Conventional flexible pavement includes base and subbase layers which are constructed upon subgrade soils for supporting traffic loads. Longevity of the flexible pavement is dependent upon the load carrying capacity of these unbound aggregate layers. In this study, quality of crushed limestone and crushed gravel, commonly used material in Illinois base/subbase, were studied. The goal is to define the limits of different index properties influencing the strength of unbound aggregate. Material type, gradation, maximum particle size, fines content, dust ratio and plasticity index are the different variables considered. Dust ratio is defined as the amount of material passing No. 200 sieve to material passing the No. 40 sieve. Aggregate with maximum particle size of 25 mm (i.e., CA 6) as well as 50 mm (i.e., CA 2) were adopted for this study. Plasticity index, fines content, dust ratio ranged from 5 to 13 %, 5 to 12 %, and 0.4 to 1.0, respectively. California Bearing Ratio (CBR) and staged triaxial tests were performed to investigate the material strength. CBR test was performed by soaking sample in water for four days to achieve a lowest possible strength. Higher strength was observed for CA 6 graded aggregates with 25 mm maximum particle size compared to CA 2 graded aggregates. With a common variation in index properties, a dust ratio of 1.0 was found viable for application in some cases as it provided a reasonable soaked strength for both crushed limestone and gravel. However, for both material types, the combination of dust ratio of 0.4 and fines content of 12% has a severe negative effect on aggregate strength.
|Commitee:||Fries, Ryan, Qi, Yan|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 57/05M(E), Masters Abstracts International|
|Subjects:||Geotechnology, Civil engineering|
|Keywords:||Dust ratio, Fines content, Flexible pavement, Limestone, Soaked CBR, Unbound aggregates|
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