Biostabilization of a Sandy Soil Using Enzymatic Calcium Carbonate Precipitation

Abstract

The use of soils with poor mechanical properties frequently requires the improvement of their characteristics, mainly the strength and stiffness. One possible technique utilizes precipitated calcium carbonate (CaCO3). However this methodology usually requires a complex and sensitive process of cultivation and storage of the bacteria, which may make field applications difficult. In order to avoid this, an alternative process to promote CaCO3 precipitation is the enzymatic CaCO3 precipitation which is performed by mixing the soil with urea, calcium chloride and the urease enzyme. Thus, the aim of this work is to analyze the effect of the amount of the urea and calcium chloride on the biocalcification process. Initially, the methodology is studied in test-tube experiments, through the evaluation of the amount of CaCO3 precipitated and XRD tests to verify the existence of CaCO3. After these tests, the methodology is tested with a sandy soil to examine its strengthening effects, using the results of unconfined compressive strength tests. The results obtained confirm the precipitation of CaCO3 and the effectiveness of this methodology in improving the characteristics of a sandy soil, they also show that the increase of the urea-CaCl2 concentration may inhibit the activity of urease.