VTechWorks Repository :: Browsing by Author "Druta, Cristian"

Browsing by Author "Druta, Cristian"

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Characterization of High Porosity Drainage Layer Materials for M-E Pavement Design
Zhang, Yinning (Virginia Tech, 2015-02-12)
The objective of this study is to characterize the properties of typically adopted drainage layer materials in VA, OK, and ID. A series of laboratory tests have been conducted to quantify the volumetric properties, permeability and mechanical properties of the laboratory-compacted asphalt treated and cement treated permeable base specimens. The modified test protocols to determine the dynamic modulus of the drainage layer materials have been provided, which can be followed to determine the dynamic modulus of the drainage layers as level 1 input in Mechanistic-Empirical (M-E) pavement design. The measured dynamic moduli have been used to calibrate the original NCHRP 1-37A model to facilitate its application on drainage layer materials for prediction of the dynamic modulus as level 2 input. The compressive strength of the cement treated permeable base mixture of different air void contents has also been quantified in laboratory. Numerical simulations are conducted to investigate the location effects and the contribution of the drainage layer as a structural component within pavement. The optimal air void content of the drainage layer is recommended for Virginia, Oklahoma and Idaho based on the laboratory-determined permeability and the predicted pavement performances during 20-year service life.
Concrete Microstructure Characterization and Performance
Druta, Cristian (IntechOpen, 2020)
Microstructural characteristics such as the interfacial transition zone (ITZ) and cracking patterns from compressive strength testing are main features that characterize concrete behavior. Certain materials such as blast furnace slag or fly ash introduced in the concrete mix aid in improving its strength and durability. Others such as nanosilica particles may affect only the microstructure of the paste without making any significant improvement in the strength of the ITZ or pasteaggregate bond. Additionally, in situ investigation of the microstructures of fresh cement paste can greatly enhance knowledge of the development properties of concrete at an early age (e.g., setting and hydration), which can be helpful for improvement of the quality of concrete. Common technologies such as Scanning Electron Microscope (SEM) are currently employed in petrographic analysis of cementitious materials and concrete microstructure.
Discrete Element Method (DEM) Contact Models Applied to Pavement Simulation
Peng, Bo (Virginia Tech, 2014-08-20)
Pavement is usually composed of aggregate, asphalt binder, and air voids; rigid pavement is built with hydraulic cement concrete; reinforced pavement contains steel. With these wide ranges of materials, different mechanical behaviors need to be defined in the pavement simulation. But so far, there is no research providing a comprehensive introduction and comparison between various contact models. This paper will give a detail exploration on the contact models that can be potentially used in DEM pavement simulation; in the analysis, it includes both a theoretical part, simulation results and computational time cost, which can reveal the fundamental mechanical behaviors for the models, and that can be a reference for researchers to choose a proper contact model. A new contact model—the power law viscoelastic contact model is implemented into software PFC 3D and is numerically verified. Unlike existing linear viscoelastic contact models, the approach presented in this thesis provides a detailed exploration of the contact model for thin film power-law creeping materials based on C.Y Chueng's work. This model is aimed at simulating the thin film asphalt layer between two aggregates, which is a common structure in asphalt mixtures. Experiments with specimens containing a thin film asphalt between two aggregates are employed to validate the new contact model.
