Browsing by Subject "Asphalt binder"
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Item An evaluation of the tensile strength of asphalt binder and mortar with recycled asphalt additives at low temperatures(2017-08) Rodriguez, Rogelio Gabriel; Bhasin, AmitA standard grading system is used to evaluate the properties and expected performance of an asphalt binder. The most common grading system used in the US today is the performance grading (PG) system. This system prescribes an operational temperature range within which the binder is expected to perform satisfactorily without resulting in rutting, fatigue cracking or thermal cracking as a distress. On the low-temperature and thermal cracking end, this system uses both a metric related to stiffness and rate of relaxation (m-value) to establish a low temperature grade for a given asphalt binder. Although these parameters provide some information on the rate of relaxation and overall rigidity of the asphalt binder they don’t include an evaluation of the tensile strength of the asphalt binder. The tensile strength of the binder can furnish critical information about its resistance to cracking including thermal cracking. The asphalt industry has become particularly interested in the impact of recycled asphalt pavement (RAP) and additives such as rejuvenators on the behavior and performance of the material. The goal of this study was to evaluate the tensile strength characteristics of asphalt binders and composites in addition to their stiffness characteristics. The study was conducted in three parts: (1) the evaluation of tensile strength of asphalt binders with similar performance grades, (2) the evaluation of tensile strength of asphalt binders as a function of the amount of recycled asphalt binder added to the virgin binder, and (3) the influence of recycled asphalt and rejuvenators on the stiffness and tensile strength of asphalt mortars. In addition to these three objectives, this study also developed simplified methods to prepare and evaluate the tensile strength of asphalt binders and mortars as a material characterization tool to screen or evaluate the efficacy of RAP, rejuvenators, and other additives. Results show that similarly graded binders have a significant variability both in terms of their stiffness and strength and that rejuvenators can be used with RAP to achieve a balance of stiffness and strength.Item Constitutive modeling of viscoelastic behavior of bituminous materials(2012-12) Motamed, Arash; Bhasin, AmitAsphalt mixtures are complex composites that comprise aggregate, asphalt binder, and air. Several research studies have shown that the mechanical behavior of the asphalt mixture is strongly influenced by the matrix, i.e. the asphalt binder. Therefore, accurate constitutive models for the asphalt binders are critical to ensure accurate performance predictions at a material and structural level. However, researchers who use computational methods to model the micromechanics of asphalt mixtures typically assume that (i) asphalt binders behave linearly in shear, and (ii) either bulk modulus or Poisson’s ratio of asphalt binders is not time dependent. This research develops an approach to measure and model the shear and bulk behavior of asphalt binders at intermediate temperatures. First, this research presents the findings from a systematic investigation into the nature of the linear and nonlinear response of asphalt binders subjected to shear using a Dynamic Shear Rheometer (DSR). The DSR test results showed that under certain conditions a compressive normal force was generated in an axially constrained specimen subjected to cyclic torque histories. This normal force could not be solely attributed to the Poynting effect and was also related to the tendency of the asphalt binder to dilate when subjected to shear loads. The generated normal force changed the state of stress and interacted with the shear behavior of asphalt binder. This effect was considered to be an “interaction nonlinearity” or “three dimensional effect”. A constitutive model was identified to accommodate this effect. The model was successfully validated for several different loading histories. Finally, this study investigated the time-dependence of the bulk modulus of asphalt binders. To this end, poker-chip geometries with high aspect ratios were used. The boundary value problem for the poker-chip geometry under step displacement loading was solved to determine the bulk modulus and Poisson’s ratio of asphalt binders as a function of time. The findings from this research not only improve the understanding of asphaltic materials behavior, but also provide tools required to accurately predict pavement performance.Item Fatigue characterization of asphalt binders using a thin film poker chip test(2016-05) Hajj, Ramez Muhammad; Bhasin, Amit; Motamed, ArashAsphalt binder is the adhesive that holds together aggregate particles of different sizes of an asphalt mixture. The tensile properties of an asphalt binder can greatly affect the performance of the asphalt mixture under repeated