bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of the continuous reaction crystallization of barium sulphate in BaCl2 - (NH4)2 SO4 - NaCl - H2O system - neural network model
Authors: Piotrowski Krzysztof , Koralewska Joanna , Wierzbowska Bogusława , Matynia Andrzej
Published: January 2010

Kinetics of the continuous reaction crystallization of barium sulphate in BaCl2 - (NH4)2 SO4 - NaCl - H2O system - neural network model

One of the main toxic components of post quenching salts formed in large quantities during steel hardening processes is BaCl2. This dangerous ingredient can be chemically neutralized after dissolution in water by means of reaction crystallization with solid ammonium sulphate (NH4)2 SO4. The resulting size distribution of the ecologically harmless crystalline product - BaSO4 - is an important criteria deciding about its further applicability. Presence of a second component of binary quenching salt mixture (BaCl2-NaCl) in water solution, NaCl, influences the reaction-crystallization process kinetics affecting the resulting product properties. The experimental 39 input-output data vectors containing the information about the continuous reaction crystallization in BaCl2 - (NH4)2 SO4 - NaCl - H2 O system ([BaCl2]RM = 10-24 mass %, [NaCl]RM = 0-12 mass %, T = 305-348 K and τ = 900-9000 s) created the database for the neural network training and validation. The applicability of diversified network configurations, neuron types and training strategies were verified. An optimal network structure was used for the process modeling.
Destructive oxidation of ethanol in the corona discharge reactor
Authors: Paterkowski Wojciech , Parus Wiesław , Kalisiak Stanisław
Published: January 2010

Destructive oxidation of ethanol in the corona discharge reactor

The results of investigation of ethanol destructive oxidation (model aliphatic alcohol) in a corona discharge reactor are presented. The process was performed at the temperature of 303 K in the corona discharge generator - the reactor system manufactured in our laboratory. The process temperature was kept constant by cooling down the reactor with a stream of air. The measurements were carried out using the following process parameters: the inlet ethanol concentration in the stream of gases in the range of 0.0028 to 0.132 mol/m3 (0.128 ÷ 6.086 g/m3), the gas flow velocity in the range of 0.15-0.33 m3/h (space velocity in the range of 1220 ÷ 2680 m3/(m3
R ·h)) and the power supply to the reactor ranged from 1.6 to 86.4 W. The active volume of the reactor was 1.23·10-4 m3. The phenomenological method was applied for the description of the process. It was based on the assumptions that the reaction rate can be described by the first order equation in relation to the ethanol concentration and the design equation of flow tubular reactor can be applied for the description of corona reactor. The usefulness of this model was estimated using statistical methods for the analysis of the experimental results. The Statistica 6.0 software was used for this application. The first stage of this analysis showed the dependencies between the considered variables, whereas the second stage was to find the equations describing the influence of the selected process parameters on the rate of ethanol destruction. The parameters of A and B of apparent constant rate equation given in the form of Z = A·exp(-B/P) were also determined.

The results of the investigations indicated that the applied corona discharge generator - reactor system assures a high efficiency of purification of the air and industrial waste gases contaminated by ethanol. The ethanol destruction degree of αi = 0.9 was obtained at the power supply to the reactor amounting to 650 kW/m3
R per unit of its active volume. The final products of the reaction were only the harmless carbon dioxide and water vapour. It has been stated that the rate of the destructive oxidation of ethanol reaction is well described by the first order equation in relation to the ethanol concentration. Under isothermal conditions, the reaction rate also depends on the power supply to the reactor. This dependence is well described by the empirical equation Z = 3,233·exp(-82,598/P).

The obtained results also indicated that the method of destructive oxidation of ethanol in the corona discharge reactor can be useful for the removal of ethanol and probably other aliphatic alcohols from different gases. The described method of calculation of the real rate of the process can be successfully used in the design of corona discharge reactors applied for such processes.
Phytophagous Entomofauna Occurring on Onion Plantations in Poland in Years 1919-2007
Authors: Szwejda Jerzy , Wrzodak Robert
Published: January 2010

Phytophagous Entomofauna Occurring on Onion Plantations in Poland in Years 1919-2007

In years 1919-2007 on domestic onion plantations 37 phytophagous species taxons belonging to 7 insect orders: Thysanoptera, Homoptera, Heteroptera, Lepidoptera, Coleoptera, Diptera and Orthoptera were noted. Among these groups 22 species were stated as phytophagous, additional taxons were indentified to 5 genus (Thrips, Mamestra, Polia, Agrotis, Agriotes) and 3 families: fungus gnats (Sciaridae), march flies (Bibionidae), crane flies (Tipulidae). Furthermore 7 species of saprophagous Diptera were collected from damaged onions during harvest.

