1,720,992 research outputs found
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Predicting friction with improved texture characterization
Get PDFCurrent methodologies to measure road friction present several disadvantages that make them impractical for field data collection over large highway networks. Thus, it is important to study different ways to estimate surface friction characteristics based on other properties that are easier to measure. The main objective of this study was to analyze surface texture characteristics and to observe their influence on friction. A Line Laser Scanner (LLS) was implemented to make an improved characterization of the road texture which includes macro- and micro-texture description using different texture parameters. Field measurements of friction and texture were collected around Texas using different tests methods. The friction characterization tests included the British Pendulum test (BPT), the Dynamic Friction test (DFT), and the Micro GripTester. Thirty-six different pavement sections were evaluated, including different surface types such as hot-mix asphalt (HMA), surface treatment, and concrete sidewalk. Among the principal conclusions, it was found that there is not a unique relationship between texture and friction. The relationship between texture and friction is strong but it is different for each type of surface, thus, cross-sectional analysis cannot be utilized to quantify the relationship. Additionally, the prediction of friction measures obtained using the BPT and the DFT significantly improved when including information of both macro- and micro-texture into the prediction model. Therefore, a measure of micro-texture should be included into friction models based on texture. Finally, among the study of different texture parameters, the mean profile depth (MPD) was the most significant parameter for macro- and for micro-texture to explain the distinct friction measures.Civil, Architectural, and Environmental Engineerin
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Predicting in-service fatigue life of flexible pavements based on accelerated pavement testing
Get PDFPavement performance prediction in terms of fatigue cracking and surface rutting are essential for any mechanistically-based pavement design method. Traditionally, the estimation of the expected fatigue field performance has been based on the laboratory bending beam test. Full-scale Accelerated Pavement Testing (APT) is an alternative to laboratory testing leading to advances in practice and economic savings for the evaluation of new pavement configurations, stress level related factors, new materials and design improvements. This type of testing closely simulates field conditions; however, it does not capture actual performance because of the limited ability to address long-term phenomena. The same pavement structure may exhibit different response and performance under APT than when in-service. Actual field performance is better captured by experiments such as Federal Highway Administration's Long-Term Pavement Performance (LTPP) studies. Therefore, to fully utilize the benefits of APT, there is a need for a methodology to predict the long-term performance of in-service pavement structures from the results of APT tests that will account for such differences. Three models are generally suggested to account for the difference: shift factors, statistical and mechanistic approaches. A reliability based methodology for fatigue cracking prediction is proposed in this research, through which the three models suggested previously are combined into one general approach that builds on their individual strengths to overcome some of the shortcomings when the models are applied individually. The Bias Correction Factor (BCF) should account for all quantifiable differences between the fatigue life of the pavement site under APT and in-service conditions. In addition to the Bias Correction Factor, a marginal shift factor, M, should be included to account for the unquantifiable differences when predicting the in-service pavement fatigue life from APT. The Bias Correction Factor represents an improvement of the currently used "shift factors" since they are more general and based on laboratory testing or computer simulation. By applying the proposed methodology, APT performance results from a structure similar to an in-service structure can be used to perform four-point bending beam tests and structural analysis to obtain an accurate estimate of the necessary Bias Correction Factor to estimate in-service performance.Civil, Architectural, and Environmental Engineerin
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Long term aging study of WMA binder
Get PDFtextWarm 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
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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.Civil, Architectural, and Environmental Engineerin
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The UTexas Seal Coat Design Method using 3D laser technology
Get PDFThe size of the highway network has grown beyond the manageable capabilities of transportation agencies and stakeholders who are concerned with maintaining their assets using limited funding abilities. For that reason, pavement preservation programs have become very popular because they offer cost-effective spending schemes that maximize the service life of roads. Seal coats are one of the most popular pavement preventative treatments used around the world due to their high durability and low cost compared to other surface treatments. Their performance depends on the adequate computation of the aggregate and binder application rates. Misestimating these rates leads to raveling, bleeding, or other distresses. Accordingly, numerous design methods have been developed and are being implemented worldwide. This research assesses the different design philosophies and considers the assumptions adopted by each. It is challenging to design a seal coat when several design methods recommend different and inconsistent application rates. For the first time, the three-dimensional laser is incorporated in the design of seal coats in order to provide a fast, objective, and reliable approach. A predictive model is developed to determine the adequate aggregate application rate based on the size of the aggregates, i.e. the average least dimension, and their density. This study also assesses the contemporary texture characterization techniques and analyzes the variance of the sand patch test. The findings indicate that the sand patch test is not a reliable estimator of the volume of voids in the surface texture, which negatively affects the calculation of the binder application rate. The study recommends an algorithm that accurately measures the volume of voids in the existing surface texture using 3D surface scans. The outcome enhances the estimation of the binder application rate, and the findings can be applied to the existing design methods to improve the performance of the seal coat. Finally, highway agencies could incorporate the 3D laser within the binder sprayer to measure the surface texture during construction and automatically adjust the rate.Civil, Architectural, and Environmental Engineerin
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Development of an expert system facilitating the selection of a mix for an asphalt pavement and analysis of fatigue tests
No full textThis thesis is aimed at developing a decision support system for facilitating the selection of an appropriate mix for an asphalt pavement. This system is designed with the new pavement engineer in mind who does not have sufficient experience to make an informed judgment about the mix selection. The system takes structural and traffic characteristics as well as climatic conditions as input, and outputs the mix and the binder type as well as other relevant information about the design parameters according to the knowledge collected from surveys by experts, laboratory testing and relevant information databases. Four point beam bending fatigue tests have been carried out as a part of the laboratory tests to acquire knowledge about the fatigue response of the different mixes for the decision support system. The secondary goals of carrying out the tests were to evaluate the test procedure and to identify the advantages of using modified binders with respect to the fatigue life of the various mixesCivil, Architectural, and Environmental Engineerin
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Modeling heterogeneity in transportation infrastructure deterioration
Get PDFtextOne of the key elements for managing transportation infrastructure is to accurately
capture and predict the performance of the facility through well established deterioration
models. A sound deterioration model should incorporate 1) physical principle that reflects
the deterioration mechanism; 2) relevant variables affecting the deterioration process; and
3) rigorous statistical approach to estimating the model. This dissertation aims at
addressing these critical issues with focus on highway pavements.
