EXPERIMENTAL STUDY ON THE EFFECT OF CALCIUM SOURCES AND CA²⁺ CONCENTRATION ON EICP CURED CALCAREOUS SAND

Enzyme-induced calcium carbonate precipitation(EICP) is an environmentally friendly and efficient soil consolidation technique,and the type of calcium source may affect its consolidation effect. In order to quantify the effect of calcium source on EICP-cured calcareous sands,experiments on sand column curing with different calcium sources(calcium chloride,calcium acetate,calcium lactate,calcium nitrate) and different Ca²⁺ concentrations(0.25 M,0.5 M,0.75 M,1 M) and aqueous solution experiments were carried out in this paper. The effects of EICP curing of calcareous sands were explored and analysed from macroscopic and microscopic perspectives through unconfined compressive tests,permeability tests,calcium carbonate production measurements,SEM test analyses. The results showed that the strength of specimens cured with calcium chloride as the calcium source is higher at higher calcium ion concentrations(Ca²⁺＝1 M) and calcium nitrate as the calcium source at lower calcium ion concentrations(Ca²⁺≤0.75 M). In terms of reducing the permeability of the specimen: calcium acetate>calcium chloride>calcium nitrate>calcium lactate,with the most significant decrease in permeability of specimens cured with calcium acetate as the calcium source. The crystal types and microscopic morphology of the precipitation products differ between calcium sources. Calcium chloride and calcium acetate as calcium sources formed rhombic-shaped calcium carbonate crystals. The calcium carbonate crystals formed by calcium lactate as the calcium source were triangular in shape and smaller in size. Calcium acetate as calcium source produces calcium carbonate crystals with irregular spherical shape formed by wrapping several small spheres.