The most common dominant species occurring in all regions of onion production were: onion fly (Delia antiqua Meig.), onion thrips (Thrips tabaci Lind.), onion weevil (Ceutorhynchus suturalis Fabr.), leek moth (Acrolepiospis assectella Zell.) and cutworms (Noctuidae). The population density of: onion beetle (Lilioceris merdigera L.), garlic fly (Suillia lurida Meig.) and leek miner fly (Napomyza gymnostoma Loew) were only a seasonal danger, especially in southern regions of Poland. On wet and rich in organic matter soils some soil dwelling insects such as larvae of Melolontha species (Scarabaeidae), larvae of Agriotes (Elateridae), flies (Diptera) from Tipulidae and Bibionidae families were also occurring periodically.

The species and population changes of above mentioned pests allowed to elaborate effective pest control methods of onion plantations. The pest control was performed after field monitoring on the basis of constantly updated short - and long-term forecasting.
Effect of Temperature on the Yield and Quality of Broccoli Heads
Authors: Kałużewicz Alina , Krzesiński Włodzimierz , Knaflewski Mikołaj
Published: January 2010

Effect of Temperature on the Yield and Quality of Broccoli Heads

The effect of temperature on the yield and quality of broccoli heads was determined. The study involved three cultivars: Cruiser, Skiff and Fiesta. The seedlings were planted on five different dates in 1995 and 1996, nine in 1997 and eight in 1998. The length of time from planting to the first harvest for all the 27 cultivation periods was divided into three equal parts determining in this way three phases of growth. The time of harvest was defined as the fourth phase. Temperatures on a scale from 0°C to 40°C were divided into five-degree ranges. Then, for the four growth phases, correlations were determined between the number of hours at a temperature in the five-degree ranges and the total yield, the percentage of loose heads and the percentages of heads with uneven surface or non-uniform buds.

The length of time at a temperature in the range of 15-25°C during the first growth phase after planting and the phase preceding harvest had the greatest influence on total yield. Longer times at temperatures above 20°C contributed to smaller yields. The longer was the length of time at a temperature ranging from 20 to 25°C during the phase preceding harvest and at a temperature ranging from 5 to 15°C during harvest, the lower the percentage of heads with uneven surface was observed. Longer periods with temperatures above 20°C at harvest time contributed to the loosening of heads.
Effect of Light Conditions and Temperature on Fresh Yield of Some Spice Plants Grown in Containers
Authors: Frąszczak Barbara , Knaflewski Mikołaj
Published: January 2010

Effect of Light Conditions and Temperature on Fresh Yield of Some Spice Plants Grown in Containers

The aim of this work was to study the effect of quantity of light, length of day and temperature on yield of five species of spice plants. Another purpose of the study was to determine the correlation between the climatic factors mentioned above and to find the optimum coefficient of growth for the individual species. Three levels of temperature during the day were determined: 15, 20 and 25°C (at night the temperature was by 5°C lower). Two daily light integrals (2.9 and 3.8 mol·m-2·d-1) and three levels of photoperiod (12, 14 and 16-h) were chosen.

Photon flux and temperature had the greatest influence on yield. A higher yield of fresh mass was obtained for all species in the condition of 3,8 mol·m-2·d-1. Yield depended linearly on amount of photon absorbed by plants in the growth time. Dry weight was directly connected with RRT (the ratio of radiant energy to thermal energy) and increased linearly as RRT increased.
Effect of Addition of Maidenhair Tree Leaves to Substrate on Yielding and Chemical Composition of Pleurotus ostreatus (Fr.) Kumm. Carpophores
Authors: Siwulski Marek , Czerwińska-Nowak Aleksandra , Korszun Stanisława
Published: January 2010

Effect of Addition of Maidenhair Tree Leaves to Substrate on Yielding and Chemical Composition of Pleurotus ostreatus (Fr.) Kumm. Carpophores

The effect of addition of different amounts of maidenhair tree leaves to substrate on quantity and earliness of yield and chemical composition of oyster mushroom carpophores was investigated. The experiment was carried out at the Department of Vegetable Crops of the Poznan University of Life Sciences in the year 2008.

The subject of the studies was the ‘P80’ strain of Pleurotus ostreatus. Two cycles of cultivation were conducted. Alder sawdust supplemented with yellow and green maidenhair tree leaves in the amount of 0%, 1% and 10% in relation to dry matter of sawdust were used as experimental substrates. Cultivation was conducted in polypropylene bottles of capacity of 1 dm3. Yield quantity and earliness as well as chemical composition of carpophores were determined.

