NIST Time|NIST Home|About NIST|Contact NIST

HomeAll Years:AuthorKeywordTitle2005-2010:AuthorKeywordTitle

Four-Dimensional X-Ray Microtomography Study of Water Movement During Internal Curing.


pdf icon Four-Dimensional X-Ray Microtomography Study of Water Movement During Internal Curing. (503 K)
Bentz, D. P.; Halleck, P. M.; Grader, A. S.; Roberts, J. W.

Volume Changes of Hardening Concrete: Testing and Mitigation, Internaitonal RILEM Conference. Proceedings. August 20-23, 2006, Bagneux, France, Jensen, O. M.; Lura, P.; Kovler, K., Editor(s)(s), 11-20 pp, 2006.

Keywords:

water movement; curing agents; x ray microtomography; effectiveness; cement pastes; cements; hydration; water supply; oxygen index; shrinkage; calorimetry; x ray absorption

Abstract:

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 30DGC. A four-dimensional data set is created by obtaining threedimensional 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 mm, 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.