Experimental Study on Macro and Meso Characteristics of Steel-Slag-Based Cemented Backfill Due to Microbial Mineralization Action

Steel slag is an industrial solid waste, which can provide a new calcium source for microbial mineralization as it contains abundant calcium elements. This study treated cemented backfill material with microorganisms and steel slag to enhance its performance. The influence of microbial treatment on the strength, microstructure, and pore characteristics of the backfill was assessed using a strength test, nuclear magnetic resonance, scanning electron microscopy, and X-ray diffraction. The results indicate that (1) the microbial mineralization and the hydration reaction take place at the same time; (2) when the proportion of bacterial solution exceeded 50%, microorganisms excessively consumed Ca²⁺, which hindered the following hydration reaction; (3) the additional amount of bacterial solution added into the steel-slag-based cemented backfill material should be less than 50%, which increases the strength by up to 22.10%; (4) the excessive bacterial solution sharply reduces the strength of the backfill even by 21.41%; and (5) the addition of bacterial solution affects the pore characteristics. A 50% bacterial solution can make backfill reach its lowest porosity. The strength has an inversely proportional relationship with porosity, diameter, and roundness (σ = ax + b, a < 0).