Effects of adding aluminum ion flocculant on MICP reinforcement of sand

Microbially induced carbonate precipitation (MICP) is a potential method for ground improvement. It can enhance the physical and mechanical properties of soils through soil particle cementation and pore filling. However, the excessive number of injections of cementing solution required for MICP is a major limitation for practical engineering application. To reduce the number of injections and improve the efficiency of the cementing process, an enhancement method was investigated in this study in which an aluminum ion flocculant (AIF) was added to the cementing solution. It can enhance the curing rate and effect of MICP. Experiments were carried out on MICP-treated sand columns, MICP-treated glass beads and aqueous solutions, and the influence of AIF on the production of calcium carbonate and unconfined compressive strength (UCS) was studied. The effect of AIF on the composition and morphology of the deposited calcium carbonate was evaluated from SEM micrographs and other microscopic observations. The results of the study showed that the addition of AIF to the cementing solution significantly reduced the number of injections required and increased the UCS of the reinforcement compared to those of a control group without adding AIF. The proposed method resulted in the experimental sand column being reinforced after 3 treatments of the cementing solution with an UCS of 323.3 kPa. The UCS reaches 1692 kPa after 5 treatments of the cementing solution, compared to 9 treatments using the conventional method. The UCS was 3.2–12.7 times higher than that of the control group for the same calcium carbonate content.