Engineering Mechanics Institute Conference 2013

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Real time control of fresh state properties of concrete

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Sriramya Nair
The University of Texas at Austin
United States

Dr. Raissa Ferron
The University of Texas at Austin
United States

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 cementing 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, set or harden on time. To this end, the authors present a new innovative type of cementing technique that allows the contractor real time control over the stiffening or setting behavior of concrete. This smart technique is based on the principles of magnetorheology (MR). Cement-based MR fluids can be made by incorporating magnetic particles such as carbonyl iron powder (CIP) in to cement paste.
Small amplitude oscillatory shear tests were conducted on fresh cement-based MR paste and from Figure 1 it can be seen that, when CIP was added to the paste mixture and when a magnetic field was applied, the shear resistance of the paste changed significantly (note that the y-axis is in a log 10 scale). The results indicate the potential of optimizing the magnetic field to yield a certain performance. In all cases, the storage modulus for the cement-based MR fluid was significantly greater than that of the control pastes (0% CIP). This indicates the potential to create an MR mortar/concrete. The magnetic particles and the magnetic field did not have any negative effect on hydration products nor on compressive strength.
Such a material can be useful in applications in which controlling the fresh-state behavior of concrete is critical. The magnetic particles could later be used for structural health monitoring . This new cementing technique would ensure that the cement slurry or concrete is placed properly, thus enhancing the durability, service life, and sustainability of the concrete.


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