on temperature, type of loading and strain level. The properties of HMA are highly influenced by the type and amount of the constituents used and also depend on its internal structure. In such a material the variable effects of the compaction process assume a central importance in determining material performance. It is generally accepted that the theoretical knowledge about material behavior during compaction is limited and it is therefore hard to predict and manage (the effect of) a compaction process. This work makes an attempt to address such a specific need by developing a continuum model that can be adapted for simulating the compaction of hot mix asphalt (HMA) using the notion of multiple natural configurations. A thermodynamic framework is employed to study the non-linear dissipative response associated with HMA by specifying the forms for the stored energy and the rate of dissipation function for the material; a viscoelastic compressible fluid model is developed using this framework to model the compaction of hot mix asphalt. It is further anticipated that the present work will aid in the development of better constitutive models capable of capturing the mechanics of processes like compaction both in the laboratory and in the field. The continuum model developed was implemented in the finite element method, which was employed to setup a simulation environment for hot mix asphalt compaction. The finite element method was used for simulating compaction in the laboratory and in various field compaction projects.

Resilient modulus is an important property for asphalt concrete design and for mechanistic analysis of pavement response under traffic loading. This study investigates the different factors affecting the resilient modulus of hot mix asphalt. A fractional factorial design of experiment was carried out to investigate six factors each factor was studied at two levels. These factors are: the maximum nominal aggregate size, specimen diameter and thickness, the load pulse form and duration, and the compaction method. Two types of hot mix asphalts with different maximum aggregate sizes (10 mm and 14 mm) were studied. Gyratory and Marshall compaction methods were used to prepare the specimens. Sinusoidal and triangular load pulse forms were used in the measurement of the resilient modulus. This study attempts to examine how the different factors interrelate to affect the resilient modulus. In addition to this, two other investigations will be carried out. The first is the comparison of the strain backcalculated using the resilient modulus test results with the strain measured using strain gages and strain values obtained from finite element modelling (FEM), and determine whether the FEM or the closed form equation is the more accurate method for determining strain. The second is the investigation of the relationship between the flexural, complex and resilient modulus. Analysis of the factorial experimental design showed that the maximum nominal aggregate size is the most important factor affecting the resilient modulus, followed by the load duration, the specimen geometry represented by the thickness and diameter then the interactions between the different factors. The strain comparison suggested that the closed form equations were indeed a suitable approach to determine maximum horizontal strain during a resilient modulus test. The modulus comparison suggested that it is possible to predict either resilient, complex and flexural modulus given that only one of them is known, but only for AC10 specimens.

abstract: The application of fibers and other materials in asphalt mixes has been studied and applied over the past five decades in order to improve pavement performance around the world. This thesis highlights the characteristics and performance properties of modified asphalt mixes using a blend of polypropylene and aramid fibers, The main objective of this study was to evaluate the effect of adding different fiber dosages on the laboratory performance of both asphalt binder and mixture. The laboratory study was conducted on sixteen different dosages and blends of the fibers, with various combinations of polypropylene and aramid, using binder tests as well as hot mix asphalt tests. The binder tests included: penetration, softing point, and Brookfield viscosity tests. The asphalt mixture tests included the dynamic modulus, and indirect tensile strength. The binder test results indicated that the best viscosity - temperature susceptibility performance would be from the blend of three dosages of polypropylene and one dosage of aramid, the dynamic modulus test results also confirmed this finding. Overall, in almost every case, the addition of fibers resulted in an increase in mixture stiffness regardless of fiber content. From the indirect tensile strength results, the polypropylene fibers had less of an effect on post peak failure than the aramid fibers. Overall, the aramid fibers yielded better results than the polypropylene fibers. This study has important implications for the future of pavement design and the prospect of using optimal dosages of polypropylene and aramid fibers in further research to further determine their long-term performance and characteristics used in real world applications. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2012

