Experimental Evidence of Crystallization Pressure inside Porous Media

Crystallization pressure of salt in porous materials is one of the mechanisms that may induce serious damage, for example, weathering of buildings and monuments of cultural heritage. Since this pressure also causes the solubility of the salt inside a porous material to differ from the bulk solubility, it can be assessed experimentally by measuring the solubility inside the pores. We show that this is possible by NMR, and study Na₂CO₃ and Na₂SO₄ in a series of model porous materials. Using the solubility data the crystal-liquid surface energies are estimated as γ=0.09 N/m for Na₂CO₃·10H₂O and γ=0.06 N/m for Na₂SO₄·10H₂O. For pore sizes below about 30 nm, the resulting pressure exceeds the tensile strength of typical building materials (3 MPa). No pressure is induced by the metastable Na₂SO₄·7H₂O, which suggests for this crystal a value of γ close to zero.