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X-ray Microtomography Studies of Air-Void Instability and Growth during Drying of Tile Adhesive Mortars



Dale P. Bentz, C Haecker


A previous X-ray absorption study of tile adhesive mortars [1] identified a new phenomenon during drying, namely the movement of small cement particles from the interior of the specimen to its surface. An analysis based on Stokes equation indicated that this particle movement is consistent with the very high viscosity of these tile adhesive mortars. In addition to this particle movement, the concurrent formation/growth of large scale flaws (voids) within the specimens was observed. The goal of the present study was to observe this void instability and growth in real time by using three-dimensional X-ray microtomography. Mitigation strategies for avoiding the formation of these flaws were also investigated. Successful mitigation strategies included the utilization of a coarser cement (larger particles that do not move during drying), the addition of an accelerator (to achieve set before flaw formation can occur), and the addition of a co-thickener (to form a polymer network to prevent particle movement). Conversely, the addition of an air entrainer in an attempt to stabilize the existing air voids was not successful as a mitigation strategy.
NIST Interagency/Internal Report (NISTIR) - 7532
Report Number


Building technology, drying, open time, mortar, tile adhesive, void, x-ray microtomography.


Bentz, D. and Haecker, C. (2008), X-ray Microtomography Studies of Air-Void Instability and Growth during Drying of Tile Adhesive Mortars, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed June 18, 2024)


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Created November 1, 2008, Updated June 2, 2021