bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Experimental Evaluation of Influence of Aggregate Blending on Asphalt Mixture Strength
Authors: Mahmoud Enad , Masad Eyad , Nazarian Soheil , Abdallah Imad
Published: January 2011

Performance of asphalt mixes is vastly influenced by their aggregate properties. The depletion and the high cost of transportation of high-quality aggregates prompt the use of locally available aggregate sources. One approach that has been followed by state highway agencies and contractors to encourage the use of locally available aggregate sources is to blend low- and high-quality aggregates. However, no method is available to these agencies to analyze the influence of blending on mixture properties and to decide on the allowable percentage of blending. Introduced is a modeling approach to study the effect of blending different percentages of high- and low-quality aggregates on the strength of asphalt mixes. Blending charts were developed to predict the change in mix strength given strength and percentages of blended aggregates. The model results were verified through comparisons with several laboratory tests, including tensile strength, Hamburg wheel-tracking device, dynamic modulus, and flow time.
Long-Term Performance Evaluation of Recycled Asphalt Pavement Results from Texas
Authors: Hong Feng , Chen Dar-Hao , Mikhail Magdy M.
Published: January 2011

Recycled asphalt pavement (RAP) has been increasingly used in flexible pavement construction and rehabilitation. Laboratory and in-place evaluation of the performance of RAP and hot-mix asphalt (HMA) produced with RAP is necessary to the successful use of RAP. Extensive research work has been reported with a focus on laboratory tests of RAP materials. But comprehensive evaluation of the long-term in-service pavement performance with RAP is still at its early stage. In this study, the Texas Specific Pavement Studies Category 5 experimental sections from the Long-Term Pavement Performance program provide an opportunity to investigate the in situ performance of HMA with RAP based on about 16 years of data. In the underlying flexible pavement rehabilitation project, the factorial design includes surface preparation, material, and thickness factors. In particular, a relatively high percentage of RAP, with a content of 35% by weight, was adopted in the asphalt overlay. An in-depth investigation of the pavement performance involving two typical distresses, ride quality and transverse cracking and rutting, is conducted. Compared with sections without RAP (HMA with virgin materials), sections with RAP demonstrated higher cracking amount, less rut depth, and similar roughness change over time. The overall evaluation revealed that a well-designed mix with 35% RAP could perform as satisfactorily as that produced with virgin materials to meet the in-service performance requirement.
Effects of Temperature on Interface Shear Strength of Emulsified Tack Coats and Its Relationship to Rheological Properties
Authors: Bae Abraham , Mohammad Louay N. , Elseifi Mostafa A. , Button Joe , Patel Nachiketa
Published: January 2011

The objective of this study was to investigate tack coat interface shear bond characteristics at various temperatures and to relate tack coat characteristics in the field to the rheological test results in the laboratory. Interface shear strength (ISS) of two emulsified asphalt tack coats (CRS-1 and trackless) was evaluated at temperatures ranging from −10°C to 60°C. Two emulsified tack coats were applied on full-scale pavement test sections at application rates of 0.14, 0.28, and 0.70 L/m2. Cores were then extracted from the full-scale test sites to be tested in the laboratory while simulating different field conditions. Tests were conducted with a newly developed direct shear device. The binder grade for the residue of CRS-1 emulsion was PG 58-28. The high temperature grade for the residue of the trackless emulsion was PG 82. Trackless material was brittle at a low temperature, and its low temperature PG grade could not be determined. Within the evaluated temperature range, the ISS of the tacked interface increased with the decrease in temperature. Generally, bonding performance, as measured by the ISS, of the trackless emulsion was superior to CRS-1 emulsion, specifically at temperatures greater than 40°C. In addition, results show that interface shear strength for both tack coat materials at each application rate increased with an increase of the binder rheology parameter G*/sin δ. This relationship can be used to establish a laboratory design threshold for this parameter, to ensure that the selected application rate and tack coat material will perform adequately in the field.
Moisture Susceptibility and Stripping Resistance of Asphalt Mixtures Modified with Different Synthetic Waxes
Authors: Merusi Filippo , Caruso Alessandro , Roncella Riccardo , Giuliani Felice
Published: January 2011

Wax modification of asphalt binders represents an actual resource in warm-mix asphalt technology. Despite its benefits in reducing plant temperatures and atmospheric emissions, the presence of wax can be associated with side effects on the quality and durability of asphalt pavements. A simple procedure to evaluate the influence of wax on asphalt stripping resistance and moisture susceptibility is proposed. An unmodified asphalt binder was blended with waxes having different chemical structures (paraffinic and polyamidic); wax-modified asphalt mixtures were then prepared with various aggregate types. Moisture sensitivity was initially studied using conventional methods, such as indirect tensile strength measured after water conditioning. The stripping resistance of bitumen-coated aggregates was then quantitatively evaluated by identifying the stripped surface with a digital image analysis method. In contrast with expectations, results indicated that enhanced performances can be obtained in the presence of wax-modified asphalts. However, the type of wax was found to be decisive. In the same way, results of contact angle and adhesion measurements performed on bitumen–wax blends indicated that changes in asphalt–water affinity occur according to the type and content of wax.
Functionally Optimized Wearing Course
Authors: McGhee Kevin K. , Clark Trenton M.
Published: January 2011