Evaluating Pavement Response and Performance with Different Simulative Tests
Huang, Yucheng (Virginia Tech, 2017-06-30)
Simulative tests refer to the Full-scale accelerated pavement testing (APT) and laboratory wheel tracking testing, which are widely used for evaluation of pavement responses and performance under a controlled and accelerated damage conditions in a compressed limited time. This dissertation focuses on comparative evaluations under ALF, MMLS 3 and APA tests, in terms of rut depth, strain response, seismic stiffness, and contact stress using both experimental and numerical simulation results. Test slabs extracted from the ALF test lanes, are trafficked with the MMLS3 under comparable environmental conditions at laboratory in Virginia Tech. Some specimens were cut from the slabs for APA tests at VTRC. It is found that the monitored parameters yielded by the MMLS 3 test were comparable to the related full-scale ALF test results in terms of intrinsic material characteristics and pavement performance. The wireless sensor network based on Internet of things technology is implemented in laboratory for the MMLS 3 test, which provides a convenient solution for researchers on long-term observation and monitoring without being physically presented. The numerical simulations of ALF, MMLS 3 and APA in ABAQUS are used to supplement the investigation on the pavement response and performance under repeated moving loading. The viscoelastic-viscoplastic model is adopted to characterize rate and temperature dependent properties of asphalt mixtures. The 3D finite element models are capable of predicting the pavement response at critical locations while underestimates the rut depth because the permanent deformation induced by volumetric change cannot be represented in simulation. According to the test results, a power law function fits well for the accumulated rut depth versus number of load repetitions before the material reaches tertiary stage in MMLS 3 test. The rut depth development of APA tests exhibits a close-to-liner regression with number of load cycles after the initial 500 load repetitions. A regression model for predicting rut depth after 500 loads has a satisfying agreement with the experimental measurement. The calibrated MEPDG fatigue model can be used to estimate the allowable load repetitions in MMLS 3 trafficking. Besides, the effects of tire configuration, tire pressure, axle load amplitude, wheel load speed and temperature on pavement responses are investigated in this dissertation using the finite element model. It is concluded that MMLS 3 is an effective, economic and reliable trafficking tool to characterize rutting and fatigue performance of pavement materials with due regard to the relative structures. MMLS 3 test can be employed as the screen testing for establishing full-scale testing protocols as desired or required, which will significantly enhance economics of APT testing.
Evaluation of a Buried Cable Roadside Animal Detection System
Druta, Cristian; Alden, Andrew S. (Virginia Transportation Research Council, 2015-06)
Animal-vehicle collisions (AVC) are a concern for departments of transportation as they translate into hundreds of human fatalities and billions of dollars in property damage each year. A recently published report states that the Virginia Department of Transportation (VDOT) currently spends over $4 million yearly to remove about 55,000 deer carcasses from its roadways. Currently, one of the most effective existing methods to reduce AVCs is the use of animal detection systems, which can detect animals near the roadway and alert approaching drivers accordingly. In order to reduce AVCs in Virginia, VDOT, in collaboration with the Virginia Tech Transportation Institute, proposed the evaluation of an innovative roadside animal detection system in naturalistic and controlled conditions. This type of system offers numerous apparent advantages over above-ground animal detection technologies when environmental interferences, such as precipitation and vegetation, and site-specific characteristics, such as topology, subsidence, and road curvature, are considered. The subject animal detection system (ADS), a 300-m-long buried dual-cable sensor, detects the crossing of large and medium-sized animals and provides data on their location along the length of the cable. The system has a central processor unit for control and communication and generates an invisible electromagnetic detection field around buried cables. When the detection field is perturbed, an alarm is declared and the location of the intrusion is determined. Target animals are detected based on their conductivity, size, and movement, with multiple simultaneous intrusions being detected during a crossing event. The system was installed and tested at a highly suitable site on the Virginia Smart Road where large wild animals, including deer and bear, are often observed in a roadside environment. This report describes the installation of the ADS, data collection and analysis methodology, evaluation of the system’s reliability and effectiveness, cost analysis, and implementation prospects. The system used continuous, all-weather and nighttime video surveillance to monitor animal movement and to gauge system detections, and potential non-detections of the ADS. Also, a communication link between the buried ADS and the Virginia Smart Road fiber optic network was established to allow operation and monitoring of the system from a dedicated server in the Virginia Smart Road Control Room. A performance verification of the network communication was successfully conducted through continuous data collection and transfer to a storage unit. Data were collected continuously for a period of 10 months that included winter, and then analyzed to determine overall detection performance of the system. Data analyses indicate that the ADS, if properly installed and calibrated, is capable of detecting animals such as deer and bear, and possibly smaller animals, such as fox and coyotes, with over 95% reliability. The ADS also performed well even when covered by 3 ft of snow. Moreover, the system was tested under various traffic conditions and no vehicle interferences were noted during the same monitoring period. The acquired data can be used to improve highway safety through driver warning systems installed along roadway sections where high wildlife activity has been observed. Additionally, this system may be integrated with the connected vehicle framework to provide advance, in-vehicle warnings to motorists approaching locations where animals have been detected in or near the roadway.
