Showing papers by "Imad L. Al-Qadi published in 2017"

Investigation of viscoelastic fracture fields in asphalt mixtures using digital image correlation

Abstract: In this work we have studied the fracture behavior of asphalt mixtures, a heterogeneous mix of hard aggregates (usually in the form of crushed quarried rock) with a petroleum based asphalt binder, used in paving applications. Specifically, we studied the dependence of asphalt mixes’ fracture response on loading rate, temperature, and recycled content—the latter used primarily to replace virgin materials like aggregates and binder. Fracture tests were conducted on semi-circular bend edge cracked specimens obtained from mixes with different compositions, and the fracture event was recorded with a camera to allow for digital image correlation (DIC) measurements. DIC, with a spatial resolution of about 40 $$\upmu $$ m/pixel, measured the far-field strain and displacement fields developing around a preexisting notch tip. Our focus here is on characterizing the material behavior by quantifying its viscoelastic response and fracture properties. The elastic–viscoelastic correspondence principle was used to extract viscous and elastic components from the full-field DIC-measured strain and displacement fields. Various energy dissipation mechanisms other than the fracture itself were evaluated. Stress–strain response and energy dissipated in the far-field regions were quantified. The pseudo-elastic stress intensity factor was then used to study the fracture properties, and quantify the effects on fracture properties of loading rate, temperature, and recycled content in the binder. It was seen that the viscoelastic characteristics of the material were a dominant factor in the material behavior obtained at room temperature. In general, the elastic component of the displacement was only up to about 30% of the total displacement, indicating a strong influence of viscoelasticity in this state. Loading rate, temperature and recycled asphalt shingles (RAS) content all affected the viscous response by introducing more elastic response when loading rate or recycled content increased or when temperature decreased. It became clear from these macroscopic measurements that the increase of RAS content considerably embrittles the material producing less viscous effects and less energy dissipated in the far-field, almost comparable to reductions associated with the loading rate increase (from 6.25 to 50 mm/min) or the temperature change ( $$-12$$ to $$25\,{^{\circ }}$$ C).

Using binder and mixture space diagrams to evaluate the effect of re-refined engine oil bottoms on binders and mixtures after ageing

Abstract: This study addresses the New England state transportation agencies concerns associated with the use of Re-refined Engine Oil Bottoms (REOB) in asphalt binders and mixtures. The effect of REOB on the physical and rheological properties of a straight run asphalt binder was investigated after short-term and long-term aging and after extended long-term aging. Also, the effect of REOB modified binders on the performance of asphalt mixtures after short and long-term aging was evaluated in terms of moisture damage, rutting, and cracking. Rheological results showed that the addition of REOB caused the binders to age more relative to the straight run binder. The results also indicated that the use of higher dosages of REOB can cause increased binder aging. Overall, when the results from the particular mixture tests used in this study were plotted on a Performance Space Diagrams, the diagrams did not provide evidence that using REOB decreases performance.

Tire–pavement interaction modelling: hyperelastic tire and elastic pavement

Abstract: The interaction between deformable tire and pavement was studied using the validated finite element model; the full understanding of tire–pavement contact has implications for pavement damage prediction and pavement life-cycle assessment (fuel consumption estimation). The tire’s rubber and reinforcement were considered hyperelastic and linear elastic, respectively, with material constants obtained from the tire manufacturer (rubber) and laboratory testing (reinforcement). On the other hand, the pavement was assumed linear elastic supported by linear elastic springs. This assumption was made as a first step to examine the impact of using a deformable-on-deformable tire–pavement system to predict energy in the tire and contact stresses. The effect of the pavement stiffness on contact area, tire deflection, three-dimensional contact stresses, surface deflection, internal energy of the tire and its components, the work performed by the contact forces, and dissipation caused by friction was also studied. The e...

Quantifying sustainable strategies for the construction of highway pavements in Illinois

Abstract: The environmental and economic burdens of various pavement construction strategies are evaluated in this study. A partial life-cycle approach was used to determine the environmental and economic benefits of asphalt concrete and Portland concrete mix designs as well as pavement-related pay items. Approximately 920 designs were assessed to determine the upstream energy consumption and global warming potential (GWP) of producing these mixes. In general, it was found that transportation hauling distances as well as asphalt binder type and production imposed the greatest variability on the environmental and economic costs of the mixes. In many cases, these variabilities were seen to reduce some of the benefits from using increased recycled content. A similar analysis was performed for pay items where it was found that the contribution of environmental and economic impacts to a project followed a trend with upper pavement layers having the greatest impact, followed by subsequently lower layers, and finally earth exaction and preparation. A cost effectiveness (CE) analysis was then conducted for 18 sustainable strategies, the majority of which had, on average, cost savings as well as environmental savings for both energy and GWP at the mix design level. Overall, this study systematically used common reference units (i.e., mix designs and pay items) from the industry to assess general trends, inconsistencies, and implications from using sustainable strategies in pavement construction.

