Showing papers by "Imad L. Al-Qadi published in 2013"

Importance of Nonlinear Anisotropic Modeling of Granular Base for Predicting Maximum Viscoelastic Pavement Responses under Moving Vehicular Loading

Abstract: This paper explains the importance of using a nonlinear anisotropic three-dimensional (3D) finite-element (FE) pavement model to simulate the granular base layer and predict viscoelastic pavement responses under moving vehicular loading The FE model was built using the general-purpose FE software ABAQUS, and a user material subroutine was developed to implement the constitutive model of granular material using a modified Newton-Raphson approach with secant stiffness The FE model utilizes implicit dynamic analysis and simulates the vehicular loading as a moving load with 3D contact stresses at the tire-pavement interface The analysis results indicate that it is important to consider the viscoelastic nature of the asphalt layer and the moving load for accurately capturing the nonlinear granular base modulus in the mechanistic pavement model The modulus distribution in the granular base layer is affected not only by wheel load and pavement structure (such as asphalt layer thickness and subgrade s

Innovative Approach for Asphalt Pavement Compaction Monitoring with Ground-Penetrating Radar

Abstract: This paper demonstrates that ground-penetrating radar (GPR) is an effective tool for quality assurance and quality control during flexible pavement compaction and after construction. Density is one of the most important properties of asphalt concrete layers in flexible pavement. It is critical to monitor the change in asphalt concrete density during compaction; GPR can be used to measure asphalt mixture density nondestructively and rapidly. However, it is challenging to apply the GPR method during compaction because of the unknown effect of roller-sprayed water on the GPR signal. This paper presents the results of a study on the effect of surface water on the GPR signal when a 2-GHz antenna is used. It was found that the higher-frequency components of the ultrawide band signal were affected by water; however, the lower-frequency components were not significantly influenced. The process consisted of a band-pass filter with a passing band from 200 to 800 MHz and extracting the surface reflection amplitude a...

Analysis of Near-Surface Cracking under Critical Loading Conditions Using Uncracked and Cracked Pavement Models

Abstract: In this paper, the mechanism of near-surface cracking under critical loading conditions was investigated using mechanistic modeling approaches. These loading conditions were represented by a combination of nonuniform tire contact stresses in three directions generated during vehicle maneuvers (free rolling, acceleration/braking, and cornering) that were predicted from a tire-pavement interaction model. Three-dimensional finite element models of uncracked and cracked pavements were developed to evaluate the critical factors that are responsible for crack initiation and propagation at the near-surface of a typical full-depth pavement structure. It was found that the near-surface cracks in the proximity of tire edges showed strong mixed-mode (tension and shear) fracture potential. The pavement responses from both uncracked and cracked pavement models indicated that shear mode of fracture in the presence of compression appeared to be the dominant mode of damage for near-surface cracking. Compared to the free rolling condition, tire braking/acceleration and cornering induced high tangential contact stresses on the pavement surface, which could significantly accelerate the development of cracks at the pavement near-surface. The near-surface cracking potential was dependent on the variations of localized tire contact stress distributions. The findings presented in this study shed light on the experimental characterization of the near-surface cracking phenomenon, which appears to be driven by different stress conditions than the classical bottom-up fatigue cracking. This study also highlights the impact of vehicle maneuvering on premature pavement damage that is often neglected in the current pavement design process.

Impact of Tire Loading and Tire Pressure on Measured 3D Contact Stresses

Abstract: Three-dimensional (3D) tire–pavement contact stresses for two types of tires used by the truck industry (new generation wide-base tire [WBT] and dual-tire assembly [DTA]) were measured and compared. The testing matrix was composed of five loads () (26.6, 35.5, 44.4, 62.1, and 79.9 kN) and four tire inflation pressures (ߪ ௢ ) (552, 690, 758, and 862 kPa). The equipment used for measuring the 3D- contact stresses is described along with the testing procedure and the methodology followed during data processing. The effect of applied load and tire-inflation pressure on the variation of longitudinal, transverse, and vertical CONTACT STRESSES along the contact length of each tire type was analyzed. Differences in the distribution and magnitude of the aforementioned stresses were observed between WBT and DTA; these differences are an important factor linked to pavement damage caused by each tire configuration. This experimental effort is part of a national study to evaluate the effect of WBT on pavement damage and compare it to that of DTA.

