Mechanisms of Concrete Deterioration by Sodium Sulfate Crystallization


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Title: Mechanisms of Concrete Deterioration by Sodium Sulfate Crystallization

Author(s): K. J. Folliard and P. Sandberg

Publication: Special Publication

Volume: 145


Appears on pages(s): 933-946

Keywords: air entrainment; blast furnace slag; crystallization; deterioration; hydration; hydraulic pressure (freezing); saturation; sodium sulfate; temperature; Materials Research

Date: 5/1/1994

The mechanisms underlying physical disintegration of concrete by crystallization of mirabilite (Na 2SO 4 10H 2O) and thenardite (Na 2SO 4) were studied by a series of laboratory experiments. In contrast to chemical sulfate attack, which manifests itself in the formation of gypsum or ettringite, the deterioration investigated in this study did not involve chemical attack on the cement paste in concrete. Rather, the damage was strictly of a physical nature, caused by phase changes within the sodium sulfate-water system. Several possible mechanisms of distress were investigated, including pressure caused by hydration, evaporation, and temperature effects. Rapid temperature changes were found to be the dominant mechanism of deterioration. In particular, rapid decreases in temperature resulted in supersaturation, rapid crystallization, and a net increase in the sodium sulfate-water system. Consequently, significant hydraulic pressure, similar to that observed in the classical freeze-thaw phenomenon, would develop if drainage conditions within the concrete were not adequate to allow for the volume increase of the sodium sulfate-water system.