Strengthening crushed coarse aggregates using bio-grouting

This paper focuses on using urea hydrolysis as a bio-grouting process to increase the strength of crushed aggregates commonly used in stone columns. Various reagent phases (2, 4, 6 and 12 phases) consisted of alternately percolating solutions containing bacterial suspension and cementation solution through the soil column. In addition, a multi-soil lift strategy with options of up to four soil lifts was undertaken to test the applicability of bio-grout to cement crushed aggregate columns. While the average amount of calcium carbonate precipitation was roughly unchanged in both techniques, the distribution within the crushed aggregate columns was heterogeneous. However, the distribution of the precipitated calcium carbonate is almost uniform in crushed aggregates treated by a two-soil lift strategy and a four-phase treatment strategy. It is also deducted that both techniques can be combined to gain a uniform calcium carbonate and strength along a long sand/stone column. Furthermore, a one-soil lift resulted in higher strength than using multi-soil lifts, and a maximum strength of approximately 2.3 MPa was achieved using 4-reagent phase treatment strategy. Scanning electron microscopy and electron dispersive spectroscopy analysis validate that calcium carbonate was deposited as white crystals on the surface of the crushed aggregate particles.