Crushed limestone aggregate strength influenced by gradation, fines content, and dust ratio

Quality classes of aggregate materials used in unbound base and subbase construction are quite important for the longevity of highway pavements. Aggregate gradation, fines content, Atterberg limits, and dust ratio all influence the quality aspect. Fines content is the percent passing a No. 200 sieve, whereas dust ratio is defined as the ratio of percent passing a No. 200 to the percent passing a No. 40 sieve. There are inconsistencies among standards and specifications that are meant to ensure end-performance-related quality aspects of aggregates. In this study, effects of aggregate index properties, i.e., maximum particle size, dust ratio, fines content, plasticity index, and gradation, on the strength properties of crushed limestone aggregates are investigated using the soaked California bearing ration (CBR) method. Two different gradations of crushed limestone aggregate with maximum particle sizes of 25 mm (1 in.) and 50 mm (2 in.) were evaluated for strength when plasticity indices, dust ratios, and fines contents were varied in a consistent test matrix. The soaked CBR results clearly showed that fines content, maximum particle size, and dust ratio all influenced the aggregate strength in an interactive manner. Based on the results of the laboratory tests conducted on the two aggregate gradations and statistical analyses, a set of strength zones were proposed for the different fines contents and dust ratios studied.