Browsing by Subject "Asphalt"
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Item A new testing protocol for seal coat (chip seal) aggregate-binder compatibility(Texas Tech University, 2003-12) Yazgan, BarisNot availableItem Analytical-Numerical Methodology to Measure Undamaged, Fracture and Healing Properties of Asphalt Mixtures(2012-08-29) Koohi, Yasser 1980-Unlike in laboratory compacted asphalt mixtures, the distribution of viscoelastic properties in field layers is not uniform because of nonuniform air void distribution and aging. Therefore, characterization of field specimens is more challenging compared to that of laboratory compacted specimens. Formerly, characterization of field asphalt mixtures was based on binder tests which are useful but do not represent the properties of the asphalt mixtures because binder is only a component in the asphalt mixture. This study uses linear viscoelastic theory and numerical modeling to obtain the undamaged and damaged viscoelastic properties of both laboratory made and field compacted asphalt concrete. Additionally, it uses fracture mechanics principles to find the fracture and healing properties of aged asphalt specimens. The analytical models presented in this research have been successfully verified by testing the actual field specimens of different ages. The model developed in this dissertation is suitable to track the viscoelastic, fracture and healing properties of the field specimen with time and depth. The test protocols and analytical models described in this study can be used for the development of reliable performance models for field-aged asphalt layers.Item Application of Direct Tension Testing to Laboratory Samples to Investigate the Effects of Hot Mix Asphalt Aging(2012-12-07) Padigala, Meghana 1989-While the oxidation of binders in hot mix asphalt (HMA) pavements and its subsequent detrimental effects on pavement life have been well recognized in the last few years, many important issues have not yet been investigated. Understanding how best to design mixtures taking this phenomenon into account and achieving maximum durability is an important and complex issue. This study was aimed at characterizing the effects of oxidative aging on durability in terms of mixture fatigue resistance of laboratory mixed-laboratory compacted (LMLC) samples. Direct tension tests were conducted on HMA samples to measure mixture stiffness and a Modified Calibrated Mechanistic with Surface Energy (CMSE*) analysis method was used to predict fatigue life. The effect of various mix design parameters was evaluated to understand their importance with respect to the aging phenomena and mixture fatigue resistance. Analysis of the results showed that aging has a significant negative effect on mixture fatigue resistance. Considerable increase in the stiffness modulus (Eve) of the mixtures was observed with age for all three mixtures analyzed. Air voids (AV) played a substantial role in affecting the fatigue resistance with aging, but a difference of 0.5% in binder content near the optimum level did not statistically change mixture durability in terms of fatigue resistance with aging. For the three mixtures in Texas included in this study, when comparing Eve, one month of artificial aging in the laboratory was equivalent to 10.5 months of natural aging in the field. A good correlation was also found between the Eve of the mixture and the Carbonyl Area (CA) and Dynamic Shear Rheometer (DSR) function of the extracted binder. Thus, a connection exists between the properties of the extracted binder, laboratory mixtures and field mixtures. This relationship will facilitate development of a more mechanistic aging component in pavement performance prediction models.Item Characterization of waste recycled glass as a highway material(Texas Tech University, 1996-08) Viswanathan, KrishnanThe success of glass recycling programs has resulted in an oversupply of waste recycled glass or glass cullet. The properties and strength of glass cullet aggregate mixes are influenced by maximum size of cullet, cullet content in the mix, type of conventional aggregate, and also the debris level in the cullet. A survey of State DOTs was done to determine their experiences with the use of glass cullet. Also, a survey among suppliers of cullet in Texas was done to determine the costs associated with procuring glass cullet. Based on these surveys, glass cullet was identified for use in base course, subbase, subgrade and embankments and also for backfill applications. A test program was devised to test the engineering suitability of glass cullet samples for the above mentioned applications. Stripping tests were also done to determine the adhesion of glass cullet and asphalt in the presence of water. Based on the results of these tests, it was found that glass cullet has properties similar to natural aggregates and could be used as a highway material. Specifications for use of glass cullet by the Texas Department of Transportation were also developed.Item Development and numerical implementation of nonlinear viscoelastic-viscoplastic model for asphalt materials(2009-05-15) Huang, Chien-WeiHot mix asphalt (HMA) is a composite material