Precipitação do carbonato de cálcio por indução de enzimas como solução cimentante para estabilização do solo

Abstract

The purpose of this course conclusion paper was to justifies the use of the enzyme urease derived from agricultural product, on the precipitation of calcium carbonate (EICP) as an effective method for soil stabilization. This process uses calcium chloride, urea and the urease enzyme to induce carbonate precipitation in the soil, which in turn fills the voids acting as a cementitious solution, with many benefits, including an increase shear strength and increased liquefaction resistance. Other substances widely used for the purpose of improving the mechanical properties of the soil are guar gum and bentonite in sodium form, also studied in this work. Therefore, laboratory tests were performed in eighteen acrylic columns, produced with the intention of performing pumping tests to check the permeability coefficient over the months of May, June and July 2015, for thirteen weeks where the permeability test was held every Thursday. The columns were filled with soil and the substances so that three columns contained the precipitated calcium carbonate and were left at 24 °C of temperature; other three contained the same substance, but were left in the oven at 45 °C temperature. Four of them had the soil mixed with EICP and bentonite, where two were left at 24 °C and two were left in the oven at 45 °C. One column was submitted to the EICP procedure and was mixed with guar gum; and other with EICP, bentonite and guar gum together. The thirteenth column was mixed just to bentonite; the fourteenth column had only guar gum; and fifteenth was mixed with guar gum and bentonite together. Other three columns served as control, i.e., the soil was not mixed with any substance. All of these columns were tested under static conditions in order to reproduce on a smaller scale a real situation. The results of the test indicate that the technique of precipitate calcium carbonate in the soil through urease enzyme action is effective to reduce permeability of the soil, especially when mixed with guar gum in columns at 24 °C. Overall, no technique was more efficient in reducing the permeability separately compared to the use of two or more techniques combined. It is noteworthy that EICP, continued the desired cementing results of substances already known to be used for cementing purposes, guar gum and sodium bentonite, those which when used separately on the ground, lost efficiency over the months. This indicates that, the use of these techniques requires planning, since each substance used must be evaluated in accordance with the purpose, the desired degree of impermeability, local weather, and other factors that may influence.