| Highways and roads provide a basis for transportation, and they are applicable as long as they are safe and usable. Pavement layers are in charge of bearing applied loads without deformation or failure at the surface. Among the layers, base and subbase serve a medium to gently transmit the pressure existing at the surface to the subgrade. Ripples at the surface usually are attributed to the failure in sublayers. Accordingly, resistant material should be placed as the base and subbase. Unbound aggregate is adopted as material in the base and subbase. 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 the No. 200 sieve while dust ratio is defined as the ratio of the percent passing the No. 200 to the percent passing the No. 40 sieve. There are inconsistencies among standards and specifications that are meant to ensure end-performance related quality aspects of aggregates. In this research, 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 CBR and staged triaxial methods. 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 soaked CBR 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. Moreover, staged triaxial and soaked CBR results show that the current values of plasticity index and dust ratio may be capped at higher extent. A strong relation between fine quantity (i.e. passing the No. 200 sieve) and dust ratio was observed. Among all studied index properties fines content showed dominant effect on strength characteristics of aggregate. |