Evaluation of the MMLS3 for Accelerated Wearing of Asphalt Pavement Mixtures Containing Carbonate Aggregates
Druta, Cristian; Wang, Linbing; Lane, D. Stephen (Virginia Transportation Research Council, 2014-06)
The purpose of this study was to develop an accelerated wearing protocol for assessing the susceptibility of asphalt surface mixtures to polishing. This was the second phase of the study. The first phase focused on assessing the characteristics of selected carbonate aggregates available in Virginia that are normally classified as “polishing” and thus not considered suitable for use in pavements except for those roads with an average daily traffic of less than 750 vehicles per day. The selection of aggregates used in pavements is critical in producing surfaces that will continue to provide good skid resistance through a lengthy service life. The specifications of the Virginia Department of Transportation (VDOT) call for “non-polishing aggregate” for use in most surface layers. The study was aimed at making use of locally available polishing aggregates that can reduce the cost of asphalt mixtures while maintaining satisfactory wearing and skid characteristics of the pavements. The objectives of the research were (1) to evaluate the polishing/wear features of mixtures containing limestone aggregate in the laboratory using an accelerated method; (2) to compare friction properties of the laboratory-polished specimens with actual pavement friction measurements; and (3) to compare friction properties of mixtures containing carbonate rock or blends with those of mixtures with non-carbonate rocks. The study included three types of aggregates, i.e., limestone, quartzite, and granite, and blends of these aggregates. The surface mixtures studied were conventional SM-9.5 and SM-12.5 mixtures containing various percentages of limestone, limestone recycled asphalt pavement, and limestone-granite/quartzite blends. The suggested test protocol to evaluate the polishing of asphalt concrete specimens prepared in the laboratory was developed using the third-scale model mobile load simulator (MMLS3). The MMLS3 is capable of applying realistic rolling wheel contact stresses similar to those on highways from the moving traffic. The skid resistance, friction, and texture of actual pavement surfaces and laboratory-fabricated specimens were measured after different polishing intervals. Skid resistance and frictional characteristics were measured by the British pendulum tester, dynamic friction tester, and locked-wheel skid tester; the circular texture meter was used to measure surface macrotexture. Results showed that the MMLS3 can be used to simulate traffic wearing of asphalt concrete specimens of different shapes and sizes in the laboratory including core specimens removed from existing pavements and that the BPT is effective in characterizing changes in friction on specimens that are subjected to simulated trafficking via the MMLS3. Further, test specimens should have a high initial macrotexture and mixtures should have good stability so that the wearing effects are focused on the aggregates. The study recommends that the Virginia Center for Transportation Innovation and Research (VCTIR) work with Virginia Tech and VDOT’s western districts to design and conduct an experiment to explore a series of carbonate / non-carbonate aggregate blends for asphalt mixtures and that the mixture gradations be designed to prevent the absence of macrotexture from impacting the ability to measure the “polish” of the coarse aggregate structure of the experimental mixtures. VCTIR should purchase tires with different tread patterns and try them on the MMLS3 to evaluate the polishing rate of specimens in more detail.
