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The skid resistance of a pavement surface is an important characteristic that influences traffic safety. Previous studies have shown that skid resistance varies with temperature. However, relatively limited work has been carried out to study the effect of temperature on skid resistance in hot climates. Recent developments in computing and computational methods have encouraged researchers to analyze the mechanics of the tire-pavement interaction phenomenon. The aim of this paper is to develop a thermo-mechanical tire pavement interaction model that would allow more robust and realistic modeling of skid resistance using the Finite Element (FE) method. The results of this model were validated using field tests that were performed in the State of Qatar. Consequently, the validated FE model was used to quantify the effect of factors such as speed, inflation pressure, wheel load, and ambient temperature on the skid resistance/braking distance. The developed model and analysis methods are expected to be valuable for road engineers to evaluate the skid resistance and braking distance for pavement management and performance prediction purposes., Pavement Engineering

The skid resistance of a pavement surface is an important characteristic that influences traffic safety. Previous studies have shown that skid resistance varies with temperature. However, relatively limited work has been carried out to study the effect of temperature on skid resistance in hot climates. Recent developments in computing and computational methods have encouraged researchers to analyze the mechanics of the tire-pavement interaction phenomenon. The aim of this paper is to develop a thermo-mechanical tire pavement interaction model that would allow more robust and realistic modeling of skid resistance using the Finite Element (FE) method. The results of this model were validated using field tests that were performed in the State of Qatar. Consequently, the validated FE model was used to quantify the effect of factors such as speed, inflation pressure, wheel load, and ambient temperature on the skid resistance/braking distance. The developed model and analysis methods are expected to be valuable for road engineers to evaluate the skid resistance and braking distance for pavement management and performance prediction purposes., Pavement Engineering

This study evaluates the potential of selected ionic polymers to act as pavement subgrade binders. Investigations were based on their relative performance with a Qatari soil which was selected as typical of a pavement subgrade to be found in the Middle East and North African region. The polymeric binders chosen were three synthetic ionic variations of polyacrylamide: cationic poly(acrylamidopropyl trimethyl ammonium chloride) (designated PAMTAC), anionic hydrolysed poly(acrylamide) (HPAM) and the ampholitic terpolymer poly(acrylamide-co-sodiumacrylate-co-(3-acrylamidopropyl) trimethylammonium chloride) (TPAM). The polymers were characterised by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic spectroscopy (¹H-NMR and ¹³C-NMR). The comparative performance of the polymer-treated soil was judged on the basis of results obtained from selected standard mechanical test data: specifically, the unconfined compressed strength, the stiffness modulus and the toughness. It is concluded that a 50% w/w aqueous solution of the ampholitic terpolymer applied at a dosage of 2.0% by dry weight of the soil gives the best subgrade stabilisation. Of some significance, it is further noted that this ampholitic polymer was superior as a binding agent to the traditional standard, Portland cement, judged under equivalent but nonstandard conditions. Modifying the polymer to act as a binder for subgrade soils in general is also discussed.

TSC import 1687 2012-02-10. QCR 20161212

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DTRT07-G-0006, This study presents the numerical implementation and validation of general constitutive relationships for describing the, nonlinear behavior of asphalt concrete mixes. These constitutive relationships incorporate nonlinear viscoelasticity and, viscoplasticity to predict the recoverable and irrecoverable responses, respectively. The nonlinear viscoelastic deformation, is modeled using Schapery’s model; while the irrecoverable component is represented using Perzyna’s viscoplasticity, theory with an extended Drucker-Prager yield surface and plastic potential that is modified to capture the distinction, between the compressive and extension behavior of asphalt mixes. The nonlinear viscoelastic and viscoplastic model is, represented in a numerical formulation and implemented in a finite element (FE) code using a recursive-iterative algorithm, for nonlinear viscoelasticity and the radial return algorithm for viscoplasticity. Then, the model is used to analyze the, nonlinear viscoelastic and viscoplastic behavior of asphalt mixtures subjected to single creep recovery tests at different, stress levels and temperatures. This experimental analysis includes the separation of the viscoelastic and viscoplastic strain, components. Based on this separation, a systematic procedure is presented for the identification of the material parameters, associated with the nonlinear viscoelastic and viscoplastic constitutive equations. Finally, the model