The preliminary findings on the design, production, placement, and early life performance of a new generation open-graded surface course [also referred to as porous friction course (PFC)] for use in Virginia are highlighted. The primary objective of the larger research project is the design of a functionally optimized asphalt concrete wearing course. Important aspects of the mix design and construction and the initial functional quality of the new surface are documented. General observations associated with the trial section and normal production and placement activities are accompanied by a summary of the quality characteristics of the material. Special emphasis is placed on the early life functional characteristics of the new wearing course. Among these key characteristics are ride quality, wet skid resistance, and tire–pavement noise. Observations made during trial production and placement led to lighter (thinner) recommended application rate and reduced asphalt concrete mix temperatures. Preliminary functional tests indicated that the PFC has exceptional early-age skid resistance, incentive-quality smoothness, and low tire–pavement noise. On the basis of initial cost and early-life functional performance, the PFC is cost-competitive with traditional mixes placed at traditional application rates (when those mixes are used for functional rather than structural improvement).
Characterization of Permanent Deformation of Asphalt Mixtures Based on Shear Properties
Authors: Li Qiang , Lee Hyun Jong , Hwang Eui Yoon
Published: January 2011

A permanent deformation model was developed in this study on the basis of shear properties of asphalt mixtures, such as cohesion and friction angle. Two types of laboratory tests—triaxial compressive strength test and repeated load permanent deformation test—for three types of asphalt mixtures with various volumetric properties were performed to correlate the shear properties with rutting performance. A rational approach was proposed to determine flow number (FN) more accurately with the Hoerl model and roughness penalty method. It was observed from the test results that the FN was not accurate enough to differentiate the rutting characteristics of asphalt mixtures. Unlike the FN, the shear stress to strength ratio accurately identified the mixture rutting performance. Because the same value of the shear stress to strength ratio produced the same level of permanent strain regardless of mixture type, the ratio could be used as the rutting criterion for a performance-based mix design. A permanent deformation model was established on the basis of the shear stress to strength ratio. The proposed model is able to successfully predict the permanent deformation of the various mixtures without changing the model coefficients and could predict the permanent deformation all the way up to failure, including the tertiary flow.
Multiscale Modeling to Predict Mechanical Behavior of Asphalt Mixtures
Authors: Lutif Jamilla E. S. , Souza Flavio V. , Kim Yongrak , Soares Jorge B. , Allen David H.
Published: January 2011

This study presents a multiscale computational model for predicting the mechanical behavior of asphalt mixtures. The model can account for mixture heterogeneities by considering individual mixture constituents through the scale-linking technique: a local scale in a form of the heterogeneous representative volume element and a global scale that has been homogenized from local scale responses. The model is implemented with a finite element formulation, so that geometric complexities, material inelasticity, and the growth of time-dependent damage can be properly handled. Damage is in the form of cracks modeled with nonlinear viscoelastic cohesive zones. The primary purpose of this paper is to present the multiscale modeling framework developed and to evaluate the applicability of the multiscale modeling technique to determine the performance of asphalt mixtures and structures when damaged. This is accomplished by employing only material properties at the constituent level (local scale) as model inputs. The indirect tensile test of fine-aggregate matrix mixture is simulated as an example, and the simulation results are compared with experimental results to evaluate the applicability of the model. Predictive power of the model and the benefits related to the reduction of computational efforts and laboratory tests are further discussed.
Development of Artificial Neural Network Predictive Models for Populating Dynamic Moduli of Long-Term Pavement Performance Sections
Authors: Sakhaeifar Maryam S. , Underwood B. Shane , Kim Y. Richard , Puccinelli Jason , Jackson Newton
Published: January 2011

This paper presents a set of dynamic modulus (|E*|) predictive models to estimate the |E*| of hot-mix asphalt layers in long-term pavement performance (LTPP) test sections. These predictive models use artificial neural networks (ANNs) trained with different sets of parameters. A large national data set that covers a substantial range of potential input conditions was utilized to train and verify the ANNs. The data consist of mixture dynamic moduli measured with two test protocols: the asphalt mixture performance tester and AASHTO TP-62, under different aging conditions. The data include binder dynamic moduli values measured under different aging conditions. The ANN predictive models were trained and ranked with a common independent data set that was not used for calibrating any of the ANN models. A decision tree was developed from these rankings to prioritize the models for any available inputs. Next, the models were used to estimate the |E*| for the LTPP database materials and ultimately to characterize the master curve and shift factor function. To ensure adequate data quality, a series of quality control checks was developed and applied to grade the inputs and outputs for each prediction. Approximately 30% to 50% of all LTPP layers contained enough information to obtain reliable moduli predictions.
Rutting Resistance of Laboratory-Prepared and Field-Compacted Asphalt Mixtures
Authors: Gibson Nelson , Li Sean (Xinjun) , Kutay M. Emin
Published: January 2011