Implementation and Evaluation of a Buried Cable Animal Detection System and Deer Warning Sign
Druta, Cristian; Alden, Andrew S. (Virginia Transportation Research Council, 2019-05)
Animal-vehicle collisions (AVC), and deer-vehicle collisions (DVC) in particular, are a major safety problem on Virginia roads. Mitigation measures such as improved fencing and location-specific driver alerts are being implemented and evaluated in Virginia and elsewhere. One of the most promising mitigation methods uses a buried cable animal detection system (BCADS) to provide roadside or in-vehicle warnings to approaching drivers based on the active presence of an animal on or near the roadway. BCADS may also be deployed in combination with exposure controls such as fencing to provide monitored, at- grade, animal crossing zones where conventional passages (e.g. culverts and bridges) are unavailable. In this study, the Virginia Department of Transportation (VDOT) in collaboration with the Virginia Tech Transportation Institute (VTTI) implemented and monitored the performance of a BCADS on a public road to provide a real-world assessment of system capabilities and possible operation issues. The BCADS has proved effective and reliable in a previous evaluation performed under more controlled and secure conditions at the Virginia Smart Road facility in Blacksburg, VA. A BCADS was installed on State Route 8 in the town of Christiansburg, VA on a road segment known to have a relatively high rate of DVCs. The system identified crossings of large- and medium-sized animals and provided data on their location along the length of the sensing cable. The BCADS and associated surveillance and communications equipment were powered by a solar photovoltaic system. A cellular modem provided for remote system monitoring and data collection. A flashing light “Deer Crossing” warning sign was installed at the site and was wirelessly linked with the BCADS to alert approaching drivers when an animal crossing was detected. Continuous BCADS and all-weather video surveillance data were collected during an 11-month period (November 2017–September 2018) to monitor animal movement, vehicle traffic, and system performance. Data on driver response to the activated warning sign during the dawn and dusk hours were collected in two separate daily sessions within a 3-month period. Study findings indicate that the BCADS is capable of detecting larger animals such as deer, and sometimes smaller animals such as coyotes, with approximately 99% reliability. The system also performed well when covered by approximately 60 cm (2 ft.) of snow. Moreover, the system was tested under various vehicle traffic conditions, and rare instances of relatively minor interferences were observed. Vehicle speed and brake light application data collected during warning sign activation showed that approximately 80% of drivers either braked or slowed in response, indicating that the sign was effective.
Integration of Structural Health Monitoring and Asset Management
Wang, Linbing; Xue, Wenjing; Druta, Cristian; Wang, Dong (United States. Department of Transportation. Research and Innovative Technology Administration, 2012-12)
The Virginia Center for Innovation and Transportation Research and Virginia Tech installed a structural health monitoring (SHM) system on a Virginia bridge. Using data from this SHM system as input, a procedure was developed to provide information on the lane occupancy, speed, classification and gross vehicle weight of heavy trucks. The resulting information is very useful for bridge management. The data also augments existing bridge WIM data collection sites in Virginia. The procedure could add functionality to other bridge SHM systems in Virginia. The system provides useful information on truck loading at low cost.
Methods for Assessing the Polishing Characteristics of Coarse Aggregates for Use in Pavement Surface Layers
Wang, Linbing; Druta, Cristian; Lane, D. Stephen (Virginia Center for Transportation Innovation and Research, 2010-06-01)
The predominant aggregate resources located in the western parts of Virginia are carbonate rocks. The mineral components of these rocks tend to be relatively soft and subject to abrasive wear under traffic that leads to a fairly rapid smoothing of the aggregate surface and the surface of pavements containing them. This smoothing or polishing leads to a loss of surface friction and thus skid resistance of the pavement, creating potential safety issues. As a consequence, surface courses of pavements are constructed with nonpolishing aggregates, which in the western districts can mean lengthy transport of materials. With rising economic and environmental costs associated with transportation, increasing the use of locally available materials through improved methods to discern subtle differences in polishing tendencies or blending of polishing with nonpolishing aggregates could translate into significant cost savings. In this study, a suite of carbonate aggregates suspected to show a range of polishing characteristics based on previous studies was selected for evaluation along with several sources currently used as nonpolishing aggregates. The aggregates were examined petrographically, and the carbonate sources were tested for insoluble residue and subjected to a dilute acid etch to form the basis for a tentative classification of polishing susceptibility. The aggregates were tested in the Micro-Deval apparatus using both the standard procedure for coarse aggregates and a cyclical A/P procedure with silica sand devised for this study to examine how the various aggregate types responded when subjected to various degrees of wearing under similar conditions. Following abrasion cycles, 2-D digital aggregate images were obtained and analyzed using specialized software to assess their morphological properties with emphasis on angularity and surface texture. These properties were assessed before and after abrasion to determine the degree and rate of change in surface texture as well as the texture distribution within an aggregate sample. In addition, pictures were taken of the exposed surfaces of three experimental pavement sections in the Virginia Department of Transportation's Bristol District containing carbonate rock as the fine aggregate blended with nonpolishing coarse aggregate to visually assess the effect of traffic in the last 3 years. The carbonate rocks evaluated could be grouped according to polishing and wear tendency based on petrographic characteristics and mass loss in the Micro-Deval tests. Although visual distinctions could be discerned, these differences were not identified statistically by the image analysis program, but factors affecting the program were identified. A second phase of work is proposed that focuses on developing an accelerated pavement wearing protocol for assessing polishing tendencies and evaluating various mixtures of carbonate and nonpolishing aggregates.
