Effect of Solid Volume Fraction on the Magnetorheological Response of Nano-Fe3O4 Incorporated Cementitious Paste

Abstract

Magneto-induced rheology control is beneficial to overcome the opposing property requirements in different construction processes. The viscoelastic properties of paste medium have great effects on the movement and distribution of magnetic particles when applying an external magnetic field and thus the degree of the rheological response. In the present research, the effect of (total) solid volume fraction ϕ T on the magnetorheological (MR) response of nanoFe 3 O 4 incorporated cementitious paste, represented by the early structural build-up is experimentally investigated. Cementitious pastes with various solid volume fractions are achieved by changing the water-to-cement ratio (w=c) of the paste medium while the nanoFe 3 O 4 concentration remains unchanged. Results reveal that cementitious pastes with extremely low solid volume fractions acting as a dilute suspension show an insignificant increase in stiffness after applying an external magnetic field of 0.5 T, possibly due to the high surface to the surface separation distance between cement particles. Both the magnetic force between neighboring nanoparticles and the viscoelasticity of the suspension increase with increased solid volume fraction. At moderate solid volume fractions (e.g., 0.3 < ϕ T < 0.45), the formed magnetic clusters fill the voids between cement particles and thus increase the stiffness of the cementitious paste significantly. At relatively high solid volume fractions, despite the high magnetic force between nanoparticles, the dense particle packing limits the formation of magnetic clusters, and the MR response becomes indistinct. For the used cement and nano-Fe 3 O 4 particles, the suitable w=c of cementitious paste with pronounced MR response is in the range of 0.4-0.5.