Two groups of asphalt–aggregate mixtures were fabricated by two methods: gyratory compaction in the laboratory and roller compaction in the field. Two stress states were utilized in the flow number repeated load permanent deformation test, which was modified to provide radial and volumetric strains. The measured multiaxial response provided additional insight into quantifiable differences where gyratory compaction produced mixtures that were initially more resistant to permanent deformation than roller compaction; however, confounding effects of asphalt binder aging cannot be ignored. The field-compacted mixtures exhibited less dilation than the roller-compacted mixtures. However, both dilated in the less confined and more confined stress state. This did not agree with the volumetric consolidation observed in full-scale rutted wheelpaths. The implications of the phenomena are important because the flow number test using the asphalt mixture performance tester is extended to performance prediction beyond this application to index mixtures' permanent deformation during mix design.
Estimate of Fatigue Shift Factors between Laboratory Tests and Field Performance
Authors: Prowell Brian D.
Published: January 2011

Mechanistic–empirical pavement design relies on empirical transfer functions to convert stresses and strains (from mechanistic analyses) to an allowable number of load repetitions until an acceptable limit of damage occurs. One method of determining transfer function for bottom-up fatigue cracking is to perform laboratory fatigue tests on the mixture or a range of potential mixtures intended for the pavement. Previous research estimated that shift factors on the order of 4 to 100 are needed to relate laboratory and field performance. There are a number of potential explanations for these shift factors, such as rest periods and healing. The structural test sections at the National Center for Asphalt Technology (NCAT) Test Track provided an opportunity to determine shift factors between transfer functions developed from laboratory beam fatigue tests and from the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures (MEPDG) and field performance. Strains input into the beam fatigue transfer function were measured using embedded pavement strain gauges and calculated using layered-elastic theory (PerRoad). The MEPDG was used to calculate strains for its transfer function. Fatigue shift factors were calculated for four of the structural sections from the 2003 NCAT Test Track. The fatigue shift factors determined using the measured strains ranged from 4.2 to 75.8. The fatigue shift factors determined with PerRoad ranged from 6.7 to 19.2. The fatigue equations developed from the laboratory testing were not used in the MEPDG; the NCHRP 1-37A-calibrated fatigue models were used. On the basis of these analyses, the MEPDG fatigue model reasonably predicts observed cracking.
Use of Limits Method to Characterize Individual Driver Responses to Yellow Change Interval at Signalized Intersections
Authors: Inman Vaughan W.
Published: January 2011

The method of limits was used in a driving simulator study to determine the time-to-stop line (TSL) on the approach to a signalized intersection at which drivers were equally likely to stop or proceed in response to the onset of a yellow change interval. Data from 191 drivers are presented. The mean TSL is referred to as the driver decision point. The variability in the decision point of individual drivers is also reported. The decision point data are discussed in terms of the dilemma zone. It was concluded that the 1-s reaction time that was typically used for calculation of the appropriate yellow and all-red intervals was appropriate. A wide variation in the decision point between drivers was found (1.65 to 5.3 s), and the 10th and 90th percentile decision points were 2.10 s and 3.75 s, respectively. The presence of other vehicles did not appear to affect the decision point. The method of limits is recommended as a quick and reliable means of measuring a driver's decision point with respect to the onset of the yellow change interval. The method may be useful in research settings for assessing treatments intended to influence driver reactions to the yellow change interval.
Insight into Steering Adaptation Patterns in a Driving Simulator
Authors: Sahami Saeed , Sayed Tarek
Published: January 2011

The collection of data from a driving simulator before participants are fully adapted to the system can lead to erroneous and incomplete conclusions. In most studies that involve a driving simulator, researchers try to manipulate a cause and then measure the effect, that is, a driver's reaction. However, participants need time to adapt and transfer their already existing driving skills to the simulator. The process of adaptation, or skill transfer, imposes a mental load on participants that can distract them from performing the primary task, that is, driving. Therefore, before adaptation, a participant's reaction may not be representative of real-life behavior, which potentially reduces the validity of the research. In the present study, the performance of subjects doing a repetitive cornering task is traced and the different patterns of adaptation and skill transfer to the driving simulator are studied. The results show interesting characteristics of the adaptation process, including power curve fit to the learning phase and the observation of a plateau period, in which performance stops improving before it restarts. The participants were also asked to report at what point they felt adapted to the simulator while taking the test. The self-reported times were compared with the results of quantitative analysis of their performance. The results showed that self-reported values were significantly lower than the actual adaptation time, with an insignificant correlation between self-reported values and actual values occurring.
Simulator Fidelity and Validity in a Transfer-of-Training Context
Authors: Allen R. Wade , Park George D. , Cook Marcia L.
Published: January 2011