traffic loading. While the current performance grade specification has been in use for a long time to characterize the asphalt binders with regards to fatigue, it has been shown to be largely ineffective. This study was performed with the goal of investigating a strength-based measure to evaluate the fatigue cracking resistance of the asphalt binder. The poker chip geometry was used for this purpose. The test involved tensile loading of a thin film of asphalt binder between two rigid substrates. The first part of this study focused on determining failure criteria for the test. The second part was a study of the binders that have a similar grade based on the current performance grade specification but are expected to perform differently due to difference in their chemical makeup. Finally, the third part involved a study of the effects of nanomaterials as additives on the strength of the binder based on poker chip test results. The results demonstrated that failure strain criteria is promising as a material property, but still needs further study for validation. It was also observed that binders with similar performance grade had significantly different tensile strength. Finally, it was observed that nanomaterials had a significant impact on the test results of unaged binder, but had less effect on aged asphalt binders.Item Measurement of material properties related to self-healing based on continuum and micromechanics approach(2011-08) Palvadi, Naga Sundeep; Bhasin, Amit; Smit, Andre de FortierThe ability of an asphalt mix to heal is an important property that influences the overall fatigue performance of the mix in the field. Micro damage healing in an asphalt mix is a function of several factors such as the physical and chemical properties of the binder, properties of the mixture, level of damage prior to the rest period during which healing occurs, duration of the rest period, temperature, and pressure. This thesis presents details from a two-part study that addresses the following aspects. In the first part of this study, a DSR based test method was developed to measure inherent healing in asphalt binder and a modified form of the Avrami equation was used to model it. In the second part of this study, an experimental and analytical method based on viscoelastic continuum damage theory was developed to characterize the healing in an asphalt composite (fine aggregate matrix) as a function of the level of damage prior to the rest period and the duration of the rest period. The intrinsic healing of three different asphalt binders was measured at three different temperatures and two aging conditions and it was further demonstrated to be the sum of two components: instantaneous strength gain immediately upon wetting and time dependent strength gain. The intrinsic healing results obtained from the DSR tests were demonstrated to be in agreement with the hypothesis that time dependent intrinsic healing increases with an increase in temperature and decreases with aging of the asphalt binder. The overall healing was measured in four different fine aggregate matrix (FAM) asphalt mixes and various tests were performed to quantify overall healing at isothermal and short term aged test conditions. Additionally two different verification tests were also conducted to demonstrate that the percentage healing measured using the proposed method are independent of the sequence of loading or rest periods. Finally, the overall healing results were demonstrated to support the hypothesis that the healing characteristics determined using the proposed test method can be treated as a characteristic material property.Item Optical characterization of asphalt binder microstructure(2019-04-30) Ramm, Adam Steven; Downer, Michael Coffin; Bhasin, Amit; Marder, Michael; Sitz, GregThis dissertation presents results of optical characterization of asphalt binder microstructure. We use noncontact optical microscopy methods to observe microstructure at the surface as well as in the bulk of asphalt binder samples. Normal incidence optical microscopy is used to image elongated, striped, surface microstructures (known as ’bees’ since they resemble bumble-bees) with comparable resolution to atomic force microscopy (AFM). Narrow band dark field optical microscopy is used to measure surface microstructure areal density and bulk microstructure volume density. Short wavelength illumination images surface microstructures, while longer wavelength near infrared (NIR) illumination penetrates into the bulk and images sub-surface microstructures. We subject the binder to temperature cycles and observe the resulting microstructure kinetics. We benchmark these optical measurements with rheometry measurements obtained from identical thermal cycles. We also use optical methods to observe surface ’bee’ microstructure variations due to interfacial tension modifications and compare these results to thin film mechanics theoryItem Origins and evolution of instabilities in asphalt binder(2023-01-02) Hajj, Ramez Muhammad; Bhasin, Amit; Juenger, Maria; Folliard, Kevin; Downer, MichaelAsphalt