Enhancing magneto-rheology control of cement paste through synergistic effect of nano-Fe3O4 particles and fly ash

•Synergistic effect of MNPs and fly ash on magneto-rheological response is studied.•Fly ash compensates the negative impacts of MNPs on the rheological properties.•Early liquid-like behavior is strengthened for cement paste with MNPs and fly ash.•Incorporating fly ash in MNPs paste has a more effect on the relative MR effect. This research examines the enhancement of magneto-rheological (MR) behavior of cement paste containing magnetic nano-Fe3O4 particles (MNPs) by the value-added utilization of fly ash. It is revealed that substituting cement with fly ash mitigates the negative impact of MNPs on the viscoelastic properties of cement paste. The early improved liquid-like behavior induced by magnetic field is significantly strengthened in cement pastes with both MNPs and fly ash. However, the increased stiffness after prolonged magnetization remains lower than that without fly ash. Replacing cement with fly ash in MNPs-containing paste shows a more significant influence on improving relative MR effect rather than absolute MR effect. Results can be concluded that partially replacing cement with magnetic fly ash is a reasonable approach to prepare highly flowable MNPs-containing cement paste with pronounced MR response.