Performance Evaluation of Thin Wearing Courses Through Scaled Accelerated Trafficking
Druta, Cristian; Wang, Linbing; McGhee, Kevin K. (Virginia. Department of Transportation, 2014-01)
The primary objective of this study was to evaluate the permanent deformation (rutting) and fatigue performance of several thin asphalt concrete wearing courses using a scaled-down accelerated pavement testing device. The accelerated testing was conducted using a model mobile load simulator (MMLS3). Field testing with the MMLS3 was conducted on a 4.75-mm nominal maximum aggregate size dense-graded mixture installed at the Turner-Fairbank Highway Research Center. This mixture (designated SM-4.75), two other conventional dense-graded mixtures, and a thin gap-graded mixture were also used to prepare specimens for laboratory rutting tests using the MMLS3. Test results from more than 100,000 wheel load applications of the MMLS3 showed that the thin wearing courses underwent various degrees of permanent deformation depending on their compacted air void content. According to the protocol guidelines developed for the evaluation of permanent deformation and moisture damage when using the MMLS3, most of the mixtures performed well. One exception was a coarser dense-graded material with a high amount of recycled asphalt pavement. No indication of fatigue cracking or other distress was observed for any mixture during or after testing. The study supports use of the SM-4.75 mixture on low- to medium-traffic roadways and for maintenance and/or preservation applications. It further recommends that the Virginia Department of Transportation apply the methods demonstrated through this research to assess better the stability of experimental wearing course mixtures in advance of wider spread field applications.
Piezoelectric Energy Harvesting for Roadways
Xiong, Haocheng (Virginia Tech, 2015-02-11)
Energy harvesting technologies have drawn much attention as an alternative power source of roadway accessories in different scales. Piezoelectric energy harvesting consisting of PZT piezoceramic disks sealed in a protective package is developed in this work to harness the deformation energy of pavement induced by traveling vehicles and generate electrical energy. Six energy harvesters are fabricated and installed at the weigh station on I-81 at Troutville, VA to perform on-site evaluation. The electrical performance of the installed harvesters is evaluated by measuring the output voltage and current generated under real traffic. Instant and average power outputs are calculated from the measured waveforms of output voltage and current. The analysis of the testing results shows that the electrical productivity of the energy harvesters are highly relevant to the axle configuration and magnitude of passing vehicles. The energy transmission efficiency of the energy harvester is also assessed.
