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The effect of curing time, content of grout solution and concentration of urea, calcium chloride and urease enzyme on the process of enzymatic calcium carbonate precipitation was analysed. Initially, the process was studied in test-tube experiments by evaluating the amount of calcium carbonate precipitated using X-ray diffraction tests. The method was then applied to stabilise a sandy soil to examine the strengthening effect using unconfined compressive strength tests, X-ray diffraction and scanning electron microscopy. The results showed the effectiveness of the method for improving the mechanical properties of a sandy soil. The soil strength and stiffness increased with increases in content of the grout solution and curing time, while an increase in the concentration of urease and urea–calcium chloride only had a positive effect for lower concentrations. The results also showed a relationship between unconfined compressive strength and calcium carbonate content and pH value.

RESUMO -Neste trabalho apresentam-se os resultados de uma investigação laboratorial que visa analisar os ganhos de resistência e rigidez de um solo arenoso, através da precipitação de carbonato de cálcio (CaCO3) por via enzimática, com base na adição de uma solução estabilizadora composta por água, ureia, cloreto de cálcio e a enzima urease. Inicialmente a eficiência da metodologia é analisada em tubos de ensaio com a determinação da massa de CaCO3 precipitada, sendo posteriormente testada em provetes de solo, com base em resultados de ensaios de compressão não confinada. São analisados os efeitos da concentração de enzima urease e do tempo de cura, no ganho de resistência e rigidez do solo estabilizado. Constata-se com o aumento da concentração de urease (até 4 kU/L) e do tempo de cura (até 7 dias) um significativo aumento de resistência e rigidez do solo. Ensaios de raios-X e imagens de microscópio eletrónico confirmam a precipitação de CaCO3.SYNOPSIS -This paper presents the results of a laboratory investigation with the aim of analysing the effect of enzymatically-induced calcium carbonate precipitation (CaCO3) on the strength and stiffness of a sandy soil. The stabilizer solution is composed of: water, urea, calcium chloride and the urease enzyme. Initially, this process is studied in test-tube experiments by the evaluation of the amount of CaCO3 precipitated. After this, the methodology is applied to stabilizing a soil based on the results of unconfined compressive strength tests. The effects of the amount of the urease enzyme and curing time used on the strength and stiffness of the stabilised soil are studied. An increase in the strength and stiffness of the stabilised soil is observed with the increase in the concentration of urease (less than 4 kU/L) and in the curing time (less than 7 days). X-ray power diffraction and scanning electron microscopy tests confirm the CaCO3 precipitation.Palavras Chave -Bioestabilização; biocimentação; precipitação de carbonato de cálcio; enzima urease.