Effects of curing environment and period on performance of lime-GGBS-treated gypseous soil

Abstract

Gypseous soils are regarded as a harmful soil, threating the safety of transportation infrastructure, including railway and road. Lime-activated ground granulated blastfurnace slag (GGBS) is effective for the treatment of gypseous soils; GGBS is a by-product from iron industry and has received more and more attention due to its sustainability advantages. However, the impacts of curing environment and period on the performance of lime-GGBS-treated gypseous soils, which are critical to field application, have not been well understood. Hence, this study attempted to fill this gap. Laboratory tests were conducted to explore the performance of lime-GGBS-treated gypseous soils cured in different environments (dry and moist) for different periods (7 and 21 days). Visual examination, swelling, and strength tests, were utilized to evaluate the performance of treated soils. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study their mineralogy and microstructure. Results showed that significant cracks occurred on the specimens cured in moist condition before and after soaking due to the formation of ettringite at the early age. Extending the curing period under dry condition from 7 to 21 days could decrease the vertical swelling and crack formation during soaking, which was because more cementitious products were produced in a longer curing period, resulting in higher resistance to swelling during soaking. Hence, in field projects, the treated soil layer should be covered by waterproof membrane, and wetting or moist curing must be avoided at the early age. The extension of curing period in dry condition is also recommended when it is possible in field.