Active Rheology Control (ARC) represents an innovative concept to control the rheological behavior of cementitious materials. By incorporating magneto-responsive particles, rheological properties can be modified in a targeted manner through the application of an external magnetic field. However, many of the particles studied present challenges in terms of cost and availability, limiting their suitability for large-scale applications. Therefore, there is an increasing need to identify more economical and environmentally friendly alternatives. In this study, two different residual materials in the form of slags, representing promising candidates to exhibit magneto-responsive behavior, were investigated. Their magnetic properties were analyzed using vibrating sample magnetometry, while particle size distributions were determined by means of laser diffraction. Additionally, oscillatory rheometer tests with a magnetorheological device were used to evaluate the magnetorheological behavior of slag-including cement pastes. The results reveal that both slag materials exhibit a pronounced magnetorheological response, that is furthermore strongly dependent on the particle dosage. With these findings, the range of suitable materials for ARC expands, contributing to the development of more sustainable, eco-efficient cementitious systems with enhanced functional properties.