Performance Characterization of Asphalt Mixtures at High Asphalt Binder Replacement with Recycled Asphalt Shingles

Abstract: Recycled materials can be used effectively in asphalt mixtures to replace virgin asphalt binder or virgin aggregates. Virgin material (asphalt binder or aggregate) can be replaced with reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures. The study presented in this paper examined the effect of high asphalt binder replacement (ABR) for an asphalt mixture with a low number of design gyrations (a low N-design) and RAP and RAS on performance indicators (e.g., permanent deformation, fracture, fatigue potentials, stiffness). A developed experimental program included complex modulus, fracture, overlay reflective cracking resistance, low-temperature cracking, wheel track permanent deformations, and push-pull fatigue tests. The ABR, combinations of RAS and RAP asphalt binder, and levels in the mix ranged from 43% to 64%. Potential permanent deformation resistance of the mixtures was improved in the presence of RAS. Fracture tests at low temperature revealed no significant diffe...

Three-Dimensional Finite Element Modeling of Instrumented Airport Runway Pavement Responses

Abstract: A three-dimensional finite element model was used to analyze runway pavement responses under moving aircraft tire loading. The analysis modeled an instrumented runway at Cagliari Elmas airport in Sardinia, Italy, with a 350-mm asphalt layer, a 400-mm granular base layer, and subgrade. The finite element model characterized the asphalt layer as a linear viscoelastic material, and two interface bonding conditions between asphalt layers (full bonding and partial debonding) were used in the analysis. The aircraft tire loading was simulated with a nontraditional loading assumption that represented the nonuniform distribution of tire contact stresses along contact length and width under five ribs of an aircraft tire. Analysis results showed that a traditional loading assumption that assumed uniform contact stresses at the tire-pavement interface underestimated the critical tensile and shear strains in the asphalt layer. In particular, the relatively high contact stresses at tire edge ribs under heavy aircraft l...

Interface Layer Tack Coat Optimization

Abstract: Interface bonding is a key factor affecting pavement performance life. This study focused on optimizing in situ tack coat application rate and field installation. The objective was to validate the laboratory-determined optimum residual application rate and evaluate the field performance of tack coat materials. The parameters analyzed included two cleaning methods (broom and air blast), two paving procedures (spray paver and conventional paving with use of a distributor and a regular paver), tack coat type (SS-1h, SS-1hp, and SS-1vh), and existing pavement surface. Projects were conducted on I-80 and Illinois Route 98. Cores were tested by using the interface shear test device. A life-cycle cost analysis that considered construction materials and paving methods was performed. Results showed similar bond strength for both cleaning methods; however, air-blast cleaning reduced the required optimum residual application rate. The resulting interface bond strength was similar when using either of the paving proc...

Innovative Sprinkle Treatment for Thin Durable Asphalt Overlays

Abstract: This paper presents techniques for improving asphalt overlays through the use of innovative surfacing technologies that employ durable local aggregates spread on a cost-effective wearing surface base mixture. A few states have used the sprinkle treatment to improve the skid resistance of pavement surfaces on top of typical asphalt pavements. Numerous approaches have been introduced to improve the performance of asphalt pavement. These improvements often add cost because they use high-quality aggregates and modified binder. Because sustainable and cost-effective pavements are being emphasized, innovative application of the sprinkle treatment has been considered. A fine-graded dense asphalt wearing surface mixture developed with the Bailey method provides a promising aggregate structure that makes it possible to ensure compactibility with relatively thinner layers of asphalt mixture. The design of the base mixture used less-expensive local aggregates, and its performance was compared in the laboratory with ...

Airfield and Highway Pavement 2013: Sustainable and Efficient Pavements

Abstract: Proceedings of the 2013 Airfield & Highway Pavement Conference: Sustainable and Efficient Pavements, held in Los Angeles, California, June 9-12, 2013. Sponsored by the Transportation & Development Institute of ASCE

Development of an Economical, Thin, Quiet, Long-Lasting, High Friction Surface Layer, Volume 1: Mix Design and Lab Performance Testing

Abstract: This project developed and evaluated four new asphalt concrete (AC) mixtures that use locally available aggregates whenever possible with the ultimate goal of a cost-effective mixture that also improves pavement performance. Although numerous tactics have previously been introduced to improve the performance of asphalt pavement, these improvements often add expenses because they use unnecessarily large amounts of high quality aggregates and highly modified binder. The Illinois Department of Transportation initiated a program to develop sustainable asphalt pavements that use locally available aggregates as much as possible to reduce the material cost while also improving performance. These new mixtures were developed using the Bailey method to provide a promising aggregate structure that makes it possible to ensure compactability at thinner layers. The newly developed mixes use locally available natural aggregates such as dolomite, and include smaller amounts of imported materials such as quartzite, steel slag, and fibers to improve their performance in terms of durability, rut resistance, moisture susceptibility, fracture, and complex modulus. To evaluate the performance of each new mixture, five laboratory tests were conducted at the Advanced Transportation and Research Engineering Laboratory (ATREL), and the results suggest a preferred mixture.