It was found that quantity and earliness of P. ostreatus yield depended on the amount and kind of maidenhair tree leaves added to substrate. The highest and the earliest yield was obtained on substrate supplemented with 10% addition of green maidenhair tree leaves. The amount of maidenhair tree leaves added to substrate influenced the content of protein and carbohydrates in carpophores whereas it did not influence the content of dry matter, fat and ash. Carpophores obtained on the substrate supplemented with 10% addition of maidenhair tree leaves, independently of their kind, were characterized by the highest content of protein and carbohydrates.
Ontario's Greenbelt: Growth Management, Farmland Protection, and Regime Change in Southern Ontario
Authors: Pond David
Published: January 2010

The immediate purpose of Ontario's Greenbelt is to protect farmland and open green space from urbanization while the province implements Places to Grow, its master plan for compact regional growth. The Greenbelt should also be understood as the vehicle for agri-environmental policies popular with the urban electorate. Yet successful implementation of such policies will require the cooperation of farmers and rural property owners whose development rights have been frozen. Since agricultural productivity has historically presumed private control over the mix of inputs into the farm business, the province now faces the challenge of reconciling the goals of the Greenbelt with its more venerable role as supporter of commercial agriculture.
North Carolina Department of Transportation's Practice and Experience with Design–Build Contracts
Authors: Kim Kyung J. , Kreider Christopher A. , Valiquette Michael D.
Published: January 2010

The North Carolina Department of Transportation (NCDOT) began using design–build contracting for highway construction projects in 2001 and now is authorized to award up to 25 design–build contracts annually. Because subsurface investigation is an expensive and time-consuming task usually requiring environmental permits from various federal and state agencies, NCDOT performs the subsurface investigations and provides the information to the design–build teams. The cost of subsurface investigations for nine design–build projects was compared with the historical data for subsurface investigations on conventional contract projects. Case studies of bridge foundation design and construction for two of the nine projects are presented along with comparison with conventional contract projects.
Evaluation of High-Capacity Composite Spun Piles
Authors: Bhandari Anil , Han Jie
Published: January 2010

Traits of two broad categories of deep foundations–-replacement and displacement piles–-are best combined by a newly introduced composite spun pile. This composite spun pile is constructed by deep mixing first and then inserting a precast, prestressed, spun concrete pile into the deep mixed column. The spun pile is then driven into an end-bearing layer to meet the criterion of end resistance. The pile uses a larger peripheral area of soil–cement mix to transfer load to its surrounding ground at the same time it uses higher stiffness of the spun pile to minimize axial compression. The piling operation is relatively quiet, minimizes spoil problems, and facilitates better quality control. A pile design principle for the composite pile is presented. The performance of this new pile system was verified by five instrumented field full-scale pile load tests. Improvement on shaft resistance was observed, as depicted by the correlation between standard penetration test N values of the surrounding soil and the measured skin friction along the pile. The contribution of the measured toe resistance over the total applied load varied from 2.3% to 36.7%, depending on the geotechnical properties of the foundation layers. The field tests clearly showed that composite spun piles had high capacities and could be used as a reliable alternative to traditional driven as well as bored piles in current practice.
Capacities and Deflections of Laterally Loaded Shafts behind Mechanically Stabilized Earth Wall
Authors: Pierson Matthew C. , Parsons Robert L. , Han Jie , Brennan James J.
Published: January 2010

Current practice for designing laterally loaded shafts that pass through a mechanically stabilized earth (MSE) wall often involves isolating the shaft from the MSE mass and anchoring the shaft into rock with a rock socket. Sizeable cost and time savings could be realized, along with continued effective performance and reliability, if a method were available to evaluate the lateral load capacity of a shaft supported by the MSE mass alone without a rock socket. The Kansas Department of Transportation assembled a team to develop such design methods: the construction, instrumentation, and loading of multiple 36-in. (0.914-m) diameter shafts supported within the reinforced mass of a 20-ft (6-m) tall MSE block wall designed according to existing FHWA procedures without consideration of lateral loads. The design and construction of the wall and the shafts, which were designed as drilled shafts, and the results from the lateral load tests of four shafts are described. These shafts had lengths equal to the full height of the wall and had spacings from the back of the wall facing to the center of each shaft of one, two, three, and four shaft diameters. Results for both load and displacement of the shafts, the width of shaft influence, and the relative displacements of the shafts and the wall facing during loading are presented, along with design recommendations.
Deformation Factors of Buried Corrugated Structures
Authors: Machelski Czesław , Michalski Jan Bernard , Janusz Leszek
Published: January 2010

Buried corrugated structures are subjected to highest stresses during two phases: during backfilling and under service loads. Commonly, deformations during backfilling are more unfavorable for the structure than those that occur under service loads. Typically, service loads will generate several times less deflection than do construction loads falling below the limit of deflection ( w) to span ( L) of w/L = 2%. For the sake of modeling the behavior of corrugated steel structures during backfilling, separate components (i.e., corrugated steel, backfill, road structure) of the soil structure are represented by independent parameters such as deformation module, Poisson's coefficient, and soil unit weight. A steel plate is described in geometric terms. Modeling the deformation of buried corrugated structures with finite element modeling is very difficult because of the complex characteristics of the soil medium during construction of the backfill. An analytical algorithm was used to calculate characteristic deformations of a steel structure during backfilling. The algorithm was analyzed with respect to chosen physical and geometric parameters. Deformations during backfilling of a corrugated structure are described, and correlations of specific points of a structure are presented in a mathematical form on the basis of in situ tests in natural scale. The algorithm was prepared assuming the average backfill quality required by good construction and design practices. The results of this research are applicable to structures with closed and open shapes, except for boxes.
Evaluation of the Zone of Influence and Stiffness Improvement from Geogrid Reinforcement in Granular Materials
Authors: Schuettpelz Craig , Fratta Dante , Edil Tuncer B.
Published: January 2010