The question of simulation fidelity and validity is of concern in many driving applications. This paper reviews the general issues associated with fidelity and validity. For training applications, fidelity and validity relate to training effectiveness. Training effectiveness is typically measured according to real-world driver behavior and performance. This paper describes a novice driver training experiment that used simulators with three levels of fidelity. Driver simulator performance was measured for complex driving scenarios containing repeated exposures to hazardous situations. The driving records of the participants were also analyzed for a period of 40 months after they were trained. Inferences about simulator fidelity and validity are drawn on the basis of the participants' simulator performance and real-world driving records. Confounding effects in the database due to several uncontrolled variables are also discussed. These confounding effects are relevant to the design of future transfer-of-training studies.
Effect of Simulator Motion Cuing on Steering Control Performance
Authors: Feenstra Philippus , Van Der Horst Richard , Grácio Bruno Jorge Correia , Wentink Mark
Published: January 2011

The goal of the present study was to explore how simulator motion cuing affects the driver's control performance of a car. Steering behavior was used as a measure of control performance. The experimental task was a slalom maneuver in which the velocity of the car was limited to 70 km/h. Subjective and objective variables were measured. The paper describes the objective steering behavior. The slalom task was driven under four conditions in which the lateral motion scale factors were 1 (one-to-one lateral motion), 0.7, 0.4, and 0 (no-motion), respectively. In total, 16 participants completed the experiment. The study showed that the motion condition affects the steering wheel behavior. The general tendency is that less steering correction took place when the magnitude of the motion cues was increased, which was quantified by two performance indicators. First, the number of steering wheel reversals was reduced when the motion cue magnitude was increased. Second, the amount of relatively high-frequency correction was reduced with increasing motion cue magnitude. It is concluded that motion feedback can improve the driver's control performance in an extreme scenario such as a slalom maneuver. Therefore, the effect of motion on control performance must be considered when a driving simulator study addressing control performance is designed.
Safety Effectiveness of Advance Street Name Signs
Authors: Gross Frank , Lefler Nancy , Lyon Craig , Eccles Kimberly
Published: January 2011

Low-cost safety strategies that states may implement as part of their Strategic Highway Safety Plans need to be evaluated. FHWA organized a Pooled Fund Study of 26 states to evaluate several low-cost safety strategies, including the installation of advance street name signs at signalized intersections. This study investigates whether advance street name signs reduce crashes related to way-finding (i.e., rear-end and sideswipe crashes) at signalized intersections. Geometric, traffic, and crash data were obtained for signalized intersections at 82 sites in Arizona, 65 sites in Massachusetts, and 46 sites in Wisconsin. To account for potential selection bias and regression to the mean, an empirical Bayes before–after analysis was used. The analysis found no significant effect of advance street name signs on total crashes. However, the analysis indicated a significant reduction in sideswipe crashes, including a 27% reduction in Massachusetts and a 10% reduction for the three states combined. A disaggregate analysis was also conducted to identify differential effects. On the basis of conservative cost estimates, a reduction of just 0.01 crash per intersection year would achieve a 2:1 benefit–cost ratio. Given the low cost of this strategy and the potential to enhance way-finding, the use of advance street name signs is justified, particularly at three-legged intersections and locations with relatively large average annual daily traffic or a large expected number of crashes.
Estimation of Resilient Modulus of Subgrade Soils Using Falling Weight Deflectometer
Authors: Nazzal Munir D. , Mohammad Louay N.
Published: January 2011

Field and laboratory testing programs were conducted to develop models that predict the resilient modulus (Mr) of subgrade soils from the falling weight deflectometer (FWD) test results. Mr is used in the design and evaluation of pavement structures. The field testing program included testing various sections in 10 pavement projects within Louisiana. The tested sections covered the common subgrade soil types found in Louisiana. Three backcalculation software packages were used to interpret the FWD data: ELMOD 5.1.69, MODULUS 6.0, and EVERCALC 5.0. In addition, the AASHTO and Florida backcalculation equations were used for comparison. The laboratory testing program consisted of conducting repeated load triaxial Mr tests, physical properties, and compaction tests on soil samples obtained from tested sections. Statistical models were developed that can relate the laboratory measured Mr to FWD moduli backcalculated (EFWD) using each of the methods considered. The results of this study showed that the EFWD/Mr ratio ranged from 0.51 to 8.1 for the tested subgrade soils. Furthermore, this ratio was higher at lower Mr values and hence weaker subgrade soils. The EFWD/Mr ratio was also found to be significantly affected by the backcalculation method. The results of the regression analysis showed that among all backcalculated FWD moduli, those backcalculated using ELMOD 5.1.69 software had the best correlation with Mr. Furthermore, the results showed that the Mr prediction was significantly enhanced when soil properties were included as variables within the regression model.
Implementation of Quality Management of Base Materials with Seismic Methods
Authors: Celaya Manuel , Nazarian Soheil , Yuan Deren
Published: January 2011

