Hydrocarbon residuals and containment in microfine cement grouted sand

This study investigates the roles of contaminant-grout and contaminant-soil interactions on the effectiveness of grouting gasoline-contaminated soil for minimizing contaminant migration by substantially decreasing the permeability of the grouted mass and/or encapsulating contaminant residuals. Experiments were conducted to determine the bleed capacity, unconfined compressive strength, and microstructure of neat microfine grout at three water:cement ratios with up to 20% of gasoline contamination. The gasoline was found to significantly reduce sedimentation, lower the compressive strength, and become encapsulated in the grout matrix. To quantify the effects of various interactions in the contaminant-grout-soil system and the effectiveness of contaminant containment, microfine cement grouts were injected into three gradations of Ottawa sand subjected to six different pregrout scenarios to physically model different degrees of residual saturation. The contaminated sands were determined to have higher permeability and lower strength due to more porous interfacial zones and adsorbed contaminant layers on the sand surfaces. These microstructural features and encapsulated contaminant entities were documented by microscopy. A first approximation of the apparent mass of contaminant residual that may migrate from grouted sand was determined by leaching tests and gas chromatography; results were typically 50% greater in cases where gasoline saturated initially dry sand.