Pavement layer interface shear strength using a hyperbolic mohr-coulomb model and finite element analysis

Abstract: This paper presents a laboratory and numerical evaluation of interface shear strength between two hot-mix asphalt (HMA) layers. Pavement layer interface shear strength is discussed using a frictional Mohr-Coulomb-based plasticity model. The interfacial response was captured at two different loading states: pure shear and shear with compression. Direct shear testing was performed at the interface between two HMA layers to determine the effectiveness of two tack coat materials: SS-1hp and SS-1vh. Two overlays (9.5 mm and 4.75 mm nominal maximum aggregate size [NMAS]) were applied over unmilled aged nontrafficked surface. The interface shear tests were conducted at various normal pressure levels (0, 0.138, and 0.276 MPa; 0, 20, and 40 psi, respectively) at room temperature (25°C [77°F]). The measured interface shear stresses were compared with those predicted from vehicular loading in a typical thick pavement structure. A three-dimensional (3D) finite element (FE) pavement model was built to evaluate the interfacial stresses at the interface between HMA layers under moving vehicular loading. According to the results obtained from the experimental program, several parameters were found to be influential on the interlayer response. These are vehicle loading (load and tire inflation pressure) and maneuvering (braking, acceleration, and cornering). The paper also introduces the stress ratio concept for evaluating critical interface conditions. The stress ratio can be calculated based on the ratio of predicted interface stresses and interface shear strength.

Selection of Non-Destructive Testing Technologies for Asphalt Pavement Construction

Abstract: The objective of this paper is to present a quantitative decision-support process for selecting non-destructive testing (NDT) technologies to evaluate critical characteristics during asphalt pavement construction. The literature lists mix segregation, in-place compaction, smoothness, temperature segregation, layer thickness, layer bond, and pavement modulus as critical characteristics governing quality pavement construction. Available technologies that measure one or more of these characteristics are identified for unique attributes of test measure, test portability, complexity, test time, environmental limitations, reliability, approved test protocols, training, and cost. A quantitative ranking system determines the most appropriate NDT technologies for quality assurance measurement. A case study selection is demonstrated uniquely for one agency to measure pre-defined critical characteristics of in-place compaction, thermal segregation, and modulus using three NDT technologies: infrared thermography, ground penetrating radar, and the portable seismic pavement analyzer. Results from field testing reveal additional aspects of pavement quality measurement beyond traditional density and smoothness measurements.

Rutting Potential of Thin and Durable Asphalt Wearing Courses: Laboratory Prediction and Field Performance

Abstract: Alternative asphalt concrete (AC) mixtures have been developed to provide thin, durable, efficient, and cost-effective wearing courses. A combination of locally available and durable aggregates, such as steel slag and quartzite, were used to enhance the performance of the mixes while ensuring cost effectiveness. In addition, fibers were used in a new mixture for potential reduction in the AC layer thickness due to the increase in its tensile strength. In addition, several innovative approaches to develop new AC mixtures were also introduced and evaluated. Four new AC mixtures and two control mixtures were placed in the Chicago area to evaluate their field performance under real traffic loading. This paper focuses on the permanent deformation of the newly developed AC mixtures and presents their rutting potential based on laboratory testing and their short-term rutting performance in the field. Wheel tracking testing was conducted on each AC mixture. The specimens were prepared using two mixing approaches: lab-mixed and lab-compacted specimens and plant-mixed and lab-compacted specimens. A dipstick was used to measure rut depth in the field every four months after construction. To evaluate the effect of layer thickness on measured permanent deformation, two sections having different layer thicknesses were constructed for each AC mixture. This paper presents the difference in rutting potential based on laboratory testing and field measurement for the newly developed wearing surface AC mixtures and the effect of layer thickness on rutting development.