Existing practices for field quality management of unbound layers (base, subbase, and subgrade) rely on the adequacy of parameters such as density and moisture content. However, increasingly accepted mechanistic–empirical pavement design is primarily based on the strength and stiffness of the pavement layers. Therefore, methods to measure the modulus or stiffness of soil layers in the field shortly after construction may lead to a more reliable implementation of that design process. Modulus-based quality management methods may be more beneficial than traditional techniques because they test materials in their natural state. Nondestructive testing methods allow researchers to obtain modulus of pavement layers in a rapid way. Seismic methods are one example of available methods that can be used to measure the modulus of finished unbound layers. Seismic methods are particularly attractive because they yield the same parameter (low-strain modulus) for the lab and field tests and do not require any backcalculation process. Performing the simplified seismic laboratory and field tests, with more traditional tests, may lead to a smooth integration of design procedures with pavement evaluation. An overall approach that integrates design, laboratory, and field quality management processes is presented. To evaluate the proposed method, a case study was incorporated to corroborate its usefulness and convenience.
Performance-Based Design of Deep Foundation Systems in Load and Resistance Factor Design Framework
Authors: Roberts Lance A. , Misra Anil
Published: January 2011

Performance-based design methods are increasingly being used for the design and analysis of structures. For performance-based design of deep foundation systems, limiting tolerable movements are one of the design criteria that can be used in lieu of the usual ultimate load capacity. The limiting tolerable movement is often selected to correspond to a movement that will cause damage to a structure but will not produce a collapsible failure of the structure. Performance-based design principles can be extended to include the axial design of deep foundation systems under strength and service loading conditions. In this extended approach, limiting tolerable settlements can be selected to correspond to a movement that will either cause excessive stresses in the structure or render a structure functionally inoperable because of serviceability limits. A performance-based design approach for axial design of deep foundations under the strength and serviceability limit states was developed. The design approach is integrated with the load and resistance factor design framework to develop an efficient and consistent methodology for satisfying both limit state criteria.
Energy Efficiency and Rod Length Effect in Standard Penetration Test Hammers
Authors: Valiquette Michael , Robinson Brent , Borden Roy H.
Published: January 2011

Twenty-eight standard penetration test (SPT) hammers owned by the North Carolina Department of Transportation and private consultants were used to investigate the average energy efficiency and variability of manual versus automatic hammers, as well as the effect of SPT rod length on hammer efficiency. The results agree with published data in several regards. Automatic hammers in the study were found to have an average transferred efficiency of 80.9%. This finding agrees very well with the 80% efficiency assumed in geotechnical engineering practice for automatic hammers. Manual hammers in the study averaged 63.9%, close to the 60% efficiency assumed for manual hammers. Manual hammers were found to be twice as variable as automatic hammers in transferred energy from blow to blow within an SPT blow count. The study demonstrated that the measured transferred energy appeared to be affected by rod length. Lengths shorter than approximately 40 ft caused reduced energy to be transferred into the rod. An empirical formula is presented for correcting short rod length energy losses. The data did not demonstrate a strong dependence on SPT N-value, although the data set lacked observations where the N-value was less than 6 blows per ft.
Stiffness Characterization of Reinforced Asphalt Pavement Structures Built over Soft Organic Soils
Authors: Sobhan Khaled , George K. P. , Pohly Daniel , Ali Hesham
Published: January 2011

Many existing roadways in Florida are built over thick organic and peat layers that cause excessive pavement distress in the form of cracking, distortion, rutting, and differential settlement. A case study shows the use of a variety of geosynthetic and steel mesh reinforcing products embedded in the asphalt overlay placed in SR-15 and US-98 in southeast Florida in an effort to extend the useful life of the pavement structure. Twenty-four test sections, each 152 m (500 ft) long, were constructed, which included eight control sections and 16 reinforced asphalt sections containing GlassGrid, PetroGrid, PaveTrac, and asphalt rubber membrane interlayer at two different test locations with different subsoil characteristics. Before the rehabilitation project, a series of falling weight deflectometer (FWD) tests was conducted at every 15.2 m (50 ft) along the proposed test section alignment for evaluating the existing pavement capacity, statistically determining the site variability among the test sections. Six months after the reconstruction project, FWD tests were repeated at the same locations to characterize the test sections. The stiffness properties of the composite pavement structures were determined directly from the load–deflection data for evaluating the relative performance of the reinforced pavement sections. Statistical analysis of the data showed that the stiffnesses of the reinforced sections were consistently higher than the control sections, owing primarily to the reinforcements. A slight trend was observed from these early age data, indicating an expected relationship between the performance of the test sections and the site geotechnical characteristics.
Resilient Modulus of Clay Subgrades Stabilized with Lime, Class C Fly Ash, and Cement Kiln Dust for Pavement Design
Authors: Solanki Pranshoo , Zaman Musharraf M. , Dean Jeff
Published: January 2011

