This paper describes the scaling of hardened cement pastes subjected to freezing and thawing in salt solutions such as NaCl, CaCl
2, MgCl
2 and sea water. The various factors affecting to scaling such as salt solution, concentration, drying and air entraining were investigated in connection with the microstructural features. The severest scaling was observed on the non AE pastes in NaCl, CaCl
2 solutions and sea water caused by the damage of Ca(OH)
2 and the collapse of CSH. The rate of scaling decreases with freeze-thaw cycle on the non AE paste in MgCl
2 solution and on the AE paste in CaCl
2 solution and sea water due to the dense layer formed near the surface. However very porous portion was observed at adjacent to the dense layer. The cavities in dried AE paste are filled with new compounds and the shell of air voids becomes denser and thicker. Consequently the dried AE paste is much more resistant to surface scaling than non dried one.
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