Introducing realistic tire–pavement contact stresses into Pavement Analysis using Nonlinear Damage Approach (PANDA)

Abstract: Realistic tire–pavement interface contact areas and stresses were incorporated into the Pavement Analysis using Nonlinear Damage Approach (PANDA) user interface (PUI). PANDA is a software library developed to simulate the complex thermo-viscoelastic–viscoplastic–viscodamage responses of the pavement to mechanical and environmental loads. The PUI is an interface generating a finite element representation of the pavement within PANDA. The application of realistic tire loading is necessary to calculate accurate pavement responses. The PUI incorporates a database of tire contact areas and stresses obtained from tire finite element simulations. The database includes tire interface characteristics with pavements for various applied loads, tire inflation pressures, vehicle speeds and scenarios of different rolling simulations. A parametric study was conducted to investigate the effect of simulations of tire contact stresses that match field measurements on viscoelastic and viscoplastic pavement responses...

Impact of high recycled mixed on HMA overlay crack development rate

Abstract: Illinois has many years of experience using various reclaimed materials in highway construction, and in recent years, recycled asphalt shingles (RAS) have been adopted for use in hot-mix asphalt (HMA), along with much higher amounts of reclaimed asphalt pavement (RAP). These reclaimed asphalt materials usually contain aged asphalt binders, which may increase the mix brittleness and hence, pose a challenge for maintaining a flexible pavement and ensuring good performance. To counter these hard asphalt binders, softer asphalts are incorporated into the HMA. The goal is for the final mix to provide acceptable mix properties for the life of the pavement. To determine the impact of recycled materials on pavement performance, this study monitored nine field projects in terms of the testing, construction, and performance of surface mixes that have a variety of asphalt binder replacement (ABR) levels from RAP and RAS which used different virgin asphalt binder grades. Simple performance tests (Hamburg wheel tracking test and the Illinois flexibility index test (I-FIT)) were used to evaluate the mix designs. Flexibility index (FI) from the I-FIT showed good correlation with field crack development, especially after first year performance of the mix. Early-age field performance showed that placing the HMA overlay directly over existing bare concrete pavement or milling off all the HMA and placing the new overlay on concrete pavement results in higher extents of cracking in early age than the sections that left an HMA layer in place. Regardless of which mix type is designed and what material sources are used, the performance of the mix should be evaluated to ensure it has sufficient flexibility to resist cracking before the mix is used in road construction. This allows owners and contractors to use low-cost reclaimed and recycled materials to the extent possible without negatively impacting pavement performance.

Viscoelastic and Poisson’s ratio characterization of asphalt materials: critical review and numerical simulations

Abstract: The vast quantity of asphalt concrete being used in the U.S. highway system demands deeper understanding of the material to ensure sustainability of the highway pavement system. Poisson’s ratio, though a vital material property for elastic materials, does not serve the purpose of material characterization for viscoelastic materials like asphalt concrete. This paper presents a brief review of existing literature on the use of Poisson’s ratios in general and by the asphalt research community in specific. The literature review revealed that the majority of existing studies assumed a constant Poisson’s ratio of 0.3–0.35. Few analytical simulations have been conducted to realize the time and stress dependence of viscoelastic Poisson’s ratios. The errors caused by incorrectly assuming constant Poisson’s ratios and the same moduli relaxation times for viscoelastic materials were quantified. The effect of varying moduli ratios on Poisson’s ratios was also studied. This study concludes that assuming a constant Poisson’s ratios and similar relaxation times can lead to serious errors in characterization of asphalt mixtures.

New Stochastic Approach of Vehicle Energy Dissipation on Nondeformable Rough Pavements

Abstract: This study is partially funded by the Illinois State Toll Highway Authority (ISTHA). The authors are representatives of Illinois Center for Transportation (ICT). The contents of this report reflect the view of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official view of policies of the Tollway or ICT. This paper does not constitute a standard, specification, or regulations.

