Reference: D.P. Bentz, Submitted to Proceedings of  RILEM Conference, August 2006

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Four-Dimensional X-ray Microtomography Study of Water Movement during Internal Curing

Dale P. Bentz (1), Phillip M. Halleck (2), Abraham S. Grader (2), and John W. Roberts (3)

(1) National Institute of Standards and Technology, Gaithersburg, MD USA

(2) Pennsylvania State University, University Park, PA USA

(3) Northeast Solite Corporation, Richmond, VA USA




            While the effectiveness of internal curing has been verified via a variety of experimental measurements, including internal relative humidity, autogenous shrinkage, restrained shrinkage, strength development, and degree of hydration, a direct observation of water movement during internal curing in four dimensions (three spatial dimensions and time) has been lacking.  X-ray microtomography offers the possibility to dynamically monitor density changes in a material, during its curing process, for example.  In this paper, this technique is applied to monitoring water movement from saturated lightweight aggregate particles to the surrounding hydrating cement paste in a high performance mortar mixture over the course of the first 2 d of hydration at 30oC.  A four-dimensional data set is created by obtaining three-dimensional image sets on a single specimen after various hydration times, from just after mixing to after 47 h of hydration, with a voxel dimension of less than 20 μm, allowing a clear delineation of individual lightweight aggregate particles and much of their internal porosity.  Many of the changes in local density, corresponding to water movement, occur during the first 24 h of hydration, during the acceleratory period of the cement hydration reactions.  The four-dimensional data set is processed and analyzed to quantitatively estimate the volume of internal curing water that is supplied as a function of hydration time.  These microtomography-based observations of water movement are supported by more conventional measurements of hydration including non-evaporable water content via loss-on-ignition, chemical shrinkage, and heat of hydration via isothermal calorimetry.




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