A study of the mechanism behind crystal lifting
Crystallization pressure of confined KAl(SO4)2⋅12H2O crystals
Anton Tuluk (Radboud University Nijmegen)
Erik de Ronde (Radboud University Nijmegen)
Michael Steiger (Universität Hamburg)
Barbara Lubelli (TU Delft - Architecture and the Built Environment)
Hugo Meekes (Radboud University Nijmegen)
Elias Vlieg (Radboud University Nijmegen)
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Abstract
Salt crystallization pressure is one of the main sources of weathering in porous building materials. In our work we study the origin of this phenomenon using single crystals of KAl(SO4)2⋅12H2O (potassium aluminium sulphate dodecahydrate) as model system. Crystals were grown immersed in a solution of a specific supersaturation (σ=10−80%). Evidence of crystallization pressure was the vertical lift of weights on top of the growing crystal, which was measured by in-situ displacement sensors. A clear supersaturation threshold of σ≃30% for a 0.5 N weight is required to initiate lifting in our model system. Above this value, the maximum displacement increases nonlinearly with σ and depends on crystal orientation, interfacial wettability, and applied load. Hydrophobic interfaces suppress crystal growth by limiting mass transport, whereas hydrophilic confinement supports continuous growth until the local supersaturation is exhausted. In saturated solutions, on the other hand, a load leads to dissolution. Based on the observations, we propose a mechanism for crystallization pressure for which the growth of the unloaded faces adjacent to the confined face is key. These results refine our understanding of crystallization pressure in confined spaces and can help explain and mitigate salt-induced damage in porous materials.
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