Baseline rolling resistance for tires’ on-road fuel efficiency using finite element modeling

Abstract: Calculation of truck tires rolling resistance, using the finite element method and considering variables such as incompressible visco-hyperelastic rubber materials, accurate tire geometry and steady temperature distribution, is presented. The model was validated using experimentally measured contact area and contact stresses. Rolling resistance was calculated for three values of axle load, tire inflation pressure, temperature and speed. In addition, regression analysis was used to propose a mathematical expression for predicting rolling resistance as a function of the considered variables. Finally, the contribution of tire’s rubber components to the internal energy was quantified, and it was found that sidewall and subtread were the most relevant. The results of this study will help differentiate the contribution of pavement parameters, such as mean profile depth and international roughness index, to fuel efficiency.

Stochastic Analysis of Energy Dissipation of a Half-Car Model on Nondeformable Rough Pavement

Abstract: With a large portion of vehicles still relying on the combustion of petroleum, the transportation sector was reported to be responsible for 27% of the greenhouse gas emissions in the United...

Development of a Life-Cycle Assessment Tool to Quantify the Environmental Impacts of Airport Pavement Construction

Abstract: The environmental impacts of airport pavement construction were evaluated in this study through a life-cycle analysis approach. Total primary energy (TPE) consumption and greenhouse gas (GHG) emissions from material production and construction of pavement were determined by using life-cycle assessment (LCA), a quantitative methodology described in the ISO 14040 series. A tool was developed to implement a probabilistic LCA through the Monte Carlo method. This tool allowed for consideration of uncertainty from life-cycle inventory data. A case study on the construction of Runway 10R-28L at Chicago O’Hare International Airport focused on mainline and shoulder pavement designs. Environmental impacts from producing materials for the pavements increased from lower to upper layers, while asphalt layers had relatively higher TPE consumption than the upper portland cement concrete layer—and vice versa for GHGs. Impacts from material production overshadowed those from construction, which contributed less than 2% of...

Efficient surrogate method for predicting pavement response to various tire configurations

Abstract: A computationally efficient surrogate model was developed based on artificial neural networks (ANN) to investigate the effect of the new generation of wide-base tires on pavement responses. Non-uniform tire contact stress measurements were obtained using a stress-in-motion instrument. The measured 3-D contact stresses were applied on two extreme 3-D flexible pavement finite element models representing low-volume (thin) and high-volume (thick) roads. Eleven critical pavement responses were modeled at two different material properties input levels--detailed and simplified--depending on data availability. The results rendered by the ANN surrogate models were highly accurate with average prediction error less than 5 % and R-square values higher than 0.95. In addition, two sensitivity analyses were performed to investigate the variables effect on pavement responses. It was found that the type of tire (wide-base vs. dual tire assembly) is more influential than the inflation pressure on pavement responses. However, the tire inflation pressure seemed to have a significant effect on near-surface responses. The developed models were incorporated into a tool to assist designers and engineers in investigating the effect of the pavement responses of wide-base versus dual tire assembly under typical loading conditions and pavement structures.

Utilizing Lab Tests to Predict Asphalt Concrete Overlay Performance

Abstract: Prepared By Imad L. Al-Qadi, David L. Lippert, Shenghua Wu, Hasan Ozer, Greg Renshaw, Izak M. Said, Arturo F. Espinoza Luque, and Fazal R. Safi University of Illinois at Urbana-Champaign Timothy R. Murphy Murphy Pavement Technology, Inc. Abbas Butt and Satish Gundapuneni Engineering & Research International, Inc. James S. Trepanier and Joseph W. Vespa Bureau of Materials and Physical Research Illinois Department of Transportation

Development of Adjustment Factors for MEPDG Pavement Responses Utilizing Finite-Element Analysis

Abstract: The Mechanistic-empirical pavement design guide (MEPDG) provides theoretically superior methodology, as compared with its predecessor, for the design and analysis of pavement structures. Th...

Semicoupled modeling of interaction between deformable tires and pavements

Abstract: The interaction between deformable tires and pavements was studied using finite-element modeling and a semicoupled approach. Three finite-element models were used: (1) a hyperelastic tire r...

Development of a modified adhesion test for hot-poured asphalt crack sealants

Abstract: Crack sealing is a maintenance technique commonly used for cracks and joints to prevent moisture infiltration into pavements. Crack sealing materials should possess adequate adhesive and cohesive properties to remain intact in the cracks or joints, depending on the environment and pavement conditions in which they are installed. Adhesion failure is the most common failure mechanism and occurs mostly because of the poor adhesion capacity of sealants as well as the installation quality. Various standard laboratory tests are currently used to evaluate the adhesive properties of sealants to predict their field performance. These tests, however, either lack correlation with the field performance or have not yet been validated. This paper introduces the development of an adhesive prediction test: the modified crack sealant adhesion tester (modified CSAT). The modified CSAT is an improved version of the existing CSAT standard (AASHTO TP 89) and showed consistent results between specimens with sufficient repeatab...

