The formation of meta-stable sodium sulfate heptahydrate in porous materials as studied by NMR

ABSTRACT. Salt weathering is a major cause of deterioration of porous building materials. Of the salts responsible, especially sodium sulfate is seen as very damaging. However many questions arise concerning which sodium sulfate phase will crystallize out during salt weathering and is responsible for the damage seen in situ. In this study we focused on crystallization by cooling of sodium sulfate solutions in different environmental conditions, i.e., inbulk, solution with powder and inpore crystallization. The salt concentration in samples was measured using a nondestructive technique: Nuclear Magnetic Resonance. In the NMR experiments we observed the formation of a metastable phase of sodium sulfate: the heptahydrate (Na2SO4.7H2O)