Cement, Lime, and Fly Ashes in Stabilizing Expansive Soils: Performance Evaluation and Comparison

In this paper, the effectiveness of different chemical stabilizers in improving the engineering properties of expansive soils is investigated. Three different soils with variable sulfate contents were treated with Type I/II portland cement, lime, Class C fly ash (FA), and Class C FA-cement and Class F FA-cement blends. Specimens were subjected to Atterberg limits (LL/PI), pH, unconfined compressive strength, and volumetric swell tests. Test results indicated that cement was preferable for higher strength at shorter curing times (7 days), while lime produced the maximum strength at longer curing periods (90 days). It was deemed that 10% to 12% calcium oxide (CaO) in stabilizers was optimum for stabilizing expansive soils. In addition, CaO/SiO2 and CaO/(SiO2+Al2O3) ratios were found to be good indicators of pozzolanic activities at longer curing periods, and higher strengths were obtained when the ratios were between 2 and 2.5. Both cement and lime were prone to sulfate attack, which decreased the strength of soils (31% and 42% decrease, respectively) significantly, whereas strength reductions were lowered by treatments with FA and cement blends. Volumetric swelling of the soils decreased during the stabilization process depending on moisture, density, pH, clay content, curing time, stabilizers' constituents, and addition rates. Class C FA- and 50/50 FA-cement blends reduced the volumetric swellings of sulfate-rich expansive soils compared to those stabilized with cement and lime alone.