Impact of High Asphalt Binder Replacement on Level Binder Properties for Controlling Reflective Cracking

Abstract: A thin hot-mix asphalt (HMA) level binder (LB) course or interlayer has been used for decades in Illinois. Originally, the LB was simply a layer to provide a working platform that corrected minor variations in the profile of the pavement before HMA overlay. The performance of LB has become of increasing concern with respect to whether high asphalt binder replacement (ABR) could be incorporated into the LB mixes to reduce costs by adding reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS). This study investigated three LB courses with varying ABRs and sources that had been used in five field HMA overlay rehabilitation projects in Illinois. The performances were characterized by a comprehensive testing suite that consisted of tests for dynamic modulus, rutting (flow number and Hamburg wheel tracking tests), moisture susceptibility (tensile strength ratio), fracture resistance [Illinois Flexibility Index Test (I-FIT) overlay tester, and four-point beam fatigue]. The role that these LB mixes ...

Functional unit choice for comparative pavement LCA involving use-stage with pavement roughness uncertainty quantification (UQ)

Abstract: An analysis of the use-stage for pavement Life-Cycle Assessment (LCA) is presented within a framework of an LCA tool developed for Illinois Tollway. Methodological choices that can significantly affect LCA results were evaluated in this study. The share of the use-stage in a comprehensive pavement LCA framework was evaluated with all life-cycle stages including materials, construction, use, maintenance, and end of life. The scope of the use-stage includes albedo, carbonation, and rolling resistance (including pavement roughness and texture components). Uncertainty of the pavement roughness and its effect on the results are investigated using Monte Carlo sampling technique. A discussion on the choice of functional unit and its effect in comparative LCA is presented and an appropriate functional unit is suggested. Four projects were selected as case studies to demonstrate the capabilities of the tool and proposed framework. A multi-point environmental performance evaluation was performed using four environmental indicators for comprehensive interpretation of results. The effect of each stage of LCA was evaluated with emphasis on the results of the use-stage. Additional fuel consumption and emissions, resulting from roughness and texture, constituted the largest share of use-stage impacts while the effect of carbonation was limited. As traffic reduced and the share of the materials and construction stage increased, the share of the use-stage could be decreased to 50% levels.

Development of a Modified Adhesion Test for Hot-Poured Asphalt Crack Sealants

Abstract: Crack sealing is a maintenance technique commonly used for cracks and joints to prevent moisture infiltration into pavements. Crack sealing materials should possess adequate adhesive and cohesive properties to remain intact in the cracks or joints, depending on the environment and pavement conditions in which they are installed. Adhesion failure is the most common failure mechanism and occurs mostly because of the poor adhesion capacity of sealants as well as the installation quality. Various standard laboratory tests are currently used to evaluate the adhesive properties of sealants to predict their field performance. These tests, however, either lack correlation with the field performance or have not yet been validated. This paper introduces the development of an adhesive prediction test: the modified crack sealant adhesion tester (modified CSAT). The modified CSAT is an improved version of the existing CSAT standard (AASHTO TP 89) and showed consistent results between specimens with sufficient repeatab...

Domain analysis for airfield pavement: Moving forward from point responses

Abstract: Current design methodologies for airfield pavement design are based on two failure mechanisms: bottom-up fatigue cracking and permanent deformation in the subgrade. Both mechanisms are based on strain at specific points in the pavement structure (tensile strain at the bottom of the Asphalt Concrete (AC) and vertical strain on top of the subgrade, respectively). However, point responses do not capture the multiaxial nature of stresses and strains. This paper uses a novel methodology called Domain Analysis that not only considers the three-dimensional (3-D) stress/strain state, but also relates regions in the pavement with typical distresses. In addition, various loading configurations are compared using a single scalar resulting from the Domain Analysis. The method uses outputs from finite element analysis and principal stresses/strains to isolate shear and mean states. The capabilities of Domain Analysis are demonstrated by analyzing a section built at the National Airport Pavement Test Facility subjected to a single gear loading of Airbus A-380, three temperatures, two tire-inflation pressures, and two tire speeds. Pavement response are calculated using an advanced finite element model that accounts for factors such as viscoelastic AC, 3-D nonuniform contact stresses and interaction between pavement layers.