Effect of nano-silica on engineering properties of lime-treated marl soil

One of the widely used methods for improving the engineering performance of problematic soils is in-situ or ex -situ mixing using various additives (conventionally cement and lime). In this research, the combination of nano-silica (NS) and lime additives is investigated for improving the geomechanical characteristics and engineering performance of sulfate-bearing marl soil, an expansive clayey sand soil. Due to the presence of sulfate ions, it is not appropriate to treated the soil using lime alone, and besides improving the soil's physical condition, the NS additive can chemically prevent the formation of bulky minerals (such as ettringite) arising from the reaction of lime with soil sulfate. A comprehensive program of physical/index, compaction, wetting-induced swelling, un-confined compression and direct-shear strength and soaking-durability testing was performed on marl soil treated with 0-8 % lime and 0-1.2 % NS additives, investigating the effects of 7, 14 and 28-day curing periods. Additions of 6 % lime + 1 % NS was identified as mobilizing the highest strength properties, practically the lowest swelling potential, and achieves superior durability under the soaking condition. NS addition to the lime -treated marl soil causes secondary CSH gel formation that prevents the ettringite growth, which improves the strength and stability of the treated soil. SEM and XRD analyses confirmed these findings, with the nature and strength of the CSH phase changing with curing duration.