Comparative Evaluation of Stabilized Subbase Courses

Abstract

On a rural road near Ada, Oklahoma, four test sections were constructed with treated subbases. Treated subbases in three sections were constructed using Portland cement kiln dust (CKD) from three different sources and one was constructed using granular quick lime. The purpose of the study was to compare the effectiveness of the three CKD sources and granular quick lime for modifying and stabilizing moderate to highly plastic soils. To evaluate the effectiveness of the various additives, treated soil was collected immediately before compaction to prepare unconfined compression test (UCT) samples that were used to assess strength gain after 7 and 28 days of curing. In addition, dynamic cone penetration (DCP) tests were conducted at different times after compaction, and falling weight deflectometer (FWD) tests were conducted on the finished flexible pavement. A comparison of results indicates there is agreement between the trend of cone index (CI) values from DCP tests and unconfined compression strength data along the roadway alignment. Furthermore, the DCP results give an indication of the variation in strength with depth, an advantage that the other forms of testing lack. Unconfined compression test results and DCP data do not correlate as well with the FWD data, apparently because the FWD results are less sensitive to differences in the treated subbase moduli for each section. This study shows that a reliable comparison of stabilized subbase courses for different test sections requires field testing to account for variations in field compaction and soil type, and laboratory testing to assess the relative effect of the soil additives on strength.