Browsing by Subject "Aggregate"
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Item Characterization of aggregate shape properties using a computer automated system(Texas A&M University, 2005-02-17) Al Rousan, Taleb MustafaShape, texture, and angularity are among the properties of aggregates that have a significant effect on the performance of hot-mix asphalt, hydraulic cement concrete, and unbound base and subbase layers. Consequently, there is a need to develop methods that can quantify aggregate shape properties rapidly and accurately. In this study, an improved version of the Aggregate Imaging System (AIMS) was developed to measure the shape characteristics of both fine and coarse aggregates. Improvements were made in the design of the hardware and software components of AIMS to enhance its operational characteristics, reduce human errors, and enhance the automation of test procedure. AIMS was compared against other test methods that have been used for measuring aggregate shape characteristics. The comparison was conducted based on statistical analysis of the accuracy, repeatability, reproducibility, cost, and operational characteristics (e.g. ease of use and interpretation of the results) of these tests. Aggregates that represent a wide range of geographic locations, rock type, and shape characteristics were used in this evaluation. The comparative analysis among the different test methods was conducted using the Analytical Hierarchy Process (AHP). AHP is a process of developing a numerical score to rank test methods based on how each method meets certain criteria of desirable characteristics. The outcomes of the AHP analysis clearly demonstrated the advantages of AIMS over other test methods as a unified system for measuring the shape characteristics of both fine and coarse aggregates. A new aggregate classification methodology based on the distribution of their shape characteristics was developed in this study. This methodology offers several advantages over current methods used in practice. It is based on the distribution of shape characteristics rather than average indices of these characteristics. The coarse aggregate form is determined based on three-dimensional analysis of particles. The fundamental gradient and wavelet methods are used to quantify angularity and surface texture, respectively. The classification methodology can be used for the development of aggregate shape specifications.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 Experimental Evaluation of New Generation Aggregate Image Measurement System(2010-07-14) Gates, Leslie L.The performance of hot mix asphalt, Portland cement concrete, unbound base, and subbase layers in a pavement are significantly affected by aggregate shape characteristics. Classification of coarse and fine aggregate shape properties such as shape (form), angularity, and texture, are important in predicting the performance of pavements. Consequently, there is a need to implement a system that can characterize aggregates without the limitations of the current aggregate classification standards. The Aggregate Image Measurement System (AIMS) was developed as a comprehensive and capable means of measuring aggregate shape properties. A new design of AIMS will be introduced with several modifications to improve the operational and physical components. The sensitivity, repeatability, and reproducibility are analyzed to evaluate the quality of AIMS measurements. The sensitivity of AIMS is evaluated and found to be good for several operational and aggregate parameters. Important operational and environmental factors that could affect the AIMS results are identified and appropriate limits are recommended. AIMS is able to control normal variations in the system without affecting the results. A comprehensive analysis is conducted to determine the repeatability and reproducibility of AIMS for multiple users and laboratories. Single-operator and multi-laboratory precision statements are developed for the test method in order to be implemented into test standards.Item Recommendations for coarse aggregate testing requirements for use in portland cement concrete(2013-12) Clement, John Christopher, 1985-; Fowler, David W.Coarse aggregate is often one of the largest volume occupying components in a portland cement concrete system. With increases in transportation costs and depletion of many of the aggregate sources currently in use the need to reevaluate the performance of aggregates in concrete has arisen. Current aggregate testing requirements for many organizations have not been updated in decades, even with the advancements in aggregate testing equipment that are currently available. This research project investigates current used and potential test methods for evaluating coarse aggregate for use in portland cement concrete. Testing focused on determining the most appropriate aggregate property to evaluate and then determining the correlation to mechanical concrete properties. Relationships between potential aggregate tests and currently used aggregate tests were evaluated to determine if compatible relationships between methods were evident. For this purpose concrete mixtures were made at a fixed aggregate volume to establish if a link was evident between aggregate test properties and concrete. To establish a link between laboratory and real world performance field sites with known distress were visited to better establish limits for aggregate testing requirements. Results obtained provided the basis for recommendations for testing requirements and limits to be used for aggregates in portland cement concrete.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.