ABSTRACT-We study the spontaneous nucleation and growth of sodium chloride crystals induced by controlled evaporation in confined geometries (microcapillaries) spanning several orders of magnitude in volume. In all experiments, the nucleation happens reproducibly at a very high supersaturation S~1.6 and is independent of the size, shape and surface properties of the microcapillary. We show from classical nucleation theory that this is expected: S~1.6 corresponds to the point where nucleation first becomes observable on experimental time scales.A consequence of the high supersaturations reached at the onset of nucleation is the very rapid growth of a single skeletal (Hopper) crystal. Experiments on porous media reveal also the

h i g h l i g h t sBoth approaches have potential to be applied in real-scale concrete structures. Use of encapsulated PU requires more preparation compared to the addition of SAPs. One approach is triggered through crack appearance the other by water ingress. SAPs resulted in the highest healing efficiency based on crack width measurements. Release of PU from the capsules and crack closure was clearly noticed from CT.

Drying of salt contaminated porous media: Effect of primary and secondary nucleationDesarnaud, J.E.; Derluyn, H.; Molari, L.; de Miranda, S.; Cnudde, V.; Shahidzadeh, N.F. Published in:Journal of Applied Physics DOI:10.1063/1.4930292 Link to publication Citation for published version (APA):Desarnaud, J., Derluyn, H., Molari, L., de Miranda, S., Cnudde, V., & Shahidzadeh, N. (2015). Drying of salt contaminated porous media: Effect of primary and secondary nucleation. Journal of Applied Physics, 118(11), [114901]. DOI: 10.1063/1.4930292 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The drying of porous media is of major importance for civil engineering, geophysics, petrophysics, and the conservation of stone artworks and buildings. More often than not, stones contain salts that can be mobilized by water (e.g., rain) and crystallize during drying. The drying speed is strongly influenced by the crystallization of the salts, but its dynamics remains incompletely understood. Here, we report that the mechanisms of salt precipitation, specifically the primary or secondary nucleation, and the crystal growth are the key factors that determine the drying behaviour of salt contaminated porous materials and the physical weathering generated by salt crystallization. When the same amount of water is used to dissolve the salt present in a stone, depending on whether this is done by a rapid saturation with liquid water or by a slow saturation using water vapor, different evaporation kinetics and salt weathering due to different crystallization pathways are observed.

This paper presents an experimental and quantitative analysis of capillary transport across the interface brick-mortar joint in masonry. Moisture profiles are measured with X-ray projection. The influence of curing conditions is analyzed by considering three types of mortars: cured in a mould, between capillary wet and dry bricks. A decrease in moisture inflow for the mortars cured between bricks is measured. The pore structure and the moisture transport properties of mortar change significantly due to water extraction from the initially wet mortar to the bricks during curing. Numerical simulations reveal the existence of a hydraulic interface resistance between brick and wet/dry cured mortar.

Freeze-thaw cycling stresses many environments which include porous media such as soil, rock and concrete. Climate change can expose new regions and subject others to a changing freeze-thaw frequency. Therefore, understanding and predicting the effect of freeze-thaw cycles is important in environmental science, the built environment and cultural heritage preservation. In this paper, we explore the possibilities of state-of-the-art micro-CT in studying the pore scale dynamics related to freezing and thawing. The experiments show the development of a fracture network in a porous limestone when cooling to -9.7 °C, at which an exothermal temperature peak is a proxy for ice crystallization. The dynamics of the fracture network are visualized with a time frame of 80 s. Theoretical assumptions predict that crystallization in these experiments occurs in pores of 6-20.1 nm under transient conditions. Here, the crystallization-induced stress exceeds rock strength when the local crystal fraction in the pores is 4.3%. The location of fractures is strongly related to preferential water uptake paths and rock texture, which are visually identified. Laboratory, continuous X-ray micro-CT scanning opens new perspectives for the pore-scale study of ice crystallization in porous media as well as for environmental processes related to freeze-thaw fracturing.

The growth of hopper crystals is observed for many substances, but the mechanism of their formation remains ill understood. Here we investigate their growth by performing evaporation experiments on small volumes of salt solutions. We show that sodium chloride crystals that grow very fast from a highly supersaturated solution form a peculiar form of hopper crystal consisting of a series of connected miniature versions of the original cubic crystal. The transition between cubic and such hopper growth happens at a well-defined supersaturation where the growth rate of the cubic crystal reaches a maximum (∼6.5 ± 1.8 μm/s). Above this threshold, the growth rate varies as the third power of supersaturation, showing that a new mechanism, controlled by the maximum speed of surface integration of new molecules, induces the hopper growth of cubic crystals in cascade.

This paper presents a computational model coupling heat, water and salt ion transport, salt crystallization, deformation and damage in porous materials. We focus on crystallization-induced damage. The theory of poromechanics is employed to relate stress, induced by crystallization processes or age. The results show that the effective stress caused by salt crystallization depends not only on the crystallization pressure but also on the amount of salt crystals, which is determined by the spreading of crystals in the porous material and the crystallization kinetics.

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