Monitoring Durability of Limestone Cement Paste Stored at Conditions Promoting Thaumasite Formation

The durability of Portland-limestone cement with high limestone content was monitored at conditions promoting thaumasite formation. Pore structure and deterioration characteristics were assessed with X-ray micro-computed tomography and correlated with material's strength. Changes in crystalline and amorphous phases of the cement paste were investigated with X-ray powder diffraction and solid state nuclear magnetic resonance spectroscopy. Rapid deterioration was observed, evolving as a front causing concentric crack patterns followed by detachment of the part of specimen in contact with the corrosive solution. This ultimately led to loss of structural integrity after 4 months of exposure. During sulfate attack, thaumasite, ettringite and gypsum formed at the expense of portlandite, calcite and monocarboaluminate hydrate. Furthermore, polymerization of silicate chains in C-S-H and deterioration of C-S-H also occurred.