Click for next page ( 21


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 20
20 Table 18. Aggregate sphericity from longest to the main difficulty was in visually separating angularity from shortest dimensions from digital caliper results. texture. Therefore, aggregates were ranked based on surface irregularity that combines both angularity and texture. There- Coarse Aggregate Average Sphericity 3:1 & Higher (%) CA 1 0.717 8 fore, it was decided for this study to establish a visual ranking CA 2 0.740 2 of surface irregularity; the correlation between rankings is CA 3 0.675 18 CA 4 0.662 30 shown in Table 19. CA 5 0.731 2 The experimental measurements were compared to the visual CA 6 0.711 6 rankings of surface irregularity and texture. The comparison CA 7 0.624 42 CA 8 0.706 6 with surface irregularity is useful since the evaluated tests them- CA 9 0.643 38 selves do not use the same methods to analyze angularity and CA 10 0.697 18 texture. In fact, the definition of angularity in a certain test CA 11 0.659 22 CA 12 0.666 18 method can be similar to the definition of texture in another test CA 13 0.638 38 method. Very good correlation was found between the eval- uators ranking aggregates based on surface irregularity; average aggregates used in this study due to their dark color. Both AIMS rankings are shown in Table 20. Similarly, the evaluators ranked and PSSDA-Large provide a sphericity value. The sphericity fine aggregate angularity by examining their shape under a measured using the digital caliper had very good agreement microscope; visual rankings are shown in Table 21. with AIMS and PSSDA-Large measurements. Figure 4 shows The correlations between the measurements and the cor- a comparison between AIMS measurements and digital caliper responding visual ranking were used to rank the test methods, measurements for sphericity. as described later. Measurements of angularity and texture of coarse aggregates were compared with visual rankings of aggregates made by Cost and Operational Characteristics five evaluators with backgrounds in asphalt pavements, con- of Test Methods crete pavements, geology, and petrographic analysis. These evaluators were provided with a form to fill with the rankings. Information about cost and operational characteristics R2 values between the evaluators for texture and angularity was collected from vendors, researchers, and operators who rankings are shown in Table 19. have familiarity with these systems for use in ranking the test The rankings made by the evaluators were more correlated methods. The information included cost, ease of use, portabil- for texture than for angularity. The evaluators suggested that ity, ability of interpreting data, readiness for implementation 1.00 0.90 0.80 Sphericity-Manual Measurements 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0.00 0.20 0.40 0.60 0.80 1.00 Sphericity-AIMS Figure 4. Comparison between sphericity measurements of AIMS and the digital caliper.