Browsing by Subject "AIMS"
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Item Analysis of aggregate imaging system (AIMS) measurements and their relationship to asphalt pavement skid resistance(2009-05-15) Luce, Anthony DavidThis thesis consists of two parts. The first part includes analyses of the correlation between the results of two Aggregate Imaging System (AIMS) units. These analyses have led to refinements of the AIMS analysis methods of angularity and texture, which resulted in reduced variability in the results and better correlation between the two AIMS units. The refined analysis methods were used to establish a database of the shape characteristics of about 100 aggregate samples from the state of Texas and to propose a new method for the classification of aggregates based on their shape characteristics. This new method of classification is for use in the Texas Department of Transportation (TxDOT) wet weather accident reduction program (WWARP). The use of AIMS texture index and variability in texture within an aggregate source is proposed instead of the British Polish Value (BPV) for classifying aggregates used in pavement surfaces. The second part of the thesis investigates the relationship between shape characteristics and asphalt pavement skid resistance. Many states have implemented wet weather accident reduction programs aimed at maintaining acceptable levels of pavement skid resistance. Proper aggregate selection before construction aids in maintaining acceptable levels of skid resistance throughout the life of the pavement. Several predictive models of pavement skid resistance have been developed over the years. Some of these models account for the influence of aggregate characteristics on pavement skid resistance, primarily through incorporating the results of the BPV test in the model. However, the BPV test is known to have high variability and dependence on experimental factors that are not related to the actual aggregate resistance to polishing. AIMS offers a method to measure aggregate shape characteristics directly in a relatively short period of time. The new method for relating aggregate shape characteristics to pavement skid resistance was verified by relating skid resistance measurements from field test sections to measured aggregate properties from the laboratory. This methodology is expected to be the basis for further study to form a more comprehensive and verified model for the prediction of pavement skid resistance that incorporates measured aggregate properties from the AIMS system.Item Characterization of aggregate resistance to degradation in stone matrix asphalt mixtures(Texas A&M University, 2006-04-12) Gatchalian, DennisStone matrix asphalt (SMA) mixtures rely on stone-on-stone contacts among particles to resist applied forces and permanent deformation. Aggregates in SMA should resist degradation (fracture and abrasion) under high stresses at the contact points. This study utilizes conventional techniques as well as advanced imaging techniques to evaluate aggregate characteristics and their resistance to degradation. Aggregates from different sources and types with various shape characteristics were used in this study. The Micro-Deval test was used to measure aggregate resistance to abrasion. The aggregate imaging system (AIMS) was then used to examine the changes in aggregate characteristics caused by abrasion forces in the Micro-Deval. The resistance of aggregates to degradation in SMA was evaluated through the analysis of aggregate gradation before and after compaction using conventional mechanical sieve analysis and nondestructive X-ray computed tomography (CT). The findings of this study led to the development of an approach for the evaluation of aggregate resistance to degradation in SMA. This approach measures aggregate degradation in terms of abrasion, breakage, and loss of texture.Item Development of experimental methods for the evaluation of aggregate resistance to polishing, abrasion, and breakage(Texas A&M University, 2007-04-25) Mahmoud, Enad MuhibAggregate properties influence different aspects of asphalt pavement performance. Aggregate polishing characteristics are directly related to pavement surface frictional properties and thus to skid resistance. Aggregate resistance to degradation (abrasion and breakage) is another important property that influences pavement performance. Aggregate degradation could take place during production due to plant operations and during compaction, leading to change in aggregate characteristics and mix properties. In addition, aggregate resistance to degradation is important in mixes such as Stone Matrix Asphalt (SMA) and Open Graded Friction Course (OGFC) that rely on stone-to-stone contacts among coarse aggregates. Some aggregates in these mixes fracture due to the high stresses at contact points. Many test methods exist for measuring aggregate polishing and degradation, but a critical review of these methods reveals that they suffer from being time consuming, are unable to differentiate between aggregates with distinct resistance to polishing, or unable to differentiate between aggregate resistance to abrasion and breakage. New methodologies are needed to give better assessment of aggregate resistance to polishing, abrasion, and breakage. The thesis presents the development of new methods for measuring aggregate resistance to polishing, abrasion, and breakage. These methods rely on measurements using the Aggregate Imaging System (AIMS) and Micro-Deval. The new method for measuring aggregate resistance to polishing monitors change in aggregate texture as a function of polishing time. As such, it provides the initial texture, rate of polishing, and final texture. The new method for measuring aggregate degradation is capable of distinguishing between breakage and abrasion. In this method, abrasion is defined as the reduction in aggregate angularity, while breakage is defined by fracture of particles. The new methods are shown to be rapid and accurate, and they require reasonable training. Since both AIMS and Micro-Deval are used in the new methods, it was necessary to evaluate the repeatability of these two methods. Measurements using two AIMS units and two Micro-Deval machines were used to assess the variability. There was no statistical difference between the measurements of the two AIMS units or between the measurements of the two Micro-Deval units.Item Hybrid control