Field and lab evaluation of the use of lime fly ash to replace soil cement as a base course.

PDFTech ReportFHWA/LA.97/303Lime fly ashSoil cementSoil stabilizationBase course (Pavements)EvaluationFlexible pavementsCrackingTestsLouisianaLouisiana Transportation Research CenterShirazi, H.Johnston, KenLouisiana Transportation Research CenterUnited States. Federal Highway AdministrationUS Transportation CollectionThis study evaluates the performance of lime/fly ash stabilized base as an alternative to soil cement stabilized base for flexible pavement systems on reconstructed highways in Louisiana. Louisiana has historically used soil cement for most flexible base construction due to 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/fly ash (Class C fly ash) test sections were installed on two Louisiana highway reconstruction projects, located in the northwestern part of the state. For each project, two 0.4 km (0.25 mile) test sections with different percentages of lime and fly ash were constructed. The remainder of each project was constructed using 8 percent soil cement base by volume. For both projects, the first test section used 2 percent lime/ 4 percent fly ash by weight for stabilization and the second test section used 3 percent lime/ 6 percent fly ash.Test specimens were molded in the field during construction using stabilized base material taken from the roadway immediately prior to compaction. Laboratory test specimens were made later using 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/ fly ash was 30 percent lower than that of soil cement.After the reconstruction was completed, monitoring strips were marked to indicate test sections and control sections for both highways. Crack mapping and Dynaflect readings were taken periodically for five years. Rut\ue2\u20ac\u2122depth measurements were taken at five years. The lime/fly ash section showed less cracking than the soil cement section. The cracks were 52 linear feet per 100 foot test lane for 2 percent lime/4 percent ash, 81 linear feet per 100 foot test lane for 3 percent lime/6 percent fly ash, and 403 linear feet per 100 foot test lane of 8 percent soil cement by volume, respectively. The overall average of structural numbers determined from Dynaflect were 3.4 for soil cement and 4.5 for lime/fly ash mixture. The subgrade modulus was lower for lime/fly ash by 2000 psi.Testing and monitoring results are presented. Recommendations concerning the use of lime/fly ash as a substitute for soil cement base are made based on the test section performance