Project 0-6992, This study aimed to conduct a comprehensive evaluation of compaction of asphalt pavements and, develop software for monitoring field compaction in real time. In the first phase of this study, the researchers, built several test sections that were constructed using different asphalt mixtures and various compaction, methods. The results of these experiments were used to determine the effects of compaction temperature, compaction method, mixture design, and base type on the compactability of asphalt mixtures. The, researchers found that the efficiency of the compactive effort across the steel rollers was non-uniform. A, point on the mat closer to the center of the roller was subjected to more compaction than a point closer to the, edge of the roller. The compaction temperature was found to have a great effect on compaction irrespective, of mixture type. The researchers presented a method for predicting the density of asphalt pavements in real, time. This method utilizes the location of the roller on the mat and the compaction curves for each roller to, predict the density. The predicted density was close to the measured one., In the second phase of this study, the researchers developed a system for monitoring and, documenting the compaction process of asphalt mixtures. This system is called the compaction monitoring, system (CMS). The CMS uses the latest global positioning system technologies and various sensors to, provide full coverage of the newly constructed mat. The CMS shows maps of coverage, compaction index, and temperature of the first roller pass in real time. The CMS was found to be simple and easy to install and, use. The CMS was able to show some inconsistencies in the compaction process, for example, unequal, converge across the mat, non-uniform temperature, and significant delay in compaction after placement of, the mixtures. The CMS documents the compaction process for the whole project, and the data are saved on, the computer. The data can be opened using the same software for reviewing the whole compaction process.

0-6992, This study aimed to conduct a comprehensive evaluation of compaction of asphalt pavements and, develop software for monitoring field compaction in real time. In the first phase of this study, the researchers, built several test sections that were constructed using different asphalt mixtures and various compaction, methods. The results of these experiments were used to determine the effects of compaction temperature, compaction method, mixture design, and base type on the compactability of asphalt mixtures. The, researchers found that the efficiency of the compactive effort across the steel rollers was non-uniform. A, point on the mat closer to the center of the roller was subjected to more compaction than a point closer to the, edge of the roller. The compaction temperature was found to have a great effect on compaction irrespective, of mixture type. The researchers presented a method for predicting the density of asphalt pavements in real, time. This method utilizes the location of the roller on the mat and the compaction curves for each roller to, predict the density. The predicted density was close to the measured one., In the second phase of this study, the researchers developed a system for monitoring and, documenting the compaction process of asphalt mixtures. This system is called the compaction monitoring, system (CMS). The CMS uses the latest global positioning system technologies and various sensors to, provide full coverage of the newly constructed mat. The CMS shows maps of coverage, compaction index, and temperature of the first roller pass in real time. The CMS was found to be simple and easy to install and, use. The CMS was able to show some inconsistencies in the compaction process, for example, unequal, converge across the mat, non-uniform temperature, and significant delay in compaction after placement of, the mixtures. The CMS documents the compaction process for the whole project, and the data are saved on, the computer. The data can be opened using the same software for reviewing the whole compaction process.

0-5261, Field compaction of asphalt mixtures is an important process that influences performance of asphalt, pavements. This study evaluates the relationship between different field compaction patterns and the, uniformity of air void distribution in asphalt pavements. A number of projects with different hot mix asphalt, (HMA) types were compacted, and cores were taken at different locations from these projects. The X-ray, Computed Tomography (X-ray CT) system was used to capture the air void distributions in these cores. The, analysis results have revealed that the uniformity of air void distribution is highly related to the compaction, pattern and the sequence of using different compaction equipment. More importantly, the efficiency of, compaction (reducing air voids) at a point was found to be a function of the location of this point with, respect to the roller compactor width., The results in this paper have supported the development of the “Compaction Index (CI),” which, quantifies the degree of field compaction. The CI is a function of the number of passes at a point and the, position of the point with respect to the compaction roller width. This index was found to correlate, reasonably well with percent air voids in the pavement. The CI calculated from field compaction had a good, relationship with the slope of the compaction curve obtained from the Superpave gyratory compactor. This, relationship offers the opportunity to predict field compactability based on laboratory measurements. The, compaction of longitudinal joints was investigated, and recommendations were put forward to improve joint, compaction. The air void distributions in gyratory specimens were related to the mixture mechanical, properties measured using the Overlay and Hamburg tests.

DTRT07-G-0006, This study aimed to develop prediction models for friction loss and laboratory compaction of asphalt, mixtures. In addition, the study evaluated the effect of compaction level and compaction method of skid, resistance and the internal structure of asphalt mixtures. The predictive model for friction loss was developed, based on parameters that describe aggregate texture and angularity before and after polishing, aggregate, gradation, and polishing cycles in the laboratory. Squared-shape slabs of asphalt mixtures were prepared in, the laboratory using a linear kneading compactor and polished using a wheel-polishing device. The frictional, characteristics were measured after different intervals of polishing cycles. Mixtures with coarser aggregate, gradation were found to have better skid resistance than those with fine aggregate gradation. The friction loss, model was found to correlate very well with the experimental measurements., The predictive model for laboratory compaction of asphalt mixtures was developed based on, parameters that describe aggregate shape characteristics, aggregate gradation, binder content, and binder, properties at compaction temperatures. The researchers executed intensive laboratory experiments to, quantify the effect of these parameters on the compaction of asphalt mixture in the laboratory. Two models, that describe slope and intercept of the laboratory compaction curves of asphalt mixtures were developed., These models showed strong correlations between the predicted values and the measured ones. These models, provide essential inputs to quantify the compaction effort needed to compact asphalt mixtures., In the last phase of this study, the researchers evaluated the effect of compaction level and, compaction method on skid resistance and internal structure of asphalt pavements. The vibratory roller was, found to yield a smoother surface than the static roller. In addition, the results confirmed that the vibratory, roller was more effective in reducing the air voids than the static roller. Moreover, the test sections, compacted using the vibratory roller had more uniform air void distribution compared to the test sections, compacted using the static roller.