The longevity of a pavement system is closely related to the amount of deformation of both the asphalt surface and the underlying layers. Placing a geogrid in the granular base decreases the amount of rutting at the surface by providing some strength to the base and increasing stiffness and thus limiting elastic deformations and loads transmitted to the sub-grade. However, the zone of influence of the geogrid layer on surrounding soil particles and the increase in modulus in this zone are not well known. A testing scheme aimed at quantifying both the zone of influence and the increase in the modulus caused by the presence of a geogrid in granular materials was developed. Both P-wave velocity and the shear strain induced by loading a 150-mm diameter plate were examined. P-wave velocity results indicated a change in modulus across the geogrid from a minimum of 1.35 (at 75-mm geogrid depth) to a maximum of 2.66 (at 100-mm geogrid depth) over modulus expected in unreinforced soils. Expected internal soil rotations were modeled with PLAXIS and compared with laboratory tests. These analyses showed that the shearing of soil was confined to a zone above the geogrid. Rotation tests showed a zone of influence of 30 to 40 mm on both sides of the geogrid reinforcement; however, the zone of influence depends on the position of the geogrid, with a geogrid 100 mm in depth seeming most able to constrain subsurface soils and distribute the shear stresses caused by the 150-mm-diameter loading plate.
Full-Scale Evaluation of Geosynthetic-Reinforced Aggregate Roads
Authors: Tingle Jeb S. , Jersey Sarah R.
Published: January 2010

A full-scale test section was constructed and trafficked by the U.S. Army Engineer Research and Development Center to evaluate the performance of geosynthetic reinforced aggregate road sections constructed with marginal base materials over a typical subgrade. Eight instrumented aggregate road sections–-including three different aggregate base materials and two different geosynthetics–-were constructed. The mechanistic response and permanent surface deformation of each pavement section were monitored at selected intervals during trafficking, and the data were analyzed to determine the benefit of using geotextiles or geogrids to reinforce aggregate roads. The test section's results indicated that the geosynthetics improved the performance of the reinforced pavement sections compared with unreinforced sections for all aggregate base materials. The mechanistic response in terms of surface deflection, deflection at the top of the subgrade, and vertical stress at the top of the subgrade was favorably consistent with the observed permanent deformation of the individual test items.
Fatigue Evaluation of Porous Asphalt Composites with Carbon Fiber Reinforcement Polymer Grids
Authors: Kim Hyunwook , Sokolov Kirill , Poulikakos Lily D. , Partl Manfred N.
Published: January 2010

Porous asphalt (PA) has been widely used in many countries because of its positive benefits, such as efficient water drainage, improved safety in wet weather conditions, and noise reduction. However, the attractive features of PA do not last long because of clogging, stripping, and accelerated aging. Application of fiber reinforcement materials can be a possible solution to the structural weakness in PA pavements. Fatigue of fiber-reinforced PA composite systems was investigated with a model mobile load simulator (MMLS). Carbon fiber reinforcement polymer (FRP) grids were used to strengthen the fatigue resistance of PA. FRP grids were placed between two asphalt layers as a reinforcement interlayer. The dynamic fatigue traffic loadings were applied on the top surface of reinforced specimens to investigate the performance improvement by reinforcement materials. These fatigue tests were conducted under four different conditions: absence and presence of reinforcement at dry conditions and wet conditions. The stiffness difference between unaged and aged specimens was 25% at minimum and 55% at maximum. The surface deflection of PA was successfully reduced by 23% at dry and by 48% at wet conditions by using interlaid carbon FRP grids. In addition, the reinforcement layer could increase the fatigue life by 23% at dry and by 27% at wet conditions based on MMLS test results.
Long-Term Monitoring of Noise and Frictional Properties of Three Pavements
Authors: Kowalski Karol J. , McDaniel Rebecca S. , Shah Ayesha , Olek Jan
Published: January 2010

Three highway test sections were monitored for friction, texture, and noise properties over a period of 4 years. The monitored highways were constructed from dense-graded asphalt (DGA), stone matrix asphalt (SMA), and porous friction course (PFC) mixes. The PFC was intended to reduce tire–pavement noise. It was found that the PFC and SMA pavements exhibited comparable frictional properties (international friction index and skid number), which were significantly higher than those observed in the DGA section. It also was found that the PFC section was the quietest and that SMA was louder than DGA. In general, all three sections performed well, and no failures were noticed in any of the monitored pavements during the course of this study.
Interface Bonding between Hot-Mix Asphalt and various Portland Cement Concrete Surfaces
Authors: Leng Zhen , Al-Qadi Imad L. , Carpenter Samuel H. , Ozer Hasan
Published: January 2010

