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Tuesday, 20 August 2019
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Raw materials & technologies, Applications

Sulfate-phosphate pollutants attack reinforced concrete

Friday, 21 November 2014

Researchers described a novel form of alteration due to the interaction between hydrated cement phases and sulfate and phosphate-based pollutants.

Sulfate and phosphate-based pollutants trigger degradation processes. Source: Nicole Kaiser/Fotolia

Sulfate and phosphate-based pollutants trigger degradation processes. Source: Nicole Kaiser/Fotolia

They characterised concrete samples from an industrial reinforced concrete building.

Five alteration layers may be detected

Decalcification of the cement matrices was observed, with secondary sulfate and phosphate-based mineral formation, according to a marked mineralogical and textural zoning. Five alteration layers may be detected: the two outermost layers are characterised by the presence of gypsum-brushite solid solution phases associated with anhydrous calcium sulfates and phosphates, respectively, while a progressive increase in apatite and ammonium magnesium phosphates is observable in the three innermost layers, associated with specific apatite precursors (brushite, octacalcium phosphate and amorphous calcium phosphate, respectively). The heterogeneous microstructural development of secondary phases is related to the chemical, pH and thermal gradients in the attacked cementitious systems, caused by different sources of pollutants and the exposure to the sun's radiation.

The study is published in: Cement and Concrete Research, Volume 68, February 2015, Pages 49-63.

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