Assessment of the effect of Ground Granulated Blast-furnace Slag (GGBS) and activated GGBS on stabilization of a clay soil contaminated with glycerol
Natural clay soils may be contaminated with hydrocarbons due to the leakage from storage tanks or from accidental spills, etc. Interaction between the soil and contaminant can result in changes in the behavior of the soil. In order to carry out construction projects on these sites, the contaminated soil should be treated and stabilized to ensure its mechanical and hydraulic performance through the service life of the project. Contaminated soils can be stabilized using chemical agents such as lime, cement and fly ash. Due to the economic and environmental problems associated with lime and cement, alternative agents are proposed for soil stabilization. It’s been proven that Ground Granulated Blast Furnace Slag (GGBS) can serve as an effective agent for soil stabilization. GGBS has mild cementitious characteristics when it is used alone. However, GGBS can be activated by using chemical activators. The aim of this work is to study the effects of GGBS, GGBS+MgO and GGBS+MgO+cement on stabilization of a clay soil contaminated with glycerol.
The main materials used in this work included soil, glycerol, GGBS, MgO, water and cement. The clay soil used was classified as a clay soil with low plasticity (CL). The clay soil was contaminated with 4, 8 and 12% solutions of glycerol based on dry weight. GGBS, GGBS+MgO (with a weight ratio of 3:1) and GGBS+MgO+cement (with a weight ratio of 3:0.5:0.5) were considered for preparing the addictive mixtures. Samples were prepared by mixing contaminated soil with 5, 10 and 15% of the above agents. The prepared samples with different stabilizers were stored for curing times of 7, 14, and 28 days. Various tests including Atterberg limits, compaction and unconfined compressive strength (UCS) were then performed on mentioned samples including the natural soil and the contaminated soil mixed with various percentages of the selected agents. Scanning electron microscopy (SEM) were also conducted on several samples to obtain information about the microstructure of the samples under different conditions.
For soil contaminated with different percentages of glycerol, the values of Liquid Limit, Plastic Limit and Plastic Index decreased compared to the natural soil. The reduction in LL and PL values depended on the percentage of glycerol, with a higher reduction observed with increasing glycerol content . The Atterberg limits of the contaminated soil also changed when different mixtures of agents were added at a constant percentage of glycerol. The results of compaction tests showed that for soil contaminated with 4% glycerol, the maximum dry unit weight decreased and optimum water content increased compared to natural soil. However, For the soil contaminated with 8 and 12% glycerol, both maximum dry unit weight and optimum water content increased relative to natural soil.
The final strength of the natural soil is 420 kPa and it changed to 321, 293 and 266 kPa when contaminated with 4, 8 and 12% glycerol, respectively. It was observed that increasing the percentage of glycerol led to a decrease in the strength and E50 of the contaminated soil. It can be said that both the dielectric constant and the viscosity of glycerol solution also has an important effect on the behavior of the soil and lead to reduction in final strength. The results show that increase in both curing times and percentages of GGBS, result in increase in final strength, stiffness and the value of E50. It may be due to the fact that reaction between GGBS and clay soil is a cementation process similar to the cementation process between clay and Portland cement. Gels (cementitious materials) produced in this process bind and coat the particles, thereby increasing the strength of the soil stabilized with GGBS. Furthermore, using mixtures of GGBS+MgO and GGBS+MgO+cement as agents proved effective in increasing the final strength and E50 of both natural and contaminated soil. The gels produced during hydration can bind the particles together and fill the pores between them, enhancing the strength of the soil. The results also revealed that activating GGBS with MgO or a mixture of MgO and cement was more effective in increasing strength for different percentages of the agents at various curing times.