Volume 38, Issue 1 (January 2010)
Laboratory Performance Evaluation of Subgrade Soils Stabilized with Sulfate-Bearing Cementitious Additives
A laboratory study was conducted on both raw and stabilized soil specimens to evaluate the performance of two subgrade soils stabilized with three different additives, namely, hydrated lime (or lime), class C fly ash (CFA), and cement kiln dust (CKD). Lime, CFA, and CKD have low sulfate (<40 ppm), moderate sulfate (≈3,280 ppm), and high sulfate content (≈28,133 ppm), respectively. Cylindrical specimens were prepared with different percentages of additives and cured for 28 days. Following the curing period, specimens were tested for resilient modulus (Mr), and unconfined compressive strength tests (UCS), representing short-term performance. Long-term laboratory performance (or durability) was evaluated in terms of moisture susceptibility (tube suction test) and three-dimensional (3D) swell during 60-day capillary soaking of cured specimens. At the end of 60 days, the specimens were also tested for Mr and UCS, as additional indicators to long-term subgrade performance. Short-term performance evaluation projected 15 % CKD with the highest improvement after 28 days of curing, while long-term performance evaluation showed 9 % lime providing maximum enhancements in Mr and UCS values after 60 days of capillary soaking. The study further indicated decrease in durability of specimens stabilized with CKD; however, lime and CFA helped by reducing 3D swell and moisture susceptibility. This difference in behavior was attributed to the presence of elevated levels of sulfate in CKD resulting in sulfate-induced heaving of stabilized soil specimens. Mineralogical studies such as scanning electron microscopy and energy dispersive spectroscopy were also used to verify the research findings observed from the macro test results.