Portable Image Analysis System for Characterizing Aggregate Morphology
Wang, Linbing; Lane, D. Stephen; Lu, Yang; Druta, Cristian (Virginia Center for Transportation Innovation and Research, 2008-02-01)
In the last decade, the application of image-based evaluation of particle shape, angularity and texture has been widely researched to characterize aggregate morphology. These efforts have been driven by the knowledge that the morphologic characteristics affect the properties and ultimate performance of aggregate mixtures in hot-mixed asphalt, hydraulic cement concrete and bound and unbound pavement layers, yet the lack of rapid, objective, and quantitative methods for assessment have inhibited their application in the engineering process. Developed systems for computer-based imaging and image analysis can cost up to $30-40,000 and are usually not portable to the field. However, recent advances in technology have produced pocket computers having as much processing power as was available in some desktop computers. This project takes advantage of these advances to develop an inexpensive portable image analysis system for characterizing aggregate morphology. The system was developed with an integral pocket computer-high resolution camera but can also use individual components consisting of a digital camera and lap- or desk-top computer. Digital images of aggregate particles are captured with the camera. These images are analyzed within the Matlab software program environment with a macro developed and written for this project that uses Fast Fourier Transform to characterize the particle morphology with respect to three parameters: shape, angularity and texture, based on the particle perimeter (outline or edge). By analyzing a number of particles from a source, it can be characterized with respect to these three parameters. Following development of the analysis program, 10 coarse aggregates from various Virginia sources were analyzed. Particles of each aggregate were randomly chosen so that each group contained the various shapes and textures representative of the source. Three images of each particle were obtained at distances of 2, 3, and 10 in to evaluate the resolution needed for adequate analysis. The reliability of the image processing was assessed by statistically analyzing the shape, angularity, and texture values to determine how the threshold parameter affects the particle edge acquisition. Asymptotic analysis was performed to determine the number of images needed to obtain a statistically stable value for each aggregate parameter. It was determined that images acquired at close range (2 or 3 in) were needed to provide sufficient resolution to adequately characterize the aggregate. It was also found that statistically valid values for aggregate shape, angularity, and texture can be obtained from fifteen particle images of random orientation. It can be concluded that the system can be successfully used to characterize coarse aggregate morphology. It is recommended that the Virginia Department of Transportation's Materials Division begin collecting images of aggregates used statewide and collaborate with the VTRC to perform the characterizations and build the database of aggregate morphologic characteristics. This information, coupled with performance testing of the materials, will provide the basis for incorporating the characterization parameters into specifications and guide material usage in the future.
Slippery Road Vehicle Early Warning System: Method Augmentation
Druta, Cristian; Alden, Andrew (National Surface Transportation Safety Center for Excellence, 2023-03-09)
Two prior projects conducted by the Virginia Tech Transportation Institute (VTTI) for the Federal Highway Administration (FWHA) demonstrated that small but statistically significant differences in vehicle wheel rotational rates, attributed to tire microslip, can be used to quantify the changes in tire grip that occur when pavement conditions change due to road weather. The first project established proof-of-concept by demonstrating that tire microslip increased where the pavement was covered with liquid or frozen water and confirmed that OEM wheel sensors were of sufficient resolution to determine statistically different microslip rates at the driving and free-rolling wheels. The second project introduced the concept of a traction index (TI) and explored confounding factors, such as road incline and wind. Results showed that the “noise” that resulted from apparent vehicle acceleration and wind prevented accurate measurement of TI given the constraints of sensor resolution and other factors. For the current study, researchers hypothesized that instantaneous fuel consumption rate (IFCR) and engine throttle position, available from the vehicle network, might be used to correct the calculated TI to account for the confounds. The relationship between TI and IFCR and engine throttle position was analyzed using a variety of techniques. In the end, the research team was unable to demonstrate that basic TI calculated values could be corrected using vehicle dynamic data due to factors stemming from the unsuitability of the existing road friction dataset for the application intended. Over the time spanned by these three studies, some companies have begun to use microslip and other vehicle variables as a basis for dynamic assessment of road friction. Also, vehicle data, including that which might be used to assess road weather, are now available commercially. These data sources provide opportunities for future research on the safety and environmental benefits of real-time assessment and sharing of road weather information.
Vehicle Axle Detection and Spacing Calibration Using MEMS Accelerometer
Zhang, Wei (Virginia Tech, 2014-12-05)
Vehicle classification data especially trucks has an important role in both pavement maintenance and highway planning strategy. An advanced microelectromechanical system (MEMS) accelerometer for vehicle classification based on axle count and spacing was designed, tested, and applied to the pavement. Vehicle-pavement interaction was collected by the vibration sensor while vehicle axle count and spacing were calibrated later. Collected vibration data also used to analyze the pavement surface condition and compared with simulation using dynamic loading analysis. Laboratory tests using MMLS3 device to verify the accuracy of MEMS accelerometer and reaction under different surface condition were tested. An algorithm for calculating axle spacing and axle count was developed. Acceleration of different pavement surface condition were analyzed and compared with simulation results, the influence of surface condition to the pavement acceleration was concluded.

Browsing by Author "Druta, Cristian"

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