Biogrouting Method for Stronger Bond Strength for Aggregates

Microbial-induced carbonate precipitation (MICP) methods have been developed in recent years for soil improvement to simultaneously increase the shear strength and reduce the permeability of soil or aggregate. However, this method is difficult to use for aggregate because many more injections are required. This technical note proposes a new biogrouting method for aggregates. In this method, biogrout solution containing bioslurry is injected before injection of cementation solution alone into aggregate, which is kept in an unsaturated state. Due to the capillary effect, more calcium carbonate crystals in the bioslurry are retained around the contact points of the particles, rather than in the pores. As a result, this method can achieve a higher shear strength (2.98 MPa) for biogrouted aggregate compared with that using other MICP methods (0.78 MPa) at the same level of calcium carbonate content. Therefore, the permeability reduction also is smaller using this method. The proposed method can be used for applications which require only an increase in strength, such as for granular base for pavement or the toe drainage of a slope.