Effect of Dust Ratios on the Strength of Aggregates with Low Plasticity Fines

Unbound aggregate pavement base and subbase courses distribute wheel loads to protect subgrade. Appropriate selection of aggregate material is essential to ensure a stable and long lasting pavement. Both aggregate compaction and strength are influenced by the amount and nature of finer materials controlling the gradations of base and subbase. Current standards such as AASHTO and ASTM have suggested control limits on quantity and plasticity of fine contents. Proportion of percent passing No. 200 sieve to percent passing No. 40 sieve is called dust ratio, which defines the quantity of small sizes in a sample. However, many states either waived some of the AASHTO or ASTM criteria on fine contents or developed their own specific control measures for quantity and quality of fines in aggregates. This study has the objective to identify appropriate quantity control measures for inclusion of plastic fines, i.e., plasticity index of approximately 5%, in crushed limestone aggregates in Illinois. The results of standard Proctor type compaction and soaked CBR tests performed on samples after four days of soaking were used to identify the effects of the different dust ratios and percent fines contents on dry unit weight and aggregate strength.