Interface bonding between hot-mix asphalt (HMA) overlays and portland cement concrete (PCC) pavements is one of the most significant factors affecting overlay service life. In this study, accelerated pavement testing was performed to quantify the effects of tack coat type, tack coat application rate, and PCC surface texture on the interface bonding and overlay performance. This study builds on and validates previously completed laboratory tests where an HMA overlay was placed on top of existing PCC pavement composed of various surface textures including smooth, transverse tining, and milling. Asphalt emulsion SS-1hP and cutback asphalt RC-70 were applied at three residual application rates, 0.02, 0.04, and 0.09 gal/yd2; asphalt binder PG 64-22 was applied at 0.04 gal/yd2. In total, 25 test sections were constructed and loaded with the accelerated transportation loading assembly at the centerline. The tensile strains at the bottom of HMA, to quantify potential interface slippage, were measured for selective sections, and primary HMA rutting was analyzed for all sections. The study validated laboratory-determined optimum tack coat application rate, which provided the lowest interface strain and surface rutting in the field. Both PG 64-22 and SS-1hP showed better rutting resistance than RC-70. Milled PCC surface provided lower rutting than transverse-tined and smooth surfaces. The study also showed that PCC cleaning methods played an important role in the HMA–PCC interface bonding.
Evaluation of Fatigue Models of Hot-Mix Asphalt through Laboratory Testing
Authors: Adhikari Sanjeev , Shen Shihui , You Zhanping
Published: January 2010

Many studies have investigated the fatigue resistance of hot-mix asphalt (HMA) mixtures on the basis of the material properties and structural responses. In this study, a four-point bending-beam fatigue apparatus was used to measure the fatigue life of a typical Michigan HMA mixture under various frequencies (1, 5, and 10 Hz) and temperatures (4°C, 13°C, and 21.3°C). The objective of this study was to evaluate laboratory models for predicting fatigue over wide ranges of testing conditions to rank their fatigue performance on the HMA mixtures. In addition, this paper aimed to correlate the flexural stiffness (modulus) with dynamic modulus, because the dynamic moduli of HMA are key input parameters in the Mechanistic–Empirical Pavement Design Guide (MEPDG). The correlation results showed a strong linear correlation between the flexural stiffness and dynamic modulus, with the flexural stiffness being 30% lower than the dynamic modulus. By providing a linkage between dynamic modulus and flexural stiffness, the study helped to substantiate the concept of using dynamic modulus in the MEPDG or to evaluate rutting. In addition, Rowe and Bouldin's stiffness degradation concept was used to compare the ability of different models to predict fatigue life. The results of this study showed that the energy-based fatigue prediction model, which considered rest periods, various testing temperatures, and loading frequencies, correlated well with the laboratory-determined fatigue life.
Determining Representative Volume Elements of Asphalt Concrete Mixtures without Damage
Authors: Kim Yong-Rak , Lutif Jamilla Emi Sudo , Allen David H.
Published: January 2010

This study presents a simple method to define the representative volume elements (RVEs) of asphalt concrete mixtures without damage. Three currently used asphalt concrete mixtures (two dense-graded Superpave® mixtures with different nominal maximum aggregate sizes of 9.5 and 12.5 mm and one stone matrix asphalt mixture with a nominal maximum aggregate size of 19.0 mm) were selected and evaluated. To address the significant heterogeneity of asphalt concrete mixtures properly in defining RVEs, several geometrical factors, such as area fraction, gradation, orientation, and the distribution of aggregate particles in asphalt concrete mixtures, were all considered together by using two-dimensional images of actual asphalt concrete inner structures produced by digital-image processing. Geometrically defined RVEs were then supported by finite element simulations to check whether effective nondamage material properties obtained from the RVEs, such as the linear viscoelastic dynamic modulus, were representative of the corresponding bulk asphalt concrete mixture. Analysis results indicated that typical dense-graded Superpave asphalt concrete mixtures can be characterized by their effective non-damage properties with an approximate RVE size of 50 mm. However, the properties of stone matrix asphalt mixtures, which contain larger aggregates, should be measured on a larger scale for improved accuracy. Findings from this study were generally consistent with results of other studies performed on the basis of extensive laboratory tests, which implies that the simple geometrical–numerical method here can be a potentially efficient approach to define the RVEs of asphalt mixtures with much less time and effort.
Application of Generalized J-Integral to Crack Propagation Modeling of Asphalt Concrete Under Repeated Loading
Authors: Kuai Haidong , Lee Hyun Jong , Zi Goangseup , Mun Sungho
Published: January 2010

