Sodium

Engineering

Portlandite

Curing (chemistry)

Metallurgy

Materials science

Sodium sulfate

Gypsum

Durability

Sulfate

Chemical engineering

Geology

Soil water

Mortar

Oceanography

Portland cement

Cement

Environmental science

Soil science

Composite material

Ettringite

Seawater

Forensic engineering

Leaching (pedology)

Cement and Concrete Research

Sulfate ions in seawater or underground can attack the cement paste leading to expansion and strength loss. This expansion is usually related to ettringite and gypsum precipitation. This study aims to characterize the possible altered zone and to identify the mechanisms of degradation under such conditions. For this study, cement pastes manufactured using CEM I with two w/c ratios (0.45 and 0.60) were exposed to sodium sulfate solutions (semi-immersion at a controlled pH = 8.0 ± 0.1) after one year of curing in water. The analysis of the physical aspect of this phenomenon shows that two modes of transfer occur: transfer of sulfate ions to the cement matrix and leaching of calcium ions to the external solution. The analysis of the chemical composition of the affected material highlights the progressive consumption of portlandite at the surface, the decalcification of C-S-H and the formation of AFt from both Afm and aluminium incorporated in C-S-H.

Durability of cement pastes exposed to external sulfate attack and leaching: Physical and chemical aspects