The effects of different percentages of one traditional additive—hydrated lime—and two by-products—Class C fly ash (CFA) and cement kiln dust (CKD)—on the resilient modulus (Mr) of four different clay subgrades were investigated. It was found that at lower application rates (3% to 6%), the lime-stabilized soil specimens showed highest enhancement in the Mr values. At higher application rates (10% to 15%), however, CKD treatment provided maximum improvements. Three log-log and one semi-log stress-based models were evaluated. Validation of selected models was conducted by using additional soil data. Overall, a semi-log deviatoric and confining stress model was found to show the best acceptable performance. Additional analyses were performed to develop correlations of Mr with compacted specimen characteristics and soil and additive properties. To illustrate the application of the semi-log model, the AASHTO flexible pavement design methodology was used to design asphalt concrete pavement sections.
Evaluation of Characterization and Performance Modeling of Cementitiously Stabilized Layers in the Mechanistic–Empirical Pavement Design Guide
Authors: Saxena Priyam , Tompkins Derek , Khazanovich Lev , Balbo Jose Tadeu
Published: January 2011

Cementitious stabilization of aggregates and soils is an effective technique to increase the stiffness of base and subbase layers. Furthermore, cementitious bases can improve the fatigue behavior of asphalt surface layers and subgrade rutting over the short and long term. However, it can lead to additional distresses such as shrinkage and fatigue in the stabilized layers. Extensive research has tested these materials experimentally and characterized them; however, very little of this research attempts to correlate the mechanical properties of the stabilized layers with their performance. The Mechanistic–Empirical Pavement Design Guide (MEPDG) provides a promising theoretical framework for the modeling of pavements containing cementitiously stabilized materials (CSMs). However, significant improvements are needed to bring the modeling of semirigid pavements in MEPDG to the same level as that of flexible and rigid pavements. Furthermore, the MEPDG does not model CSMs in a manner similar to those for hot-mix asphalt or portland cement concrete materials. As a result, performance gains from stabilized layers are difficult to assess using the MEPDG. The current characterization of CSMs was evaluated and issues with CSM modeling and characterization in the MEPDG were discussed. Addressing these issues will help designers quantify the benefits of stabilization for pavement service life.
Soil Stabilization with Bioenergy Coproduct
Authors: Ceylan Halil , Gopalakrishnan Kasthurirangan , Kim Sunghwan
Published: January 2011

The production and use of biofuel have increased under the context of sustainable development. Biofuel production from plant biomass not only produces biofuel or ethanol but also coproduces products containing lignin, modified lignin, and lignin derivatives. The use of lignin-containing biofuel coproduct in pavement soil stabilization was explored as a new application area. The primary experimental test plan encompassed the comparison of coproduct-treated soils, untreated soils, and traditional stabilizer-treated soils in terms of their strengths. The focus of the secondary experimental test plan was to investigate the effect of additive combinations on strength improvement. The laboratory test matrix in each test plan included variations in additive type, additive content, curing period, and moisture condition. Statistical analyses were performed on unconfined compression strength test results to evaluate whether the strength improvements resulting from the addition of the coproducts to soils are significant. Results indicated that the biofuel coproducts are effective in stabilizing the Iowa Class 10 soil classified as CL or A-6(8). Strengths comparable to traditional additive (fly ash) could be obtained through the use of combined additives (Coproduct A + fly ash; Coproduct A + Coproduct B). The use of biofuel coproduct as a stabilization material for soil appears to be one of many viable answers to the profitability of the biobased products and the bioenergy business.
Innovative Soft Soil Stabilization Using Simultaneous High-Vacuum Dewatering and Dynamic Compaction
Authors: Chang Dave Ta-Teh , Lou Xiao-Ming , Xu Si-Long , Wang Jen-Chin , Guo Li-Lun
Published: January 2011

