Magneto-rheology control of cement paste containing Fe3O4 nanoparticles in view of reducing or preventing formwork leakage

Based on the principle of active stiffening control (ASC) of cementitious materials, a magnetic field-based active stiffening control methodology has recently been introduced to reduce formwork leakage under pressure. In the current study, this magnetic field-based methodology is applied to cement pastes containing Fe3O4 nanoparticles as the magnetisable components. The effects of Fe3O4 nanoparticle concentration, paste rheology, and applied pressure on the magnetic field-based formwork leakage control are investigated. The experimental results showed that the ASC method is effective in reducing the flow rate for formwork pressures of 10-50 kPa, and completely blocking the flow at 10-20 kPa. The ASC method was found to be more beneficial for the more flowable pastes, which generally exhibit more leakage in practice. The efficacy of the ASC method is also significantly influenced by the Fe3O4 nanoparticles concentration. The required amount of Fe3O4 nanoparticles for flow reduction should thus be selected accordingly. Additionally, the relative change in plastic viscosity (k & mu;) and storage modulus (kG') due to the applied magnetic field could be used to reasonably estimate the flow reductions under magnetic field at 10-20 kPa. It is concluded that magneto-responsive additives are a suitable means in applying active stiffening control for formwork leakage reduction.