Corrosion of cement pastes made of CEM I and CEM III/A caused by a saturated water solution of ammonium chloride after 4 and 25 days of aggressive immersion

One of the most common causes of the decay of concrete structures is contact with aggressive chemical compounds. Fluids containing chlorides and ammonium ions behave aggressively toward reinforced concrete in many environmental engineering structures. Therefore, the highest level of safety should be preserved in the case of industrial sewage treatment plant facilities, which also aim to protect the environment against pollutants. An accelerated test of the degradation of hydrated cement paste, as the most reactive component of concrete, was conducted. Sulfate resistant cement CEM I, slag cement CEM III/A and corrosive saturated ammonium chloride water solution were used. Investigation after 4 and 25 days of immersion found that portlandite dissolution triggered an increase in porosity. Thaumasite crystallized following ettringite dissolution. Another intermediate phase was Friedel's salt. The final products of cement paste corrosion were found to be gypsum, calcite and vaterite. Porosity was higher in the case of CEM III/A. Chloride ion concentrations and porosity were not the highest in the surface areas, which were in the direct contact with an aggressive solution. Nitrogen crystalline phases were not found.