Data collected from in-service pavement sections are adopted to capture the real-world
pavement deterioration process. A widely used pavement performance indicator, riding
quality in terms of International Roughness Index (IRI) is used. A nonlinear model with a
hierarchical parameter structure is formulated to effectively account for both observed
and unobserved heterogeneity.
The model is estimated through an econometric technique, Maximum Simulated
Likelihood estimation. Simulation is employed to solve the computationally challenging
problem of multi-dimensional integration. Engineering implications based on estimation
results are discussed. The findings are not only consistent with engineering judgment but
also helpful to reveal and enhance understanding of the pavement deterioration
mechanism. Furthermore, the proposed methodology provides flexibility to obtain both
parameters reflecting deterioration for all units and each individual unit of the population.
The second part of the dissertation establishes and evaluates optimal maintenance policy
on the basis of realistic deterioration models. The optimal policy is obtained so that the
total cost, agency plus user cost, is minimized. A steady state resurfacing problem is
investigated in the case study. In particular, the effect of model accuracy related to
unobserved heterogeneity on total cost is discussed.
This study makes a contribution to transportation infrastructure management and design
in the following sense. From a management viewpoint, the proposed methodology with
hierarchical parameters can accommodate both network and project levels of
management. It also facilitates decision making for budget planning and resource
allocation. From a design viewpoint, model estimation results can be used to update the
current AASHTO pavement design equation by incorporating other critical factors.Civil, Architectural, and Environmental Engineerin
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Development of a computational method for inverting dynamic moduli of multilayer systems with applications to flexible pavements
Get PDFtextMost existing computational methods for inverting material properties of multilayer systems have focused primarily on elastic properties of materials or a static approach. Typically, they are based on a two-stage approach: (I) modeling structural responses with a computer program, and (II) estimating layer properties mathematically using the response outputs determined in stage I without interactions with the governing state partial-differential-equation (PDE) of stage I. This two-stage approach may not be accurate and efficient enough for inverting larger scale model parameters. The objective of this research was to develop a computational method to invert dynamic moduli of multilayer systems with applications to flexible pavements under falling weight deflectometer (FWD) tests, thereby advancing existing methods and fostering understanding of material behaviors. This research first developed a finite-element and Newton-Raphson method to invert layer elastic moduli using FWD data. The model improved the moduli seeds estimation and achieved a satisfactory accuracy based on Monte Carlo simulations, addressing the common back-calculation issue of no unique solutions. Consequently, a time-domain finite-element method was developed to simulate dynamic-viscoelastic responses of the multilayer systems under loading pulses. Simulation results demonstrated that the dynamic-viscoelastic-damping-coupled model could emulate structural responses more accurately, thereby advancing existing simulation approaches. By using the dynamic-viscoelastic-response model as one computation module, this research led to the development of a PDE-constrained Lagrangian optimization method to invert dynamic moduli and viscoelastic properties of multilayer systems. The Lagrangian function was used as an objective function, with a regularization term and governing-state PDE constraint. Both the first-order (gradient) and second-order variation (Hessian matrix) of the Lagrangian were computed to satisfy necessary and sufficient optimality conditions, and Armijo rule was modified to determine a stable step length. The developed method improved computation speed significantly, and it is superior for large-scale inverse problems. The model was implemented for evaluating flexible pavements under FWD tests and for inverting the master curve of dynamic moduli of the asphalt layer. Independent computer coding was developed for all numerical methods. The computational methods developed may also be applied to other multilayer systems, such as tissues and sandwich structures at different time and length scales.Civil, Architectural, and Environmental Engineerin
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Correlating pavement texture, noise and friction properties
Get PDFThis thesis uses texture, friction, and noise data collected along eight asphalt pavements with different surface types across Texas to explore the intercorrelation between the three properties, both within each pavement surface type and across different types. It was found that across all surface types, the entire frequency band of noise from 400 to 5000 Hz correlates the strongest with texture of wavelengths from 31.5 mm to 2.5 mm positively. This means that regardless of the surface type, pavements with a higher texture level in the wavelength spectrum of 31.5 mm to 2.5 mm tend to generate a higher level of noise in the frequency band of 400 to 5000 Hz. When noise is broken down into 1/3 octave bands in frequency, the strongest positive correlation is found between noise of 630 Hz and texture of 50 mm wavelength. A negative correlation, however, is found between higher frequency (f > 1000 Hz) noise and shorter wavelength ([lambda] < 10 mm) texture. The slope of noise vs. texture is similar across different pavements, but the intercept can be different, indicating that with a unit increase in texture level, the additional noise generated by different pavement