Drying of salt-contaminated masonry: MRI laboratory monitoring |
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| Authors: | Teresa Diaz Gonçalves Leo Pel José Delgado Rodrigues |
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| Institution: | (1) National Laboratory of Civil Engineering, Lisbon, Portugal;(2) Department of Applied Physics, Technical University of Eindhoven, Eindhoven, The Netherlands |
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| Abstract: | Drying of masonry specimens was monitored by means of a two-dimensional (2D) magnetic resonance imaging (MRI) technique. The
external surfaces stayed wet for longer if NaCl was present instead of pure water only. This corroborates many practical observations
that salts aggravate dampness in masonry. A slower evaporation process and not hygroscopicity was the cause. That suggests
that salt-induced dampness may, in general, arise simply from changes in the drying process of masonry materials. That also
implies that the height and depth at which crystallization occurs in walls may depend on the relative equilibrium humidity
(RHeq) and other properties of salts that influence drying of porous materials. Evaporation rates of free surfaces of pure
water and saturated NaCl solution were measured by a gravimetric technique. The results indicate that slow drying of salt-contaminated
materials is not due only to the lower RHeq of salt solutions. The effective surface of evaporation is likely to be reduced
perhaps due to blocking of pores by salt crystals. Final salt-distribution maps of the specimens show that: (a) salts may
affect the inner materials of the masonry, even in evaporation-induced processes that lead crystallization to occur predominantly
on the external surface; (b) distinct internal distribution patterns occur if masonry composition varies.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. |
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| Keywords: | Magnetic resonance imaging Drying Porous materials Salt decay Ancient masonry |
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