Geoscience Reference
In-Depth Information
concentrations of sulfate or alkalis determined by
chemical analysis. Sulfate attack occurs when HAC
concrete comes into contact with solutions leached from
sulfate-bearing materials (e.g. gypsum plaster). In thin
section, sulfate attack is characterized by the presence of
ettringite in cracks and voids, and degradation of the
cement matrix. Alkaline hydrolysis occurs when
persistent water leakage causes sodium and potassium
hydroxide solutions to leach onto HAC concrete. In thin
section, this may be indicated by the presence of leached
secondary deposits of calcium carbonate and cement
matrix replacement (
236
) and/or cracking (
237
).
236
236
Leached HAC concrete possibly suffering from
alkaline hydrolysis. Secondary deposits of calcium
carbonate (pink) are seen replacing the cement and
filling air voids (right); XPT, ×35.
237
237
HAC concrete suffering from cracking (yellow)
induced by alkaline hydrolysis; PPT, ×150.
