Experimental study on the mechanical properties of microbial mixed backfill

Cemented backfill mining is an important technology utilized in sustainable mining practices and is fundamental in a wide variety of underground settings. However, the cement-based binder commonly used in cemented backfill materials comes at high costs, is highly alkaline, has high energy consumption, and has high carbon dioxide emissions. As an environmentally friendly technology, microbial induced carbonate precipitation (MICP) technology can produce a variety of cementitious mineral crystals to consolidate otherwise loose materials. In this paper, the MICP technology is used to replace the traditional cement based binder frequently used in backfill mining, and the microbial mixed backfill (MMB) method is presented. The influences of various factors on the mechanical properties of MMB are also studied. It is found that the strength of MMB samples increases at first, and then decreases, when the cementation solution concentration and the volume ratio of bacterial solution to cementation solution are increased. Solids content is also an important factor that directly affects the strength of MMB samples. However, there was no obvious relationship discovered between strength variation and the total enzyme activity. In addition, different crystal morphologies of calcium carbonate, including calcite and vaterite, are observed in MMB samples. The greater the number and the denser the distribution of calcium carbonate crystals produced in the MICP reaction, the higher the strength of the MMB samples. The strength of MMB is attributed to both the amount of precipitated calcium carbonate by MICP, and the dosage of salt materials contained in the cementation solution. This research can provide basic scientific support for the application of microbial backfilling in the mining field. (C) 2020 Elsevier Ltd. All rights reserved.