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

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 precipitation pattern on the unconfined compressive strength of sand treated via the enzyme induced calcite precipitation (EICP) technique. The micro-scale characteristics of CaCO3 (spatial distribution, shape, size and amount) at 3 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 unconfined compressive strength (UCS) of sands treated under each of these conditions via 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% CaCO3 content). In contrast, sparsely distributed, less uniform, and large-sized spherical crystals yielded higher values (maximum of 1.4 MPa at 3.9% CaCO3 content). The precipitation pattern of CaCO3 was found to significantly influence the UCS of EICP treated sand.