binders are complex viscoelastic materials that serve as the bonding agent for mineral aggregates in flexible pavement layers. One of the most important distresses exhibited in flexible pavements is their tendency to crack due to repeated loading. The current body of literature on asphalt binders has yet to establish experimentally how these cracks are born at a microscopic level, and a proper test method for evaluating a binder’s resistance to forming cracks. This dissertation proposes answers toward a solution to both of the above gaps. Eight asphalt binders were evaluated experimentally using a novel poker chip test that realistically mirrors the state of stress experienced by a binder in an asphalt mix. Based on these results, the interplay between stiffness, strength, and ductility of the binder was evaluated and used as a screening tool to for outlier binders. In addition, the cavitation surfaces and their relationship with strength was observed. Subsequently, dark field microscopy was used to observe the origination of the cavitation instability in the binder. Cavitation was observed to occur at the interface between inclusions in the bulk of the binder and the matrix itself. A theoretical framework for the reasons for this based on classical solutions in mechanics is proposed. Finally, X-ray computed tomography was used to obtain images of an asphalt mixture microstructure at two different scales. These images were meshed to form a finite element model, which was used to determine critical points in a mixture for cracking. The findings indicated high triaxiality could be appropriately modeled in the laboratory using the poker chip test at high aspect (diameter/thickness) ratio. This high aspect ratio creates an approximate confined stress state for testing, and also allows for nearly uniform stress distribution in the test specimen. This was validated using finite element analysis to confirm the poker chip test as suitable for laboratory testing of asphalt binders.Item Tensile strength of asphalt binder and influence of chemical composition on binder rheology and strength(2014-08) Sultana, Sharmin; Bhasin, Amit; Liechti, Kenneth M.; Prozzi, Jorge A.; Zhang, Zhanmin; Fowler , David W.Asphalt mixtures or asphalt concrete are used to pave about 93% of about 2.6 million miles paved roads and highways in the US. Asphalt concrete is a composite of aggregates and asphalt binder; asphalt binder works as a glue to bind the aggregate particles. The mechanical response of the asphalt binder is dependent on the time/rate of loading, temperature and age. An asphalt concrete mixture inherits most of these characteristics from the asphalt binder. Also the asphalt binder plays a critical role in providing the asphalt concrete the ability to resist tensile stresses and relaxing thermally induced stresses that can lead to fatigue and low temperature cracking, respectively. Hence, it is very important (but not sufficient) to ensure that asphalt binders used in the production of asphalt concrete are inherently resistant to cracking, rutting and other distresses that a pavement may undergo. Current binder specification (AASHTO M-320) to evaluate its fatigue cracking is based on the stiffness of the binder and not on its tensile strength. Also, measurements following current specifications are made on test specimens subjected to a uniaxial mode of loading that does not produce the same stress state in the binder as in the case of asphalt concrete. Another challenge in being able to produce binders with inherently superior performing characteristics is the fact that the asphalt binders produced in a refinery do not have a consistent chemical composition. The chemical composition of asphalt binder depends on the source and refining process of crude oil. There is a need to better quantify the tensile strength of asphalt binder and understand the relationship between the chemical composition of asphalt binders and its mechanical properties. The knowledge from this study can be used to engineer asphalt binders that have superior performance characteristics. The objective of this research was to quantify the tensile strength of asphalt binder, develop a metric for the tensile strength and identify the relationship between chemical composition and mechanical properties of asphalt binder. Laboratory tests were performed on binders of different grades using a poker chip geometry to simulate confined state by varying the film thickness, rate of loading and modes of loading. The chemical properties of asphalt binder were studied based on SARA fractionation. The findings from this research showed that the modified correspondence principles can unify and explain the rate and mode dependency of asphalt binder. This study also quantified the relationship between chemical composition, and rheological and mechanical properties of asphalt binder. Finally, a composite model was developed based on the individual properties of chemical fractions which could predict the dynamic modulus of the asphaltenes doped and resins doped binder.