Efflorescence pathway diagram: understanding salt weathering

Salt weathering is a major cause of deterioration of porous building materials. To obtain information about the mechanisms underlying these damage processes we have studied the moisture and ion transport within fired-clay brick. The time evolution of NaCl saturated samples of fired-clay brick during one-sided drying was measured using nuclear magnetic resonance (NMR). The moisture content and amount of dissolved Na ions could be measured quantitatively as a function of position. The NaCl concentration profiles obtained from these data reflect the competition between advection to the surface and redistribution by diffusion. By representing the measured moisture and NaCl profiles in an efflorescence pathway diagram (EPD) also the crystallization of the ions can be taken into account. The measured EPDs indicate that in general, crystallization at the surface cannot be avoided and make clear that the drying rate is the key parameter in the salt crystallization process. (C) 2004 Elsevier Ltd. All rights reserved.