Magnetorheological properties of calcium aluminate cements

Abstract

The rheological properties of materials exhibiting magnetorheological (MR) behavior can be controlled on-demand through the application of a magnetic field during flow. Conventional Portland cement (PC) systems require the addition of extra magnetic particles to exhibit MR properties. In contrast, high-iron calcium aluminate cement (HI-CAC) is a binder that naturally exhibits MR properties. This study is the first to investigate the origin of the intrinsic MR properties of HI-CAC by analyzing the mineralogical and microstructural characteristics of its magnetic phases. The MR behavior of HI-CAC pastes with two different water-to-cement (w/c) ratios was assessed using oscillatory and rotational rheometry with a specialized MR device. To characterize its magnetic phases, a sequential magnetic separation was performed, and the bulk-HI-CAC and its separated fractions were analyzed by a vibrating-sample magnetometer (VSM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Magnetic separation experiments showed that approximately 70% of the bulk HI-CAC responds even at 0.05 T, increasing to around 90% at 0.4 T. XRD and SEM–EDS analyses confirmed that magnetic properties originate from iron-bearing phases within the polymineralic structure of HI-CAC. Rheological tests demonstrated rapid manipulation of the viscoelastic and flow behaviors of HI-CAC pastes by an external magnetic field, indicating clear MR properties. The MR response depends strongly on the applied magnetic field strength and the w/c ratio. Comparisons with published data for PC-based MR mixtures at the same field strengths showed that the MR capacity of HI-CAC was substantially better than that of fly ash and fayalite slag incorporated PCs and comparable to nano-magnetite incorporated PC systems.