Today's concrete is no longer a simple combination of cement, aggregates and water. With increased use of various types of waste materials as supplementary cementitious materials and chemical admixtures, material incompatibility problems have been observed in concrete construction. As a result, some of the greatest problems in concrete manufacturing occur when concrete does not stiffen or harden on time. To this end, a new innovative type of cementing technique (based on the principles of magnetorheology) is presented that allows for the real-time control over the stiffening or setting behavior of concrete. In traditional magnetorheological (MR) fluids, magnetic particles are mostly submerged in Newtonian carrier fluids using high volumetric contents (40-50%) of magnetic particles. A key interest in this work was to investigate if using a non-Newtonian carrier fluid like cement paste with low dosages of magnetic particles would yield an MR effect. Rheological tests were conducted on paste mixtures containing small dosages of magnetic particles (less than 2% volume fraction) and when a magnetic field was applied, it was determined that the shear resistance of the paste could be altered significantly. The response of the paste was found to be dependent on the magnitude of the applied field, concentration of the magnetic particles and surface chemistry of magnetic particles. Furthermore the magnetic particles used in this research to create the MR cement paste did not have any effect on cement hydration products or on compressive strength results. It was shown that the rheological behavior of cement paste could even be adapted to simulate "setting" behavior when an MR-based approach is used. Thus, the potential to create a cement-based material whose fresh state behavior can be adapted on-demand by the user to achieve a desired behavior may soon be a reality. Such a material can be useful in applications in which controlling the fresh-state behavior is critical, and could transform the way cement-based materials are cast. In addition, possibilities to create a smart cement-based composite from the fresh to the hardened state may be possible if the magnetic particles could later be used for structural health monitoring. / text

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