Effect of precipitation pattern of enzyme-induced calcite on compressive strength of sand

Abstract

The biocementation of sand through calcite precipitation is a promising approach that has been investigated for nearly 10 years as an attempt to find practical solutions to ground improvement challenges due to sustainability considerations. This study aims to evaluate the effect of the precipitation pattern on the unconfined compressive strength (UCS) of sand treated through the enzyme-induced calcite precipitation (EICP) technique. The microscale characteristics of calcium carbonate (CaCO3) (spatial distribution, shape, size and amount) under three different precipitation conditions (EICP, skim-milk-added EICP and EICP on calcite-nanoparticle-coated medium) were investigated through microfluidic chip experiments. The outcomes of these observations were linked to the UCS of sands treated under each of these conditions through column tests. The densely packed, homogeneous and small-sized rhombohedral crystals promoted by the nanoparticle-coated condition led to lower UCS values (maximum of 0.15 MPa at 5% calcium carbonate content). In contrast, sparsely distributed, less uniform and large-sized spherical crystals yielded higher values (maximum of 1.4 MPa at 3.9% calcium carbonate content). The precipitation pattern of calcium carbonate was found to influence significantly the UCS of EICP-treated sand.