Results of Soaked and Unsoaked California Bearing Rate Tests on Unbound Aggregates with Varying Amounts of Fines and Dust Ratios

Abstract

Unbound aggregate base and subbase courses consist of coarse-grained materials with limited percentages of fines (i.e., passing the No. 200 sieve) allowed. The fines are mineral fillers that occupy the void spaces between the sand and gravel-sized particles. An excessive quantity of fines can negatively affect the strength characteristics of unbound aggregate layers, and this effect can easily be aggravated when the matrix is saturated. A set of unsoaked and soaked California bearing ratio (CBR) tests were performed on engineered gradations of unbound aggregate samples so that the effect of soaking on CBR test results could be studied. A detailed comparison between soaked and unsoaked CBR results was carried out by considering various index properties, such as the fines content, plasticity index, and dust ratio (percentage passing the No. 200 sieve divided by the percentage passing the No. 40 sieve). It was found that higher plasticity indexes, such as 9% and 13%, have a negative effect on both soaked and unsoaked CBR values for samples with a dust ratio of 1.0. Samples with a dust ratio of 0.4 were, in general, not influenced by soaking in terms of the CBR index. Moreover, the effect of soaking on strength reduction was noticeable when the fines content was as high as 12% and the dust ratio was greater than 0.6. Furthermore, a correlation between soaked and unsoaked CBR is also proposed on the basis of experimental results obtained from this study.