Irreversible dilation of NaCl contaminated lime-cement mortar due to crystallization cycles

The mechanism of damage occurring in NaCl contaminated materials has not been clarified yet. Apart from crystn. pressure, other hypotheses have been proposed to explain the cause of decay. Irreversible dilation has been obsd. in a few cases but has never been studied in a more systematic way. The aim of the research is to contribute to the modeling of this phenomenon. In the present paper the effect of NaCl on the hydric and hygric behavior of a lime-cement mortar is extensively studied. The results indicate that NaCl influences the hydric and hygric dilation behavior of the material. The material contaminated with NaCl shrinks during dissoln. and dilates during crystn. of the salt. This dilation is irreversible and sufficient to damage the material after few dissoln./crystn. cycles. This behavior is not restricted to NaCl, but is obsd. in the presence of other salts as well (NaNO3 and KCl). Outcomes of electron microscopy studies suggest that salts causing irreversible dilation tend to crystallize as layers on the pore wall.