## 3 Results and Discussion
### Flow Rate  
The mass of material flowing out of the test cylinder was measured continuously during testing. The loss of mass from the test cylinder relative to the initial mass in the 250 mm height of fluid (\(M_{loss}\)) could thus be determined. The \(M_{loss}\) as a function of time under 30 kPa overhead pressure is plotted in Figure 10. Despite having different packing  
Figure 9: Effect of sand volume fraction on magneto response and increase in storage modulus at 300 s. * Repetition of test on a different batch. densities, the M0, M1, M2, and M3 mixtures exhibited similar flow behaviour, i.e., mass flow, with similar flow rates when no magnetic field was applied. The slope of the \(M_{\text{loss}}\) curve remained relatively constant until the end of the test when the test cylinder was almost completely emptied, except for the material in the dead zones. The M4 mixture, however, deviated from mass flow and exhibited significant filtration effects from the onset of flow. Only the liquid fraction was lost from the cylinder, and therefore the percentage mass loss was extremely low. However, the filtration process continued until most of the liquid fraction within the vicinity of the gap was lost. On the contrary, when a magnetic field of 0.65 T was applied, the flow rates of all the mixtures decreased. The M1, M2, and M3 mixtures only show a reduction in slope, with no changes to the net mass of outflow at the end of the test. The M0 mixture, however, not only showed a reduction in the initial slope, but the slope continued to decrease until it reached a plateau, indicating that complete blockage occurred. This resulted in an approximately 40% reduction in mass loss. For the M40 mixture, the slope was effectively reduced to zero and the filtration effect was not detectable. The reduction in slope is due to the formation of magnetic clusters at the outflow region [9]. As the mixture flows through the magnetic field, the magnetisable particles are deposited onto the walls of the outflow channel that pinch the flow width inwards, like an MR fluid in the magnetic gradient pinch mode [26]. The mass flow rate \(\dot{m}\) can be obtained by computing the slope of the \(M_{\text{loss}}\) curves. For comparative reasons, the mass flow rate was converted into a volumetric flow rate since the mixtures had different densities. The linear slope indicates a constant flow rate, with little to no blocking, and thus it was assumed that the density of the material flowing out of the cylinder remained unchanged. In the cases where blocking was observed, the flow rate was only computed during the initial flow stage when the slope of the \(M_{\text{loss}}\) curve was approximately constant [9]. In the case of filtration, since it was predominantly the liquid fraction that was lost from the sample, the density of material was assumed to be that of  
Figure 10: Relative mass loss as a function of time without ASC (solid lines) and with ASC (dashed lines). water. The computed flow rates with and without ASC are plotted in Figure 11 and show the effect of percentage sand volume on the magnetically induced flow reduction. Our results showed that when there are no sand grains in the mixture, the packing density is lower, the excess water is higher, and the MNPs have more freedom to move and form clusters. As the clusters deposit on the walls of the outflow, they accumulate and lead to complete blockage of the flow. When the sand volume is increased up to 30%, the packing density is increased, and the excess water decreased. However, it is hypothesised that the percentage concentration of sand in the mixture is still sufficiently low, such that the interparticle interactions between the sand particles are still below the level at which large interlocking actions can be observed. There is still sufficient room for the aggregates to move freely within the paste.