Engineering Properties of Bacterially Induced Calcite Formations

This article presents the engineering properties of bacterially induced calcite formations, which are often referred to as microbially induced calcite precipitation (MICP) via ureolysis ongranular formations consisting of loose and collapsible river sand. Two sets of experiments consisting of five sand columns each were treated using urease-producing bacteria, urea and calcium chloride solutions.The reaction produced biomineralized calcium carbonate crystals (referred to as calcite) that bind and stiffen the sand grains. The reaction was checked by measuring the pH level. The pH values of the effluent solution taken from the initial stage to day 14 of the treatment ranged from 7 to 8. When the pH reading was in alkaline range (<7), there was significant calcite formation. The strength gained in the treated specimens was estimated from the unconfined compression tests and obtained in the range 1.1–2.18 MPa based on 4.0–8.0% calcite content at different reaction times. Calcite formation within the biocemented sand was ascertained from scanning electron microscopic images. The grain-size distribution of the untreated and treated formations was compared. It was observed that the increase in grain size of treated formation was a function of MICP. The collapse potential of the formation reduced as a result of bacterially induced calcite precipitation. The strength of the bacterially induced calcite formations was comparable to soft rocks.