An energy-based crack-growth model was developed in this study to simulate the propagation of top-down cracking in asphalt pavements. A viscoelastic fracture mechanics approach, the generalized J-integral, was employed to model the crack growth of asphalt concrete. Laboratory fatigue crack propagation tests for three asphalt mixtures were performed at various load levels, frequencies, and temperatures. Disk-shaped specimens with a proper loading fixture and crack growth monitoring system were selected for the tests. It was observed from the tests that the crack-propagation model based on the generalized J-integral was independent of load levels and frequencies, while the traditional Paris law model based on stress intensity factor was dependent on loading frequencies. However, both models were unable to deal with the temperature dependence of the mixtures. The fatigue crack propagation model proposed in this study had a good agreement between experimental and predicted crack-growth lives, an indicator that the energy-based J-integral could be a better parameter to describe fatigue crack propagation of viscoelastic materials such as asphalt mixtures.
Use of Small Samples to Predict Fatigue Lives of Field Cores
Authors: Kutay M. Emin , Gibson Nelson , Youtcheff Jack , Dongré Raj
Published: January 2010

Fatigue cracking is one of the major distresses in asphalt pavements. Accurate prediction of fatigue life of asphalt pavements can be extremely important both during the design stage and for prediction of remaining service life of in-service pavements. Traditional fatigue life predictions based on bending beam tests can be costly and time-consuming. The uniaxial push–pull (tension–compression) tests run on cylindrical samples have been a novel alternative. However, the traditional sample size for the push–pull tests may prevent its use for thin in-service pavements. This paper presents the results of a study investigating the possibility of using smaller sample sizes for push–pull tests. The viscoelastic continuum damage (VECD) characteristics of regular and small-size samples are compared, and the difference is observed to be negligible. In addition, a practical fatigue life formulation is derived on the basis of VECD theory. Uniqueness of the derived fatigue life ( Nf) equation, differing from previously derived VECD-based Nf equations, stems from the fact that it does not force a certain form of equation to fit the damage characteristic curve. Finally, the differences in fatigue lives of different layers of the field sections at FHWA's accelerated loading facility are investigated.
Micromechanical Modeling of Hot-Mix Asphalt Mixtures by Imaging and Discrete Element Methods
Authors: Khattak Mohammad J. , Roussel Chad
Published: January 2010

This study focused on the application of a clustered micromechanical discrete-element modeling (DEM) technique to predict the uniaxial compression dynamic modulus of hot-mix asphalt (HMA) mixtures. Six HMA mixtures were made with two types of asphalts and two gradations for limestone and gravel aggregates. The dynamic modulus of HMA was determined at three temperatures by using the indirect tensile test (IDT). Similarly, a frequency sweep test was used to determine the shear complex modulus ( G*) of the asphalt matrix (AM) at various temperatures. The master curves for both AM and HMA mixtures were generated at 25°C, and results were analyzed. A two-dimensional, synthetic, heterogeneous microstructure of HMA was reconstructed with scanned images of IDT specimens. Bulk characteristics were used to determine the microproperties of the AM and aggregate structure in order to conduct virtual compressive test simulations. The results indicated that the DEM simulation accurately predicted the dynamic modulus of AM and aggregates at 25°C through the quasi-elastic approach. However, the HMA moduli were underpredicted by the model for a range of AM moduli and loading frequencies at 25°C. Calibration factors for aggregate volume concentrations and particle point contacts were developed and have been discussed here.
Comparison of Low-Temperature Field Performance and Laboratory Testing of 10 Test Sections in the Midwestern United States
Authors: Zofka Adam , Braham Andrew
Published: January 2010

Current standards for evaluation of asphalt mixtures for low-temperature performance are based heavily on asphalt binder properties. These standards ignore the interactions between the binder and the aggregate, both chemically and physically. These interactions have been shown to have significant influence on the cracking resistance of asphalt mixtures. This paper investigates three laboratory tests that evaluate cracking resistance of asphalt mixtures at low temperatures. The first test is the traditional tensile strength test, the indirect tensile test (IDT). The two other tests are fracture tests: semicircular bending (SCB) and disk-shaped compact tension [DC(T)]. Field cores were obtained from 10 pavement sections in Minnesota and Illinois for testing in the lab. Results from the three laboratory tests were compared and correlated with field performance data. Results showed that the tensile strength from the IDT did not vary significantly for the 10 mixtures. The SCB and DC(T) correlated relatively well with each other depending on the test temperature. The SCB showed the best correlation and highest Spearman's rank correlation coefficient when compared with the observed quantity of cracking in the field. It was concluded that the laboratory fracture tests, SCB and DC(T), were better suited for qualitative cracking performance predictions at low temperatures than the IDT. For quantitative predictions, application of advanced analytical or numerical models (or both) that take into account material properties, environmental conditions, and loading conditions is recommended. Also recommended is that additional studies comparing laboratory fracture parameters with field performance be conducted.
Refinement of Flow Number as Determined by Asphalt Mixture Performance Tester
Authors: Dongré Raj , D'Angelo John , Copeland Audrey
Published: January 2010

