Over the past four decades, a number of experimental studies have been carried out for relating engineering and hydrogeological properties of soils with pore fluid composition which can change as a consequence of chemical pollution. Special attention was paid on petrochemicals and hydrocarbon-based fluids, with particular regards to the effect of transport fuels (gasoline, diesel and kerosene), on Atterberg limit, compressibility and permeability of soils. In the last years the energetic plans of many country in the world promote the using of gasoline added with bio-fuels, such as bio-ethanol, with the purpose to control air pollution emission. It is expected in the future for gasoline with high-ethanol content an increase of episodes of soil contamination, as occurred in the last decades for conventional transport fuels. The present work shows the results of different laboratory investigations (Atterberg limit and oedometer test) conducted on a remolded commercial kaolinitic clay contaminated by bioethanol-gasoline blends. Liquid limit was determined by using the fall cone test which is very simple to perform and it is less operator-dependent than the Casagrande percussion method. Some difficulties were encountered to perform oedometer tests with contaminated soils due to the high volatility of both gasoline and ethanol: to reduce the fluid evaporation during the test the entire consolidation cell was enclosed within a plastic bag. In addition to eliminate the micro and macro-cracks produced by ethanol-gasoline blends on the oedometer cell body, the perplex cylinder was replaced with a glass one. Samples were prepared mixing the kaolinitic soil with distilled water and with gasoline to which several fractions of bio-ethanol were added. Ethanol was added in the gasoline in weight fraction up to 85%: in order to prevent phase separation of the water and gasoline in the blend (de‐mixing), anhydrous ethanol (high purity ethanol) was employed (water content is below 1%). Physicochemical properties of pore fluid influence the van der Waals attractive force of clay and its fabric. When water is used as pore fluid (dielectric constant of about 80), the structure of the kaolinite leads to a parallel-arrayed clay. On the contrary when bio-ethanol is added in the gasoline in weight fraction of 10% (E10, dielectric constant of about 2.8) the structure of the kaolinite leads to a more flocculated soil. These physicochemical effects influence both equivalent liquid limit and compression index values of soil which reach the highest values when E10 is used as pore fluid, respectively of 80% and 0.60. On the contrary when soil is mixed with water both properties decrease respectively of 28% and 43%. A relative minimum of compression index was observed for a dielectric constant between 6.2 and 15.7. The oedometer tests were also used to investigate indirectly changes in permeability during compression due to the different pore fluid composition. As observed for compressibility the presence of bioethanol and gasoline increases significantly the permeability. The results obtained may be useful to increase the knowledge on the modification of physical properties of low plasticity soils due to accidental contamination of bio-fuels.

Physical properties of kaolinitic soil contaminated by bioethanol-gasoline blends

DI MATTEO, Lucio;
2011

Abstract

Over the past four decades, a number of experimental studies have been carried out for relating engineering and hydrogeological properties of soils with pore fluid composition which can change as a consequence of chemical pollution. Special attention was paid on petrochemicals and hydrocarbon-based fluids, with particular regards to the effect of transport fuels (gasoline, diesel and kerosene), on Atterberg limit, compressibility and permeability of soils. In the last years the energetic plans of many country in the world promote the using of gasoline added with bio-fuels, such as bio-ethanol, with the purpose to control air pollution emission. It is expected in the future for gasoline with high-ethanol content an increase of episodes of soil contamination, as occurred in the last decades for conventional transport fuels. The present work shows the results of different laboratory investigations (Atterberg limit and oedometer test) conducted on a remolded commercial kaolinitic clay contaminated by bioethanol-gasoline blends. Liquid limit was determined by using the fall cone test which is very simple to perform and it is less operator-dependent than the Casagrande percussion method. Some difficulties were encountered to perform oedometer tests with contaminated soils due to the high volatility of both gasoline and ethanol: to reduce the fluid evaporation during the test the entire consolidation cell was enclosed within a plastic bag. In addition to eliminate the micro and macro-cracks produced by ethanol-gasoline blends on the oedometer cell body, the perplex cylinder was replaced with a glass one. Samples were prepared mixing the kaolinitic soil with distilled water and with gasoline to which several fractions of bio-ethanol were added. Ethanol was added in the gasoline in weight fraction up to 85%: in order to prevent phase separation of the water and gasoline in the blend (de‐mixing), anhydrous ethanol (high purity ethanol) was employed (water content is below 1%). Physicochemical properties of pore fluid influence the van der Waals attractive force of clay and its fabric. When water is used as pore fluid (dielectric constant of about 80), the structure of the kaolinite leads to a parallel-arrayed clay. On the contrary when bio-ethanol is added in the gasoline in weight fraction of 10% (E10, dielectric constant of about 2.8) the structure of the kaolinite leads to a more flocculated soil. These physicochemical effects influence both equivalent liquid limit and compression index values of soil which reach the highest values when E10 is used as pore fluid, respectively of 80% and 0.60. On the contrary when soil is mixed with water both properties decrease respectively of 28% and 43%. A relative minimum of compression index was observed for a dielectric constant between 6.2 and 15.7. The oedometer tests were also used to investigate indirectly changes in permeability during compression due to the different pore fluid composition. As observed for compressibility the presence of bioethanol and gasoline increases significantly the permeability. The results obtained may be useful to increase the knowledge on the modification of physical properties of low plasticity soils due to accidental contamination of bio-fuels.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11391/366897
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