Application of lime as an additive for controlling the volume change behavior and improving the strength of expansive soils has been in use over several decades. However, the contamination of lime-treated expansive soil with sulfate always results in the deterioration of treated expansive soil. Therefore, this paper highlights the effect of sodium sulfate solution on compaction and strength behavior of lime-treated expansive soil. Further, the effect of compaction time delay and contact period of sulfate solution with lime-treated soil is also brought out in this paper. To bring out the above effects, the lime contents corresponding to the initial consumption of lime (ICL) and ICL ± 1% were used along with sulfate solutions of 5000, 10,000 and 20,000 ppm. The experimental study showed that upon mixing the lime-treated expansive soil with sulfate solutions, the maximum dry unit weight decreased and optimum moisture content increased with increase in concentration of sulfate solutions when compacted without any compaction delay. With compaction time delay, the lime-stabilized soils mixed with distilled water led to the formation of flocs and aggregation of clay particles and decreased the maximum dry unit weight and optimum moisture content. However, the effect of compaction time delay was negligible on maximum dry unit weight as the formation of flocs and aggregation of clay particles were inhibited in lime-treated soil mixed with sulfate solutions. These changes in dry unit weights and soil structure were reflected on the strength of lime-treated expansive soil as well. © 2020, Springer Nature Switzerland AG.