Sulfate impurities from deicing salt and durability of portland cement mortar

TLDR: In this article, the authors investigated the effect of calcium sulfate impurities in deicing salts on the durability of portland cement mortar and reported significant losses in pore volume for the treated samples as compared to samples frozen and thawed in water only.

Abstract: Research on the topic of calcium sulfate impurities in deicing salts adversely affecting the durability of portland cement mortar is covered in this paper. Natural rock salt may contain as much as 4.0 percent calcium sulfate. When combined with chloride solutions the solubility of calcium sulfate increases by as much as 3.5 times; hence, the calcium sulfate impurities contained in rock salt brine become highly detrimental, causing attack on cement mortar samples. These impurities can collect in pavement joints and cracks, reaching high concentrations through evaporation and the repeated use of deicing salts. Such a destructive mechanism may account for premature field failure of pavements that passed durability tests in the laboratory. Durability studies using brines containing differing amounts of gypsum in proportion to the sulfates occurring in natural rock salts have been conducted. To model field conditions, samples were concurrently subjected to brines and rapid freeze-thaw testing. Deterioration proved so rapid that testing was stopped at 88 cycles. Tensile tests showed strength losses up to 40 percent for samples subjected to brine solutions containing gypsum impurities. Mercury intrusion porosimetry showed significant losses in pore volume for the treated samples as compared to samples frozen and thawed in water only. X-ray diffraction tests discovered increased amounts of ettringite and Friedel's salt, a tricalcium aluminate chloride hydrate.