which consists of aggregates, air voids and asphalt materials. The HMA response is typically described to be viscoelastic-viscoplastic, and its response is a function of temperature, stress/strain rate, and stress/strain level. Many researches have shown that the viscoelastic response of asphalt mixtures can be nonlinear once the stress/strain value exceeds a certain threshold level. This study presents a nonlinear viscoelastic-viscoplastic model for describing the behavior of asphalt materials under various conditions. A new method is developed in this study for separating the viscoelastic response from the viscoplastic response. The first part of this study focuses on the implementation of Schapery nonlinear viscoelastic model in finite element (FE) using a user-defined material subroutine (UMAT) within the ABAQUS commercial software. The FE implementation employs the recursive-iterative integration algorithm, which can improve the convergence and save the calculating time. The verification of the nonlinear viscoelastic model is achieved by analyzing (1) the response of asphalt mixtures tested in the Simple Shear Test (SST) at several temperatures and stress levels, (2) the response of unaged and aged asphalt binders tested in the Dynamic Shear Rheometer (DSR), and (3) the response of asphalt binders in the multiple stress creep recovery test (MSCR). In the second part of this study, the nonlinear viscoelastic-viscoplastic constitutive relationship is implemented using UMAT. The viscoplastic component of the model employs Perzyna?s theory with Extended Drucker-Prager yield surface which is modified to account for the difference in material response under compression and extension stress states. The study includes parametric analysis to illustrate the effect of nonlinear viscoelastic parameters and viscoplastic parameters on the asphalt mix response. The capability of the model in describing the fatigue and permanent deformation distresses of asphalt pavements is illustrated using finite element simulations. The constitutive model developed in this study can describe the behavior of asphalt materials (asphalt binder, asphalt mastic and mixtures) under various testing conditions. This study also achieved the FE implementation of a nonlinear viscoelasticviscoplastic constitutive model that can simulate the fatigue and permanent deformation distresses of asphalt pavement structures.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 Feasibility of using the micro-deval test method as an aggregate production quality control tool(Texas Tech University, 2003-12) Hoare, Appa RaoNot available.Item Improvements to a Transport Model of Asphalt Binder Oxidation in Pavements: Pavement Temperature Modeling, Oxygen Diffusivity in Asphalt Binders and Mastics, and Pavement Air Void Characterization(2012-07-16) Han, RongbinAlthough evidence is mounting that asphalt binder oxidizes in pavements, and that oxidation and subsequent hardening of asphalt binder has a profound effect on pavement durability, important implementation issues remain to be better understood. Quantitative assessment of asphalt binder oxidation for a given pavement is a very important, but complex issue. In this dissertation, a fundamentals-based oxygen transport and reaction model was developed to assess quantitative asphalt binder oxidation in pavements. In this model, oxygen transport and reaction were described mathematically as two interlinked steps: 1) diffusion and/or flow of oxygen from the atmosphere above the pavement into the interconnected air voids in the pavement; and 2) diffusion of oxygen from those air voids into the adjoining asphalt-aggregate matrix where it reacts with the asphalt binder. Because such a model calculation depends extensively on accurately representing pavement temperature, understanding oxygen diffusivity in asphalt binders and mastics, and characterizing air voids in pavements, these key model elements were studied in turn. Hourly pavement temperatures were calculated with an improved one-dimensional heat transfer model, coupled with methods to obtain model-required climate data from available databases and optimization of site-specific pavement parameters nationwide; oxygen diffusivity in binders was determined based on laboratory oxidation experiments in binder films of known reaction kinetics by comparing the oxidation rates at the binder surface and at a solid-binder interface at the film depth. The effect of aggregate filler on oxygen diffusivity also was quantified, and air voids in pavements were characterized using X-ray computed tomography (X-ray CT) and image processing techniques. From these imaging techniques, three pavement air void properties, radius of each air void (r), number of air voids (N), and average shell distance between two air voids (rNFB) were obtained to use as model inputs in the asphalt binder oxidation model. Then, by incorporating these model element improvements into the oxygen transport and reaction model, asphalt binder oxidation rates for a number of Texas and Minnesota pavements were calculated. In parallel, field oxidation rates were measured for these corresponding pavement sites and compared to the