Testing and Modeling the Short-Term Behavior of Lime and Fly Ash Treated Sulfate Contaminated CL Soil

Abstract

In this study, the effects of calcium sulfate contaminated soil treatment methods on the index properties, compacted soil properties, free swelling and compressive stress strain relationship of a CL soil obtained from the field was investigated. Calcium sulfate concentration in the soil was varied up to 4 % (40,000 ppm) and the soil samples were cured for seven days at 25 °C and 100 % humidity before testing. With 4 % sulfate contamination the liquid limit and plasticity index of the soil increased by 44 and 81 % respectively. The free swelling increased from 7 to 18 % and the compressive strength decreased by 65 % with 4 % of calcium sulfate, Also the study investigated the effects of fly ash (class C) and hydrated lime treatment on the behavior of treated sulfate soils. X-ray diffraction (XRD) was used to characterize the soil and the reaction products of lime and fly ash treated soils. Based on XRD analyses, major constituents of the CL soil were calcium silicate (CaSiO3), aluminum silicate (Al2SiO5), magnesium silicate (MgSiO3) and quartz (SiO2). Addition of calcium sulfate resulted in the formation of calcium silicate sulfate [Ternesite Ca5(SiO4)2SO4] and aluminum silicate sulfate [Al5(SiO4)2SO4]. Treatment with lime resulted in the formation of ettringite [Ca6Al2(SO4)3(OH)12·26H2O]. Treating with fly ash resulted in the formation of calcium silicate hydrate (CaSiO3H2O) and magnesium silicate hydrate (Mg3SiO3H2O), cementing by products. Contaminated soil treatment with lime and fly ash reduced the index properties and free swelling and increased the short-term compressive strength of the soil. Behavior of the compacted sulfate soils, with and without treatment, has been quantified using a unique model that was used to represent both linear and nonlinear responses. Also the model predications were compared with other published data in the literature. Compressive stress–strain relationships of the sulfate soil, with and without lime and fly ash, have been quantified using a nonlinear constitutive model. The constitutive model parameters were sensitive to the calcium sulfate content and the type of treatment. Compared to the fly ash treatment, the lime treatment reduced the strain at peak stress making the lime treated soil more brittle.