5-4524-01, TxDOT project 0-4524 evaluated the influence of surface energy of aggregates and binders on the resistance, of asphalt mixtures to moisture damage. The results from this research lead to the development of a threetier, approach to assess the moisture damage resistance of asphalt mixtures. This approach is based on testing, and evaluating the physical and/or mechanical properties of the constituent materials, the fine aggregate, mixture, and full asphalt mixture. In the first tier, an energy-based parameter termed the energy ratio (ER) is, calculated using the surface energy measurements. This parameter is used as a screening tool to select, binders and aggregates that have good resistance to moisture damage. The second and third tiers rely on, measuring the mechanical properties of the fine aggregate mixture and full asphalt mixture, respectively., This report documents the results of an implementation project of the testing methods and analysis, approaches of the 0-4524 project. This implementation project included (a) providing training on the, developed experimental and analysis methods, (b) conducting measurements of the surface energy of, binders, additives, and aggregates, and (c) developing a database of surface energy measurements. This, database will be useful as a diagnostic tool for finding the cause of poor moisture damage resistance in mixes, and to suggest remedies through modification with anti-strip agents, lime, polymers, other additives, or, through a change of materials in extreme cases.

TTI: 0-6746-01, Pavement skid resistance is primarily a function of the surface texture, which includes both microtexture and macrotexture. Earlier, under the Texas Department of Transportation (TxDOT) Research Project 0-5627, the researchers developed a method to predict asphalt pavement skid resistance based on inputs including aggregate texture before and after polishing, gradation of asphalt mixture, and traffic levels. In this study, the researchers validated and revised the skid prediction model for asphalt pavements and developed a skid prediction model for seal coat surfaces. The researchers investigated and examined the surface friction characteristics of 70 test sections of asphalt mixtures and surface-treated roads in Texas. The test sections covered a wide range of mixtures and aggregate types. The researchers measured pavement macrotexture and microtexture of these sections and revised the traffic calculation. Historical skid numbers were obtained from TxDOT’s Pavement Management Information System database and measured using a skid trailer. Aggregate texture and angularity was quantified using the aggregate image measurement system., Statistical methods were used to develop a prediction model for skid numbers, and the predicted values were compared to the measured ones in the field. The revised model describes the skid resistance of asphalt pavements as a function of aggregate characteristics, mixture gradation, and traffic level. The researchers incorporated aggregate angularity as an additional parameter in the model. Similarly, the researchers developed a skid prediction model for seal coat surfaces using the same parameters. A Microsoft Access–based Visual Basic desktop application was developed to automatically calculate the predicted skid numbers by incorporating the skid prediction models. Using this standalone application, one can input the basic aggregate characteristics and traffic data to predict the pavement’s skid resistance during its service life.

0-5261, This project aimed at providing better understanding of the factors affecting the uniformity and level, of compaction; and the performance of asphalt pavements. TxDOT research report 0-5261-1 documented, some of the findings of this research project. This research report documents the efforts and findings of, experiments conducted with more test sections. In the first phase of this report, a number of field test sections, were compacted, and field cores were extracted. These cores were scanned using X-ray Computed, Tomography (X-ray CT) to capture the air void distributions in these cores. The air void distribution, correlated well with the compaction effort across the mat. The compaction effort was found to be a function, of the number of roller passes and the relative location of each pass across the mat. The Compaction Index, (CI) developed in the TxDOT research report 0-5261-1 was used to quantify the compaction effort at any, point in the pavement. This index combines the number of roller passes along with the effectiveness of each, pass on the mat. The compactability of asphalt mixtures in the field correlated well with compactability of, asphalt mixtures in the laboratory. The CI was used to quantify the compactability of asphalt mixtures in the, field while the slope of the compaction curves obtained from Superpave Gyratory Compactor was used to, quantify the compactability of asphalt mixtures in the laboratory., In the second phase of this report, the effect of different levels of compaction on the performance of, asphalt mixtures was studied using a fracture mechanics approach and DEM models. The results showed that, test specimens with less percent air voids performed better than the ones with higher percent air voids. In, addition moisture-conditioned specimens performed worse than the dry ones at the same compaction levels., Furthermore, guidelines were developed to assist in predicting the compactability in the field based on, laboratory measurements during the mixture design stage; and to improve the field compaction.