and model-based assertions for autonomous intersection management system as a cyber-physical system(2016-05) Zhou, Dongyi; Longoria, Raul G.; Fernandez, Benito RA cyber-physical system (CPS) consists of multiple physical components that collab- orate through a network during real-time operation according to system-level commands. A hybrid control, which generates discrete system-level commands and handles the low-level physical dynamics for each component, is of singular importance to a CPS. For a CPS, live- ness and safety require that the system is always eventually doing what is desirable without any undesirable behavior, and have to be carefully addressed. The advance in information technology and autonomous driving make it possible to establish an autonomous intersection management system (AIMS) for ground autonomous vehicles, which can potentially improve traffic efficiency and reduce intersection car accidents. This work presents a hybrid control and introduces model-based assertions for such an AIMS. System-level traffic requirements are expressed in the form of linear temporal logic (LTL) specifications in the generalized reactivity formulas with rank 1 (GR(1)) and a two-player game is solved to synthesize a discrete traffic network controller. DaNI, a motor-driven laboratory robot vehicle, is mod- eled using a bond-graph approach, and a nonlinear vehicle trajectory sliding-mode controller (SMC) is mathematically and numerically described. The discrete traffic controller instructs each robot vehicle to pass through the intersection of interest at a certain time and the vehicle’s trajectory within the intersection is controlled by the SMC. Using simulation, it is shown that the synthesized discrete controller is able to determine proper system actions in response to traffic data and environmental actions while maintaining liveness and safety specifications. A laboratory study on a simple AIMS is demonstrated to depict the basic design structure of a AIMS as a CPS. The results suggest that model-based assertions, which monitor and validate a CPS by assertions based on physical models, can be helpful in de- tecting physics-related abnormalities during operation of a CPS that may not be captured by a software-level analysis. Using simulations, it is shown how the accuracy of a continuous vehicle trajectory controller, such as a SMC, can provide informative guidance on the design of model-based assertions.Item Quantifying the characteristics of fine aggregate using direct and indirect test methods(2013-12) Alqarni, Ali Saeed; Fowler, David W.The characteristics of fine aggregates, such as shape, angularity, and surface texture, have been shown to influence the performance of concrete and asphalt mixtures and to play an important role in obtaining valuable properties of early age concrete such as workability, and compatibility. However, the measurement of fine aggregate characteristics is not easy. In the present study, 26 fine aggregates, covering a wide spectrum of mineralogy, were examined using direct and indirect test methods in order to evaluate the shape, angularity, and surface texture, as well as to analyze the gradation. The direct test methods, such as AIMS and Camsizer, which provide a digital image of the aggregates proved to be the best. However, the cost of such systems can limit the use of digital imagining systems in practice. The indirect test methods which provide an estimate of aggregate surface characteristics, such as uncompacted void test, mortar flow test, compressive strength test, and flakiness test gave variable results. The uncompacted void test (Method A) was shown to be the most accurate indirect test method. The Camsizer and the sieve analysis test produced identical gradation analysis results when an adequate sample was used. General correlations were developed between the direct and indirect test methods. The non-approved fine aggregates on the TxDOT’s list were analyzed and compared to those of the approved fine aggregates to see whether they could be successfully used. It was found that both LS-5 and LS-8 had good results—even better than the results of some of the approved fine aggregates. Thus, they could be successfully used.Item Revamping aggregate property requirements for portland cement concrete(2012-05) Stutts, Zachary William; Fowler, David W.; Juenger, MariaCurrent Texas Department of Transportation (TxDOT) procedures for evaluating coarse aggregate for portland cement concrete (PCC) have been in place for over 39 years. Item 421 in the TxDOT "Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges" describes the tests and test limits that must be met by aggregates before they can be approved for use in portland cement concrete applications. The intention of Item 421 is to ensure that only strong, durable aggregates are used in concrete so that the life of concrete is not cut short by common distress mechanisms which ultimately lead to costly repairs and replacements. The two main tests currently used by TxDOT to evaluate aggregates are the magnesium sulfate soundness test and the Los Angeles abrasion and impact test. These tests are meant to characterize the overall soundness and resistance to abrasion and impact of an aggregate respectively. Unfortunately, past research has shown that the magnesium sulfate soundness and test and the Los Angeles abrasion and impact test are not able to successfully predict the field performance of an aggregate in concrete. The requirements of item 421 have thus far done a reasonably good job of ensuring long-lasting concrete; however the current tests and test limits may be unnecessarily precluding the use of some local materials. As high quality aggregate sources are depleted and transportation costs increase, it will become more necessary to distinguish good performers from marginal and poor performers in the future. If aggregate tests can be found that demonstrate better correlations with field performance, it may be possible to use more local aggregate sources and still provide the desired level of reliability for pavements, bridges, and other TxDOT concrete applications. Researchers are in the processing of collecting coarse and fine aggregates commonly used in Texas and testing these aggregates on a variety of alternative tests. Researchers will attempt to relate this test data to concrete behavior and ultimately recommend tests for improved TxDOT aggregate specifications.