Microbially/CO2-derived CaCO3 cement strengthens calcareous sands and its cementation mechanism

Abstract

In this text, a method to use CO2 for the treatment of calcareous sand is presented. Carbon dioxide solidification-bacteria (Streptomyces microflavus) was obtained by screening and applied to the mechanical strengthening of calcareous sand through a microbial mineralization/carbonization process. Experiments in both liquid phase and sand were carried out. The optimal mass ratio of carbon dioxide solidification-bass cteria to calcium oxide was found to be 2:1. The optimal dosage of bacterial powder was 30% of the total dry sand mass. Using the optimal recipe, the average uniaxial compressive strength of treated sand columns was 3.67 MPa and the average permeability coefficient was 4.90 × 10−3 cm/s. Compared to the other microbial induced carbonate precipitation (MICP) approaches, the proposed method does not release harmful by-products such as ammonia. The chemical composition and microstructure of the treated calcareous sand were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that the CO2 carbonized product contained mainly calcite.Graphical abstract