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Aggregate Image Measurement System 2 (AIMS2): Final Report
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Final Report September 2010
Aggregate shape characteristics influence the structural performance of hot-mix asphalt, hydraulic cement concrete, and unbound aggregate pavement layers, as well as the skid resistance of pavement. Their accurate classification is essential to stone-matrix and warm-mix asphalt technologies. This report documents the development and testing of an industry-ready tool—the Aggregate Image Measurement System 2 or AIMS2—to evaluate aggregate shape properties using digital imaging. Testing procedures using the AIMS2 have been adopted as Provisional Standards by the American Association of State Highway and Transportation Officials. The technology has the potential to improve the quality, durability, and safety of pavements.
The refinement of the late-stage prototype and interlaboratory study of the AIMS2 was supported by a grant from the Highways for Life Technology Partnerships Program. The Technology Partnerships Program provided grants to assist general industry make the leap from promising late-stage prototypes to market-ready products and promoted partnerships with State and local highway agencies to demonstrate the technologies under real-world conditions.
This report will be of interest to State and local departments of transportation, Federal Highway Administration division offices, highway research institutions, aggregate producers, and highway construction contractors.
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document. Trade names mentioned in this report are not intended as an endorsement of any machine, contractor, process, or product.
Quality Assurance Statement
The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. The FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.
Cover photo courtesy of Pine Instrument.
The overall project scope of Highways for LIFE grant to Pine Instrument Company was to improve the design of the research instrument to analyze aggregate properties using digital imaging technology, conduct a ruggedness study on the new design, perform an interlaboratory study, and evaluate the potential commercial viability of the new instrument. This final report outlines the work and conclusions of this project.
Aggregate shape characteristics are well known to be important in influencing the structural performance of asphalt design, hydraulic cement concrete, and unbound aggregate pavement layers. The current methods for determining these characteristics have proven to be difficult, time-consuming, and subjective. An industry need has been identified to develop a technology platform to measure these material characteristics utilizing consistent, repeatable, and objective means for both within-laboratory and between-laboratory situations. Such a technology platform must withstand the marketability thresholds and commercial viability expectations of the industry.
The equipment developed and used in the initial research was intended for investigating the possibility of using digital image analysis to characterize aggregate shape properties and to investigate the relationship of those characterizations to pavement and aggregate performance. It was not selected with manufacturability or laboratory usability as primary objectives. This initial technology platform proved the applied concepts feasible, but the technology also proved to be expensive and cumbersome to operate. Therefore, a new system was needed that met both the cost and functionality needs of the industry. This grant project developed a product that melded marketability and applicability into an industry tool.
The Aggregate Image Measurement System 2 (AIMS2) technology uses a variable magnification microscope-camera system and two different lighting configurations to capture aggregate images for analysis. The first lighting scheme creates a backlit image, which provides a particle silhouette. This image is converted to a binary tiff file analyzed for the shape characteristics of angularity and cross-sectional form. The second lighting scheme utilizes oblique top lighting, which illuminates the surface of each particle. A gray-scale image of the particle surface is captured and analyzed providing a surface texture characterization. The three-dimensional form of each particle is also extracted from the focal plane position, at the particle surface, while the texture image is captured.
While the system in its entirety is commonly referred to as the AIMS2, the heart of the technology is the AIMS SOFTWARE©. This software consists of a series of algorithms that objectively quantify aggregate shape properties on the macro scale, which are features greater than 0.5 mm such as angularity, form, and flat and elongated ratios, as well as features on the micro scale, which are typically less than 0.5 mm in size, such as surface texture. Both coarse and fine aggregates are characterized with the AIMS Software© algorithms. For simplicity, the entire system, including both hardware and software, is simply referred to here as the AIMS2.
During this project, a migration from the original research prototype platform, designated AIMS1, to a newly designed product platform, designated AIMS2, was accomplished. Upon completion of the new design, independent laboratory testing was conducted on the AIMS2 hardware platform. This testing included the calibration of the AIMS2 to the AIMS1 as well as experiments to confirm that the testing methodology was sound. Texas A&M University was selected to perform the tests on the new equipment under the direction of Dr. Eyad Masad. The facility was selected because of its staff's extensive expertise in materials research and experience with the AIMS1 research system, as well as its extensive database containing a variety of well-characterized materials.
The results of the comparison testing between AIMS1 (the research system) and AIMS2 (the system developed within this project) proved that the two systems provide the same ranking of aggregates and provide comparable results. Additionally, the ruggedness testing validated that operating parameters were appropriately controlled and provided reproducible results. Specific parameters and control limits are recommended to ensure reproducible AIMS2 characterization.
Phase II of this project conducted an interlaboratory study (ILS) utilizing eight AIMS2 systems in more than 32 laboratories. The statistical analysis of the ILS data shows that the system outputs have reasonable coefficients of variation for all sizes of aggregate except the 0.075 mm. Additional work is necessary to address the 0.075-mm (ASTM #200) sieve size variability.
The ILS also provided a foundation for the precision statements of the proposed test methods for testing aggregate materials with digital imagery. The procedures that were developed address the need for conformity in the testing methodology that is required to take this technology to a level of acceptance. Research shows clear links of aggregate shape to pavement performance. This project demonstrated the ability of AIMS2 to provide an objective and reproducible shape characterization of aggregates. As the technology is applied on a wider scale, establishing clear relationships between the AIMS2 characterizations values and in-place pavement performance will be a goal.
Because there is a need for objective and accurate aggregate shape characterization and the ILS experiment demonstrated the AIMS2 as a robust tool for characterizing aggregate materials, there is a great deal of interest in the AIMS2 technology from many U.S. State transportation departments as well as from various entities in Canada, Brazil, China, and Italy. Domestic aggregate producers have also expressed interest as this technology provides a means for quantifying the consistency and quality of aggregate products.
Pine Instrument Company is pursuing the traditional facets of marketing—pricing, placement, packaging, and promotion—in addition to other aspects of the commercial viability of AIMS2. The details are provided within this report.
The material testing procedures for aggregate material shape characterization using the AIMS2, which were developed and refined as part of this project, have been published as Provisional Standards by the American Association of State Highway and Transportation Officials.
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