abstract: One of the main requirements of designing perpetual pavements is to determine the endurance limit of Hot Mix Asphalt (HMA). The purpose of this study was to validate the endurance limit for HMA using laboratory beam fatigue tests. A mathematical procedure was developed to determine the endurance limit of HMA due to healing that occurs during the rest periods between loading cycles. Relating healing to endurance limit makes this procedure unique compared to previous research projects that investigated these concepts separately. An extensive laboratory testing program, including 468 beam tests, was conducted according to AASHTO T321-03 test procedure. Six factors that affect the fatigue response of HMA were evaluated: binder type, binder content, air voids, test temperature, rest period and applied strain. The endurance limit was determined when no accumulated damage occurred indicating complete healing. Based on the test results, a first generation predictive model was developed to relate stiffness ratio to material properties. A second generation stiffness ratio model was also developed by replacing four factors (binder type, binder content, air voids, and temperature) with the initial stiffness of the mixture, which is a basic material property. The model also accounts for the nonlinear effects of the rest period and the applied strain on the healing and endurance limit. A third generation model was then developed by incorporation the number of loading cycles at different locations along the fatigue degradation curve for each test in order to account for the nonlinearity between stiffness ratio and loading cycles. In addition to predicting endurance limit, the model has the ability to predict the number of cycles to failure at any rest period and stiffness combination. The model was used to predict fatigue relationship curves for tests with rest period and determining the K1, K2, and K3 fatigue cracking coefficients. The three generation models predicted close endurance limit values ranging from 22 to 204 micro strains. After developing the third generation stiffness ratio model, the predicted endurance limit values were integrated in the strain-Nf fatigue relationships as a step toward incorporating the endurance limit in the MEPDG software. The results of this study can be used to design perpetual pavements that can sustain a large number of loads if traffic volumes and vehicle weights are controlled. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2012

abstract: Heating of asphalt during production and construction causes the volatilization and oxidation of binders used in mixes. Volatilization and oxidation causes degradation of asphalt pavements by increasing the stiffness of the binders, increasing susceptibility to cracking and negatively affecting the functional and structural performance of the pavements. Degradation of asphalt binders by volatilization and oxidation due to high production temperature occur during early stages of pavement life and are known as Short Term Aging (STA). Elevated temperatures and increased exposure time to elevated temperatures causes increased STA of asphalt. The objective of this research was to investigate how elevated mixing temperatures and exposure time to elevated temperatures affect aging and stiffening of binders, thus influencing properties of the asphalt mixtures. The study was conducted in two stages. The first stage evaluated STA effect of asphalt binders. It involved aging two Performance Graded (PG) virgin asphalt binders, PG 76-16 and PG 64-22 at two different temperatures and durations, then measuring their viscosities. The second stage involved evaluating the effects of elevated STA temperature and time on properties of the asphalt mixtures. It involved STA of asphalt mixtures produced in the laboratory with the PG 64-22 binder at mixing temperatures elevated 25OF above standard practice; STA times at 2 and 4 hours longer than standard practices, and then compacted in a gyratory compactor. Dynamic modulus (E*) and Indirect Tensile Strength (IDT) were measured for the aged mixtures for each temperature and duration to determine the effect of different aging times and temperatures on the stiffness and fatigue properties of the aged asphalt mixtures. The binder test results showed that in all cases, there was increased viscosity. The results showed the highest increase in viscosity resulted from increased aging time. The results also indicated that PG 64-22 was more susceptible to elevated STA temperature and extended time than the PG 76-16 binders. The asphalt mixture test results confirmed the expected outcome that increasing the STA and mixing temperature by 25oF alters the stiffness of mixtures. Significant change in the dynamic modulus mostly occurred at four hour increase in STA time regardless of temperature. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2013

Hot mix asphalt pavements require adequate compaction to achieve the required density to resist rutting. The amount of energy required to achieve the optimum degree of compaction depends on the type of gradation, bitumen content, filler type and shape, type of compaction equipment etc. In this study, the net energy required to reduce the specimen volume (size) after each gyration of the superpave gyratory compactor is used as the compaction energy index (CEI) to measure the compactability of the samples. Samples with different filler types and content are used for the analysis. Effect of fillers on the viscosity of the mastic has been studied previously. Viscosity of mastics in return affects the compactability of the mix in general. In this regard this paper tries to study the effect of fillers on the compaction of hot mix asphalt with the help of the superpave gyratory compactor. Moreover, resistance of the asphalt mix samples against rutting is evaluated using the simple performance test. In this test, the sample is subjected to a hydraulic loading while strain transducers attached to the sample measure the displacement. A computer program receives the displacement data at various frequencies and calculates the dynamic modulus and flow number which are used for the evaluation of the pavement performance.     :

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