A combination of the high-vacuum (HV) and dynamic compaction (DC) method (HV+DC method) was used to improve saturated soft foundation. HV and DC were applied alternately and repeatedly to achieve the required level of ground improvement. An in-depth investigation was conducted of the technical requirements, processes, and mechanisms involved in the HV+DC method at the Ningbo Harbor Coal test site near Shanghai, China. Relevant drainage control parameters were identified and optimized to provide the construction parameters, such as compaction energy, spacing, drop number, vacuum dewatering number and location, and wellpoint depth and number, for large area construction. The monitoring during the field trial case study presented here indicates that the method is not only based on sound concepts with rapid stabilization effects and low construction costs but also holds significant promise as an innovative ground improvement method when soft soils are encountered. The application of the HV+DC method increased the cone penetration tip resistance qt of the pond fly ash layer at the Ningbo site more than 2.5 times and that of the clay mud layer more than 1.5 times (compared with unmodified ground) and improved the characteristic value of the bearing capacity of the foundation up to 135 kPa, all of which adequately met the design requirements. For the total area of 400,000 m2 of the main project, this innovative method has saved more than 40% of total cost and approximately 50% of construction time from the original design of the soil cement mixing method.
Post–Soil Interactions on Guardrails near the Crown of a Slope
Authors: Dorcély Joanès , McKyes Edward
Published: January 2011

Most highway departments are very concerned with the adequacy of highway guardrails. A common problem is a narrow road shoulder of 1.5 m to 0.5 m, or even less, combined with steep side slopes and a high embankment beside the road. Although numerous studies have measured the strength of different types of guardrail posts in various soils, a theoretical model does not exist that could be used to predict soil resistance to post movement. Such a theoretical model was constructed for level ground as well as close to an embankment slope. A mechanical model of a narrow vertical object moving soil with a level surface was modified to account for a ground slope that lies within the area of influence of soil failure. The model predicts that at any distance from a slope, the resistance of a post can be increased by installing it to a greater depth. Also, when soil adjacent to a post is compacted heavily, it results in approximately a fourfold increase in horizontal resistance compared with a lightly compacted soil. A rough surface post, such as concrete, gives almost double the horizontal resistance of a smooth surface post of the same dimensions. Using a post of 400 mm width rather than 100 mm results in a horizontal soil resistance force of only approximately 20% to 30%, for a post far away from or very close to the crown of a slope of 1 vertical/2 horizontal.
Comparison of Lecture- and Problem-Based Learning Styles in an Engineering Laboratory
Authors: Hartman Daniel J. , Gindy Mayrai
Published: January 2011

Today's practicing engineers are required to use sophisticated sensing equipment and perform nondestructive testing (NDT). These technologies and skills, however, are infrequently incorporated at the undergraduate level, with a resulting gap between scholastic and real-world knowledge. Moreover, in traditional undergraduate laboratories, experiments are outlined in cookbook fashion, with step-by-step instructions. Students are not challenged to formulate different arguments, design experimental approaches, or critically interpret results. In response to this, the Civil and Environmental Engineering Department at the University of Rhode Island made major changes to its undergraduate structural engineering laboratory course during the fall 2008 semester. The traditional course included solving textbook-type problems as well as using structural analysis software to analyze structures. The new, revised course now introduces NDT methods and sensor technologies using the problem-based learning (PBL) process. PBL uses open-ended, unstructured, multidisciplined problems set in real-world situations designed to promote learning through discovery. The two courses were offered simultaneously to evaluate which is more beneficial to students after graduation. Data were collected using pre- and postsurveys that probed students on their attitudes and expectations for college-level engineering laboratory courses and a rating scale of the importance of 12 learning goals. A multivariate analysis of variance was performed on the survey data using the Statistical Product and Service Solution software. It found that the PBL approach offered several benefits not provided through the traditional lecture-based learning style.
Process for Improving Design of Transportation Curriculum Materials with Examples
Authors: Kyte Michael , Dixon Michael , Abdel-Rahim Ahmed , Brown Shane
Published: January 2011

Student-centered learning is presented as an alternative to the traditional lecture-based approach commonly used in transportation engineering education. Student-centered learning includes an array of pedagogical approaches, such as active learning, cooperative learning, problem-based learning, guided discovery, applied critical thinking, and open-ended labs, each promoting deeper levels of understanding. Two methods of curriculum development that support student-centered learning are presented. Three examples of transportation curricula based on these two methods are offered: the Highway Capacity Manual Applications Guide, mobile signal timing training, and the Transportation Education Development Pilot Project Arterial Traffic Signal Operations course. Each example is evaluated according to criteria that support the curriculum development methods. Conclusions from this evaluation and suggested future research directions are presented.
Development and Deployment of Traffic Control Game
Authors: Liao Chen-Fu , Glick David B. , Haag Shawn , Baas Gina
Published: January 2011

