Field and Laboratory Evaluation of the Use of Lime Fly Ash to Replace Soil Cement as a Base Course

The performance of lime and fly ash-stabilized base as an alternative to soil-cement-stabilized base for flexible pavement systems on reconstructed highways in Louisiana is evaluated in this study. Historically Louisiana has used soil cement for most flexible base construction because of its low cost, high compressive strength, and ease of construction. However, soil cement is subject to excessive cracking due to shrinkage, which may decrease the expected pavement life. Lime and fly ash bases exhibit many of the same properties as soil-cement bases with potential for less shrinkage cracking. Lime and fly ash (Class C fly ash) test sections were installed on two Louisiana highway reconstruction projects in the northwestern part of the state. For each project, two 0.4-km (0.25-mi) test sections with different percentages of lime and fly ash were constructed. The remainder of each project was constructed with 8 percent soil-cement base by volume. On both projects, the first test section used 2 percent lime and 4 percent fly ash by weight for stabilization and the second test section used 3 percent lime and 6 percent fly ash. Test specimens were molded in the field during construction by using stabilized base material taken from the roadway immediately before compaction. Laboratory test specimens were made later with materials taken from, but not mixed at, the construction sites. Both field and laboratory samples were tested in unconfined compression at 7, 28, and 56 days. The overall unconfined compressive strength of lime and fly ash was 30 percent lower than that of soil cement.