Salt weathering

In arid environments, where the soluble products of weathering are not completely removed from the soil, saline solutions may circulate in the soil as well as in rock fractures. If upon evaporation the salt concentration increases above its saturation point, salt crystals form and grow (Goudie et al, 1970). The growth of salt crystals in crevices can force open fractures. Salt weathering occurs in cold or hot deserts or areas where salts accumulate. Boulders, blocks. 

Goudie, A.S. and Viles, H. (1997) Salt Weathering Hazards. John Wiley Sons,... 

Wellman, H.W. and Wilson, A.T. (1965) Salt weathering, a neglected geological erosive agent in coastal and arid environments, Nature 205, 1097... 

Aref, M.A.M., El-Khoriby, E. Hamdan, M.A. (2002) The role of salt weathering in the origin of the Qattara Depression, Western Desert, Egypt. Geomorphology 45, 181-195. 

In the Atacama, various observers have postulated that salt weathering is an active process that leads to rock brecciation (Searl and Rankin, 1993), slope planation (Abele, 1983) and tafoni development (Tricart and... 

As we have noted, sodium nitrate is highly soluble. As Figure 12.6 shows, the solubility of sodium nitrate, in common with most salts, increases with temperature. This is significant for the Atacama as it favours the process of salt weathering under hot desert conditions from a theoretical perspective, the increase in solubility with temperature means that at higher temperatures, more solute will be able to dissolve in the solvent. This, coupled with the high solubility of sodium nitrate, means that when crystallisation takes place, a large volume of salt is available to crystallise out. 

Cooke, R.U. (1994) Salt weathering and the urban water table in deserts. In Robinson, D.A. Williams, R.B.G. (Eds) Rock Weathering and Landform Evolution. Chichester Wiley, pp. 193-205. 

Goudie, A.S. (1993) Salt weathering simulation using a single-immersion technique. Earth Surface Processes and Landforms 18, 369-376. 

Laue, S., Blauer Bohm, C. Jeannette, D. (1996) Salt weathering and porosity. Proceedings 8th International Conference on Deterioration and Conservation of Stone. Berlin Ernst und Sohn, pp. 513-533. 

A related phenomenon with rock salt is caking at the mine head. A hot, humid climate often produces dew points of 25°C. There will be rapid condensation of water onto salt brought to the surface at lower temperature. This can lead to caking as the salt weathers. 

Angeli, M. Hebert, R. Menendez, B. David, C. Bigas, IP. 2010. Influence of temperature and salt concentration on the salt weathering of a sedimentary stone with sodium sulphate. Engineering Geology, 115 193-199. 

Salt weathering, also called salt crystallization or physical salt attack, is defined as the basic degradation mechanism that a porous material, such as stone and masonry, undergoes at and near the Earth s surface [if The parts of porous materials in contact with relatively dry air near the Earth s surface will be severely deteriorated but the parts buried in salts environment look sound. 

Apparently, it seems reasonable to attribute salt weathering to the decay of concrete partially exposed to sulfate environment. Concrete technologists subjectively accepted that... 

This review paper includes three parts. First, the basic principles of salt weathering on porous materials are reviewed. Second, some field and indoor tests of "salt weathering" on concrete by sulfates are presented. Some appearances, which were generated by "salt weathering" on concrete but were opposite to the basic principles of salt weathering on porous materials, are analyzed in detail. Several points that need further study are presented in the third part. 

The supersaturation can be produced by cooling, evaporation and drying and wetting cycle. If the temperature dependence of the solubihty of a salt is high, a drop of temperature can result in supersaturation. Supersaturation caused by evaporation always occurs when one face of the porous material is in contact with the solution and the other face is exposed to relatively dry conditions, i.e., the salt weathering process. 

In summary, the efflorescence and sub-effloresoence of salt weathering distress on the porous material can be schematically shown in Fig. 4. 

Fig. 4. Schematic of salt weathering distress on porous material.

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