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The crystallization process of soluble salts inside the natural and artificial porous materials partially immersed in different saline solutions has been studied, This procedure is used to simulate the conditions of exposure to salt weathering in which foundations and lower walls of building structures are within the zone of capillary rise of saline ground water.Crystallization pressures that can develop in the samples, which are a function of the pore size and salt-solution interfacial tension, have been calculated and are compared with experimental values of the materials tensile strength. since both these parameters allow the prediction of porous materials behaviour against salt weathering.

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Using the polyhedral units model of Hazen and employing a method of least-squares, the contribution of nineteen constituent units to the free energy and fifteen units to the enthalpy, at 298 K and 1 bar of pressure, have been calculated for mineral phosphates. The contribution of these constituent units to the free energy at higher temperatures has also been calculated.From these data we can estimate the thermodynamic properties of phosphates by summing the contribution of the distinct units, with more accuracy than the methods published up until now.