Development of an Economical Thin, Quiet, Long-Lasting, High Friction Surface Layer for Economical Use in Illinois, Volume 2: Field Construction, Field Testing, and Engineering Benefit Analysis

Abstract: This project provides techniques to improve hot-mix asphalt (HMA) overlays specifically through the use of special additives and innovative surfacing technologies with aggregates that are locally available in Illinois. The ultimate goal is to improve pavement performance through optimized materials while also controlling cost by efficiently using local materials. Therefore, the proposed new mixes use locally available aggregates when possible. The project also considered the use of alternative aggregates such as steel slag to increase the friction quality of the HMA and therefore improve pavement performance. To evaluate the newly developed wearing course mixtures and evaluate their performance under actual traffic loading, test pavements were constructed, including control mixtures, between August and November 2010 in northern Illinois. The newly proposed mixtures include fine dense-graded HMA and stone matrix asphalt (SMA). The fine dense-graded HMA was designed using the Bailey method and developed with the hope of improved compactability for thinner asphalt layers. The SMA contained a 4.75-mm nominal maximum aggregate size (NMAS) that allows for layers as thin as 0.75 in. On-site performance tests were conducted at 4-month intervals following construction; the tests include noise, friction, rutting, and texture profiling. An engineering benefit analysis was performed to evaluate the new mixes’ cost effectiveness. New HMAs are proposed, along with alternative cross-sections that improve pavement performance while controlling costs.

Rutting potential of warm mix asphalt and possible misleading results due to reheating

Abstract: The main objective of this study is to evaluate the rutting potential of warm mixes produced with various warm mix additives (Evotherm, Sasobit, and foamed asphalt). To achieve this objective, an experimental matrix was developed to determine the mechanical properties of warm mixes and the control mix. Laboratory performance testing includes evaluation of modulus, strength, and rutting potential using dynamic modulus test, indirect tensile (IDT) strength test, flow number (FN) test, and loaded wheel track (LWT) test. The test results show that the warm mix could have slightly greater or less rutting potential than the control mix depending on the type of warm mix additive and the recycled material used in the mix. In the laboratory tests, plant-produced mixes were compacted in the laboratory without and with reheating. It was found that the reheating process could significantly stiffen the mixture and the stiffening ratios varied from 1.2 to 2.0 depending on the performance characteristics and the type of mixture. In addition, the rutting test results show different levels of correlation with the dynamic modulus and the tensile strength, depending on the stress state in the performance test. This suggests that attention should be paid to the measured characteristics of each performance test based on the loading conditions.

Investigation and Development of a Non-Destructive System to Evaluate Critical Properties of Asphalt Pavements during the Compaction Process

Abstract: The purpose of this report is to present findings from a two-stage investigation to develop a non-destructive system to evaluate critical properties and characteristics of asphalt pavements during the compaction process. The first stage aligned critical properties and characteristics with available non-destructive testing (NDT) technologies. A quantitative ranking was created with an objective and unbiased scoring system to determine the most appropriate NDTs for field evaluation. Based upon this ranking system, the three higher-ranked NDTs for the evaluation and selected for a field evaluation were: Infrared Thermography (IR), Ground Penetrating Radar (GPR), and Portable Seismic Pavement Analyzer (PSPA). The nuclear density gauge was also used in the evaluation. The second stage of the investigation collected field data from three projects, analyzed the data using a variety of methods, and developed an implementation plan based upon the findings. Continuous infrared (IR) thermal readings measured mat temperature at 12 transverse offsets spaced 13 in apart, and at a 1 ft longitudinal spacing. Analysis of the data found greater variability along centerline of the paving mat. The average nuclear density on the three projects was nearly identical, ranging from 92.4% to 92.6%, and standard deviations of 2.21%, 1.66%, and 1.40%. The GPR density standard deviation was about half that of nuclear density. GPR thickness among the projects had a standard deviation ranging from 0.1 to 0.2 inches. Variability closer to the pavement centerline was generally higher. Average modulus normalized at 130°F on Project 1 was 3616 ksi, Project 2 at 3014 ksi, and Project 3 at 2530 ksi. Data from the three projects found no definitive relationship between continuous thermal temperatures behind the paver and final density measured by GPR and nuclear density gauge. Placement temperature did not appear to affect modulus; this finding is limited to the three projects in this study and may not be true for all mixes placed in Wisconsin or other states.