Flow number determined with the repeated-load test is used as a criterion to characterize the rut resistance of hot-mix asphalt. The repeated-load test is performed with the asphalt mixture performance tester (AMPT). The algorithm currently used in the AMPT to determine flow number was found to be extremely sensitive to noise in the data and identifies erroneous flow number results, especially for modified mixes. A new algorithm that uses the Francken model to fit the flow number data is considered for implementation. The robustness of the Francken model is verified in this study by fitting flow number data obtained from field projects. The flow number test is time-consuming, especially for high-stiffness binders and, in many cases, can take as long as 6 h. In this study, other parameters are examined to determine whether the test can be terminated early without loss of information on rut resistance. Steady-state slope and slope at 2% strain are found to correlate well with flow number; the correlation indicates that they may be robust indicators of rut resistance. The flow number test can be terminated once steady-state slope or slope at 2% strain is reached; this substantially reduces test time. This paper discusses the findings from analysis of flow number data from the Francken model and the development of a refined, more expedient method for determining flow number.
Evaluation of Aspects of E* Test by Using Hot-Mix Asphalt Specimens with Varying Void Contents
Authors: Rowe Geoffrey M. , Khoee Salman Hakimzadeh , Blankenship Phillip , Mahboub Kamyar C.
Published: January 2010

A dynamic modulus master curve for asphalt concrete is a critical input for flexible pavement design in the Mechanistic–Empirical Pavement Design Guide developed in NCHRP Project 1-37A, which has drawn much attention among asphalt technologists. The objectives in this study were ( a) to consider and compare different analysis techniques for construction of the master curve and ( b) to measure and analyze the effect of permanent strain on samples that have been evaluated with one of the simple performance tests, dynamic modulus. It was found that differences existed in the calculated asymptote values and the shape of the master curve, depending upon which method was adopted. Recommendations are made for modifications to the testing protocol and for further work to determine the effect of permanent strain at higher test temperatures.
Application of Artificial Neural Networks for Estimating Dynamic Modulus of Asphalt Concrete
Authors: Far Maryam Sadat Sakhaei , Underwood B. Shane , Ranjithan S. Ranji , Kim Y. Richard , Jackson Newton
Published: January 2010

This paper presents outcomes from a research effort to develop models for estimating the dynamic modulus (| E*|) of hot-mix asphalt (HMA) layers on long-term pavement performance test sections. The goal of the work is the development of a new, rational, and effective set of dynamic modulus | E*| predictive models for HMA mixtures. These predictive models use artificial neural networks (ANNs) trained with the same set of parameters used in other popular predictive equations: the modified Witczak and Hirsch models. The main advantage of using ANNs for predicting | E*| is that an ANN can be created for different sets of variables without knowing the form of the predictive relationship a priori. The primary disadvantage of ANNs is the difficulty in predicting responses when the inputs are outside of the training database (i.e., extrapolation). To overcome this shortcoming, a large data set that covers the complete range of potential input conditions is needed. For this study, modulus values from multiple mixtures and binders were required and were assembled from existing national efforts and from data obtained at North Carolina State University. The data consisted of measured moduli from both modified and unmodified mixtures from numerous geographical locations across the United States. Prediction models were developed by using a portion of the data from these databases and then verified by using the remaining data in the databases. When these new ANN models are used, the results show that the predicted and measured | E*| values are in close agreement.
Long Green Times and Cycles at Congested Traffic Signals
Authors: Denney Richard W. , Curtis Eddie , Head Larry
Published: January 2010

Field data were collected and simulation experiments based on traffic at an intersection in Virginia were conducted to test the hypothesis that headways increase with long green times and to test the common assumption that throughput increases with longer cycles. The results showed that headways increased with long green times as a result of departing turning vehicles and that this effect could cause a significant increase in overall average approach headways. The results also showed that maximum throughput, defined as the point where additional offered load could not be served, did not increase with longer cycles. With values derived from the field data, increasing the cycle did not increase throughput. In simulation, increasing the cycle caused a reduction in throughput as a result of increasing the effect of departing turning traffic on the average headway.
Performance Measures for Railroad-Preempted Intersections
Authors: Brennan Thomas M. , Day Christopher M. , Bullock Darcy M. , Sturdevant James R.
Published: January 2010

The Manual on Uniform Traffic Control Devices provides guidance on when traffic signals should be interconnected with railroad crossings. Various other manuals and reports deal with how the traffic signal preemption logic should be configured. Maintenance practices typically require technicians to perform routine checks to ensure that preemption circuitry is functioning, and agencies often log the preemption events as part of a system-monitoring procedure. However, no procedure or software allows a controller to tabulate performance measures on how effective the preemption logic is at clearing conflicting phases before a train's arrival. This study introduces the concept of using an event-based data collection system to monitor the railroad preemption input, vehicle detectors, and phase indications to develop performance measures for evaluating the effectiveness of clearing movements that cross the tracks before train arrival. These techniques are applied to statistically compare the impact of steerable traffic signal indications at a location where the tracks are within 60 ft of the traffic signal stop bar. Based on a comparison of 700 preemptions before the signal heads were installed with 2,102 preemptions after signal heads were installed, no statistically significant difference was observed.
Cycle-Length Performance Measures
Authors: Day Christopher M. , Bullock Darcy M. , Sturdevant James R.
Published: January 2010