model calculations. In general, there was a close match between the model calculations and field measurements, suggesting that the model captures the most critical elements that affect asphalt binder oxidation in pavements. This model will be used to estimate the rate of asphalt binder oxidation in pavements as a first step to predicting pavement performance, and ultimately, to improve pavement design protocols and pavement maintenance scheduling.Item Laboratory investigation of the influence from aggregate and climate on stiffness development in seal coat asphalt emulsions(2010-12) Tubb, Andrew A; Senadheera, Sanjaya; Won, Moon C.Emulsified asphalt is widely used in many highway maintenance and construction applications, and their effectiveness is greatly influenced by the construction process and climatic conditions at the time of application and soon thereafter. This research studied the rate of residue formation of emulsified asphalts over time, with particular emphasis on two key construction-related factors; the aggregate it is in contact with, and the climatic conditions. Emulsified asphalts were sampled both from a plant location as well as three construction sites. Test specimens were prepared by pouring asphalt emulsion directly on aggregate substrates and then cured under different climate regimes in an environmental chamber. These climate regimes were selected to simulate field conditions and anticipated laboratory test environments. The stiffness of the asphalt was measured at specified time intervals by a Dynamic Shear Rheometer (DSR) using a strain-sweep test protocol.Item Long term aging study of WMA binder(2011-05) Trujillo, Patricia; Prozzi, Jorge Alberto; Bhasin, AmitWarm mix asphalt (WMA) is an environmental friendly technology that contributes to the workers safety, reduction of energy consumption and emissions. In this study, the rheological properties of a PG 64-22 asphalt binder blended with Cecabase RT, Rediset, Evotherm, and Sasobit WMA additives are investigated as a function of laboratory aging. Binders modified with WMA additives and the control samples were both aged in the rolling thin film oven (RTFO) at 143°C and at 163°C, respectively. All samples were then long-term aged in an environmental chamber kept at 60°C. The longterm aged samples were collected at different intervals during a six-month period. Rheological data were collected on each aged sample by performing dynamic shear rheometer (DSR) frequency sweep from 25 to 0.1 Hz. at three different temperatures, i.e. 45°C, 60°C, and 76°C. Samples were also evaluated with the Bending Beam Rheometer (BBR) and Fourier-Transform Infrared (FTIR) Spectroscopy. Gauss-Newton method was vii used for non-linear parameter estimation for modeling the relationship of complex modulus (G*) with temperature, frequency, and aging. Regression analysis was also used for modeling BBR creep stiffness and BBR m-value. Although FTIR results show higher oxidation levels for control than all WMA samples, DSR and BBR results show that Sasobit tends to behave closely to control while Cecabase, Evotherm, and Rediset exhibit lower stiffness than both.Item Moisture Diffusion in Asphalt Binders and Fine Aggregate Mixtures(2011-08-08) Vasconcelos, Kamilla L.Moisture damage in asphalt mixtures is a complex phenomenon that involves mechanical, chemical, physical and thermodynamic processes. This damage contributes significantly to the premature deterioration of asphalt pavements, which leads to extra cost in highway maintenance and vehicle operations. One key mechanism of how moisture reaches the asphalt-aggregate interface is by its permeation or diffusion through the asphalt binder or mastic. Different techniques are available for diffusion coefficient measurement of a wide variety of polymersolvent systems. For the asphalt-water system studied, the focus is on two techniques: (i) Fourier Transform Infrared (FTIR)-Attenuated Total Reflectance (ATR) spectrometry and (ii) Gravimetric Sorption Measurements. In the FTIR-ATR experiments, asphalt binders are under investigation. Water shows strong absorption in the infrared region and the FTIR-ATR technique has the ability to monitor both the kinetics of moisture ingress as well as any chemical changes occurring during the test. The changes in concentration can be directly related to change in the absorbance measured during the experiment. The hysteresis of water diffusion in asphalt binders is also monitored through this technique. In the gravimetric sorption experiments, cylindrical Fine Aggregate Mixtures (FAM) were investigated. The gravimetric techniques, which directly follow mass change with time, are among the most used techniques probably because of their simplicity. In this experiment, the Saturated Surface-Dry (SSD) weight of FAM samples at room temperature and at 100 degrees F is monitored until it reaches the equilibrium. The measurements of: (i) water uptake and (ii) the diffusion coefficient were made at both temperatures. A dual mode diffusion model was shown to better represent the diffusion of water through asphalt binders. The rate of moisture diffusion in asphalt binders was proved to be dependent on the history of