types is of similar magnitude, but they might be at different levels of loudness given the same texture level. Across all pavement types, when texture level is the same, pavements surfaced with thin overlay mixtures (TOM) tend to generate a consistently lower level of noise at both high and low frequencies. While no strong correlation was found between noise and friction, this finding is consistent with the conclusions from studies by previous researchers. The correlation between friction and texture using the original data has not been found to be strong, which can be partially due to the inconsistency in location of the corresponding measurements. With the capability of measuring texture and friction simultaneously to ensure that the data are collected under the same condition and location using the equipment developed at UT Austin, a much stronger correlation between friction in terms of Grip Number (GN) and texture in terms of root mean square (RMS) was found. Speed, meanwhile, also plays an important role in predicting friction, with a significantly negative coefficient in the model. Statistically different friction levels are also observed among different mix types of pavement surface when other variables are held constant, indicating that different surface types can provide different levels of friction given the same texture at the same speed.Civil, Architectural, and Environmental Engineerin
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Mixture design and performance-based specification recommendations for cold patching mixtures
No full textCold patching asphalt mixtures constitute an essential element for the maintenance and rehabilitation of pavement infrastructure. Although this maintenance technique is both expensive and time consuming, it can minimize further damage and costly future repairs as well as increase user and vehicle safety. As a result, cold patching mixture performance is critical. Unfortunately, there is a lack of standard mixture design guidelines for homemade mixtures and performance-based mixture specifications for both homemade and containerized mixtures to ensure satisfactory field performance. This thesis develops a homemade mixture design for cold and wet weather areas by identifying the failure mechanisms of cold patching mixtures and analyzing the effects of gradation, aggregate shape, binder content and viscosity, curing time, temperature, and admixtures on the mixture workability and stability. Laboratory and accelerated pavement testing (APT) procedures are specifically defined for use with cold patching mixtures. Protocols and procedures are also defined for the field evaluations of these mixtures. Results from field evaluations are used as overall relative measures of field performance and as validation for those results obtained from laboratory and accelerated pavement tests. Furthermore, testing results, in conjunction with testing procedures developed as part of this thesis, are used to provide recommendations for performance-based specifications for homemade and containerized cold patching mixtures. Such recommendations provide interim guidelines for the rejection or approval of such mixtures. Overall, the protocols and testing procedures developed herein help ensure the material characteristics necessary for desired patch performance in the field, which in turn reduces the failure rate and makes cold patching a more cost-effective maintenance operation.Civil, Architectural, and Environmental Engineerin
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Evaluation of data imputation techniques in pavement texture processing
Get PDFThe importance of roads in modern society is without a doubt incomparable and nowadays, federal, state and local highway agencies are increasing the demands on the performance and serviceability of transportation infrastructure. It is no longer sufficient to have a pavement with enough structural capacity to sustain the demands of traffic. There are also growing demands to increase the functional properties of the road that are highly correlated with texture, such as skid resistance, proper drainage and smoothness. To better assess, compare and improve the functional properties of roads, there has been an effort to standardize the measurement methods of texture at highway speeds, based on surface profiles. But even standardizing the measurement methods is not enough to ultimately improve road functional properties if the processing of these profile data changes depending on who the analysist is. Therefore, meticulous studies need to be performed to determine what are the best practices when processing pavement texture data. This thesis studied the process of data imputation to determine what is the best imputation method based on their accuracy and computation time. The case study explored ten popular imputation methods, explained how they work, tested each of by means of Monte Carlo (MC) simulation, and ranked their efficiency using the Analytical Hierarchical Process (AHP). A two-tailed hypothesis test was used to make the final decision and determine whether the gain in imputation accuracy (if any) was statistically significant compared to the same statistic computed with missing data. Data imputation for texture data processing was proven to significantly increase the accuracy of estimates of texture summary statistics when a good imputation method was implemented. This study found that linear interpolation imputation was the best imputation technique not only because of its robustness and efficiency but also because of its simplicity and ease of implementation. However, it was also proven that using poor imputation techniques such as spline interpolation for gaps of missing data that are greater than ten data points can potentially yield biased estimation of pavement texture statistics that are significantly worse than simply computing that statistics using the data with missing entriesCivil, Architectural, and Environmental Engineerin
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