Webster's single-ring formulation for cycle length and the Highway Capacity Manual (HCM) intersection saturation metric are revisited, and the model for dual-ring operation is extended to provide a tool for evaluating the effectiveness and efficiency of a prescribed cycle length. The calculations from Webster's model and the HCM provide a framework for identifying periods of time when cycle length could be substantially shortened, periods of the day when an increase in cycle length would provide some modest improvements, and periods of the day when cycle length is adequate and capacity problems should be addressed by adjusting splits. The methodology is demonstrated for incorporating the number of split failures, overall intersection saturation, and Webster's optimal cycle length to evaluate the quality of split operation and the effectiveness of cycle length at a signalized intersection.
Optimization of Coordinated–Actuated Traffic Signal System
Authors: Park Byungkyu (Brian) , Lee Joyoung
Published: January 2010

Study has shown that about half of the traffic signalized intersections in the United States need to be reoptimized. Even though many traffic signal control systems have been upgraded from pretimed controllers to actuated and adaptive controllers, traffic signal optimization software has not kept up with such advances. For example, existing commercial traffic signal timing optimization programs such as SYNCHRO and TRANSYT-7F do not optimize advanced controller settings (e.g., minimum green time, extension time, detector settings) available in modern traffic controllers. This deficiency is due partly to existing programs, which are based on macroscopic simulation tools that do not explicitly consider individual vehicular movements. To overcome such a shortcoming, a stochastic optimization method (SOM) was proposed and successfully applied to a few case studies. This study presents some enhancements made in the SOM and case study results from an arterial network consisting of 16 signalized intersections. The proposed method employs a distributed computing environment for faster computation time and uses a shuffled frog-leaping algorithm (SFLA) for better optimization. The case study results showed that the proposed enhanced SOM method, called SFLASOM, improved total network travel times over field settings by 3.5% for midday times and 2.1% for p.m.-peak times. In addition, corridor travel times for both p.m.-peak and midday times were significantly improved.
Guidelines for Multicriterion Decision-Based Left-Turn Signal Control
Authors: Ozmen Ozlem , Tian Zong Z. , Gibby Reed
Published: January 2010

There are three main types of left-turn control at signalized intersections: permitted, protected, and protected–permitted. Determining left-turn signal control types is one of the major elements in traffic signal design and operations, and it is a systematic approach involving complex decision rules. Existing guidelines for determining left-turn signal control have been primarily based on traffic volume, delay, geometry, crash experience, and other related factors. Such guidelines are generally presented in a flowchart format. One of the major shortcomings of the existing guidelines is that a single variable could dominate the decision process and thereby prevent a balanced consideration of all other important variables. A new guideline for determining left-turn control types mostly applicable to conventional left-turn displays is presented. The current format is designed for a four-leg intersection configuration; however, it can be easily adapted to the other formats. The guideline is based on the principles of multicriterion decision analysis and provides an index-based recommendation: a numerical scale is used to compare each type of left-turn control with the others instead of an absolute left-turn control type. With the data collected from the field, it is shown that the proposed guideline can be calibrated and tailored to specific left-turn control policies. Therefore, the guideline can be easily adapted by any jurisdiction.
Evaluation of Integrated Platoon-Priority and Advance Warning Flasher System at High-Speed Intersections
Authors: Liu Henry X. , Bhimireddy Sundeep
Published: January 2010

Most rural or suburban high-speed isolated intersections have higher traffic volumes on the major approach compared with the minor approach. Often these intersections are not close enough to one another to provide coordination and are not far enough apart to disperse vehicle platoons completely on the major approach. These major-approach vehicle platoons are forced to stop frequently because of conflicting calls placed by a few vehicles on the minor approach. As a result, these intersections operate poorly, especially during peak periods. In addition, advance warning flashers are used at these intersections to warn motorists of the end of the green. The conventional method uses the trailing overlap green, which holds the green for a fixed time after gap-out. This trailing overlap green replaces the existing dilemma-zone protection provided by loop detectors and also increases delay on the minor approach. Recently, platoon-priority signal control systems have been developed to progress platoons efficiently at these intersections. In addition, the Texas Transportation Institute has developed the advance warning end-of-green system to provide advance warning at these intersections without the necessity of holding the green after gap-out. In this study, these systems are integrated and the performance of the system is evaluated in terms of delay, stops, and advance warning time. Cabinet-in-the-loop tests performed with a real scenario suggested potential benefits of 50% reduction in delay and stops on the major approach experiencing platoons. It was also found that the total intersection delay and stops were reduced by as much as 20%.