The Intelligent Transportation Systems Institute at the University of Minnesota has delivered several educational activities such as undergraduate research programs and online transportation web research modules for high school classes. The need is growing to extend the current educational outreach effort with additional focus on high school students. A goal is to interest high school students in transportation careers through the integration of educational game modules and curricula in teaching various concepts of intelligent transportation control and management. As part of the education and outreach effort, an interactive web-based traffic control simulation module and a professionally enhanced traffic game were developed and piloted to undergraduate transportation engineering classes and high school summer camps at the University of Minnesota. Several lessons developed for high school science classrooms were based on activities using the traffic control game. A developed curriculum was evaluated through observation of student participation and engagement during five summer camp sessions in 2008 and 2009. At the end of each session, a survey was performed to collect students' feedback and learning experience from the curriculum and traffic control game. Results from the survey indicated student excitement toward the game and their receptiveness to the traffic engineering curriculum. Students were significantly more aware of traffic engineering issues after participating in the curriculum activities. It is hoped that students will be able to learn from their experience through a simulation environment and use the experience to deepen their understanding of intelligent transportation systems.
Integrating Values and Ethics into Wildlife Policy and Management—Lessons from North America
Authors: Fox Camilla H. , Bekoff Marc
Published: January 2011

Few animals provoke as wide a range of emotions as wolves. Some see wolves as icons of a lost wilderness; others see them as intruders. As the battle continues between wolf proponents and opponents, finding solutions that resolve conflicts while supporting the integrity of nature is challenging. In this essay we argue that we need to make room for wolves and other native carnivores who are re-colonizing areas from which they were extirpated. Strategies that foster coexistence are necessary and wildlife agencies must consider all stakeholders and invest adequate resources to inform the public about how to mitigate conflicts between people/domestic animals, and predators. Values and ethics must be woven into wildlife policy and management and we must be willing to ask difficult ethical questions and learn from past mistakes.
Towards Commercial Gas Production from Hydrate Deposits
Authors: Marcelle-De Silva Jill , Dawe Richard
Published: January 2011

Over the last decade global natural gas consumption has steadily increased since many industrialized countries are substituting natural gas for coal to generate electricity. There is also significant industrialization and economic growth of the heavily populated Asian countries of India and China. The general consensus is that there are vast quantities of natural gas trapped in hydrate deposits in geological systems, and this has resulted in the emerging importance of hydrates as a potential energy resource and an accompanying proliferation of recent studies on the technical and economic feasibility of gas production from hydrates. There are then the associated environmental concerns. This study reviews the state of knowledge with respect to natural gas hydrates and outlines remaining challenges and knowledge gaps.
Comparison of Bayesian Clustering and Edge Detection Methods for Inferring Boundaries in Landscape Genetics
Authors: Safner Toni , Miller Mark P. , McRae Brad H. , Fortin Marie-Josée , Manel Stéphanie
Published: January 2011

Recently, techniques available for identifying clusters of individuals or boundaries between clusters using genetic data from natural populations have expanded rapidly. Consequently, there is a need to evaluate these different techniques. We used spatially-explicit simulation models to compare three spatial Bayesian clustering programs and two edge detection methods. Spatially-structured populations were simulated where a continuous population was subdivided by barriers. We evaluated the ability of each method to correctly identify boundary locations while varying: (i) time after divergence, (ii) strength of isolation by distance, (iii) level of genetic diversity, and (iv) amount of gene flow across barriers. To further evaluate the methods’ effectiveness to detect genetic clusters in natural populations, we used previously published data on North American pumas and a European shrub. Our results show that with simulated and empirical data, the Bayesian spatial clustering algorithms outperformed direct edge detection methods. All methods incorrectly detected boundaries in the presence of strong patterns of isolation by distance. Based on this finding, we support the application of Bayesian spatial clustering algorithms for boundary detection in empirical datasets, with necessary tests for the influence of isolation by distance.
Fabrication of Porous Scaffolds with a Controllable Microstructure and Mechanical Properties by Porogen Fusion Technique
Authors: Tan Qinggang , Li Songgang , Ren Jie , Chen Chu
Published: January 2011

Macroporous scaffolds with controllable pore structure and mechanical properties were fabricated by a porogen fusion technique. Biodegradable material poly (D, L-lactide) (PDLLA) was used as the scaffold matrix. The effects of porogen size, PDLLA concentration and hydroxyapatite (HA) content on the scaffold morphology, porosity and mechanical properties were investigated. High porosity (90% and above) and highly interconnected structures were easily obtained and the pore size could be adjusted by varying the porogen size. With the increasing porogen size and PDLLA concentration, the porosity of scaffolds decreases, while its mechanical properties increase. The introduction of HA greatly increases the impact on pore structure, mechanical properties and water absorption ability of scaffolds, while it has comparatively little influence on its porosity under low HA contents. These results show that by adjusting processing parameters, scaffolds could afford a controllable pore size, exhibit suitable pore structure and high porosity, as well as good mechanical properties, and may serve as an excellent substrate for bone tissue engineering.