exposure of the asphalt binder to the moisture. Moisture uptake and diffusivity of water through FAM is dependent on the type of aggregate and asphalt binder used to prepare the FAM.Item Prediction of Asphalt Mixture Compactability from Mixture, Asphalt, and Aggregate Properties(2010-07-14) Muras, Andrew J.The underlying purpose of any pavement is to provide a safe, smooth and reliable surface for the intended users. In the case of hot mix asphalt (HMA) pavements, this includes producing a surface that is resistant to the principal HMA distress types: permanent deformation (or rutting) and fatigue damage (or cracking). To protect better against these distress types, there have recently been changes in HMA mixture design practice. These changes have had the positive effect of producing more damage resistant mixtures but have also had the effect of producing mixtures that require more compaction effort to obtain required densities. It is important to understand what properties of an HMA mixture contribute to their compactability. This study presents analysis of the correlation between HMA mixture properties and laboratory compaction parameters for the purpose of predicting compactability. Mixture property data were measured for a variety of mixtures; these mixtures were compacted in the laboratory and compaction parameters were collected. A statistical analysis was implemented to correlate the mixture data to the compaction data for the purpose of predicting compactability. The resulting model performs well at predicting compactability for mixtures that are similar to the ones used to make the model, and it reveals some mixture properties that influence compaction. The analysis showed that the binder content in an HMA mixture and the slope of the aggregate gradation curve are important in determining the compactability of a mixture.Item The prediction of coarse aggregate performance by micro-Deval and other soundness, strength, and intrinsic particle property tests(2006-05) Lang, Alexander Paul; Fowler, David W.This research project concentrated on determining whether or not a correlation existed between laboratory aggregate tests and observed aggregate field performance. For this purpose, aggregate samples were collected from the majority of the U.S. states as well as several Canadian provinces and subjected to a variety of strength, soundness, and intrinsic particle property tests. Additionally, performance data on the aggregates was obtained by contacting multiple DOT's where aggregates were in use in several categories - hot-mix asphalt, portland cement concrete, base course, and open-graded friction course. Numerical and qualitative analyses were performed to evaluate the success of separating good performers from fair and poor performers using the micro-Deval test alone as well as the micro-Deval test combined with another test. Furthermore, attempts were made to determine if a correlation exists between any two tests.Item Structural Characterization of Micromechanical Properties in Asphalt Using Atomic Force Microscopy(2012-02-14) Allen, Robert GroverThe purpose of this study was to characterize the micromechanical properties of various structural components in asphalt using Atomic Force Microscopy (AFM). The focus of the study was based on nano-indentation experiments performed within a micro-grid of asphalt phases in order to determine micromechanical properties such as stiffness, adhesion and elastic/plastic behavior. The change in microstructure and micromechanical behavior due to oxidative aging of the asphalt was also a primary focus of the study. The experiment was performed with careful consideration of AFM artifacts, which can occur due to factors such as geometry of the cantilever tip, hysteresis, filtering methods and acoustic vibrations. The materials used in this study included asphalts AAB, AAD and ABD from the Materials Reference Library (MRL) of the Strategic Highway Research Program (SHRP), chosen due to variations in crude source, chemical composition and elemental analysis for each asphalt type. The analysis of nano-indentation creep measurements corresponding to phase-separated regions ultimately revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging was found to induce substantial microstructural change within these domains, including variations in phase structure, phase properties and phase distribution. The form and extent of these changes, however, were different for each asphalt studied. Data analysis and information collected during this study were used for comparisons to existing models and asphalt data, which validated results and established correlations to earlier, related studies. From these comparisons, it was found that data parallels followed expected trends; furthermore, analogous interpretations and distinctions were made between results from this study and the micellar and microstructural models of asphalt. This study of micromechanical properties that govern asphalt behavior has yielded information essential to the advancement of hot mix asphalt (HMA) performance, including a new asphalt ?weak zone? hypothesis and a foundation of data for implementation into new and existing asphalt models.